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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Bob Hunt on December 28, 2020, 09:03:19 AM
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A few years ago I designed a twin electric Stunt model that has a 530 square inch wing, a built-up fuselage, and profile nacelles. It was much the same in aesthetics as my big test bed twin, but with no retracts. It was reasoned that a small electric twin might be attractive to those who might wish to try an electric twin Stunt model, but with much reduced building time and much reduced cost. As for overall size, think of a Nobler with a longer tail moment.
As with the original big test bed twin, the smaller ship (name will either be "Double Take" or "Two Small") features a "Lost-Sheeting" wing. That's the name I gave to my adaptation of the Combat world's treatment of foam cores. They cover them with a low-temp plastic material, while I chose to apply .2 carbon mat using water thinned Titebond II glue. In either case the strength of the wing mainly comes from two imbedded 1/8 x 3/8-inch basswood spars - one on top and one on the bottom - that run full span and have a couple of 1/8-inch balsa shear webs installed between them. The basswood spars are glued into a slot in the top and bottom of the foam panels and are also glued to the shear webs, preventing "racking." This yields an incredibly strong wing at very low cost and very little building/assembly time.
The new small twin will be powered by E-Flite Park 450 motors (with the option to go to Park 480 motors if needed).
My question is: Would the readers/contributors here be interested in a photo essay of the build, and if so would they also be interested in plans and foam parts for this model?
Thanks - Bob
PS: Attached are a couple of photos of the original big twin test bed for reference as to what the new small twin will look like, and also a couple of photos of the Lost-Sheeting wing construction on one of the Joe Nall Cadets. - Bob
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Yes.
Craig
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Oh yeah Bob!
(But you already knew I would be very interested!)
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Yes Bob, I would be very interested! As our good friend Jim Aron (aka Uncle Jimby) would say, "Twins are cool"! ;D ;D ;D
Dennis
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Bob,
What is the motor/ESC/Timer/Battery set up for this ship? For the ESC how is it sized for amps?
Best, DennisT
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Hi Dennis:
Still pondering a few of those details, but right now it appears that the E-Flite Park 450 motors (870 Kv) will be pared with Castle Talon 25 ESCs and a 4S 2,800 mAh battery. I'll either use the Hubin twin timer or the Fiorotti active twin timer.
Later - Bob
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OK Bob. You now get a new name. You are, hence forth, known as the King of Cool. I like it.
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Hi Randy:
Well, it is certainly better than a lot (most?) of the nicknames that I've been given by my flying buddies...
RJ still calls me "White Shoes" and I still call him "Iceman." Sure hope he recovers soon. :-\
Later - Bob
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You've got me on the edge of my seat now
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Bubba,
I like it a lot Ol Buddy. Send me the drawings and I’ll CAD them out for you. After thinking about this, I like the name “Bubba’s Double Trouble” seems to fit perfectly.
Mikey
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Bob,
So are you using two Castle Talon 25 ESCs (one for each motor) and a single 4S 2,800 mAh battery with Y harness and single timer with a Y harness? Just trying to understand how these twins are set up.
Best, DennisT
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Hi Dennis:
Yes, that's the plan. The twins use a lot less battery than you would imagine, so running two motors on one fairly small battery is doable. My big twin that was powered by two E-Flite Power 10 motors, and had retracts that ran off the same battery, used 1800 mAh per flight! That ship weighed in at 66 ounces!
Later - Bob
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Bob,
So are you using two Castle Talon 25 ESCs (one for each motor) and a single 4S 2,800 mAh battery with Y harness and single timer with a Y harness? Just trying to understand how these twins are set up.
Best, DennisT
Can't drive two motors with a KR timer. So you need ESCs that have RPM control and a Hubin timer. In an earlier post it was mentioned that some one makes a twin motor timer. Is that true? How does it work?
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Hi John:
I've never used a KR timer, so I was unaware that it doesn't have a retract function. Will Hubin does make a twin timer with retract function. In fact, he sent me the first one (well, at least to my knowledge it was the first one...) to use in the big twin test bed model that Buddy Wieder and I built to test out motors and retracts. When we were ready to fly it, Will flew in from Ohio in his private plane to the airport that is about a mile from my house. He wanted to see it fly and make sure the retract and twin functions worked as planned. They did! In fact, in all the time we used that timer system we never had a malfunction. I used it in my Second Wind twin, and Buddy used it in his Ryan's Evil Twin model. I wouldn't even consider switching from that timer now except for the fact that it isn't an active timer. I've become so used to being able to dial in the boost and brake aspects of the Fiorotti to suit my needs that I don't think I'd be happy with any other system. And, yes the Fiorotti has a retract function as well, and each motor is able to be set for RPM independently, as was the case with the Hubin timer. To be fair here I must also mention the Igor Burger timer. It too has the retract function and independently adjustable RPM settings for each motor.
I'm pretty sure the Talon 25 ESCs will work with the E-Flite Park 450 motors in the small, light new twin, but only time and testing can prove that out. Going to the Talon 35 ESCs from the get go may be the safer bet; I'll think on that... Im sure my power system gurus, Will DeMauro and Dean Pappas will give me lots of input on this.
Attached for your reference are a couple of photos of the twins that Buddy and I have built and flown that had the Hubin twin/retract function timer on board. In fact, Will Hubin took the in-flight shots of the test bed model.
There will be lots more to come on this new project, so stay tuned.
Later - Bob
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Bob,
I think this is a very interesting thread. It would be great if you could go through the process for the Twins of initially selecting motors, props, ESC size, Timer options (with and without retracts) and battery size so it could be applied to different size ships. Would also be good to layout the wiring arrangements (like a one line diagram) and component hook-up arrangements (like the "Y" harnesses needed). Then the build pictures for the actual ship which you do a great job on always.
Best, DennisT
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Great idea, Dennis! I will have to lean heavily on Will DeMauro and Dean Pappas for the motor/battery/ESC/timer aspects; I'm certainly not an expert on those things. The actual build sequence is more in my comfort zone.
I'll be working on this project all weekend; heck I'll be working on it until next year! LL~
I will have some photos to share by Monday at the latest.
Happy New Year everyone - Bob
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Even though I will probably never build one, the old DOC will keeping watching for the results of a true craftsman. H^^
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I think I could see myself flying something like this. The more I look, and read through this... the more excited I get to see it develop. I'm a big fan of a "smaller" plane. Not that it's small, but I don't fly a lot of 60 sized ships. I stay around the sig twister size.
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I am very interested in this as it will relate almost directly to the OV-10 Bronco I've been designing (based off the Pathfinder Twin - big thank you to John Miller for helping on initial CAD and plan review, and to Keith Trostle for his help on design considerations).
Steve
Sent from my Lenovo TB-X505F using Tapatalk
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I always enjoy your builds!
Rob
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Bob,
Yes and yes.
James
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Okay then. It's time to get started with the build.
The first photo attached below shows the fuselage side view shape and construction. It is a typical slab-sided fuselage made from 3/32-inch thick balsa sides with 1/32-inch plywood doublers, and 3/32-inch thick formers. Note that in this photo the nacelles are not depicted. It would get confusing to have the nacelles drawn in on top of the fuselage crutch. And besides, I will not know their length until I get the wing, fuselage and tail assembly together, along with the top and bottom shells, the battery and the nose gear, so I can put the motors onto some "dummy" nacelles and move the motors around until I find the balance point . At that point I can draw up the actual nacelles. That is exactly how I did it on my other twins and it worked to perfection.
The second third and fourth photos attached below show how I make up a template wing panel that is the exact same shape as the actual wing will be, and then mark it where the fuselage side will pass over the actual wing, and also mark it where the center line of the nacelle will be on the actual wing. I then cut the template panel to give me sections that can be used to accurately "open" the fuselage sides and the nacelles later on. Note that I centerline the piece of foam that will be used to mark the opening for the wing so that it can be placed onto a centerline on the fuselage sides and traced. This will become more clear as we progress.
That's a teaser for tonight. I'll resume the typing and posting tomorrow.
Later - Bob Hunt
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Can't drive two motors with a KR timer. So you need ESCs that have RPM control and a Hubin timer. In an earlier post it was mentioned that some one makes a twin motor timer. Is that true? How does it work?
I ran three motors with my KR. Worked fine.
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Dave,
Would be good if you could show a wiring one-line and some photos of the hook-ups.
Best, DennisT
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Bob,
Can you post the layout sketch of the twin so we can understand the dimensions and how you arrived at the location for the nacelle. What wing airfoil did you select? Why?
Best, DennisT
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Hi Dennis:
Well, I don't actually have a "layout sketch" of the plane; I just drew the plans... The nacelle location on the wing was determined by the maximum diameter prop that might be used. In this case it was a 8-inch prop. I left enough room between the nacelle center line and the fuselage side to be able to use a 9-inch prop if that becomes possible. In any case there is enough clearance between the tip of the prop and the fuse side. I know that doesn't sound too technical, but I've always worked more out of "feeling" than out of science. Hey, it's worked pretty well for me so far.
This build thread is about showing how I build a Lost-Sheeting twin-motor model, and I won't go into too much design theory. I'm using proven airfoils and "numbers" that I know will produce a good flying model (at least I hope so...). When the build is done and the model has been flown, then I will release plans for the ship and also offer cores and some other parts for it.
I'll post more photos and information later today.
Happy New Year - Bob
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Hi Dennis:
Well, I don't actually have a "layout sketch" of the plane; I just drew the plans... The nacelle location on the wing was determined by the maximum diameter prop that might be used. In this case it was a 8-inch prop. I left enough room between the nacelle center line and the fuselage side to be able to use a 9-inch prop if that becomes possible. In any case there is enough clearance between the tip of the prop and the fuse side. I know that doesn't sound too technical, but I've always worked more out of "feeling" than out of science. Hey, it's worked pretty well for me so far.
This build thread is about showing how I build a Lost-Sheeting twin-motor model, and I won't go into too much design theory. I'm using proven airfoils and "numbers" that I know will produce a good flying model (at least I hope so...). When the build is done and the model has been flown, then I will release plans for the ship and also offer cores and some other parts for it.
I'll post more photos and information later today.
Happy New Year - Bob
Hi Bob we chatted on the phone a bit a few months ago about my Legacy build I was going to use a power 25 but you suggested a 15 would be enough which I did switch to, now I see you are designing a Nobler size twin with little 8 inch props, I have to say this is quite fascinating, I'm looking forward to the rest and if you offer plans and cores put me down for a set. ;D
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Hi Dwayne:
Will do, but let's see how it flies first...
I did not, as promised, post any new photos and text last night; my wife and I got engrossed in the movie "Hidden Figures." By the time it was over we were tired and went to bed. Sorry about that. To make reparations I'll post a whole bunch of stuff today, starting now...
No matter how good a foam cutter you are, the surface of the core will not be absolutely perfect. It will require sanding. This is especially critical for the Lost-Sheeting method where carbon mat will be applied directly over the foam core. All imperfections need to be sanded smooth. The first photo below depicts this. Sand until the cores are perfectly smooth, but don't sand so much as to alter the airfoil.
The second photo below shows the two cores sanded and vacuumed and dry fit together on the bench in their cradles (pieces of foam left after cutting the cores).
During the layout process I drew very accurate construction lines on the ends of the cores. These lines show where the front of the slot for the basswood spars will be located and allow me to position the plywood slot-cutting templates accurately. The templates have marks that allow me to position them to cut a 1/8-inch deep by 3/8-inch wide slot. One template will be positioned at either end of the core. Slots will be cut into the top and bottom of each panel. Check out the third photo below for some clarification on this.
The last photo shows the templates in position on the top of one of the cores and the hot wire apparatus suspended above, waiting for the action to begin. I wanted to stage a photo that showed me cutting the slots, but, alas, I didn't have someone handy to take the photo while I was working. So, this staged photo will have to suffice...
Stay tuned... - Bob
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The first photo below shows one of the slots cut into one of the cores. This process will be repeated until all the slots are cut. Those who have computer cutting devices can do this without the need for templates. I'm old fashioned; I like to do the work myself. <=
The next two photos below shows one of the 1/8-inch by 3/8-inch basswood spars dry fit into a slot.
Stay tuned... Bob
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In this installment the subject is vertical spar slotting and vertical spar installation.
There will be two vertical 1/8-inch Lite-Ply spars positioned directly below the two basswood surface spars.These spars when glued to the basswood surface spars will prevent the core from "racking" under cornering loads. If these spars were not installed the top of the wing and the bottom of the wing would tend to want to "clap hands" due to the opposite stresses when maneuvering. During an inside loop the top of the wing experiences compressive loads while the bottom of the wing experiences tensile "stretching." Of course these loads are reversed during outside maneuvers. The vertical spars that will glue to the surface spars act as shear webs and help to keep the two surface spars from moving in opposition to each other and give the wing great bending strength. The first photo below shows the beginning of laying out a 1/8-inch wide vertical spar slot position in the center of one of the basswood spar slots that we cut in the previous segment. The Lite-Ply vertical spars will go out into the core to a few inches past where thew nacelles will be positioned. In this case they are 10-inches long. They will have a cutout at the center to allow bellcrank swing, and they will have numerous lightening holes.
The second photo shows the position of the vertical slots in the bottom of the basswood surface spar slots.
The next photo shows the spar slotting templates pinned in place on the core; one on top and one on the bottom. The hot wire apparatus will be used to cut the slots. Again, I didn't have a helper to take photos on this occasion, so you will have to use your imagination and picture the slots being cut...
The last photo for this segment shows the piece of foam that was cut to form the vertical slot. I can now use this piece of foam to layout the actual spar shape!
Till later; my wife is making waffles and I don't want to miss out on that! An added bonus is the homemade maple syrup that Rick and Saramarie Huff always gift us. They actually tap their own Maple trees up there in Vermont! - Bob
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The waffles were delicious; thanks again Rick and Saramarie!
Back to work: The next four photos depict the Lite-Ply spar layout and installation. The photos show only one, but two must be made and installed; one for each core half.
Note the lightening holes and the bellcrank swing clearance slots in the spar half in the third photo. Note also that the lower basswood surface spar is dry fit into its slot to act as a positioner for the vertical Lite-Ply spar. It is important that the Lite-Ply spar is positioned to allow both the top and bottom basswood spars to sit flush with the top and bottom of the core.
I install the Lite-Ply vertical spars by smearing Titebond II Aliphatic Resin on both sides of the spar. I then carefully spread the slot in the core open to allow the vertical spar to be positioned without wiping off any of the glue. Then I position the core in its cradle with the lower basswood spar in position and double check that the vertical spar is flush with the bottom of the surface spars slots on both sides.
More to come... _ Bob
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Of course, Bob. Glad you like the syrup.
I'm looking forward to the rest of this thread,
Rick
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While the Lite-Ply vertical spars are drying in the wing cores, let's begin making the fuselage. While the nacelles for this model will be profile units, the fuselage is a normal built-up box structure.
I start out by selecting two pieces of 36-inch long, 3-inch wide, 3/32-inch thick, medium density, straight grain (A or AB grain) balsa. I intentionally designed this model to be built with 36-inch length balsa; longer balsa is getting to be "onobtanium" of late. Of course you could splice pieces together if need be, but in this case the normal 36-inch balsa is fine.
I tape the two pieces together and then slide the joined pieces under my tracing paper plan. I can easily see the top and bottom of the fuselage sides and I position the joined pieces of balsa to be covered by those portions of the plan. See photos one and two below.
The next step is to use map pins to mark on the outline of the fuselage side by sticking the pins through the plan at the edges of the fuselage drawing. Note that for the wing cutout there needs to be a pin punch at the front of the wing opening and at the rear of the opening and that punch should be exactly on the center line of the wing. Pull the joined wood from beneath the plan and use a straightedge and pen to connect the punch marks. The last two photos for this segment show these steps. Note that the wing center line mark is also made at this time.
Note: Not shown in photos is the sequence of cutting out the fuselage sides along the layout lines. It is important that you keep the two sides firmly together and in alignment to one another while cutting them out. I cut one edge at a time, sand it smooth, re-tape that edge and then cut the next edge. This process is repeated until all the edges are cut and sanded.
Bob
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After cutting out the fuselage sides along the layout lines, the next step is to accurately mark out the wing opening. Remember that in the very first posting on this build thread that I showed a template panel cut chordwise at the point where the fuselage side will pass over the wing? Well now we are going to use that piece of foam to position and mark the wing opening on the taped up fuselage sides This is a tapered wing, and the point at which the fuselage passes over the wing needs to be made to fit the wing perfectly with no need for additional sanding or shimming. The foam "plug gauge" (as I like to call it) does this job perfectly.
In the first photo the plug gauge is positioned with its center line directly on the center line that we drew on the fuselage side at the wing position. Photo two shows the opening accurately scribed onto the fuselage side sandwich.
In photos three and four you can see that a piece of sharpened brass tubing is being used to make a hole that is the same diameter as the leading edge of the core. Actually the one I'm using here is a special tool that Tom Huff made for me (actually he made a whole range of diameter tools for me!) that cuts the hole by twisting and pushing the tool through the balsa. The tool has a plunger that then ejects the balsa disk! Thanks a bunch, Tom; I've found myriad uses for these tools. Hopefully I can convince Tom to do a photo essay on how to make them.
Bob
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Hi Bob, thanks for sharing you new plane construction with us! I'll be watching along the way. I'm building a profile Pathfinder electric twin right now.
Dave
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Hi Dave:
If your Pathfinder Twin flies as well as Gordy's does you'll be a happy camper! Happy New Year man!
Okay, the Eagles threw the game last night and my Giants are out of it; even though we beat the dreaded Cowboys! Take that Mike Scott! LL~ I'm bummed, but we need to press on...
We left off last time in the middle of cutting out the wing hole in the fuselage sides. After making the hole at the leading edge with the sharpened brass tubing I cheat and use the actual foam cutting root template as a sort of French Curve to guide the knife. Whatever method you decide to use, be very careful to not make the wing hole too large. I typically cut inside the desired line and then use the plug gauge to check the opening. I trim and sand the opening until the plug gauge fits perfectly into the opening with its center line on the center line drawn of the fuselage side when it was laid out. The first three photos below should clarify this operation sufficiently.
Next, un-tape the fuselage sides and lay them top to top on a clean bench (don't want any dings left in the sides by old dried glue), and transfer the former positions as shown in the fourth photo.
Bob
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The next step is to make and glue the 1/32-inch plywood doublers to the fuselage sides. Back in the early 1970s my very good friend, Richie Tower came up with the idea of molding the doublers to the fuselage sides in a foam fixture. That allowed us to get the nose of our planes faired into the spinner much more easily. It remove the stresses from having to bend the fuse side and doubler sandwich to conform to the shape we desired. Even though this model's fuselage doesn't have to fair into a spinner, it does have to fair into a nose block later on. The first two photos below show the custom made foam fixture for this model. Later on I will make another fixture to make the nacelle sides fair into the spinners. (Yes, I can supply these custom made fixtures for any model...).
I cut my fuselage doublers to be about 1/8-inch outside the fuselage side perimeter on the top, bottom and in the front. I cut the rear of the doubler to size so that it can be positioned where required on the fuse side. Photo three below shows the fuselage sides taped in place in the fixture.
I use Z-Poxy Finishing Resin to glue the doublers onto the fuselage sides. Be careful to not use too much resin as it is heavy!
Note that the rear of the glued-up doublers are positioned just in front of a former station. Later on that former will fit up against the rear of the doublers. I tape the back end of the doublers in place so they won't move when the top piece of the fixture is put in place. See photo four.
I carefully position the top fixture piece and then weight down the assembly overnight. See photo number five.
Bob
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When the doublers have cured, remove them from the fixture and use a #11 blade knife and a straightedge to trim the doublers flush with the outside perimeter of the fuselage sides. See photos 1 and 2 below.
I use a 1/8-inch diameter carbide bit in my hand tool to remove most of the doubler material in the wing opening. Obviously I staged photo three below because I could not hold the fuselage side, the running hand tool and the camera all at once! Man, do I miss having a cameraman... Be very careful to not let the carbide bit get too close to the fuse opening; it can ruin your day... Photo four shows the removed piece.
I finish off the wing opening with a sanding drum in the hand tool. Again, work very slowly and carefully to not remove too much material. See photo five below.
Bob
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Use the plug gauge to insure the wing/fuselage fit is perfect after removing the excess doubler material. See photo 1.
Photo 2 shows the fuselage sides ready for crutch construction. At this point I am going to go back to the preparation of the wing cores. I will show some fuselage construction in this thread, but the method I use has been well covered in a manual that I have prepared called Tru-Fit Fuselage Construction. That manual in PDF form is available for free. Just send me an email request for it to robinhunt@rcn.com.
That's it for today; I have to go and do some actual work... Darn, I thought 2021 would be different...
Later - Bob
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I glued a few spars into foam cores and they are drying. That gives me a chance to do another segment or two today.
Since this is a non-sheeted wing, and it will have nacelles attached to it, I thought it wise to "harden" up the areas on which the nacelles will reside. There will be a lot of stress on them from cornering inertia and from landing loads as the main gear will be attached to the nacelles. This worked well on the "big" twin test bed model and we never had any problem with the joint between the wing and the nacelles.
The center of the nacelles on this model will be located 7-inches out from the center line of the wing. I decided to install a 3/8-inch wide medium density balsa "rib" at that point on each core half. The back of the rib will butt up against the Lite-Ply vertical spar, and the inboard rib will have to be relieved to allow the front leadout to pass through it. So, photo one shows the laid out position of one of the ribs on one of the cores.
In photo two you can see that I've made plywood templates to allow me to cut an accurate slot to accept the ribs.
In photo three you can see that the slot has been accurately cut with the hot wire apparatus.
Photo four shows a piece of 3/8-inch balsa pushed into the slot and all the way back to the Lite-Ply spar.
Note: Due to photo file size I can only post four photos at the size I want at one time.
Bob
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In photo one the shape of the rib is being scribed onto the 3/8-inch balsa piece.
Photo two shows the two ribs laid out on the balsa. Note that the inboard rib has been laid out to include a passage for the forward leadout.
Photo three depicts the two ribs cut to size. I use a jig saw for this.
Before these ribs can be glued into the cores, the front section of the core must be cored out. Photo four shows the cored piece coming out of the wing core.
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After a quick test fitting (see photo one below) the ribs are ready to be glued into the cores. The ribs should be just proud of the surface of the core to allow for final sanding to match the core's surface later on.
I use Titebond II Aliphatic Resin glue to install the ribs. See photo 2 below. I place a piece of waxed paper under the rib to prevent it sticking to the cradle.
After the glue has dried throughly, carefully block sand the ribs to match the airfoil of the core. See photo 3.
That's it for today; I have to size more photos before I can continue.
Later - Bob
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The next step on the Lost-Sheeting wing is to install a vertical grain shear web between the end of the Lite-Ply vertical spar and the wing tip in each core half. The Lite-Ply spars on this particular wing are a bit longer than I typically use on single motor airplane because they go out beyond the area where the nacelles are located and I wanted to have the additional strength at that point. For that reason the additional shear webs may not actually be needed, but I'm installing them anyway; belt and suspenders...
Split the difference between the end of the Lite-Ply vertical spar and the tip of the core and make a mark there in the bottom of the basswood surface spar channel. In the case of this wing that dimension is eight inches.
Photo one shows the tools I use to make the shear web slot in the channel. Needed are two 1/16-inch plywood templates that have a 1/8-inch by 2-inch slot, and location lines on their surface that allow them to be accurately positioned. Also needed is a piece of 3/32-inch diameter music wire with one end imbedded in a wooden dowel. The 3/32-inch diameter wire should be about ten inches long.
Photo two shows the upper template masking taped in place above the basswood spar channel. The other template should be taped to the bottom of the wing in the same orientation to the spar channel.
Photo 3 shows that s a needle file has been pushed through the core between the two templates. This will allow our 3/32-inch diameter tool to be inserted through the core.
In photo five the wire tool has been pushed through the core far enough to allow its outer end to be heated with a propane torch. After heating the end of the tool it will be withdrawn to point where it can be moved along the template slot. It will melt out the foam to form a nominal 1/8-inch by 2-inch slot. Be very careful when removing the tool to not let it touch the surface of the core!
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Continuing on from the last post, photo 1 here shows the heated wire tool retracted into the core to cut (melt?) the shear web slot.
Photo 2 here shows the tool the templates and the shear web slot. Yes, I did wait for the tool to cool down before laying it on the core... <=
Photo three shows that a piece if 1/8-inch thick balsa cut to a 2-inch width has been inserted into the slot we just made. I place a basswood spar into the lower spar channel to act as a stop. Not shown (forgot to take the photo. Hey, I'm getting old..) is marking the top end of the shear web to match the surface of the channel. I think that one is obvious...
And finally, photo 4 shows the shear web installed using Titebond II glue. There will be one additional "anchor" for the basswood spar to prevent racking. A Lite-Ply wing tip piece will be installed on each core and they will be notched to accept the spar.
Bob
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Time to make the tip plates.
Photo 1 below shows me tracing the tip airfoil onto a piece of 1/8-inch thick Lite-Ply (Poplar Plywood). Layout two plates; one for the inboard wing and one for the outboard wing.
Photo 2: Measure and scribe a center line on the tip plate pieces.
Photo 3 shows one of the tip plates cut out and the spar locations marked for cutting.
In photo 4 a fully prepared outboard tip plate is ready to glue to the outboard core. The inboard tip plate will need a bit more work as we shall cover starting in the next segment.
Bob
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You are a master Bob. Everybody, pay attention on how Bob does things. It will serve you well!
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Wow! Thanks for those amazing words, Crist. All I'm trying to do is "pay it forward." If those who follow the thread get something out of it, I'm a happy guy.
I'll post a couple more segments later today. Next up will be how to make a very simple adjustable leadout guide for this model.
Thanks for the kudos - Bob
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The flat plate Lite-Ply tips allow for a very simple adjustable leadout guide. The technique I'm going to show now is one I learned from Billy Werwage.
Along the center line on the inboard tip plate I mark and drill a number of 1/8-inch diameter holes. See photo one below. I space these holes 1/4-inch apart on center. The number and spacing of the holes is determined by how much adjustment you think you will need. I've always put in more than I will probably ever need, but lately I've been experimenting outside the envelope, so a few more in this case couldn't hurt.
Photo two shows a 1/8-inch thick by 3/8-inch wide basswood strip that will thicken up the area where the nylon leadout guide bushings will later reside. Glue this strip over the area where the leadout guide holes are drilled.
The last hole (most rearward one) should be drilled out to a diameter that will allow you to snake a jig saw blade through it. I place a couple of pieces of scrap 1/8-inch by 3/8-inch basswood adjacent to the thickener to prevent the tip plate from rocking on the jig saw table, and then carefully saw forward through the holes to make the beginning of a slot through which the leadouts can pass when adjusting them. Photo three below will hopefully clarify this...
Photo four below shows me using a piece of Permagrit to open the slot to be just a bit wider than the leadouts are in diameter. It's best to test the size of this slot with an actual leadout to be certain that you've opened the slot enough! The Permagrit plate is a replacement piece for the Permagrit sanding bars. Any thin sanding tool will suffice to do this job, by the Permagrit plates are just great. I strongly suggest doing a search on the Internet for Permagrit tools.
Bob
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Photo one below shows the inboard side of the inboard tip plate with the thickener piece. Note that the slot between the leadout adjustment holes has been widened out to allow the leadouts to slide fore and aft in the plate.
Photo two shows the outboard side of the inboard tip plate.
It is important here to mention that the foam spar between the front and rear cored out areas in the inboard wing panel needs to be relieved out near the tip to allow the front leadout to swing back as far as might be required without rubbing against the foam spar. Don't take too much foam away spanwise as that might cause the outboard end of the core to "dish." I usually use a coarse rat tail file to contour the front foam spar inside the wing to allow the proper amount of clearance. Again, there is no photo showing this.
Next, glue the plates (both inboard and outboard) to the end of the core, being very sure to line up the basswood spar slots. I use Titebond II glue to do this. Tape the tip plates in place and let them dry. There is no photo showing the gluing procedure.
The tip plates should be made just a tiny bit oversize to allow for a detail sanding. Be very careful to block sand the tip plates until their edges are flush with the foam. Work slowly here, being very cautious to not tilt the sanding block towards the foam core; it would be easy at this point to concave the core with the sanding block. And that would be bad... %^@ See photo three.
Hey, I'm out of photos. That means I have to go do more work and take more pictures. I'll try to have something ready to post tomorrow.
Later - Bob
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I have no particular interest in twins --- but this is going tobe good.
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IMO, what Bob is trying to do here really should motivate guys who wish to experience a twin , but desire minimal work and cost.
I built a full fuse twin," TURNING POINT", that Bob designed a few years back.
It's full house ; retracts and all.
A treat to fly.
In the hands of someone like Bob, it's a weapon !
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Dam. I'm jealous of yous guys that paint and make those so beautiful
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wow Bob. Cool!
Two Park 480's???
I flew the first B-17 with 4 Park 480's at 120 ounces, and power was NOT the issue!
I suspect you will have "ample" power!
Good luck.
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IMO, what Bob is trying to do here really should motivate guys who wish to experience a twin , but desire minimal work and cost.
I built a full fuse twin," TURNING POINT", that Bob designed a few years back.
It's full house ; retracts and all.
A treat to fly.
In the hands of someone like Bob, it's a weapon !
Saweet!! y1 #^ %^@ ;D
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Bob, the old DOC gets a lot of info from your construction posts and I've borrowed a lot of them on different planes. Thanks for all you do here. H^^
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Whew! Glad to hear that Paul! Actually I have two Park 450 motors. I figured that if I was light on power I could go to the 480s. Looks like I won't have to. I'd opt for an even smaller motor if I could find one with 4mm shafts. Actually I was hoping to find a small motor with a 5mm shaft. Guess your experiences with the B-17 and the 480s should assuage my worries.
I'm thinking that a 5S 2400 pack would be more than sufficient to run both motors for 5 minutes and 20 seconds.
Doc: Glad you are getting something out of this thread. I enjoy doing these build threads. Keeps me active...
Dwayne: The photo of Frank's Turning Point twin does not do it justice; it is just gorgeous. And, it is one of the finest flying models I've ever flown. It's right up there with Gordan Delaney's Pathfinder Profile Twin, and anyone who had flown that ship will tell you that is high praise. I'm finally building a Turning Point for myself. When I designed it I was in the midst of another project and didn't want to start yet another stunt model (I already have 7 projects underway...)
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Bob, that is a great idea that you have made a reality! Yea, and its cool too!
Doug
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I left off at the point of opening the sawn slot between the leadout adjustment hole locations in the inboard Lite-Ply tip plate. That slot needs to be wide enough top to bottom to allow that leadout wires to pass through it easily. The tip plates had been glued to the core and then sanded carefully to make the edges of the pates match the core, without altering the airfoil of the wing.
At this point there are two tip options: You can simply leave the tip plates as they are and have a squared-off wing at the tips (as I did with the big test bed twin pictured somewhere above), or you can opt to add carved balsa tips as you would on a normal wing stunt model. On this occasion I chose to go with the carved balsa tips. I decided to make them about an inch wide to allow for a pleasant curve. Photo 1 below shows the two balsa tip blanks. They were cut just a bit oversize to allow them to be sanded flush with the top and bottom of the core at either end of the wing.
The next step is to tack glue the wing tip blanks to the Lite-Ply tip plates. See photo 2. Be sure to align the wing tip blanks so that there is sufficient balsa proud of the tip plates all around to allow them to be sanded flush with the plates.
When the glue has dried, carefully block sand the wing tip blanks flush with the tip plates as shown in photo 3.
Photo 4 shows that a center line has been drawn on the outer edge of wing tip blank, and that two more lines have been drawn that are parallel to the center line. In this case these lines are 3/8-inch above and below the center line.
More to come... - Bob
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I begin shaping the tips by using a number 26 Whittler's blade and a #2 X-Acto knife handle to make a 45 degree angle cut between the upper line and the top of the tip and then from the lower line to the bottom of the tip. See photos 1 and 2 below.
Carving is an acquired skill, and it was my father who taught me how to do it. He almost gave up on me because it took me so long to understand the sequence that is required and the techniques that must be mastered. I did finally "get it." The single most useful tip he gave me was to "take off the high points." To achieve the shape you want, you need to first visualize the finished product and then work slowly and carefully towards making that shape a reality. Every time to shave off a sliver of balsa you will leave two high points; one at the top of the cut, and one at the bottom of the cut. The next swipe with the blade should be to take a smaller sliver off of each of those high points. You will have to repeat this process dozens (if not hundreds...) of times in ever-diminishing amounts until the shape is complete. I hope the above is somewhat clear; it is difficult to explain such a concept in words and still photos. Like the artist said about the statue he was sculpting, "I just take off everything that doesn't look like the thing I'm trying to sculpt." Sound reasonable, but it does take a lot of practice, and a lot of patience! Work slowly and try to bring the shape on the top and bottom down equally until you are happy with the result. The carved tip - ready for sanding - should look a bit like photo #3 below.
When I have carved the tip to almost the shape I want, I use a 1-inch wide sanding stick to blend the shape to a smooth contour. Again, I look for the high points and take off the edges! See photo 4.
Moving on... - Bob
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Photo1 below shows the tip finish sanded and ready to be "popped" off the tip plate for hollowing.
Note: I decided to go with the carved balsa tips after I had already made the adjustable leadout guide in the tip plates. If you know in advance that you are going with carved balsa tips, you can opt to put the adjustable leadout guide in the tip using whatever method you prefer.
In photo 2 the carved tip has been removed from the tip plate. And in photo 3 you can see that I have made a center line on the tip to guide me in making the opening for the leadouts.
Photo 4 Shows a 1/2-inch diameter brass tube with a sharpened end. I twist the tube while pushing down to make a clean hole in the end of the tip.
Bob
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Photo 1 below shows that I have made two 1/2-inch dimeter holes with the sharpened brass tube, and have connected them by carefully cutting with a knife. The edges of the slot have been sanded smooth. Note that If you opted to make the adjustable leadout guide reside in the end of the wing tip, this large clearance hole is not required. I needed a wide slot to prevent the leadouts from hitting the top and bottom of the tip in case the model rolled to any degree in turbulence.
Use a router and a gouge to hollow out the tip to remove excess weight. See photo 2.
Note that with the leadout guide method that I use, the leadouts will pass through two Delrin "bushings." The bushings press fit into the holes that were drilled in the Lite-Ply tip plates. They can be retracted and moved as required to trim the model. See photo 3.
In photo 4 the carved and hollowed balsa wing tip has been permanently glued to the Lite-Ply tip plate. When the glue dries the joint will be sanded smooth with a sanding block.
Bob
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Sweeeet!
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Thanks, Crist!
Okay, it's time to think about a control system.
For this model I used a Brett Buck style bellcrank. It was positioned on a 1/8-inch diameter music wire shaft and secured with two 1/8-inch wheel collars. I made shallow flats in the 1/8-inch shaft to be certain that the set screws in the wheel collars were not just hitting on the outside radius of the shaft. After the bellcrank had been positioned and secured, I mixed up some JB Weld and "welded" the wheel collars to the shaft to fully insure that they would not move in the future. See photo 1 below. Also shown in this photo is the ball link and the 3/16-inch diameter carbon fiber pushrod. Note that the aft end of the pushrod does not yet have the rear ball link installed. This will be explained later. Note also that clearance has been cut into the top of the inboard core to allow the pushrod to exit the top of the wing. Another slot to mirror this one will have to be cut in the top of the outboard core.
This model has a built-up fuselage and I wanted the pushrod to exit the wing on the center line of the two cores when they are joined. To achieve this I dry fit two 1/8-inch by 3/8-inch basswood spar pieces in the slots in the top and bottom of the inboard core, and then used a 1/8-inch diameter needle file to make a slot that was 3/4-inch deep into the core just behind the basswood pieces. Photo 2 should clarify this. There will still be room between the bellcrank mount post and the inboard side of the fuselage when the wing is installed. Two plywood plates - one on top and one on the bottom will be fit over the bellcrank mount shaft and the fuselage sides. Those plates will form the actual bellcrank mount.
Dry fit the bellcrank assembly into the inboard core. At this point you will need to verify that the bellcrank can swing through the opening in the Lite-Ply spars with no rubbing anywhere. Note that the 1/8-inch bellcrank mount shaft has been shortened so that only about 3/16-inch of the shaft extends above and below the core. Shortening the shaft requires a cutoff disk and a hand tool. The cutting generates a lot of heat. Too much heat will melt foam... Get the picture? Shorten the shaft before installing the bellcrank!
Photo 3 shows the bellcrank assembly glued into the slot in the inboard core half. I use 30 minute epoxy and micro balloons to do this. Here's a tip: Use a round toothpick to position the epoxy accurately in the slot. Put the bellcrank assembly into the slot, check the alignment one more time, and then put some more epoxy onto the bellcrank mount post. If you look closely in Photo 3 below you will be able to see the epoxy.
Photo 4 shows the bellcrank swung aft. Check its swing in both directions before moving on.
Bob
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Big piece this time! We are going to prepare to join the cores into a wing! #^
The lower cradles (the pieces from which the cores were cut) need to have about i-inch of material removed at the root from their length. The reason for this is that we are going to lay the cores in their respective cradles and use the cradles as fixtures in which the wing halves will be joined. If the cradles were left full span, the glue might seep down from the joint and glue the cores to the cradles. We will line up the tip end of the cores with the tip end of the cradles to insure that everything is in proper orientation. See photo 1.
On this wing the flaps are integral in the cores and will be separated from the wing after the carbon mat has been applied. You can see in the photos below that I have marked the foam portion of the flap leading edge, and the rear of the foam on the core. The separation between these two lines indicates where balsa framing will be glued on later. This piece of foam will be removed later. The flaps will have a 3/8-inch wide leading edge piece installed that will have a bevel for proper movement, and accept the hinges. The rear of the wing portion will have a 3/16-inch wide trailing edge cap installed to accept the hinges. The lines I drew may not be visible trough the carbon later on, so I have made saw cuts at the leading edge of the foam portion of the flaps and the trailing edge of the foam on the wing side at the tip on both top and bottom. I've also cut away the foam at the root to allow me to know where to later position the straight edge to enable me to cut the flaps loose and remove the foam piece between the flap leading edge and the wing trailing edge. Hopefully this is clear; if not, it will become clear later on... See photos 2 and 3 below.
Next, position the cores into their respective lower cradle pieces and line up the tip of the core with the end of the cradle. Tape the core to the cradle in several places along its length to insure that it will not shift. See photo 4.
Bob
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Quick note here: I forgot to mention that I carved and hollowed the outboard wing tip and then installed a tip weight box into the tip. Everyone has their own favorite method of making a tip weight box, so I won't go into detail on that.
Photo 1 below shows what you will need for the next step - joining the cores into a wing! Note that the cores are taped in place in their respective lower cradles, and that a piece of 48-inch long, 1/8-inch by 3/8-inch basswood has been selected to be the top spar piece. Yes, the wing is longer than 48 inches when joined, so you will have to center the basswood spar in its slot and then add short filler pieces at the ends of the slot later on. The stresses are so low at that point on the wing that it really doesn't matter...
You can use either Titebond II Aliphatic Resin glue or 30 minute epoxy to join the cores. On this wing I used the Titebond.
Time to join the cores! Note that I glue and insert round toothpicks into the holes that held the cutting templates onto the foam blank when the cores were cut. These holes are right on the center line and they help a bit in sliding the wing together accurately. Not a must, just something I do... Apply glue to the mating face of one of the cores (see photo 2) and then carefully slide the cores together on a FLAT bench. Your wing will only be as accurate as the bench on which you join it together!. Pull the cores together using strips of masking tape.
Next, run a generous bead of glue along the bottom of the spar slot and then push the basswood spar into the channel. Some glue may ooze out from around the edges of the spar. Just use a paper towel wetted with water to clean those areas. Next, place a number of weights onto the basswood spar to hold it down firmly in the spar channel. The weights need to be supported just by the basswood spar and not be pressing down on the adjacent foam. See photo 3 Let this assembly dry throughly and then invert the wing and realign it in the cradle pieces and glue in the bottom basswood spar in the same manner as you did the top spar piece. Again, let everything dry throughly! Photos 3 and 4 should clarify the above steps for you.
Bob
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Awesome build, everything is so easy to understand. Question- Why not have the slot for the vertical bellcrank support in the middle of the spar slot, then just have a hole drilled in the spar that fits over it?? That way it's supported by the spar? Or is this something I'll understand in the next step y1
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Hi Bill:
Glad you find this easy to understand; that was my goal...
I didn't want to compromise the integrity of the basswood spar in any way; it is the heart of the Lost-Sheeting method. The way I showed to mount the crank is exactly how I do it in my fully sheeted foam wings and in my built-up wings. The two aforementioned plywood bellcrank mounts that will reside between the fuselage sides and brace up against the fuselage doublers has proven to be very effective. In this model those plywood plates will also be glued to the outside of the basswood spars for even more strength.
Also, the basswood spar is centered over the Lite-Ply vertical spar and there just isn't room fo anything else at that location.
Later - Bob
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I cut the cores so that the trailing edge of the flap section is 3/32-inch thick. That allows me to glue a strip of 1/4-inch by 3/32-inch basswood onto the back of the flap area to give that area some stiffness and to prevent it from getting dinged from use. See photo 1 below. I attach this strip with Titebond II glue and use several strips of masking tape to hold it in position accurately.
When the glue on basswood strip has dried, I lay the trailing edge down against a flat bench to support it and very carefully taper it to conform to the wing's airfoil shape. It is very important here to not allow the sanding block to mar the core's surface. See photo 2.
I next cut a piece of .2 carbon mat that is an inch to two inches larger all around than needed to do one half of one wing panel. I lightly sand the root edge of that piece of carbon to feather its edge. This prevents the carbon from forming a stress riser at one point along the wing's chord line. See photo 3.
Position the wing in the lower cradle pieces. I like to place a piece of waxed paper under the wing to prevent the glue from getting onto the cradle during the next step. Note that outboard panel is the first one that will be covered, and that I've laid the root end of the carbon over the center joint and out onto the the inboard panel a bit. Later I will overlap the inboard piece of carbon out onto the outboard panel a bit to yield a double overlap of carbon on the area where the fuselage will reside. See photo 4.
Bob
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The carbon is attached to the wing using a mixture of Titebond II Aliphatic Resin glue and water. The exact mixture is about 5 parts glue to 1 1/2 parts water. You will understand better how much of each to use when you actually start trying this method. The important thing is to use just enough water to allow the glue to be brushed easily through the carbon and onto the foam below. It's a "feel" thing... I use either an acid brush or a 1-inch wide chip brush to apply the glue/water mixture. See photo 1 below. You need to work fairly quickly, and insure that the carbon is laying down perfectly against the foam's surface. You can brush out any wrinkles. Be very careful trying to smooth the wrinkles out with your hand as that may actually move the fibers in the carbon enough to separate them and leave a bare spot - not good... (Don't ask me how I know...)
When you are finished brushing the glue through the carbon and the entire wing is covered, hold the wing up to a light and "candle" the surface to insure that the carbon is laying down perfectly. See photo 2. I like to wrap the carbon just a bit more than half way around the leading edge of the wing and then trim it with a sharp #11 blade knife. before the glue starts to dry. There is no photo showing this.
After the glue has dried, you can use a sanding stick to "trim" the carbon against the trailing edge. See Photo 3.
Repeat this process to cover the other three panels on the wing. See photo 4. When the entire wing has been covered and the glue is throughly dry, very lightly sand the surface of the wing to make it smooth. Don't sand too much!
Bob
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Nice!
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Thanks, Crist!
Just a note about the carbon covered foam, its strength and rationale for making wings in this manner. I covered (no pun intended...) some of this earlier, but it needs repeating and perhaps clarifying.
The genesis (you just knew I'd get that word in here somewhere...) of this idea goes back to the days when I was the Contest Director of the Brodak Fly-In. We were adding Slow Combat to the contest menu and I needed an event director. I called my very good and long-time friend, Phil Cartier and asked him if he would serve in that capacity. He agreed, but with one big stipulation; I had to enter and fly in the slow Combat event! I told him that I didn't have any combat planes and hadn't flown in Combat since the 1960s (well, except for one flight at a meet somewhere in the 1970s). Actually I started my competition career in Combat and even flew in the Junior division at the 1961 Nats in Willow Grove.
Phil said not to worry; he'd lend me a plane, engine and arrange for a pit crew. He told me all I had to do was go as far as I could in the contest until I was eliminated and he'd be happy. Okay, that sounded fair to me. Little did I know that he planned (now, he will deny all this, but you be the judge...) to set up the "stunt kid" to be knocked around by some of the very best Combat fliers in the area, starting with our now departed good friend Gil Reedy, and followed by Bub Reece and the man himself, Phil Cartier. Hey, it was all in good fun. At least it was for me; at the end of the contest I gave Phil back his plane and engine, thanked him for the loan, and then collected my first place trophy in Slow Combat! I had won every match!
Well, naturally Phil, Bub and Gil had some well-deserved egg on their faces, but we all got a good laugh out of it. The problem was, Phil had lit an old fire and now I wanted to fly Slow Combat and Stunt competitively! I started calling Phil almost every day with questions about how to get started with the best equipment. He suggested building one of his Gotcha series Slow Combat models. Being a foam cutter myself, I opted to work from plans and make my own fleet of planes. Phil schooled me about the construction techniques required to make a foam wing model without any sheeting. The basswood spars with shear web technique all came from Phil. He advised me to also use his plastic film covering material over the wing (I forgot the name of that material...). I fully understood the practicality of using that material, but to be truthful, I really didn't like the look of it. Yeah, my aesthetic sensibilities from years of building Stunt models kicked in.
At that point the Stunt world had discovered the .2 oz/Sq. Yd. carbon mat material, and we were attaching it to the balsa airframes using Nitrate dope. I liked the way the Stunt models looked covered with the carbon before the painting process started. I reasoned that the carbon could be attached to the raw foam wing cores using water thinned Titebond, and quickly did a test panel using that method. It worked so well, added so little weight, and imparted so much strength that I went ahead and used it on my first Slow Combat model, which, by the way I named "Slip Knot," after the Grateful Dead song of the same name. Hey, I'm a huge Jerry Garcia fan...
There was a Slow Combat event scheduled for the next weekend at Middlesex, NJ, and Phil, Gil, and Bub said that they would stop by (my house was on the way to the contest) and pick me up. I kind of felt like the "rookie" member of their Combat team at that point. They arrived at my house early in the morning and walked into my shop. I had my new carbon covered model all ready to go. I had built it like a small Stunt model; everything was carefully fitted, sanded and finished, and I even had made up a "Slip Knot" logo to go on the wing! It looked like a competition profile stunt model! I'll never forget what Phil said when he first saw that model; "You are going to fly that in Combat? It's too good looking!"
That model flew very well; albeit for a very short time. I got mid-aired during my first match with the Slip Knot. But, I did get to have a few practice flights with it before the destruction began. Suddenly my bubble had burst; I wasn't going to repeat my performance at the Brodak meet... I probably should have quit while I was ahead. :P
I did finish a second Slip Knot and took it out to a practice session with Phil, Bub and Gil at their field near Hershey, PA. Phil took a flight on that model and told me that it was about the best flying Slow Combat model he'd ever flown. That just amazed me.
Well, as you probably guessed, my Slow Combat career never really got off the ground (so to speak...). But, a few years later the lessons learned from building those models would pay some dividends. My good buddy, Mark Weiss called and asked me if I would like to come down to South Carolina and help out with the CL portion of the Joe Nall Fly-In. Mark and his crew had been teaching people to fly control line using the Ringrat models that are manufactured by Stevens Aero. They did the job of basic flight training perfectly, and proved to be so rugged that they have survived that duty for many years now.
Mark had the idea to have a more advanced model available at the "Nall" for those who had graduated from the Ringrat and were ready for some aerobatic training. I volunteered (was volunteered...?) to design and build five simple profile models for that year's upcoming Fly-In. Trouble was, it was only a couple of weeks away! That's when Dean Pappas and I brainstormed the Joe Nall Cadet. It was designed to look a bit like the Yak full-scale aerobatic design that had a big radial engine. Hey, that look was the vogue at that time.
I enlisted an all-star team to help make parts for the Joe Nall Cadet, including Ken Armish, Tom Hampshire. Frank Imbriaco, Mark Weiss and Buddy Wieder. I took on the chore of making the foam wings and the foam core/balsa sheeted fuselages for that model and it hit me that the carbon mat method used on the Slip Knot would be the perfect way to expedite these models. I have no idea how we did it, but on the day Ken Armish and I were scheduled to leave for the Fly-In, there were five ready to fly Cadets to put in Ken's trailer. I must at this point give some credit to my good friend, Warren Walker, who used his amazing metal working skills to produce the custom dural landing gear legs for those models in record time. Some things are just meant to be.
I reasoned when getting ready to cover the wings for the Joe Nall Cadets that only the leading edge and trailing edge areas really needed to be covered. The strength in those wing came from the basswood spars and the shear webs between them. And, those models flew very well They were full pattern capable and impressed a lot of people with their performance at the Fly-In.
Around that same time Buddy Wieder and I had built the big test bed twin that was pictured earlier in this thread. Again we covered the leading edge and the trailing edge areas - and the flaps - with the carbon mat. The test bed twin flew very well, but Dean Pappas suggested that it might fly even better with the entire wing covered with the carbon mat. And so we did that, and he was right; it flew a bit better! We then retrocovered (new word?) some of the surviving Joe Nall Cadets in that manner and they too flew better.
I did one more model using the carbon mat/Titebond glue method recently. It is the E-Bug Lite, a profile electric version of Bob Baron's Humbug with some updated aesthetics to make it look more jet-like. See photos below.
So, when it was decided to design a simple to build, inexpensive electric twin, the carbon mat/Titebond glue method just made sense. Of course, if someone wanted to build this model with a balsa covered foam wing, it would work just as well, and I will supply that type of wing for this design in the future, as well as the Lost-Sheeting cores. Let's get it finished and test flown first...
Okay, that is a bit of backstory on this technique, and some history of the models on which it was used (thank you Sheldon...).
Later - Bob
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Hope everyone had a great weekend. And I hope Mahomes is going to be okay to go against the Bills on Sunday... Hey, I'm a life-long Giants fan, but it is hard to not root for an amazing talent like Mahomes. Come to think of it, Allen isn't to shabby either!
Okay, back to work...
In photo one below I've cut strips of .2 ounce/Sq. Yd. carbon with which to double cover just the flaps.
In photo 2 you can see that one strip of carbon has been positioned on the flap. Actually I cover forward into the area that will be removed to allow for a 3/16-inch thick balsa trailing edge cap on the wing and a 3/8-inch balsa cap on the front of the flaps. This insures that all of the flap will be covered with the second layer of carbon, but that none of the wing portion will get a second layer.
Photo 3 shows the carbon wetted with the Titebond II glue and water mixture. It will be allowed to dry thoroughly before the flaps are separated from the wing.
In photo 4 you can see that I'm using a straightedge and a sharp #11 blade to cut through the carbon and the foam along the flap separation line. Note that the knife is tilted. Repeat this on the bottom of the wing along the flap separation line and the result will be a "tent peak" of foam that can be block sanded to yield a flat surface onto which the flap leading edge cap can be glued.
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Repeat the process of tilting the knife to cut along the back of the wing where the trailing edge cap will reside, only this time tilt the knife as shown to leave the "tent peak" of foam rearward. See photo 1.
Photo 2 shows the separated parts and the piece of foam between the wing and the flap that will be discarded.
Sand the trailing edge of the wing flat and then sand the leading edge of the flaps flat. See photo 3.
I threw photo 4 in just because it is a neat perspective of the wing. Looks long doesn't it? Looks can be deceiving...
Bob
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Cut two strips of 3/16-inch thick balsa that are just a bit wider than the trailing edge of the wing, and then glue them to the wing and use strips of masking tape to hold them in place. See photo 1 below. Don't use too much glue as the tape will cause it to ooze out of the joint and make it much more difficult to trim and sand in the next step .
Lay pieces of 3M Blue Painter's tape along the edge between the wing's surface and the trailing edge strips See photo 2.
I then use a Solingen Razor Plane to carefully trim the trailing edge cap down close to the tape's surface. See photo 3 below.
The next step is to sand the trailing edge caps down flush with the tape's surface as shown in photo 4.
Next, remove the tape and very carefully sand the trailing edge cap flush with the wing's surface (no photo).
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Bob's build logs are the best! He is very detailed and his pics are perfect.
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That is so cool. I like the process.
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Hi Bob;
Saw in a pervious reply that someone said the KR does not have a retract feature. That is incorrect. KR has a retract version. It works as follows: 15 seconds after the motor starts the retract come up (this time can be adjusted) when the motor "blips" (10 seconds before the flight ends) the retracts come down.
When Dave Sabon built his electric twin I sent him one of the KR's which he used with good success. Dave also used two motors with ESC's plus a single battery.
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Good information , Eric. I have never used the KR system, so I couldn't comment on its features. I do know that the active timer I am currently using, and intend to use in my competition twins, has a retract feature that insures that the gear will come down whenever the motor (s) stop running - for any reason... That is comforting. y1
The Hubin retract function is by timer, and I used that in my Second Wind twin with no problems; I just like the added safety of the motor off/gear down feature no matter where it happens in the flight. The Fiorotti system I am using now has that feature. I'm pretty sure the Igor timer system has that feature as well, but I'm not certain of that. Someone enlighten me...
This thread has come to a brief (hopefully) stop while I'm waiting for some more .2 carbon mat. I did a stupid thing (latest in a long line of them...) and broke one of the flaps. I cut a new one, but I ran out of carbon. It should be here this week and I'll get going again.
I guess I could get started on the crutch construction as the fuselage sides are ready. Again, I have a manual that shows how I build my fuselages. I call my technique Tru-Fit Fuselage Construction. That manual (and a few others) is available for free. Just send me an email at robinhunt@rcn.com and I'll forward it (them) immediately.
Hope to be posting photos and text again soon.
Later - Bob Hunt
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I'm pretty sure the Igor timer system has that feature as well, but I'm not certain of that. Someone enlighten me...
I see I again missed great thread here, sorry Bob I did not see it before. I like that building, I see I must show it to our kids, I am sure they will make milion of different models this way :- ))))
But to your question -
Yes and no ;D. My timer does not do anything only controlls motor. I always concentrate to make the function fully implemented tested and well working and not to give other side fancy functions. So no, my standard timer does not have any buttons, landing gears lights and similar things. However my timers are modular, so in case that model needs another function there is no problem to add any other specialized gadget. In this case I have specialized timer for landing gears synchronized with main timer. Of course it is programmable by Jetibox and beside its normal function it has also input for RPM sensor with adjustable rpm. It can be any standard R/C device, so it will work with sensor for standard motor, or also magnet sensor for IC engines etc. That means it can be used also without my timer with accelerometer. Optionally it can be also connected to speed sensor or centrifugal sensor, but that is not good solution because it needs very good ajusting (so that does not extend when model slows in fugures, but act safely when it is really needed, does not react to whipping etc.) and I think it is not good idea to test landing gears with risk of landing to belly. Setting RPM is much simpler, exact and repeatable even on ground. Timer has many settings, beside RPM for emergency gear down with adjustable servo angle, it has slow motion retracting to look better (but emergency gear down function is quick). Unfortunately speed setting has no effect with electronic LGs. And of course it has "go home" button/jumper.
It also works with normal servos and standard hardware with lock arm, also servos without lock arm (so that it make hardware much simpler) and it is also tested with servo-less electronic landing gears which has little bit tricky controlls. Chris can tell stories about it :- ))
Here is picture how to connect it with my normal timer.
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Hi Igor:
Thanks for that clarification! H^^
Later - Bob
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Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?
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Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?
Welcome aboard Maksim. y1 #^
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Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?
Hi Maxsim:
Thanks for the interest in my little build blog.
The wing span of the Double Take (working title) twin is 54 1/2 inches, with a wing area of 538 square inches (including flaps). The hinge line to hinge line measurement is 16 inches. Te all up projected weight with battery is in the 45 to 47 ounce range. That may seem high for the area, but we have found that twins supply a lot more span of artificial air blast over the surfaces and hence a lot more lift, so the projected weight is actually very light for a twin.
It is my hope to be able to continue this thread very soon; still waiting for the carbon mat to make the new flap to replace the one I broke.
Later - Bob
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Hey Bob, I'm seriously considering this at around 600 sq in. range.
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Hey Bob, where are you getting you're carbon veil?
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Hey Bob, I'm seriously considering this at around 600 sq in. range.
You are a better (and braver...) man than me Gunga Din...
Bob
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Hey Bob, where are you getting you're carbon veil?
I get mine from Aerospace Composite Products, but Fiberglast and CST also carry it.
Later - Bob
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Thanks, Bob.
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projected weight with battery is in the 45 to 47 ounce range.
Wow, It seems that this will not be easy to do, given that the moto setup will weigh about 20 ounces, an empty plane should weigh no more than 26 Oz. What density foam are you using? And how much does a wing weigh without flaps now? And another question: will the model be painted?
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Hi Maksim:
The wing without flaps weighs 8.8 ounces. The flaps each weigh .80 ounces for a total of just over 11 ounces. The leadouts are not yet served, so there is some extra weight to be lost there, and there is no Flap horn installed yet, so there will be a few grams added there, but I think it is safe to say that the entire wing with flaps and controls will weight not over 12 ounces, and that is with the finish on! That gives me 14 ounces to hit the 26 ounce dry weight mark. That is easily doable.
See the photos below.
Later - Bob
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Great job, Bob!
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How's it going Bob, are you still working on this build?
Thanks
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Hi Dwayne:
It will be finished after the NAts. I've been working on my "real" twin in hopes of having it ready for the Nats.
Later - Bob
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Wow! Thats BA!
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Wow! Thats BA!
Ditto!
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Hi Dwayne:
It will be finished after the NAts. I've been working on my "real" twin in hopes of having it ready for the Nats.
Later - Bob
Thanks for the reply Bob, looking forward to it, plane looks very nice good luck at the Nats y1
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Looks awesome Bob!! Can’t wait to see it!!
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Bob, thanks for the directions and help.
Here is how my lost sheeting attempt came out. I am going to build one more of an Oosa-Amma. I wanted the two to look similar in the air and be able to reuse some of the templates. It will go a lot faster the second time. I will also keep in mind that this is not a long term model and be a little less concerned about some things being just right. Other than paint, I am not sure this one would have taken me any longer to do as a standard plane with sheeted wings and molded fuse shells. The wing can definitely be done quickly and it turns out light.
The foam fuse shells were a bit of a pain. On the second attempt, I made a template similar to a mold buck. I stuck the foam block in with double sided tape and then sanded to template shape. That turned out well. I used a hot wire to cut out the hollow in block and then used slices of the cut out for formers. Covered the fuse foam the same way I did the wings with veil and Titebond.
Double coats of veil work pretty well for numbers and the cockpit.
Page
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Looks really great Page! I'm looking forward to seeing this in person soon.
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Yikes, Page, that looks great! Very nice job! Please keep us informed of your progress with this model as you get some flying time on it.
Bob Hunt
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Page,
Nice job, could you give a brief summary of the vail/Titebond method you use to attach the vail to the foam. Was it easer to stick down with the Titebond then with Nitra? How much weight did the Titebond add?
Best, DennisT
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I did it the same way Bob outlines in this thread. Adding veil is very easy with thinned down Titebond. The wing is small. The area without flaps is 425. Covering added 35 grams to the wing.
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I had a chance to see Page's plane in person today. Very nicely done! It flies really well. Page did a great job building this plane and the wiring is cleanly routed.
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Well it's been a while since I focused on finishing up this small test bed electric twin. The spirit hit me this past week and I made a lot of progress on it.
I'm posting some photos here of the Double Take just before the nacelles are attached. Actually the model is mounted to the nacelles, not the other way around. The nacelles are assembled on a fixture and are in the proper location relative to each other. The fixtures hold the nacelles above the layout table (a piece of 2 pound foam in this case). The model gets mounted to the nacelles and is lined up to insure that the center lines of the nacelles are in line with the center line of the airframe. The skew is also aligned at this point, and when everything is perfectly aligned, the nacelles are glued to the wing. There are hard points in the wing core onto which the nacelles rest. The aft end of the nacelles also extend past the basswood surface spars on the top and bottom for added strength.
The Double Take will be powered by two E-Flite Park 450 motors. It has a wing area of 538 square inches (with flaps installed...), and the projected weight all up will be around 40 to 45 ounces.
I'll keep you all informed as this project proceeds. It's on the fast track now...
Later - Bob Hunt
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Here's one more photo of the assembly...
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Outstanding!
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Here's one more photo of the assembly...
I love your work. Every one of your designs from the Genesis on. H^^
Ken
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Wow! Thanks for the comments Crist and Ken!
The actual fuselage shapes on the Double Take were stolen from my Wildfire design (see attached photo). I like the jet-like canopy treatment because it makes it easy to hide the hatch lines with a painted-on canopy design. It also makes tricycle gear look better. Hey, most jets (with the possible exception of a British design or two) have/had tricycle gear. I've received much higher takeoff and landing scores with trike gear than I have with taildragger type gear. Yes, it is a bit heavier, but not so much as to make it a detriment.
The jet-style look also lends itself to having a jet exhaust hole at the rear of the plane. I "Swiss Cheese" the formers in my top and bottom fuselage shells and that allows the cooling air that comes in the front to be sucked through the fuselage and out the back. The air rushing past the opening in the back causes a low pressure area at the point and the hot air is scavenged very neatly.
I'll be adding faux gear doors around the front LG leg, and between those doors will be a ramp that scoops the cool air into the battery compartment. So, a jet-style fuselage aesthetic is also a very practical one! Check these faux doors out on the Wildfire photos below; the ones on the Double Take will look the same.
Later - Bob
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Here's a photo that shows the simulated gear doors to better effect. If you look close you will see the "ramp" between the doors that scoops the air up and into the battery compartment.
I'm attaching another photo of a "Swiss Cheesed" molded top shell. This allows the air from the battery compartment to flow through the fuselage and be scavenged at the back of the plane through a simulated jet exhaust.
Later - Bob