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Author Topic: New small electric twin build thread  (Read 12849 times)

Offline Bob Hunt

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New small electric twin build thread
« on: December 28, 2020, 09:03:19 AM »
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

   



 
« Last Edit: January 14, 2021, 05:24:45 AM by Bob Hunt »

Offline Craig Beswick

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Re: New small electric twin question
« Reply #1 on: December 28, 2020, 03:44:07 PM »
Yes.

Craig
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Online Brent Williams

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Re: New small electric twin question
« Reply #2 on: December 28, 2020, 05:08:49 PM »
Oh yeah Bob! 
(But you already knew I would be very interested!)
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Online Dennis Nunes

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Re: New small electric twin question
« Reply #3 on: December 28, 2020, 06:01:41 PM »
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

Offline Dennis Toth

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Re: New small electric twin question
« Reply #4 on: December 29, 2020, 01:51:05 PM »
Bob,
What is the motor/ESC/Timer/Battery set up for this ship? For the ESC how is it sized for amps?

Best,   DennisT

Offline Bob Hunt

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Re: New small electric twin question
« Reply #5 on: December 30, 2020, 02:05:50 PM »
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

Offline Randy Powell

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Re: New small electric twin question
« Reply #6 on: December 30, 2020, 05:07:33 PM »
OK Bob. You now get a new name. You are, hence forth, known as the King of Cool. I like it.
Member in good standing of P.I.S.T
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Offline Bob Hunt

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Re: New small electric twin question
« Reply #7 on: December 30, 2020, 06:22:41 PM »
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

Offline Dane Martin

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Re: New small electric twin question
« Reply #8 on: December 30, 2020, 06:37:52 PM »
You've got me on the edge of my seat now

Offline MikeyPratt

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Re: New small electric twin question
« Reply #9 on: December 30, 2020, 06:41:25 PM »
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

Offline Dennis Toth

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Re: New small electric twin question
« Reply #10 on: December 30, 2020, 07:25:37 PM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #11 on: December 30, 2020, 07:40:13 PM »
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

Offline John Rist

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Re: New small electric twin question
« Reply #12 on: December 30, 2020, 09:40:22 PM »
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?
John Rist
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Offline Bob Hunt

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Re: New small electric twin question
« Reply #13 on: December 31, 2020, 06:12:33 AM »
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



   

« Last Edit: December 31, 2020, 07:48:50 AM by Bob Hunt »

Offline Dennis Toth

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Re: New small electric twin question
« Reply #14 on: December 31, 2020, 07:23:08 AM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #15 on: December 31, 2020, 07:47:16 AM »
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 

Offline john e. holliday

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Re: New small electric twin question
« Reply #16 on: December 31, 2020, 11:03:47 AM »
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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Offline Dane Martin

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Re: New small electric twin question
« Reply #17 on: December 31, 2020, 11:32:24 AM »
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.

Offline Steve Berry

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Re: New small electric twin question
« Reply #18 on: December 31, 2020, 03:13:27 PM »
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

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Offline Rob Smith

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Re: New small electric twin question
« Reply #19 on: December 31, 2020, 05:51:42 PM »
I always enjoy your builds!

Rob

Offline James Mills

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Re: New small electric twin question
« Reply #20 on: January 01, 2021, 07:11:08 PM »
Bob,

Yes and yes.

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Offline Bob Hunt

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Re: New small electric twin question
« Reply #21 on: January 01, 2021, 08:34:39 PM »
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

 

Offline Shorts,David

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Re: New small electric twin question
« Reply #22 on: January 02, 2021, 12:01:27 AM »
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.

Offline Dennis Toth

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Re: New small electric twin question
« Reply #23 on: January 02, 2021, 06:46:09 AM »
Dave,
Would be good if you could show a wiring one-line and some photos of the hook-ups.

Best,    DennisT

Offline Dennis Toth

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Re: New small electric twin question
« Reply #24 on: January 02, 2021, 06:50:07 AM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #25 on: January 02, 2021, 07:44:02 AM »
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

Offline Dwayne Donnelly

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Re: New small electric twin question
« Reply #26 on: January 02, 2021, 10:55:35 AM »
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
My purpose in life is to serve as a warning to others.

Offline Bob Hunt

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Re: New small electric twin question
« Reply #27 on: January 03, 2021, 06:49:37 AM »
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 



   

Offline Bob Hunt

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Re: New small electric twin question
« Reply #28 on: January 03, 2021, 06:58:17 AM »
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       

Offline Bob Hunt

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Re: New small electric twin question
« Reply #29 on: January 03, 2021, 07:22:27 AM »
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


 
« Last Edit: January 03, 2021, 08:43:35 AM by Bob Hunt »

Offline Bob Hunt

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Re: New small electric twin question
« Reply #30 on: January 03, 2021, 08:06:31 AM »
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

 
« Last Edit: January 03, 2021, 08:40:59 AM by Bob Hunt »

Rick_Huff

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Re: New small electric twin question
« Reply #31 on: January 03, 2021, 08:34:57 AM »
Of course, Bob.  Glad you like the syrup.
I'm looking forward to the rest of this thread,

Rick

Offline Bob Hunt

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Re: New small electric twin question
« Reply #32 on: January 03, 2021, 09:22:42 AM »
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
« Last Edit: January 05, 2021, 06:18:56 AM by Bob Hunt »

Offline Bob Hunt

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Re: New small electric twin question
« Reply #33 on: January 03, 2021, 09:36:47 AM »
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



 
« Last Edit: January 04, 2021, 07:02:37 AM by Bob Hunt »

Offline Dave Heinzman

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Re: New small electric twin question
« Reply #34 on: January 04, 2021, 06:59:14 AM »

  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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #35 on: January 04, 2021, 07:17:22 AM »
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



Offline Bob Hunt

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Re: New small electric twin question
« Reply #36 on: January 04, 2021, 07:52:26 AM »
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

       

Offline Bob Hunt

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Re: New small electric twin question
« Reply #37 on: January 04, 2021, 08:08:32 AM »
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

   

 

Offline Bob Hunt

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Re: New small electric twin question
« Reply #38 on: January 04, 2021, 08:17:39 AM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #39 on: January 04, 2021, 11:54:18 AM »
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
« Last Edit: January 05, 2021, 06:25:34 AM by Bob Hunt »

Offline Bob Hunt

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Re: New small electric twin question
« Reply #40 on: January 04, 2021, 12:03:51 PM »
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. 

Offline Bob Hunt

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Re: New small electric twin question
« Reply #41 on: January 04, 2021, 12:11:29 PM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #42 on: January 05, 2021, 06:57:15 AM »
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!

Offline Bob Hunt

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Re: New small electric twin question
« Reply #43 on: January 05, 2021, 08:03:31 AM »
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

 

Offline Bob Hunt

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Re: New small electric twin question
« Reply #44 on: January 05, 2021, 12:10:42 PM »
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



 


Offline Crist Rigotti

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Re: New small electric twin question
« Reply #45 on: January 05, 2021, 03:25:11 PM »
You are a master Bob.  Everybody, pay attention on how Bob does things.  It will serve you well!
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Offline Bob Hunt

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Re: New small electric twin question
« Reply #46 on: January 06, 2021, 07:26:43 AM »
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

Offline Bob Hunt

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Re: New small electric twin question
« Reply #47 on: January 06, 2021, 09:36:09 AM »
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

 

   

 
 

Offline Bob Hunt

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Re: New small electric twin question
« Reply #48 on: January 06, 2021, 09:48:57 AM »
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

   
« Last Edit: January 08, 2021, 02:55:49 AM by Bob Hunt »

Offline PerttiMe

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Re: New small electric twin question
« Reply #49 on: January 06, 2021, 11:51:45 PM »
I have no particular interest in twins --- but this is going tobe good.
I built a Blue Pants as a kid. Wish I still had it. Might even learn to fly it.


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