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General control line discussion => Open Forum => Topic started by: Bob Hunt on May 16, 2024, 06:17:09 AM
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Hi all:
I've been working on and off for the past few years on a smaller test-bed twin design that I call "Double Take." The idea was to find out how a smaller (read that easier to build, less expensive, less intimidating…) electric twin would perform, and just how light a power package could be achieved while still having plenty of power.
The Double Take was built using what I call the “Lost Sheeting” method of wing construction. The Combat guys have for years used raw foam wings covered with various thin, iron-on films very successfully. Some years ago I decided to build a few Slow Combat ships and opted to use .02/oz. carbon mat in place of the film. I applied it using water thinned Titebond II glue, and it worked to perfection. Phil Cartier stopped by my house to pick me up to go with him, Gil Reedy and Bub Reese (both now passed…) to a Slow Combat contest in New Joisey. When he came into my shop and saw the two “Slip Knots” (really just aesthetically adjusted Gotcha 500s) he said that I couldn’t fly them at the contest. “They are too beautiful to fly in Combat” he said.
In the Lost-Sheeting method of building, a foam core wing is cut and sanded to as smooth a surface as possible. Then 1/8 x 3/8-inch slots are cut from root to tip in each panel, top and bottom. These slots will eventually accept full span 1/8 x 3/8-inch basswood strips. A full-depth spar slot is then cut to accept a 1/8-inch Lite-Ply spar. In the case of the Double Take this spar extends out past where the profile nacelles will reside on the wing panels. A couple of shear web slots are also cut outboard of the full depth spar to grip the basswood surface spars and prevent “racking.” In inside maneuvers the forces tend to compress the top spars and “stretch” or tension the bottom spars. The shear webs help prevent these forces from collapsing the wing. In normal foam wing construction the balsa sheeting and the full depth Lite-Ply spar does this job.
In the case of the Double Take I chose to go with foam flaps, and so cut the panels with the flaps integral. They were separated and framed after the carbon mat was applied. And, I double covered just the flaps for added rigidity. Trust me, they are more rigid done in this manner than balsa covered flaps!
The control system was installed and the panels joined prior to gluing in the basswood surface spars and applying the carbon mat with the thinned Titebond II glue. Balsa tips were added, and the wing was ready for installation in the fuselage.
The remainder of the plane was constructed in the normal manner with a fuselage crutch and molded balsa shells top and bottom. The stab and elevators were made from sheeted foam.
I did try something different when I made the large canopy/battery hatch. I didn’t want to “waste” a big block of light balsa on a simple test-bed model, so I made the large canopy using the Dow Buoyancy Billet foam that I have been using for years to make my fuselage mold bucks for the top and bottom shells. I glued a piece of the Buoyancy Billet foam to a firm balsa base, tack-glued the assembly in place on the fuselage, and carved and sanded it to the desired shape. The I applied two coats of Z-Poxy finishing resin (sanded between coats). Next the canopy section was covered with a piece of 1/2-ounce glass cloth, also applied with Z-Poxy. After trimming the excess glass from the edges and sanding the surface smooth, I removed almost all the foam (left about a 1/16-inch wall), and the result was a very light and smooth piece. I'll most certainly use this technique to make the large canopy/hatch sections on future contest models.
The wood parts of the airframe were given two coats of Z-Poxy done in the following manner: A coat of resin was applied to small sections at a time, heating and wiping all excess material off the airframe. A light sanding was done between coats. This yielded a very light satin finish that will protect the model’s wood parts from moisture. I decided to also coat the wing with Z-Poxy in the same manner to guard against moisture (read that, rain…) from softening the Titebond II Glue that was used to apply the carbon mat. And again, every bit of excess glue was wiped off the wing, leaving just an extremely thin film of epoxy to form a barrier. That coat added almost an imperceptible weight gain.
Vital stats:
The Double Take mounts two E-Flite Park 450 motors fitted initially with two Zoar 9 x 5 wooden props (one tractor and one pusher). The all up weight is 45 ounces, including the battery. I’m using two Castle Creations Talon 25 Amp ESCs and a Fiorotti timer with twin function. The plan is to try it on .014 braided lines that are 64-feet from center of the model to center of the handle and adjust from there as required.
The initial spin-up and first flights are scheduled for tomorrow. I’ll give a full report on how it went tomorrow night (unless I’m depressed for some unexplained reason…). I’ll also add to this thread a lot of the construction technique photos for the processes mentioned above as I get some time.
My plan is to develop this concept as a model with which modelers can try an electric twin at minimal cost in time and materials.
I won’t be getting too much sleep tonight…
Later - Bob Hunt
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Beautiful plane Bob!
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Beautiful plane Bob!
Where is he Canard? LL~ LL~
I have been experimenting with using very thin CF Plate/Sheet to replace plywood. When I made the flaps for my new twin I used too light of wood for the built up part and they have more twist than I like. Would the 02/oz. carbon mat be stiff enough over the rather small open areas (about 1 sq" each) or perhaps over/under polyspan? Where did you find it? I have burned up the search engines looking for .02 plate or sheet in anything > 12". .02 would weigh just about the same as 1/32 Balsa.
Ken
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This could have a real impact on our hobby Bob. Exciting.
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Bob,
Really nice, love the design. Would love to get a little more information on doing the covering with the Titebond II, how much to thin and what surface prep do you use?
Best, DennisT
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I don't recognize the belcrank. What belcrank did you use?
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Another silly question, how does your foam canopy compare weight and strength wise to balsa? Just wondering if this method could be used for non structural parts in other places. This could be something the normal builder could do. Would it be easy to finish in dope?
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I have a question. Since the wing has spars top and bottom (which I would thing take the loads) would a couple layers of Doc paper be sufficient? It sure would be a whole lot cheaper!
Cheers, Jerry
PS: Love the design.
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That is an excellent series of construction photos!
I read your Genisis Saga stories and appreciate the pioneering aspect of this sport and your contributions. You have done it again here.
Thank you.
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Bobby, you are making the old DOC think hard about this design. You do stupendous work. H^^ H^^ H^^
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Wow Bob
What a great series of build photos.
I’m hoping the movie will be out soon. 😉🍿
I think someone has a CnC foam cutter.
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All in all one of the better first days I've had with a new ship in years! Got in three full patterns and lots of 1 minute, 20 second trim flights. I'm pumped!
I never cease to be amazed at your creativity, and willingness to try something new! I said this before, and you know I wouldn't just say it if I didn't mean it - but I can't think of *anyone* who has contributed more to the advancement of stunt than you have, it's not even close!
Thanks for showing us yet another one!
Brett
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I just returned from a full day at the flying field. 4 to 6 winds, overcast and the grass cut to the nubs; nirvana!
The Double Take twin flies much better than I anticipated; now I wish I'd put s finish on it... mw~ mw~
I have a couple of brand new BadAss 2310 motors, and tomorrow I'm going to retrofit the Double Take with them at Rick and Paul Walker's suggestion. They should spin the 10 x5 props a bit better than the Park 450 motors that are currently in the ship. They came down just a bit hot with the 10 x 5 props.
Be sure and post the results. That is the combo I am putting in Endgame IV. It is a bit larger than yours so I am using the 2320-850. I am still a bit leery of these tiny motors!
Ken
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Bob,
Great prestation and photos. Can you give us a bit more info on the battery packs and major trim adjustments you made.
Best, DennisT
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Brett has earned the respect of everyone in the Stunt community for not only his designing and flying prowess (which is considerable), but also for his ability to look at everything from a clear technical and logical perspective, and then present his findings in a manner that we can all understand. So, right back at you my friend for your creativity and service to our community.
Bob, I couldn't agree more with your compliments. I have the privilege of flying with Brett, when he can get out, for several years now. He has a unique gift for seeing what a model airplane does in the air that the majority of flyers can't or don't see. Along with the willingness to help, Brett also possesses the ability to communicate the issues and let's you know what needs to be done to fix them. And he does this in simple terms that even a second grader (like me) can understand. Thanks Brett!
Dennis
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Ken:
The .02 carbon is a tissue-like material with indiscriminate weave. Good for over solid surfaces; not good over open bays. I get mine from Aerospace Composite Products in San Leandro, CA. It used to be very affordable, but - like everything else - it has gone up in price significantly. I'm looking around for a more affordable replacement
I got some of the more affordable stuff, and it won't be a nightmare the next time -- I tried putting it on the way folks tell you to do the ACP stuff, and it was a disaster.
It turns out that some of the carbon veil has sizing that's soluable in the thinners found in dope, and some doesn't. This isn't too surprising, because epoxy isn't dope. After a disaster of wrinkles and failed attempts at sanding them out and cursing and another layer of tissue, etc. I heard the factoid about the sizing. Took a scrap of the stuff, dampened it with water like it was silkspan, and it went on like a dream.
So, when you're looking, if you find something, try out a sample patch with just dope, and if that doesn't work try dampening it with water or alcohol.
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I know that August is a long way off Bob, but do you think we will see you and this airplane in Muncie?
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Cool. That's what I was thinking. That you might bring it for fun.
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how it the wing joined at the center section?
doeste plywood carry though? or just glass cloth over the top?
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Looks great Bob!
I noticed the nacelles place the motors closer to the leading edge than is possible with an IC twin. Do you find this motor placement to be an advantage for flying performance, or CG management, or some other reasons?
I made a quicky line drawing of this. Scale is to the nearest 'ish. Kinda fun to use for imagineering purposes.
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Bob,
Interesting progress. Could you post the rpm and lap times that you are flying it at? Also, with the twins where do you set the CG? Last, since you went to the 10x5's relative to the CG where did the leadout position land?
Best, DennisT
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Hi Bob
Greetings from Canada EH
Love the new model. That fuse style is magnificent. I fly IC but you are tempting me to electric. Don’t tell my friends.
What’s the wing span and wing area?
Will you be producing plans?
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I just returned from a full day at the flying field. 4 to 6 winds, overcast and the grass cut to the nubs; nirvana!
The Double Take twin flies much better than I anticipated; now I wish I'd put a finish on it... mw~ mw~
Seriously, Rick and Sara Marie Huff, and Tom Huff joined me for a great day of flying. Rick has a ton of twin experience and he made some suggestions that made the little twin fly better and better with each flight. I initially had Zoar 9 x 5 props on it, and they worked okay, but then we threw on a matched set (L & R) of BadAss 10 x 5 props and the ship came alive in a big way. I discovered that I have a couple of brand new BadAss 2310 motors, and tomorrow I'm going to retrofit the Double Take with them at Rick and Paul Walker's suggestion. They should spin the 10 x5 props a bit better than the Park 450 motors that are currently in the ship. They came down just a bit hot with the 10 x 5 props...
All in all one of the better first days I've had with a new ship in years! Got in three full patterns and lots of 1 minute, 20 second trim flights. I'm pumped!
Later - Bob
P.S.: The takeoff roll on grass at full power is less than six inches (actually a lot less!). Of course on asphalt I could hold in a bit of down elevator and achieve a longer roll, but it's fun to watch it looking like it was shot out of a cannon! - Bob
Congratulations Bob, another landmark model! pretty and practical to build. As always pushing the envelope and develpoing new technics! awesome desing and great construction pictures!
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Hi Bob, Great design.......as always! I've been playing with foam models and various coverings with wood glues like Titebond etc. My .15 size stunt trainers were made completely out of Isoboard which is similar to Depron being extruded foam. At first I covered them with medium weight silkspan or in my case teabag tissue, but I found that it is not that ding-proof. I improved this by changing from PVA glue to Aliphatic resin which dries a lot harder and even sands quite well. My latest attempts use the light weight glass cloth (25 grams/sq.metre) with the aliphatic resin. The tail feathers come out real nice and strong and can be painted even with the lacquer paint if you don't go too crazy on the thinners for the first coats. I would thin that the aliphatic would work really well with that carbon matt.
I also make a filler from baby powder and a small amount of aliphatic plus water. You need to experiment with the quantities but it makes a nice filler for foam parts. With the price of balsa right now, especially here in Darkest Africa, these foam parts are a blessing. I made a few WW2 combat models completely out of Isoboard using this method.
Keith R
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Thanks Bob. The other things that I'd like to know are where do you hide the battery and ESC's? Your 900 Kv on those BadAss motors seems high for a 5 cell setup, so what rpm are you turning? Thanks!
Keith R
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Thanks a ton Bob! I appreciate the info greatly. That's such a great project. Please tell us the present rpm as well if you don't mind. That would also be interesting.
Keith R
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While I understand it would be hard to give all the dimensions here, I am curious as to the tail moment and nose moment. That would give me a good idea of size. As for a problem of making cores. Do just like the good old days and give the tip and root template and leave it up to the builder to figure out how to get the cores cut. Just say, don't look at me.
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So, Bob, where are you getting the carbon veil? We used to get it from Justin Sparr, but ACP seems to have gone away from hobby/small order business. I am down to 1 roll of the "hard"/uniform type that gives excessive pinholes and don't know where to get the good kind.
Brett
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Really inspiring. All it is missing is the Canard! LL~ I love your arming plug. I always have two because I keep losing them. You have those motors really close to the wing. I thought I was doing good at 1". Are you using bullets on both ends of the motor leads or just one long set of wires to the ESC. I personally don't like connectors where I can't see them. I found the perfect tunnel to the nacelle. Plastic Smoothie straws. 3 #13 wires with bullets fir perfectly.
Ken
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Finding the room for the tube and the linkage might be a problem, though...
Later - Bob
It is contagious. I can't picture Endgame III without it now. Ah, the nose linkage. I spent most of today on that. When I went to the 5" bellcrank I had a bump put on the outside to drive the Canard. The hole in the bellcrank is as close to the pivot as possible and still clear the ball link. I test mounted the wing and tested the controls and they worked great except for one minor detail. Way too much Canard movement. Like 40 degrees. If I put a taller post on the pushrod will be running through the pilot. Only solution - an intermediate reducing lever in that huge canopy area behind the pilot's seat. I had originally drawn that up but thought I could get away with a straight shot. I failed to consider that making it in line also meant that the canard and the batttery would be lower. Oh well, when you compose planes instead of building them you get days like this! Picture is the way it was hooked up to my balsa construction bellcrank I use to lay things out.
Ken
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Again, with the hinges sealed the ship was way too responsive. I told my old buddy, Dean Pappas about this and he asked me where the elevator slider was set. Homer Simpson moment number two (the first HS moment happened at last year's Nats when Howard Rush asked me the same question about the slider position on my Turning Point twin). On both occasions I was so anxious to get the birds flying that I did not do a proper bench trim check. In both cases the slider was at the very top of the adjustment, giving me a ton of elevator movement versus flap movement. And, in both cases moving the slider down (significantly...) made each of the planes very easy to corner and bottom. Lesson learned; bench trim EVERYTHING!
You just got me thinking of my plane. I had my slider moved up as far as it would go. I did this on my IC planes and never gave it a second thought until I read this. I moved it down and now things are smoother. I had to widen the handle spacing just a bit and will probably move the battery a bit farther foreword but the plane is settling down more now. What works on IC engined planes don't always apply to electrics.
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Bob, that is a really sharp looking electric twin you are building, love the design. Also, I really like the pictorial tutorial styled thread you are posting, gives very clear details on how to do your particular method of construction of foam core wings and how you keep the fuselage clean, functional and lightweight.
Looking forward to seeing your completed results and first flight reports.
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Bob:
You asked about the Canard linkage. I posted it over on my Endgame IV build thread. I am still curious how you handled the motor wires with the mounts virtually on the wing LE.
https://stunthanger.com/smf/building-techniques/endgame-iv-build/
Ken