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Author Topic: Eve of a spin-up  (Read 4580 times)

Offline Bob Hunt

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Eve of a spin-up
« on: May 16, 2024, 06:17:09 AM »
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
« Last Edit: May 18, 2024, 05:59:41 AM by Bob Hunt »

Offline Dick Pacini

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Re: Eve of a spin-up
« Reply #1 on: May 16, 2024, 06:22:08 AM »
Beautiful plane Bob!
AMA 62221

Once, twice, three times a lady.  Four times and she does it for a living.  "You want me on that wall.  You need me on that wall."

Online Ken Culbertson

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Re: Eve of a spin-up
« Reply #2 on: May 16, 2024, 06:34:28 AM »
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
« Last Edit: May 16, 2024, 08:00:51 AM by Ken Culbertson »
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline John Skukalek

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Re: Eve of a spin-up
« Reply #3 on: May 16, 2024, 06:43:20 AM »
This could have a real impact on our hobby Bob. Exciting.

Online Dennis Toth

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Re: Eve of a spin-up
« Reply #4 on: May 16, 2024, 07:00:06 AM »
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

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #5 on: May 16, 2024, 10:27:49 AM »
Okay, in order...

Thanks, Dick!

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

Bill: I had the same feeling/thought when I first designed this ship.

Dennis: Thanks for the kudos on the design. Thinning the Titebond is more a matter of feel than of a specific ratio. Start with a small amount of water and add as necessary to achieve a brushable consistency.

Now for some photos. I posted these elsewhere on this forum a few years ago, but I'll post them again here with no verbiage, as the photos pretty much tell the story. I'll, of course, answer questions as they are posted. I'll only be able to do a few photos per post, so bear with me...

Enjoy - Bob   
« Last Edit: May 16, 2024, 01:31:15 PM by Bob Hunt »

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #6 on: May 16, 2024, 10:29:27 AM »
Four more...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #7 on: May 16, 2024, 10:30:36 AM »
and four more...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #8 on: May 16, 2024, 10:31:51 AM »
four more yet...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #9 on: May 16, 2024, 10:33:16 AM »
and again...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #10 on: May 16, 2024, 10:34:22 AM »
Ditto

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #11 on: May 16, 2024, 10:35:19 AM »
Yawn...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #12 on: May 16, 2024, 10:36:24 AM »
More

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #13 on: May 16, 2024, 10:37:23 AM »
and more

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #14 on: May 16, 2024, 10:38:24 AM »
More

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #15 on: May 16, 2024, 10:39:30 AM »
You know the drill...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #16 on: May 16, 2024, 10:39:50 AM »
Four more...


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #17 on: May 16, 2024, 10:41:59 AM »
Again...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #18 on: May 16, 2024, 10:43:14 AM »
Wake me when this is over...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #19 on: May 16, 2024, 10:44:30 AM »
More...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #20 on: May 16, 2024, 10:45:49 AM »
More...

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #21 on: May 16, 2024, 10:47:32 AM »
More yet...


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #22 on: May 16, 2024, 10:48:37 AM »
And more

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #23 on: May 16, 2024, 10:49:42 AM »
more yet

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #24 on: May 16, 2024, 10:50:59 AM »
77 to 80


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #25 on: May 16, 2024, 10:52:09 AM »
81 to 84

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #26 on: May 16, 2024, 10:53:11 AM »
85 to 88

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #27 on: May 16, 2024, 10:54:23 AM »
89 to 92

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #28 on: May 16, 2024, 10:55:27 AM »
93 to 96


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #29 on: May 16, 2024, 10:56:24 AM »
97 to 100

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #30 on: May 16, 2024, 10:58:02 AM »
101 to 103


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #31 on: May 16, 2024, 10:59:24 AM »
104 to 107

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #32 on: May 16, 2024, 10:59:49 AM »
108 to 111

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #33 on: May 16, 2024, 11:02:28 AM »
112 to115

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #34 on: May 16, 2024, 11:03:53 AM »
116 to 119

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #35 on: May 16, 2024, 11:06:12 AM »
121 to 125

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #36 on: May 16, 2024, 11:08:39 AM »
126 to 129

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #37 on: May 16, 2024, 11:09:48 AM »
130 to 133

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #38 on: May 16, 2024, 11:10:51 AM »
134 to 137

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #39 on: May 16, 2024, 11:11:57 AM »
138 to end

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #40 on: May 16, 2024, 12:43:02 PM »
I know a lot of steps were skipped; I forgot to pick up the camera... My bad.

But, here are a few of the canopy section and a few on how to mount the airframe to the nacelles to ensure perfect alignment.

Later - Bob


Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #41 on: May 16, 2024, 12:47:57 PM »
Assembly of airframe to nacelles...

Offline Matt Neumann

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Re: Eve of a spin-up
« Reply #42 on: May 16, 2024, 03:46:51 PM »
I don't recognize the belcrank.  What belcrank did you use?
Matt Neumann

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #43 on: May 16, 2024, 04:32:18 PM »
I don't recognize the belcrank.  What belcrank did you use?

That's a Brett Buck-style aluminum and balsa sandwich bellcrank that was made by Tom Morris.

Later - Bob

Offline Matt Neumann

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Re: Eve of a spin-up
« Reply #44 on: May 17, 2024, 08:33:19 AM »
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?
Matt Neumann

Offline Gerald Arana

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Re: Eve of a spin-up
« Reply #45 on: May 17, 2024, 08:55:33 AM »
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.

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #46 on: May 17, 2024, 03:22:43 PM »
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?

Hi Matt:

The weight is about a wash. And, yes, since the canopy is coated with 1/2 ounce glass,I think it would take dope fine, just so long as you don't get it on the inside. It wold melt the raw foam... It's mongo strong!

Bob
 

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #47 on: May 17, 2024, 03:23:58 PM »
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.

Hi Jerry:

I think just one layer of the doctor paper would do the job. Heck, a piece of newspaper might just work!

Later - Bob

Offline Bob Hunt

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Re: Eve of a spin-up
« Reply #48 on: May 17, 2024, 03:31:59 PM »
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 
« Last Edit: May 19, 2024, 12:26:54 AM by Bob Hunt »

Offline Steve Thompson

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Re: Eve of a spin-up
« Reply #49 on: May 17, 2024, 03:33:30 PM »
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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