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  • February 21, 2018, 04:25:05 AM

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Author Topic: Ercoupe Build (slow)  (Read 784 times)

Offline Tim Wescott

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Ercoupe Build (slow)
« on: January 14, 2018, 02:40:59 PM »
My ride for the Regionals in May, if I can get it done.  I just got the plans from the printer -- they lack detail.

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Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #1 on: January 21, 2018, 07:58:05 PM »
And ain't I making fast progress?  I'll be lucky to have something flyable -- I think I have too many irons in the fire.

I haven't decided yet whether I'm going to drill holes for my usual stunt jig.  I've chosen to use the original airfoil, so there's not a flat line anywhere to set on a building board.  I'll probably do this on a jig -- it just seems more sane.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #2 on: January 28, 2018, 05:07:59 PM »
Nineteen ribs cut, at least nineteen more to go.  So far I've been progressing without drawing up plans, but I should maybe at least sketch out the rib layout & which ribs need to be shortened as I go into the wing tips.  Hmm.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline wwwarbird

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Re: Ercoupe Build (slow)
« Reply #3 on: January 28, 2018, 08:45:06 PM »

 Just curious, what will the wingspan be?
Narrowly averting disaster since 1964! 

Wayne Willey
Albert Lea, MN U.S.A.
IC Aircraft Modeler, Ex AMA member

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #4 on: January 28, 2018, 08:52:13 PM »
Just curious, what will the wingspan be?

1/8 scale, 60".  I'm trying for not to big, not too small.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline wwwarbird

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Re: Ercoupe Build (slow)
« Reply #5 on: January 28, 2018, 09:29:41 PM »

 That's a pretty good sized model, a nice size for scale though. A whole different ballgame, but over the years I've considered doing an Ercoupe stunt model many times. This one will be an interesting build to watch.
Narrowly averting disaster since 1964! 

Wayne Willey
Albert Lea, MN U.S.A.
IC Aircraft Modeler, Ex AMA member

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #6 on: February 03, 2018, 05:00:40 PM »
All ribs cut.  I had originally planned on a 2" spacing, but I got to thinking and I decided that 2.5" would be OK (I'm not trying to match the original).  I have the main rib in a CAD program, so I just scaled it down to fit between the LE and TE for the two tip ribs.

20 main ribs
2 mid-tip ribs
2 end-tip ribs

I need to cut holes for lines in the ribs next, then start bending wood for the wingtips.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Fred Cronenwett

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Re: Ercoupe Build (slow)
« Reply #7 on: February 03, 2018, 09:03:09 PM »
That is a great size, big enough you can install a servo and other hardware and not be worried about wing loading. Small models can not tolerate adding the scale details and heavy items such as extra servos.

Another thing that happens with the larger models is that the wing loading per square foot can go up and still fly great. My 96" span B-29 flies with a 39 ounce per square foot wing loading, that same wing loading on a smaller model it would not get the off the ground. the 14 lb overall weight for the B-29 is a pig by stunt standards but flies just like the real B-29 so it's a good model for CL scale.

Math is on your side, if you double the size of the model from 30" to 60" you have doubled the size of the model but the wing area is 400% the area of the smaller model.

30" model would have 142.6 sq inches
60" model would have 570.4 sq inches

You can easily fly the larger model even if the model comes in at 5.5 lbs, but with the smaller 30" model you would be lucky to get airborne if the model came in at 1.25 lbs (or 20 ounces). I tend to round to the nearest 1/4 lb with the scale models instead of quoting model weight to the nearest ounce.

Fred
Fred Cronenwett
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Model Aviation CL Scale columnist

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #8 on: February 10, 2018, 06:25:40 PM »
Small progress made on airplane - large progress made on shop.

Sunday or Monday I went into the back shop to find some wood for a tip form, and found that the last of the florescent fixtures had died.  I am sick and tired of florescents, so I've spent my evenings this week installing LED shoplights.  The good news is that it's brighter back there than it has been for years, and I still have the other half of the fixtures to install.  The better news is that it was all overhead work, and my right shoulder hasn't been bugging me for it -- so maybe in 2019 I can get back to flying stunt!

After taking a break from building to fix up my back shop where all the carpentry stuff lives, I ended up making the tip form out of cardboard, in the front shop.  I've got six 22x3/8x1/8 sticks soaking in ammonia water now; tomorrow I'll see if I can bend them.  If I can't hand bend them, I'll heat bend them.  I was going to say "I'll have to figure out how", but as I typed that a solution popped into my head.  Now that I can SEE my welding bench Igrab some pipe and make up a 4" or 6" diameter form that I can hold in my vise and heat up with a propane torch while I'm bending wood over it -- that should be both effective and gonzo, and if I'm careful, perhaps even let me finish the job before I burn down my house.

One of these days I'm going to have to try steam bending balsa.  I've had really, really good success bending wet balsa over a soldering iron for small rubber-powered airplanes.  So balsa seems to be good for heat-bending.  On the other hand, I've seen web sites that say you just cannot steam-bend kiln-dried wood.  I'm not sure if that means that other heat-bending techniques work, or that when you're working with thin sections of wood you can effectively undo the kiln drying by overnight soaking in water.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Will Hinton

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Re: Ercoupe Build (slow)
« Reply #9 on: February 11, 2018, 10:13:39 AM »
Tim, I heat bend kiln dried wood all the time, and hardwood at that when I'm building acoustic guitars.  I've bent maple, rosewood, koa, cherry, mahogany and the like.  I do soak them over night before doing it, but I can't imagine having problems heat bending balsa, even really hard balsa if it's plenty wet.
I feed the torch into one end of an aluminum tube with a baffle an inch from the opposite end to retain as much heat as possible.  I use a four inch and a two inch tubing, depending on the radius of the bend I need.
Just go slow and watch the fingers!  Good luck with it.
John 5:24   www.fcmodelers.com

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #10 on: February 11, 2018, 02:27:45 PM »
Tim, I heat bend kiln dried wood all the time, and hardwood at that when I'm building acoustic guitars...

Thanks.  It sounds like you do the same as I do -- wet wood over a hot dry thing.  Have you even steam-bent, or does that just not fit into your process?

I'm going to try today with a heat gun, because I don't have any hunks of metal that are a nice 4" radius, other than a cookie tin.  If I get desperate I'll shove the torch into that, but I'm worried about burning up the tin.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline John Rist

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Re: Ercoupe Build (slow)
« Reply #11 on: February 11, 2018, 03:09:05 PM »
Balsa wood bends if you soak it in a mixture of household ammonia and water.  I did some molded ringmaster leading edges this way.
John Rist
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Offline Will Hinton

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Re: Ercoupe Build (slow)
« Reply #12 on: February 11, 2018, 07:50:34 PM »
I would like to have a steam bender, but the way I'm doing it works well enough for me to not spend the extra money on one.  The main thing I have to watch is burning the surface of this expensive exotic wood if I am too slow on my process.  The burns sand out, but at a huge cost of time.
Some of the bending machines available for luthiers are also wonderful machines, but also expensive.  If I were ever to up my output on a steady basis I would likely go that route, but for now; status quo is working well.  I just delivered two new acoustics last week and will start two new acoustic instruments in a couple of weeks.
John 5:24   www.fcmodelers.com

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #13 on: February 11, 2018, 08:43:23 PM »
Balsa wood bends if you soak it in a mixture of household ammonia and water.  I did some molded ringmaster leading edges this way.

You can get it around a much tighter radius with heat.  I've done both.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #14 on: February 11, 2018, 08:55:20 PM »
You can get it around a much tighter radius with heat.  I've done both.

I need to expand on that:

You can bend a thicker piece of wood around a tighter radius, and when you're done it'll stay there.  If you soak the wood in ammonia water (or plain water for longer, or water with a touch of soap), you can bend a piece around a form tighter than you can dry, and it won't break, and it'll take a bit of a set.  But if you bend it around a hot form you can get it much tighter, and it'll stay.

I've got a Bostonian I call the "Square Coupe" (I have this thing about Ercopes) with tips and tails bent out of 1/16" balsa over a soldering iron: the tail feathers are bent around a 5/16" radius (the radius of a penny, more or less) in places, and while that's as tight as I'd ever want to go with that sized wood, it worked great.  Basically, the vertical stabilizers were bent so that just sitting there they had the right shape on the plan.



AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #15 on: February 11, 2018, 09:42:38 PM »
One wingtip bent.  I'll let it cool and dry overnight, or until I get a chance to get down to the shop again.

I ended up using a monocoat gun pointed at a round cookie tin loaded with scrap iron to hold it in place.  You let the wood heat up, it gets flexible, and then you can gently pull it around the form.  If you push it into a bend, or if you get impatient, then it buckles -- which I did, and it did, because I got impatient ("I got impatient and then screwed up" is a running theme in my building, I'm sorry to say).

If I do better tomorrow with the other wingtip, I may go for a 3rd round and see if I can make more pieces with less buckling this time.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #16 on: February 18, 2018, 05:01:17 PM »
Wingtips bent, sorta kinda acceptably.  (meaning, it's good I'll be using opaque covering).

My cousin is learning guitar building; he bends moistened wood that's wrapped in foil -- I'm gonna try that next time, because I've noticed that the wood seems to bend nicely until it dries out, and then bends no more.

Oh, and wing plans done, such as they are.  Masking tape on the building board and a sharpie marker.
« Last Edit: February 18, 2018, 05:45:14 PM by Tim Wescott »
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #17 on: February 18, 2018, 07:57:54 PM »
Wing taking shape.  It's beginning to look like progress!

Note that the plan is for a very "stunt-ish" wing structure: LE sheeting, capstrips, TE sheeting, with center-section sheeting.  I'm just closing my eyes to what the actual structure of the wing may have been, or whether my particular full-scale example had a fabric- or metal-covered wing (they came both ways, fabric wings have been converted to metal, and sometimes converted back to fabric -- it's very much a question of what your particular example did).  If this were a more precision event, I'd care -- which is exactly why I chose Profile Scale.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Trostle

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Re: Ercoupe Build (slow)
« Reply #18 on: February 19, 2018, 10:05:24 AM »
That's a pretty good sized model, a nice size for scale though. A whole different ballgame, but over the years I've considered doing an Ercoupe stunt model many times. This one will be an interesting build to watch.

Just a comment here on the Ercoupe for semi-scale stunt.  Bob Palmers Mars, Model Airplane News, August 1952, sort of looks like an Ercoupe with it twin verticals, bubble canopy, and tricycle gear.   Cowled in side mounted engine with apple cheeks. (And it is OTS legal.)

Charles Lickliter's Ballerina, Flying Models, October 1959, is another that gives an impression of an Ercoupe with it twin vertical, bubble canopy, but had a conventional gear.   Cowled in inverted engine.  I-Beam construction.

Both of these models were attractive in their own ways particularly if you like twin vertical tails.

Keith



Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #19 on: February 19, 2018, 05:54:36 PM »
LE and bottom half of the TE sheeting in place.  I've agonized about the order of the TE sheeting vs. getting the tip hoop & ribs in place -- I finally realized I was suffering from analysis paralysis, and just got 'er done.  Done and wrong can be fixed.  Never done can't.

TE sheeting is being held up by a 1/2" square stick that's held up by wedges cut to match the angle of the bottoms of the ribs.  The top TE sheeting will be tapered in the back, and will, well, set on top.  If you squint, you'll (maybe) be able to see that I had to block the spar up to make room for the LE to glue on.  I'm going to make all the screwups on this side, so that the inboard side will be perfect.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Tim Wescott

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Re: Ercoupe Build (slow)
« Reply #20 on: February 19, 2018, 06:00:38 PM »
I was just reading an Ercoupe pilot's website, and see that there's a scale maneuver unique to the Ercoupe that can best be described as "mush to landing".  Basically, if you fear overshooting the runway, you throttle way back and hold the stick back as far as you can.  The Ercoupe is stall- and spin-proof, so it'll sink pretty fast in a mushing glide.  The trick is to remember that you simply don't have enough airspeed for a flair, so you absolutely need to put the nose down at 200 feet so that you have enough airspeed for landing (and, apparently, to clean the passenger's seat of any residue if you're flying with a non-Ercoupe pilot who you failed to warn).  1/6 scale 200 feet is 33 feet -- so, probably not a maneuver for CL scale.

Note that I've never flown a scale Ercoupe -- but I've had RC planes with similar stall characteristics, and by golly I've done similar things trying to get them to spin.  It does work, sorta.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline wwwarbird

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Re: Ercoupe Build (slow)
« Reply #21 on: February 19, 2018, 06:28:31 PM »
Just a comment here on the Ercoupe for semi-scale stunt.  Bob Palmers Mars, Model Airplane News, August 1952, sort of looks like an Ercoupe with it twin verticals, bubble canopy, and tricycle gear.   Cowled in side mounted engine with apple cheeks. (And it is OTS legal.)

 Thanks Keith, yeah, I've eyeballed the Mars before thinking the same thing, it could easily be bashed into an Ercoupe.
Narrowly averting disaster since 1964! 

Wayne Willey
Albert Lea, MN U.S.A.
IC Aircraft Modeler, Ex AMA member


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