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Author Topic: Waco SRE by Earl Stahl  (Read 764 times)
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marcin_pl
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« on: May 14, 2021, 04:45:23 AM »

This part of our forum is rather asleep, so I'll try to blow some fresh air into it Wink

I've just started a conversion of classic Waco SRE by Earl Stahl to R/C. The plan is well known and was built mamy times with a reputation of a good flyer.
At the beginning I thought about building her as a free flying model with CO2 engine, but my available flying sites are shrinking so finally I decided to convert her into electric R/C.
During my other builds I noticed that old hand drawn plans have many inaccuracies and distorions caused by scanning and copying. That's why I decided to redraw the plan in CAD. I introduced some minor changes into the structure but generally I'm following according to the original plan by Mr Stahl.
I enlarged the plan slighty - the span of my model is 604mm, so a scale is about 1:17.5.

Marcin
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Waco SRE by Earl Stahl
Waco SRE by Earl Stahl
Waco SRE by Earl Stahl
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billdennis747
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« Reply #1 on: May 14, 2021, 06:28:42 AM »

To those who have built this model, it has very little longitudinal dihedral/decalage. Did this need adjustment during trimming?
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Kevin M
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« Reply #2 on: May 14, 2021, 08:48:08 AM »

I have built a light electric R/C WACO SRE in the past, slightly bigger than the Stahl one (about 30" span). It has little difference between wing and tail incidence (say 1.5 degrees by eye) but flies nicely as an R/C model. I would probably use a bit more for FF.
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Kevin M
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« Reply #3 on: May 14, 2021, 01:48:50 PM »

Just took a look at my Mooney Peanut WACO SRE which has the wing at 3.5 degrees with the tailplane at zero. Nice stable flier but needed a fair bit of down thrust, perhaps that wing incidence could be reduced a bit.
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marcin_pl
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« Reply #4 on: May 15, 2021, 04:42:04 AM »

I built stabilizers. In fact I started with them, so a photo shows the original version of the horizontal stabilizer built for a free flying version. Now I rebuilt it with separate elevators.
Main structure of the empannage is ready and I've started adding bulkheads.

Marcin
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Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
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marcin_pl
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« Reply #5 on: May 20, 2021, 03:23:25 PM »

Started building an udercarriage. I like using jigs that help keep things true. Main legs are made of 1.2mm steel wire, additional of 1.0mm. Wires of the undercarriage are sewn and glued with CA to pine cross pieces. I decided to use pine instead of balsa in these points, because my landings are often not the best. I keep adding bulkheads and stringers.
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Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
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simpsd
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« Reply #6 on: May 26, 2021, 05:21:56 PM »

Wow, such nice clean work... that's what I aspire to. I like your landing gear jig. I have a lot of trouble getting my wire bent right - and the same on both sides. And your solder joints ... so nicely done. Looking forward to seeing more of this one. Thanks for posting.
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marcin_pl
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« Reply #7 on: May 30, 2021, 05:01:59 AM »

Not much progress, but I was able to add front cowling. It's made of 1mm balsa. I tried to redesign the original plan and eventually made it a bit too complicated in this part. In my version longerons are located flush with the cowling, so I had to glue it by parts from one longeron to another. It makes getting the cowling consistent in shape more difficult. I'd prefer longerons under the balsa cowling (like in Mr Stahl design) that could have been made from one piece of balsa (or maybe one per side). I wanted to avoid a step on the edge of the cowling and get longerons flush with the cowling outer surface. We are learning all the time...
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Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
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simpsd
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« Reply #8 on: May 31, 2021, 03:07:24 PM »

The cowl to fuselage transition looks smooth. I have been frustrated by similar transitions on some of my models. If the sheeting goes over the longerons and there is supposed to be a stepped transition, then when the tissue goes on and shrinks the step disappears unless you plan ahead snd put in some extra wood right there for the tissue to adhere to. Then, on models like your Waco, when there is supposed to be a smooth transition, I have found plans are sometimes frustratingly ambiguous about how to achieve it. Anyhow your smooth transition looks great even if it was a small feat to achieve it.
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marcin_pl
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« Reply #9 on: June 10, 2021, 04:43:01 AM »

Thanks for your kind opinion. I think I went a bit too far in my chase for lightness and used too thin balsa sheet for cowling and it went a bit concave.
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DavidJP
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« Reply #10 on: June 10, 2021, 05:05:11 AM »

I built one of these a few years ago and was very pleased that it flew quite well.  I did not allow weight to influence me too much but now think perhaps I should have done.  It would have gone even better.  It has done a few hours now so it looking rather weary!

Yours looks extremely light already and so with your skill at building I am sure your model will fly beautifully.  Well done so far and I await further posts.  I like the tidy work area too - I think that helps produce a neat model.
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marcin_pl
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« Reply #11 on: July 11, 2021, 11:06:29 AM »

Sometimes s*** happens ;-) I wanted to smooth the balsa sheeting around a nose of my Waco. Because I didn't have any factory-made putty at hand so I used a self-made putty of non-shrinkig nitrocellulose lacquer and talcum powder. The sheeting got smooth but after a day or so I observed effect a of starved-horse look and my sheeting got a bit concave (photos 1,2). I'm of the opinion that it happened because of shrinkage of the (nominally) "non-shrinking" lacquer.
At first I had tried to convince myself that I can live with it but later I decided to strip all that sheeting and do it again. Stripping wasn't that easy, because I didn't know where to stop  Wink
To avoid this concave shape I decided to add some more additional stringers under the sheeting. I had to glue those stringers according to the unspoiled part of the sheeting around cabin and to a front cowl.
Now I'm going to add a new sheeting flush with the existing part. Hope it'll look good.
Attached files Thumbnail(s):
Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
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marcin_pl
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« Reply #12 on: November 12, 2021, 01:54:05 PM »

I made a new engine cowling. My understructure works and there is no concave shape. Lesson learned: sometimes don't make things too thin. Chase for lightess has it's limit.
By the way - I noticed that some WACO SRE models have improper shape of the front part with a "kink" between the cowl and the rest of a fuselage. In a real plane engine cowling blends smoothly with fuselage, transitioning from circular to semi-rectangular cross-section.
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Re: Waco SRE by Earl Stahl
Re: Waco SRE by Earl Stahl
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marcin_pl
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« Reply #13 on: November 20, 2021, 02:32:17 PM »

In this thread I feel a bit like a lunatic - talking only to myself  Wink

And now something completely different: the wings are ready. I added thin hardwood dowels to strenghten the wing - fuselage joints, beacause a butt joint didn't convince me. It facilitates proper incidence setting also. I made laminated wingtips - they look better and are much stronger.
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Re: Waco SRE by Earl Stahl
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piecost
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« Reply #14 on: November 20, 2021, 03:42:10 PM »

Marcin,

Please keep posting. I am sure that many people, Like me,.are enjoying your build and fine craftsmanship, even if they are not posting.

Cheers

Tim
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Russ Lister
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« Reply #15 on: November 20, 2021, 04:00:48 PM »

I agree ... keep the posts coming. I must admit that I get a bit lazy sometimes and don't check out some threads until the model is really getting there. The model looks great.
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Kevin M
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« Reply #16 on: November 20, 2021, 04:45:39 PM »

I've been following too, not least because this model is on my list. Nice work.
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faif2d
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« Reply #17 on: November 20, 2021, 09:13:19 PM »

I love the craftsmanship you are showing us.  I seldom comment because I feel so inadequate.
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« Reply #18 on: November 21, 2021, 03:28:57 AM »

Marcin, enjoying watching this come together, and the way you're solving problems in advance and in arrears.  Smiley

Jon
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Konrad
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« Reply #19 on: November 21, 2021, 10:58:34 AM »

To those who have built this model, it has very little longitudinal dihedral/decalage. Did this need adjustment during trimming?
Is this question aimed at FF trim, or RC trim? Generally I like a decalage angle of around 0.5° for my gummy band to RC conversions. This is measured at the chord line of the airfoil. Sometimes if I'm lazy I draw the stab parallel to the bottom of the wing. But with high wing cabin ships I like the 0.5° value as the down wash from the high placed wing adds the up trim. Note, I also like rather aft CG placement. My aim to to get as close to a neutral trim as possible. This is for RC aircraft as I want the plane to go where I point it, not have  mind of its own. I hate models that zoom up as the speed increases.

All the best,
Konrad

P.S.
Most forums are black holes unless you actually ask for input. I for one don't like adding that looks great comments. Rather I like to ask questions or comment if I see a problem developing. Your builds are often so well done there is little I can comment on.
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Cut it twice and it's still too short!
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