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Author Topic: Waco SRE by Earl Stahl  (Read 417 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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