Waco SRE (oz7341)

 

Waco SRE (oz7341) by Jim Kostecky 1986 - plan thumbnail

About this Plan

Waco SRE. 1/2A scale model biplane for radio control.

Quote: "I have always found the lines of Waco biplanes truly appealing. The proportions and curves seem exactly right. If the old adage 'If it looks right it will fly right' is true then the Wacos must have been a joy to fly. Based on discussions with pilots who have actually flown them, I have no reason to believe otherwise. The Waco SRE seems to me to be the ultimate expression of beauty in the long line of biplanes the company produced. From the massive cowl, balanced by a long flowing fuselage ending in graceful tail surfaces the SRE is, in a word, elegant.

My first glimpse of a model SRE was many years ago when I watched a Berkeley kit built by Harold Keller (a gentleman and master modeler I admired as a kid) fly majestically at the local flying field. This was when Harold De Bolt was flying hot low wingers with Space-Control radios and pattern flying was on the brink of sophistication that we witness today. By contrast, this elegant airplane which flew 'on its wings' not on the brute power of its engine, and controlled by this mild-mannered gentleman etched itself in my mind as something I had to build someday. More than twenty years later, 'someday' has come and my version has enabled me to relive some pleasant memories and to re-capture part of a time in aviation that I was too young to witness.

The model as presented is very close to scale in outline except for three compromises. The tail surfaces have been enlarged slightly for stability. With such a long tail moment I wonder if that was necessary. Better safe than sorry. Secondly: the landing gear is missing a spreader and two little braces that run from the upper rear landing gear fairing to the fuselage near the lower wing leading edge. The braces looked like they would puncture or fracture the fuselage where they connected. So I left them off. The major, and third deviation and one which I'm sure will offend some purists is in the cowl area. Since this is a 'Schoolyard-Scale' model, I felt I could live with the aesthetic compromise I made in the interest of cooling my trusty Golden-Bee .049. Much of the beauty of the SRE is in the way the radial cowl makes a smooth transition into the flat fuselage sides. As you'll notice in the photos and plan I sharply pinched the fuselage from the front of the cabin forward and left the sides flat where they meet the rear of the Sig formed plastic cowl. This allows two very efficient cooling outlets and eliminates a very draggy area where air entering the front of the cowl would have no place to go.

As always, my schoolyard models are designed with performance as the primary emphasis. I was not disappointed as this was one of the prettiest little models ever to fly under the football uprights at the local school.

Let's build. Light weight with more than adequate strength is one of this design's best features. Please do not add anymore structure, it just isn't necessary..."

Direct submission to Outerzone.

Update 09/12/2017: added article, thanks to RFJ.

Supplementary file notes

Article.

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Waco SRE (oz7341) by Jim Kostecky 1986 - model pic

Datafile:
  • (oz7341)
    Waco SRE
    by Jim Kostecky
    from Flying Models
    February 1986 
    35in span
    Scale IC R/C Biplane Civil
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 28/12/2015
    Filesize: 916KB
    Format: • PDFbitmap
    Credit*: JJ
    Downloads: 1937

ScaleType:
  • Waco_E_series | help
    see Wikipedia | search Outerzone
    ------------
    Test link:
    search RCLibrary 3views (opens in new window)


    ScaleType: This (oz7341) is a scale plan. Where possible we link scale plans to Wikipedia, using a text string called ScaleType.

    If we got this right, you now have a couple of direct links (above) to 1. see the Wikipedia page, and 2. search Oz for more plans of this type. If we didn't, then see below.


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    ScaleType is formed from the last part of the Wikipedia page address, which here is https://en.wikipedia.org/wiki/Waco_E_series
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Waco SRE (oz7341) by Jim Kostecky 1986 - pic 005.jpg
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Waco SRE (oz7341) by Jim Kostecky 1986 - pic 006.jpg
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User comments

Photo of the Waco SRE [main pic] attached. Just a few comments for future builders on this plan. The main one concerns incidence. The plan shows different incidences for all three horizontal surfaces. I'm not sure I'd do that again. I needed all the down-trim available at full throttle and almost none at low throttle, I think because the higher-incidence lower wing overcomes the upper at low angle of attack and high speed. If I built it again, I'd make them the same. Of course, that means redesigning the N-struts, which I did anyway, using sheet metal tabs and screws. It was much easier to rig accurately than the tube-and-wire method shown in the plan.
The article mentions that the author used the "new" shrinkable plastic film, so I did as well (Neucover, ironically), but the tail surfaces didn't hold up to shrinking. I held the heat to 275 (Fahrenheit), but even the lower longerons deflected a bit. It's really a better design for silkspan or tissue, but not due to weight concerns. Ignoring the trim issue, it flew fine at 19 oz -- really slow, in fact, and practically stall-proof.
Mine was heavy because I didn't use a plastic cowl, and instead blended it in from built-up balsa, to better match the full-scale plane. It still came out tail-heavy, and needed 3/4oz(!) in the cowl. Total all-up weight, with 3s800-30 battery and 3/4oz ballast was 22.25oz.
I used a Gforce E370/14T-1400kv motor and 7x4 prop (the 6" prop mentioned in the article barely cleared the cowl -- it wouldn't even roll).
It was a somewhat difficult build, but came out OK in the end. I enjoy flying it -- at half throttle.
Jon - 27/09/2023
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