Cranwell (oz6701)

 

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User comments

Added two superb photos of the finished model, thanks to Eric Holmes [model photo & more pics 003].
Mary - 27/05/2019
And another one :) [more pics 005]
Mary - 04/06/2019
Dear Mary & Steve, All the best for the Season! Just finished my version of the Cranwell [pics 006, 007]. A long anticipated build - finally got around to it. A Czech prop and Esaki tissue covering for 53 grams without rubber. A couple of pics attached. Cheers,
Adrian Culf - 08/12/2021
Finally got around to flying the Cranwell. The lifting tail - tailplane aerofoil profile - was a huge problem when trimming. The use of a flat plate tailplane is to be recommended. Either all sheet (eg. KK Gemini) or built up with 3/32" sq. or 1/8" sq. balsa strip. Is this a common experience with this model?
Adrian Culf - 03/05/2022
Hi Mary & Steve, I would like to submit this photo [pic 008] for your site's Cranwell plan (oz6701). This model was built in the late 1960s by Paul Penna. I recently restored the model with new Japanese tissue with domestic tissue trim. It now has a 9.5" Peck prop and weighs 55.0g without rubber. Thanks,
John Cooper - 18/08/2022
Dear Mary & Steve, attached is the black and white picture of the model that was printed on the kit box for the Contest Kits Cranwell [pics 009]. Photo taken by Paul Penna, who made the original model in our flying group from the kit. It is the only bit of the kit box that he kept from way back in the 1960's. Following trimming issues with the lifting tail, another flyer in our Ottawa group, John Cooper, modified the tailplane to be a flat plate and, with the C of G at the wing’s spar, the model flies well with the trailing edge of the new tailplane raised by about 1/8” with a balsa shim.
Adrian Culf - 31/01/2023
Now, it will be interesting to learn if the plan contributor, Mike Stuart and the builder of the orange model, Eric Holmes, have any comments on trimming their models with the lifting tail. I can’t remember what I knew about lifting tails in the 1960’s. I can only remember one flight launched from the top of a huge mound of top soil in the middle of a vacant field in Scarborough on a calm summer afternoon. Maybe I had the C of G way back on the wing TE, or maybe I had the tailplane TE jacked up. I only remember a great flight.
Paul Penna - 31/01/2023
Here's my experience with lifting tails. They're not good. Once I built two Ugly Duck models, one with a symmetrical airfoil tail and one with a flat plate. The symmetrical section seemed to be a lot easier to land than the flat plate, less sensitive to elevator. If you think about it, the tail actually lifts Down , not Up in flight, so a lifting airfoil is actually lifting backwards. What it amounts to is a tail with a really bad airfoil. The famous Telemaster touted it's lifting tail as an advantage and the reason it flew so well, but I think it flew well in spite of its lifting tail. The only advantage I can see for a lifting tail is structural, being thicker than a flat plate and thus stronger while still light. Some old timers actually used tail airfoils with the curve upside down, possibly to make the tail more effective. Look at a late model F-4 fighter. It featured a leading edge curve upside down, probably to get a tighter turn from a heavy airplane. Only way to find out for sure is to build three tails and try them all, more than I want to do. It's the old downwind turn all over again.
Doug Smith - 01/02/2023
Our interest in the Cranwell began a couple of years ago when I showed Adrian Culf and John Cooper my Cranwell that I had built in the late 1960’s, with its brittle and torn tissue [pics 010]. After he examined my old Cranwell, John Cooper said: “The structure looks sound: let me re-cover it for you!”. The result is shown in John’s photo that he uploaded to OZ (the red and yellow “G-CRAN” model) [pics 008]. Adrian’s yellow and green version and my G-CRAN flew quite well last summer with “flat plate” tailplanes, with the C of G set as Adrian described.
Paul Penna - 02/02/2023
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