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Frog Minx

I want something that can be flown in this era.

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Erfolg13/12/2019 14:51:28
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As many of a certain age group, I am into nostalgia. Be it cars, motor bikes and models. To that end I am going to builds a Frog Minx as a side project.

In this age, there are no longer the fallow fields, nor the open spaces, particularly in Northern England. With that in mind FF is not a viable option for me, even if the space was available, I am not into running any distance, nor clambering over fences and ditches. To that end I want to use very light weight RC.

Another aspect of this age, winding rubber and all the palaver of lubricating and stretching motors is a no, no. So it has to be a low powered electric.

Some ten, or so years back, I built a VS Tomboy, to get it to fly in anything other than a dead calm, I ended up modifying it extensively.

Which brings me back to, the Minx. I cannot help but notice that its AoA relative to the tailplane is very high. On that basis the CL must have been near the max. Also the CG is way back, when compared to current RC.

I have noticed that a number of people have done something similar with models such as the KK Ajax, Senator etc. My question have these guys stuck with the original arrangements or undertaken subtle mods. If so what and why.

J D 813/12/2019 18:49:34
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All the aircraft you name were designed for free flight and tend to be one flying speed machines with lifting tails and rearward c of g. With radio control it is easy to put the aircraft outside of its happy fight envelope.

Like your Tomboy I also found I had to alter the Veron Cardinal I built last winter for wider RC use with smaller horizontal tail, less incidence, less dihederal and more forward c of g.

As standard I recon most of these vintage types should be regarded as "radio assist " to be just steered gently around the sky.

Cheers John.Cardinal

Erfolg13/12/2019 20:11:48
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Possibly the third model I built was the Veron Deacon. Also the first model that I thought I made a half way decent job of. I would have been about 10. The engine that I put in was a ED Hornet(because the only other engine was a 1.5 Elfin), a big tank. Of course I knew that you needed a decent sized tank. Good job it was not trimmed very well. It met its end when the window pelmet fell off, taking the wing tip off, where it was residing on top of my wardrobe. At that time, I did not know or believe you could repair a model.blush

Like yourself I have had doubts with such a rearward CG, as I thought/think that the static margin, would result in the CG and NP being co-incident.

I have also thought, what is the lifting tail all about. I have tried envisaging what happens at various airspeeds with regard to the lift on each of the flying surfaces. I then thought, the downwash will be changing in value.

I now have a glass of whisky, as my head hurt and I haven't a clue.

wp_20191213_20_32_17_pro.jpg

To give an idea about what we are talking about

Edited By Erfolg on 13/12/2019 20:39:12

PatMc13/12/2019 21:14:12
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4254 forum posts
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I've had Veron Deacon (which of course is really an enlarged Cardinal) flying RC for about 10 years. Dihedral, wing & incidencies are as per plan. First flights were with a more forward cg position but that's since reverted to the design position.
The model flies fine with no bad habits.

The generous tail area is a design feature that allows the cg to be so far rearwards. Having elevator & throttle control make a variable speed range & climb rate possible.

IMO the auto correction ability of a "lifting" tailplane is a free flight myth, one with a flat plate or a symmetrical section would be equally effective.

This is it's first flight.

J D 813/12/2019 23:27:42
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1340 forum posts
78 photos

The lifting tail [ or foreplane ] was a common feature of early aeroplanes at a time when there was much experimentation with airframe layouts and sections. As PatMc notes it allowed for a more reward c of g and spread the load between wing and tail helping low powered aircraft into the air

I fly a large Bleriot XI that has a lifting tail that has more engine power for the size of airframe than any full size Bleriot ever did. I have to be careful not to give it to much throttle in level flight or it starts to miss behave the nose going down even with up elevator being applied.9.jpg

Erfolg14/12/2019 12:55:02
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11504 forum posts
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It is very interesting to re look at these designs from the past. At the time I knew even less than i know now, in fact I knew nothing. I did not understand in the slightest way, what was happening, even less than why. A good flight was a delight, the next flight more often than not, did not go well. I would read the plan, pack this or that, not a clue why. I would be even more frustrated that sometimes it worked, although often just the once.

I knew nothing of vectors, although not as relevant to RC control. Static margin, certainly the concepts of "Instrumentation and Control" would have frightened me, the maths would frighten me now.

Now in my dotage, I have some ideas, with respect to what was going wrong. With such small static margins, the models would essentially be stable in one set of conditions only, typically a change in airspeed would be outside the correcting parameters (I have avoided all the terms and concepts). So that is almost certainly why replicating a flight would be so difficult by a numpty. Those who knew what was required, would understand when and how to launch etc.

Patmac, your Deacon certainly looks better than my model did, plus it will be better built. My model was FF only, I had no money for SC RC.

JD, it looks like you have raised the LE a bit?

I have found that the higher camber models seem to have a number of issues, as these early designs generally seem to use. Like JD I am tempted to reduce the incidence, as JD dihedral will be reduced, as with my Tomboy, rudder induced Dutch Rolling if used beyond used to almost guide it.

Weight is the thing that is concerning me as well. I need a low weight motor, RC equipment that weighs nothing where the complete package including Lipo weights no more than a rubber motor. Covering is also now an issue as the lightweight covering from Solarfilm is no more. Some one must do something similar.

Hmm the lack of a proper spar will be an issue. Non is quite as easy as I at first thought. Perhaps the modern world does not have all the answers to hand, then again it will be me that is the issue.

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