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Dethermalizing with R/C

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Old 04-24-2003, 04:18 AM
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mustang4me
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Default Dethermalizing with R/C

In Radio Modeller Mar 1984, a diagram was published of an r/c operated dethermalizer to fit to to a fully flying stab replacing the usual horn. You fly normally, but if full up trim is selected, then full up stick applied, the stab went to 30-40 degrees up, causing a deep stall. The airplane then descended almost vertically, but horizontal, and fell more or less gently. Normal control could be recovered by reverting the stab to normal. I can not figure out how to make the linkages because the outlines are confusing. Has anyone made one? It could be done by using 2 servos, but this neat as it only used the one servo. I can email a pic if anyone can help. I want to try it as I want to fly in a clearing in the midst of trees, and this would be the way to "land"!
Thanks,
Adrian
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Old 04-24-2003, 06:47 AM
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Default Dethermalizing with R/C

It's an interesting idea but I would much rather use a third channel to operate the DT angle. All those linkages look like a lovely place for slop to take place unless the machining of the bellcranks was meticulous.

With two channels you could use a simple set of two control horns. One with the normal throw that is mounted on the second. When the second is activated it would compound with the first for the extreme throw you need. The slots to accomadate the elevator link rods would be pretty weird looking.

This would still need some fancy designing and craftwork but at least it would all be just holes and simple tube bearings.

Also you should be aware that in some rare cases 45 degrees isn't enough to ensure a proper deep stall. The 45 degree angle isn't something magical but rather a guidline. Some models only need 35 to 40 and others need around 50 to get a proper stall and vertical descent. If it isn't enough it can get into a nasty whip stall effect. And there's no way to tell beforehand.

On my free flighters I usually go for 45 and move it a little from there if needed. 45 is USUALLY enough but I've seen some of the more extreme models that needed more. Short coupled old timers generally only need 40 to 45.

And finally.... I've flown in a couple of tighter tree areas that would have been a cadidate site to fly as you are thinking of. Believe me when I say I wouldn't want to fly gliders in such a place. Sure it would survive but it wouldn't be any fun trying to find and stay with thermals.

Obviously this would be electric or gas powered as you wouldn't need this arrangement if you had enough room for a highstart or winch so..... Good Luck if you try this.
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Old 04-25-2003, 01:04 AM
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Default Dethermalizing with R/C

Thanks for that Info etc Bruce. Much appreciated. I was thinking more of park fly and maybe speed 400 type models only. Plus, I like messing around with other stuff....flaps etc. hence the curiousity with the D/T. I'll keep watching!
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Adrian.
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Old 04-25-2003, 01:53 AM
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Default Dethermalizing with R/C

Another thing to think of.

If you retract the DT then the recovery would be similar to a deep stall recovery for height requirements. So if you're 1 1/2 stalls high then good. But once it falls lower than that you're commited to a DT landing or it's crash city.

Obviously the stall height is less for very light models with lots of area but it's something to think of.

Also, the lower the angle the more forward "glide" there is. It wouldn't be much but with a large rudder you could point the nose into the wind a little and prevent a small portion of downwind drift.
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Old 04-25-2003, 02:43 AM
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Tall Paul
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Default Dethermalizing with R/C

I've seen fun flies with +- 90 throws on the tail... No explanation how it's done, but I doddled up this a while back.. with dual rates????
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Old 04-27-2003, 11:20 PM
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Default Dethermalizing with R/C

What transmitter are you using? With a Futaba 9C, you can program some rediculous dual rates/ exponential, that would probably allow this kind of motion.

FWIW - it looks to me like they didn't mark the location of one axle. I can see how this gizmo would work. If you want, I'll add my notes and repost it. I would make this out of thin aluminum, use very tight tolerances, and keep it lubed with silicone
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Old 04-28-2003, 12:17 AM
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Default Dethermalizing with R/C

I certainly would be interested in your thoughts John.....it figures about the axle missing. I once built a c/l throttle/bellcrank from scrap metal with sliding parts, and it worked well. So this would be an interesting project. The fellas at work here haven't sussed it yet, so we await your diagam etc. with interest!
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Old 04-28-2003, 01:00 AM
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Default Dethermalizing with R/C

Take a look at the drawing I attached:

You need 2 of part A. SInce this part is fixed to the fin, it could be integral to the fin, and doesn't need to be this exact shape.

Part B has a tang that rides axle 1 between the 2 part A's. It also has 2 lower arms that engage the slot in part C. You could most easily make part B from sheet stock by using one "tang" piece and two "lower arm" pieces. Axle 1 is also the main axle/ carrythru for the stab.

Part C rides on axle 2, which wasn't clearly shown on the original. The slot in C, engages the 2 arms from B with a pin.

It's all just a mechanical way to provide extreme exponential.
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