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Author Topic: How to add a dethermalizer  (Read 359 times)
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Romeo_Delta
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« on: October 17, 2020, 03:03:35 PM »

How would you guys add to a DT to British Champ?
Also applies to any streamliner model ie GB3, Frank Zaic streamliners Bullock Streamliners etc.
A lot of builders use this kind of fuselage but how to flip up the tail do you guys have any suggestions?
I noticed Al Pardue has a well known British Champ and I see it has a timer D/T but I can’t tell how it works.
Any ideas are greatly appreciated.
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flydean1
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« Reply #1 on: October 17, 2020, 04:27:07 PM »

Where are you located RD?
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Romeo_Delta
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« Reply #2 on: October 21, 2020, 05:29:32 PM »

Moorpark, CA
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TimWescott
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« Reply #3 on: October 21, 2020, 08:03:43 PM »

Disclaimer: I've read -- wistfully -- FF construction articles about dethermalizers.  I've even made FF models with dethermalizers that didn't need them, because I build for crap.  The only flyaways I've had involved ACE RC receivers breaking in flight, with the controls stuck on "nice glide".  But I've never actually used a dethermalizer to good effect.

How original do you want it to be?  Why can't you make a pop-up stab DT by hinging the front of the stab to the fuselage, and gluing the fin to the stab?  You'll either need to make a slot in the fuse for the front of the fin (for maximum "looks like stock"), or notch the front of the fin -- in which case it can be your DT stop.
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lincoln
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« Reply #4 on: October 22, 2020, 06:31:39 PM »

It's probably not your building, unless you use oak and cover with window screen. You're probably just good at picking bad air. ;-p

I've lost several ff catapult gliders and a rocket glider, without DT's, to thermals. Also lost a glider to a failed DT. That doesn't count incidents with RC. I've seen a model wing get picked off the ground by a thermal and stay aloft 30 seconds or a minute. Ditto a paper bag. I guess when thermals get that powerful we start calling them dust devils, but they're not rare. Once, I had to go around two or three times with an RC glider. I should have gone around again, because I planted it so hard it broke.

I wonder how well a stopped prop would work as a DT on a Wakefield. I have a twin pusher without freewheels that comes down fairly quickly when the props stop. I suspect a prop that was working against resistance would work even better. Or maybe spoilers or flaps. Or make half the stab an elevator which can flip up to 90 degrees.

I've heard of a DT method where a weight is fastened by a line to the tail and is dropped from the nose. A few models, long ago, even deployed parachutes. I don't know how well these methods work.
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ffkiwi
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« Reply #5 on: October 22, 2020, 09:20:54 PM »

They all work-to a greater or lesser degree-although the dropped reel of thread DT usually works only once....the spiral drive it creates is usually terminal...    Parachutes are heavily dependent on size for effectiveness-to small and the have no effect, too large and the model can travel miles before landing-not to mention the risk of tangling. Dropped tethered weights-work like a treat.........UNTIL the model noses up on deployment, and the weight catches and winds round the fuselage of tail feathers-either just destabilising (usually stally) the model or worst case cutting into or through the fin and stab.

 Time and time again we come back to the tipping tail or tipping wing as the most reliable option-and even here there can be issues...high performance F1A gliders can be tricky things to DT safely-being critical in DT angle to the tune of 1 or 1 degrees in the overall angle-and often tend to helicopter in a nose down attitude-great for visibility at a distance-but not good for your wingtips on impact....

And finally-the best detheremaliser in the world will not save you if the thermal is ascending at a faster rate (no matter how slight) than the model's natural rate of descent in a DT'd state.   I've seen this happen personally at the Omarama World cup events-even to F1A models....fortunately not for very long. Even there with the killer thermals that place can generate-I've had F1A models take 8 minutes to descend on DT-after a 3 min flight. Fortunately after many years of learning we realised that most thermals there had a lifespan of approximately 15 minutes-and provided you could keep things in sight, eventually they'd descend...

 ChrisM
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lincoln
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« Reply #6 on: October 22, 2020, 10:28:35 PM »

If one had a cheap supply of identical weights, one would't have to use a thread. Alternatively, the weight could move back inside the model. Maybe it could slide back along a string. Hmmm....
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