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Design => Stunt design => Topic started by: Dennis Toth on July 05, 2011, 05:29:56 PM
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Guys,
I'm starting on an Olympic Mk IV. This ship is basically a modified Nobler but there is one feature, the twin tails on the tips of the stab, that is an interesting design change. What I am curious about is are they more then just a for looks? Do the twin fins increase the effectiveness of the stab making it act aerodynamically like a larger stab/elevator closer to more modern numbers? Since they are large it seems that they would reduce tip loses and channel airflow over the surface. Anybody add these to an existing design and see a difference?
Best, DennisT
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Bob Gieseke and I have discussed this at length. He experimented a lot with the tip plates in developing his "Bear". Since we both new Ed Elasick very well, Bob commented that Eddie had something with the rudders on the "Impala". Bob feels that the tip plates definitely add to the effectiveness of the elevator. Others who have flown the "Bear" with and without the tip plates agree.
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I usta know a couple of F1B (Wakefield) fliers who used tip plates (John Lenderman) or tip fins (Bob White) on the stabalizer. I asked why. The theory was that they increased the effectiveness of the stabalizer, essentially "free area" or increased aspect ratio. My take at the time was that there would be a drag penalty to be paid, plus some weight and fragility that I didn't want.
For stunt, the drag is not an issue for IC power, but you might not want to do it on an electron burner. There is still a weight and fragility penalty to be paid, but otherwise, tip plates or fins should be a good thing. H^^ Steve
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Flew an Olympic once for a guy to check it out and didn't like not being able to see the elevator.
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Guys,
Thanks for the feed back, anyone have some parameters for how big they need to be to be effective?
Best, DennisT
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The ones on my new plane seem to work pretty well.
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Guys,
As Ty said the 1/2 area seem what has been mostly used. What I wonder is with the tip plates funneling airflow over the stab/elevator and preventing air slipping off the tip does it make the stab work like it is bigger and if so does it allow a stable more rearward (modern) CG location than a non-plate arrangement? Seems like it should.
Best, DennisT
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I think so. The vertical things are like winglets. They increase the effective aspect ratio of the tail, which should make the plane more stable or allow a farther aft CG. I don't know how to calculate how much the effect is.
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I can tell you the new plane I have with the twin rudders has too far aft a CG and it is touchy but not really squirrelly. It can use a bit of nose weight (or a lighter tail), but it seems to handle the rather far aft CG reasonably well.
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...or you can just go with tip plates rather than full-on vertical stablizers. Probably accomplish the same thing. 8)
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Guys,
I'm starting on an Olympic Mk IV. This ship is basically a modified Nobler but there is one feature, the twin tails on the tips of the stab, that is an interesting design change. What I am curious about is are they more then just a for looks? Do the twin fins increase the effectiveness of the stab making it act aerodynamically like a larger stab/elevator closer to more modern numbers? Since they are large it seems that they would reduce tip loses and channel airflow over the surface. Anybody add these to an existing design and see a difference?
Best, DennisT
Hi Dennis
Tip plates work very well, They do make the Elev. Stab act larger than it is, and you can make them as small as 1 inch high and they are very effective. make sure you center them, with the same amount on top and bottom. Be careful to keep the close to the elevators but not so close that they will touch
Regards
Randy
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If I had not got side tracked I was going to build another Olympic Brodak kit. This time it would get more time making it lighter even tho mine flew great off the board. It was Brodak powered. I set the handle using the flaps for neutral as the elevators can't be seen. It was one of my better flying planes. H^^
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Flew an Olympic once for a guy to check it out and didn't like not being able to see the elevator.
Make them transparent perhaps?
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I believe I attached mine according to the plans. The outboard edge of the elevator is pretty much aligned with the TE of the vertical fin. As the inboard part of the elevator is wider than the outboard you can see the position of the elevator from the handle...but you've gotta look close.
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My eyes were/are not that good. LL~ LL~
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Just an observation here, if tip plates are employed to reduce tip vortexes and these vortexes are more prevalent towards any trailing edge due to directional travel then why not simply install them only on the rear most part - the moving elevator only?
Please see the preceding post, there is a functional angled gap built into the model between the tip plate and the elevator, and at that gap the air would accelerate through, create the very vortex the plate seeks to avoid thus the plate as installed becomes partially redundant.
Better to use a half chord plate fixed only onto the elevators tip that travels through the same range range of deflection.
Doing this would make the elevators deflection visible to the flier as both the tip and elevator would move as one, cut down on drag evidenced by the slot or 'angled gap', stiffen the moving part and be lighter to construct.
Thoughts?
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...tip plates ... why not simply install them only on the rear most part - the moving elevator only?
If I can succeed in posting photos I'll post a pic. of the T/P of my F2B under construction. Time I learned to do this anyway.
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What would happen if you put them on the wing-tips as well? (I assume this has been done.)
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What would happen if you put them on the wing-tips as well? (I assume this has been done.)
I would think that due to the higher aspect ratio of the main wing the law of diminishing returns would kick in a bit and the extra drag may not be worth it.
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Wing Tips , They Do . On P-51s with clipped wings . Tho small, the plates are to enhance Aileron effectiveness .
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Here is something interesting..
Id love Doug moon to try this - but it would involve surgery.
In late 1999 I added Tip plates to one of my models, and found no improvement at all....
I repeated the experiement in 2004 with same results.
I have been running Vortex Generators since mid 90's - I think all of the effect you get with Stab plates is nulified when used on a model running VG technolgy.
I have no doubt they (stab plates) increase effectiveness of the tail surface thereby improveing performance / stability and repeatable control inputs. However the wing as far as a flying surface is far larger, and we are using coupled controls.
When doug tried the VG's he noticed a dramatic improvement - id like to know if he removed the stab plates if he notices any change - my experiements indicate he wouldnt.
Interesting information if nothing else..
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Russell..
I recall in the World champs 1980 Wu Dazhong ran a very different approach to tip plates.
(http://i1115.photobucket.com/albums/k554/pjaussie/1980wc-05.jpg)
Wing tip fences with high lift aerofoil sections, heavily off set to increase line tension.
Makes me wonder if it was for an outward lift senario or just the tip plates increasing effectivenss of the wing toward the tip.. Either way redundant technology in my opinion.
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I remember this photo, I think it is the same pilot that had the lines connected to rings that he had on his fingers .... :o
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Correct for 10 points.
( first time you ever got 10 points for anything :) )
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RUBBISH!!!!!!!!!! S?P
10 pts for starting within one minute....and er,.......let me think............ :P
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Touche'
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Guys, He took them off after the first round as I remember ,Don't know why He didn't' speak English and I don't speak Chinese. Regards Noel.
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Guys, He took them off after the first round as I remember ,Don't know why He didn't' speak English and I don't speak Chinese. Regards Noel.
Probably they provided almost zero lift and maximum drag at their aspect ratio and thickness.
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The ones on my new plane seem to work pretty well.
Tip plates need to be at least one airfoil thickness all the way around.
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RUBBISH!!!!!!!!!! S?P
10 pts for starting within one minute....and er,.......let me think............ :P
Hi Russell,
Unfortunately the "starting points" have been dropped from our pattern........... ;D
Big Bear
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:( :( :(