Shape of tail feathers

[birdy]

Ted, its an airofoil.[section of rotor blade.]Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

Mitch,What are the dimensions of the Butterfly's tail, and when compared to say a 68" or larger prop, how much of the prop does it cover?Given that the "the most accelerated airflow in the propwash is about 2/3 the way out from the prop hub." this could well place a significant percentage of the Butterfly tail "inside" of the most effective area. Ted

[asra]

Birdy,Every shape is an airfoil of some sort. What I'm looking for here, is there a better shape than others, and where should it be placed, how big does it be to be effective, and more importantly will it be effective in a power on or power off situation?From the comments being derived at this point, we still have some way to go to determine the what where and why.Ted

[asra]

Brian,The tails on the modified RAF's should be (and are) a lot bigger and a lot futher back to allow for the large cabin area..The tail on the tandem machine started out at 5 inches from the prop. Its now about 11 inches from the prop hub and it hangs over the tail wheel about 3 inches.The extra 6 inches made a big differance(Where have I heard that before?) Even pushing down hard on the rotor blade you cannot come anywhere near the top of the tail.Re the Butterfly tail, from talking to pilots that have flown them the tail area seems to be more than adequate,a symetrical airfoil would be better but how much rudder authority do you need?The horizontal component of the tail would certainly be improved with a change to a symetrical airfoil section.Most single engine fixed wing aircraft manufacturers seem to put the horizontal stab somewhere near the center of the prop flow,so did the very first autogyro builders back in 1930's,thats good enough for me.M Barker

[asra]

Murray,I hear what you are saying. The Butterfly from all reports flies well, but if we follow Greg's thinking what would be the moment arm if the stab was lengthened to use the accelerated air flow that he talks about?Would the fact that the stab being bigger in surface area than the vertical fin have a negative effect on its flight performance?Would this allow the use of winglets if fitted, to come into play in an engine out or idle approach?Ted

[Brian]

Thanks Murray for that info !Do you have the weight of a tall tail anywhere handy? The airfoil shaped tall tails made of fiberglass would be fairly heavy you would think.I agree Murry, I cant see a lot of sense in an airfoil shaped tail[rudder] whereas the stab giving extra lift would be welcomed.Brian

[Brian]

Ted, seems it doesnt matter too much where its located, no one yet has run out of rudder authority even in engine outs. I think you will be still here in 100 years time if there is a debate between conventional tais and tall tails .Personally, I dont care as long as the tail is as light as possible, is effective as possible and gives long service !!Weight is another factor I'm concerned with.Brian

[birdy]

Ted, an airfoil H stab is much more powerful in the prop wash than a flat plate, which means it don't need to be any where near as big to have the same effect.And you don't need the horisontal stab effect without power, coz without power, you can't have a power push over.Tim, Murry, I noticed a weired thing today.Was cruis'n bout for round 3 hours look'n at all the fresh water ona ground, and being still halfcast[as opposed to overcast], the air was perfectly still.Everyone knows the fin/rudder on a RAF is inadiquate, especialy with the doors on, and I found in this unusualy still air, if I crabbed right[nose pointing left] the engine rpm would drop by bout 50rpm. If I crabbed left, they would increase by bout 50rpm.[bout a 100rpm difference between left n right yaws] But with the changes in rpms[obviosly prop efficiancy being affected by the changing airflows], there wasn't any noticable effect in prop output[didn't increase in alt or AS.????Just thought you might av been interested.Ignorance is bliss............but only till you realise you were.You can always get the answer you want, if you ask enough experts.

[asra]

Brian I think the TT's are about 9 LBS,and I have a photo of me and Owen Dull standing in the middle of one while its suspended between two chairs, so they are pretty strong.I think there is a limit of how how big you should make a H S,but i havt a clue what that is.If you have a look at helicopters their HS's are very small but a long way back.There was a Jetranger lost in the bay up here about 15 /20 years ago and all on board were killed.Million $$ aircraft,millions spent on reserch and development by the factory,and the cause of the accident?.... PIO.M Barker

[asra]

Birdy, If you make some vortex generators and put them on the sides of your cabin you may stop that side to side "hunting" you seem to get with RAF cabins with the doors on.I'd start with a vertical row just before the rear of the doors.If you can work out where the airflow seperation starts on that cabin(Probably at its widest point)start the VG's a few inches before that.M Barker

[Tim]

Good one Birdy. I would suspect that it is because one side of the prop is going down into dirty air while the other is going up into cleaner air, and crabbing one way or the other amplifies this effect. Thats my guess.Tim McClure

[asra]

Murray can you post that photo? I would be really interested to see that one!Cheers!

[Brian]

Thanks Murray for the info, I would have guessed the weight at being heavier than 9 lbs, so there you go !!I know R22's can get the mast knocking happening but I would have thought a Jet ranger would have been a lot less to PIO. Goes to show that the quality of pilot skills could still be a sought after commodity, even in these times of computers etc !!!I agree with you there Tim, I get a similiar thing happening in my gyro doing big yaws!!Brian

[asra]

Just checked, the weight of the Tall tails made by Owen Dull are 6.5 Kilo's.I'll get that photo and ask Waddles to scan it for me for the forum.M Barker

[asra]

Isn't it interesting that almost all low speed fixed wing aircraft use flat plate tails, is this because at these airspeeds it doesn't make much difference, or is it just a cost cutting thing? The trouble with flat plates is that they need bracing, which is more weight and drag, perhaps the drag is supposed to keep the tail behind you, like the tail of a kite!Fabricated airfoils can be very light and strong, as their depth allows the use of a deep section spar, mine is metal, but my next one will be ply, wonderfull stuff.John EvansThink logically and do things well, think laterally and do things better.