summerwind

ok, posted similar question in Aerodynamics forum, and it's no use.

so since my main interest is in this forum and i'm going to go deeper and deeper into this speed thing as my goal is to get into the 170-200mph bracket, let me ask this.

inlaying a 1/64" piece of ply into my ailerons, elevator and rudder TE's is not something i consider work. as far as i know, sharp TE's are better aerodynamically.
my concern is elevator efficiency.....mainly during the landing sequence.
so am i wasting my time to sharpen a TE on the elevator?

combatpigg

My Feedback: (3)

You can't do any better than razor sharp.

A flat plank elevator might be more responsive than a tapered elevator. The tapered shape has some "Aerodynamic Exponential" near zero deflection. The flat elevator gets into the airstream sooner and would make pitch control more coarse. The tapered elevator should contribute to smoothness.

Only a C/L stunt Guru would notice the difference on a plane that he flys all the time with an eagle eye while doing the precision stunt routine.

summerwind

OK, now this is getting somewhere.
my first go is a GP Patriot with sharp edges.
my second bird of starting out here is an ARF as i am limited on building time and really just want to get the Jett 56LX into something, so the choice is a Sundowner 50.
would i want to leave the elevator on this ARF as is, or sharpen it?

Bundubasher

I agree with Combatpig. With all the horsepower needed to get up to the speeds you mentioned, flat (rounded) edge or sharp elevators won't make mucha difference -not on models- thee are other factors having effect too. andyou will need to come in faster anyway. Flat ones , as per his explanation may even work better.

I'm talking prop plane speeds- most full scale cropdusters,a great number of recreation and aerobatic full scale planeshave flat tail feathers - elevators, fin, rudder and elevators.

Going even higher speeds, look at thecurrent planes in this year's international Red Bull air races.... faster than them you cannot go and stillhave manouvreability - some have thin airfoil tailfeathers. While at it, have a look at the fairly"blunt" leading edges too.Use them for guidence.

They have experimented with razor sharp LE and TE in the 1960's on jets and found no real advantage - in fact, it induced turbulence.

Want to go fast? slap a well balanced large electric motor/ESC/battery setup on a lightdelta and youwill outrun anything that runs on methanol - and I love my IC engines too, but that is reality.

mk1spitfire

[youtube]http://www.youtube.com/watch?v=qM87GKoMGJk[/youtube]

summerwind

so these are speed planes?

Bundubasher

You asked a question on elevator TE originally, you got a lead to follow. These Red Bull Racing planes fly the speeds you mentioned - 200 mph.Attend a race to see these planes at speed in real...... or go to Reno but they fly faster than the speeds you mentioned..
Both will give you good ideas of how to go forward with what pilots/engineers do regarding TE's for speed.... where better to look?

summerwind

don't get me wrong, i am looking for answers........but i am only interested in what effects we have on our models.
fullsize aircraft is always going to be a passion of mine.

i'm not building full size planes, but a model.
i know the posts are trying to show things of interest, but what has been tried and true with our models is of interest here.

so to rephrase, will a sharp trailing edge on an elevator of a model set up for speed be efficient at slow speeds, or will it lose it's efficiency.

ChrisAttebery

My Feedback: (15)

Summerwind,

I think CombatPig has is right. Look at the F5D, F3D and Q40 planes. They all have relatively sharp trailing edges.


Chris

Crazy4Flight

My Feedback: (540)

Go with sharp!

AS SHARP AS POSSIBLE !!!

The cleaner the two layers of air ( above and below the wing ) come together the faster you will go.

A squared off TE will create turbulance resulting in drag.

It works for spped planes and a friend proved it works with rubber-band powered planes too!

combatpigg

My Feedback: (3)

I wouldn't worry about tearing into an ARF to sharpen the elevator, unless I figured the time spent would be repaid with enough speed to see a difference.
For a "from the ground up" build that you're serious about, then going sharp is the only way to go.
If you've got the plane sitting on the threshold of a mph milestone that you want to see it blast through, then any amount of work you can do makes more sense to me.

freakingfast

My Feedback: (3)

Be warned, twice I've sharpened TE control surfaces, and both times I fought flutter AFTER modifying the ARF. You may have even more mods than you planed on.

MJD

My Feedback: (1)

I don't think sharpening the TE of a typical flat plate ARF hor or ver stabilizer makes enough difference to be worth the trouble, and everything I have read or experienced tells me it can aggravate a flutter condition. A modest flat area on the back softens that. Most ARF's have far larger drag issues to deal with than subtleties like this. As to the wing, if the aileron follows the wing airfoil profile with some fidelity, I'd try to make it a thin edge but wouldn't obsess over sharpness, unless you have a very precisely formed airfoil. To me, sharpening the TE on most ARF's is like tackling the second or third decimal point when you haven't dealt with the first one. But yes, on a clean design like an F40

As to full scale, many aircraft have flate plates because it is a simple and economical solution that works okay. Many also have exposed struts, wires, brackets, fasteners, draggy landing gear etc. for the same reason. This does not mean that flate plate tail surfaces are ideal or highly efficient. Profile, induced and trim drag are improved by more efficient tail surfaces. You can see the trend towards flate plate stabilizers trail away as you progress through the performance envelope and design purpose of the aircraft. What does a Lancair stab look like? An RV-6? Even a typical Cessna spam-can?

The Red Bull aircraft are not speed planes, they are highly powered aerobatic designs weaving around a tight course that requires great maneuverability. They would be left in the dust in a regular pylon race with other aircraft using the same hp in cleaner designs.

MJD

lfinney

My Feedback: (44)

and not to mention the Reynolds numbers disparity between our size of planes and full size planes, and the actual weight of the flying surfaces, which affects the resonant frequencies

summerwind

thx for all the info and education on this subject.
i have my Jett 50 powered Patriot done....woohoo came in at 5.75lbs AUW even with the Spring Air gear.

i post pictures in a few days of the control surface edges along with overall pics.

guess i'll find out soon enough how it all works.