[NSRCA-discussion] Aero design question
Fred Huber
fhhuber at clearwire.com
Sun Sep 3 20:05:52 AKDT 2006
You got the progression backward...
Helical pitch is "steeper" at the root than the tip of the prop. Since you want the whole prop to go forward 1 inch.. and the root essentially has little movement it has to be steep to keep up with the tip's large movement.
If you want to simulate the same thing with an aileron.. you would have more aileron chord near the root than the tip. This would inhibit tip-stalls if the wing is constant chord (See the way the Four Star series does it)
For a tapered wing, as is common in Pattern, to get the "helical" effect you'd need the ailerons to make up 50% or more of the difference in chord from root to tip.
Depending on aileron deflection angle... a different % chord ratio from root to tip would be required to achieve the "helical" incidence(tapered or straight chord wing) For any given tapered aileron, there will be one deflection angle that comes closest to producing helical incidence.
If Helical incidence is the goal.. you'll have to choose at what percentage of full aileron throw you want to hit helical incidence... cunch some numbers and then cut the ailerons.
Constant chord ailerons in effect gives more AOA change at the tip than the root with a tapered wing. (encouraging tip-stalls... this is why its inadvisable to use flaperon function with a Pattern design when landing... but spoilerons will help prevent dropping a wing.)
But.... it may be a good thing to get the higher AOA change near the tip...
As pointed out... the Sig Four Star uses the tapered ailerons in a manner which can approach a helical incidence, so its been tried at least in one design series. Its probably been tried in a Pattern design at some time... (if not... someone should try it)
----- Original Message -----
From: Nat Penton
To: NSRCA Mailing List
Sent: Sunday, September 03, 2006 9:31 PM
Subject: Re: [NSRCA-discussion] Aero design question
Hey Tom
I'm not providing solutions - just putt'in more wood on the fire. In steady state roll the least drag position of the ailerons would be constant AOA root to tip. This would call for the percentage of chord to progress linearly so that it would be double at the tip vs the mid span position - no different than helical pitch. A ( severe ?) negative would occur, though, when the ailerons are initiated, potentially causing a tip stall.
Martin Simmons provides a curve showing Cl vs % of chord for the aileron. Going over 20% doesen't get you much for the dollar - just much more servo wear and tear ( especially with the 160 <G> ).
IMO it is not worth the extra work to stop the ailerons short of the tip. Nat
----- Original Message -----
From: Koenig, Tom
To: NSRCA Mailing List
Sent: Sunday, September 03, 2006 6:46 PM
Subject: Re: [NSRCA-discussion] Aero design question
Hi lads,
This is what I have found to work well on my Merlin designs. Now,I am ready to be corrected by those much more knowledgeable than myself-I just do things empirically!
I ended up using a percentage of the span of the panel (60% in my case). I have tried various sizes, but somewhere in the 55-65 percentage area worked well. I also came in from the tip by 30 mm, to get the aileron out of the tip vortex. Now that I am flying a Synergy with the ailerons running all the way out, I'm not so sure how much of a difference it makes. Maybe servo life is a bit shorter, but that is hard to quantify with the YS shaking things to bits anyway. As far as aileron chord dimension goes, well, I have tried various sizes there too, and I do use different percentages at the tip vs inboard aileron. I actually like to run a slightly smaller percentage at the tip. I felt it to give me a more 'linear' feel to the aileron.
I also applied this to 'elevator' design. I wanted the tips of the elevator to be less effective. I felt it helped pull corners better afterwards, as in this case the inboard section is doing more of the work. But now I am running a straight elevator hinge line on the Synergy...............L.O.L
It all gets very confusing, and in the end, what does it all mean in 30 knot cross wind, sun in your eyes and thermals to boot???
Trim as good as possible, burn heaps of fuel ( or charge them packs) and learn to fly the PIGS!!
Ofcourse good design helps.
Tom
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Dean Pappas
Sent: Sunday, 3 September 2006 4:58 AM
To: NSRCA Mailing List
Subject: RE: [NSRCA-discussion] Aero design question
Hi Gang,
The excellent axial rolling charecteristic of some designs is due to a lot more than where the inboard end of the ailerons end. Nonetheless, all of my designs used ailerons that ended far from the fuse! The only downside is that having a bit of aileron in front of the stab offers a useful trimming tool: trailing the ailerons up or down will change the effective stab incidence, and this was a powerful adjustment tool back when we didn't have plug-in adjustable "everything".
You note Akiba's well trimmed airplanes. There is some smart design going on there!
later,
Dean
-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org on behalf of John Ferrell
Sent: Sat 9/2/2006 7:48 AM
To: NSRCA Mailing List
Cc:
Subject: Re: [NSRCA-discussion] Aero design question
I have spent a fair amount of time considering this situation. I have concluded there is no reason to take the risk of adding unnecessary turbulence to the empennage.
In gentle maneuvering it probably has little effect. In aggressive maneuvering (think snaps) it likely leads to inconsistent behavior. Inboard ailerons may contribute additional available force in 3D maneuvers (hanging on prop?).
Other related considerations are aileron shape and the hinging geometry. I also suspect fat fuselages reduce these effects by dispersing the turbulence over a greater volume of air.
Just my two cents worth!
John Ferrell W8CCW
"My Competition is not my enemy"
http://DixieNC.US
----- Original Message -----
From: Peter Pennisi
To: 'NSRCA Mailing List'
Sent: Friday, September 01, 2006 8:35 PM
Subject: [NSRCA-discussion] Aero design question
My current model has ailerons which extend a fair way towards the fuselage (Comp-ARF IMPACT) What effect does the turbulence coming off the aileron have on the tail plane. I am currently building another IMPACT (IMHO flies extremely well) which I am considering to reduce their size by cutting and fixing the inboard part to the wing in an attempt to clean up the airflow over the tail plane during rolling maneuvers . The model does roll well but it could be better.
Am I barking up the wrong tree – any thoughts!
Peter
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