Airfoiling stabs on a Dominator
05-17-2002, 08:37 PM
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Airfoiling stabs on a Dominator
I posted this in the Aerodynamics area but no-one had an answer there:
A guy at my club built one and built the stabs with a pointed leading and trailing edge.
I read somewhere that aerodynamically it is better to have a more rouned leading edge. Something about turbulence ceated by a pointed LE. I want this plane to be fast, so which is better?
Intuitivly I would think that Pointed would create less drag, but will I sacrifice control? The control surfaces are relatively small, and at speed you need very little deflection to cause the desired movement. If I point the LE, will I sacrifice control? Will it be worth it in reduced drag/increased speed?
A guy at my club built one and built the stabs with a pointed leading and trailing edge.
I read somewhere that aerodynamically it is better to have a more rouned leading edge. Something about turbulence ceated by a pointed LE. I want this plane to be fast, so which is better?
Intuitivly I would think that Pointed would create less drag, but will I sacrifice control? The control surfaces are relatively small, and at speed you need very little deflection to cause the desired movement. If I point the LE, will I sacrifice control? Will it be worth it in reduced drag/increased speed?
05-18-2002, 07:47 PM
#2
Airfoiling stabs on a Dominator
Most Q-500's with non composite wood stabs it is normal to knife edge the stabs as well as the Aluminum gear. Many choose to inlay 1/64 ply in the edges to get an even sharper edge. Blunt edges may have some advantages for some aerobatics but that is not what that airplane is about. Are you with the club in that area that has been talking about doing one design 424 pylon races?
John
John
05-19-2002, 05:33 AM
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Airfoiling stabs on a Dominator
I fly with Palomar RC flyer's. I'm new to Pylon, so I'm not sure what "424 pylon races" means.
We're all going to fly the Dominator with standard tail, 40FX engines and 9x6 props. 3.5lb minimum. I'm planning on putting HiTec 225MG's on aileron and elevator. I was surprised to learn that they put out more torque and are faster than the 425BB's that I have on most of my aerobatic planes. Wish I had known that sooner, coulda saved some weight. Any cautions on using these servos?
Since most of the Dom's that I've seen so far have knife edged the LE's, I guess I will too. The ply inserts are a good idea. I guess I'd just put a Dremmel "saw" type bit in a drill press, raise the table and run the balsa part around the bit to make a slot. Any other ideas? How about making lightening holes in the fuse/ stabs? Are you aware of any issues with pointing the LE and sacrificing the authority of the control surfaces due to increased turbulence?
All advice appreciated.
Jet
We're all going to fly the Dominator with standard tail, 40FX engines and 9x6 props. 3.5lb minimum. I'm planning on putting HiTec 225MG's on aileron and elevator. I was surprised to learn that they put out more torque and are faster than the 425BB's that I have on most of my aerobatic planes. Wish I had known that sooner, coulda saved some weight. Any cautions on using these servos?
Since most of the Dom's that I've seen so far have knife edged the LE's, I guess I will too. The ply inserts are a good idea. I guess I'd just put a Dremmel "saw" type bit in a drill press, raise the table and run the balsa part around the bit to make a slot. Any other ideas? How about making lightening holes in the fuse/ stabs? Are you aware of any issues with pointing the LE and sacrificing the authority of the control surfaces due to increased turbulence?
All advice appreciated.
Jet
05-19-2002, 08:09 PM
#4
Airfoiling stabs on a Dominator
Jet, welcome to the wonderful, chaotic and gut wrenching world of Of pylon I am delighted to hear you are going to get involved. I am aware of the Palomar clubs efforts to get started. I am involved in mostly 424 Apra races around southern Ca. and in Arizona. 424 is the AMA rulebook event 'sport Quickee' and is considered the entry level pylon event. APRA is Arizona Pylon race association which is supplimentary rules for sport quickee that involves an approved engine list and some other considerations that is used mostly in a three state area.
With a Quickee You will find no control authority issue with the ruddervators and the sharp leading edge is not a consideration in this regard. As a matter of fact most people particularly set throws far to high on their first flights. The speed range of these airplanes is so high that excessive throw at top speed is a problem. Generally for elevator a low rate of 1/8 inch and no more than 3/16 for high. In the case of the dominator the ailerons are a bit smallish and it helps to cut them with perhaps a quarter inch deeper cord. If already cut no problem just set for 3/16 inch throws on high.
You do want to shoot for that magic 3.5 lbs and you are on the right track with the HS 225's these servos are ideal. I use the plastic gear version as the only stripping occurs in crashs and the three dollar gear replacment is far cheaper than the metal types.
Another suggestion is to use a 270mah pack at half the weight it is plenty for six heats and two practice flights. Making holes in the stabs is a bad idea since this is a very high stress area.
do pop up over at the Q-500 race forum at this site as well as the race planes forum at www.rcshowroom.com and you will find plenty of help at both places as well as info on the dominator/preditor.
John
With a Quickee You will find no control authority issue with the ruddervators and the sharp leading edge is not a consideration in this regard. As a matter of fact most people particularly set throws far to high on their first flights. The speed range of these airplanes is so high that excessive throw at top speed is a problem. Generally for elevator a low rate of 1/8 inch and no more than 3/16 for high. In the case of the dominator the ailerons are a bit smallish and it helps to cut them with perhaps a quarter inch deeper cord. If already cut no problem just set for 3/16 inch throws on high.
You do want to shoot for that magic 3.5 lbs and you are on the right track with the HS 225's these servos are ideal. I use the plastic gear version as the only stripping occurs in crashs and the three dollar gear replacment is far cheaper than the metal types.
Another suggestion is to use a 270mah pack at half the weight it is plenty for six heats and two practice flights. Making holes in the stabs is a bad idea since this is a very high stress area.
do pop up over at the Q-500 race forum at this site as well as the race planes forum at www.rcshowroom.com and you will find plenty of help at both places as well as info on the dominator/preditor.
John
05-20-2002, 03:48 PM
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Airfoiling stabs on a Dominator
About the ailerons: You mentioned that they are a bit small. Should I build the sport ailerons in instead of the race? They are maybe 30% longer.
Jet
Jet
05-20-2002, 07:21 PM
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Airfoiling stabs on a Dominator
Jet I have tested a number of Dominators for other people but I have not actually seen the plans so I am not sure what you mean
by sport or race ailerons. But I suspect 'sport ailerons' is not the way to go, at top speed on the pylons your roll rate will probably be to great and this makes it almost impossible to fly an accurate course. Contrary to popular belief pylon racing is about flying very smoothly with accurate roll in and outs to a heading while holding altitude. this is not easy to do and thats why unlike akro airplanes pylon ships have very small surfaces and throws. I do recommend to use if available about 30% negative expo on aileron and elevator. Virtually all modern Quickees use inboard ailerons to soften high speed roll rate and help prevent tip stalling at the very slow landing landing speed they are capable of.
With Quickees because of the slow landing speeds roll tends to be soft on approach so always use rates set for high on landings while takeoffs and fly at low rates. What I mean by smallish ailrons on some I have tested the cord seemed kinda narrow about three quarter of an inch and the really need to be about an inch roll good control on slow approach. I am not sure if this was by the plans or perhaps the individuals just cut them to narrow. Its not a major problem but you will need to use just a bit higher throw. The sport ailerons is probably a bad idea since you are using a reasonable .40 engine.
Here in Kingman we run a series of 'slow Quickee' races to get new people involved on two poles and any wood Quickee air frame with sport .28's or less and with these slower ships the domi ailerons are a bit narrow.
Enjoy and pop up over at either of the race forums to let us know how it goes
John
by sport or race ailerons. But I suspect 'sport ailerons' is not the way to go, at top speed on the pylons your roll rate will probably be to great and this makes it almost impossible to fly an accurate course. Contrary to popular belief pylon racing is about flying very smoothly with accurate roll in and outs to a heading while holding altitude. this is not easy to do and thats why unlike akro airplanes pylon ships have very small surfaces and throws. I do recommend to use if available about 30% negative expo on aileron and elevator. Virtually all modern Quickees use inboard ailerons to soften high speed roll rate and help prevent tip stalling at the very slow landing landing speed they are capable of.
With Quickees because of the slow landing speeds roll tends to be soft on approach so always use rates set for high on landings while takeoffs and fly at low rates. What I mean by smallish ailrons on some I have tested the cord seemed kinda narrow about three quarter of an inch and the really need to be about an inch roll good control on slow approach. I am not sure if this was by the plans or perhaps the individuals just cut them to narrow. Its not a major problem but you will need to use just a bit higher throw. The sport ailerons is probably a bad idea since you are using a reasonable .40 engine.
Here in Kingman we run a series of 'slow Quickee' races to get new people involved on two poles and any wood Quickee air frame with sport .28's or less and with these slower ships the domi ailerons are a bit narrow.
Enjoy and pop up over at either of the race forums to let us know how it goes
John
05-20-2002, 07:35 PM
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Airfoiling stabs on a Dominator
Thanks for the advice.
The kit has an option to build either sport or race ailerons. both flavors start at the same spot on the wing, but the sport ailerons are slightly longer so they extend out farther toward the tip of the wing. I'll build the race ailerons, and as per your advice, I'll watch for sluggish roll at low speeds, and increase the high rate/low speed throws as necessary.
I've just found the Pylon World section of this forum, so I guess I'll be spending alot of time there!!
Jet
The kit has an option to build either sport or race ailerons. both flavors start at the same spot on the wing, but the sport ailerons are slightly longer so they extend out farther toward the tip of the wing. I'll build the race ailerons, and as per your advice, I'll watch for sluggish roll at low speeds, and increase the high rate/low speed throws as necessary.
I've just found the Pylon World section of this forum, so I guess I'll be spending alot of time there!!
Jet
04-14-2003, 06:57 PM
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Airfoiling stabs on a Dominator
"You do want to shoot for that magic 3.5 lbs and you are on the right track with the HS 225's these servos are ideal. I use the plastic gear version as the only stripping occurs in crashs and the three dollar gear replacment is far cheaper than the metal types."
One additional point on the good advice for plastic gears.... contrary to what you may think... plastic gears will actually last longer than metal (if not crashed). The metal gears are stronger and will not strip, however, the most important servo characteristic in pylon racing is zero slop which metal gears will quickly develop at the loads they will receive while the plastic gears will perform slop free for many seasons if not bathed in dirt.
One other point... while the magic 3.5 lb limit is good to work toward... it is far more important to have a racer that is major stiff in all the right places... I know... I have built some "Flexible Fliers" in the past!
Good luck.
One additional point on the good advice for plastic gears.... contrary to what you may think... plastic gears will actually last longer than metal (if not crashed). The metal gears are stronger and will not strip, however, the most important servo characteristic in pylon racing is zero slop which metal gears will quickly develop at the loads they will receive while the plastic gears will perform slop free for many seasons if not bathed in dirt.
One other point... while the magic 3.5 lb limit is good to work toward... it is far more important to have a racer that is major stiff in all the right places... I know... I have built some "Flexible Fliers" in the past!
Good luck.
