Stabilizer halves of different incidence? What gives?
04-09-2010 | 03:46 PM
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From: pound ridge,
NY
Stabilizer halves of different incidence? What gives?
So I went to work today on adjusting the wing incidence on my Delro E-Motion because it was needing a couple degrees of up elevator for level flight and I figured I'd rather have it "correct" meaning zero elevator trim for level flight. Anyways, after carefully checking my starting point and adding a tiny additional amount of positive incidence, I decided to check the stabilizer halves for comparison to the wings just for fun. What was intriguing is that there is a 0.5 degree difference between the two. The right half has a 0.5 negative incidence compared to the left half of the stabilizer. Could this be by design to counter act the torque of the prop? If not by design then what, and what would be the best way to adjust for it?
The good news is even with this tiny quirk the plane flies awesomely well, and my biggest concern is that I will mess it up in trying to "refine" the trim, but as always trying and learning is half the fun.
Lost and confused in NY [
]
Joe
EDIT: This post was edited on 4/17/2010 to reflect the proper term of stabilizer instead of elevator.
The good news is even with this tiny quirk the plane flies awesomely well, and my biggest concern is that I will mess it up in trying to "refine" the trim, but as always trying and learning is half the fun.
Lost and confused in NY [
]Joe
EDIT: This post was edited on 4/17/2010 to reflect the proper term of stabilizer instead of elevator.
04-09-2010 | 04:05 PM
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From: Sydney, AUSTRALIA
RE: Stabilizer halves of different incidence? What gives?
Joe,
What are you using to measure the incidence? Robart?
Are you rotating the meter from each side so it's easier to read the scale?
Also take a looks at Bryan Hebert's website with his trimming triangulation procedure.
Cheers
Jason.
What are you using to measure the incidence? Robart?
Are you rotating the meter from each side so it's easier to read the scale?
Also take a looks at Bryan Hebert's website with his trimming triangulation procedure.
Cheers
Jason.
04-09-2010 | 04:49 PM
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From: pound ridge,
NY
RE: Stabilizer halves of different incidence? What gives?
Hi Jason!
I'm using a laser meter. First I used the canopy as a reference point set to zero. Then I took readings around the plane 5 times to be sure I got everything right. I don't know how to check my motor thrust lines with what I have, but from the best I can tell using a level and my eyeballs it looks like I have the normal right thrust and down thrust built in. And, yes I found Bryan's article on trimming during my search for insight on incidence. Really a wealth of information in his [link=http://hebertcompetitiondesigns.com/triangulation.aspx#]Triangulation Article[/link]. Thanks for the tip though. Definitely a "must read"!
Joe
I'm using a laser meter. First I used the canopy as a reference point set to zero. Then I took readings around the plane 5 times to be sure I got everything right. I don't know how to check my motor thrust lines with what I have, but from the best I can tell using a level and my eyeballs it looks like I have the normal right thrust and down thrust built in. And, yes I found Bryan's article on trimming during my search for insight on incidence. Really a wealth of information in his [link=http://hebertcompetitiondesigns.com/triangulation.aspx#]Triangulation Article[/link]. Thanks for the tip though. Definitely a "must read"!
Joe
04-10-2010 | 04:08 AM
#4
RE: Stabilizer halves of different incidence? What gives?
Different incidence on the elevator halfs influence the knifedgetrim. The elevator half pointing up in knifeedge is partialy blanked by the fuselage. Therfore the lower elevatorhalf controls the tracking. This results in different trim in right ond left knifeedge position when the incidence differ.
In the old days, before computerradios allowed the luxury of electronic mixing, this was used to trim an aircraft that tracked differntely in left and right knifeedge. If the stab was`nt adjustable the elevatorhalfs neutrals were slightly separated. This proved very sensitive. On my Joker i wished it was possible to adjust the linkage 1/4 of a turn.
Regards/
Anders Johansson
Sweden
In the old days, before computerradios allowed the luxury of electronic mixing, this was used to trim an aircraft that tracked differntely in left and right knifeedge. If the stab was`nt adjustable the elevatorhalfs neutrals were slightly separated. This proved very sensitive. On my Joker i wished it was possible to adjust the linkage 1/4 of a turn.
Regards/
Anders Johansson
Sweden
04-10-2010 | 05:43 AM
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From: Leesburg, VA
RE: Stabilizer halves of different incidence? What gives?
Joe,
Subtle differences in leading edge or trailing edge sanding or even placement and angle of your meter relative to the fuse centerline can lead to different readings. Since the E-Motion has front and rear carbon fiber tubes, any side being low will cause the opposite side to be a little high which will show up as the stab out of square to the fin. The stab halves are not adjustable so whatever happens to one side would affect the other side. Since the fin and stab are square, I would look to a tool or possibly placement induced cause.
Subtle differences in leading edge or trailing edge sanding or even placement and angle of your meter relative to the fuse centerline can lead to different readings. Since the E-Motion has front and rear carbon fiber tubes, any side being low will cause the opposite side to be a little high which will show up as the stab out of square to the fin. The stab halves are not adjustable so whatever happens to one side would affect the other side. Since the fin and stab are square, I would look to a tool or possibly placement induced cause.
04-13-2010 | 07:05 PM
#6
RE: Stabilizer halves of different incidence? What gives?
I've been using negative incidence in the right stab relative to the left stab for 20+ years. Geometrically straight and aerodynamically straight are not the same when there is a single propeller on the front of the plane (causing spiral airflow). When you have the amount of bias in the stab correct, the plane will have the same pitching behavior in both KE's, and then you can you wing incidence, CG, or thrust to perfect the KE. Mixers are not preferred as they will only be 100% correct at a single airspeed and angle of attack.
Regards,
Dave
Regards,
Dave
04-13-2010 | 08:41 PM
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From: pound ridge,
NY
RE: Stabilizer halves of different incidence? What gives?
Dave,
You are a veritable "fount" of information! Thanks for the insight! I was befuddled for sure and didn't want to come across as disparaging the E-Motion as it flies so incredibly well, but I was certain of my readings and now we have a perfect explanation.
Thanks again,
Joe
You are a veritable "fount" of information! Thanks for the insight! I was befuddled for sure and didn't want to come across as disparaging the E-Motion as it flies so incredibly well, but I was certain of my readings and now we have a perfect explanation.
Thanks again,
Joe
04-13-2010 | 09:02 PM
#8
RE: Stabilizer halves of different incidence? What gives?
Joe,
You are welcome!
And as followup to Anders, who seems to have been using this trimming tool for many years.....I agree that tweaking the elevator halves on the older designs could often be frustrating when a 1/4 turn was not available. However, I've not found this sensitivity on most modern designs.
Regards,
Dave
You are welcome!
And as followup to Anders, who seems to have been using this trimming tool for many years.....I agree that tweaking the elevator halves on the older designs could often be frustrating when a 1/4 turn was not available. However, I've not found this sensitivity on most modern designs.
Regards,
Dave
04-15-2010 | 11:32 AM
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From: New Milford,
CT
RE: Stabilizer halves of different incidence? What gives?
Matt - judging by the pictures it looks like what he means is the stab + elevator pitch which would of course translate to stab incidence. With split elevators like we have on pattern planes, I always try to lock the elevators to some known point when I adjust the stab. incidence - I take the pushrods out of the equation because they can be slightly biased. If the elevators don't go all the way to the tip this is easy. I disconnect the pushrods, clamp the elevators to the stabs at the tips and take my incidence measurements. On planes that have full-length elevators I make a fixture that slides over the stab + elevator and hold the elevator in the same position on both stab + elevator halves.
While we're sort of on this subject, what has more effect, an incidence change or a control surface "trim" change? What I mean is, say you're trying to trim your downlines. You notice that you're carrying some "up" elevator trim to maintain SAL flight. You also notice that the plane pulls out of a downline more than you'd like (i.e you can't hold a downline for very long without "doing something"). Now, if you increase the wing incidence to reduce / remove your elevator trim, how will it affect the downlines? Will that solve your problem? What if, instead of increasing wing incidence, you decreased the stab incidence (and neutralized the elevator trim)? What would the difference be with each of these methods? Is it sometimes beneficial to split the difference between incidence and control surface "trim"? I think in some cases it may be, I'm just not sure what has a "stronger" affect and which one is more sensitive to speed changes. I would think that control surface trim is more speed sensitive but I'm by no means a Master in this area.
John Pavlick
Team Black Magic, Tech-Aero Designs
While we're sort of on this subject, what has more effect, an incidence change or a control surface "trim" change? What I mean is, say you're trying to trim your downlines. You notice that you're carrying some "up" elevator trim to maintain SAL flight. You also notice that the plane pulls out of a downline more than you'd like (i.e you can't hold a downline for very long without "doing something"). Now, if you increase the wing incidence to reduce / remove your elevator trim, how will it affect the downlines? Will that solve your problem? What if, instead of increasing wing incidence, you decreased the stab incidence (and neutralized the elevator trim)? What would the difference be with each of these methods? Is it sometimes beneficial to split the difference between incidence and control surface "trim"? I think in some cases it may be, I'm just not sure what has a "stronger" affect and which one is more sensitive to speed changes. I would think that control surface trim is more speed sensitive but I'm by no means a Master in this area.
John Pavlick
Team Black Magic, Tech-Aero Designs
04-17-2010 | 01:25 PM
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From: pound ridge,
NY
RE: Stabilizer halves of different incidence? What gives?
ORIGINAL: MTK
2 Sunny,
Do you mean the stabilizer or the elevator?
MattK
2 Sunny,
Do you mean the stabilizer or the elevator?
MattK
Matt,
Thanks for pushing me to use the correct terminology. Yes, I meant stabilizer, and I have now edited the original post to prevent any confusion.
Thanks again.
Joe
04-17-2010 | 01:31 PM
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From: pound ridge,
NY
RE: Stabilizer halves of different incidence? What gives?
ORIGINAL: jrpav1
Matt - judging by the pictures it looks like what he means is the stab + elevator pitch which would of course translate to stab incidence. With split elevators like we have on pattern planes, I always try to lock the elevators to some known point when I adjust the stab. incidence - I take the pushrods out of the equation because they can be slightly biased. If the elevators don't go all the way to the tip this is easy. I disconnect the pushrods, clamp the elevators to the stabs at the tips and take my incidence measurements. On planes that have full-length elevators I make a fixture that slides over the stab + elevator and hold the elevator in the same position on both stab + elevator halves.
While we're sort of on this subject, what has more effect, an incidence change or a control surface ''trim'' change? What I mean is, say you're trying to trim your downlines. You notice that you're carrying some ''up'' elevator trim to maintain SAL flight. You also notice that the plane pulls out of a downline more than you'd like (i.e you can't hold a downline for very long without ''doing something''). Now, if you increase the wing incidence to reduce / remove your elevator trim, how will it affect the downlines? Will that solve your problem? What if, instead of increasing wing incidence, you decreased the stab incidence (and neutralized the elevator trim)? What would the difference be with each of these methods? Is it sometimes beneficial to split the difference between incidence and control surface ''trim''? I think in some cases it may be, I'm just not sure what has a ''stronger'' affect and which one is more sensitive to speed changes. I would think that control surface trim is more speed sensitive but I'm by no means a Master in this area.
John Pavlick
Team Black Magic, Tech-Aero Designs
Matt - judging by the pictures it looks like what he means is the stab + elevator pitch which would of course translate to stab incidence. With split elevators like we have on pattern planes, I always try to lock the elevators to some known point when I adjust the stab. incidence - I take the pushrods out of the equation because they can be slightly biased. If the elevators don't go all the way to the tip this is easy. I disconnect the pushrods, clamp the elevators to the stabs at the tips and take my incidence measurements. On planes that have full-length elevators I make a fixture that slides over the stab + elevator and hold the elevator in the same position on both stab + elevator halves.
While we're sort of on this subject, what has more effect, an incidence change or a control surface ''trim'' change? What I mean is, say you're trying to trim your downlines. You notice that you're carrying some ''up'' elevator trim to maintain SAL flight. You also notice that the plane pulls out of a downline more than you'd like (i.e you can't hold a downline for very long without ''doing something''). Now, if you increase the wing incidence to reduce / remove your elevator trim, how will it affect the downlines? Will that solve your problem? What if, instead of increasing wing incidence, you decreased the stab incidence (and neutralized the elevator trim)? What would the difference be with each of these methods? Is it sometimes beneficial to split the difference between incidence and control surface ''trim''? I think in some cases it may be, I'm just not sure what has a ''stronger'' affect and which one is more sensitive to speed changes. I would think that control surface trim is more speed sensitive but I'm by no means a Master in this area.
John Pavlick
Team Black Magic, Tech-Aero Designs
Fascinating point you bring up John!
My quick reaction would be to lean towards minimizing opposing forces and trim surface deflections with the idea that less drag is better, but even that premise may be false I suppose. Anyways, thanks for expanding my area of thought! Looks like I've got more reading to find as I'm certain someone has been through this issue before.
Thanks,
Joe
04-17-2010 | 05:11 PM
#13
Senior Member
RE: Stabilizer halves of different incidence? What gives?
ORIGINAL: 2Sunny
Matt,
Thanks for pushing me to use the correct terminology. Yes, I meant stabilizer, and I have now edited the original post to prevent any confusion.
Thanks again.
Joe
ORIGINAL: MTK
2 Sunny,
Do you mean the stabilizer or the elevator?
MattK
2 Sunny,
Do you mean the stabilizer or the elevator?
MattK
Matt,
Thanks for pushing me to use the correct terminology. Yes, I meant stabilizer, and I have now edited the original post to prevent any confusion.
Thanks again.
Joe
Having said that, I don't put any offsets into the stab incidence for each half on purpose. Some folks believe this helps and that's fine...yet others believe that offsetting wing halves also helps and that's also fine. Yet others don't want engine offsets and adjust the right thrust electronically by mixing rudder with throttle
To me, some of these offsets essentially make a crooked airplane out of straight one, assuming the plane was built straight to begin with. This is a very big assumption because accuracy is tough to reach....it's an absolute.
I prefer simply to know my starting point, adjusting certain things like wing and stab incidence (whole surfaces not halves), cg and very slight engine offsets, and once these things are exhausted, only then do very small amounts of e-mixing.
I think the main points are that first you really need to know what you are doing and second, almost anything goes regards to trim preference. Asking people for a certain type of help is generally a good idea if you can't figure it out youself. And BTW, don't expect miracles right away...often it takes several tries before the desired result can be achieved. Don't get discouraged...it can be frustrating.
MattK
