flutter in aileron and flaps
08-22-2006 | 06:10 PM
#51
Senior Member
RE: flutter in aileron and flaps
kewl,
Now. You are going to solder or epoxy one of those clevis, aren't you?
Honest, I landed a buddy's big old 4Star the other week with one aileron connector hanging down. Both clevis were still solidly connected, but the threaded rod had rotated right into one clevis and out of the other.
Now. You are going to solder or epoxy one of those clevis, aren't you?
Honest, I landed a buddy's big old 4Star the other week with one aileron connector hanging down. Both clevis were still solidly connected, but the threaded rod had rotated right into one clevis and out of the other.
08-22-2006 | 08:21 PM
#52
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From: Fenton,
MI
RE: flutter in aileron and flaps
yes, I actually had written in my original post that I planned on doing that. I'm just going to solder one end. I was waiting to see if I fixed the problem before a soldered.
08-22-2006 | 08:52 PM
#53
Senior Member
RE: flutter in aileron and flaps
A bit behind the discussion I am.
After you solder one of the clevises, put a jam nut on the other. How much slop is in the clevis pin to the respective horns?
After you solder one of the clevises, put a jam nut on the other. How much slop is in the clevis pin to the respective horns?
08-22-2006 | 09:58 PM
#54
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From: Fenton,
MI
RE: flutter in aileron and flaps
none that I noticed. Of course, not something I am used to judging since this fixed wing stuff is new to me. Since everything is brand new, I would assume everything is still tight.
08-23-2006 | 09:20 AM
#55
Senior Member
RE: flutter in aileron and flaps
Since everything is brand new, I would assume everything is still tight.
BTW, I was just kidding, pulling your chain, about the epoxy/solder. I knew you'd said you were going to do it. But couldn't resist pulling....
08-23-2006 | 09:25 AM
#56
Senior Member
RE: flutter in aileron and flaps
Oh heck, I forgot to mention what I meant to mention..... old age......
It's always a good idea to check the fit of a clevis on the threaded rod. If the fit is loose, it's not good. I bet half the ARFs I've messed with in the last year have threaded rod that fits the metal clevis loosely. When they've included the nylon clevis, those thread on tightly, but the metal usually doesn't.
It's always a good idea to check the fit of a clevis on the threaded rod. If the fit is loose, it's not good. I bet half the ARFs I've messed with in the last year have threaded rod that fits the metal clevis loosely. When they've included the nylon clevis, those thread on tightly, but the metal usually doesn't.
08-23-2006 | 09:55 AM
#57
Senior Member
RE: flutter in aileron and flaps
I've had to drill new holes in servo arms because the existing holes were too large. Most commonly these holes are a tad too small. I've also seen the post type of control surface horn come with a hole a tad large for US size clevises. I always use jam nuts on threaded stock and steel clevises.
09-27-2006 | 07:51 AM
#58
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From: Moscow, RUSSIA
RE: flutter in aileron and flaps
When speaking about aileron/flap flutter there is a lot of factors we have to take into account. Let me briefly summarize my own knowledge for European molded ships.
1. Linkage slop (linear). All holes should perfectly match clevises (0.01mm tolerance). Clevises should be glued to the rods. Linear servo shaft slop is nonexistent with BB servos.
2. Servo slop (angular). Some models like HS-(5)125 have significant angular play from the very beginning. Sooner or later it happens to every servo with metal gear. You cannot change that -- just take it or leave it.
3. Servo mount slop. In molded wings servos are attached to the skin. It does not matter how good the servo or the servo mount is glued to it -- skin plays a LOT! This fact is usually overlooked. The simplest way to reduce this play is to glue a thin (0.2mm) carbon/glass patch. The size is limited by your ability to extend it sideways through the servo opening. Anyway it should reach the wing spar. The ultimate solution is a large size servo base, which forms quite rigid structure when glued to the skin and wing spar (picture attached).
The worst thing is that we just reduce the play to some acceptable level, not totally eliminate it. Our final goal is to achieve the minimal control surface play with given sum of different slops. And now we start the most interesting part -- turn on our own common sense.
1. Linear travel. It is very easy. The bigger the radius, the bigger linear rod travel thus smaller linear slop effect. So both servo arm and horn should be as long as possible.
2. Angular travel. The rule of thumb is -- you should use the full range of angular servo arm movement. In this case you reduce negative angular slop effect.
3. Transfer ratio. The most tricky to understand. A lot of unjustified opinions. Just remember -- reduced transfer ratio makes control surface immune from the effects of both linear and angular slops.
So it is time to turn theory into several practical steps:
a. In molded sailplanes the limiting factor is a wing thickness. You should be happy if servo cover allows you to use hole #2 from the center.
b. Engage the full servo travel on your computer radio or servo tester. In case of digital Hitec servos I suggest to use Hitec HFP-10 servo programmer to set hardware endpoints to their respective maximums.
c. Take a full breath. Remind yourself that this moldie is a sailplane, not a 3D monster. You do not need big control surface movement, limit yourself to sophisticated adequacy. Speaking of ailerons, UP travel should be twice as DOWN travel. Speaking of flaps, 3-4 mm UP and 70-90 degrees DOWN.
d. Connecting pushrod. The common mistake is to connect "servo arm @ neutral (1'500us) to control surface @ level with profile trailing edge. Do not forget, in accordance with everything said we are going to use the full servo travel. So we are to find transfer ratio, when the servo endpoints correspond with control surface deflections as per previous step. If you are not good in trigonometry, make a kind of threaded horn and play with it. Or better yet, make a simple test bench from any piece of sheet material. Then print wing cross-section 1:1 scale and glue it to your test bench. Find rotation centers and bolt-on two servo arms. Find and mark servo arm and control horn endpoints according to wing cross-section. Connect them with temporary threaded pushrod/clevises at corresponding endpoints. Move to other side. See if control horn hole should be closer/further to the rotation center. Drill the new hole and check again. When the correct transfer ratio is found, measure the distance between rotation center and the hole. Do not forget that on the wing it should be a distance from a hinge, not a horn length.
e. Temporarily fix your horns to control surfaces and check, how good you were in trigonometry. If everything is OK, glue horns and clevises. Actually with some experience it was possible to skip step "d" but these beautiful moldies do not give you chance to UNDO if horn is glued out of place. I personally prefer to make very simple tool to hold the control horn with adequate and repeatable accuracy while epoxy cures.
f. Now we have control surfaces deflected at servo neutral. Ailerons are 1/2 UP, flaps are 35-40 degrees DOWN. Turn on your computer radio and use appropriate functions to set ailerons/flaps. In Futaba 9Z it can be done through conditions menu or better yet, through trim sets.
Rejoice. Your molded beauty will pay you back for your efforts.
Sincerely,
Alexander
Moscow, Russia
P.S. And the last but not the least. Landing with flaps fully deployed usually strips servo gear, but not in my case. When flaps are FULL DOWN, servo arm is coaxial with pushrod and no torque could be transferred to the output shaft.
1. Linkage slop (linear). All holes should perfectly match clevises (0.01mm tolerance). Clevises should be glued to the rods. Linear servo shaft slop is nonexistent with BB servos.
2. Servo slop (angular). Some models like HS-(5)125 have significant angular play from the very beginning. Sooner or later it happens to every servo with metal gear. You cannot change that -- just take it or leave it.
3. Servo mount slop. In molded wings servos are attached to the skin. It does not matter how good the servo or the servo mount is glued to it -- skin plays a LOT! This fact is usually overlooked. The simplest way to reduce this play is to glue a thin (0.2mm) carbon/glass patch. The size is limited by your ability to extend it sideways through the servo opening. Anyway it should reach the wing spar. The ultimate solution is a large size servo base, which forms quite rigid structure when glued to the skin and wing spar (picture attached).
The worst thing is that we just reduce the play to some acceptable level, not totally eliminate it. Our final goal is to achieve the minimal control surface play with given sum of different slops. And now we start the most interesting part -- turn on our own common sense.
1. Linear travel. It is very easy. The bigger the radius, the bigger linear rod travel thus smaller linear slop effect. So both servo arm and horn should be as long as possible.
2. Angular travel. The rule of thumb is -- you should use the full range of angular servo arm movement. In this case you reduce negative angular slop effect.
3. Transfer ratio. The most tricky to understand. A lot of unjustified opinions. Just remember -- reduced transfer ratio makes control surface immune from the effects of both linear and angular slops.
So it is time to turn theory into several practical steps:
a. In molded sailplanes the limiting factor is a wing thickness. You should be happy if servo cover allows you to use hole #2 from the center.
b. Engage the full servo travel on your computer radio or servo tester. In case of digital Hitec servos I suggest to use Hitec HFP-10 servo programmer to set hardware endpoints to their respective maximums.
c. Take a full breath. Remind yourself that this moldie is a sailplane, not a 3D monster. You do not need big control surface movement, limit yourself to sophisticated adequacy. Speaking of ailerons, UP travel should be twice as DOWN travel. Speaking of flaps, 3-4 mm UP and 70-90 degrees DOWN.
d. Connecting pushrod. The common mistake is to connect "servo arm @ neutral (1'500us) to control surface @ level with profile trailing edge. Do not forget, in accordance with everything said we are going to use the full servo travel. So we are to find transfer ratio, when the servo endpoints correspond with control surface deflections as per previous step. If you are not good in trigonometry, make a kind of threaded horn and play with it. Or better yet, make a simple test bench from any piece of sheet material. Then print wing cross-section 1:1 scale and glue it to your test bench. Find rotation centers and bolt-on two servo arms. Find and mark servo arm and control horn endpoints according to wing cross-section. Connect them with temporary threaded pushrod/clevises at corresponding endpoints. Move to other side. See if control horn hole should be closer/further to the rotation center. Drill the new hole and check again. When the correct transfer ratio is found, measure the distance between rotation center and the hole. Do not forget that on the wing it should be a distance from a hinge, not a horn length.
e. Temporarily fix your horns to control surfaces and check, how good you were in trigonometry. If everything is OK, glue horns and clevises. Actually with some experience it was possible to skip step "d" but these beautiful moldies do not give you chance to UNDO if horn is glued out of place. I personally prefer to make very simple tool to hold the control horn with adequate and repeatable accuracy while epoxy cures.
f. Now we have control surfaces deflected at servo neutral. Ailerons are 1/2 UP, flaps are 35-40 degrees DOWN. Turn on your computer radio and use appropriate functions to set ailerons/flaps. In Futaba 9Z it can be done through conditions menu or better yet, through trim sets.
Rejoice. Your molded beauty will pay you back for your efforts.
Sincerely,
Alexander
Moscow, Russia
P.S. And the last but not the least. Landing with flaps fully deployed usually strips servo gear, but not in my case. When flaps are FULL DOWN, servo arm is coaxial with pushrod and no torque could be transferred to the output shaft.
09-27-2006 | 06:01 PM
#59
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From: Tullahoma,
TN
RE: flutter in aileron and flaps
At last! A good post in this thread. I haven't read all of it but I have never seen so much bad information in one thread. This and Dr. Drela's post are the only ones I would pay any attention to.
The internet has been most instructive. I have learned things my aero professor never taught me, my instructors never showed me, I never experienced in 30 years as a pilot, and I never saw in 32 years as a wind tunnel test engineer. Very amazing indeed.
On the internet, everybody is an expert even if they didn't stay at Holiday Inn Express.
The internet has been most instructive. I have learned things my aero professor never taught me, my instructors never showed me, I never experienced in 30 years as a pilot, and I never saw in 32 years as a wind tunnel test engineer. Very amazing indeed.
On the internet, everybody is an expert even if they didn't stay at Holiday Inn Express.
ORIGINAL: AlexanderMikhailov
When speaking about aileron/flap flutter there is a lot of factors we have to take into account. Let me briefly summarize my own knowledge for European molded ships.
1. Linkage slop (linear). All holes should perfectly match clevises (0.01mm tolerance). Clevises should be glued to the rods. Linear servo shaft slop is nonexistent with BB servos.
2. Servo slop (angular). Some models like HS-(5)125 have significant angular play from the very beginning. Sooner or later it happens to every servo with metal gear. You cannot change that -- just take it or leave it.
3. Servo mount slop. In molded wings servos are attached to the skin. It does not matter how good the servo or the servo mount is glued to it -- skin plays a LOT! This fact is usually overlooked. The simplest way to reduce this play is to glue a thin (0.2mm) carbon/glass patch. The size is limited by your ability to extend it sideways through the servo opening. Anyway it should reach the wing spar. The ultimate solution is a large size servo base, which forms quite rigid structure when glued to the skin and wing spar (picture attached).
The worst thing is that we just reduce the play to some acceptable level, not totally eliminate it. Our final goal is to achieve the minimal control surface play with given sum of different slops. And now we start the most interesting part -- turn on our own common sense.
1. Linear travel. It is very easy. The bigger the radius, the bigger linear rod travel thus smaller linear slop effect. So both servo arm and horn should be as long as possible.
2. Angular travel. The rule of thumb is -- you should use the full range of angular servo arm movement. In this case you reduce negative angular slop effect.
3. Transfer ratio. The most tricky to understand. A lot of unjustified opinions. Just remember -- reduced transfer ratio makes control surface immune from the effects of both linear and angular slops.
So it is time to turn theory into several practical steps:
a. In molded sailplanes the limiting factor is a wing thickness. You should be happy if servo cover allows you to use hole #2 from the center.
b. Engage the full servo travel on your computer radio or servo tester. In case of digital Hitec servos I suggest to use Hitec HFP-10 servo programmer to set hardware endpoints to their respective maximums.
c. Take a full breath. Remind yourself that this moldie is a sailplane, not a 3D monster. You do not need big control surface movement, limit yourself to sophisticated adequacy. Speaking of ailerons, UP travel should be twice as DOWN travel. Speaking of flaps, 3-4 mm UP and 70-90 degrees DOWN.
d. Connecting pushrod. The common mistake is to connect "servo arm @ neutral (1'500us) to control surface @ level with profile trailing edge. Do not forget, in accordance with everything said we are going to use the full servo travel. So we are to find transfer ratio, when the servo endpoints correspond with control surface deflections as per previous step. If you are not good in trigonometry, make a kind of threaded horn and play with it. Or better yet, make a simple test bench from any piece of sheet material. Then print wing cross-section 1:1 scale and glue it to your test bench. Find rotation centers and bolt-on two servo arms. Find and mark servo arm and control horn endpoints according to wing cross-section. Connect them with temporary threaded pushrod/clevises at corresponding endpoints. Move to other side. See if control horn hole should be closer/further to the rotation center. Drill the new hole and check again. When the correct transfer ratio is found, measure the distance between rotation center and the hole. Do not forget that on the wing it should be a distance from a hinge, not a horn length.
e. Temporarily fix your horns to control surfaces and check, how good you were in trigonometry. If everything is OK, glue horns and clevises. Actually with some experience it was possible to skip step "d" but these beautiful moldies do not give you chance to UNDO if horn is glued out of place. I personally prefer to make very simple tool to hold the control horn with adequate and repeatable accuracy while epoxy cures.
f. Now we have control surfaces deflected at servo neutral. Ailerons are 1/2 UP, flaps are 35-40 degrees DOWN. Turn on your computer radio and use appropriate functions to set ailerons/flaps. In Futaba 9Z it can be done through conditions menu or better yet, through trim sets.
Rejoice. Your molded beauty will pay you back for your efforts.
Sincerely,
Alexander
Moscow, Russia
P.S. And the last but not the least. Landing with flaps fully deployed usually strips servo gear, but not in my case. When flaps are FULL DOWN, servo arm is coaxial with pushrod and no torque could be transferred to the output shaft.
When speaking about aileron/flap flutter there is a lot of factors we have to take into account. Let me briefly summarize my own knowledge for European molded ships.
1. Linkage slop (linear). All holes should perfectly match clevises (0.01mm tolerance). Clevises should be glued to the rods. Linear servo shaft slop is nonexistent with BB servos.
2. Servo slop (angular). Some models like HS-(5)125 have significant angular play from the very beginning. Sooner or later it happens to every servo with metal gear. You cannot change that -- just take it or leave it.
3. Servo mount slop. In molded wings servos are attached to the skin. It does not matter how good the servo or the servo mount is glued to it -- skin plays a LOT! This fact is usually overlooked. The simplest way to reduce this play is to glue a thin (0.2mm) carbon/glass patch. The size is limited by your ability to extend it sideways through the servo opening. Anyway it should reach the wing spar. The ultimate solution is a large size servo base, which forms quite rigid structure when glued to the skin and wing spar (picture attached).
The worst thing is that we just reduce the play to some acceptable level, not totally eliminate it. Our final goal is to achieve the minimal control surface play with given sum of different slops. And now we start the most interesting part -- turn on our own common sense.
1. Linear travel. It is very easy. The bigger the radius, the bigger linear rod travel thus smaller linear slop effect. So both servo arm and horn should be as long as possible.
2. Angular travel. The rule of thumb is -- you should use the full range of angular servo arm movement. In this case you reduce negative angular slop effect.
3. Transfer ratio. The most tricky to understand. A lot of unjustified opinions. Just remember -- reduced transfer ratio makes control surface immune from the effects of both linear and angular slops.
So it is time to turn theory into several practical steps:
a. In molded sailplanes the limiting factor is a wing thickness. You should be happy if servo cover allows you to use hole #2 from the center.
b. Engage the full servo travel on your computer radio or servo tester. In case of digital Hitec servos I suggest to use Hitec HFP-10 servo programmer to set hardware endpoints to their respective maximums.
c. Take a full breath. Remind yourself that this moldie is a sailplane, not a 3D monster. You do not need big control surface movement, limit yourself to sophisticated adequacy. Speaking of ailerons, UP travel should be twice as DOWN travel. Speaking of flaps, 3-4 mm UP and 70-90 degrees DOWN.
d. Connecting pushrod. The common mistake is to connect "servo arm @ neutral (1'500us) to control surface @ level with profile trailing edge. Do not forget, in accordance with everything said we are going to use the full servo travel. So we are to find transfer ratio, when the servo endpoints correspond with control surface deflections as per previous step. If you are not good in trigonometry, make a kind of threaded horn and play with it. Or better yet, make a simple test bench from any piece of sheet material. Then print wing cross-section 1:1 scale and glue it to your test bench. Find rotation centers and bolt-on two servo arms. Find and mark servo arm and control horn endpoints according to wing cross-section. Connect them with temporary threaded pushrod/clevises at corresponding endpoints. Move to other side. See if control horn hole should be closer/further to the rotation center. Drill the new hole and check again. When the correct transfer ratio is found, measure the distance between rotation center and the hole. Do not forget that on the wing it should be a distance from a hinge, not a horn length.
e. Temporarily fix your horns to control surfaces and check, how good you were in trigonometry. If everything is OK, glue horns and clevises. Actually with some experience it was possible to skip step "d" but these beautiful moldies do not give you chance to UNDO if horn is glued out of place. I personally prefer to make very simple tool to hold the control horn with adequate and repeatable accuracy while epoxy cures.
f. Now we have control surfaces deflected at servo neutral. Ailerons are 1/2 UP, flaps are 35-40 degrees DOWN. Turn on your computer radio and use appropriate functions to set ailerons/flaps. In Futaba 9Z it can be done through conditions menu or better yet, through trim sets.
Rejoice. Your molded beauty will pay you back for your efforts.
Sincerely,
Alexander
Moscow, Russia
P.S. And the last but not the least. Landing with flaps fully deployed usually strips servo gear, but not in my case. When flaps are FULL DOWN, servo arm is coaxial with pushrod and no torque could be transferred to the output shaft.
09-28-2006 | 07:43 AM
#60
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From: Moscow, RUSSIA
RE: flutter in aileron and flaps
ORIGINAL: ChuckA
At last! A good post in this thread. I haven't read all of it but I have never seen so much bad information in one thread. This and Dr. Drela's post are the only ones I would pay any attention to.
At last! A good post in this thread. I haven't read all of it but I have never seen so much bad information in one thread. This and Dr. Drela's post are the only ones I would pay any attention to.
While working on the previous post I had to get deeper into servo resolution. The result was discouraging.
Hitec HS-5125 digital servo. Datasheet states 1us dead-band width. Very nice number as it gives user 1400 steps and even exceeds the possibilities of 1024PCM. Actually only Futaba 2048PCM could fully exploit 1us resolution advertised for HS-5125.
I personally like these servos and use them a lot. However my feeling was that HS-5125 actual dead-band was wider than 1us. Being curiuos I decided to test real servo resolution.
Test bed.
Hitec HS-5125 v.1.04 digital servo
Hitec HFP-10 servo tester/ digital servo programmer
Results.
1. DB width test. Servo comes to user with factory default dead-band setting DB=2 (=6us). When I asked MikeMayberry from Hitec about my finding he explained it was a "typo" in manual and DB=2/DB=1 just mean the lowest possible settings, not 6us/3us.
2. Servo resolution test. It shows again 6us for factory default servo. User can improve resolution to 3us if he buys Hitec servo programmer and changes dead-band setting to DB=1. Even then 3us is far from advertised 1us. When I contacted MikeMayberry again and informed him about my second test results, the answer was:
My thoughts are that the servos are 1-2us out of the box and when reset with the programmer.
This is the first time this has been questioned so if the servos were only capable of a minimum of 6us then their performacne would be nowhere near as good as they are. I would suggest you search here and rcuniverse for your answer since you don't beleive what I say.
Mike.
So according to his instructions I ask gurus to point what was wrong with my tests and my interpretation. Better yet if somebody with proper test equipment could repeat these tests and publish their data.
To publish your comments/data and read the full story please follow the link: http://www.rcgroups.com/forums/showthread.php?t=575183
