Trim tabs

[wolfy]

Given the stalled region on a gyro rotor is different to a chopper in flight, could inboard trim tabs be used on a gyro to help reduce a climbing blade with increasing airspeed?

wolfy

 

[Doug Riley]

Wolfy, could you explain what you mean in more detail?

 

[hillberg]

Given the stalled region on a gyro rotor is different to a chopper in flight, could inboard trim tabs be used on a gyro to help reduce a climbing blade with increasing airspeed?

wolfy

Bell helicopter added 'inboard' trim tabs and they did little to smooth the rotor system - the Hughes 500 on the other hand had nearly full span tabs
and you could smooth it very well, the S-58 had no tabs but we bent the trailing edge of a blade pocket for the effect.

With the Bell 205 rotor system the factory issued a template to reform the trailing edge along the whole blade and it did great for smoothing and performance

 

[wolfy]

My chopper had a blade that would climb with increased airspeed, above 70kn the tracking would get quite rough.
I made and installed trim tabs about 6" wide (span wise) at about 70% span. They worked very well to control indavidual blades, I was able to keep the vertical IPS below .2 throughout the entire speed range.
I am trying to help a mate balance his gyro and one of his problems is his tracking vibrations increasing with airspeed.
So I was wondering if tabs could be used, or is it just the nature of the beast with gyro rotors?

wolfy

 

[skyguynca]

I don't think so. I rarely have experience vibe changes with airspeed. Then again I have always either had or installed trim tabs to track my blades.
I did have one set of Brock Blades that I purchased new that would never fly together no matter what. I talked to Ken about it and he replaced them no problem.

 

[wolfy]

I don't think so. I rarely have experience vibe changes with airspeed. Then again I have always either had or installed trim tabs to track my blades.
I did have one set of Brock Blades that I purchased new that would never fly together no matter what. I talked to Ken about it and he replaced them no problem.

So are you saying you made and installed trim tabs onto gyro rotors skyguynca?
Sounds interesting.

wolfy

 

[XXavier]

So are you saying you made and installed trim tabs onto gyro rotors skyguynca?
Sounds interesting.

wolfy

So, and if I understand it correctly, you can change the effective AoA of one blade by adding a trim tab, thus correcting the tracking...
A simple way of adding that trim tab could be by placing a Gurney flap of the right length at the right place along the trailing edge...

 

[wolfy]

Yes Xxavier that is exactly what it is a gurney flap, they are only about 6" wide and extend the trailing edge by about an inch.
On a helicopter application, where it is located on the span dictates the speed range you are trying to correct.
For example out near the tips (80-90% span) has effect for hover tracking, around 70% might be about cruise speed 60% high speed.
This is where it could become more complex for a gyro with more of the retreating rotor stalled.

wolfy

 

[skyguynca]

So are you saying you made and installed trim tabs onto gyro rotors skyguynca?
Sounds interesting.

wolfy

Yes I have. Just a 1.5 wide tab, 6 inches long, riveted to the trailing edge with 4 rivets. You have to support the trailing edge when bending them as not to induce cracks. I had to do it with a set of wooden blades I made and a set of extruded blades I got from Vortec. The wooden blades were made from Monte' s plans.

 

[Doug Riley]

Many older gyro blade designs, including Bensen's wood blades, had trim tabs extending back from the trailing edge. Bensen's tabs were located around 70% of span.

Some gyro blades do vibrate more at higher airspeeds. The McCutchens on my Air Command did that. I have not noticed this effect with Dragon Wings.

As the gyro flies faster, the difference in airspeed between the advancing blade and the retreating blade becomes greater. This, in turn, means that there is a wider angle of oscillating motion around the teeter hinge. Any friction in that hinge will lead to 2/rev vibrations, but not out-of-track.

If the blades fly out of track, it necessarily means that the two blades are different from each other in some way. If the out-of-track appears (or worsens) at high airspeeds, then perhaps one blade reacts differently to higher or lower airspeeds. One blade may be more limber torsionally than the other, or may be balanced at a different point chordwise, or may have a slightly different airfoil section. Any of these differences can throw the blades out of track at higher airspeeds. I'd look for these differences first.

If you're certain that the problem is tracking, then, yes, trim tabs may help. They work by twisting the blade slightly chordwise; down-tab pushes the leading edge of the blade down, while up-tab pushes the leading edge up (i.e. trim tabs work the opposite way from ailerons). The twisting effect is greater at higher blade airspeeds, less at lower blade airspeeds. As a result, the tabs will produce a cyclic pitch change (via periodic twist) as the blade passes from advancing to retreating --a cyclic change that will increase in magnitude as the gyro's airspeed increases.

 

[hillberg]

Many older gyro blade designs, including Bensen's wood blades, had trim tabs extending back from the trailing edge. Bensen's tabs were located around 70% of span.

Some gyro blades do vibrate more at higher airspeeds. The McCutchens on my Air Command did that. I have not noticed this effect with Dragon Wings.

As the gyro flies faster, the difference in airspeed between the advancing blade and the retreating blade becomes greater. This, in turn, means that there is a wider angle of oscillating motion around the teeter hinge. Any friction in that hinge will lead to 2/rev vibrations, but not out-of-track.

If the blades fly out of track, it necessarily means that the two blades are different from each other in some way. If the out-of-track appears (or worsens) at high airspeeds, then perhaps one blade reacts differently to higher or lower airspeeds. One blade may be more limber torsionally than the other, or may be balanced at a different point chordwise, or may have a slightly different airfoil section. Any of these differences can throw the blades out of track at higher airspeeds. I'd look for these differences first.

If you're certain that the problem is tracking, then, yes, trim tabs may help. They work by twisting the blade slightly chordwise; down-tab pushes the leading edge of the blade down, while up-tab pushes the leading edge up (i.e. trim tabs work the opposite way from ailerons). The twisting effect is greater at higher blade airspeeds, less at lower blade airspeeds. As a result, the tabs will produce a cyclic pitch change (via periodic twist) as the blade passes from advancing to retreating --a cyclic change that will increase in magnitude as the gyro's airspeed increases.

Blade pitch at hover - tabs for flight (helicopter) For gyros tabs good always because of what you do...

 

[skyguynca]

I use trim tabs to adjust tracking for smoothest for the speed range I operate in the most. Usually cruise speed being the upper limit.

 

[wolfy]

Yes I have. Just a 1.5 wide tab, 6 inches long, riveted to the trailing edge with 4 rivets. You have to support the trailing edge when bending them as not to induce cracks. I had to do it with a set of wooden blades I made and a set of extruded blades I got from Vortec. The wooden blades were made from Monte' s plans.

Very interesting thanks mate, I will definitely be thinking about trim tabs on any future gyros I am balancing then.

wolfy

 

[wolfy]

Many older gyro blade designs, including Bensen's wood blades, had trim tabs extending back from the trailing edge. Bensen's tabs were located around 70% of span.

Some gyro blades do vibrate more at higher airspeeds. The McCutchens on my Air Command did that. I have not noticed this effect with Dragon Wings.

As the gyro flies faster, the difference in airspeed between the advancing blade and the retreating blade becomes greater. This, in turn, means that there is a wider angle of oscillating motion around the teeter hinge. Any friction in that hinge will lead to 2/rev vibrations, but not out-of-track.

If the blades fly out of track, it necessarily means that the two blades are different from each other in some way. If the out-of-track appears (or worsens) at high airspeeds, then perhaps one blade reacts differently to higher or lower airspeeds. One blade may be more limber torsionally than the other, or may be balanced at a different point chordwise, or may have a slightly different airfoil section. Any of these differences can throw the blades out of track at higher airspeeds. I'd look for these differences first.

If you're certain that the problem is tracking, then, yes, trim tabs may help. They work by twisting the blade slightly chordwise; down-tab pushes the leading edge of the blade down, while up-tab pushes the leading edge up (i.e. trim tabs work the opposite way from ailerons). The twisting effect is greater at higher blade airspeeds, less at lower blade airspeeds. As a result, the tabs will produce a cyclic pitch change (via periodic twist) as the blade passes from advancing to retreating --a cyclic change that will increase in magnitude as the gyro's airspeed increases.

Thanks Doug, as you say there are a few reasons that can cause a climbing blade.
But as no gyro's have provision for internally adjusting individual blade chord balance (unlike large certified choppers) we are limited to trim tabs. Well I guess we could use external chord weights.

wolfy

 

[wolfy]

Blade pitch at hover - tabs for flight (helicopter) For gyros tabs good always because of what you do...

Yes right you are Don, I could have worded it better.
I meant to say I believe tabs can be used at hover to reduce cyclic feedback, no for actual tracking.

Why do say tabs are always good for gyro's because of what they do?

I know how good tabs are from what I found with using them on my chopper, but they are a whole nother can of worms making the balancing process more complicated.

wolfy

 

[skyguynca]

Yes right you are Don, I could have worded it better.
I meant to say I believe tabs can be used at hover to reduce cyclic feedback, no for actual tracking.

Why do say tabs are always good for gyro's because of what they do?

I know how good tabs are from what I found with using them on my chopper, but they are a whole nother can of worms making the balancing process more complicated.

wolfy

They never hover, not really. Always flying forward.

 

[Mike G]

Jim
I would suggest that once you've tracked and balanced your rotor you simply capture 1/rev vibration across your speed range. If the difference is significant then tabs would probably be useful.
Don't forget that if you've done a reasonable job with your RTB you should have your 1/rev at the mast below 0.2 IPS (ideally <0.1) but you are also experiencing between 2.5 to 5.0 IPS at 2/rev in a typical Eurotub so to be significant it has to be quite a lot of difference across the speed range.
Mike G

 

[hillberg]

Yes right you are Don, I could have worded it better.
I meant to say I believe tabs can be used at hover to reduce cyclic feedback, no for actual tracking.

Why do say tabs are always good for gyro's because of what they do?

I know how good tabs are from what I found with using them on my chopper, but they are a whole nother can of worms making the balancing process more complicated.

wolfy

You can smooth the rotor system to how 'you' fly, gross weights and airspeeds. Pitching and weights for balance tabs for flight smoothing

Not on the same route

Once had a Sheriffs pilot used to the usual "hop" when we installed the Simplex fire water tank on the 205s belly -
I modified the tank and removed the annoying bounce. What a surprised look I got from ole James . "What you do?"

 

[wolfy]

They never hover, not really. Always flying forward.

I was talking about helicopters there, sorry.

wolfy

 

[skyguynca]

I was talking about helicopters there, sorry.

wolfy

Oh, thought gyrocopter, sorry