Throttle quadrant vibrations

clutch22 · #1 01-25-2018, 09:40 AM

Is anyone else's throttle quadrant a magnet for engine vibrations? I feel like my engine is pretty smooth, and I had it dynamically balanced to, I believe .03 IPS.

Basically, my quadrant vibrates so much in flight that I can hear it, and it's annoying. I end up leaning my knee on it to dampen it out, but that becomes uncomfortable after a while.

I've been considering doing another dynamic balance. It was balanced prior to first flight, so maybe enough prop grease has moved around to cause a greater imbalance.

Thought I'd ask to see if others have this issue, and if there is some trick to isolating it. I thought about putting baffle seal between the quadrant and the panel, but figured the vibrations would still transfer through the attach screws.

Zuldarin · #2 01-25-2018, 10:27 AM

Keep in mind that a significant amount of the vibrations we feel in the cockpit actually come from exhaust pulses on the floor of the cabin. Since your throttle quadrant is attached to the tunnel (I assume) which is attached to the floor you may be feeling those pulses.

clutch22 · #3 01-25-2018, 11:51 AM

Mine is attached to the panel per the plans.

David Paule · #4 01-25-2018, 12:51 PM

You could add weight to the knobs... that would tend to reduce the frequency of the vibration and might get it out of the range of interest. It would probably take a significant increase in the knob weight, though, since it takes the square root of any ratio of new/old weight to change it. Double the weight, cut the frequency to about 71%, if you get the weight in the right place; we don't know the right place, though. The part that's moving the most is the right place.

You could run the engine at a different rpm so that the vibration doesn't get excited.

Are you missing a stiffener in the structure between the quadrant and the engine? It would probably be relatively closer to the quadrant than the engine, and would tend to prevent something from diaphragming or bending. Same square root effect in that doubling the stiffness increases the natural frequency by about 41%. This is the second thing I'd look for.

Is the quadrant a non-standard one? Or mounted differently than most of them? That might cause this, but I'd think it's unlikely.

Check the direction that the exhaust faces. Darin's comment is a very good one. Do they point directly aft, or are they also pointed down? This is the first thing to check.

If you do decide to rebalance the prop/engine, have the mechanic put an accelerometer on the quadrant so he can see what the corresponding engine rpm is to the vibration.

If you have an Apple device like an iPhone, the AKlite app can show you the sound as a function of frequency. Get the quadrant so that it's humming and let the phone listen to the hum. The peak of the graph shows the loudest resonant frequency. Won't fix it but at least you'll know the vibration frequency which should relate to an rpm.

Whatever you do, please let us know what you did and how it worked out.

Dave

Bill.Peyton · #5 01-26-2018, 07:12 AM

You might want to read some of the threads on prop re-clocking. That's what I ended up doing.

Carl Froehlich · #6 01-26-2018, 07:22 AM

When I built the RV-10 I was not impressed with the per plans engine control bracket. It as just suppended on the bottom of the panel.

I added a piece of 0.063 aluminum 3/4?x3/4? angle running forward from that point on the panel to the firewall frame. It really stiffened it up.

Carl

clutch22 · #7 01-26-2018, 10:21 AM

Thanks for the info guys. I have some ideas brewin' now. First, I think I'll go with the stiffener angle method and see if that takes care of it. I think it will.

rleffler · #8 01-26-2018, 10:28 AM

Quote:

Originally Posted by clutch22

Is anyone else's throttle quadrant a magnet for engine vibrations? Thought I'd ask to see if others have this issue, and if there is some trick to isolating it. I thought about putting baffle seal between the quadrant and the panel, but figured the vibrations would still transfer through the attach screws.

I have mine installed in an Aerosport Products panel, which is installed differently than the plans. I have never experienced any vibrations.

clutch22 · #9 01-26-2018, 11:15 AM

Quote:

Originally Posted by rleffler

I have mine installed in an Aerosport Products panel, which is installed differently than the plans. I have never experienced any vibrations.

Yeah, the Aerosport way would get rid of vibration. The problem with the plans way of installing, is that it just hangs down from the structure, so it makes it easy for any vibrations to show up in it.