Instrument panel vibration isolation

[Zzz]

Many Cessnas have a rubber bushing-mounted subpanel whose purpose is to isolate instruments from vibration. To the best of my knowledge, Super Cubs, Huskies, and the Bearhawk use no design of this type. Instruments are directly mounted to the panel, which is a firmly fastened to the fuselage and boot cowl.

Is it a concern? Especially in this age of solid state instruments?

[Battson]

I would think it would be hard to replicate that kind of design in a Bearhawk...? Seeing as the panel is structurally supporting the top part of the boot cowl.

So hopefully it's not a concern.. maybe more of an issue with delicately calibrated gauge instruments.

Certainly I haven't noticed a great deal of vibration in my panel, no more than the rest of the aircraft, and it's yet to cause any problems.

I did get my prop professionally balanced as soon as possible after testing.

[Zzz]

I agree, I think the better endeavor is to chase smoothness via prop balancing and a well-built engine.

A suspended panel would not be difficult to fabricate, they are just attached using rubber bushings and screwed to the structural panel. I'm just wondering if it's necessary. I suspect most here would answer no because they've been fine for ____ hours without problem.

[jaredyates]

I think you are right Zane, instrument vibration isolation does not seem to be anything to be concerned about for what we are doing.. There is a bit of instrument panel lore about the early bizjets being so smooth that they had to install vibrators on the panel, because the mechanical instruments were needing a small amount of vibration to work correctly. That may just be urban legend though.

[Bcone1381]

The Boeing 727 had a tapper on the standby altimeter that was going ALL the time. It hit about 3x per second. One day a mechanic pulled the CB and that white noise went away...it was like a fresh wind to experience the silence.

[Enewton57]

I thought I would share my experience with instrument panel vibration on my Bearhawk. I kept getting a fairly significant vibration in my panel only at full throttle during takeoff and climb out. The vibration went away after I leveled off and throttled back to cruise settings.

Prop balancing didn't help. The engine was running great, I couldn't figure it out. I finally discovered that when I installed the engine baffles I didn't trim them enough to provide adequate clearance from the aluminum angle pieces at the cowling hinge area at the top. You have to make sure you have a minimum of 1/2" clearance everywhere. Those angle prices were about 1/4" from the engine baffle that runs along the aft, top of the engine. With full throttle, torque caused the engine to rotate just enough to make contact with the angle pieces. The angle pieces run from the nose bowl to the firewall. The firewall is attached to the boot cowl and the instrument panel is connected to the boot cowl.

Once I cut the baffle back a little, the vibration went away completely.


Eric Newton
Bearhawk Tailwheels LLC

Http://bhtailwheels.com

Bearhawk Builder Manuals

Http://mybearhawk.com

[bestbearhawk1231]

Back when I worked avionics, I had the opportunity to spend six months on the instrument bench overhauling instruments. While the certifications and tests were being done, we were taught to roll the handle of a screwdriver across the case (just the weight of the screwdriver) once movement stopped when the test equipment reached its test point to verify that the reading was accurate. The needles and pivots all ride on jewels that get sticky as they get dirty. The fresh overhauls I don't remember having one that stuck on final check out, but you could tell which ones had gone several decades since the last overhaul and who smoked in the cockpit...those were horrendous on the initial incoming test. We would have to roll the screwdriver non stop to keep the needle moving. During the OH, the jewels and pivots are polished with a diamond dust paste and cleaned off with alcohol.

If you are running gyro instruments, those are sensitive to vibration and shock but the other instruments are not as vibration sensitive and actually run a bit better if there is a bit of vibration.

[fly_n_low]

Vibration helps to overcome static friction. Many missile systems I used to work on had dither motors. They basically vibrate the control surfaces to keep them constantly moving to minimize friction and required torque in flight.