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What RPM to Dynamically Balance Prop ?

P

petersb

Well Known Member
I have an RV7A with an O-360 and new Hartzell C/S prop.

I dynamically balanced it to .06 IPS at 2300 rpm.

I still feel vibration through my heals and small of back, have 3/4 inch sound proof rubber mat on floor.

I have checked that the exhaust is mounted firm and no parts of engine are touching cowl.

My main concern is vibration at higher rpm, from 2200 to 2550 the vibration frequency and level changes as expected, however, from 2550 to 2700 there is quite a change in the type, level of vibration. I dont like using full rpm for takeoff and climb.

Should I dynamically balance at a higher rpm, say 2500, instead of the 2300 cruise rpm I used.

Currently from 2200 to 2400 it gives .06 IPS and at 2100 .09 IPS

Thoughts please

Peter
 
Make sure the timing is set right, plugs are cleaned and gapped, wires and in good shape.
 
The answer is, balance it at whatever rpm you will cruise at most often.
.06 is good but I have seen zero at 2400, once.
You seem to be chasing a vibration you feel rather than what the engine/ prop feel. These are different animals. The team balanced our new advanced composite props after installation and we immediately noticed smoothness in both engine and body feel.

The feet vibration you have is likely exhaust pulses.
 
tadsargent said:
The answer is, balance it at whatever rpm you will cruise at most often.
.06 is good but I have seen zero at 2400, once.
You seem to be chasing a vibration you feel rather than what the engine/ prop feel. These are different animals. The team balanced our new advanced composite props after installation and we immediately noticed smoothness in both engine and body feel.

The feet vibration you have is likely exhaust pulses.
Click to expand...

Tad

I am currently flying without wheel fairings or pants. Wonder if they could be vibrating at the higher rpm

Peter
 
petersb said:
Currently from 2200 to 2400 it gives .06 IPS and at 2100 .09 IPS

Thoughts please

Peter
Click to expand...

Sounds to my like you have some other issue going on, the dynamic balance would likely change very little from 2400-2700 (in fact quite often it will improve).
 
Walt said:
Sounds to my like you have some other issue going on, the dynamic balance would likely change very little from 2400-2700 (in fact quite often it will improve).
Click to expand...

Walt

Any suggestions as to what?

The engine has 250 hours since overhaul, EGT's are running around 1400 with only 30 degree low to high, cylinder heads are also very similar around 340 degrees with 30 degrees low to high.

Prop tracks within 1/16

Peter
 
Walt said:
Sounds to my like you have some other issue going on, the dynamic balance would likely change very little from 2400-2700 (in fact quite often it will improve).
Click to expand...

Not to hijack the thread Walt but I'm thinking about a prop balance and I am wondering what rpm to tell the balancer I want it set for. I usually cruise 2450-2700ish but static ground run only produces around 2200rpm, of course.

Maybe this info will also help the OP.
 
Last edited:
petersb said:
Walt

Any suggestions as to what?

The engine has 250 hours since overhaul, EGT's are running around 1400 with only 30 degree low to high, cylinder heads are also very similar around 340 degrees with 30 degrees low to high.

Prop tracks within 1/16

Peter
Click to expand...

I would suggest getting the fairings and wheel pants installed, the prop pulse can excite airframe vibrations which can be hard to track down.

GLPalinkas said:
Not to hijack the thread Walt but I'm thinking about a prop balance and I am wondering what rpm to tell the balancer I want it set for. I usually cruise 2450-2700ish but static ground run only produces around 2200rpm, of course.

Maybe this info will also help the OP.
Click to expand...

I do fixed pitch prop at max static which is generally around 21-2200. If you get it balanced there it will be fine.
 
Vibration

Have vibration on the floor also. I think Post 3 is right. Everyone here thinks it is exhaust pulses.
 
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