Dynamic Propeller Balancing

[Matelot B'stard]

Can anyone recommend someone who will do this on site at a reasonable price? How much, roughly could I expect to pay?

[IO540]

In the UK, this is a rarely done thing (except on turboprops) so very few firms offer it at all.

Arrow Aviation in Exeter do it but you have to fly there. It takes most of a day, about 200 quid.

Well worth doing, especially if you have a 3-blade prop. The reduction in aircraft vibration (with probable improvements in avionics life) can be very significant.

However a small % of engines (esp Lycoming) are so badly balanced that one cannot do a great deal with prop balancing; I've seen this happen.

There is some debate about whether it should be done in flight. Propeller-related vibration is related to prop pitch, and you cannot reach cruise prop settings on the ground, at the cruise power settings.

A lot of people in the USA go for this; it is almost always needed on the 3-blade props which are very popular over there.

[Flytest]

Dynamic Prop balancing is available to ALL prop driven aircraft, Microlites, etc. Don't let anyone tell you different, a well balanced prop makes a world of difference, in terms of airspeed for a given power setting, reduced component wear (cracked manifolds, panels and cowlings, not to mention heavy engine wear)

A small % of lycomings cannot be balanced, but this depends on whether the aircraft has suffered a tip strike at any time and then had the same crankshaft re-fitted. The fact that said crank passes bench concentricity checks, or output flange trueness checks is irrelevant.

If you want to know more about it, and who will do it contact Andrew Brinkley, Brinkley Aircraft Services, Meppershall Airfield, Cambs, he has a very good guy who does his planes. Alternatively pm me, I have a contact.

[IO540]

Flytest

A small % of lycomings cannot be balanced, but this depends on whether the aircraft has suffered a tip strike at any time and then had the same crankshaft re-fitted. The fact that said crank passes bench concentricity checks, or output flange trueness checks is irrelevant.

According to several engine shops I have discussed this with, the reason a few % of Lycos can't be balanced properly is because Lyco have rather wide margins when it comes to matching up their pistons, rods, etc, and also they don't dynamically balance the cranks well enough.

Would a crank bent enough to noticeably vibrate still pass the post-prop-strike NDT and the concentricity test?

[Flytest]

IO540

Yes it would, the crank looks serviceable to all intents and purposes, however when the crank itself is spun on a test bed, it bends at certain rpm's notably within the normal operating ranges. its a strange effect, but one which I have actually seen proven by a guy who does prop balancing and RTB work freelance. He did the tests on several shafts in conjunction with a crank balancing specialist from Bicester, it was scary to watch.

Your other point about "agricultural" tolerances is correct, these engines do generate vibration from idler gears, pistons etc, however the frequencies and amplitudes are usually undetectable by the pilot. As I said, the guy I knew does a full vibration survey of the engine, and he can pinpoint any real defects. One thing I do know is that the tolerances you refer to, do not prohibit prop balancing. As I said, having seen this one particular guy in action, I recommend him to anyone.