Microlighters

I have had 4 or 5 situations on take-off runs (between 4500 and 5300 rpm) when it felt as if the propellor cavitates (as with motor boats). It is almost the same feeling as when a car's clutch slips. Refs pick up faster than normal, let go of throttle and prop "bites" in again. Always happened with pax and not when solo.
IVO prop is set fairly fine rather than coarse. Any suggestions or similar cases?
Is cavitation, other than in liquied form, possible ?

P.S. It is a 503 with E - gearbox. Runway altitude, if relevant, is 3500 ASL.

HI Koot

Im no expert but can confirm something like this. Testing with a 68' and a 72' prop on the same ratio, (yes Duck I know what you said but shut up now..... ) I had to go very fine with the 72' to get RPM. The plane felt VERY positive on the runway and accelerated fast. Taking off was fine until I got close to 50mph. she would continuously surge. I'm not quite sure how to describe this feeling but there was enough power to sustain flight at that speed but it felt like the plane would cavitate. Just as you said. Lucky it was a loooong runway But yes if it isnt called cavite it sure as hell fgeels that way.....

Koot

Prop balanced? 3 Blades? Has 1 blade not changed pitch? All blades same length & pitch?

Give Pieter de Necker a call... he has a wealth of experience and information that could prove worthy of your cause....

Kloot
I had the same experience on my previous trike. ALso IVO prop, but a six blader on 582.
The problem was ( and i am not mechanical) as follows. The shaft that goes form the prop into the gearbox is tapered somewehere. It must be tightened at a certain "talk" otherwise it slips. The engine picks up refs and the prop does not turn as it should. Normally when you take off with pax or give a LOT of power. It start happening only now and then , but believe me it becomes worse. I also thought it was cavitation at first, but it was that shaft slipping in the end. Indeed a VERY serious problem. In the end it happened to me in mid air and i JUST made it back to the field on very low refs. That problem will become worse and worse, but is very easy to fix.

Aerosan wrote:HI Koot

Im no expert but can confirm something like this. Testing with a 68' and a 72' prop on the same ratio, (yes Duck I know what you said but shut up now..... ) I had to go very fine with the 72' to get RPM. The plane felt VERY positive on the runway and accelerated fast. Taking off was fine until I got close to 50mph. she would continuously surge. I'm not quite sure how to describe this feeling but there was enough power to sustain flight at that speed but it felt like the plane would cavitate. Just as you said. Lucky it was a loooong runway But yes if it isnt called cavite it sure as hell fgeels that way.....

Good heavens Sanna!
That's a moeroffa big aerrie
A 72 feet prop.......... Bliksem!

Hi Duck.... Help the man!

72"

Feet - '
Inch - "

Duck gaan gedonner word ja ja toe mou all I can say is " to shift or not to shift- that is the soulution"

Soul-lution?

Aerosan, I am sure there were some typo errors in the 72' thing!

Bachus, your description is spot on and confirms what I am experiencing. You say it gets worse but also say it is easy to fix. Please PM me on who or what is needed to get it fixed, or how you had it fixed.
It happened again today, but this time whilst doing a full a full-power engine run-up on threshold. It almost felt as if a rev-limitter wasn't doing its job. Ran for a split-second into red and then came back to 6 400rpm.

As for the rest of the comments, Duck, San and .. Nav. Pleasure was never meant to be measured in inches or feet ! So please, stop fiddling over size ! Leave that for the eye of the beholder !

Kloot...........you have a PM

Kloot....you have PM.

I have only just picked up on this topic now, and yes, pleeeze have that nut torqued. You will soon lose almost all your prop RPM while the engine RPM runs away.

It has happened twice during my time at La Mercy. Just one of those things...........

The torque is high, something like 350 Nm, so you need to take it in to an engineering shop to do it......

Have you sorted it out yet?

Regards.

Had the same probleme.Split the gearbox.Need a puller to take the big gear of the taper shaft.Use locktite648 on the shaft and torque to 250Nm.Get a new packing from Aviation engines.

And by the way........that nut is on a LEFTHAND thread.
Made my own puller and jig. Piece of pie
Don't need to get a new gasket from AE. Make your own at a fraction of the price