There are two planes hangered at my field with Rotax 582 engines which
are both having the same problem. Each engine has about 30 to 40 hours
on them and suffer from surging and/or power failure during climb-out or
shortly after. Typically, the RPMs will drop from 6000 to around 4800
after about 2 to 5 minutes after take off. The EGTs on both cylinders
remain stable at 1100F during the power loss, but one engine does show a
marked increase in the CHT on one of the cylinders (300+).

The fuel system on both planes has been replaced twice now. The carbs
were disassembled and inspected with no indication of any blockage or
defect. The jugs were pulled on one of the engines with no indication of
seizure or carbon fouling of the rings or pistons. The plugs look
normal. Switching from one mag to the other has little effect during the
power loss.

I'm pretty much out of ideas what could be causing this problem. The
only other thing I can think of is that maybe a crank bearing is failing
and dragging the engine down as a result. But splitting the engine case
is a pain in the butt so I wanted to exhaust the simpler causes first.

Any suggestions out there?

I have an acquaintance with a 582 powered kitfox that had this same
problem...It turned out that the prop was very slightly changing pitch....I
remember it took a lot of time before this was found out. There was wear in
the hub area. It was fixed by adding a shim. It seems like (I'm trying to
remember here) the prop hub was slightly distorted where it clamped
together. What type of prop are on the planes? Are they using GSC props?

--
Yosimite Sam

Yosimite Sam wrote:
> I have an acquaintance with a 582 powered kitfox that had this same
> problem...It turned out that the prop was very slightly changing pitch....I
> remember it took a lot of time before this was found out. There was wear in
> the hub area. It was fixed by adding a shim. It seems like (I'm trying to
> remember here) the prop hub was slightly distorted where it clamped
> together. What type of prop are on the planes? Are they using GSC props?
>

Hmmm... Very interesting. The props on both planes (actually Pegasus
powered parachutes) are 3-blade Powerfins. They are similar to the
WarpDrive props in that they have a CNC machined hub which clamps down
on the end shank of the blade.

I'll try to round up a WarpDrive prop and try that on them and see what
happens. The Powerfins have a lot of twist in the blades so I guess it's
possible that they are flexing and changing the pitch.

Regarding the prop shims, I know that the early (and possibly later)
versions of the ground adjustable Ivoprop had a problem with the tip of
torque rods that rides on the swash plate that varied the pitch would
wear and allow the pitch to wander.

If you decide that this might be the problem, I can put you in e-mail
contact with the guy that went through this problem.


--
Yosimite Sam

"Yosimite Sam" > wrote:

>I have an acquaintance with a 582 powered kitfox that had this same
>problem...It turned out that the prop was very slightly changing pitch....I
>remember it took a lot of time before this was found out. There was wear in
>the hub area. It was fixed by adding a shim. It seems like (I'm trying to
>remember here) the prop hub was slightly distorted where it clamped
>together.

It seems to me that the prop would be much more likely to go to a
flatter pitch and produce MORE RPM if the blade(s) slipped. Am I
missing something?

Mark Hickey

Mark Hickey wrote:
> "Yosimite Sam" > wrote:
>
>
>>I have an acquaintance with a 582 powered kitfox that had this same
>>problem...It turned out that the prop was very slightly changing pitch....I
>>remember it took a lot of time before this was found out. There was wear in
>>the hub area. It was fixed by adding a shim. It seems like (I'm trying to
>>remember here) the prop hub was slightly distorted where it clamped
>>together.
>
>
> It seems to me that the prop would be much more likely to go to a
> flatter pitch and produce MORE RPM if the blade(s) slipped. Am I
> missing something?
>
> Mark Hickey

I guess it would depend on the rigidity of the blade and where it wants
to twist. A cambered airfoil should produce a pitching moment in such a
way as to reduce the angle of attack.

BTW: I did try the WarpDrive prop and the problem went away. I then put
the original prop back on to make sure that was indeed the cause, and
was unable to reproduce the problem anymore. So I don't know what's
going on at this point. :P

Something else to check might be the exhaust. I had a friend who
changed his muffler and the inside of it had broken loose (I believe
it was the baffle) and was moving around and would seal off or change
the back pressure and the RPM would die off. We tore the pipe apart
and rewelded everything in place and it works fine now. It was an R&D
pipe that he bought used. Of course he does still have a "flat spot"
around 5400 RPMs it drops off to 4800 RPM. You might also look at
adjusting the piece of the end of the pipe in and out too to change
the pressure build up in the pipe.


On Thu, 06 May 2004 03:59:57 GMT, "L. Darte" > wrote:

>There are two planes hangered at my field with Rotax 582 engines which
>are both having the same problem. Each engine has about 30 to 40 hours
>on them and suffer from surging and/or power failure during climb-out or
>shortly after. Typically, the RPMs will drop from 6000 to around 4800
>after about 2 to 5 minutes after take off. The EGTs on both cylinders
>remain stable at 1100F during the power loss, but one engine does show a
>marked increase in the CHT on one of the cylinders (300+).
>
>The fuel system on both planes has been replaced twice now. The carbs
>were disassembled and inspected with no indication of any blockage or
>defect. The jugs were pulled on one of the engines with no indication of
>seizure or carbon fouling of the rings or pistons. The plugs look
>normal. Switching from one mag to the other has little effect during the
>power loss.
>
>I'm pretty much out of ideas what could be causing this problem. The
>only other thing I can think of is that maybe a crank bearing is failing
>and dragging the engine down as a result. But splitting the engine case
>is a pain in the butt so I wanted to exhaust the simpler causes first.
>
>Any suggestions out there?