Pathfinder Problem

[Bob Zambelli]

I received a note that a friend is having some vibration problems with a Brodak Pathfinder (Profile).
It is powered by an LA .46.

I have no experience with this plane so I'll ask - have any of you had a vibration issue with this combination?

If so, what was/is the fix.

THANKS!!
                     Bob Z.

[Roger Vizioli]

Hi Bob,
Don't have one, but all I have seen are smooth. a few ideas are,
On ground -First thoughts are: prop balance, bent engine crank, glue joint-wing to /fuselage at LE, soft motor mounts.
Flying - push rod resonance, loose controls, again, glue joint @ fuse/wing LE. soft motor mounts, bent shaft.
or -
does engine run smoothly on test stand?
Just a few "thoughts".
Roger

[steven yampolsky]

I received a note that a friend is having some vibration problems with a Brodak Pathfinder (Profile).
It is powered by an LA .46.

I have no experience with this plane so I'll ask - have any of you had a vibration issue with this combination?

If so, what was/is the fix.

THANKS!!
                     Bob Z.

Bob,

I fly Pathfinder ARF + LA46 combo. No excessice vibration there. One thing I would suggest  in addition to Roger's suggestions is to check aluminum clamp system. Brodak ARFs use fairly thin aluminum strip to clamp the engine to the engine mounts. I've seen people overtighten the clamps to the point where they will bow and grab onto one edge only. For example, it would grab onto the rear edge effectively leaving the front of the engine loose.

Best fix for it is to make up a clamp out of thicker aluminum stock to prevent bow effect. Just make sure the NVA clears it.

[Tom Perry]

I received a note that a friend is having some vibration problems with a Brodak Pathfinder (Profile).
It is powered by an LA .46.

I have no experience with this plane so I'll ask - have any of you had a vibration issue with this combination?

If so, what was/is the fix.

THANKS!!

Another thin you might suggest is drilling two 1/8th holes from the top throgh the engine mounts, one right behind the engine and one close to the rear of the mounts.  Epoxy a couple of 1/8th dowls through both holes.
                     Bob Z.

[Alan Hahn]

Sometimes with profiles it is hit or miss regarding vibration. A lot depends on how stiff the front end of the plane is. A very stiff front end will tend to resonate at higher frequencies than a one that is softer. How stiff it is depends on the wood and aspects of construction. Also a softer front end will tend to absorb more of the vibration energy (low "Q") than a stiff one.

One thing to try, assuming that the propeller is balanced (no reason not to try and lower the amplitude of the driving force), is to lower or raise the engine rpm with a different prop selection. So if he is running (or trying to run in a deep 4 stroke like my LA46 likes), perhaps a smaller lower pitch prop running at higher rpm. Vice-versa of course if the vibration is at higher frequency.

[peabody]

Bob...
If it is an instruction built ARC/ARF, I suspect the cheesey engine mounting clamps ....have him check those for tightness....

[Steve Fitton]

If its got the stock clamp mounts, then right there is the problem.  I've watched Willis tighten the motor down and have it vibrate loose in one flight.....

[Dennis Moritz]

I've seen lots of Cardinal ARFs use the engine clamps as engine pads. The pads are drilled out and the engine is mounted in a conventional manner, holes through the motor mounts, bolts backed by nuts. The ply ring around the engine crankcase is dremeled or filed to fit. Not elegant. But functional. It's an ARF.

[Dennis Vander Kuur]

Bob,
I fly an LA .40 powered Pathfinder built from a Brodak kit. It is 3 years old and has logged about 280 flights. Until a month ago there was no problem running different prop sizes or different engine speeds. However, it recently started buzzing the front end badly. At lower or normal rpms the front end would buzz. However, if the engine was leaned out and allowed to run at a higher speed then the buzz went away. So I installed an APC 10.5x4.5 prop and let the engine rev. Now it is back to its well-mannered ways and that little prop pulls well. I think Alan Hahn is right and somehow (through repairs, different tank mounting, different spinner, etc.) the plane developed a resonant frequency in the normal rpm range. Hope this helps.
Dennis

[Bob Zambelli]

Thanks for the input - Craig is trying various fixes.
Bob Z.

[Ward Van Duzer]

I never understood why the inboard tripler didn't go back to the high point of the wing...