What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

PRU Failure???

M

meadeduck

Well Known Member
On Saturday, George and I made a trip to a local pancake fly-in, with no problems. When we tried to return, we couldn't pull more than about 4300 rpm on takeoff and we got a bad shake/miss/vibration and couldn't/wouldn't get into the air, so we aborted the takeoff and returned to the ramp. We checked the fuel and we had some particles in the tester but George seems to think it was in the propeller drive. We tried again to leave but encountered the same problem.
We're taking the plane back to our hangar on trailers to check out what we can check out. We've got almost 20 hours on it so I thought we might as well do the first oil change, and we might drain the fuel tank and strain the fuel while we're at it. We're the guys that had the engine 'squeal/screech' noise at startup and shutdown; I really hope that wasn't a foreboding of what we have now.
Meade and George
N612RV
 
I doubt it is the gear box. It would not cause missing.

Check the carb socket and make sure they are secure.
Try re-syncing the carbs.
Clean the gascolator screen.
Check tightness of boots on spark plugs wires to spark plugs. They kinda snap on.

Maybe time to have a good Rotax mechanic take a look at your set up.

Sorry to hear about your problem.
 
Last edited:
Doesn't sound like the gearbox - more like a fuel / air mixture issue. Could be one of the following:
- Choke not completely in
- Carbs not in sync - this could happen, if a throttle cable has moved / is hung up, etc. or if the carb overflow hoses see different pressures.

Good luck

Thilo
 
PRU Failure

We've got a little more than 20 hours on the engine, so we decided to change the oil, the coolant, and then when the weather (wind) gets reasonable, we'll try again. I was wondering if ONE of the propeller blades was turned to a different pitch, if that could have produced the vibration and lack of engine speed. We've been moving the plane by pulling on the blade close to the spinner. I'm going to talk to my partner about that today; I thought of that overnight.
Meade
 
Doubt it

If you torqued the hub bolts, I don't think you could turn a blade if you tried to. They get locked down very well.

How did you set the blades ( protractor ) ?
Have you checked the throttle movements thru the entire range ?
Have you checked the carbs themselves. If you did not get the 'o' rings correctly in place, could be the issue.

Just some ideas for you to check.

John Bender
 
meadeduck said:
...... I was wondering if ONE of the propeller blades was turned to a different pitch, if that could have produced the vibration and lack of engine speed. .......
Meade
Click to expand...

Yes, had it happen on a Rans, 912 with a Warp prop. Not sure how your prop is adjusted or locked down, but worth checking.

Also another 912 I know of had a throttle cable come undone and the vibration was severe enough the pilot shut down the engine and deadsticked it to a perfect landing. Carb imbalance will produce a vibration. So I would check cable travels and carb synch.
 
you might have flooded it and one or more spark plugs are all wet. Remove the spark plugs clean them and reinstall. The rotax is real sensitive on the choke.
 
PRU (?) failure

We've changed out all the fluids, now we're just waiting for a windfree day to do a take it out and test it. George DID do a static runup to 5400 with no indication of any problems.
I want to thank everyone for all their suggestions and we've just about everything except pulling the plugs and we'll probably do that next time we get to the airport.
Meade
 
meadeduck said:
On Saturday, George and I made a trip to a local pancake fly-in, with no problems. When we tried to return, we couldn't pull more than about 4300 rpm on takeoff and we got a bad shake/miss/vibration and couldn't/wouldn't get into the air, so we aborted the takeoff and returned to the ramp. We checked the fuel and we had some particles in the tester but George seems to think it was in the propeller drive. We tried again to leave but encountered the same problem.
We're taking the plane back to our hangar on trailers to check out what we can check out. We've got almost 20 hours on it so I thought we might as well do the first oil change, and we might drain the fuel tank and strain the fuel while we're at it. We're the guys that had the engine 'squeal/screech' noise at startup and shutdown; I really hope that wasn't a foreboding of what we have now.
Meade and George
N612RV
Click to expand...

I agree with the other guys, doesn't sound like gearbox or prop to me.

FWIW, one time after a fuel line change I got virtually exactly this same symptom with my 912uls. The engine ran fine at lower throttle settings so the taxi and runup were uneventful. But on the takeoff roll, as I approached full throttle, there was a sudden very hard shake and miss as if a couple cylinders had shut down. Backing off the throttle, they came back.

I checked things with the EGT on the ramp, the 1/3 side sure enough went cold as the throttles opened indicating fuel starvation on that side. Adding in the choke improved matters and it ran up a little better, but still faltered approaching WOT with the dropping EGT's. Again pointing to fuel starvation. Back at the hangar I ended up cleaning out a fairly hefty sized slice of fuel line from the main jet passage. That done, the engine ran normally (and I changed my fuel line change procedure after that ;)).

So your symptom sounds similar to mine, I'd check for debris in the carburettors. If you're getting stuff out of the fuel drain, there's definitely some contamination there....

LS
 
Last edited:
PRU (?) failure

I went up after church today and finished draining the tank by siphon. Then I tried to use the fuel pump to finish the job but couldn't get the fuel pump to come on (somebody doesn't want us to fly this thing...) so I just let it drip for a while. THEN I got the bright idea of getting a large tube, wrapping it so that it wedged in the filler tube, and then I blew into the tank, thinking I could get some more of the gas out...which I did but it still dripped so I guess I'll wait until Tuesday when George and I will worry over it some more. I continue to get little flakes in my MR FUNNEL filter.:confused:
Meade
 
meadeduck said:
I went up after church today and finished draining the tank by siphon. Then I tried to use the fuel pump to finish the job but couldn't get the fuel pump to come on (somebody doesn't want us to fly this thing...) so I just let it drip for a while. THEN I got the bright idea of getting a large tube, wrapping it so that it wedged in the filler tube, and then I blew into the tank, thinking I could get some more of the gas out...which I did but it still dripped so I guess I'll wait until Tuesday when George and I will worry over it some more. I continue to get little flakes in my MR FUNNEL filter.:confused:
Meade
Click to expand...

Meade,

I will speak up. Please find a fellow chapter member that can assist you. Find someone familiar with the 912ULS, there are plenty of them around in the ultralight fraternity. The problems you describe and the solutions you suggest are not what I would find comfortable. Sorry, but, I do not want you to find a forced landing in your future. You should not find debris in your sample.:(
 
PRU failure

We did some more checking yesterday and our fuel pump isn't working AND we're not getting any voltage at the pump either. We pulled the floor up in the back and pulled the connectors apart and detected no juice at that point, so we ran a line directly from the battery to the back and we barely got ANY indication of functioning from the pump. (it hummed). George is going down to AC Spruce and pick up a new unit today.
Meade and George
 
meadeduck said:
We did some more checking yesterday and our fuel pump isn't working AND we're not getting any voltage at the pump either. We pulled the floor up in the back and pulled the connectors apart and detected no juice at that point, so we ran a line directly from the battery to the back and we barely got ANY indication of functioning from the pump. (it hummed). George is going down to AC Spruce and pick up a new unit today.
Meade and George
Click to expand...

Meade and George,

At this point, the battery may simply be low.

You guys need some outside help to get this airplane squared away. There must be a local EAA Chapter to contact for assistance.
 
PRU/Fuel Pump Failure

Today, George and I replaced the fuel pump and installed a switch on the dash to activate the pump for takeoffs and landings. We made three successful takeoffs and landings with no problems.
Meade
 
meadeduck said:
Today, George and I replaced the fuel pump and installed a switch on the dash to activate the pump for takeoffs and landings. We made three successful takeoffs and landings with no problems.
Meade
Click to expand...

Good news George.

Any indication of what the original problem was?
 
Last edited:
You must log in or register to reply here.
Back
Top