I have a Jetcat P70 (Version 5 ECU) that had 3 or 4 successful runs today no problem whatsoever.
On the 4th or 5th flight it started up no problem. I taxied out and took off again, no problems. After climbing to about 50-100 ft there was a puff of white smoke and everything went quiet.
I was able to get the plane down without any damage whatsoever! (Thank goodness for great gliding planes) When I plugged the GSU it was reading something along the lines of 'OverRPM' or 'OVERREV' or something like that.
Ok, everything was checked over and nothing was loose or out of place.
Re-Fuel and take off no problem. After reaching about 100 ft I banked the plane to the right and was on the downwind leg, when there was a horrible noise that could probably be best described as a Bzzzz going from high pitched to silence over the span of about a half second and then silence. It also looked like there was about 4-6 inches of flame out the Turbine exhaust... This time there was no smoke puff (Like there needed to be with that noise)
After making a bee line for the ground and narrowly missing a snow bank and barbed wire fence on top, it ended up upside down in a field with the plane aft of the turbine exhaust smoldering and the inside of both the engine bay and the back half of the electronics compartment covered in Kero.
When it was taken back to the pits area and the wing was taken off (Hi Wing) to reveal the engine bay, it was more or less complete carnage in there. Bits of plastic shattered, the purple cowl to the motor had torn (Yes, the screw holes were converted to slots) and the impeller blades could not be turned by hand. (I'll try to have pictures here later on tonight or tomorrow).

My questions would be... What the heck could have caused the over rev error and could it have subsequently caused the self destruction of the turbine?

The ONLY thing that was different to the previous weekends flying was some new 5% fuel mixed up.

Thanks
George

Hi George,

Sorry to hear about the plane. The only time I have seen anything approaching an overrev it was because there were restrictions in the fuel system (usually in the shutoff valve) in the form of dirt or some other contaminate. This restricts the fuel flow and to compensate, the pump voltage starts to get very high. At some point the crap breaks free (like a blood clot) and the high pump voltage causes a big surge of fuel to go to the turbine and before the ECU can react the RPM shoots way up.

I will talk to Bob to see if he has any ideas and get back to you.

Regards,

Here are some images of the remains of the P70 still in the airframe. I hope they come out ok...

If anyone is interested in the full sized pictures, here are the links
[link=http://www.georbeckha.com/P70Logs/PICT0025.jpg]Picture 1[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0027.jpg]Picture 2[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0028.jpg]Picture 3[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0031.jpg]Picture 4[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0033.jpg]Picture 5[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0034.jpg]Picture 6[/link]
[link=http://www.georbeckha.com/P70Logs/PICT0037.jpg]Picture 7[/link]

They are large pictures but easier to make out stuff on than the uploaded files above
George

from the looks of the compressor I'd take a stab in the dark and say you had complete bearing failure or a broke shaft.

I did not see a fod guard.
Were you using one?

Johnny

Not a FOD Guard as such. I had screens over the intakes. the one on the side that the picture shows got taken out by a piece of the inlet ducting as it shot forward.

personally i wouldn't run a turbine without a FOD screen on the turbine its self, just screening the intakes doesn't prevent FOD from inside the jet (loose screws/wires/etc......) from getting sucked in, but from the looks of the compressor as far as i can see, FOD wasn't the cause.

More pics of the removed turbine...
As you can see, it looks like the impeller at the front is pushed 2-3mm to one side! A couple of the blades do have little nicks out of them but I can't tell if this is an indication of something being sucked in there causing this or if something was sucked in there as a result of this.
I'm thinking I'll take this to bits myself as I'm pretty sure that Jetcat Warranty does not cover this and it has expired anyway.
I don't think the shaft has broken because the front impeller and the rear exhaust vanes cannot be turned.


[link=http://www.georbeckha.com/P70Logs/Top.jpg]Top[/link]
[link=http://www.georbeckha.com/P70Logs/Underside.jpg]Bottom[/link]
[link=http://www.georbeckha.com/P70Logs/Front1.jpg]Front 1[/link]
[link=http://www.georbeckha.com/P70Logs/Front2.jpg]Front 2[/link]
[link=http://www.georbeckha.com/P70Logs/Front3-gap.jpg]Front showing the Gap[/link]


George

Looking at what I assume is a filter inside of the turbine cowl (Where the fuel goes into the Turbine itself there is a festo 'T' fitting. One outlet goes directly into the turbine and the other outlet to the fitting appears to have a filter of some sort on it. this goes about 180 degrees to where the T fitting is then into the turbine.)
The Turbine side of this filter appears to have a length of wire coming out of it. Can anyone tell me if this is normal or if it is another part of the puzzle?

Thanks
George

That is an incowl filter and is normal. IMHO what happened is related to the first run with an "OVERSPEED" shutdown condition. Contrary to conventional wisdom the weak point in the turbine, related to RPM is not the wheel but the compressor. The compressor is the limiting factor for RPM topend. That is one reason the manufacturers are going to CNC billet compressors. They are much stronger. I think that your compressor was overstressed during the first overspeed and deformed enough to cause you the next problem. On the next run the weakened and stretched cast aluminum blades deformed even more (especially if it oversped again), made contact with the compressor housing and you see the result. The millisecond that the blades contacted the housing it went into a friction/heat/expansion cycle that caused the compressor to instantly seize. All that considerable energy has to go somewere and that somewhere is what turned your engine into a pretzel.
Unfortunatly there is probably very little left useable of your turbine. The Wheel and NGV might be OK if they didnt touch during the violence. Your chamber is probably ok but that is about it. Shaft, compressor, shaft tunnel, compressor housing, diffuser, can, starter and bearings are done.
In retrospect I would not run a engine that had a overspeed shutdown without a check out by the factory-I know that doesnt help you now though. Sorry, Scotty

GSR, I see what you're saying.

In one pic I see 3 or 4 compressor blade ends 'broomed' out and ground down and resting against the intake wall, on the opposite side the is a huge clearance between blades and wall. Wouldn't ALL the blade ends 'Broom out" if it were expansion like you suggest? To my eye and not being into turbines for too long it seems a bearing failure.. I'm just throwing it out there, I'm not challenging your experience/knowlege at all.


For Georbeckha,
Yoou had 3 or 4 successful runs that day. On the last 2 flights did you fill the tank with your fuel, or was it someone else's suppy?... I'm thinking an oil issue.

***
Deleted... Same post done twice.

Its rare to loose a front bearing and it looks like the rear did not let go in the pics as the wheel is intact. Oil for the bearings starts by being sprayed on the front then travels down the shaft to the rear. The rear being exposed to heat and end of the line lube lives a much harsher life.When you loose a rear it is shrapnel city. It is possible it was a front bearing failure-you end up with the same result-just different causation. I am just leaning to compressor rub due to the overspeed issue. As soon as the compressor hit the housing all bets are off as to what it is going to look like two seconds later. Hopefully Bob can do a postmortem on the can. Scotty

Actually, I was using a fresh can of fuel all day. I know that the Jet Central guys only use 2.5% in their fuel versus the 5% Jetcat does.
The Oil was Aeroshell 500 turbine oil I had gotten from BVM a few months ago.
I can tell you all that the Starter motor miraculously survived with no scratches at all on it. The ECU has Kero/oil on it as well as some other electronics but according to the log data it seems to still work with no problems.
It is interesting that the last 5 or 6 readings that it got after the incident the rpm was 0, the fuel pump voltage was 0, the actual RPM was 0 and the temp was within 5 or so degrees of <Shudder> 1260 degrees Celsius (2120 degrees Fahrenheit!!!!!!!) And all that was burned was the Aluminum foil on the Fuse underside and a little charred wood. The wires for the 2 tail feather servo go right above it and there is no sign at all of heat there (Between 1/2 inch to an inch away from the turbine and charring)! I guess that I still have a flyable jet out of this (After some beefing up of the charred bits or replacement of said parts) and that's pretty good.
I do need to either go get another kero start or convert it to propane start for my P60 though as when the engine rotates the kero plug (Being inside the front and back 'straps' that attach the engine to the frame) is bent at a nice 20-40 degrees when it stopped the engine from rotating any more!

George

Ouch!! Hate to see this happen to anyone, and while we all have our theories, it would be very helpful to find out what really happened....

<SIGH> Here we go again...
This is the repaired engine I got back form JetCat on Monday. This is the first flight (About 2 minutes into the flight this time)
For noise description see the first post in this thread...
This time, the flames did not go out BUT I got the planer down onto the runway dead center PRIOR to the flames melting the elevator and rudder servo wires.
Also, I can still somewhat turn the compressor wheel and the bearing is very very rough feeling!

Mr_Matt, if you're reading this you may want to let Bob know that I'll be calling them on Monday to get this sent back in and repaired again...

George

I know that it is a long shot, but was this the same fuel as last time?
Is there any chance that you got the wrong fuel? like 100LL instead of jetA1 or gas instead of kero?
I have seen people get the wrong fuel from an airport.

Nope, 'fraid not.

This time it was a brand new mix of fuel. Fresh Aeroshell 500 Turbine oil (5%)
And Kero from a fresh drum purchased from Lowes and mixed the friday before the 2nd problem.
I had the same thought about what if something got into the fuel mix and temporarily blocking the fuel flow then giving way causing a surge in fuel and over revving the engine.
This time, with the data I was ablt to download from the ECU it didn't indicate anything out of the ordinary. It was at full throttle at 500 odd degrees then the temp shot to 1000+ (After the engine stopped and the flames poured out) and according to the ECU, the RPM ramped down over 4 or 5 samplings (Not to sure the interval that the ECU saves samples at)

The engine has been sent back to JetCat. I'll keep everyone updated about what they say.

George

while i don't recommend you do it, IF someone had used 100LL the turbine would run just fine.

You guys are very smart. Im sorry about the engine man. How much does this engine cost?