juanjulian

My Feedback: (9)

Hi Guys

Will try to make my problem explanation short and hopefully can help me in getting a solution.

Bought a used wren 44 silver case(manual start) turbine used, and intermediately sanded to WREN USA to service it and ship to me. It got balanced and new front bearing, and told internally was ok. Turbine is old but with 728 run minutes (7 hours run time). Turbine was never run at wren USA since manual start. Turbine starts ok and runs with no issues but NEEDS A BIG, BIG, BIG, BIG, ACCELLERATION DELAY NUMBER 125 or flames out, with fast throttle up.

HAVING ABOVE 12 SECONDS LAG TIME.....

Ambient conditions at flying club:
Altitud: almost sea level
Temperature: 28-35 celsius
Relative Humidity: 80%

Programmed parameters
Full power: 190,000 rpm
Idle power: 60,000rpm
Min rpm: 35,000 rpm
Max tempt: 850 C
Start temp: 100 C
Acceleration delay: 125
Stability delay: 100
Deacceleration delay: 20 Ok
Pump start: auto+1
Ramp start: 6

Pump battery: lion 3.6 v or 3 cel nicd

Suspect the culprit of the problem is the pump,MTH and original pump, that is to tight.

Did my homework and found some old FADEC manuals with instructions on how to adjust pump start and notice is pump is ok or tight.

TEST ON PUMP
1.reduced start temp to below ambient temperature to cheat fadec ant start fuel ramp. Spooled engine to make pump ramp start.
2. Connected the output fuel line to a tank reservoir and see when the pump starts to move fuel.
3. The pump has extra wire lead with servo conector to purge pump manually, and in this case to monitor voltage to pump.

TEST 1 start pump (manual parameters 9-255)
Played with the manual parameters of pump start from 9-255 and pump never moved any fuel on line on fuel ramp. The max voltage read was 0.2 Vdc and pump made sound but did not start.

Test 2 start pump (auto0-9)
Played with outo 0-9 and in all the pump started working but voltage had to get to 0.4 Vdc to start moving fuel in the line. Noticed that the fuel starts to move faster in AUTO 0 and assume that Auoto 1 is slower than auto 0 and so on.

SO IN RESUME
I think that need a new pump, and since not turbine guru will appreciate your concurrence.

Thanks

Juan
Guatemala

Boomerang1

Hi Juan, Just noticed your post with no replies.

I have two of these engines & have experienced the same problem but with two causes.

First cause, and the easy fix, is that the screws holding the exhaust nozzle can fall out causing the case pressure to leak
out & resulting in a longer than normal acceleration delay to prevent the engine flaming out.

The second, more expensive cause, is the nozzle guide vane can become cracked or distorted with the same problem, flame out
on acceleration. Replacement means returning the engine as Wren says the new NGV must be precision matched, by grinding, to
the turbine wheel. I was told you cannot just fit a new NGV & expect it to run properly.

Hope that's a help, John.

juanjulian

My Feedback: (9)

Thanks for your reply.

I had a very* short joy with this engine. Realized that part of the lag time was imperative of a old engine so coped with it.

Only burned 5 gal of jet a-1 before engine totaled due to rear bearing failling. Repair cost were the same for what paid for used turbine. So decided to leave it as is.

So have front cover, case, ngv, turbine wheel, difusor, and fadec as spares if you have a interest on this parts.

Will like tu buy a new turbine but for the moment with no budget to do so. This time will go with a 80N type turbine and new to avoid getting screwed by being cheap.

Learned a lot and probably think know more about turbines than the fellows with their automated turbines.

Cheers

Juan