17th Mar 2012, 14:19
Can anyone tell me if there is a maximum density altitude to start an L-39?
Can anyone tell me what would happen if you attempted to start an L-39 at 5000 msl with a density altitude of 7500, if the saphire sucked some FOD into it's intake restricting the airflow into the turbine by approximately 40%?
17th Mar 2012, 14:35
Which is cheaper ,Tom... change the APU or risk the engine...? Suggest you e-mail Bernd....
edit; not knowing why/how /what Fod you`ve got in the APU ,I would be inclined not to use it,as residual `stuff could end up in the engine......
however,if the Injuns are coming over the hill,you may consider a `COLD ROTATION`/no ignition/no fuel,and check the `time of the APU cycle,and how many HPC Rpm you get( you need 20 % as an absolute minimum,24 % for a reasonable start).
Remember the `start cycle` for the main engine runs 45 secs,and then cuts out at 43% HPC Rpm...
If you are at a `normal` airport,I would have thought you could find a mechanic who would be familiar with the Saphir..
Further alternative if the Injuns are closing ,get a ground APU ,stuff the hose in the intake and get 15% HPC,then `airborne relight`...
You could also try that with a `friendly jet or C-130` to park in front and get a `blow-job`...!!
PPS.the APU can be used up to 20000ft..
17th Mar 2012, 21:49
Tom,I notice you haven`t posted on `L39.com....?
And,how have you managed to FOD the APU...? It`s inside,or did you leave a rag in there....?
18th Mar 2012, 07:01
I purchased an L-39 and had it restored.
After the first 20 hours of flight I had a hot start. When we investigated we found the wire/cable bundle in the belly had not been secured to the bulkhead. What we believed happened was that the bundle was in the airflow causing the plastic/rubber tie downs to expand and fall into the belly.
On the 20th start, the rubber/plastic tie downs were sucked into the intake of the Saphire. We found this out when we took the plane apart after the Hot Start. It appears two or possibly three of the bands were sucked in the saphire intack at the same time ( two were found stuck to the intake and blocking at least 40% of the entrance, the third was found on the belly immediately beneatht the intake )
I am in discussion with the insurance Company trying to resolve if it was pilot error, or a problem beyond the pilots control.
My position is that with a high density altitude, and the restriction in airflow ( not knowing exactly when the FOD was introduced ) caused excessive fuel to be introduced into the main turbine causing a fire that could not have been prevented by the pilot.
What say you? do you concur?
FYI some have asserted that the pilot could have/should have been able to shut down with no damage..... I don't think that is correct.
18th Mar 2012, 11:11
Tom,check your Private Messages...