Slow flight problems with top mounted engine planes
03-09-2004, 03:45 PM
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Slow flight problems with top mounted engine planes
This is an aerodynamic question I guess. Without getting into airplane brands, is there a problem with slow, high alpha flight creating a turbulent, low pressure area infront of the turbine that would cause the engine to not be able to respond to increased throttle demand due to high exhaust gas temp, or not be able to increase RPM because there is not enough air to support the increase in fuel.
We have had two power failures with subsequent pancake landings when after a long - 30 seconds, slow, high alpha flight at approximately half throttle, the turbine would not respond to the throttle. In both instances there was sufficient time, 4 seconds, for the system to spool up from the half throttle setting. We could not detect any change to the engine sound during the decent, once throttle was advanced.
The first incident was chalked up to pilot error, but the second one was definitly lack of response from the turbine.
The engine is a JC P-120 and it is mounted on a Hot Spot, what do you think?????????????
We have had two power failures with subsequent pancake landings when after a long - 30 seconds, slow, high alpha flight at approximately half throttle, the turbine would not respond to the throttle. In both instances there was sufficient time, 4 seconds, for the system to spool up from the half throttle setting. We could not detect any change to the engine sound during the decent, once throttle was advanced.
The first incident was chalked up to pilot error, but the second one was definitly lack of response from the turbine.
The engine is a JC P-120 and it is mounted on a Hot Spot, what do you think?????????????
03-09-2004, 05:25 PM
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RE: Slow flight problems with top mounted engine planes
I guess one of the first questions, perhaps Matt can answer this, would be, is it even possible to create a low enough pressure area ahead of the turbine to cause it to exhibit these symptoms (i.e., not accelerating), or would it compressor stall or overheat and shutdown first? The second question would then be, could you create such a low pressure area in high alpha flight in a Hot Spot. My quess would be no, but I could be wrong. Of course the third question would be, what else could cause the engine to not respond to throttle commands in this way?
Bob
Bob
03-09-2004, 07:03 PM
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RE: Slow flight problems with top mounted engine planes
We have not communicated with Jet Cat yet, we thought it would be worthwhile to see if there had been other experiences like ours.
Bob your comments are valuable and follow what we think also. There must be some anomaly that causes the lack of response from the engine. Thanks.
Bob your comments are valuable and follow what we think also. There must be some anomaly that causes the lack of response from the engine. Thanks.
03-09-2004, 09:20 PM
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RE: Slow flight problems with top mounted engine planes
I would have to say no. First of all, the low pressure in front of the compressor (caused by the P-120) is going to be so low compared to ambient that atmospheric pressure is going to force plenty of air in the direction of the intake. Yes, it may be turbulent air, but centrifugal compressors are known for being VERY tolerant (much more so than axial) of turbulent air ingestion.
Perhaps the engine just hung-up, both times just in this situation. Or perhaps the engine is on the ragged edge of hanging up all the time and the slightly lower pressure during the high alpha passes kicks it over the edge into a hang up.
Whatever the cause, many HotSpots and P-120 combos have performed these maneuvers over and over again with no issues (I used to do it all the time with my HotSpot/TJT-3000 combo), so it is unique to your configuration (I would think). Could it be a fuel system issue when the nose is high and fuel is getting low? Let us know what you discover.
Perhaps the engine just hung-up, both times just in this situation. Or perhaps the engine is on the ragged edge of hanging up all the time and the slightly lower pressure during the high alpha passes kicks it over the edge into a hang up.
Whatever the cause, many HotSpots and P-120 combos have performed these maneuvers over and over again with no issues (I used to do it all the time with my HotSpot/TJT-3000 combo), so it is unique to your configuration (I would think). Could it be a fuel system issue when the nose is high and fuel is getting low? Let us know what you discover.
