Piper Navajo zero thrust power setting

[Pilot DAR]

Does anyone have an authoritative zero thrust power setting applicable to any of the Piper Navajo models? The flight manual I am referencing does not offer one for the subject aircraft.

I have some single engine climb performance demonstration to do for mod certification, and I would rather not actually shut down an engine (at all, but certainly in the cold temps this time of year). Transport Canada will allow me to demonstrate the single engine climb for this purpose with a zero thrust power setting, if I present a good plan. Any ideas?

Thanks, Pilot DAR

[Birthday Boy]

None of the PA31 POH's that I have include a zero thrust power setting, the operating tips only state to slowly retard the throttle to idle to simulate an engine failure.
However, when teaching PPC training I used the Seminole zero thrust configuration of 2000 rpm and 12-13" MP.
I hope this helps.

BB

[ReverseFlight]

For the Seminole we use 13" 2300 rpm which comes roughly to the same thing I guess. Don't know about the Navajo although I am aware they use much higher manifold pressures.

[DFC]

In this case I recomend that you contact the aircraft manufacturer and request a figure from them. I would be very surprised if they can't provide a figure.

With no published information I would be surprised if an Authority would accept some number that was obtained on a discussion board.

For test flying I would be surprised if an Authority would certify something on the basis of what normally passes for zero thrust in many manuals i.e. a very general figure.

The alternative is to go flying (perhaps somewhere warmer) and obtain it through a proper documented test and after making appropriate adjustments for the actual conditions use this as a basis for the proposed test flight(s).

The test to obtain the zero thrust setting would require very minimal time with the engine feathered - to establish true performance and most of the time would be spent with the engine running finding a suitable power setting that accurately represents what one found during the brief period that the engine was feathered.

Doing it this way enables you to make a complete report and not having any areas that the Authority could question after all that money has been spent doing the tests.

[Tinstaafl]

It's easy enough to find a zero thrust power setting for your aircraft. Bear in mind that it will change with changes in weight, speed and configuration. Also smooth flying conditions help.

Shutdown & feather an engine.
Establish stabilised & trimmed flight at the desired airspeed and configuration. Note any residual pressure you may have to apply to the controls.
Without changing trim settings, restart the feathered engine. Adjust the restarted engine and fiddle with it's power setting until aircraft performance & control inputs match the shutdown case.

If necessary repeat for the other engine eg critical vs. non-critical, different speeds eg Vxse or Vyse or configuration changes. Ideally you should calculate the Density Altitude you do this at and fly at that DA when using zero thrust.

[Pilot DAR]

As the required test is of a lower level of critcality, the authority has agreed that shutting down an engine (as it's cold around here these days) will not be required. I'll be flying the aircraft both pre mod, and post mod, and comparing the results.

I agree that possibly data provided here (discussion board) may be a little casual, but in asking about "authoritative" information, I'm hoping for a pointer towards someone's operations training manual or such quazi approved or recognized data. Piper has not been able to be of assistance for this. My requests of Piper for such things in the last year have been very politely declined, so I don't come to expect much from Piper, for product support of the "legacy" Piper aircraft.

It will be acceptable to not be right on with the power, as long as it is close, and I can use the same power, in the same conditions, both pre and post mod flying. When I get a number, I will probably err a little to the draggy side anyway.

Your thoughts are appreciated....

[Big Pistons Forever]

How about calculating the single engine rate of climb for the weight/conditions from the POH manual, then starting with one engine at full power and the other at idle, slowly add power untill you get the calculated performance ?

[DFC]

and I can use the same power, in the same conditions, both pre and post mod flying.


Once you get the power setting, I would not worry too much about the conditions provided that they are accurately recorded since you (or the FTE) will be adjusting them to ISA and the relevant operating envelope anyway - won't you?

Since it seems that the Authority are not overly worried about obtaining very accurate figures then why not ask the Authority to provide you with a list of PA31 operators and by talking with these and their examiners you will find what they are using. You can then say in your report that in the absence of documented information the Authority provided you with the details of A, B and C PA31 operators who use X, Y and Z as their zero thrust settings.

Alternatively, you can use a power setting that you know will be less than zero thrust. Measure performance pre mod and after mod and simply describe the performance change in percentage terms i.e. following the mod the single engine climb performance was improved by x% at SL, y% at 5000ft and Z% at 10,000ft ISA etc etc etc.

Remember that part 23 aircraft in the normal category only need very simple performance figures at specific altitudes ISA. Unless you are seeking the Authority's endorsement of a performance enhancing mod then provided that the aircraft still meets the part 23 requirements there should be no issues.

[Tinstaafl]

Seems like a lot of phoning, emailing & time consumed for something that is simple to find. If you're on the ball you can determine zero thrust in 20 or 30 mins of flight time. Account for staff time / hr and time waiting for an answer and it may even be cheaper.

[Horatio Leafblower]

My copy of the Chieftain POH has zero-thrust numbers in it... sorry but I'm away from my office until 8th January, will post them here then.

Cheers

[Pilot DAR]

Thanks Horatio, that would be quite appreciated, and perfectly timed. May I ask that you also let me know the affected model of the Navajo, and Flight Manual document number, and revision date, so I can provide that information in my report, should the authority wish to verify independantly.

Cheers, Jim

[Brian Abraham]

From a library copy complete to revision 9 of May 4, 1984. Unable to provide revisions beyond that. Piper Navajo Chieftain PA-31-350 Information Manual, Handbook Part Number 761 725

http://i101.photobucket.com/albums/m56/babraham227/g0003.jpg

[Pilot DAR]

That is a great help, thanks so much Brian...