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A question about throttle settings

Posted: Thu Jul 09, 2015 9:47 am
by vololiberista
If I set the throttle to 100% at ISA I'll get say 100% n2. If the temperature is much higher e.g ISA +15 would I have to set the throttle to 90% or could I set it still to 100% and the engine automatically reduce n2 according to the ambient temperature. I'm not aware of any FADEC controls on the RR Conways.

Re: A question about throttle settings

Posted: Thu Jul 09, 2015 11:02 am
by Jelle Hieminga
Indeed the Conway is not a FADEC engine (far from it). That means that Throttle Lever Angle (TLA) is not directly related to a power setting as this relationship varies with ambient conditions. At a higher ambient temperature you may find that the TLA is much reduced to make sure that you don't exceed one of the engine's limits (N or T somewhere).

One of the more knowledgeable folks here will surely correct me on this. :wink:

Re: A question about throttle settings

Posted: Thu Jul 09, 2015 3:45 pm
by vololiberista
Jelle Hieminga wrote:Indeed the Conway is not a FADEC engine (far from it). That means that Throttle Lever Angle (TLA) is not directly related to a power setting as this relationship varies with ambient conditions. At a higher ambient temperature you may find that the TLA is much reduced to make sure that you don't exceed one of the engine's limits (N or T somewhere).

One of the more knowledgeable folks here will surely correct me on this. :wink:
Thanks Jelle,
I though that was correct. But placing the throttle in the correct position to get maximum benefit must have come from experience I imagine.

Re: A question about throttle settings

Posted: Thu Jul 09, 2015 3:56 pm
by Tonkenna
Before each take-off a calculation was made as to what P7 reading had to be achieved by the engines depending on the current conditions. We could take-off using either 93%/96%/Full Power depending on a number of factors. However, if the required P7 was not reached at the Factored Power (93/96) then Full Power would be applied. If an engine still failed to reach the calculated Full Power P7 then we would abort (happened to me twice).

I have the calcs somewhere upstairs... will try and dig them out later...

Andy

Re: A question about throttle settings

Posted: Thu Jul 09, 2015 5:28 pm
by bobisqueen
Regardless of ambient conditions, if you wanted a full power take off you would put the throttles to max.

Although not a FADEC controlled engine, HPRPM, LPRPM, EGT and P3 (compressor outlet Px) were all protected. The LPRPM and EGT we're protected by the top temp controller which would trim the servo fuel pressure within the FCU to reduce fuel flow. P3 and HPRPM were protected in a similar way in the FCU but mechanically

The TLA results in you getting a % of available thrust depending on outside conditions. Ie if you put the throttles to half way you would get 50% of the thrust the engine could produce for those given conditions.

I hope that all makes sense....! I'll try and dig out my notes later about P7. We used to check for min and max P7 during engine tests

Re: A question about throttle settings

Posted: Thu Jul 09, 2015 5:49 pm
by vololiberista
Tonkenna wrote:Before each take-off a calculation was made as to what P7 reading had to be achieved by the engines depending on the current conditions. We could take-off using either 93%/96%/Full Power depending on a number of factors. However, if the required P7 was not reached at the Factored Power (93/96) then Full Power would be applied. If an engine still failed to reach the calculated Full Power P7 then we would abort (happened to me twice).

I have the calcs somewhere upstairs... will try and dig them out later...

Andy
i'd be interested to see anything you have Andy. Thanks.

Re: A question about throttle settings

Posted: Fri Aug 14, 2015 9:29 am
by vololiberista
Obviously when calculating max P7 it is based on the pressure altitude at the airfield. Which would be the QFE I presume. Correct?

And another Q. What was P7 at idle thrust in ISA conditions?

A question about throttle settings

Posted: Sat Aug 15, 2015 1:34 pm
by Jelle Hieminga
About your first question: not directly I think. Pressure altitude is the equivalent altitude in the standard atmosphere that provides the same conditions as are present on your subject airfield. Generally it is the difference between QNH and 1013, multiplied by 28 (or something between 27 and 30) and added or subtracted from the field elevation.

Re: A question about throttle settings

Posted: Sat Aug 15, 2015 4:07 pm
by vololiberista
Thanks Jelle,
While over in the UK last week I acquired this "for your collection!"
P1000078x.jpg

Re: A question about throttle settings

Posted: Sun Aug 16, 2015 4:58 pm
by Jelle Hieminga
That's a very nice Cruise Control manual! Looks like the larger version (I have an A5 sized version as well). Where did you manage to find that?

Re: A question about throttle settings

Posted: Sun Aug 16, 2015 6:30 pm
by vololiberista
Jelle Hieminga wrote:That's a very nice Cruise Control manual! Looks like the larger version (I have an A5 sized version as well). Where did you manage to find that?
I was over in the Uk for a few days and went to Brooklands. It was one of the manuels in the Sultan's aircraft. Which by the way is in a sorry state externally.