Quite, and there always seems to be a howling crosswind on pprune;)

I think MarkerInbound pretty much nailed it. Torque as an absolute number(or power/thrust) isn't a particularly relevant number to the driver. Does a pilot really care if the engine is putting a 1 million whatevers, or does he(she) cares about how much of what's available is being used? Hence percent makes the most sense. If the pilot is thinking they need more power and looks down and sees the gauge is already at 100%, then they know they better come up with another plan. OTOH, if the gauge says 50%, well then bring on the power http://images.ibsrv.net/ibsrv/res/sr...ies/thumbs.gif


Same reason turbine engines display percent rpm, rather than rpm (ignoring for the moment that in most cases, redline is significantly higher than 100%http://images.ibsrv.net/ibsrv/res/sr...y_dog_eyes.gif )

Our Proteus engines were limited to 11,775 CRPM on T/O, with the F/E getting those last 5 crpm manually.


As an "interested pilot" I was invited, on my own, to visit the people concerned. They were able to assure me that we "always flew at I.S.A." . They appeared to have no other information.


( Or did we not understand one another ? Sometimes it WAS hot, and sometimes it was cold... Was there a difference ? Could we use a higher cruising CRPM sooner when it was cold ?) Perhaps I was asking too much !

on bigger aircraft the value is often presented in percent since the raw number might get too high to write it usefully down on the instrument.

the interest for a pilot is a gauge which shows him the limits not too overstress the engine , not the factual number what it is.

no gauge in output of horsepower since only chasing a certain power output may result in bursting limits of temperature , torque or core speed in different ambient conditions or prop rpm settings.

cheers

Aero Commander 690B

Torque gauge in Horse Power

Photos: North American Rockwell 690 Turbo Commander Aircraft Pictures | !!!!!!!!!!!!!!


Top gauge on the instrument stack.

The 690 has TPE331s, single shaft engines, so meeting my criteria in post #11.

The torquemeters in the DC-6 are calibrated in psi of Brake Mean Effective pressure (BMEP) which is intended to be the mean pressure acting upon each piston, minus mechanical losses, which is a particularly arcane and useless quantity to all but an engineer designing engines. But, like Lord Lucan said, it's just a number, representing a certain value of torque. know what number you need to see on the gauge and it doesn't matter what the units are.

Other Pratt and Whitney radials had torque meters calibrated in PSI of torquemeter pressure, and the actual measured quantity in the torquemeters in P&W radials was oil pressure in a set of hydraulic pistons in the gear reduction drive. Again, a completely meaningless unit to the pilot.

Yeah, provided the engine is turning at 2800 RPM The torquemeter reading for the 1400 hp power setting is actually greater than the torquemeter reading for 1500 HP, as the you use 2200 rpm for 1500 hp and 2000 RPM for 1400 RPM, so torquemeter readings are not directly a measure of power, RPM needs to be considered also.

I used to remember the formula for 2800s, BMEP and RPM and k and I think phase of the moon and out came HP. Now all I remember is 243 and 165, I can't remember what RPM we cruised at.

Let's not get started on Water Methanol Check Pressure.

Then there's EPCP on the RR Dart, which was only correct at 15000 rpm IIRC.
Purely PSI, something like 450 dry or 500 wet I think, for the Mk 532.

Well since you did...

On the RR 542s we called it Min Torque if we were going dry and WMCP if wet. The number varied for each engine but if you saw it's number you knew you were getting at least 2305 or 2750 shp, dry or wet.

Ahh the old RR computer. Indeed it was a min torque to. Confirm the necessary performance. When using the jepp performance charts on the garrett there was a reduced torque, problem is that you could only use it if fullpower was available, and couldn't use it on contaminated runways, in other words no good for summer, and no good for winter