RPM/Power Settings

[Heliplane]

I would like to work out the power settings for my engine/propeller combination and wondered if anyone had any thoughts or insights as to how this might be done.

The aircraft is an American General AG5B Tiger and, as AG pilots will be aware (and I believe Grumman pilots too), the performance data in the POH is based on percentage power settings. Unlike, for example, the Cessna POHs, the AG5B POH does not show what RPM will result in the relevant percentage power under specified conditions (altitude, temperature, etc). As such, the cruise performance data in the POH is pretty useless.

The engine is a Lycoming 0-360-A4K and, to slightly complicate matters, the aircraft has a (fixed pitch) cruise prop (a Sensenich 76EM8S10-0-65). AG5B props can be pitched for climb (-61), cruise (-65) or in the middle (-63).

The Lycoming engine manual requires manifold pressure data and, with the plane having a fixed pitch prop, we don't have a manifold pressure gauge.

Does anyone have any insights as to how a power setting grid might be worked out? Ideally I'd be able to input data such as RPM, altitude and temperature in order to obtain percentage power and fuel flow information.

Thanks in advance.

[Above The Clouds]

Here is a link to the Lycoming engine operators manual for all O-360 variants I think it tells you everything you need to know for both variable and fixed pitch props.

http://11hc.44rf.com/manuals/engine-...structions.pdf

[Heliplane]

Thanks - unfortunately nowhere near the detail I need.

[Monocock]

I'm prolly missing something, but what will you achieve by working all this out? If you fly her enough you'll quickly learn the difference between cruise speed and fuel consumption at different power settings, and will therefore know the best way to operate her.

Any numbers you generate after lots of clever theoretical prop-tech and propulsion efficiency research will be somewhat irrelevant won't they?!

I'll put a fiver on 2350rpm being a pretty good "ASI return on fuel expended" in a Grumman with a greedy prop

[Above The Clouds]

Heliplane
Thanks - unfortunately nowhere near the detail I need.

Page 14 onwards seems to give exactly what you asked for, an RPM setting relating to percentage power.
And as Monocock already said fly it and you will soon figure out what you need and what it does, 65% pwr is 2350 rpm with 8 and bit gph
Also you will probably find that when the aircraft was delivered new it would have come with the Lycoming engine manual that's most likely why the AFM is sparse on figures. Of course the other way is to get an AFM from another aircraft type fitted with the same engine model and see if they have produced the figures you want after all it's engine performance you are after so the airframe it is attached to is fairly irrelevant.

[piperboy84]

If you look on the side of the engine there will be a plate that says something along the lines of

"2300/65%. 2400/75%. 2500/80% 2700/100%"

I assume this is benchmarked to sea level at ISA.

My Lyc 180 with FP sweet spot for noise, speed, economy and hopefully engine longevity is 2350rpm leaned from just after take off up to cruise levels of about 2 to 3k then adjusting the RPM and mixture incrementally to suit higher alitudes, essentially using 65% power for everything other than TO and VX climb. I hate wasting gas.

[c100driver]

Or for a few hundred you could just install an Manifold Gauge. Possibly the simplest and least expensive engine instrument.

[piperboy84]

I have a question about the chart the previous post linked to. I have 2 aircraft same make and both with pretty much the same airframes. One has a FP and a o-360-C1F engine and the other has a CSP and a 0-360 C4F, if I'm reading the chart correctly the C4F burns 1.2 GPh less running at the same 65% of power, can the CSP really make that much of a saving ?

[Mach Jump]

...can the CSP really make that much of a saving ?

Yes.

Most normally aspirated Lycomings can be run 'oversquare' by up to 4 'units'. eg. 30"/2,600 rpm (often seen at the start of the takeof run on high pressure days), or 26"/2,200 in the cruise. This is considerably more fuel efficient than running 'square' settings for the same power/same airspeed.


MJ

Ps.

"2300/65%. 2400/75%. 2500/80% 2700/100%.

I assume this is benchmarked to sea level at ISA

And to a particular fixed pitch prop as well. I've never noticed this plate, but I'll look more closely at the next opportunity!

MJ

[vector4fun]

Get a graphic engine monitor, and you can see for yourself how your particular installation likes to run. In my case, with a Lyc O-320, 2450 rpms results in the best balance of egts, (all four cylinders within 25 deg), decent fuel economy, and reasonable chts of 340-360 deg. Every installation is going to be a bit different, especially after a couple decades since leaving the factory. Just overhauling my carb made lots of difference. (for the better)

[Mark 1]

Unfortunately, you will need to know MP and RPM to ascertain power, unless the manufacturer has calculated a table of RPM and altitude for power for your particular engine/prop combination.

If you are running at peak EGT or leaner then fuel flow correlates closely with power at about 0.4 lbs/hp/hr. E.g 8 galls/hr = 48 lbs/hr = 120HP which would be 75% for an O320 or 67% for an O360. If you're rich of peak that would be an over-estimate.