Economy flying.

[AdamFrisch]

Has anyone explored the range and endurance of normal GA aircraft and have some experiences to share?

I'd imagine that pulling back on the throttle on, say, a 152 to 1500 rpm or lover would increase your range quite substantially. I don't have a POH handy, so I can't reference anything, but it would be fun to know how much range you could get out of a 152, or any typical GA airplane. Anyone had any experiences or can reference a POH on their make and model on this?

[flybymike]

I'd imagine that pulling back on the throttle on, say, a 152 to 1500 rpm or lover would increase your range quite substantially.

I dont think a 152 would remain airborne for long at 1500rpm or lower...;)

[fuzzy6988]

For the C-152s I typically fly:

Range:
From 315nm at 75% power at 100KTAS. Up to 430nm at 45% power at 77KTAS. This varies with altitude - generally the higher you go, the slight lengthening of range.

Endurance:
From just over 3 hours at 75% power. Up to 5.6 hours at 45% power. Again varies with altitude - generally the higher you go, the slight shortening of endurance.

The above figures assumes full weight, leaned mixture for cruise, standard temperature, zero wind and standard (ie. not long-range) fuel tanks. There is another 45 minutes reserve.

Where I learnt to fly in Florida, A.R.R.O.W. documents must legally remain on board. A good thing IMHO.

Now that I'm back in the UK, I've gone and bought a C-152 "Information Manual" which is essentially photocopied pages out of the original 1981 POH/FM. I think it's a good idea to study the POH/FMs when you've got time.

I plan conservatively. This means max 2h30m (fuel pump to fuel pump) for me - less if flying in IMC - although I'm sure more experienced pilots could squeeze more out of it.

More advanced GA aircraft actively measure fuel consumed since the last fill.

[AdamFrisch]

Interesting.

Has anyone tried even lower settings than the published ones? I can't remember the flaps up stall speed for a 152 at the moment, but let's say you flew +5 knots faster than that - what would your range be? At some point I'd imagine that the effects of a headwind or a crosswind component would start to effect adversely at such slow speeds.

I know the twin Skymaster drops from 23 gph to about 13,5 gph from 165 knots to 125 knots. That's a lot. But still way above stall speed - how much more range could be had if you dropped it to 90 knots?

[flybymike]

I know the twin Skymaster drops from 23 gph to about 13,5 gph from 165 knots to 125 knots. That's a lot. But still way above stall speed - how much more range could be had if you dropped it to 90 knots?

Speed is irrelevant. The lowest and highest attainable speeds are only attainable at maximum power.

[Pilot DAR]

Adam,

Some research (Google search) of "power curve airplane" will provide the answers you are looking for. Depending upon the pitch of the propeller, most of your GA fixed pitch propeller aircraft will not maintain level flight below about 1900 RPM. Roughly, whatever speed the plane is flying at that power setting, will be the speed for best economy. It's a little more complicated than that, but it'll get you close. Best climb and glide speed factor into this too.

Should you choose to fly at a lower speed than that, in level flight, you will find that considerably more power will be needed, right up to full power around stall speed. Don't do this without competent instruction. Don't do it for very long even with instruction, as it is just terrible for air cooled engines.

You are not going to change the operating cost of a 152 much by flying at differing power settings lower than 2500 RPM. Yes, if you are flying a 230 to 300 HP larger GA aircraft, you will economize noticeably at lower cruise speed, but it still has to be a "cruise speed".

Once you've looked at the power curve theory, you can go and figure out the power curve for the aircraft you fly. Just plot the points on graph paper of indicated airspeed vs RPM. get as many points as you can. you will see that the points you plot form a "bucket" shaped power curve for your aircraft. You will come to notice that for every power setting other than the "bottom of the bucket" power setting, there are two airspeeds at which the aircraft will maintain level flight. One is in front of the power curve, and the other "behind the power curve".

Once you've done it, it will all make sense...

[AdamFrisch]

I seem to remember that time when I thought, "damn, this plane is a dog in climb", only to realize that the friction nut had come loose on the power and the rpm had dropped to somewhere around 2000 rpm. This was in a fully loaded 172 and she still gave about 300 fpm.

Next time I'm up I'll experiment with this and see what rpm I can get. But I think that 1900 rpm sounds a bit high, but I could be terribly wrong.

[Pilot DAR]

Hmmm.... I'd do some more checking. A heavy 172 is not going to climb at 300 FPM at 2000 RPM. It's probably not going to climb at all... 'Sure you weren't flying a Caravan?

[palou89]

AdamFrisch (http://www.pprune.org/members/152041-adamfrisch)
The speed you would need to fly for maximum time aloft is Vx corrected by weight and not so high up as it decreases endurance. I'd say that is about 1700 to 1800 rpm on a c152. If you slow down past Vx you enter the reverse command region and you will need more power to maintain altitude.

Maximum range on non wind conditions is Vy, again corrected for weight and altitude.

I think I once tried the max endurance thing on msfs and the thing went on for like 10hrs on a 172 (I accelerated the sim time of course) :}

[IO540]

I (and many others) have found that lower prop RPMs deliver better MPG. I reckon 10% better at 2200 than at 2500, for example.

The reason for this is not clear but appears to be principally due to LOP combustion taking place more slowly, and a slower RPM matches the combustion pressure/time profile more optimally to the crankshaft angle.

Of course, flying slower gives you better MPG anyway, so to test this one needs to do it carefully, keeping IAS (i.e, thrust) constant, etc.

But all this is viable only with a constant-speed (variable pitch) prop. With a fixed pitch prop you may not be getting enough power to fly, at the lower RPM. And if you reduce the RPM you will fly slower, so you will get a better MPG, but this is not (mainly) due to the lower RPM; it is due to being closer to Vbg :)

[hhobbit]

CTSW, 912 ULS, 7-7.5 l/hr one up with half fuel, 8-8.5ish two up. Informal check Speed 64-70 kts IAS did not appear very fussy, but flow meter resolution was 0.5 l/h. using Dynon flow meter.

[Big Pistons Forever]

One of the most effective ways to improve the economy of any flight is to effectively lean the aircraft. In simple fixed pitched prop , carbureated aircraft
running at low power settings, like 55%, it is pretty much impossible to hurt the engine by overleaning. Slowly lean the engine untill it is starting to run rough and then enrich it just enough to obtain smooth operation. However make sure you go to full rich before increasing power !

[palou89]

Have anyone ever calculated the fuel savings achieved by leaning rather agresively and compared them to the extra cost of actually having to fly 10 to 15% more time to get to the destination? Makes me think if it isnt better just to haul ass at full rich and get there asap (75%MCP).

I'm going to assume the increased engine wear will outweigh the benefit of actually having flown more NM from TBO to TBO.

[PilotPieces]

I have done 5.1 hours in a C-172. Landed with just under half tanks, but a full to the brim bladder :\