Author Topic: RPM adjustments (Read 855 times)

Kruger · « **on:** April 14, 2004, 05:16:31 PM »

In what kind of situations should engine RPM be adjusted - does it give some significant advantages?

SlapShot · « **Reply #1 on:** April 14, 2004, 05:38:51 PM »

When trying to return to base with very little fuel, I will turn down the RPMs first, and then if needed, I will also reduce manifold pressure.

I have laned many times where the engine cut out on final or on the runway ... all leading to a successful landing ... instead of a ditch.

Outside of saving on fuel consumption, I have not done anything else with it.

MOSQ · « **Reply #2 on:** April 14, 2004, 07:38:45 PM »

When gliding it is very important to reduce RPMS all the way down.
Example: You're low on fuel, or you're losing oil pressure, turn off your engine and glide. Reduce RPMs all the way down, you will glide much farther.
Second trick, when gliding use your autopilot. The same setting that gives you your best climb speed just happens to also give you your most efficient glide angle. So cut your engine, reduce RPMs, and engage your autopilot for speed.

SixxGunn · « **Reply #3 on:** April 15, 2004, 09:05:33 PM »

Cutting your manifold presuure and reducing RPMs will greatly extend the range of any plane in the arena.

Here is a cut and paste from the HTC help section for the P51D.
---------------------------------------------------------------
Operating Instructions

Max Permitted Airspeed- 505 MPH

Max Airspeed Gear Extended- 170 MPH

Max G Loading- +8/-4 @ minimum weight

Max Airspeed 10° Flaps- 400 MPH
Max Airspeed 20° Flaps- 275 MPH
Max Airspeed 30° Flaps- 225 MPH
Max Airspeed 40° Flaps- 180 MPH
Max Airspeed 50° Flaps- 165 MPH

Packard Merlin V-1650-7
Emergency Power- 67" @ 3000 RPM, 210 GPH (5 minutes)
Military Power- 61" @ 3000 RPM, 150 GPH
Normal Power- 46" @ 2700 RPM, 86 GPH
Max Cruise- 36" @ 2400 RPM, 71 GPH
-----------------------------------------------------------------
As you can see dropping your MP to 36" and reducing RPMs to 2400 you can more than double your range by cutting fuel consumption by half.

I fly the Yak 9U alot and here is what I do most nights to extend its range. Remember the Yak 9U has no WEP.

Climb at full power to operating alt 42" MP/3000 RPM

Set MP to 36" and RPM 2800 for cruise into operating area.
Make mental note of amount of fuel used to reach objective.
Operate at full power while engaged.

When fuel state reaches my set minimum climb to egress alt and set MP to 33" and RPM to 2500 for max cruise for RTB.

If its a short hop 2-3 sectors to fight I dont worry alot about max fuel consumption.

The above settings will greatly increase the legs of the YAK.

MOSQ · « **Reply #4 on:** April 15, 2004, 11:00:01 PM »

SixxGunn,
You are 50% correct. The fuel burn rates are not affected on all planes. There has been several threads on this in the past. Notably, the P-47 can be drastically increased. It's great to hear the Yak can to, I'll have to test it to see the difference.
Other planes actually fly just as far under WEP as they do on max cruise. For instance the A-5 has cruise settings in the help pages. However I have tested it, It flys the exact same range using WEP and then 100% throttle until dry, as it does if flown with the listed cruise setting. The only difference is the cruise setting takes much LONGER to get there!

HTC is changing this in AH2. Apparently the fuel burn rates will be affected by RPM and manifold.

SixxGunn · « **Reply #5 on:** April 16, 2004, 01:46:09 PM »

Ah thanks MOSQ.

i really didnt know that all planes were not affected. Thats nice to know.

I fly the Yak 9U and on maps like Pizza and Big Isles I use Cruise and Max Cruise settings to extend the range and still leave enough loiter time over target.

A squadie flys the Yak 9T and says has mentioned that he cant get as far as I have in the 9U.

Thanks for the info, I to will pay closer attention to some other AC to see how MP/RPM settings affect burn time.

beet1e · « **Reply #6 on:** April 18, 2004, 11:03:46 AM »

Quote

Originally posted by SlapShot
When trying to return to base with very little fuel, I will turn down the RPMs first, and then if needed, I will also reduce manifold pressure.

I have laned many times where the engine cut out on final or on the runway ... all leading to a successful landing ... instead of a ditch.

Outside of saving on fuel consumption, I have not done anything else with it.

Slap - in AH, how do you adjust manifold pressure and RPM independently of oneanother? I'm not sure I understood you correctly.

snake339 · « **Reply #7 on:** April 18, 2004, 11:12:26 AM »

adjust rpm with the -or + on number pad manifold set with throttle