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lindyman
05-22-2004, 04:49 AM
If you've read ORR, you might know that I'm working on a simple autopilot for the purpose of performance measurements.

One of the things I'd like to be able to measure is which RPM gives the best speed, all other things being constant.

This turned out to be trickier than I thought due in part to the slowliness of response, and in part due to the energy stored in the prop.

My idea was to meaure indicated airspeed at a high sampling rate. From that I can deduce acceleration. I can then try to make small adjustments in prop pitch and see the effect it has on acceleration.

Unfortunately, the energy stored in the prop, gives a false positive effect for reducing RPM (for a short while,) which makes this system almost always strive for a value close to the lowest setting.

I can of course add a delay, so that the false positive has died out, but it's not easy knowing how long delay is a good delay, since all planes are different.

Any ideas for a better way to achieve this?
_
/Bjorn.

lindyman
05-22-2004, 04:49 AM
If you've read ORR, you might know that I'm working on a simple autopilot for the purpose of performance measurements.

One of the things I'd like to be able to measure is which RPM gives the best speed, all other things being constant.

This turned out to be trickier than I thought due in part to the slowliness of response, and in part due to the energy stored in the prop.

My idea was to meaure indicated airspeed at a high sampling rate. From that I can deduce acceleration. I can then try to make small adjustments in prop pitch and see the effect it has on acceleration.

Unfortunately, the energy stored in the prop, gives a false positive effect for reducing RPM (for a short while,) which makes this system almost always strive for a value close to the lowest setting.

I can of course add a delay, so that the false positive has died out, but it's not easy knowing how long delay is a good delay, since all planes are different.

Any ideas for a better way to achieve this?
_
/Bjorn.

IL2-chuter
05-22-2004, 08:48 AM
IRL, the most power available is at redline. Max RPM. There is no other possibility. This assumes the throttle is wide open.

If you find out differently in the game, well . . . http://ubbxforums.ubi.com/images/smiley/16x16_smiley-indifferent.gif

"I fly only Full Real in Il2 Forgotten Battles." -Mark Donohue

lindyman
05-22-2004, 08:54 AM
The most power is available at max RPM, but that doesn't necessarily mean max speed, I think (I don't fly constant speed props yet, so bare with me.)
_
/Bjorn.

BaldieJr
05-22-2004, 09:05 AM
Hush hush on the prop intertia http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

I've told people before that you can get max speed+++ buy dumping pitch percentage for a few seconds. No one listens. The keep beating that old drum "MAX RPM = MAX POWER!!".

Yeah sure. But it doesn't equal max speed.

I think RBJ discovered it, and someone said it was an exploit, when in truth, its just physics.

The more you play with that bot, the more you'll understand that most FM experts on these forums are way way wrong.

<pre class="ip-ubbcode-code-pre">
My Specs (read 'em and weep):
* Automatically grinds whole beans before brewing
* Fully programmable 24 hours in advance
* Brew Pause feature lets you enjoy a cup before brewing has finished
* Automatically shuts off when brewing is complete
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lindyman
05-22-2004, 09:24 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BaldieJr:
The more you play with that bot, the more you'll understand that most FM experts on these forums are way way wrong.
<HR></BLOCKQUOTE>

I've already found one rather surprising thing. I'll post stall figures soon. It's exiting to ride the edge of the stall 3m above the water http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif
_
/Bjorn.

Chuck_Older
05-22-2004, 10:09 AM
I keep on hearing about "max power=max rpm".

I am into old cars. I build my own engines. Let's talk about just internal combustion engines here, for a moment.

My 7.5L engine has a redline of 5500 rpm. It will actually go to around 7000 rpm before it blows up.

It makes max horsepower at 3500 rpm (340 hp)
It makes max torque at 2800 rpm (500 ft/lbs). I built this engine to 1970 Buick 455 specs, with 10.1:1 pistons instead of the stock 10.25:1 pistons, and my heads are not Stage 1 heads, so I make a tad less 'power'. If anyone cares to, they can look up specs for the engine to see that I am not making this up.

On Desktop Dyno 2000, when you simulate this engine, the sim calculates my power band almost perfectly. Flat torque curve from 2000 rpm (lowest DD2K will go) to 2800, then a slow drop to 4000 rpm, then it drops like a rock. HP ramps up quickly from around 250 at 2000 rpm to 340 at 3500, then takes the express elevator down once you get past 3500 rpm.

If I went to "max rpm" with this engine, it would make about 50 horsepower, and 100 lb/ft of torque.

Max rpm doesn't equal max "power" just because the engine won't revolve faster.

OK. that engine is not designed to make all it's power at maximum rpm, right? Well, mathematically, rpm and torque meet at 5500 rpm. It's how you determine hp, it's derived from torque. So to me, it is as confusing as hell to know all those things and yet constantly hear "max power= max rpm" (in the flight sim AND car communities) all the time, when I know it's not true.

If we are going to talk about specific situations in which an engine is designed to make maximum "power" (whatever that is supposed to be) at a certain rpm or manifold pressure, can we talk about those as specifics, instead of making sweeping statements like "max rpm=max power"? Because it's ignoring things like manifold pressure as a measure of available power.

*****************************
The hillsides ring with, "Free the People",
Or can I hear the echoes from the days of '39?
~ Clash

[This message was edited by Chuck_Older on Sat May 22 2004 at 09:22 AM.]