Auto-Climb Model Testing

[EagleDNY]

OK - so I got curious after reading Fritz Wendel's (Messerschmitts 262 test pilot) flight testing notes and did a few of tests of my own.  Specifically, the notes had a chart of the optimum climbing speed of the 262 in 2,000m increments up to 10,000m.  

The "official" optimum climb speeds are listed as follows:
00000m - 475kph (295 mph)
 2000m  - 500kph (310 mph)
 4000m  - 525kph (326 mph)
 6000m  - 550kph (341 mph)
 8000m  - 600kph (372 mph)
10000m - 650kph (403 mph)
along with a note to "always climb at optimum speed, never more slowly".  There is also a note that the 262 has an "altitude compensated ASI so indicated speed is equivalent to true speed above 400kph".

Figuring that I wouldn't be able to get true speed accurately, I did a simple "time to altitude" test using the auto-climb, and then I'd see if I could beat it manually using the chart above as a reference.

Run 1: Autotakeoff / Autoclimb - autopilot kept flaps out entire time.
Run 2: Autotakeoff / Autoclimb - flaps retracted by me on takeoff
Run 3: Manual / flaps out on takeoff, retracted at 1,000 ft, flown to keep speed as close to chart as possible.

Data - 0 - 18,000 ft.
Altitude   -   Run 1 --   Run 2  --   Run 3
3,000 ft   -   01:26 --  01:34  --   01:41
6,000 ft   -   02:44 --  03:03  --   02:42
9,000 ft   -   04:04 --  04:17  --   03:44
12,000 ft -   05:25 --  05:33  --   04:51
15,000 ft -   07:04 --  06:58  --   06:06
18,000 ft -   08:53 --  08:38  --   07:31

Obviously, this tells me that the autoclimb settings aren't giving me the best climbing performance available in this aircraft.  So my question becomes - why?  Is this an indication of a flaw (or limitation) of the autopilot - is it simply unable to figure my best climb speed at any altitude?  Is it just picking a "single best climbing speed" and sticking to it throughout the climb?  

You folks who have been compiling rate of climb charts for the various rides...  if you are using autoclimb to collect the data, you might want to think again about the methodology.

EagleDNY

[hitech]

is it just picking a "single best climbing speed"

Yes it is.

[mussie]

I thought auto climb was dependant on the .speed nnn setting

[EagleDNY]

Hmmmm.  Is it trying to keep an indicated or true airspeed setting for each ride?  

Looks like I'm going to have to start posting climb charts all over my computer room walls to get the best climb performance....

[Krusty]

Originally posted by mussie
I thought auto climb was dependant on the .speed nnn setting

It is, however every plane has a default value set that is "best general speed" for that plane. I.e. 170 in Fw190, 160 in spitfire, 150 in P51 or whatever.

[scottydawg]

Originally posted by Krusty
It is, however every plane has a default value set that is "best general speed" for that plane. I.e. 170 in Fw190, 160 in spitfire, 150 in P51 or whatever.

How do you clear that setting if you screwed up and set it different?

[Krusty]

It resets to default every time you up a new plane. If you change it without checking first -- you're SOL. You can estimate without much loss of climb rate. Most US planes are about 150. P47s are about 170. 190s are about 165-170. 109s are about 150. Most RAF planes are 160 (including the lancaster). Most VVS planes 150-ish. I've noticed you can +/- 10 mph or so from the default without much loss in rate of climb.

I've gotten into the habit of pulling up E6B and checking the default climb rate before I type in a .speed command. That way I'll know what to set it back to if I want.

[parin]

Looks like I am going to have to find some operation manuals to get the most out of my rides. Thank for the very interesting post.

[EagleDNY]

I'm happy the new patch has the climb rate listed in the e6b - it should make it easier to determine the best climb speed for each ride that way.

The problem really is that the best climb speed varies with altitude, and that the autoclimb doesn't adjust for that.  It isn't a "bug" or anything, it is apparently just a limit of the autopilot.  With a few charts and some .speed settings on my part, I figure I can get a better result than just letting the autopilot climb out the entire way.

The way I figure it is a minute or two shaved off my climb to altitude is that much better for my bomber intercepts.

EagleDNY

[Badboy]

Hi EagleDNY

The rule of thumb you should use in Aces High is:

For a Prop' fighter fly the constant IAS given by the auto pilot. That means you can simply leave the autopilot on.

For a Jet fighter fly the constant Mach number that corresponds to the IAS at SL given by the auto pilot. That means you need to adjust continuously to maintain that Mach number, which is very easy once you get the hang of it. (If you have a problem with that, we can meet in the TA to resolve it)  So, the best climb for the 262 should be flown at a Mach number of 0.37 if you do that you should be able to make a significant improvement in your climb times.
 
For example, you posted a time to 18k of 7:31. I just did a climb out in the main arena, starting with 100% fuel. I got to 18k in 6:40 by using the rule explained above.

Originally posted by EagleDNY
The problem really is that the best climb speed varies with altitude, and that the autoclimb doesn't adjust for that.  It isn't a "bug" or anything, it is apparently just a limit of the autopilot.  With a few charts and some .speed settings on my part, I figure I can get a better result than just letting the autopilot climb out the entire way.

For practical purposes, the best climb speed is constant, but for Prop's you should use constant IAS, and for Jets you should use constant Mach number.

Hope that helps...

Badboy

[0verlag]

what hitech said, but also i think with jets, the power sorta increases the faster you go.

I never use autoclimb in a Me262 or Ar234...they need better management, where as a prop fighter seems fine on autoclimb