Badboy is right!

[Dwarf]

Conducted my own set of very unscientific tests.  Here's what I did:

Using a P-51D and full fuel to give time for several tries -
From 11k and 200 on the speedo -
Full power and immediate 0G noseover to what I judged to be 15-20 degree dive angle -
Wait for speed to reach 400 -
Engage autopilot for roundoff to level -
(autopilot usually resulted in an instant of tunnel vision as it took control)
Disengage autopilot as soon as level and initiate an immedite gentle 1.2-1.5G pullup to climb -
Stop pullup as soon as the ROC needle buried at 4 -
Engage autopilot for climb -
Disengage autopilot and roundoff as close to 11k as I could get -

There was some variation in results depending mostly on how closely I hit the desired dive angle.

Once speed decayed to about 275 in the climb, the Pony hung on very tenaciously, and I usually made it back to 11k at about a speed of 225.  A gain of 25 in airspeed from where I started.  Thus a gain in Energy from where I started.

If I let the dive get very much steeper, the gain evaporated.  Or, if I held the pullup a little too long.

Did not test at other altitudes or fuel loadouts, so YMMV, but I wouldn't guess by much.

Badboy was right and I was wrong.

Congratulations, Badboy.  Well done.

Dwarf

[EDIT]  Don't try this at altitudes much below 7k.  I used up about 5k in altitude getting to 400.  More if I dove too steeply.

[This message has been edited by Dwarf (edited 02-09-2001).]

[LLv34_Snefens]

You should time how long it took for your dive and climb back up and then test how much you will accelerate in level flight from 200mph in that time.

[Lephturn]

Thanks for doing some testing!

As long as we gather information, we all win, regardless of the outcome of the tests.  



------------------
Lephturn - Aces High Chief Trainer
A member of The Flying Pigs  http://www.flyingpigs.com
 
Check out Lephturn's Aerodrome!

[Virage]

"From 11k and 200 on the speedo -
Full power and immediate 0G noseover to what I judged to be 15-20 degree dive angle -"

Are you adding power during this stage?

[Dwarf]

 

Originally posted by Virage:
"From 11k and 200 on the speedo -
Full power and immediate 0G noseover to what I judged to be 15-20 degree dive angle -"

Are you adding power during this stage?

I went to full power and started the noseover at the same time.  Thereafter I didn't touch the throttle.

Dwarf

[Dwarf]

Ran more tests handflying all the way.  Only Combat Trim was active.

P-51D and full fuel again.

Roundoff to climb was one continuous 1.5G pull.

Results were very inconsistent with times when I didn't get back to 11k until speed was below 200.  Someone with a smoother stick hand should be able to get better, more consistent results.  Had one run where I had to fight Combat Trim to keep the nose down in the climb.

The entire evolution averaged 127 seconds for me.  

I then timed straight line acceleration starting from 200 at 11k.  Plane on autopilot the entire time.  By this point fuel was down to 1/2.

With WEP: at the 127 second mark plane was clocking approx. 335.

Full Power, no WEP: at 127 seconds speed was just inching past 325.

Did not use WEP for any of the dive tests.  My guess is it wouldn't shorten the evolution by more than a very few seconds.

I was only trying to see if I could return to starting altitude at a greater speed than I started with, not fly any kind of simulated pursuit.

Will try to see if these results hold for other sims as well.

Dwarf



[This message has been edited by Dwarf (edited 02-09-2001).]

[Lephturn]

Dwarf,

If you are testing AH, it's best to do it in the Training Arena online.  In this way you can pick a fuel load, and the gas basically doesn't burn at all.  This will keep your results more consistent.  I'm sure you can set the fuel multiplier offline as well, but I'm not sure what the command is exactly.  I'll look around, and if I can find a reference I'll post it here for you.  It might make things easier.

Also, if you are testing in the TA or offline, be aware that there are fields with a 5k altitude runway.  In Bishop on the current map, A16 is one I believe.  It's always a "rear" field on each contry's home island.  This will let you get to a testing altitude a bit quicker.  Also, I would recommend a less than 100% fuel load to better approximate combat conditions.  50% is usually a good compromise.

Also a couple of comments about your testing procedures.  First, auto-level to level at the bottom of the dive will pull more G's than I think you would hand flying it.  I think that's going to skew the results.  Second, I think 400 might be a bit fast.  I'll try about 325 or 350 I think tonight.

There is also a feature in AH that may help you test this.  We have an auto-trim for speed feature in Aces High that will maintain speed for the airplane by climbing or diving.  This will be a great tool for running these kinds of tests.  Before you start, in the text buffer type ".speed 350" where 350 is the speed you think might be the "magic number".  Now, when you start your test, manually do a smooth 0G shallow dive until you get to 350 Mph.  You may have to ease off of 0G to keep a shallow enough dive angle, but you get the idea.  Now as the plane reaches your "magic number", engage auto-trim for speed by hitting <shift><X> (I think that's the default mapping) on your keyboard.  The airplane will then try to maintain that magic speed, and will slowly ease into a climb as excess power is converted to energy.  You'll have to engage it right at your magic number though, or it will pull too many G's and likely oscillate a bit before it stabilizes.

Ideally, you can now compare the airplane's time to reach 350 in level acceleration to the time it takes for the dive-zoom test to get back to the starting altitude at the target speed.  How's that sound for a methodology?  I think it might help you get more consistent results.

I have to go home and try this tonight in my Jug.    I'll post my results as well.  Thanks for doing some testing.    

------------------
Lephturn - Aces High Chief Trainer
A member of The Flying Pigs  http://www.flyingpigs.com
 
Check out Lephturn's Aerodrome!

[This message has been edited by Lephturn (edited 02-09-2001).]

[Dwarf]

For the first set of tests, I kept testing until the fuel tank was dry.  Fuel load did not seem to make an appreciable difference in the results.

It may have a greater effect for the straight line accel tests.

Dwarf

[Dwarf]

Leph there's gotta be at least 50 better ways to test than what I devised off the top of my head.  What you outline is certainly one.

Done with better methodology, people should be able to achieve much better results than I have.  I encourage them to.

My main concern was to maintain enough climb angle to be sure I got back to 11k in all tests, so I could see what my arrival speed was to determine if any energy gain was really possible.  Beyond that I just tried to remove my own inputs from the process as much as possible.

I'm guessing that the autopilot will have to level you out before you get back to starting altitude at 350.  I'll conduct some further tests at other speeds myself to see what the highest speed is that allows the Pony to continue to climb.

Dwarf

[Robert]

hiya guys
I've been looking at these threads for some time now and was very interested in it all.
so I went and tested some on my own.
At 11k the P-51's top "true airspeed" without wep is 405. At 8k it is about 390. So I tested the zero G dive starting at 200 Indicated to a speed between these speeds and used a 2 G or less pull out and no auto trim at all. Fuel load out was 50%. after the pull out I started a 3.5k climb and held it steady. I tested this 20 times and returned to 11k some 75mph faster everytime.

looks like we've learned something very valuable here.

RWY

[Lephturn]

Your hunch was right Dwarf, the trim levels you too soon.

Just as an FYI, here is what I did.

P-37-D30.  50% Gas.

Start at 150 Mph, go to 275. 10k.

Level, takes about 58 Seconds.

Now, a 0G dive until I hit about 300, then a gentle pull-out and engage auto-trim for speed at 275.  It took me 1:34 on average to get back to altitude at the target speed.

Now that isn't telling us much.  The auto-trim levels me at about 9k every time, and I then sloooowly climb up to 10k.

Here is the second part of the equasion... I get to a high speed earlier... so in terms of my distance from the other guy, I may have gained.  It's tough to tell.

This will be interesting to try with two planes.  Netlag and getting a valid starting position might be a challenge, but I'm sure we can do it.  

------------------
Lephturn - Aces High Chief Trainer
A member of The Flying Pigs  http://www.flyingpigs.com
 
Check out Lephturn's Aerodrome!

[Dwarf]

Pretty much mirrors my results, Leph.

The method I used was to setup my target climb speed.  Go to full power and engage the speed autopilot, letting it handle the pushover, dive, roundoff, and climb back to alt.  I used the level autopilot to finish off at starting altitude.  The only control I touched was the throttle to get things rolling.

Same Pony and (as usual) too much fuel.

Speeds 300 and above resulted in a porpoise partway back up as the autopilot tried to correct for its initial too steep climb angle.  Using 300, I actually bottom out at 350, and use up about 3k in altitude.  The last thousand feet of climb are agonizing, as the climbrate falls to about 500 fpm.

Higher speeds are worse.  325+ results in the climb ending at about 100 fpm for the last thousand + feet.

At higher speeds the autopilot tries to get to target speed too quickly leading to a steeper than optimal dive.  It then tries to return to target speed too quickly, leading to a too steep pullup and the need for the porpoise to correct.

275 and below seem to work much better.  No porpoise and only 2k or less altitude loss depending on speed.

The really bad news is that I could never get back to alt less than 2 seconds behind when a level flier accelerating at the same power level would have reached my speed.  Higher speeds put me even farther behind.

The 250 evolution only takes about 33 seconds, and uses about a thousand feet, but the level aircraft reaches 250 in 31 seconds.  At 28-30 seconds out, the hunter might have a shot opportunity, but I can't guarantee that.

I think the answer for a pursuit situation is going to require flying some kind of rhomboid looking thing.  The hunter will need to level and continue accelerating from his new higher speed before pulling back up into the prey.

So, while you can gain Energy at your current altitude by diving away and then climbing back, it probably doesn't make much difference because it seems you'd gain faster staying where you are.  Average speed over distance covered always seems to be slightly less when you dive.

[EDIT] My best guess at this point is that you may need to assure an average speed 1.414 (square root of 2) times the target aircraft's speed for the length of time the evolution involves.  For very shallow dives and climbs it may be slightly less.  With prop aircraft I don't think that's possible.[/EDIT]

My head's starting to hurt  

If there is a way to get there, I'm not sure what it is at this point.


Dwarf

[This message has been edited by Dwarf (edited 02-09-2001).]

[This message has been edited by Dwarf (edited 02-10-2001).]

[Dwarf]

Let me recap what I believe both Lephturn's and my tests demonstrate.  If anybody has test results that demonstrate a favorable time difference, please jump in and correct this.

Yes, you can gain Energy by diving and climbing back to the same altitude.

Unfortunately that doesn't buy you anything, because the aircraft that remains level can always gain the same amount of Energy in less time.  Thus, by the time you get back to altitude he's already had time to get to an even higher speed.  You've then fallen a step behind on the acceleration ladder.

Once the aircraft involved get much above a speed of 300, you'll probably lose even more ground because you just can't go fast enough to make up for the extra distance you have to cover.  Compression will set in before you can reach the speed you'd need.

Props produce less Thrust with more speed.  All subsonic aircraft generate exponentially more Drag with more speed.

It's the prop's inability to generate the Thrust needed to pay the increassed Drag bill that accounts for the time you lose.

Dwarf