What happened to LW?

[Squire]

Its a thread with many contributors Wilbus, you assume I was aiming at one-and-all, I wasn't.  I have been around long enough to know the "mysteries" of "what its really about", we aren't covering any new ground here...you could cut and paste from any number of previous threads. Thx.

[JAWS2003]

Originally posted by DoKGonZo
OK ... so what you're saying is that if you took the airframes of a Spit-V and a Fw190A, gave them the exact same power available, and threw some sandbags into the Spit to get it's weight the same as the Fw, that they'd climb and accelerate the exact same?

Physics was my worst subject in school, and it shows, but I just want to be sure I understand this.

    -DoK

[Crumpp]

Crummp, do you have any really usefull 190 acceleration numbers? That is time from speed A to speed B for some alts flying level.

Yes.

You are correct about your thoughts on acceleration . But they have nothing to do with grits statment about the releation ship between Acceleration and climb. Gritts is not talking only about max climb rates, but climb rates for any given speed. Infact the relation ship can even been seen and stays true when faster then max flat level speed for any plane.

Yes and you misunderstood my post or I was not clear.  Acceleration in an aircraft is NOT constant.  Your statement is only true for the measurement of the extreme ends of the scale.  In other words from stall speed to maximum speed.  Some aircraft accelerate better in certain portions of the range.  

So while one aircraft may “out accelerate” another in the whole, this may not hold true throughout the envelope.

Good example is the P47D4 using water injection vs FW 190.  No matter what the altitude, in the sprint the FW190 outaccellerated the P47D4.  However in the "long haul" the P47D4 overtook the FW-190.

All the best,

Crumpp

[Glasses]

Sort of like a Marathon runner and a sprint runner.

[Crumpp]

Good example is the P47D4 using water injection vs FW 190. No matter what the altitude, in the sprint the FW190 outaccellerated the P47D4. However in the "long haul" the P47D4 overtook the FW-190.

The FW190G3 was at 1.42ata Start u Notleistung, BTW.

Sort of like a Marathon runner and a sprint runner.

Yes.  An aircraft which can "sprint" is optimized to take advantages that occur in the dogfight.

All the best,

Crumpp

[Karnak]

Crump,

You misunderstood what HiTech was saying.  He is saying that climb and acceleration are the same and any point you choose to measure them at they will be directly related.

Look at it this way (made up numbers), an aircraft that climbs at 1500fmp at 200mph has an acceleration of 10 on our imaginary acceleration measurement.  Further down this speed scale at, say, 225mph, the climb has dropped to 1350fpm.  At that point is must have an acceleration value of 9.  At 260mph it has dropped to 1000fpm, so the acceleration must now be 6.67.

Further, due to the way drag acts, the faster you go the higher it is, you will never see sustained climb rate go back up anywhere on an aircraft's performance chart after peak climb rate has been passed.  Some aircraft are cleaner than others and so will eventually climb faster at a given speed than the other aircraft which when slower, climbed/accelerated better.

It is all very linear.

[Crumpp]

It is all very linear.

It is NOT linear.  You can say that all day long but the reality in the air is different.

Your drag is not linear, why would you think accelleration would be?

All the best,

Crumpp

[DoKGonZo]

Originally posted by Crumpp
...


Yes.  An aircraft which can "sprint" is optimized to take advantages that occur in the dogfight.

...

Which kind of goes back to my race car analogy. Watch an F1 race some time, the cars all have to be within a very narrow range of weight, size, and output due to FIA rules. But it's obvious that some cars accelerate better, some have higher top speeds, and some handle better in turns - all based on factors beyond just weight and power output.

The cars which use more aero for downforce and handling pay for it in top end. The cars which are tuned to pull better out of the turns don't have the grunt available at higher speeds to pass down the straights. There's a balance. It's logical.

Maybe its apples and oranges, but it feels like something's missing.

[Grits]

Max speed is a known for a particular plane. Any speed below that there is potential acceleration. If you are say, 150mph, under your max speed that balance can be traded to produce climb. If you were level, and at full power you would be accelerating, but you are not, you are maintaining 150mph under your max (whatever that number may be). So in reality you ARE accelerating, but part of the energy is used in climb.

It really is a theoretical concept that is different in specifics for every particular plane, but the mechanics of it are the same regardless of drag, wingload or anything else. Excess acceleration is used in climb performance.

[Crumpp]

Max speed is a known for a particular plane. Any speed below that there is potential acceleration.

Aircraft do not accellerate at a constant rate.  It's not theory, it is fact.

All the best,

Crumpp

[Krusty]

A 109E can accelerate from 0 to 150 inside 20 seconds (taking off) but it may take 4 minutes of level flight to accelerate to 350mph. Even in AH acceleration isn't constant.

[Karnak]

Crump,

It is linear.  Perhaps you think "linear" means a straight line on a graph?  I don't know, but you seem to be having a hard time of it.

The faster you go the greater the drag on any particular airframe.  There is never a point at which drag is reduced as speed increases.  I don't think you are claiming that, but your insistance that it is not linear is begining to make it sound like you are suggesting such an absurd thing.

Originally posted by Crumpp
Aircraft do not accellerate at a constant rate.  It's not theory, it is fact.

Nobody has suggested such a ridiculous thing other than you in your descriptions of what others have suggested.  You are reading things into our statements that are not there.

[Grits]

Originally posted by Crumpp
Aircraft do not accellerate at a constant rate.  It's not theory, it is fact.

I never said that, you are making this more complicated than it is. Its more abstract, you are taking it too literally.

Like HT said, if you are at max speed acceleration=zero.

At any speed below max speed (down to stall speed) there is potential acceleration which also=potential climb.

If you can not accelerate you can not climb.

It is not "constant" and every plane will have different potential to accelerate/climb when below max speed.

But...a given plane's ability to accelerate=ability to climb. They are directly related.

[Wilbus]

Saying the best climber should be the best accelerator? If they are directly related I mean.

[Crumpp]

There is never a point at which drag is reduced as speed increases.

Actually there is just such a point.

The lowest point in the total drag force curve corresponds to VL/D, and gives the best lift-to-drag ratio. Using the standard lift/drag model and a little calculus, it can be shown that this occurs right at the point where the induced drag force curve crosses the parasite drag force curve.

http://www.av8n.com/how/htm/4forces.html#fig-force-ias

But...a given plane's ability to accelerate=ability to climb. They are directly related.

Sure over the total envelope.  Other Aircraft may still accelerate faster however depending on the portion of the envelope examined.

The relationship is sort of like wingloading.  A lower wingloaded aircraft does not always outturn a higher wingloaded plane.  Velocity and Power have a large effect.

All the best,

Crumpp