A fundemental view on Weight and E state and its role in ACM

[Mace2004]

This is exactly what I mean about the dangers of over-generalization.  Looking at the velocity history you can't conclude the impact of mass.  The reason the velocity graphs cross at 1/3 is because the increasing thrust of both aircraft play a factor.   Thrust just doesn't kick all of a sudden even for the heavier A-20 but it's impact grows at some exponential rate.  What you're seeing with velocity history is also the interaction of the thrust of even the heavier A-20 that contributes.  The P_S curve uncovers what's going on and tells exactly when the effects of mass are negated.  The velocity curve doesn't.  Nor does the altitude-time history.

  This is why you'll never find charts of velocity history in aircraft performance manuals....however; you will find P_s.

[humble]

Thank you very much for the clarification, didn't mean to run you thru all the math

[BaldEagl]

Wow.  Just wow.  dtango you know WAY too much.

Thanks for the post.

[TequilaChaser]

Guys,

I'd like to inject a little science into this discussion. The result may be surprising to some, and will demonstrate the truth of Mace's and dtango's excellent posts, and also explains Humble's contention in the original post that the much heavier A20 can outzoom a much lighter aircraft like the NIK2.

The first thing I hear you asking, is how can Mace, dtango, and humble all be right at the same time, they seem to be saying different things?

Just bear with me, I can show how they can all be right, and to do that I'm going to start with Newtons second law. f = ma. and we must resort to a little math, just to maintain clarity and credibility.


Hope that helps.

Badboy
  

I think this post proves no misinformation was given by the OP........and it helps clear it up and clarify different methods of retrieving the nearly same outcome.....

another question, if it even has any part of the overall picture ? would be how much does a prop planes ability to generate the most thrust it can muster the slower it gets plays into the scheme of things when talking "Zoom ability"?


btw......I truly enjoyed reading this thread.......

[Badboy]

I think this post proves no misinformation was given by the OP

Not quite, the conclusion regarding the A20s zoom performance was generally good, but the reasoning leading to it was not, as explained earlier in this thread by Mace.

Badboy

[mechanic]

From this day forth let us recognise the creation of a new dweeb.
The Ps dweeb

eg: "Oh yeah, great cherry pick you Ps dweeb. Try fighting me on equal Ps and you will die!"

[dtango]

another question, if it even has any part of the overall picture ? would be how much does a prop planes ability to generate the most thrust it can muster the slower it gets plays into the scheme of things when talking "Zoom ability"?

TC:

The variation of thrust with velocity is a big reason thrust is a significant factor in zoom climb performance.  As you probably know one basic equation for thrust is:

Thrust = Engine BHP * propeller_efficiency / Velocity

Looks simple but there's a lot going on even with this equation.  First thrust is a function of airspeed.  Thrust INCREASES as airpseed DECREASES. 

Second thrust is also a function of propeller efficiency.  Propeller efficiency is a non-linear curve.  It is a function of propeller and blade geometry and also varies with airspeed.  In my basic model I've used a generalized prop efficiency equation.  For our purposes propeller efficiency varies directly with airspeed (increases or decreases with increasing or decreasing airpseed).

So how does all this play out in a zoom climb?  As speed decreases, thrust overall increases.  We can see this in our acceleration component breakdown graph.



The acceleration-due-to-thrust curves (solid lines) are nothing more than thrust divided by mass (thrust/mass) and is representative of the thrust curves.  As you can see thrust increases over the time history because in our zoom climb we are decreasing in speed.  As we get slower and slower, thrust's contribution grows.  Of course it's hard to visualize what this means in terms of aircraft energy by isolating thrust like this.  That's where the P_S graph comes into play because it gives us a combination view of how thrust, drag, weight, and airspeed interact.



So from my basic model the answer to your question is embedded because we've factored in thrust variation with airspeed and propeller efficiency.

One caveat I should point out here: engine BHP also varies with altitude as well because of variation in air density.  Super-charging and turbo-charging play a role in engine BHP output and it's variation with various gearing etc.  I assume constant engine BHP in my basic model vs. trying to model engine power output variation with altitude.

Tango, XO
412th FS Braunco Mustangs

[humble]

I've got no issues at all with any of my initial statement/comments being corrected. It was in fact invited and is appreciated. What I do find interesting is the feeling that the overall thread and math do validate that within a certain band of parameters the A-20 does enjoy a superiority over most fighters in short sprint type of zooms. Obviously the actual physics and math are beyond my understanding and previous exposure but what I tend to get is that the A-20 in a powered dive to zoom has a window where the combination of mass and thrust act together to create a benefit before the mass begins to counteract the thrust. I tend to use a lot of "pop up" verticals or porpoising to generate climbing rolling scissors and have found the A-20 very effective in that regard. I'm trying to better understand an observed set of events. I know that if I put the a-20 under load in the verticals it wears down quickly. However if I can "cycle" the plane in a largely unloaded state it does a tremendous job of retaining E vs other planes.

What i'm finding is that my evolution of tactics via trial and error matches up pretty well with what I'm reading here....

[SlapShot]

you never go angles with an A-20...always suck the E out then pick it apart...

A lesson that Cobia taught me the HARD way ...

[TequilaChaser]

Not quite, the conclusion regarding the A20s zoom performance was generally good, but the reasoning leading to it was not, as explained earlier in this thread by Mace.

Badboy

my Bad..... guess I was 1/2 right..thank you for fixing my post, BB <S>


and thanks for your detailed reply, dtango <S>

[Agent360]

I've got no issues at all with any of my initial statement/comments being corrected. It was in fact invited and is appreciated. What I do find interesting is the feeling that the overall thread and math do validate that within a certain band of parameters the A-20 does enjoy a superiority over most fighters in short sprint type of zooms. Obviously the actual physics and math are beyond my understanding and previous exposure but what I tend to get is that the A-20 in a powered dive to zoom has a window where the combination of mass and thrust act together to create a benefit before the mass begins to counteract the thrust. I tend to use a lot of "pop up" verticals or porpoising to generate climbing rolling scissors and have found the A-20 very effective in that regard. I'm trying to better understand an observed set of events. I know that if I put the a-20 under load in the verticals it wears down quickly. However if I can "cycle" the plane in a largely unloaded state it does a tremendous job of retaining E vs other planes.

What i'm finding is that my evolution of tactics via trial and error matches up pretty well with what I'm reading here....

I have read this thread with much interest.

The math proves the increased mass does not help in a zoom.

But in regards to the A20 having a zoom advantage in certain slices of the equation is only fleeting. I think this is all related to the "impression" of energy.

Looking at the whole of it all it is very apparent that there is NO WAY an A20 has ANY advantage over a more nimble fighter. It all comes down to angles.

Although the A20 can create angles based on the aforementioned zoom advantages that is easily neutralized by the lighter and more nimble fighter.

In my opinion the only advantage the A20 vs any fighter is the "greed" factor. If one chooses to go for guns on the A20 at the WRONG time then you will be in guns on the next maneuver.

However, if the fighter recognizes the E state of the A20 it is a very simple matter of maneuvering into the correct angle or just bleeding the A20's energy. Its not like the A20 is going to "exit" any close fight. The A20 isn't going anywhere. He is screwed once the dance begins.

The only pilots falling for the A20 "zoom moves" are ones who don't know much...new players...etc. Now I will admit I was suckered by some A20 moves a few times myself....Cobia is the one I remember shooting my arse down.

As long as the A20 can maintain an excessive energy state it can pull the vertical. But as I said that is only fleeting.

Beware of the fighter who pulls up and exits in the vertical for it is only a matter of two turns before the A20 is caught.

[mechanic]

Good point, Agent.
Would you say that the rare 'masters of the A20' are the one's who best make use of that fleeting advantage before reality sets in? Similar for me in a mosquito, or indeed maybe for you in a 109K4 vs something like a Spitfire MkIX. You will stand a chance defending that fight if and only if you make use of the fleeting advantages that can be forced into the fight. Missing with that 30mm shot can then spell disaster even for the most experienced. At the top of your game, almost every fleeting advantage will be a decisive one. Only a well versed spitfire mkIX flyer will deny those advantages completely.
 Not sure if i even have a point here, just thinking outloud. What I think I'm trying to say is that the theory of any combat is a simple and obvious scientific study whereas the actual practice, even simulated, is a much more hit and miss procedure with no real way to predict an outcome before the fight. One of the strongest factors envolved in the actual practical experiement will be who can turn fleeting advantage into decisive.

[Hap]

Intetresting thread!

[humble]

I've always felt cobia does a masterful job of using the drag, not the "zoom". He has a tremendous feel for the nose low turn and the ability to control the wing tip stalls exceptionally low. Basically he'll force the overshoot in a nose low configuration, use the controlled stall to set the nose and the inherent stability of the A-20 to saw you apart at almost any range. You cant ever really get as good a feel for your own style as someone else's but I always feel I fly the A-20 much more as an in/out of plane vs overshoot. I look for ways to gain angles up hill and then recoup E while keeping the angles on the downhill runs.

[Agent360]

Good point, Agent.
Would you say that the rare 'masters of the A20' are the one's who best make use of that fleeting advantage before reality sets in? Similar for me in a mosquito, or indeed maybe for you in a 109K4 vs something like a Spitfire MkIX. You will stand a chance defending that fight if and only if you make use of the fleeting advantages that can be forced into the fight. Missing with that 30mm shot can then spell disaster even for the most experienced. At the top of your game, almost every fleeting advantage will be a decisive one. Only a well versed spitfire mkIX flyer will deny those advantages completely.
 Not sure if i even have a point here, just thinking outloud. What I think I'm trying to say is that the theory of any combat is a simple and obvious scientific study whereas the actual practice, even simulated, is a much more hit and miss procedure with no real way to predict an outcome before the fight. One of the strongest factors envolved in the actual practical experiement will be who can turn fleeting advantage into decisive.

What you say here is true. I agree 100%