Why still no dive acceleration difference?

[MadBlaster]

come on now. 30 seconds...40 seconds??? in la7 or tempest or whatever, you cruise at 3000 meters then enter dive, it takes just few seconds to hit max level speeds and few seconds more to hit max dive speeds. not that long.

[Crumpp]

As I said above, if you are stealing 500HP from your enemy for 30 seconds

Who is stealing 500 hp???

How much excess excess thrust does a P47 have at 20,000 feet in level flight at Vmax?

NONE

How much excess thrust does any propeller airplane have at Vmax?

NONE

If our airplanes Vmax is 420mph EAS and we dive to Vne at what speed does our Excess Thrust produced by the Propeller = 0?

Vmax

How much Excess power does a CSP propeller aircraft have from cruise flight to Vmax to devote to a dive excess thrust?

All of the excess thrust produced to Vmax...at Vmax our excess propeller thrust = ZERO

What speed does a CSP equipped aircraft traveling at cruise flight reach zero excess propeller thrust at in a dive?

At Vmax....the same speed as in level flight

What is the design propeller efficiency for a CSP in an aircraft envelope from Vs to Vmax?

n = .85 from Stall to Vmax

[MadBlaster]

Crumpp, that doesn't seem quite right based on the diagram you posted a few pages back. Peak efficiency 2.2 at Vmax. but, you can still move down and to the right of the curve towards less efficient (advance ratio increasing for a given blade pitch) as the tip speeds increase and approach mach??? As long as the efficiciency value is > zero, don't you have some thrust being produced by the propellar?

edit:
referring to post #143.

[Crumpp]

As long as the efficiciency value is > zero, don't you have some thrust being produced by the propellar?

Sure you have some thrust being produced but it is not EXCESS thrust. It is excess thrust that accelerates the airplane.

In a dive from Vmax, the only excess thrust is the component of weight.


Propeller thrust only accelerates the aircraft within its envelope.

[MadBlaster]

okay, I think I get it. you said it three posts back, I just didn't sink when I read that the first time.

[MadBlaster]

btw, this has been a very interesting thread. thnks for your input guys. i learned some things.

[BlackBerry]

Originally Posted by Crumpp

Sure you have some thrust being produced but it is not EXCESS thrust. It is excess thrust that accelerates the airplane.

In a dive from Vmax, the only excess thrust is the component of weight.


Propeller thrust only accelerates the aircraft within its envelope.

Crumpp, I totally disagree with you. Imagine that you are now flying a la7 with 110% throttle and you get Vmax speed. The efficiency of propeller is 80%, yes, you propeller are producing thrust(not big) which is equal to La7's drag force. Namely, La7 is in equilibrium. You have no excess propeller thrust, right? Till now, we should have no bifurcation.

And then you suddenly turn off your engine and feather your propeller, It's obvoius that you are about to lose speed because your engine is dead, but you push the stick forwards and begin to dive. A portion of gravity will help you counteract the dargforce and make you maintain Vmax during your "dead enigine" dive. If you dive in a more steep angle, you could even faster than Vmax. in another word, you are spending altitude to maintain your Vmax or get even more speed.

During your "dead enigine" dive, if you suddenly turn on your 1850HP engine, will you dive faster? Will engine give you excess thrust?

In my opinion, definitely, you will get greater dive acceleration because your propeller efficiency is 80-60%.

In your opinion, prropeller efficiency suddenly become zero from 80% when aircraft speed is somehow higher than Vmax.

Propeller thrust only accelerates the aircraft within its envelope.

Propeller thrust could accelerate the aircraft beyond its envelope, as long as gravity force comes to help aircraft-----DIVE.

[BlackBerry]

Originally Posted by Crumpp

Who is stealing 500 hp???

How much excess excess thrust does a P47 have at 20,000 feet in level flight at Vmax?

NONE

How much excess thrust does any propeller airplane have at Vmax?

NONE

If our airplanes Vmax is 420mph EAS and we dive to Vne at what speed does our Excess Thrust produced by the Propeller = 0?

Vmax

How much Excess power does a CSP propeller aircraft have from cruise flight to Vmax to devote to a dive excess thrust?

All of the excess thrust produced to Vmax...at Vmax our excess propeller thrust = ZERO

What speed does a CSP equipped aircraft traveling at cruise flight reach zero excess propeller thrust at in a dive?

At Vmax....the same speed as in level flight

What is the design propeller efficiency for a CSP in an aircraft envelope from Vs to Vmax?

n = .85 from Stall to Vmax

I've got your logic, Crumpp. If you still believe that engine could NOT provide excess thrust in a high speed dive, simply shut down your engine. There is a saying:

After loses only then understood treasures.

[Crumpp]

no, that is not what I'm saying. it may provide thrust. but it is not "excess" thrust. that is the key here. excess thrust, excess thrust, excess thrust. it is not excess thrust because Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax. The only way to get beyond vmax and create excess thrust is to dive at the necessary angle. go back and look how he defined excess thrust. it's the difference between the two force vectors. in level flight, the force vector from gravity has no forward direction. at vmax and level flight, there is no more opportunity to create excess thrust from the prop. you have to dive to create excess thrust and acceleration.

You got it!

One small tweak though....

Crumpp posted a diagram on csp propellar that shows you can not have peak efficiency beyond Vmax.

It is not that you cannot have peak efficiency beyond Vmax. You could design such a propeller but there is little point as all performance the airplane cannot sustain is instantaneous. Of course there would be some serious design trade off's to gain such performance as well. A supersonic propeller design would not work very well on a WWII Piston fighter.

http://www.aerospaceweb.org/question...s/q0031b.shtml

The CSP is designed to maintain peak efficiency through the designs sustainable envelope.

[BlackBerry]

I drew these pictures. Hope you understand my opinion about excess thrust.

When speed above Vmax, engine thrust is always smaller than air drag force.

w.jpg

q.jpg