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FM ANALYSIS of the HSFX 4.1 P-47Ds - Printable Version

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- BillSwagger - 07.04.2010

ACE-OF-ACES Wrote:
BillSwagger Wrote:What changes from sea level to 30kft is the pitch angle (and yes AoA angle)

You start of climbing at a steep angle at lower altitudes and end up climbing at a very shallow angle at higher altitudes.

Thus pilots were very use to the idea of changing the climb angel as they climbed

I agree there, but this isn't an extended climb to 30kft, its an extended climb to 10,000ft from 1500 ft. In the context of this test the climb angle doesn't change much.




Bill

- ACE-OF-ACES - 07.04.2010

BillSwagger Wrote:I agree there, but this isn't an extended climb to 30kft, its an extended climb to 10,000ft from 1500 ft. In the context of this test the climb angle doesn't change much.
Well one mans small is another mans big Wink

The only point I am making here is that it was not constant

And that pilots were very use to adjusting the climb angle to obtain the best climb speed as they climbed

Thus I would expect they would changed the climb angle during the zoom to obtain the best time to climb

- BillSwagger - 07.04.2010

I hear what you are saying, but what i'm pointing out is that a plane doesn't typically zoom to a better height if you climb steeper or even straight up. (except jets) There is an optimum angle of climb for each aircraft.

For example, if the pilot was trying to get to 5000ft as quickly as he could, he might opt to point his nose more upward, maybe even straight up. In that case he might beat the tested time to climb to 5000ft but then not have sufficient energy to beat the time to climb to 8000ft, or 10,000ft.

A pilot knows that a zoom climb that points more vertical is not the most effective way to trade energy for height, but it does so in the quickest time.




Bill

- ACE-OF-ACES - 07.04.2010

BillSwagger Wrote:I hear what you are saying, but what i'm pointing out is that a plane doesn't typically zoom to a better height if you climb steeper or even straight up. (except jets)
Agreed 100%

The end height/alt of the manuver is for all intents and purposes fixxed

physics wise (perfect energy transfer wise)

In that the extra 'energy' can only do so much 'work'

The 'work' being done in the 'displacment'

But to be crystal

I never said it would change the end height/alt

What I did say is it would affect the time to took to get to that end height/alt

That is to say differnt angles of zoom will affect the time it takes

Keep in mind the goal of the test was to see how the zoom improved the time to climb (time to alt)

In that if they didn't care about how long it took (ie time)

Then they would just do a standard climb and not care about a zoom climb

A zoom climb is all about the time it takes

BillSwagger Wrote:There is an optimum angle of climb for each aircraft.
Yes and it changes with altitude

- BillSwagger - 07.04.2010

I think that its splitting hairs to think that their climb angles were that much different than the optimum climb angles at those altitudes.



I understand that the steeper the angle the faster the climb, its just that in that context you'd have less height after the initial zoom, and then the extended time to

climb would be lower because you'd be climbing at 165IAS for a longer duration than if you maximized your speed by using a shallower (optimum) angle.

- ACE-OF-ACES - 07.04.2010

BillSwagger Wrote:I think that its splitting hairs to think that their climb angles were that much different than the optimum climb angles at those altitudes.
Well the important thing to note here is there is no

- BillSwagger - 08.04.2010

I guess in my head, i'm thinking the steeper you climb the less the wing helps in lifting the aircraft against gravity.

So the steeper you climb the more thrust is required to achieve the same height as you might at a shallower angle. I don't think displacement is the same.


I think in the context of the test, the optimum angle of climb does not change much from 1500ft to 10,000ft.



Quote:The reason it is so close to a constant is that the best climb speed tends to be slightly above the stall speed.

Actually, Ace this speed is determined more out of engine efficiency than anything else. The plane may infact climb steeper at 140IAS but would not be an efficient use of fuel or power. Furthermore, it may not actually increase the rate of climb at all, so climbing steeper would waste fuel and engine life with out any gain.

There are several German tests on the 109 for determining the appropriate angle of climb and much of the discussion involved airspeed because it helped keep the engine cooler.


Bill

- ACE-OF-ACES - 08.04.2010

BillSwagger Wrote:I guess in my head, i'm thinking the steeper you climb the less the wing helps in lifting the aircraft against gravity.

So the steeper you climb the more thrust is required to achieve the same height as you might at a shallower angle. I don't think displacement is the same.
But in a zoom climb your not using your thrust as much as you are converting your speed to height

BillSwagger Wrote:I think in the context of the test, the optimum angle of climb does not change much from 1500ft to 10,000ft.
Well that depends

One mans big angle is another mans small angle

I will say this

That 'I think' the angle changes alot between 1500ft and 10,000ft during a standard roc test

So with that said

Help me calibrate your statment

How much angle change do you consder to be 'not much'?

BillSwagger Wrote:
Quote:The reason it is so close to a constant is that the best climb speed tends to be slightly above the stall speed.

Actually, Ace this speed is determined more out of engine efficiency than anything else. The plane may infact climb steeper at 140IAS but would not be an efficient use of fuel or power. Furthermore, it may not actually increase the rate of climb at all, so climbing steeper would waste fuel and engine life with out any gain.

There are several German tests on the 109 for determining the appropriate angle of climb and much of the discussion involved airspeed because it helped keep the engine cooler.
Note I did't say how they determined the best climb speed

Only that it is for all intents and purposes constant from SL to 30kft

Unlike the best climb angle which changes alot from SL to 30kft (ie not constant)