Author Topic: The return of Climb and acceleration (Read 747 times)

SC-Mutt · « **Reply #15 on:** October 26, 2002, 10:17:10 PM »

Interesting thread ! (S!)

SO; If I understand correctly, the RAM AIR effect, (as it relates to Angle of Attack), could be demonstrated by tipping a beer bottle up, to the horizontal, and blowing into the opening.

The amount of beer that remains in the bottle is directly proportional to the density, and velocity of the air pushing against it at the opening.

However, as the angle of attack increases, So does the pitch of the sound made at the opening, indicating that more and more air is moving ACROSS the opening, than INTO it. Thereby reducing the effect of RAM AIR, (which is no longer needed to keep your lap dry).

Yeah.... THAT'S the ticket!

Thanks!
S!

SC-"Mutt"
CO
The Skeleton Crew

"Fly with Honour!"

AcId · « **Reply #16 on:** October 28, 2002, 08:17:57 AM »

I wonder if any of this has anything to do with the fact that I get roughly the same climbrate in my -1 at the default climbspeed (160?) as I do at 200mph.

F4UDOA · « **Reply #17 on:** October 28, 2002, 09:10:19 AM »

SC-Mutt,

I think you just said what I have been trying to say for the last several post but have been unable to articulate.

So the answer to Hitechs original question would be, what he said . Which is.....

Quote

the RAM AIR effect, (as it relates to Angle of Attack), could be demonstrated by tipping a beer bottle up, to the horizontal, and blowing into the opening.

So basically that is why RAM would not be as effective in climb as it would be in acceleration. And that is why it is possible to accelerate better than you climb.

Kapish??

AcId · « **Reply #18 on:** October 28, 2002, 09:18:18 AM »

Quote

Originally posted by F4UDOA
SC-Mutt,

I think you just said what I have been trying to say for the last several post but have been unable to articulate.

So the answer to Hitechs original question would be, what he said . Which is.....

So basically that is why RAM would not be as effective in climb as it would be in acceleration. And that is why it is possible to accelerate better than you climb.

Kapish??

I would agree if it was the Air that was being moved and the Aircraft was stationary, but in the case of flight we are moving an object through the air so I wouldn't think that it would matter what angle the Aircraft was at as long as the RAM AIR intakes are always facing the direction of motion. I wouldnt think the angle of a climb would effect the air flow too much because we are moving in that direction and the intakes are much larger than the opening of a beer bottle. However, I could be crazy.

hitech · « **Reply #19 on:** October 28, 2002, 11:13:03 AM »

F4UDOA: Your AOA is less in climb than in level flight for the same speed and throttle settings. There for if you wish to adjust the ram air it would be just the oposit effect you are trying to prove.

HiTech

F4UDOA · « **Reply #20 on:** October 28, 2002, 01:13:12 PM »

HT,

How is it possible for the AOA to be less in climb than in level acceleration?

I can't even imagine how that is possible to reply to your comment:confused:

In anycase what I have gathered from the post of other contributors is that the Ram Air effect increases with speed and therefore would increase acceleration beyond the linear corresponding climb rate with every mile per hour beyond best climb speed. How much more I do not know.

HoHun · « **Reply #21 on:** October 28, 2002, 02:10:13 PM »

Hi F4UDOA,

>How is it possible for the AOA to be less in climb than in level acceleration?

Extreme example: Think of a vertical climb. The G meter has to read zero in such a climb - you don't need any aerodynamic lift to counteract gravity. (What you need is thrust :-) No lift means zero angle-of-attack, at least as long as our example is based on a symmetrical airfoil.

>therefore would increase acceleration beyond the linear corresponding climb rate with every mile per hour beyond best climb speed.

Could it be that you're thinking that acceleration ability at all speeds is tied to climb rate at best climb speed? In that case, you'd indeed have uncovered a contradiction, so I'll better explain it here:

Acceleration and climb are linearly connected only if you examine both at the same speed. (And it can be quite difficult to deduce the climb rate and acceleration at any specific speed from the climb rate at speed of best climb.)

Thanks to the ram effect, the Corsair does indeed gain acceleration capability in comparison to the F6F without ram when both aircraft are flying at the same high speed.

The good news for you is that because climb is linearly tied to acceleration as long as you look at both of them at the same speed, the Corsair also gains in climbing capability! :-)

That really means that if you go fast enough, the Corsair will not only out-accelerate, but also outclimb the Hellcat! Of course, a very shallow high-speed climb is required, but there's no way the Hellcat can stay with the Corsair in such a situation.

Regards,

Henning (HoHun)

dtango · « **Reply #22 on:** October 28, 2002, 02:29:57 PM »

F4UDOA:

AOA is not the same as pitch angle of the nose. Comparing same airspeeds, in level flight you will need more AOA in order to satisfy the Lift=Weight equation than you will in a climb.

Why? In level flight you have pretty much L=W (lift and weight directly oppose each other). In a climb, 100% of the weight doesn't oppose lift therefore less lift is needed to maintain flight hence lower AOA. In constant speed climbs this difference is neglegible.

Tango, XO
412th FS Braunco Mustangs

niklas · « **Reply #23 on:** October 28, 2002, 05:11:18 PM »

Quote

Originally posted by HoHun
Hi F4UDOA,

Thanks to the ram effect, the Corsair does indeed gain acceleration capability in comparison to the F6F without ram when both aircraft are flying at the same high speed.

Henning (HoHun)

Your example about the vertical tail stand was right, but i disagree with the influence of ram effects. I already said in the other thread that ram effects will only help you when the supercharger can´t build up desired MAP.
If the supercharger does build up desired MAP even without RAM effects, it has actually a negative influence.

niklas

F4UDOA · « **Reply #24 on:** October 28, 2002, 05:52:44 PM »

Niklas,

Could you explain that part about having a negative affect if the engine can acheive Max MAP without it??

If so why would Grumman Test Pilot Corkey Meyer say this??

Quote

The reason that the Corsair was faster in the Main stage blower was because the engine and carburator were provided with Ram Air coming in directly from the forward facing airduct in the wing, where as the Hellcat had the carburator air coming in from the accessory compartment of the fusalauge just behind the engine, with no Ram Air affect. Our airplane was getting carburator air at the same pressure as if it were motionless on the ground and the Corsair was getting supercharged air from the speed of the aircraft giving it more power (speed) in the main stage blower

Could it be that there is no supercharging used in the Neutral blower stage.

Dtango,

I'am just going to have to push the accept button and move on with this AOA thing. Unless you type really slowly I may not get it.

However just to explain my thought. I am looking at this in terms of pressure in the main supercharger stage. I don't see that the A/C is flying at a true 45 degree angle and that it is really slipping forward as it climbs and therefore looses much of it's Ram Air effect. I just don't think that WW2 fighters had the power to do that unless in Zoom climb. So what would happen is airflow across the air intake instead of directly in as in level flight reducing pressure as in a Venturi rather than "Ramming" the air. Again this is my vision and not necessarily reality. If indeed the A/C truely flew straight even when climbing I believe evn I would understand that the only variable would be speed, not AOA.

HoHun,

No I don't think that acceleration is tied to best climb speed but that they are linear at corresponding speeds. My point being that if Ram Air provides any assist at all then it provides greater assistance at moderate to higher speeds rather than lower speeds. For instance if it provides 1% greater power at 100MPH then 5% at 200MPH and 10% at 300MPH. I am making these numbers up of course. However if Ram Air provides any additional power in level flight than in climb then that advantage would be greatest at higher speeds.

HoHun · « **Reply #25 on:** October 28, 2002, 05:54:54 PM »

Hi Niklas,

>Your example about the vertical tail stand was right, but i disagree with the influence of ram effects.

You're correct that it depends on the exact supercharger configuration, and it depends on the speed and altitude as well, but for the sake of the example, I just assumed ram effect was always beneficial :-)

(Another factor not usually evident from power charts is exhaust thrust, which also gives more power at higher speeds so that it's somewhat similar to ram effect in that aspect.)

Regards,

Henning (HoHun)

HoHun · « **Reply #26 on:** October 28, 2002, 06:08:01 PM »

Hi F4UDOA,

>However if Ram Air provides any additional power in level flight than in climb then that advantage would be greatest at higher speeds.

Yes, exactly, that's the point :-)

Here's a quote from the FM-2 manual:

"12. CLIMB

a. DISCUSSION.-The best climbing airspeed for this airplane is about 125 knots indicated. Speeds slightly higher than this have very little effect on the rate of climb but result in better cooling. At these relatively low speeds it should be noted that the resulting reduction in Ram brings about a lower airplane critical altitude. [...]"

Regards,

Henning (HoHun)

dtango · « **Reply #27 on:** October 28, 2002, 09:40:15 PM »

F4U:

Yes, I understand what your logic is which is increased AOA leads to reduced ram-air effect.

What I'm saying is that AOA is lower (not higher) in a climb vs. in level flight. This is what HT is saying. Using your logic this would mean increased ram-air effect in a climb vs. decreased.

As for ram-air effect I'm not an expert on that topic and need to do just a little research on it to make sure I understand the impact to WW2 piston engine performance. From what I can gather though ram effect has negligible impact when you're talking about the same altitude and just minor impact when comparing different altitudes (in higher alts ram effect will lead to a slight increase in available horsepower due to lower air temperatures).

Performance differences for rate of climb / acceleration characteristics is predominantly a function of understanding and analyzing "excess power" and the major variables contributing to the relationship.

Tango, XO
412th FS Braunco Mustangs

niklas · « **Reply #28 on:** October 29, 2002, 04:18:50 PM »

Quote

Originally posted by F4UDOA
Niklas,

Could you explain that part about having a negative affect if the engine can acheive Max MAP without it??

If so why would Grumman Test Pilot Corkey Meyer say this??
[(QUOTE]

I already explained it in the other thread.

And the test pilot was wrong.

At the end the Corsair was faster because it had a better aerodynamics. It was maybe the first american design with radial engine where they didn´t make the fuselage even larger after the huge engine.

Oh btw, air inlet ducts are pointed are bit downwards, to have optimum effects at certain AoA. It is a design question, and NACA did some tests.
Anyway it won´t help you at full MAP.

And imo F6F climbs too good in AH, and it isnt the F4U that climbs too bad.

niklas

funkedup · « **Reply #29 on:** October 29, 2002, 04:35:56 PM »

Niklas, if you increase inlet pressure to a compressor, and hold outlet pressure and flow rate constant, it requires less power to run the compressor.