Author Topic: The return of Climb and acceleration (Read 760 times)

F4UDOA · « **on:** October 25, 2002, 11:14:08 AM »

Well I have argued that these two areas are not completely linear for a long time and have been shouted down many times.

But I will be short and sweet with this expanation.

The F4U has RAM AIR effect in the main blower stage under 8K and the F6F does not. Why compare to the F6F? Well they have the same engine with the same rated HP, MAP and RPM but the F6F climbs better in AH and therefore accelerates better because as everyone here knows climb and accleration are the same.

Except for Ram Air.

It only affects the F4U in level flight and provides greater engine efficiency at the main Blower stage and should provide for greater acceleration because the engine requires far less effort to reach max map and RPM and HP leading for higher top speed and greater acceleration.

Any comments?

hitech · « **Reply #1 on:** October 25, 2002, 12:56:12 PM »

Quote

Except for Ram Air.
It only affects the F4U in level flight

And why would this be true?

HiTech

F4UDOA · « **Reply #2 on:** October 25, 2002, 01:17:20 PM »

It's not actually. It does affect it in climb but the affect reduces very quickly as the climb is prolonged.

Look at the F4U-1D climb chart and the spike it the climb at sea level in main blower. Niklas mntion he thought that was a Ram Air effect a long time ago but I didn't realize what he meant.

The first 3K are the effect of Ram Air.

Then the F4U reaches 160MPH and stops accelerating and sustains climb at 60" of MAP 2700RPM and 2250HP the same as the Hellcat. Remember the F4U-1D and F6F-5 have the same exact prop blade and number of blades. 6501A-0 for both.

The RAM air effect helps you get there more quickly and efficiently. Once you have achieved your max MAP the advantage is only in engine efficiency.

BTW. I have no source for your Hellcat performance. And I have many. I have requested that you guys share the wealth with some only documentation but I have not heard anything back.

F4UDOA · « **Reply #3 on:** October 25, 2002, 01:34:31 PM »

Hitech,

Here is a quote from Corkey Meyer (Grumman test pilot) on the effect of Ram Air in the two A/C.

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

If both A/C have the same MAP, Prop, HP and RPM then what effect do you believe this would have?

funkedup · « **Reply #4 on:** October 25, 2002, 01:42:17 PM »

Quote

Originally posted by F4UDOA

If both A/C have the same MAP, Prop, HP and RPM then what effect do you believe this would have?

Didn't you read Shiva's post? The F4U will exceed rated power under those conditions.

funkedup · « **Reply #5 on:** October 25, 2002, 01:46:03 PM »

F4UDOA it seems you are still having trouble understanding excess power and how it relates to climb and accelerations. You seem like a smart guy, so I can only assume that our explanations have been inadequate.

This book explains it very well and I suggest you buy it and read the relevant chapters, instead of repeatedly banging your head against the wall in here.

PS, I'm serious, not being a smart-ass.

PPS, It's overpriced on that site. I think I paid about $50 for a used copy.

OIO · « **Reply #6 on:** October 25, 2002, 02:02:49 PM »

dang, I thought he was talking about RAM.

Hair on me neck stood up seeing F4UDOA quoting our beloved RAM as a source!

pssst.. HT.. look at the lil' dive flaps on ze 38 pls? I know you can fix them.. umm... take the laptop with you when you in the toilet, I hear closet coding is a karmic experience.

F4UDOA · « **Reply #7 on:** October 25, 2002, 02:18:20 PM »

Funked,

I didn't see where Shiva said anything about overboost. I whish he did. Then I would say overboost all of the R2800 in AH. But what I understood was that it required less effort to acheive the same boost. Therefore reaching desired MAP faster and with less parasitic loss of power to the engine and prop.

Shiva said

Quote

What ram air does is increase the pressure in the intake, allowing the blower to raise the pressure with less effort, so that more of the engine's power goes to the propellor. If an F6F and an F4U are at 18,000 feet, the intake blower on the F6F would have to add 38 inches of pressure to the incoming air to bring the engine to its maximum rated manifold pressure. The F4U, however, at the same speed as the F6F, would be getting, say, 15 inches of pressure from ram air, meaning that the intake blower would only have to raise the pressure 23 inches to get to the same maximum manifold pressure. This leaves more torque to be applied to the F4U's propellor.

funkedup · « **Reply #8 on:** October 25, 2002, 02:49:02 PM »

Quote

I didn't see where Shiva said anything about overboost. I whish he did. Then I would say overboost all of the R2800 in AH. But what I understood was that it required less effort to acheive the same boost. Therefore reaching desired MAP faster and with less parasitic loss of power to the engine and prop.

Yes that's right, and the "less parasitic loss of power" means there will be increased power output at the crankshaft. Which means the plane goes faster.

HoHun · « **Reply #9 on:** October 25, 2002, 02:55:10 PM »

Hi F4UDOA,

>The first 3K are the effect of Ram Air.

Actually, they're the result of using "neutral blower". The ram effect at climb speed is much smaller than the ram effect at top speed, anyway.

Regards,

Henning (HoHun)

F4UDOA · « **Reply #10 on:** October 25, 2002, 03:48:49 PM »

Funked,

I thought you meant overboosted.

HoHun,

The Neutral Blower stage or main stage is the only one of the three blower stages where the Ram Air effect is different between the F4U and F6F.

That's why it looks somewhat different on the charts at sea level between the two A/C in both speed and climb.

Notice the speed chart shows a clear spike at sea level.

And climb

Surely this also carries over into acceleration.

HoHun · « **Reply #11 on:** October 25, 2002, 04:03:57 PM »

Hi F4UDOA,

>Notice the speed chart shows a clear spike at sea level.

That has nothing to do with ram effect.

You can see the ram effect in these charts, but it's very different from what you're suggesting:

In high-speed level flight with full ram effect, the full pressure altitude of the high blower is at 20000 ft (see speed graph).

In low-speed climbing flight with very much diminished ram effect, the full pressure altitude of the high blower is down at 17000 ft (see climb graph).

The ram effect applies to the entire speed graph uniformly and will leave no trace in form of a spike or something because the aircraft is in a high-speed flight condition all of the time.

Regards,

Henning (HoHun)

Zigrat · « **Reply #12 on:** October 26, 2002, 08:14:13 AM »

ok i will try to explain it

to accelerate or climb your airplane has to have work performed on it, conservation of energy.

so when this work is being done, it can either work against the earth's gravitational force to add potential energy to the system, or accelerate the airplane and add kinetic energy.

F4UDOA · « **Reply #13 on:** October 26, 2002, 04:42:36 PM »

HoHun,

So your saying the faster the A/C goes the more Ram Air helps the engine.

So at speeds above the best climb speed Ram Air helps the A/C accelerate correct.

Am I missing something here?

HoHun · « **Reply #14 on:** October 26, 2002, 07:07:57 PM »

Hi F4UDOA,

>So your saying the faster the A/C goes the more Ram Air helps the engine.

>So at speeds above the best climb speed Ram Air helps the A/C accelerate correct.

Yes, that's right.

The ram effect gives some power at any speed, helping the aircraft to accelerate, but the gain is much larger at high speeds than at the speed of best climb.

Regards,

Henning (HoHun)