Why still no dive acceleration difference?

[MadBlaster]

Originally Posted by BlackBerry

I know you are trying to get best propeller efficiency by adjusting rpm manually, thinking that fw190 is quite an automatic plane but the pilot is oblidged to be so busy....

I'll carefully calculate Fw190 A8's prop. efficiency.




Prop diameter: 11.98feet=3.33 metre

Prop rpm: 2700*0.54=1458rpm =24.2 rps(100% pitch)

Notice that "B" point is just Fw190A8 max. level speed @19500 ft, that is 648km/h=180m/s

advance ratio=180/(3.33*24.2)=2.23

P47's advance ratio=2.0

So fw190's ratio is NOT so bad as 2.66, just 2.23. My 3-meter vs 4-meter comparation is just a demonstration of how important the diameter of prop. is.



You can see Fw190A8 gets its max. level by using 2700rpm-engine, this is the best rpm for A8, if you fly A8 at "B" point, don't decrease rpm because this will increase your advance ratio, which leads to the moving to rightside on the curve.



At "B" point, A8's tip speed=(180^2+253^2)^0.5=310m/s.

Mach number is 310/316=0.981 Mach, almost 1 Mach.

That means @19500ft, fw190A8 have to make it's propeller's tip speed just equal to 1 Mach, this is the best result, if you decrease rpm, you lose efficiency because "advance ratio" will be greater.

Actually, fw190A8's prop. working piont is "D" with efficiency 0f 60%+, less than P47's 70%, if P47 using 16:9 reduction, thundebolt's working point is "E", 75% efficiency.
Attachment 9555
I am not saying that manual operating rpm is useless, it may help you a bit, but not much.

P47's efficiency advantage may or may NOT overcome its huge weight at high speed, but at least P47 could shrink the third part of the formular which is propitious to fw190. Even fw190 could maintain 100% efficiency all along diving, the importance of 3rd part of firmualar will also be less and less. Don't forget another foumular:

output(HP)=speed(m/s)*thrust(KN)

When you double your speed, the 3rd part of formular will become 50% (and even smaller due to efficiency lose) important as before, the 2nd part will become 400% important as before.
When P47 building up speed quickly, fw190A is doomed to be outdived.

yes. recall, at point A when you enter the dive at ~400 kph, your rpms are at ~2100. So going manual mode allows you to spool up the engine to 2700 rpm at cruise speeds and transfer that power in short order to the prop for better acceleration than auto mode would give you. most of the time you fly in auto mode. just certain situations, you apply manual mode adjustments to the power band, imo. entering a dive, nearing stall speed, ground taxi, air braking, etc.

But to maintain top speed at level flight, agree. don't use manual mode for that.

Maybe they called it 'thunderbolt' because of the dive limit?

Okay, I'm out. Thanks for the discussion.

[BlackBerry]

Maybe they called it 'thunderbolt' because of the dive limit?

It's dive acceleration not dive limit made P47 succesful in history.

It's totally useless for having 1 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away. Even if you fly the same a/c 500m behind your wingman, you couldn't catch up him when following his dive, could you?

While both German fighters could break hard downwards, and leave all models of the Spitfire trailing[/B], no German piston-engined aircraft could out-dive the Thunderbolt.

Although SpitfireIX/XIV has the same dive limit(if not better than) as fw190A/bf109G, he couldn't over take Germans in a dive.

Speed and altitude records
The Spitfire Mk XI flown by Sqn. Ldr. Martindale, seen here after its flight on 27 April 1944 during which it was damaged achieving a true airspeed of 606 mph (975 km/h).Beginning in late 1943, high-speed diving trials were undertaken at Farnborough to investigate the handling characteristics of aircraft travelling at speeds near the sound barrier (i.e., the onset of compressibility effects). Because it had the highest limiting Mach number of any aircraft at that time, a Spitfire XI was chosen to take part in these trials. Due to the high altitudes necessary for these dives, a fully feathering Rotol propeller was fitted to prevent overspeeding. It was during these trials that EN409, flown by Squadron Leader J. R. Tobin, reached 606 mph (975 km/h, Mach 0.891) in a 45° dive. In April 1944, the same aircraft suffered engine failure in another dive while being flown by Squadron Leader Anthony F. Martindale, RAFVR, when the propeller and reduction gear broke off. Martindale successfully glided the Spitfire 20 mi (32 km) back to the airfield and landed safely.[120] Martindale was awarded the Air Force Cross for his exploits.[121]

A Spitfire was modified by the RAE for high speed testing of the stabilator (then known as the "flying tail") of the Miles M.52 supersonic research aircraft. RAE test pilot Eric Brown stated that he tested this successfully during October and November 1944, attaining Mach 0.86 in a dive.[122]

On 5 February 1952, a Spitfire 19 of 81 Squadron based at Kai Tek in Hong Kong reached probably the highest altitude ever achieved by a Spitfire. The pilot, Flight Lieutenant Ted Powles,[123] was on a routine flight to survey outside-air temperature and report on other meteorological conditions at various altitudes in preparation for a proposed new air service through the area. He climbed to 50,000 ft (15,240 m) indicated altitude, with a true altitude of 51,550 ft (15,712 m). The cabin pressure fell below a safe level and, in trying to reduce altitude, he entered an uncontrollable dive which shook the aircraft violently. He eventually regained control somewhere below 3,000 ft (900 m) and landed safely with no discernible damage to his aircraft. Evaluation of the recorded flight data suggested that, in the dive, he achieved a speed of 690 mph (1,110 km/h, Mach 0.96), which would have been the highest speed ever reached by a propeller-driven aircraft, but it has been speculated this figure resulted from inherent instrument errors.[120]

That any operational aircraft off the production line, cannons sprouting from its wings and warts and all, could readily be controlled at this speed when the early jet aircraft such as Meteors, Vampires, P-80s, etc, could not, was certainly extraordinary.—Jeffrey Quill

[124]The critical Mach number of the Spitfire's original elliptical wing was higher than the subsequently-used laminar-flow-section, straight-tapering-planform wing of the follow-on Supermarine Spiteful, Seafang and Attacker, illustrating that Reginald Mitchell's practical engineering approach to the problems of high-speed flight had paid off.[125]

[MadBlaster]

mach 1, sound barrier and 'loud noise'. what is 'thunder'??? get it now??? What other WW2 prop planes had mach 1 dive limit??? I can't recall any other that did. Even the great Ta 152 falls short. So, if Republic makes the only plane that can get to sound barrier with out breaking up, calling it 'thunderbolt', seems a good fit to me. So, I simply was speculating on the origination of name.

"it's totally useless for having 1 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away. Even if you fly the same a/c 500m behind your wingman, you couldn't catch up him when following his dive, could you?"


Huh? We already know that the fw190a-4 was quicker off the line in the dive! Go back and read your own posts and theory as to why. I already stated your conclusion seemed reasonable. I don't know why you seem to be contradicting your own conclusion now? Most of the other prop planes couldn't touch that dive limit, so p47 acceleration is moot beyond their dive limits. But it did not have the best acceleration in the dive as per the test record.

Also, even if fw 190 does get some lucky shots off in the first part of the dive, p47 is built like a tank. Good chance it gets home.

[BlackBerry]

mach 1, sound barrier and 'loud noise'. what is 'thunder'??? get it now??? What other WW2 prop planes had mach 1 dive limit??? I can't recall any other that did. Even the great Ta 152 falls short. So, if Republic makes the only plane that can get to sound barrier with out breaking up, calling it 'thunderbolt', seems a good fit to me. So, I simply was speculating on the origination of name.

It's totally useless for having 0.85 Mach dive limit when your enemy could outdive you with better acceleration within 0.7 Mach and pull to level run away.

It's totally useless for having 0.75 Mach dive limit when your enemy could outdive you with better acceleration within 0.65 Mach and pull to level run away.

It's totally useless for having 0.65 Mach dive limit when your enemy could outdive you with better acceleration within 0.55 Mach and pull to level run away.

Now, do you understand me?

Huh? We already know that the fw190a-4 was quicker off the line in the dive! Go back and read your own posts and theory as to why. I already stated your conclusion seemed reasonable. I don't know why you seem to be contradicting your own conclusion now? Most of the other prop planes couldn't touch that dive limit, so p47 acceleration is moot beyond their dive limits. But it did not have the best acceleration in the dive as per the test record.

It seems that you misundertand me. P47 can outdive fw190 WITHIN fw190's dive limit.

(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

In your opinion, fw190 from 3000m @400km/h dive to deck will lost its wings?
No, no, no.
When hit ground, the speed of fw190 is BELOW its diving limit. But fw190 was outdived by P47, wasn't it?

I'll use estimated numbers to show you, if you don't aunderstand, I 'll give up.

acceleration=g*cos(65)-dragcoefficent*(TAS)^2/weight+Propellerthrust/weight


1)from 400km/h to 570km/h,Fw190G outdives P47D
acceleration=g*cos(65)-dragcoefficent*(TAS)^2/weight+Propellerthrust/weight

For fw190G:acceleration=4.1-1.5+3.5=6.1 m/s^2

For P47D:acceleration=4.1-1+2=5.1 m/s^2


6.1>5.1, So fw190G outdives P47D.



2)from 570km/h to 750km/h, P47D doutdives fw190G

For fw190G:acceleration==4.1-5+1=0.1m/s^2

For P47D:acceleration=4.1-3.3+1=1.8 m/s^2


1.8>0.1,So P47D outdives fw190G.

[MadBlaster]

(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

Okay, I guess it is just a words mix up. Look at the underline bold above. You posted it from the test record. It says 190 was quicker off the line. This is from the test record. You reasoned it out. I agreed. Then you said this:

It's dive acceleration not dive limit made P47 succesful in history.

which contradicts the test observation we have been talking about. So, imho, I don't think it's p47 acceleration abilities in a dive that gave it the name 'ThunderBolt'. http://en.wikipedia.org/wiki/Thunder It is the fact that it had a dive limit capability like no other prop plane at that time, near the sound barrier. It took time for p47 to catch up and pass the 190. It was not the quickest. It was the fastest. So, I don't think you can say dive acceleration was it's leading attribute in history. There's nothing to argue here. I think we just got a word mix up.


The wings obviously did not fall off the 190 in that test. So, I guess we can assume that at that dive angle, starting altitude, starting speed...etc, that the 190 stayed within the dive limits. Probably a vertical dive angle is a different story and the wings fall off.

[BlackBerry]

What's name for P47 isn't important, you may call it "old woman", but p47's acceleration is still one of the best.

In 1943 July, p47 was equipped with old naca-16 propeller whose efficiency is low at low TAS, but when P47 had a paddle prop., story changed.

I guess fw190G can only slightly outdive P47 (paddle) at the beginning.

[Crumpp]

Hi Blackberry,

You have drawn some of the right conclusions but there is some work required still.

First of all, these are constant speed propellers. They change pitch as required. I am sure you got confused looking at that single F4U graph but it is a fact, you cannot compare CSP propellers at different advance ratios.

The advance ratio does not tell you a thing except in the context of that specific pitch angle. Now what you are doing is how that pitch stops are determined. A good propeller design will keep the polar at the flat area on the top as the pitch of the blade changes throughout the flight envelope.

This is what a complete CSP efficiency over advance ratio graph looks like:



The best aircraft/engine for this propeller will achieve Vmax at ~2.2 advance ratio and the propeller will have the stops at 15 degrees and 45 degrees.

That is the advantage of a CSP, you maintain peak efficiency over a wide range of velocities.

The F4U graph looks like it comparing airfoil selection at a specific velocity.