Revised HP/f vs TAS chart, including S.L. data

[Widewing]

I reworked my HP/f vs TAS chart to include sea level data. I also dropped the XP-72 into the chart for comparision sake.

 

My regards,

Widewing

[Andy Bush]

Whoa!!

That P-72 is really honking at SL. TAS and IAS would be about the same...nearly 500mph indicated on the deck is pushing it for a prop.

Andy

[funked]

So you are saying all these planes make the same power at altitude as at sea level?  Or do they magically reduce their flat plate area at altitude to compensate for power loss?

Also remember that drag is the area times dynamic pressure.  And dynamic pressure varies with density (altitude) for a given TAS.

But instead of just sitting here posting nitpicks of your work, I need to make a chart of my own.  This may take a while because I am busy calculating this kind of stuff for a class.  I guess I need to talk my professor into giving me credit for doing calculations for this BBS.  LOL  

[This message has been edited by funked (edited 02-20-2001).]

[Zigrat]

hehe funked

[Widewing]

 

Originally posted by funked:
So you are saying all these planes make the same power at altitude as at sea level?  Or do they magically reduce their flat plate area at altitude to compensate for power loss?

Since profile drag diminishes with the decrease in density, yeah, in a sense, you could conclude that magic is a player. Indeed, the reduction in profile drag mimics a magical reduction in flat plate area.

Three of the aircraft charted do not suffer any power loss at altitude. These are the P-47B, P-47M and XP-72 with its unique variable
speed supercharger that produces sea level density pressure in the intake plenum at  operating altitudes up to 27,000 ft. So, these aircraft have the same power rating at their best operating altitude as they do at sea level.

All other power ratings are for sea level. However, the purpose of the chart is to plot
horsepower per square foot of flat plate area in relation to maximum speed attainable at sea level. Speed at altitude is for comparision sake only.

 

Also remember that drag is the area times dynamic pressure.  And dynamic pressure varies with density (altitude) for a given TAS.

Dynamic pressure does not vary with altitude, it goes down. Both induced drag and pressure drag diminish with increasing altitude. This is why most aircraft make their best speeds altitudes significantly above sea level density. For most aircraft with a mechanical supercharger, speed begins to go down once the airplane reaches an altitude where the pressure density of the intake charge can no longer be maintained at sea level ambient. Turbocharged aircraft generally make their best speeds considerably higher than supercharged aircraft due the greater efficiency of the turbo at maintaining sea level density pressure. I some cases, performance of turbocharged aircraft is limited by propeller tip speeds, as they enter into the transonic range at extreme altitudes. This was a problem for the P-38. Speeds dropped rather sharply at altitudes above 30,000 ft because of very high tip speeds, not a lack of horsepower. Throughout its life, the P-38 was saddled with a reduction ratio of 0.5 to 1. Lockheed's P-38K overcame this with a better 0.42 to 1 ratio and paddle blades. However, for political reasons this was never incorporated into production aircraft.

It is virtually impossible to accurately calculate total drag. That is why wind tunnels are employed. If you tried to do such a calculation, you had better use a standard atmosphere chart as the basis of the calculation. The reason for this should be obvious. The temperature aloft is directly related to that at sea level, and unless you have specific knowledge of the sea level temperature where an aircraft was tested, your data suffers from an uncontrolled variable. Using the standard atmosphere chart allows for a controlled baseline of temperature and density. Since the coefficient of drag is a measurement of how much dynamic pressure is translated into drag, it becomes rather important to be able to define the dynamic pressure.

That is why I created my chart with known coefficient of drag numbers. However, this does not take into account induced drag. Why, because this is another uncontrolled variable. Certainly, we can look at induced drag as being a signicant factor in relating to speeds at sea level vs those at altitude.
However, to have a true baseline for comparison, induced drag is not factored in.
The rise experienced in the coefficient of drag as speed increases is generally similar for all aircraft. When graphed, this becomes apparent. However, the drag rise is delayed on those aircraft employing a laminar flow wing. This allowed for higher speed on less power. Nonetheless, the curves for all others are essentially equal with the difference being the initial coefficient.

My chart uses zero-lift, emperically determined drag coefficients to calculate flat plate area and HP per sq/ft.

My regards,

Widewing

[F4UDOA]

Widewing,

What Cdo are you using to determine the Flat plate area of the XP-72?

It seems very strange that an A/C with such low drag and a turbo supercharger keeping horsepower constant would not be significantly faster at 26,000Ft than sea level.

This means the P-47M/N was just as fast at alt. as the XP-72 and would have to had less drag since it had less HP?

Another example is the F4U-3 with a Turbo super charger. This A/C had a max sea level speed 378MPH and a Max speed of 486MPH at 30,000FT with a constant 2800HP throughout. Just as fast as the XP-72 with 600HP less at alt but 100mph slower on the deck?? It doesn't seem to make sense.

Do you have a speed and climb chart to go with your data??

[F4UDOA]

Widewing,

Here is a picture of a 4,000HP laminar flow A/C with less flat plate area that is barely capable of 480MPH at sea level.

 

[juzz]

Duh, not enough red paint!  

They must have painted every square inch of the XP-72 bright red for it's speed trials.

The Germans once painted the Me 163 red, and it did over 1,000km/h!  

[juzz]

BTW: The He 100 V8, used on 30-3-39 to achieve 463.92mph at approximately 250ft asl, only had about 1800HP. It also had surface evaporative cooling of engine oil and coolant, only 118ft^2 of wing area, and the whole airframe was filled and polished.

[SC-DeMutt]

hehehe;
  You guys an' fancy number crunchin' don't scare me! I'm old enough to know both the Slide rule, And the Slide rule CALCULATOR!
  I own both 'Flight Sim Toolkit' And 'X-Plane'! I was also held in High esteem, and Nicknamed "Th' Perfessor" By none other than Mr. Pete Hill, Confirmed by a knee buckling slap on the shoulder by Gen. Chuck. (I remain Honored).
   After my baptism into true humanity, I quickly put into proper perspective my earlier, yet far too costly efforts at gaining knowledge thru practical science. I now knew that way led to Hair loss, And Dementia!!

  Because you are all of good stock, And most of you worthy; I will share with you now, The TRUE relationship of Plate area, as a function of overall Aerodynamics, resulting in Applied Functional Dynamics...
.....OK?.....  Here goes....

1}MEN... Good looking MEN... Fly Aircraft.
2}MONKEYS... And Old, Bald Men, Fly Spacecraft.
3}WOMEN.. Good LOOKING Women.. Find Monkeys and Old Bald men.. Cute.
4}They find Good looking Aviators/Racers... Exciting!
5}Women also know that their chances of getting in an Aircraft/Boat/Car/Motorcycle, Being thrilled to tittlation, By someone actually controlling the dynamics of a given thrill, And returning them safely to do so again, and again, and again... Are ... Lots better, OK?

So, Given these factors, We simply reduce the cockpit area of a given craft, Make it a two seater, with just enough HP 'A', to vibrate that second seat at frequency 'X', or.. was that...'B'?.., No..errr ...
Well, Basically, What yer lookin for, Is an Aerodynamic device fast enough to make that Monkey's lips peel back enough to make HER giggle, And a seat that vibrates enough to make her Smile and Wiggle  
  (But don't forget the 'Eject Button'!! Speed is a dangerous buisness, Ya know?)

 Well, I'm off to Dusseldorpf.. S!

SC-Mutt

PS;
If at any time, you read a line twice, or scratched yer head... I REALLLLLY Got ya!!

[Widewing]

 

Originally posted by F4UDOA:
Widewing,

What Cdo are you using to determine the Flat plate area of the XP-72?

I used the the same coefficient as the P-47B, which is probably very close. The XP-72 utilized the same wing as the XP-47J, which was marginally thinner in cross section than the standard P-47 wing. This was one of the reasons that the XP-47J was 30+ mph faster than the P-47M at the same altitude, using the same engine and available power.

 

It seems very strange that an A/C with such low drag and a turbo supercharger keeping horsepower constant would not be significantly faster at 26,000Ft than sea level.

[/b]

Republic never performed max speed testing at altitude. Probably due to the fact that the engine was not that which was scheduled for production, and the supercharger did not represent the final configuration. They did attain 490 mph @ 25,000 ft., but at considerably less than maximum power.

 

This means the P-47M/N was just as fast at alt. as the XP-72 and would have to had less drag since it had less HP?

It did have less drag than the P-47M. Over all, the XP-72 was a cleaner design.

 

Another example is the F4U-3 with a Turbo super charger. This A/C had a max sea level speed 378MPH and a Max speed of 486MPH at 30,000FT with a constant 2800HP throughout. Just as fast as the XP-72 with 600HP less at alt but 100mph slower on the deck?? It doesn't seem to make sense.

You're right, it doesn't make sense. Something else was going on but I have no idea what that may have been, until today.

Last evening, I placed a phone call to Warren Bodie who has several hours of interviews with Carl Bellinger on tape, which he has used in several books. I asked
Warren to check the tapes and his notes and
see if Bellinger is more specific about the low altitude speed runs. Well, he sure is.

Bellinger described these flights as being part of the engine reliability program. Republic performed several hundred hours of bench testing on the R-4360-13 engine. Included in this was 100 hours at extremely high boost pressures. How high? Up to 80 in/Hg! This is not unlike the testing done with the R-2800 C series engines that produced power outputs in excess of 3,600 hp without a failure.

Carl Bellinger stated that the speed runs were made at a whopping 76 in/Hg at 2,900 rpm. According to Carl, this resulted in as much as 4,200 hp being generated. Apparently, this was part of a test program and did not reflect actual allowable production power settings. So, I guess that the "Red Baron" in your photo would have its hands full with the XP-72.

I'm assuming that this engine was fitted with water injection.

As a final note, Bellinger projected that the production P-72 would have little difficulty exceeding 515 mph at height, in level flight.

 

Do you have a speed and climb chart to go with your data??

No. Bodie has some test documentation, but I can't say specifically what he has. I will check with him again this evening and pass along anything that I learn. I do have some data (second or third hand) at home. I believe that Pete Bowers has quite a bit on the aircraft too.

Remember, the highest power setting used at high altitudes was just 46 in/Hg.

My regards,

Widewing

[funked]

 

Dynamic pressure does not vary with altitude, it goes down

Going down is a form of variation.

The decrease in power with altitude is significant for the non-turbosupercharged aircraft on the chart, especialy the ones with just a single-stage mechanical supercharger (N1K2-J, P-39D, F4F-3).  Plotting hp/f vs TAS is not going to give you any useful information unless the HP and TAS for each point correspond to the same altitude.

Like I said, I need to make a chart instead of just nitpicking yours like a weenie.  Thanks for your work.  <Salute>

[F4UDOA]

CC Widewing,

I didn't realize that he was running at less than full power. Still seems like an amazing achievement for the time when considering the task is still difficult today considering the technology available. Also you mentioned the program was cancelled in favor of the P-80 production. The P-80 would have had a hard time keeping up with th P-72 considering the limitations of straight wing jet designs.

Good stuff
Thanks
F4UDOA

[Badboy]

 

Originally posted by SC-DeMutt:
Well, Basically, What yer lookin for, Is an Aerodynamic device fast enough to make that Monkey's lips peel back enough to make HER giggle, And a seat that vibrates enough to make her Smile and Wiggle  

I laughed so much my sides hurt... Poetry and humor... love it!!

Badboy

[Widewing]

 

Originally posted by F4UDOA:
CC Widewing,

I didn't realize that he was running at less than full power. Still seems like an amazing achievement for the time when considering the task is still difficult today considering the technology available. Also you mentioned the program was cancelled in favor of the P-80 production. The P-80 would have had a hard time keeping up with th P-72 considering the limitations of straight wing jet designs.

I was able to dig up the climb rate of the XP-72. It could reach 20,000 ft in 5 minutes flat. Therefore we can assume that its initial climb from sea level was well into the 4,300 fpm range, and probably in the 3,700 fpm range at 20k. That's pretty good when you consider that the XP-72 was not a stripped prototype, but was tested at normal combat weight. However, the above climb data was recorded at a power setting that produced just 3,000 hp. Up the power to 3,450 hp and I would expect climbs rates in the mid to upper 4,000 fpm range.

I don't think that the P-80A would have any trouble running away from the P-72, especially at sea level. Down low the P-80A could reach nearly 560 mph. However, at high altitudes the P-72 was right up there in terms of speed. The best the P-80A could manage at 40,000 ft was 410 mph. The P-47M and N would be in competition up there. At 30,000 ft, the XP-72 was likely as fast or faster than the A model Shooting Star. Later models of the P-80, such as the B and C were much better and would have left the XP-72 far behind. Where the XP-72 really had an advantage was in acceleration. The early jets were terribly slow to build speed, largely because it took 20 to 30 seconds to get the engines spooled up to maximum rpm. The Me 262 was especially poor in this regard. Yet, we must remember that turbojet design was still in its infancy in 1945.

My regards,

Widewing