Bearcat vs Corsair

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Hi Bill,

Regarding post 201 above from about 2 years ago, it is difficult for me to believe that the V-1650-9 engine was materially larger or longer than a V-1650-7. Both were 2-stage Merlins. So, it should fit into a P-51D without major surgery. That is assumption #1.

I simply used a tried and true old formula and the new top speed for an aircraft with more power would be an easy estimate. I know that a P-51D has a top speed of 437 mph on 1490 HP at somewhere around 22,500 feet. Or close to that. For the purpose of illustration, assume it is correct.

I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.

The new power is 2,200 HP. Leaving k as a constant, V becomes 486.5, assuming a 7% increase in frontal area due to a larger radiator (assumption #2 on my part). It is a good first-order estimation. It isn't a complete analysis, but I also didn't have complete data or the desire to go that deeply into a supposition, so a first-order approximation was OK with me. It will likely be off by a little, but the basic number should be pretty valid and should be at least close, according to several lectures and professors back in 1969 - 1970.

Nothing magic and not very thorough, either. But it gives me a place to start thinking about it. When I suggest an aircraft modification, I will likely never go to the effort to do an analysis just for alternate suggestions in a thread that wanders into what-if and, truth be know, I would have to dig up old college notes to DO the analysis, and probably would handle it wrong anyway just due to the fact that it has been since 1970 that I was in aero. That was the year I decided to leave aero and go into electrical engineering.

They had just finished the F-111 and General Dynamics (and almost everyone else, too) everyone laid off many, if not all, of their the aero engineers. That was widely reported, and was a watershed day for me at college. I SHOULD have chosen mechanical engineering, but went with electrical. It has been OK but, in hindsight, I probably should have either stayed in aero or gone mechanical engineering. Both were more along my lines of actual interest than electrical ever has been, though I have enjoyed coming up with several circuit inventions.
 

Hi Greg,

The V-1650-9 should fit in the same place that a V-1650-7 or V-1650-3 could.


The -9 doesn't have 2200hp @ 22,500ft. Probably about 1800hp

http://www.wwiiaircraftperformance.org/mustang/p-51h-booklet-pg10.jpg
 
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FLYBOYJ said:
The engine mounts were incorporated into the structural engine cradle, thus saving weight. The engine would not be the newer RS.14.SM Merlin as in some of the lightweight prototypes. The Rolls Royce Merlin V-1650-9 was chosen.
Click to expand...
What's the RS.14 SM Merlin?

pbehn said:
The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S.
Click to expand...
This might be a big question despite it's small size: What were the US landing-gear, angle of attack, and side-engine loads, and what were the British comparisons?

GregP said:
I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.
Click to expand...
Questions
  1. Does k = P/V^3 apply to true airspeed or indicated airspeed when calculating performance of aircraft at altitude?
  2. 1.78543E-5 = 1.78543 * 10^-5?
  3. E = Exponent?
 
Zipper730 said:
What's the RS.14 SM Merlin?
Click to expand...

It's a family of 2 stage Merlin engines with medium and full supercharging.


Zipper730 said:
This might be a big question despite it's small size: What were the US landing-gear, angle of attack, and side-engine loads, and what were the British comparisons?
Click to expand...

42


Zipper730 said:
Questions
  1. Does k = P/V^3 apply to true airspeed or indicated airspeed when calculating performance of aircraft at altitude?
  2. 1.78543E-5 = 1.78543 * 10^-5?
  3. E = Exponent?
Click to expand...

1. drgondog would answer this better, but I suspect it applies to both
2. yes
3. -5 is the exponent, 10 is the base. Don't think E has a name - it is just shorthand for calculators and computers.
 
Zipper730 said:
Three speeds (Low-speed, medium-speed, full-speed), two-speed.
Click to expand...

2 speeds - MS and FS gears (often denoted simply as S).

3 speeds would be SML.

The code does not identify the engine as a 2 stage or a single stage.


 
Zipper, I have had enough of you lumping posts together for others to sort out into a sensible reply. Your "quote" of a post by me was not actually by me (as you know). It was itself a small part of a quoted text from an article linked by Flyboy TWO AND A HALF YEARS AGO . Do your own research, don't try tricking me into doing it for you. Here is my full post as a starter, note the "quote" and "unquote" statements

"Flyboy from your quoted article it says this, which surprised me (apart from the spelling of "Brittish")
quote
Brittish fighters were lighter than U.S. fighters. Schmued ask for detailed weight statements from Supermarine on the Spitfire. Schmued wanted to know why the Spitfires were so much lighter than the P-51. Supermairne did not have such data on the Spitfire, so they started weighing all the parts they could get a hold of and made a report for Schmued. The Brittish had design standards that were not at strict in some areas of design as the U.S. Landing gear, angle of attack and side engine design loads were higher in the U.S.
unquote

I am no expert but I cannot believe that it took until the design of the "H" to notice that British fighters were lighter, the P51 was always heavier than a Spitfire with the same engine. I think the above quote was really the US going to a lower design standard that had worked in practice to allow a weight reduction not allowed under USA design regs. I personally find the statement "all the parts they could get hold of" amusing, since the US operated Spitfires and the lease lend agreement meant sharing all British technology there is no part of a Spitfire that wasnt available to any US scientist/engineer who the US wanted to have it, I think the weighing and evaluating of components was to see just how much (or little) they could get away with. This is a soft ball soft Flyboy, upon your reply depends the status of the P51H, did North American really have to weigh parts of a Spitfire to get the design right? I think they did an engineering/design revue to see where weight could safely be saved using other almost comparable designs as a precedent/base for study.


edit...from the original post I cannot really tell who did the weighing, Supermarine or US engineers working for Schmeud? "
 
Zipper, we don't mind newbees asking questions, even us old farts are here to learn, but please stop with the long drawn out multi posts and asking multitude simplistic questions, it is getting tiring to read and its obvious you're pissing off some of the membership. Some advise....

 
Hi Wuzak,

OK, I'll bite. So, you say the V-1650-9 had about 1,800 HP at about 22,500 feet. That's about 82% of the rated power. Let's say the V-1650, either a -3 or -7, is rated also at about 82% of rated power. That's 1,219 HP.

So, the P-51D goes 437 mph at 22,500 feet on 1,219 HP.

Enter the V-14650-9, with a WER rating of 2,200 HP, but 1,800 HP at 22,500 feet. Using the same formula, I still get 486 mph for the P-51D on 1,800 HP at 22,500 feet, when fitted with a -9 engine (still assumes a 7% increase in frontal area for cooling). In real life, it might be closer to 470 mph, but that's still a damned good P-51D airframe number. I am inclined to believe the P-51H was a great advance in the P-51 family, and only suggested the -9 engine for the P-51D airframe as an interim measure, until the P-51H airframe was available.

I am also not really up on when the engine dash numbers and airframes were available, but just thought that adding the big HP to the P-51D airframe has long been a factor at Reno every year. Why not in WWII?

Not suggesting the -9 version of the P-51D airframe replace the P-51H, I was just thinking in print, and wondering where the P-51D might go if fitted with a -9 engine. No other agenda here.
 
I do not have all the documents that I would like to have on the
RR Merlin V-1650-9, but the USAAF Summery that I do have
from 1949 and 1950 give this engine the power ratings of
2,220 hp./3,000 rpm./9,000 ft.
1,790 hp./3,000 rpm./22,700 ft.

, Jeff
 
FLYBOYJ said:
it is getting tiring to read and its obvious you're pissing off some of the membership.
Click to expand...
I am completely exasperated more than pissed off. I have told Zipper to stop posting multiple questions, it means he saves his time but spends everyone elses trying to make a coherent reply. I have told him to stop quoting a single sentence out of a statement. It is literally taking things out of context, this means I (and others) must go back and rebuild the context. His question about a selected quote from a selected quote by myself from two and a half years ago took the biscuit. Having rooted through the previous posts and found where it was buried it is perfectly obvious to anyone I don't know what the answer is anyway. I find this increasingly impolite to the point of ignorance but more importantly I cannot see how Zipper or anyone else can learn from the discussion, I cannot even follow it at times, sliced, diced and cut to pieces with one word comments like "mmmmmph"
 
GregP said:
OK, I'll bite. So, you say the V-1650-9 had about 1,800 HP at about 22,500 feet. That's about 82% of the rated power. Let's say the V-1650, either a -3 or -7, is rated also at about 82% of rated power. That's 1,219 HP.
Click to expand...

No, I checked a flight test of a P-51D which had a maximum speed of 442mph @ 26,000ft using 1400hp.

At 26,000ft the V-1650-9 at WEP had aroun 1800hp.

Which I calculate would give the P-51D a speed of about 480mph at that altitude.

Jeff's numbers confirm the power of the -9.


GregP said:
I am also not really up on when the engine dash numbers and airframes were available, but just thought that adding the big HP to the P-51D airframe has long been a factor at Reno every year. Why not in WWII?
Click to expand...

I assume the -9 came along relatively late, otherwise it, or a similar engine, would have been put in the P-51D.


GregP said:
I am inclined to believe the P-51H was a great advance in the P-51 family, and only suggested the -9 engine for the P-51D airframe as an interim measure, until the P-51H airframe was available.
Click to expand...

The P-51H was lighter and had improved aerodynamics. If nothing else, the climb rates for the H should have been better with the same engine.


GregP said:
Not suggesting the -9 version of the P-51D airframe replace the P-51H, I was just thinking in print, and wondering where the P-51D might go if fitted with a -9 engine. No other agenda here.
Click to expand...

I think it is clear that a P-51D/V-1650-9 combination would go very well.
 
Hi Bill,

Regarding post 201 above from about 2 years ago, it is difficult for me to believe that the V-1650-9 engine was materially larger or longer than a V-1650-7. Both were 2-stage Merlins. So, it should fit into a P-51D without major surgery. That is assumption #1.

I simply used a tried and true old formula and the new top speed for an aircraft with more power would be an easy estimate. I know that a P-51D has a top speed of 437 mph on 1490 HP at somewhere around 22,500 feet. Or close to that. For the purpose of illustration, assume it is correct.

I also know that k = P / V^3. Since we know P- and V, k = 1.785E-5. Actually, 1.78543E-5.

The equation is an excellent rule of thumb (at best), and only approximate for incompressible flow... it loses granularity as M ~ .5M. In that region the Parasite drag rise escalates non-linearly and significantly different between different aircraft as V ~ 0.6M and above. That is the first 'complication'. The second important contribution to total Drag in those regions, is Form Drag due to CL. More linear but also non-linear. The third issue is that Performance estimates may start with Thrust HPr = (W/375)*CD/CL)*V (where V=mph). It does Not start with T=D (in pounds-force).

These calcs start with known altitude density ratio, know weight and desired velocity. Tables will be generated with each set of calculated data to recalculate as potential velocity desired reveals that more HP than the engine you use is capable of delivering

Sequentially CL is calculated, CD is derived by a.) deriving a CDp which includes the zero lift Low RN wind tunnel data at (RN1/RN2) to an empirical power, b.) calculating the CDm for compressibility (CDm=CDp/Sqrt(1-M^^2), c.) calculating the form drag as function of CL, d.) calculating CDi and e.) summing up for CDtotal. The process usually reveals that the velocity you desire is higher than the HP you have available and you drop the original V to a lower value and begin again until your V achievable approximates HP available.

The new power is 2,200 HP. Leaving k as a constant, V becomes 486.5, assuming a 7% increase in frontal area due to a larger radiator (assumption #2 on my part). It is a good first-order estimation. It isn't a complete analysis, but I also didn't have complete data or the desire to go that deeply into a supposition, so a first-order approximation was OK with me. It will likely be off by a little, but the basic number should be pretty valid and should be at least close, according to several lectures and professors back in 1969 - 1970.

The Hard part begins, because for a conventional prop system, the discussion launches into Power Available versus Power Required for each set of flight conditions (level, climb, high speed, climb speed) which require RN, pressure losses in the plenum, the carb intake, increased drag due to higher velocity over the airframe within the prop vortex..

Power Available includes prop thrust and exhaust thrust. Because drag due to momentum loss of the engine air and increased velocity within the area immersed by slipstream/vortex they are subtracted from the total thrust (prop/exhaust). Calculating Exhaust thrust without the tables requires a very strong Thermo background. It requires ability to accurately calculate Mass flow rates of exhaust gasses per cylinder, area of each stack, angle of inclination of exhaust stack from flight line, fuel to air ratio, mechanical efficiency, atmospheric properties, fuel combustion properties, and I forget the rest.

Curves and plots available to the aero include Ram as function of A/C Mach number, impeller mach number, adiabatic temp rise. Like the earlier V vs THPreqd, calculating Ram is also iterative.

Calculating slipstream velocities also depend on Prop Thrust and Freestream velocity.

Once the slipstream velocities are derived, you have to calculate what the incremental Power Required value has to be before arriving to point where you can close on the velocities attainable, in theory.

Nothing magic and not very thorough, either. But it gives me a place to start thinking about it. When I suggest an aircraft modification, I will likely never go to the effort to do an analysis just for alternate suggestions in a thread that wanders into what-if and, truth be know, I would have to dig up old college notes to DO the analysis, and probably would handle it wrong anyway just due to the fact that it has been since 1970 that I was in aero. That was the year I decided to leave aero and go into electrical engineering."


Greg - I didn't post all this BS above to refute your assumptions and beginning point for thumbnail performance estimates. I was trying to point out that so much of what we learned in Aero 101 (and 201 and 301) started and ended with basic Cl, Cd and T=D. Professors like Hoerner smooth the way into doing basic Speed and Drag and Thrust equations which lead to the Power and Velocity relationships you posted to start this dialogue.

That said, you among a few of our community on this forum understand that "performance Calcs are complicated". I am eternally amused at guys like Soren, and even Ho Hun who was a level above Soren, were so glibly distributing bovine fecal matter when pontificating on turn and climb calculations. As I hope I showed, Total Drag for high angle of attack, airframes immersed in prop vortex, low speed (where Cooling drag soars and prop efficiencies wither) and asymmetric flight where stall conditions are very different from one wing to the next at the 'break points', and trim drag of ailerons and rudder become important - are 'kinda like rocket science'.

High speed level flight more straightforward if aware of all the major drag rise components and where they occur on the Mach meter - but still not calculable with high degree of confidence with simple, easy to understand equations.

To answer the fundamental question, the P-51H with and installed V-1650-3 or -7 would have out performed the B/D at same combat loading, same fuel, same MP, same RPM, same altitude, same airframe condition and stores. The only area I have reservations in is roll. The ailerons of the B/D were smaller but greater throw at max 15 degrees +/- compared to H with larger aileron area at +/- 10 degrees. Flight tests suggested parity in roll.

The V-1650-9 was the same as 1650-3 and -7. The improvements included a much better shaft/bearing lubrication for the -9 as well as carburation and WI to boost to 80" w/o WI and 90" w/WI. Net net, when the 9 finally got bugs worked out, the thrust HP was greater at WEP at all altitudes and the CDmin of the H was ~ 3% less at all altitudes. More thrust/less drag.
 
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I'll do a search if you'd like
 
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