P-51D maneuvrability - what it was in reality ...

[Deleted member 68059]

A V1 didnt change direction or fire back.

It was extremely small and difficult to see though, and did sort of fire back as many pilots were killed by the blast of cannon detonated warheads

 

[pbehn]

It was extremely small and difficult to see though, and did sort of fire back as many pilots were killed by the blast of cannon detonated warheads

From what I read apart from the warhead itself the "kill area" on a V1 amounted to the motor itself and the single most telling factor was having cannon not MGs.

 

[Deleted member 68059]

RAE 1501

www.wwiiaircraftperformance.org

Thanks for posting that, the corresponding correspondence files have useful letters too>

 

[Clean32]

Laminar-flow is not the same as "thin". A laminar-flow wing has the thickest part of the wing positioned along the wing's chord in such a manner that the airflow at the boundary doesn't separate so quickly.

uumm Laminar flow wing is when the top surface and bottom surface are near identical. thus when compressibility occurs it happens at the same time and at the same distance from the leading edge. as a result there is no compressibility torque imposed on the wing.
a Laminar flow wing produces lift only by managing the angle of attack.
the P51 middle and out wing profiles are not the same top and bottom, and the chord is too far back to be a true laminar flow profile.
BUT having said that, the Chord or thickest part of the wing being so far back and being where compressibility occured, was the same profile to and bottom. thus did not produce torque on the wing. add to that the supper. brilliant tail didn't enter compressibility and was not effected by the turbulence by the wing. thus control was maintained for longer.

 

[Clean32]

Doesn't matter if it is a spelling bee site. Sometimes my typing isn't all it should be, either.

It matters if you communicate what you intend.

If you're trying to get technical, be as correct as possible since that minimizes misunderstanding.

The critical Mach number has not too much to be with overall drag; it defines critical Mach: the speed at which a supersonic shock wave begins to form on the wing and/or fuselage. Overall, the P-51 is MUCH less "draggy" than the Spitfire. The main drags were profile drag of the lifting surface, profile drag of the fuselage, cooling drag, and friction drag.
The P-51D has the best fuselage drag of any WWII piston combat aircraft. Period.
The P-51D has very low drag near its top speed, compared with other aircraft of the time.
The cooling drag is close to zero due to the Meridith effect.
Friction drag is quite low compared with most other fighters.
The combined effects of these account for the P-51 being so fast on such ordinary power. Definitely faster than most Spitfires, despite being a ton or more heavier. Late Spitfires were faster than earlier ones, but that came with considerably more power. By the time the P-51H showed up, it had more power, too, and showed all Spitfires a clean pair of heels easily.

But, by that time, it didn't much matter because everyone was interested in jets anyway. The Hunter, F-86, and Gnat were all pretty decently close to one another in performance. The Gant just couldn't perform well for very long on only internal fuel. The EE Lightning, despite being a Mach 2 airplane, was similarly range-limited. I once had a former Lightning pilot tell me he COULD get to Mach 2, but only if he was headed "toward the fuel." He said, tongue in cheek, that if he ever got going Mach 2 headed away from the fuel, he'd never get back to the fuel.

The P-51 wing IS a laminar flow wing back about as far along the chord as any laminar wing in WWII was. Later, we got even better laminar flow wings, but not during WWII on a piston combat aircraft. For all it's supposed mastery, the Ta 152 wasn't faster than P-51H and not much faster than a Tempest/Fury/Sea Fury (close to the same family). Most the late-war super-pistons were quite good and quite comparable, regardless of country of origin. Everyone learned a lot during wartime development. Everyone had decent engines, at least when manufactured with care, decent fuel, and decent airframes.

The British were flying 4 and 5-blade props while the Germans were using very wide-chord 3-blade props all with similar power. The difference in top speed wasn't much.

Cheers.

nice post
The cooling drag is close to zero due to the Meredith effect.. misleading. all fighter aircraft uses meredith effect to some existent. the P51 did this well.
But the original north american XP51 plans had a chin mounted radiator. this was changed due to British air ministry influence. firstly thinking the P51 as a P40 replacement. so the british North africa exspericans came into play.
the Hurricanes had less radiator damage than the P40. north americans purchase of curtis P46?? and the gaining of the internal flow Tech. but this was just the start point.
the real advantage was the scoop itself.

the bleeding edge scoop, so you are 100% correct when you wrote the P51 fuselage was quite slippery and not wrong when you wrote about the meredith effect but the meredith effect is a smaller part of the story than it really is. so its not so much that the meredith effect was increased to a point where it zeroed out drag. is more that the drag was decreased to match the meredith effect.

you compared to a spitfire. i have never found the numbers to do a good direct comparison. that's even after converting from Rabble gallons to real gallons. and its even just not what spitfire Mk but what wings it had, what blower etc. this gets really messy on the spitfire side really quickly.

so i would be interested in what anyone else has used?

but is we just look at 3 numbers, altitude, cruise speed in conjunction with fuel consumption. the spitfire could cover more distance, thus it is more slippery at cruse speeds of about 260Knts

But i would expect and the number seem to confirm, that at higher speeds. the spitfires more conventional wing, the drag would increases more than that of the P51 wing, and with speed the p51 wing would lose " angle of attack" and the conventional profile of the spitfire wing would keep on producing life, or excessive lift requiring a negative angle of attack.

 

[Clean32]

If you can deduce drag and laminar flow just by looking at a wing why did or do thy need wind tunnels? F1 cars dont look fast, only the fact that they are makes them seem so and they all look equally fast or slow while in practice there are huge differences. Nobody at NAA claimed the P-51 Mustang I had a laminar or lamellar flow wing, it had a high speed low drag wing and being "fat" is a distinct advantage, giving more room for fuel, munitions wheels and any other stuff. With the same engine the P-51B /D was faster and more economic than the Spitfire at all speeds up to the transonic range but at those speeds you are in danger of structural damage and props falling off. The lower drag of the P-51 was only partly due to its wing, the cooling set up was better and the overall design and build of the fuselage was better. A layman's logic dictates that fat = draggy but research by NACA showed that putting the thickest part of the chord further back delayed the onset of turbulence giving less drag in the speed ranges that prop aircraft use.

Edit, I studied metallurgy the words laminar and lamellar were used as synonyms, I have also seen the same in aerodynamics, is there actually any difference?

uummm i said you can look at the profile of the P51 wing and compare it to a profile of a laminar flow wing and see the difference.

i didn't say NAA claimed the P51 had a laminar flow wing. but i have observe may posts claiming that. and it these posts i am addressing.

the P51 was not more efficient at all speeds. the spitfire was more economic at cruse for example, and had a much higher Mach number as examples.

correct the cooling set up was a real advantage

you wrote

putting the thickest part of the chord further back delayed the onset of turbulence

this is the onset of compressibility, not drag.

 

[Clean32]

None of this adds ups. One, the Spitfire's wing could house 1 .50 Browning and 1 20mm Hispano cannon, or 2 20mm Hispano cannons in each wing.

And two, the P-51 overall is significantly less draggy than the Spitfire. On the same power, the P-51B/D was 35-40 mph faster at least than the Spitfire IX. That speaks to better aero alone.

I'm far from knowledgeable on the detailed intracices of aircraft, but even I understand this.

the spitfire wing? which one?

the short answer is
the browning .303 as modified by the RAF was 1/2 the weight and 1/2 the size of a .50 browning.
the .50 browning is about the same size and weight as a 20mm cannon

as for fitting the browning this started before BOB and was a hard path.
the first operational spits with cannon was the MkIII. which was withdrawn due to ejector problems.
then fixed and re issued. then with drawen again before the Mk III was dumped.

the Mk5 came into service,, then the MkV got the MkIII wing ( universal wing) but there was a cost in climb performance so it got dumped.

then finally with the Mk IV the RAF finally got a cannon wing that worked. BUT, even though the cannons were mounted on their sides, the wings still had blisters to make room.

so i guess you could say the Cannons did not fit in the wing. they stuck out a bit.


as for drag, the spitfire could cruse further on the same volume of fuel. so efficacy of an airframe is dependant on speed, in the spitfire vers P51 the P51 was more efficient at high speed where the spitfire efficiency dropped off, but then the spitfire was more efficient at transonic speeds than the P51. so its not so simple.

 

[Clean32]

From what I've been able to understand the Laminar flow wing wasn't as good as it is made out to be, the reason being that manufacturing imperfections, damage, general wear and tear and even dirt and debris caused the laminar effect to be decreased so that's why I question it's overall effect, the real world is very different to a nice clean lab. Much is written about the 30mph advantage the P51 had over the Spit but how much of that is caused by the wing?, I feel it's the less glamorous drag caused by cannon barrels, blisters, stubs, tail wheel, exhaust and windscreen angle that has more of an effect on speed and drag between the two than the difference in the wings, as for maneuverability you only have to look at the Spiteful, the first one was a MkXIV with laminar flow wings, the overall consensus was it had worse handling than a standard MkXIV, particularly at lower speeds.

Qute correct, add to that the dragging of ammo boxes over the wing, denting the shit out of them

 

[Clean32]

I have read on here that the windscreen on the Spitfire is the first to "shock", I have no idea whether that means it causes high drag at lower speeds, as compared to the buckets they call radiator scoops on the Mk XIV Spitfire, for example.

first to shock, the first part of the airframe to accelerate the airspeed into compressibility, not a low speed issue but a high speed problem.

the bucketts were in the boundary layer. so were taking up air that had already been slowed down. so you could call then 1/2 bucketts
they were not as draggy and you would first expect. but nowhere as good as the P51 Tunnel ram.

 

[pbehn]

first to shock, the first part of the airframe to accelerate the airspeed into compressibility, not a low speed issue but a high speed problem.

the bucketts were in the boundary layer. so were taking up air that had already been slowed down. so you could call then 1/2 bucketts
they were not as draggy and you would first expect. but nowhere as good as the P51 Tunnel ram.

One bucket was just as draggy as I expected because the MkI and Mk V only had one, the Mk XIV I specifically mentioned had two.

 

[pbehn]

uummm i said you can look at the profile of the P51 wing and compare it to a profile of a laminar flow wing and see the difference.

i didn't say NAA claimed the P51 had a laminar flow wing. but i have observe may posts claiming that. and it these posts i am addressing.

the P51 was not more efficient at all speeds. the spitfire was more economic at cruse for example, and had a much higher Mach number as examples.

correct the cooling set up was a real advantage

you wrote

this is the onset of compressibility, not drag.

Since no profile of any WW2 aircraft actually was laminar flow we can all look at as many profiles as we think fit, what do they look like? How/ why was the Spitfire more economic on cruise settings, that isnt what I have read at all.

 

[GrauGeist]

the .50 browning is about the same size and weight as a 20mm cannon

ummm no, the HS.404 aircraft cannon variant, was 38kg amd the U.S. AN/M2 was 28kg, which is a considerable difference.

The AN/M2 was also much shorter in length overall, too.

 

[Clean32]

ummm no, the HS.404 aircraft cannon variant, was 38kg amd the U.S. AN/M2 was 28kg, which is a considerable difference.

The AN/M2 was also much shorter in length overall, too.

compare British ww2 models as used.

 

[Clean32]

Since no profile of any WW2 aircraft actually was laminar flow we can all look at as many profiles as we think fit, what do they look like? How/ why was the Spitfire more economic on cruise settings, that isnt what I have read at all.

B24, was a true laminar flow wing.
laminar flow as designated by the aviation industry.

because the P51 wing was a near identical profile top and bottom. and the spitfire profile was a more traditional profile with a larger length top of the wing than the bottom of the wing.

the spitfire wing would produce lift with minim angle of attack, where the p51 wing could only produce lift with a lot of angle of attack.

so the slower the P51 is the more angle of attack it needs to crate lift, more angle of attack = more drag = more power = more fuel. until its traveling fast enough to need no angle of attack, at this point it has its minimum drag

the spitfire wing which produces more lift needed much less angle of attack as speed increased less and less angle of attack was needed. until it needed 0 deg. the most less drag at this point. BUT the down side is if speed increase past this point the wing is producing more lift than is needed. then you need a negative angle of attack. stick forward, nose down. to maintain level flight. and this increases' drag.

if you played with Kites when you were a kid. your string was attached further back in light winds and forwards in higher winds, same thing.

 

[GregP]

nice post
The cooling drag is close to zero due to the Meredith effect.. misleading. all fighter aircraft uses meredith effect to some existent. the P51 did this well.
But the original north american XP51 plans had a chin mounted radiator. this was changed due to British air ministry influence. firstly thinking the P51 as a P40 replacement. so the british North africa exspericans came into play.
the Hurricanes had less radiator damage than the P40. north americans purchase of curtis P46?? and the gaining of the internal flow Tech. but this was just the start point.
the real advantage was the scoop itself.

the bleeding edge scoop, so you are 100% correct when you wrote the P51 fuselage was quite slippery and not wrong when you wrote about the meredith effect but the meredith effect is a smaller part of the story than it really is. so its not so much that the meredith effect was increased to a point where it zeroed out drag. is more that the drag was decreased to match the meredith effect.

you compared to a spitfire. i have never found the numbers to do a good direct comparison. that's even after converting from Rabble gallons to real gallons. and its even just not what spitfire Mk but what wings it had, what blower etc. this gets really messy on the spitfire side really quickly.

so i would be interested in what anyone else has used?

but is we just look at 3 numbers, altitude, cruise speed in conjunction with fuel consumption. the spitfire could cover more distance, thus it is more slippery at cruse speeds of about 260Knts

But i would expect and the number seem to confirm, that at higher speeds. the spitfires more conventional wing, the drag would increases more than that of the P51 wing, and with speed the p51 wing would lose " angle of attack" and the conventional profile of the spitfire wing would keep on producing life, or excessive lift requiring a negative angle of attack.

The cooling drag of the P-51 was near net zero, no matter how it was achieved. No other airplane in WWII achieved zero cooling drag ... only the P-51.

A P-51 variant with a chin radiator was never built.

A Spitfire never flew that could match a P-51 for range.

A P-51D at 300 mph TAS burned about 55 - 60 U.S. gallons per hour at typical cruise altitudes in the ETO. 1 U.S. gallon is 1.2 Imperial gallons.

For cruising, the Spitfire IX recommended speed was 170 - 200 mph. There is no chart for power, speed, and fuel burn all at the same time that I can find in the pilot's manual. Go figure. For a Spitfire Mk XVI or a Mk IX, about +4 psi boost, 2650 rpm and will burn 71 Imperial gallons per hour, which is 60 US GPH. So, at 60 gph, the Mustang was cruising about 300 mph and the Spitfire speed is basically unknown. But we KNOW the Merlin Spitfires were slower than the Merlin Mustang at maximum power, so we can assume they were slower at cruise, too, without much chance of an error. Likely they were a bit slower, but not that much ... but we can't prove that with the standard pilot's manual. I could ask tomorrow at the Planes of Fame, assuming Steve Hinton is there. Maybe. We'll see.

But the Merlin Spitfire didn't generally out-speed or out-range the Mustang, ever. It DID climb better and was a better maneuvering turner. I'd prefer the Spitfire's cannons to the P-51's MG, too. But a Spitfire was never very good at stretching range or going especially fast ... except in a dive. It WAS the best diving piston fighter of the war, as far as I know. That has much more to do with gravity and a slightly better critical Mach number than any drag number at cruise speed though.

 

[GrauGeist]

compare British ww2 models as used.

That spec is for the RAF's HS.404...

The British never manufactured the M2 .50, the limited supply they used, were American AN/M2s.

 

[Simon Thomas]

B24, was a true laminar flow wing.
laminar flow as designated by the aviation industry.

"Laminar Flow" wrt aerofoils is always good for an argument. I subscribe to Eastman Jacob's definition, as he was the man who joined the dots with the research results and first coined the term.

 

[Clean32]

The cooling drag of the P-51 was near net zero, no matter how it was achieved. No other airplane in WWII achieved zero cooling drag ... only the P-51.

A P-51 variant with a chin radiator was never built.

A Spitfire never flew that could match a P-51 for range.

A P-51D at 300 mph TAS burned about 55 - 60 U.S. gallons per hour at typical cruise altitudes in the ETO. 1 U.S. gallon is 1.2 Imperial gallons.

For cruising, the Spitfire IX recommended speed was 170 - 200 mph. There is no chart for power, speed, and fuel burn all at the same time that I can find in the pilot's manual. Go figure. For a Spitfire Mk XVI or a Mk IX, about +4 psi boost, 2650 rpm and will burn 71 Imperial gallons per hour, which is 60 US GPH. So, at 60 gph, the Mustang was cruising about 300 mph and the Spitfire speed is basically unknown. But we KNOW the Merlin Spitfires were slower than the Merlin Mustang at maximum power, so we can assume they were slower at cruise, too, without much chance of an error. Likely they were a bit slower, but not that much ... but we can't prove that with the standard pilot's manual. I could ask tomorrow at the Planes of Fame, assuming Steve Hinton is there. Maybe. We'll see.

But the Merlin Spitfire didn't generally out-speed or out-range the Mustang, ever. It DID climb better and was a better maneuvering turner. I'd prefer the Spitfire's cannons to the P-51's MG, too. But a Spitfire was never very good at stretching range or going especially fast ... except in a dive. It WAS the best diving piston fighter of the war, as far as I know. That has much more to do with gravity and a slightly better critical Mach number than any drag number at cruise speed though.

correct

correct, i did say built but was the original North american design.

correct

i have a 51B 65 imp gallons and 220 knots and spitfire lX at 55 imp Gallons at 200 Knts. as i said hard to get data at 8000 feet

you are comparing Griffon powered spits. apples with Lemons.

correct, and out dive

 

[Clean32]

View attachment 736167

"Laminar Flow" wrt aerofoils is always good for an argument. I subscribe to Eastman Jacob's definition, as he was the man who joined the dots with the research results and first coined the term.

that he did.
intrestinthough, north american did not uses a Nacc profile. neither did super marine. to the best of my knowledge the only two who didn't.

 

[BarnOwlLover]

I'm not an expert, but one, I do know what I'm talking about, and two, when I do have questions or curiosities, I ask, and I do know that a lot of people here know a lot more than I do.

There was never (at least known) a Mustang with a chin radiator. Going back to the P-509 (which evolved into the NA-73X), all Mustang developments had a ventral radiator. The closest was the Rolls-Royce Mustang X Merlin engine test beds that were converted from RAF Mustang Is. The "chin" intake housed the intercooler and supercharger intake.

The Spitfire IXe and XIVe had 2 .50 Browning MGs and 2 20mm Hispano cannons. Spitfires from the Mk V onwards that were fitted with the "C" universal wing (of which the "E" was a variant of) could house 4 20mm cannons (not standardized until the Spitfire 21).

And the Hispano cannon was much larger than the .50 MG. The numbers I've seen for the .50 Browning aircraft model ranged between 52-65 lbs, the Hispano Mk II/M2 was 100-110 lbs, the Mk V/M3/M24 was 83-88 lbs. Numbers probably vary due to presence of extra equipment vs the basic weapon. Not to mention that it was quite a bit longer.

Also, until the XP-51F/G and P-51H, the Spitfire could easily outclimb the Mustang (better power to weight ratio due to being built to lower max load standards, which means lower weight), and should've been more maneuverable (especially at lower speeds) due to lower wing loading (again related to weight, though the P-51 could easily out roll the Spitfire unless the Spitfire had clipped wings until the Mk 21).

With the XP-51F/G (which weighed roughly the same as a Spitfire IX, though it carried more than twice the fuel), you had a plane with similar wing loading to the Spitfire and combined with improved control surfaces should've been more agile than a P-51D even with the D "flying light". The P-51H (production evolution of the F/G models) was comparable in weight to the Griffon Spitfires, with a similar power to weight ratio and wing loading. Of course, no comparative flights with the F/G/H was never done against the Spitfire.

Also, for extra credit, those aforementioned planes (as well as the XP-82/P-82B at least, and maybe the Allison powered P-82E/F/G/H and XP-51J) did have a radiator design that produced a positive thrust to drag ratio (so it actually produced more thrust than drag).

Otherwise, all I can say (not being an insane expert), is, paging drgondog...