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

[pbehn]

In regards to the Spit one of the biggest causes of drag is the one thing never mentioned, the angle of the windscreen.

Lednicer focused on the windscreen drag of the Spit IX and showed a stagnation region at the base of the P-51B windscreen in his CFD pressure distribution plots form VSAERO. IIRC he also speculated that the first indication of a Mcrit transition occurred there,

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.

 

[PAT303]

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.

You can't climb like a rocket without good cooling, she still did 450mph so they couldn't have been that bad.

 

[Thumpalumpacus]

It's interesting that you aren't able to understand that they were trying to achieve, they tested at low level to increase the level of bug debris which is the purpose of the testing, they wanted real world data, likewise how do P51's get to 25,000ft?, are they just magically get there or do they take off from the ground and fly at low altitude, say 500ft first?.

And how much time do they spend @ 500 AGL compared to high? And I'm pretty sure we had the technology to, you know, wash the planes.

No one is arguing these wings are perfect solutions. What is being pointed out is that they're a big reason for the plane's efficient use of power. Given that drgondog has written a very thorough book on this plane's development, I weight his words more that I do yours.

 

[GrauGeist]

Of course, the P-51 (and literally every other aircraft made) would see flight at 500 feet, but how long did the P-51 operate at this height as opposed to standard operations?

Landing and taking off as well as ground attack involved a small portion of a typical P-51's mission and even then, insect contact would primarily occur during certain times during spring into summer, weather permitting.

 

[pbehn]

Of course, the P-51 (and literally every other aircraft made) would see flight at 500 feet, but how long did the P-51 operate at this height as opposed to standard operations?

Landing and taking off as well as ground attack involved a small portion of a typical P-51's mission and even then, insect contact would primarily occur during certain times during spring into summer, weather permitting.

With the Mustang Mk I and II 500 ft and lower was where they frequently did their work.

 

[drgondog]

That's true but from what I've read Laminar flow wings need to be perfect to work, and I mean perfect, dirt dust grass is enough to effect the laminar flow. I've never read anything other than a poor finish such as chipped paint causing issue's with elliptical wings which is true for every other type also.

Laminar flow 'exists' at approximately RN 500,000 - or just about taxi speed out of the chocks. Laminar Flow per se, never existed in any wing including P-51 45-100 series. That said, the Mustang wing did achieve 'Laminar Flow like' results in comparison to conventional NACA 23xxx wings - namely in delayed boundary layer separation. The region behind the BL separation is extremely turbulent, low energy flow which is a factor to increase friction drag.

Where the NAA High Speed/Low Drag excelled, was a.) extremely low profile drag due to the shape of the airfoil, b.) extended attached boundary layer before adverse pressure gradient caused separation - due to the aft location (relative to every conventional fighter with T/C max~ 25-30% Chord) of 37.5%, and c.) extreme care inproduction process relative to butt joints, small openings in the surfarce of the wing, sealed control surfaces, flush rivets, puttying/sanding and priming Leading Edge to 40% Chord. Additionally the ammo/gun bays were aft of Max chord Thickness. RAF ran some experiments at RAE to polish the surface and found little improved speed gain.

The lore of chipped paint and scuff marks are way overstated as detrimental to the Mustang wing. Obviously operating out of muddy airfields without some cleaning would be detrimental, but dirt/dust/grass was not a big issue.

Friction drag is what you are talking about, and three of the primary causes are a.) very grainy paint, b,) pan head rivets or poor countersink for flush rivets, c.) gaps in the wing skin - all of which tend to trip boundary layers 'before they should with reasonable production standards.

Elliptical wings optimize lift distribution and as such, reduce Induced drag due to the downwash.

Trapezoidal wings are 'nearly as good' depending on tip/root chord ratio - and far more easier to construct with consistency.

Flying at 10 feet was not any more deliterious (measurable) relative to friction drag than 500 feet. What is true however, is that Friction Drag is proportional to RN and will decrease for same velocity as altitude increases

 

[Deleted member 68059]

In regards to the Spit one of the biggest causes of drag is the one thing never mentioned, the angle of the windscreen.

+6mph for the screen.

Supermarine thought about +10mph for a laminar wing

 

[PAT303]

I weight his words more that I do yours.

Seriously mate you have totally lost what I said, the P51's laminar flow wings weren't the be all to end all, like the Spitfires drag, windscreen angle, cannon's, blisters, undercarriage it all added up, the Mustangs speed came from a combination of many small details too, flush riveting, radiator, wings etc added together, there was no silver bullet.

 

[PAT303]

+6mph for the screen.

Supermarine thought about +10mph for a laminar wing

View attachment 735834

With the external bullet proof windscreen and mirror it was even worse.

 

[Thumpalumpacus]

Seriously mate you have totally lost what I said, the P51's laminar flow wings weren't the be all to end all, like the Spitfires drag, windscreen angle, cannon's, blisters, undercarriage it all added up, the Mustangs speed came from a combination of many small details too, flush riveting, radiator, wings etc added together, there was no silver bullet.

Nowhere did I say any of that you seem to be arguing against. I'd suggest that you're not really reading what has been written. Where've I written that LF wings were the be-all and end-all? Where've I written that it was only laminar-flow wings that made the Mustang a great fighter?

Aside from this red-herring/strawman here, you still haven't answered the questions I've laid to you, anyway.

 

[Thumpalumpacus]

Of course, the P-51 (and literally every other aircraft made) would see flight at 500 feet, but how long did the P-51 operate at this height as opposed to standard operations?

Landing and taking off as well as ground attack involved a small portion of a typical P-51's mission and even then, insect contact would primarily occur during certain times during spring into summer, weather permitting.

There's also that washing and waxing for best-performance thing. Like bugs couldn't be washed away.

 

[GrauGeist]

There's also that washing and waxing for best-performance thing. Like bugs couldn't be washed away.

I'd be more concerned about Cosmic Dust and Negative Waves...

 

[pbehn]

Seriously mate you have totally lost what I said, the P51's laminar flow wings weren't the be all to end all, like the Spitfires drag, windscreen angle, cannon's, blisters, undercarriage it all added up, the Mustangs speed came from a combination of many small details too, flush riveting, radiator, wings etc added together, there was no silver bullet.

Second degree conics is another I learned recently.

 

[pbehn]

With the external bullet proof windscreen and mirror it was even worse. View attachment 735841

Supermarine were of course aware, PR Spitfires had a curved windscreen. The problem being that even if you can make a curved screen from BP glass it becomes a lens.

 

[Deleted member 68059]

With the external bullet proof windscreen and mirror it was even worse. View attachment 735841

I`ll dig out info on wing cleaning up of the p-51 and the effect compared to other aircraft, they did a lot of that for V1 chasing.

 

[PAT303]

Supermarine were of course aware, PR Spitfires had a curved windscreen. The problem being that even if you can make a curved screen from BP glass it becomes a lens.

From what I have read it caused optical distortion so it wasn't followed through.

 

[pbehn]

From what I have read it caused optical distortion so it wasn't followed through.

With the laws of physics being what they are it is very hard not to.

 

[PAT303]

I`ll dig out info on wing cleaning up of the p-51 and the effect compared to other aircraft, they did a lot of that for V1 chasing.

RAE 1501

 

[PAT303]

With the laws of physics being what they are it is very hard not to.

Reading the report they wanted to fit the curved windscreen to V1 chasers also.

 

[pbehn]

Reading the report they wanted to fit the curved windscreen to V1 chasers also.

A V1 didnt change direction or fire back.