Best Piston Engined Fighter Ever...

[drgondog]

Originally Posted by kool kitty89

I think by "suction" Soren meant the lower preassure on the aft part of the bubble canopy (a slight vacuum), similar to the phenomon at the tail of a bullet.

KK- possibly that is what he meant. However, in the case of the Lednicer model Gene Davidson was kind enough to give both of us it has the classic meaning for 'suction' - meaning 'lower pressure' relative to free stream dynamic pressure.

In the case of the models 'suction is another word for 'lift' and more importantly area where the flow has not separated and created wake (or Profile Drag). In the case of the model that is 'good' for the 51D and 'bad' for the Spitfire and fw 190D and the P51B.

The red area is alternatively 'suction' or 'lift'.. you may note the 'red area' on the wing/body model. The model show a very nice aerodynamic effect on the P-51D by virtue of both the lower angle slope on the front windscreen and the near 'high camber/thickness airfoil' curvature of the canopy. The very nice surface coverage represents OPTIMAL laminar flow region, never fully achieved but instructional nevertheless.

The wake behind a Spitzer bullet is 'bad' and represents the key parameter for Profile/wake drag. Ditto the Spitfire and fw 190 'bad' regions as the flow moves up over the windscreen.

[drgondog]

Originally Posted by kool kitty89

The phrasing seems a little confusing, but I assume the added 600 lbs from going to the B to D Mustang. (I don't think switching to the Bubble canopy changed weight much)

No, the Bubble canopy effectively was offset by removing the extra top bulkhead/skin and stringer of the P-51B 'turtleback'. The bigger increases were beefed up spar for vertical stabilizer and adding two more 69 pound M-2's plus 700 rounds of .50 caliber ammo..

The worst result of removing the turtleback was slight loss of yaw stability requiring first a 'dorsal' fin modification the the production P-51D-5 tail, then a permanent change for all succeeding D/K models, and then a new, 'taller tail' for the P-51H

The bubble canopy was one of the reasons in drop in speed. Plus weight has a much larger effect on climb than speed. Streamining has the opposite effect. (speed much more than climb)

In my opinion it (bubble canopy) had the opposite effect and at worst was neutral based on Lednicer's model. As far as weight, remember that for same relative speed, Lift (and therfore Induced Drag) is increased for the heavier aircraft.. so that an airplane with exactly the same engine with the same basic aero flown at same speed (and Lednicer says the 51B and D had the same wetted drag coefficient) the heavier bird will not perform as well

On the P-47 the bubble canopy lost it ~5 mph top speed. The wing pylons cut 10-15 mph off speed. (much more on early versions, though not on any standard production versions iirc)

The nose of the P-47J helped speed as well. (prabably added ~20 mph)

Absent any actual wind tunnel comparisons I woul tend to disbelieve the razorback was any more aerodynamically sound with respect to drag and probably had the same effect for yaw stability as the 51B to 51D.

I also suspect when the late model 47D's added the bubble canopy they also added the wing pylons as well as internal fuel capacity.. Weight in moving from one model of the same airframe to the next was usually a far more important factor, even with bigger engines, unless the wing area was increased. The pylons ALWAYS increased drag as did gun gondolas.

The radiator/cooling designs were the real plus of the Mustang over the Spitfire, when combined with the proprietary Mustang 'laminar flow' wing.. that's why the same engine in a heavier airplane was faster and travelled farther.. it also lost energy slower (usually) in similar manuevers with an a/c with similar thrust to weight ratio but more drag.

[kool kitty89]

And also why the P-51A (along with the overall streamlining) was much faster and fuel efficient than the P-40M/N with the same engine and similar weight. Climb was about the same (slightly better for the P-51A) and turn rate was a tad better on the P-40. (radius was more noticeable, as the P-40 had better lift loading nut the cleaner airframe of the P-51 gave it better energy retention)

IMO the P-40/P-51 comparison is alot closer than the Spit/P-51 comparison, though both are valid. (on a side note: the close location of the radiator and oil cooler to the engine mad the P-40 a good deal less volnerable than the P-51, Spitfire, or Me 109)

No, the Bubble canopy effectively was offset by removing the extra top bulkhead/skin and stringer of the P-51B 'turtleback'. The bigger increases were beefed up spar for vertical stabilizer and adding two more 69 pound M-2's plus 700 rounds of .50 caliber ammo..

According to: The WWII Fighter Gun Debate: Gun Tables the M2 was only ~64 lbs, but close enough. And only the innermost guns on the P-51 carrier 350 rpg, the outboard 2/4 guns of the P-51B(C)/D carried only 280 RPG according to JoeB's site. (as well as others)