That involves calculations and assumptions way above my pay grade
The Grandslam wasn't bothered about pulling out of its dive.
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Comparison in Diving Performance
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The Grandslam wasn't bothered about pulling out of its dive.Shortround6
Major General
The problem with using the engine/prop past a certain speed in the dive is that at some point the planes speed exceeds the rate of advance of the propeller (pitch X rpm) and even exceeds a fair amount of overspeed and the prop becomes a rotating air brake, may planes in dives were supposed to be operating at around 1/4 throttle.
So, yes the max speed in the dive is gravity vs aerodynamic drag (plus the prop).
So, yes the max speed in the dive is gravity vs aerodynamic drag (plus the prop).
The Hawker Tempest was also a great diving plane. Note also in the test Me109G is good also!
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Dive
34. The Tempest gains on the Spitfire XIV.
COMBAT TRIALS AGAINST FW.190 (BMW.801D)
Dive
40. The Tempest pulls away rapidly in a dive from all heights.
COMBAT TRIALS AGAINST Me.109G
Dive
46. Initial acceleration of the Tempest is not marked, but a prolonged dive brings the Tempest well ahead.
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......................
Dive
34. The Tempest gains on the Spitfire XIV.
COMBAT TRIALS AGAINST FW.190 (BMW.801D)
Dive
40. The Tempest pulls away rapidly in a dive from all heights.
COMBAT TRIALS AGAINST Me.109G
Dive
46. Initial acceleration of the Tempest is not marked, but a prolonged dive brings the Tempest well ahead.
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DarrenW
Staff Sergeant
I'm still trying to fully understand the attributes that made one air frame 'superior' in a dive over another. My general impression is that a very clean design will normally build up speed quickly (high acceleration possible) but maximum dive speed can be limited due to how it behaves as it enters compressibility (the P-38 comes to mind here). I also imagine that engine power and overall weight will affect these figures as well. But after reading some of the posts here I may be misunderstanding what truly affects this particular aspect of performance.
Although the P-38 was a relatively clean design for a twin-engine aircraft, the P-47 still maintained a lower zero-lift drag coefficient and smaller equivalent flat plate area, however total engine power goes to the P-38 which probably mitigated much of this. But the P-47 remained far more controllable as it entered into compressability (not sure how dive brakes might have changed the equation though). Because of these factors I can easily see how the P-47 can be close in acceleration to the P-38 but have a higher maximum sustainable dive speed.
Of course the P-51 was one of the war's most aerodynamic designs so it accelerated rapidly too and because of it's more advanced airfoil experienced compressibilty at a greater speed than either the P-38 or P-47. From what I read the P-47 was equally as fast in a dive as the P-51, the Thunderbolt's greater weight and power probably making up for it's larger aerodynamic footprint and more traditional airfoil.
I always was under the impression the P-51 could out accelerate the P-47 in a dive but some here seem to feel the opposite is true.
So I'm thinking it must be a combination of air frame drag, engine power, loaded weight, airfoil design, and to some extent structural strength, and depending on how they all "add up" determines an aircraft's overall all dive performance.
Can anyone elaborate further on this?
reason for edit: spelling
Although the P-38 was a relatively clean design for a twin-engine aircraft, the P-47 still maintained a lower zero-lift drag coefficient and smaller equivalent flat plate area, however total engine power goes to the P-38 which probably mitigated much of this. But the P-47 remained far more controllable as it entered into compressability (not sure how dive brakes might have changed the equation though). Because of these factors I can easily see how the P-47 can be close in acceleration to the P-38 but have a higher maximum sustainable dive speed.
Of course the P-51 was one of the war's most aerodynamic designs so it accelerated rapidly too and because of it's more advanced airfoil experienced compressibilty at a greater speed than either the P-38 or P-47. From what I read the P-47 was equally as fast in a dive as the P-51, the Thunderbolt's greater weight and power probably making up for it's larger aerodynamic footprint and more traditional airfoil.
I always was under the impression the P-51 could out accelerate the P-47 in a dive but some here seem to feel the opposite is true.
So I'm thinking it must be a combination of air frame drag, engine power, loaded weight, airfoil design, and to some extent structural strength, and depending on how they all "add up" determines an aircraft's overall all dive performance.
Can anyone elaborate further on this?
reason for edit: spelling
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- #26
Yeah, it's bullshit.
Actually there were at least two cases where the Spitfire lost a prop. One occurred during dive tests of the Mk.VII/VIII designs, the other was a PR variant that was modified with an all-moving tail for the Miles M.52 program.
That was during the Korean War, but it was a WWII design. If I recall he ended up stalling at around 50000' and ended up accelerating to around 0.96 Mach at around 40000'. The aircraft might not have been under ideally controlled conditions, but it was undamaged during the dive, as crazy as that happened.
While this will slightly detour from the topic, I remember that some spitfires had a "bead" like shape added to the elevator or tabs. Was this after WWII?
If you want to use unmanned aircraft, then you should have gone with the V-2. It reached around Mach 5. That said, I was kind of thinking of manned aircraft. That said, the Me 262 and P-80 could be good candidates. I don't know how the Me 163 would rank because, while it was slippery in shape, it also was out of fuel at high altitudes.
As for the Grand Slam and Tallboy, I thought they actually did reach supersonic speed when dropped from 18000-25000 feet?
As I understand it, the variables are how streamlined it is versus it's mass, and how much propulsive force is shoving it down along with the help of gravity.
From what I remember the P-47 would out-dive a P-51: The P-51 was slicker, but the P-47 wasn't bad, and it was considerably more massive. I'm not sure how the P-38 compares to the P-47.
What's a zero-lift drag coefficient? I assume that would be what the plane would do in a ballistic arc? As for flat-plate equivalency, I'm guessing that's what it says on the box, the drag produced by the aircraft correlating to a given amount of area of a flat object in the wind...
From what I remember, the P-47's placard limit seemed to be around 0.745 Mach. If I recall that's like 3 miles an hour different from the P-51 (Mach 0.75). If I recall they did dive speeds of 0.78 with the P-47B/C, so that was do-able early on. It was stated that they did 0.82 Mach with the use of dive-recovery flaps. I'm not sure if it was possible to recover without them at that speed, but that's a pretty good dive speed (the P-51 was limited to around 0.84), though.
As for the P-38's dive recovery flaps, as well as the P-47's: As I understand it, the way it helped facilitate recovery was by producing a large increase in drag and producing a nose-up trim. In other words, you were just as out of control at higher speeds in terms of elevator authority, but they slowed you down and popped the nose up.
Actually the Seversky airfoil, which was used on the P-35, and was modified on the P-47, was a pretty good airfoil. As for dive performance, from what I remember, the P-51 and P-47 were pretty close to each other.
GregP
Major
According to some modern P-47 pilots, the P-47 isn't all THAT fast in a dive. I spoke with one warbird pilot who took one to 30,000 feet in dived as vertically as he could. The airspeed went to 450 and stayed there. I am assuming it was IAS, so you can do the math.
The P-47's forte' was high altitude combat where the turbo allowed it to have an excess power advantage over many other opponents. Down lower than about 25,000 feet, though it was formidable, it was slower than many opponents. It was also very good as a fighter-bomber down really low with good firepower and good load-carrying ability but was less than top rank at medium altitudes as a pure fighter.
The P-47's forte' was high altitude combat where the turbo allowed it to have an excess power advantage over many other opponents. Down lower than about 25,000 feet, though it was formidable, it was slower than many opponents. It was also very good as a fighter-bomber down really low with good firepower and good load-carrying ability but was less than top rank at medium altitudes as a pure fighter.
The tall boy and grand slam were dropped from air breathing aircraft, not sent in a sub orbital lob by a rocket. As I understand it they couldnt go supersonic if dropped in the atmosphere, but as I said it involves "stuff" above my pay grade. I just used it as a comparison, if a grand slam doesn't go supersonic how would a P-47? Its engine at the front could have been designed as an air brake and the wings are huge. Reaching speeds of mach 0.9 in a dive doesn't mean you are in any way close to reaching mach 1, it is the equivalent to being at the base camp of Mt Everest. The 262 and P-80 weren't "good candidates", they were just above base camp too.
I also have comprehensibility-related issues...
The nacelles and pod on the P-38 created the venturi, that further accelerated the air stream. That, coupled by less-than-ideal airfoil (NACA 23016 at root) meant compressibility issues skyrocketed. NACA suggested, on the YP-38 they got, that chord need to be increased by 10% or 20% at the inboard wing section in order to decrease the thickness-to-chord ratio. Alternatively, they suggested the newly fanged 'laminar flow' wing section for P-38. The proposed 20% increase in chord also meant that center of lift is moved too far tot he front, so NACA further suggested that in the new 'free' volume the radiators need to be housed to balance things out.
Another problem on P-38 was the pod, particularly the too steep windscreen and rear end of the pod, that was also modified by NACA to improve critical Mach number.
NACA report
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- #30
This source seems to indicate the weapon could achieve a terminal velocity of 3600-3700 fps, though I don't know what altitude it was dropped from to achieve this speed.
I do remember in a documentary regarding the sinking of the Tirpitz, that the bomb was specifically said to achieve supersonic speeds on the way down.
Okay, I guess we sort of got off topic, focusing on supersonic flight rather than dive-acceleration rates. I was mostly interested in manned aircraft acceleration rates in dives.
My mentioning of the V-2 was that it reached Mach 5 in flight: The truth is, I don't know how fast it accelerated on the way up/down. That said, for acceleration rates, for manned aircraft, the Me-163, Me-262, or P-80 seem like good candidate as they have a streamlined fuselage, thin wings, and no propeller to produce air resistance at higher speeds.
Both the booms and the gondola did it?
I didn't know the windscreen caused a problem, but I knew about the gondola and the pod-afterbody. I'm surprised they didn't add the tail-cone extension.
DarrenW
Staff Sergeant
fastmongrel
1st Sergeant
I read somewhere that the sound barrier would be broken by a Tallboy dropped at 40,000ft but it would barely break the barrier mach 1.001 or some such
People routinely discuss supersonic speeds, a passenger plane just crossed the Atlantic at "supersonic speed" it had a 200+ MPH tailwind. The V2 got to 100miles above the earth, easy to tell how fact it was going when it hit the ground, if we had no atmosphere, which is the point.
Gentlemen:
P-47C compared to P-38F as reported by Air Fighting Development Unit (AFDU) Jan 1943
P-47C v. P-38F
36. At the request of the U.S.A.A.F., the trials included comparative flights and mock flights between 20,000 and 30,000 feet against the P-38F "Lightning", which develops its full power at 25,000 feet.
37. Performance – At 20,000 feet the P-38 was able to pull away from the P-47 at 10 to 15 m.p.h., though the acceleration of both was almost identical. By 24,000 feet the performance of the two aircraft was approximately equal and above 25,000 feet the P-47 had obtained a speed superiority of about 10 m.p.h.
38. Climb – In comparative climbs both between 20,000 feet and 25,000 feet, and 25,000 feet and 30,000 feet, the P-38 was easily able to out-climb the P-47 at a better rate of climb and far steeper angle.
39. Dive – In comparative dives there was nothing to choose between the two aircraft, save that the P-38 is limited by buffeting in high speed accelerated flight.
40. Manoeuvrability – In turning circles the P-38 was slightly better and was certainly able to turn so slowly in a climbing turn, especially to the right, that the P-47 was unable to follow. When 'bounced' by the P-47, the P-38 was able to turn very sharply and decelerate much more quickly than the P-47.
(My bolding)
Source
P-47 Tactical Trials
For your consideration.
Eagledad
P-47C compared to P-38F as reported by Air Fighting Development Unit (AFDU) Jan 1943
P-47C v. P-38F
36. At the request of the U.S.A.A.F., the trials included comparative flights and mock flights between 20,000 and 30,000 feet against the P-38F "Lightning", which develops its full power at 25,000 feet.
37. Performance – At 20,000 feet the P-38 was able to pull away from the P-47 at 10 to 15 m.p.h., though the acceleration of both was almost identical. By 24,000 feet the performance of the two aircraft was approximately equal and above 25,000 feet the P-47 had obtained a speed superiority of about 10 m.p.h.
38. Climb – In comparative climbs both between 20,000 feet and 25,000 feet, and 25,000 feet and 30,000 feet, the P-38 was easily able to out-climb the P-47 at a better rate of climb and far steeper angle.
39. Dive – In comparative dives there was nothing to choose between the two aircraft, save that the P-38 is limited by buffeting in high speed accelerated flight.
40. Manoeuvrability – In turning circles the P-38 was slightly better and was certainly able to turn so slowly in a climbing turn, especially to the right, that the P-47 was unable to follow. When 'bounced' by the P-47, the P-38 was able to turn very sharply and decelerate much more quickly than the P-47.
(My bolding)
Source
P-47 Tactical Trials
For your consideration.
Eagledad
DarrenW
Staff Sergeant
Total drag (CD) - induced drag (CDi) = zero lift drag coefficient (CD0)
Both total drag and induced drag take wing area into account, while zero lift drag removes the induced portion of drag (or that which produces lift i.e. wing) of total airframe drag.
The value of the zero-lift drag coefficient is often used as an indicator of the aerodynamic cleanliness or refinement of an aircraft, or the amount of parasitic drag present.
Equivalent flat plate area (or "drag area") is zero lift drag x wing area. Some say that this is a true representation of an aircraft's physical "foot print" in the air and will indicate how much thrust is needed to overcome total drag in order to produce a desired performance.
This is about the extent of knowledge I have on the subject.
That's why I posted the calculations are above my pay grade. The atmosphere becomes thicker and thicker, then you hit the ground.
Back to my pet peeve, static ports! No way an aircraft designed for pre supersonic flight is going to give you reasonably accurate airspeed indications once you bump up against the transonic range. Once shock waves form and Center of Pressure shifts, static port installations carefully developed for subsonic flight are likely subject to faulty sampling of static pressure. As SR6 mentioned above, the propeller arrives at an overrun condition near critical Mach, where it's an airbrake, creating cavitations and low pressure areas all around the fuselage. This is going to result in an absurdly high airspeed indication, especially considering that also the pitot tube is likely starting to push a pressure wave.
I agree, those IAS numbers are BOLLOCKS.
Cheers,
Wes
As for Tallboys/Grand Slams/V2s and Mach busting; it seems to me that it's all a function of how much acceleration is achieved in the thin atmosphere before the drag rise of the lower atmosphere sets in.
My experience in my one and only supersonic ride confirmed what I'd been told, that drag rises exponentially in the last 10% before Mach 1. Burners came on at .72, and with my helmet pinned to the head rest, I could look down past my oxygen mask just enough to see the Machmeter advance rapidly to about .92, then gradually slow and creeeep up to 1, then 1.05, then somewhat faster to 1.15, where there was a slight but noticeable reduction in N1, and speed stabilized.
That's when "Preacher", my pilot, said: "There we are, 1.15, welcome to the club! Notice the fuel flow and fuel remaining? We're flying AWAY from the fuel and about to penetrate Pensacola's practice area. Deselecting afterburner, now." WHUMPFF! We flew into a brick wall, and my head flew off the headrest and arms off the armrests. A more convincing proof of shock wave drag would be hard to devise. We rolled into a 3.5 G turn and headed for homeplate.
Cheers,
Wes
My experience in my one and only supersonic ride confirmed what I'd been told, that drag rises exponentially in the last 10% before Mach 1. Burners came on at .72, and with my helmet pinned to the head rest, I could look down past my oxygen mask just enough to see the Machmeter advance rapidly to about .92, then gradually slow and creeeep up to 1, then 1.05, then somewhat faster to 1.15, where there was a slight but noticeable reduction in N1, and speed stabilized.
That's when "Preacher", my pilot, said: "There we are, 1.15, welcome to the club! Notice the fuel flow and fuel remaining? We're flying AWAY from the fuel and about to penetrate Pensacola's practice area. Deselecting afterburner, now." WHUMPFF! We flew into a brick wall, and my head flew off the headrest and arms off the armrests. A more convincing proof of shock wave drag would be hard to devise. We rolled into a 3.5 G turn and headed for homeplate.
Cheers,
Wes
That is my understanding, I believe that in a theoretical situation with an unlimited atmosphere as we have at sea level and a force of 1G a tallboy would never break the sound barrier. Take one up to 100 miles high in the real world and it will on the way down then hit the earth before it has slowed down to its terminal velocity in air again. Unfortunately no Lancasters flew to 100 miles high and since the tallboy and grand slam were dumb bombs even dropping from 40,000 ft would mean you just didn't get any close enough.
The USAF man that jumped from a balloon at 100,000+ feet in the early 60's exceeded the speed of sound.
He even had a small stabilizing parachute trailing him to prevent tumbling.
Can't remember his top speed , but somewhere around 600 mph, corrected, I think.
