davparlr
Senior Master Sergeant
This would make sense. Calibrated AS is Idicated AS corrected for installation error. With good CAS, IAS would not be needed.
The sound barrier
- Thread starter Velius
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This would make sense. Calibrated AS is Idicated AS corrected for installation error. With good CAS, IAS would not be needed.
Evening Wayne.
Stumbled across an article describing an unintentional "rapid" descent (48,000ft in less than 60sec) by one Flt Lt Powles in 1952 piloting a PR MK XIX. Mach 0.96, although I don't know how they determined this if the dive was by "accident".
Either way, nice painting by Keith Woodcock of the event...
so, let me, a big noob, ask something here:
how can a prop plane reach such speeds, even in dive?
From what i've read and only from that, at a certain point of the dive, the airflow hitting the propeller is higher than the speed of the propeller itself, at that point, the propeller becomes an air brake,not letting the airflow passing through.(or something like that)
So, what logic (and math) is behind the magic 0.94M dive of the spit with its 3meters wide airbrake? For me, such speeds with a propeller made in the 40's are simply male cow excrements.
how can a prop plane reach such speeds, even in dive?
From what i've read and only from that, at a certain point of the dive, the airflow hitting the propeller is higher than the speed of the propeller itself, at that point, the propeller becomes an air brake,not letting the airflow passing through.(or something like that)
So, what logic (and math) is behind the magic 0.94M dive of the spit with its 3meters wide airbrake? For me, such speeds with a propeller made in the 40's are simply male cow excrements.
delcyros
Tech Sergeant
Altough the M= 0.96 incident appears to be suspect from the first view, one has to carefully read the report first. I have not but I remain open for surprises.
Things which make it suspect in my subjective perspective:
A) -The Spitfire PR mk XIX was a service plane and not specially treated or enjoiing fine calibrated instrumentation.
B) -The Spitfire PR mk XIX has a lower crit Mach than the MK IX
C) -The high speed Spit mk IX used for dive tests earlier was equipped with a special low drag, fully feathering rotol airscrew to avoid overspeeding the engine, the PR mk XIX was equipped with stdt. prop.
D) -the PR mk XIX didn´t had one prop airbrake discs but two of them
E) -as far as I remember, the pressure increase alone broke the gear prop in M= 0.89 high speed dive tests on the Spit IX -while no such damage was reported in the PR mk XIX
F) -the cockpit carries it´s own shockwave and starts buffeting before the wing, contrary to description and art drawing.
....all on the level of speculation, I admit.
When it comes to breaking the sound barrier, I don´t think that any ww2 plane could really do this on a normal condition.
It is one thing to go past the barrier -a fuselage seperated from the wings may achieve this- but it´s another thing to come back into normal speed regimes survive.
If I had the eggs to try and choose a plane to carry me there back, I would choose the Me-163. Fortunately I am just a nerd and not in any opportunity...
Things which make it suspect in my subjective perspective:
A) -The Spitfire PR mk XIX was a service plane and not specially treated or enjoiing fine calibrated instrumentation.
B) -The Spitfire PR mk XIX has a lower crit Mach than the MK IX
C) -The high speed Spit mk IX used for dive tests earlier was equipped with a special low drag, fully feathering rotol airscrew to avoid overspeeding the engine, the PR mk XIX was equipped with stdt. prop.
D) -the PR mk XIX didn´t had one prop airbrake discs but two of them
E) -as far as I remember, the pressure increase alone broke the gear prop in M= 0.89 high speed dive tests on the Spit IX -while no such damage was reported in the PR mk XIX
F) -the cockpit carries it´s own shockwave and starts buffeting before the wing, contrary to description and art drawing.
....all on the level of speculation, I admit.
When it comes to breaking the sound barrier, I don´t think that any ww2 plane could really do this on a normal condition.
It is one thing to go past the barrier -a fuselage seperated from the wings may achieve this- but it´s another thing to come back into normal speed regimes survive.
If I had the eggs to try and choose a plane to carry me there back, I would choose the Me-163. Fortunately I am just a nerd and not in any opportunity...
drgondog
Major
so, let me, a big noob, ask something here:
how can a prop plane reach such speeds, even in dive?
From what i've read and only from that, at a certain point of the dive, the airflow hitting the propeller is higher than the speed of the propeller itself, at that point, the propeller becomes an air brake,not letting the airflow passing through.(or something like that)
So, what logic (and math) is behind the magic 0.94M dive of the spit with its 3meters wide airbrake? For me, such speeds with a propeller made in the 40's are simply male cow excrements.
It's complicated. First thing is the Propeller creates Thrust by virtue of changing the momentum of the freestream air as it passes through the blade plane. As you note the Propeller as a system also creates drag which increases dramatically at high speeds.
The question (and I don't have an answer) is a.) how much if any thrust in excess of drag remains in the .8-9 Mach range, and b.) how much drag is created by the total wing/body combination in the specific dive profile in question, c.) does the residual thrust of the propeller system plus the weight of the airframe slightly overcome the drag so that the airplane continues to accelerate, even if very slightly?
When all these forces are in balance the system will be in equilibrium (a very fast but constant velocity 'equilibrium').. so long as the aerodynamic (the 'q' ) loads do not cause a structural failure.
So the questions regarding both the Spitfire Me 262 results are, in my opinion, 1.) what was measured accurately, and 2.) where are the limts to areodynamic loads to the airframe structure?
If the latter, then a large mass of parts will separate and become a cloud of debris.
drgondog
Major
Delcyros - I tend to agree but confess that I have no clue what a.) the transonic characteristics were for the Me 163, no do I really have any insight to the specific wing design. I suspect that the 163 could not go supersonic because of the wing, despite the beneficial sweep angle
One of the ways flying wing designer's 'cheated' was to design a lot of camber into the wing to alter the CMac characteristics to compensate for a lack of a horizontal stabilizer. Unlike a 262 wing with a CMac causing a nose down on stall, the opposite is true for the type cambered wing normally associated with flying wings, and no elevator to compensate.
Also, IIRC the 163 had a pretty thick wing??
Recall that Glenn Edwards' fatal crash of the YB-49 when it was believed to completely roll about the wing axis, onto its back and go into a spin - after it stalled out. That Cardenas survived the first experience was a miracle.
Even today we are fooling around with subsonic a/c despite 70 years of development. The B-2 flight control systems allegedly PREVENT any possible stall attitude that can be initiated by the pilot.
Everything I just said is 'old memory' so take with a grain of salt.
Anyone know if "Mach Buster" ever came close to its namesake?...
Photos: Rose Mach Buster Aircraft Pictures | Airliners.net
Photos: Rose Mach Buster Aircraft Pictures | Airliners.net
Hello
I have read on Powles dive from two articles a while ago and I also have my doubts but at least atmosphere conditions are known because Powles took up measurements during his climb, that was one of the purposes of the flight, IIRC the main purpose.
To Delcyros comments a couple corrections:
RAE test plane(s) in high speed dives was/were PR XIs and later Mk 21 not Mk IXs
Quote:"E) -as far as I remember, the pressure increase alone broke the gear prop in M= 0.89 high speed dive tests on the Spit IX -while no such damage was reported in the PR mk XIX"
RAE made numerous dive tests up to speed .89 and usually without damage to the plane (PR XI) but there were two exceptions, Martindale's .91 dive on 27 April 44 when reduction gear and propeller broke away and later, again when Martindale was the pilot when he suffered a complete supercharger failure and engine fire.
And I don't understand the following:
Quote:"D) -the PR mk XIX didn´t had one prop airbrake discs but two of them"
PR XIX didn't have contra-propelling propeller but normal 5-blade propeller
Juha
I have read on Powles dive from two articles a while ago and I also have my doubts but at least atmosphere conditions are known because Powles took up measurements during his climb, that was one of the purposes of the flight, IIRC the main purpose.
To Delcyros comments a couple corrections:
RAE test plane(s) in high speed dives was/were PR XIs and later Mk 21 not Mk IXs
Quote:"E) -as far as I remember, the pressure increase alone broke the gear prop in M= 0.89 high speed dive tests on the Spit IX -while no such damage was reported in the PR mk XIX"
RAE made numerous dive tests up to speed .89 and usually without damage to the plane (PR XI) but there were two exceptions, Martindale's .91 dive on 27 April 44 when reduction gear and propeller broke away and later, again when Martindale was the pilot when he suffered a complete supercharger failure and engine fire.
And I don't understand the following:
Quote:"D) -the PR mk XIX didn´t had one prop airbrake discs but two of them"
PR XIX didn't have contra-propelling propeller but normal 5-blade propeller
Juha
delcyros
Tech Sergeant
my mistake Juha, thanks for correcting me.
Additional damage received on the PR mk IX was a good deal of engine cowling carried away by buffeting forces. I am very surprised that no such damage occurred on the 1952 M=.96 dive albeit the PR mk XIX would be subject to more severe buffeting effects into the compressibility range.
Additional damage received on the PR mk IX was a good deal of engine cowling carried away by buffeting forces. I am very surprised that no such damage occurred on the 1952 M=.96 dive albeit the PR mk XIX would be subject to more severe buffeting effects into the compressibility range.
To me max speed achieved by Spitfire is Mach .89 (or .91, see my next message) because it was highest speed measured scientifically when the a/c stayed together incl. the propeller. And one must remember that the Spit was PR XI, so it was without protruding gun barrels, ejection chutes, overwing blisters and bullet-proof windscreen and with fully feathering propeller. Probably max possible to standard fighter version was appr. Mach .85. And that is only a guess, I'm not aerodynamist but a historian.
Juha
Juha
Hello Delcyros
It easy to become confused on these dive tests, I just checked Dennis' Royal Aircraft Establishment at war at according to it max recorded speed for PR XI was Mach .91, again flown by Martindale. It seems that that dive was made earlier than the famous 27 April dive.
Juha
It easy to become confused on these dive tests, I just checked Dennis' Royal Aircraft Establishment at war at according to it max recorded speed for PR XI was Mach .91, again flown by Martindale. It seems that that dive was made earlier than the famous 27 April dive.
Juha
drgondog
Major
Juha - just a note. First I subscribe to your basic premise regarding achievements made with verifications and adequate instrumentation are the only ones worth debating.
As a former aerodynamicist/Structural analyst/airframe designer (long retired and 'old') PREDICTIONS regarding propeller driven a/c near Mach 1 would be as much art as science for many of the reasons well discussed in this thread.
As a former aerodynamicist/Structural analyst/airframe designer (long retired and 'old') PREDICTIONS regarding propeller driven a/c near Mach 1 would be as much art as science for many of the reasons well discussed in this thread.
kool kitty89
Senior Master Sergeant
At least at the root, according to: The Incomplete Guide to Airfoil Usage it had:
Me 1.8 25 14-1.1-30 (root) NACA 00008-1.885-20 (tip)
So the root was certainly thicker than the Me 262's (and possibly similar to the Spitfire's with sweep taken into account) and uses an airfoil with a lot of chamber. The tip is thinner than the Me 262's however (and of a similar symmetrical type as the Me 262), so without knowing how the wing tapers (and where the airfoil changes -I'd guess it's where the slots start) it's difficult to make comparisons.
claidemore
Senior Airman
kool kitty89
Senior Master Sergeant
The greater weight of the griffon powered versions should also counter the added drag from the increase in prop blades.
delcyros
Tech Sergeant
The Me-163 has quite thick wingroots and wooden wings (structurally questionable in the transsonic regime) but this is why I would choose her in a dive:
A) The Me-163 has a smaller frontal area than everything else in question
B) The engine delivers ca. 2 tons of thrust regardless of altitude (unlike jet engines). It´s powerplant in fact accelerates any serial Me-163B past it´s critical Mach speed at all but low altitudes* in level flight, let alone in a dive from very high altitude as one might need to engage in order to hit Mach 1 in that A/C. The rocket engine also don´t shuts down following a Mach stall.
C) There is no washout at the wingtips and no stabilizer to carry it´s own (additional) shockwave
D) the (comparably) thick wings do allow more strength structurally (well it´s wood, so it needs it, don´t know what Mach 1 would mean thermally but if You have the right wood and the right glue agent with the right treatment perhaps?) and are framed with tight subdivision.
E) Following earlier tests, the vertical rudder was structurally enforced to deal with increased forces of transsonic regimes and the elevons were reshaped for the same reason
*) High speed level flights carried out at 4000m had to be abandoned after reaching M=0.85
A) The Me-163 has a smaller frontal area than everything else in question
B) The engine delivers ca. 2 tons of thrust regardless of altitude (unlike jet engines). It´s powerplant in fact accelerates any serial Me-163B past it´s critical Mach speed at all but low altitudes* in level flight, let alone in a dive from very high altitude as one might need to engage in order to hit Mach 1 in that A/C. The rocket engine also don´t shuts down following a Mach stall.
C) There is no washout at the wingtips and no stabilizer to carry it´s own (additional) shockwave
D) the (comparably) thick wings do allow more strength structurally (well it´s wood, so it needs it, don´t know what Mach 1 would mean thermally but if You have the right wood and the right glue agent with the right treatment perhaps?) and are framed with tight subdivision.
E) Following earlier tests, the vertical rudder was structurally enforced to deal with increased forces of transsonic regimes and the elevons were reshaped for the same reason
*) High speed level flights carried out at 4000m had to be abandoned after reaching M=0.85
I still say the Me-262 came the closest, although there is a possibility the Me-163 could go faster and infact went supersonic. But structurally the Me-262 is the soundest of any of the a/c who came close, the problem is the pitching down above Mach 0.86 and the possible stall of the engines.
Soren
in Me 262 the pitching down began earlier, Mach 0.84 was the max E Brown thought he could handle, in fact he dived faster in Spit PR XI (Mach 0.86)
Of course while testing the behavior of Me 262 in dive Brown only needed to get enough in troble to confirm German findings but when he made his dives in Spit XI he was a member of a team studing a/c behaviour at high Mach numbers (at the time) but also then other members of the team achieved higher speeds.
Juha
in Me 262 the pitching down began earlier, Mach 0.84 was the max E Brown thought he could handle, in fact he dived faster in Spit PR XI (Mach 0.86)
Of course while testing the behavior of Me 262 in dive Brown only needed to get enough in troble to confirm German findings but when he made his dives in Spit XI he was a member of a team studing a/c behaviour at high Mach numbers (at the time) but also then other members of the team achieved higher speeds.
Juha
