Question about intakes - Page 3

glyn · 07-12-2007, 15:24 PM

Quote:

Originally Posted by pdf27

Source on that is private comments by a former B-52 groundcrewman. It didn't particularly surprise me though - official figures quote a maximum speed of 550kts at 20,000ft, or about 0.95 Mach. 20,000ft is implausibly low for maxiumum speed to be measured at for a jet aircraft - the official figures note "limited by structure". Move up to a more normal operating height of 40-50,000ft and that structural limit pretty much goes away due to reduced air density. The thrust figures used are also for "military power" - again, suggesting that more power was available.

I have the Flight Manuals and the Operating Data Manuals for the type. Without revealing what the actual figures are, suffice it to say that they were (and are) firmly sub-sonic. The actual altitude for maximum performance depends on which country or even service you belong to. For the US Navy and Marine Corps it is 36,089 feet. For the USAF 36,090 feet, while the laid back Brits make do with 36,100 feet!

1957 or later, correct?

Armament Pracice camp, late summer 1958. Good deduction!

It would have been pretty much obselescent by then, as the last were retired in February 1959. Incidentally, their combat ceiling was rated at 40,000ft or so with their service ceiling (rate at which climb drops to 100 fpm) at around 30,000ft. At least, that's what the official numbers say

Again, I have the Dash Ones and the ODMs for the type. Collecting the things has been my hobby for virtually half a century!

pdf27 · 07-12-2007, 19:15 PM

Quote:

Originally Posted by glyn

I have the Flight Manuals and the Operating Data Manuals for the type. Without revealing what the actual figures are, suffice it to say that they were (and are) firmly sub-sonic.

Ummm... you'll have to forgive me being a little sceptical on that one. If something can do 0.95 Mach at 20,000ft there is no fundamental aerodynamic reason it isn't supersonic under the right conditions. Controllability is a minor issue, but one that I'd be stunned if they didn't fix during the flight test programme.

Incidentally, those manuals remind me of the pilot's notes for a glider I once flew. One part went something like this:

Quote:

This aircraft is non-aerobatic and must not be looped.
Minimum loop entry speed is 85 knots

Scurrilous rumours that I've personally verified this speed are of course quite untrue.

Quote:

Originally Posted by glyn

Armament Pracice camp, late summer 1958. Good deduction!

Not hard given the mark of Hunter involved. Late summer 1958 makes it one of the very last B-36s, with most of the rest already retired.

glyn · 07-13-2007, 04:55 AM

[quote=pdf27;389279]Ummm... you'll have to forgive me being a little sceptical on that one. If something can do 0.95 Mach at 20,000ft there is no fundamental aerodynamic reason it isn't supersonic under the right conditions. Controllability is a minor issue, but one that I'd be stunned if they didn't fix during the flight test programme.

I have the manuals here. Who said anything about M0.95 at 20,000'?

Where did this figure come from?

I think it is just one of those 'facts' bandied about that originated in: a) Mis-information, b) dis-information, c) a typographical error, d) a 'slip of the tongue', e) a guess, f) a boast or g) anything else!

What glider were you referring to?

pdf27 · 07-13-2007, 06:36 AM

Glider was a Schleichter K-8b, which can be semi-aerobatic if a g-meter is fitted. This one didn't have one fitted so is clearly non-aerobatic.

Data is from some USAF publication - I'll chase down which one when I get home from work later on today.

pdf27 · 07-13-2007, 08:21 AM

OK, source is "Encyclopedia of US Air Force Aircraft and missile systems, Volume II, Post-World War II Bombers 1945-1973". Author is Marcelle Size Knack and it is published by the "Office of Air Force History, Unites States Air Force, Washington, D.C., 1988". This quotes maximum speed for a variety of aircraft, and includes the various marks of B-52. That gives maximum speed as being in the range 546 to 553 Kts at altitudes from 19,800 to 23,800ft depending on mark. Some pretty simple number crunching gives a value of about M=0.95.

glyn · 07-13-2007, 09:26 AM

Quote:

Originally Posted by pdf27

OK, source is "Encyclopedia of US Air Force Aircraft and missile systems, Volume II, Post-World War II Bombers 1945-1973". Author is Marcelle Size Knack and it is published by the "Office of Air Force History, Unites States Air Force, Washington, D.C., 1988". This quotes maximum speed for a variety of aircraft, and includes the various marks of B-52. That gives maximum speed as being in the range 546 to 553 Kts at altitudes from 19,800 to 23,800ft depending on mark. Some pretty simple number crunching gives a value of about M=0.95.

Thank you for identifying the source. However, I must tell you that they are wrong. The Office of Air Force History also greatly overestimates the speeds and capabilities of many US aircraft. As you know, speeds, whether maximun, cruising or stalling depend on many variables - and the only publications which can do this are the type Flight Manuals and the Appendix 1 Performance Data manuals (Operating Manuals in other countries). I have those for the B-52 in front of me now. A look at the fuel flow charts for the different altitudes and weights tells the story! Incidentally, the maximum speed clean at altitudes in excess of 36,000' and no external fuel tanks is Mach 0.93. Other than on acceptance flights I would doubt that speed has ever been achieved in service. Call me an old curmudgeon if you will, but I can only accept the evidence of the 'Dash Ones' and their appendixes. What a pity the Office of Air Force History does not take the same position.

pdf27 · 07-13-2007, 17:40 PM

Fuel flow charts tend to be a tad simplistic - L/D will vary with altitude if only for reasons of skin friction/wetted area.
Peak speed being at greater than 36,000 ft is plausible unlike the 20,000 ft I quoted previously. It would be very interesting indeed to see if that's airframe or power limited, and where exactly on the transonic L/D curve the worst point is compared to aircraft performance at that point. That may be indicated by any differences given between level and diving flight or varing with all-up weight.
However, I suspect that we may be getting into finger-breaking territory here given that the B-52 is still in service so I think we'd better leave the subject at this point.

glyn · 07-13-2007, 18:18 PM

Quote:

Originally Posted by pdf27

However, I suspect that we may be getting into finger-breaking territory here given that the B-52 is still in service so I think we'd better leave the subject at this point.

Sure. And will be in service until 2040 according to some reports I've seen. It makes you wonder just what is original. (Reminds me of the 'original' executioners axe that had 5 new heads and 15 replacement handles during its career!

)
The manuals also show the various 'Limitations' applied to the airframe, power units etc. If you wish specific information on this bird, or any other type I have the FMs for, just pm me.

Jimmy · 07-13-2007, 18:46 PM

From what I've heard (this is in no way confirmed) there are literally tons of excess/unused wiring left in the current BUFF fleet, just left there as obsolete systems have been removed or replaced. Its fairly believable.

glyn · 07-13-2007, 19:07 PM

Quote:

Originally Posted by Jimmy

From what I've heard (this is in no way confirmed) there are literally tons of excess/unused wiring left in the current BUFF fleet, just left there as obsolete systems have been removed or replaced. Its fairly believable.

That has the ring of truth! Every squadron I have ever served with or heard about during my service managed to get a units worth of aircraft with no two weighing the same! Some had previous redundant mods left on - others not. Some had been painted more than others (I dread to think how much paint a BUFF needs!

)

gf0012-aust · 07-13-2007, 22:26 PM

Quote:

Originally Posted by pdf27

Mix of truth and rubbish there. The reason for variable inlets is that an oblique shockwave is more efficient than a perpendicular shockwave in slowing down air flows (less kinetic energy is converted into heat). These shockwaves are generated by turning the flow slightly.

Isn't there an issue of the reynolds effect as well? (as it applies to an inlet shock ramp rather than boundary layer issue?

Tin Man · 07-14-2007, 14:43 PM

Quote:

Originally Posted by glyn

I'm not sure. The Rolls Royce Conway 11s were perfectly good. Like the Vulcan, the Mark 2 versions were no faster than the Mark 1s in level flight .

Interesting that the Vulcan B2 was no faster than the early B1. I thought the Olympus 301s`were much more powerful than the 201s`? What was their comparable IAS at sea level?

Quote:

Originally Posted by glyn

I hope it said SITTING!

It was indeed quoted as "SAT" on the ground! Well, it was said by one of our cousins across the pond!

pdf27 · 07-14-2007, 18:34 PM

Quote:

Originally Posted by gf0012-aust

Isn't there an issue of the reynolds effect as well? (as it applies to an inlet shock ramp rather than boundary layer issue?

In what sense (I'm not familiar with the term "reynolds effect")? If you're referring to subsonic flow then yes in theory there is some benefit to be gained from movable inlets but to be honest it really isn't worth the added weight and effort. It's only when you start getting into major stagnation pressure losses in the region of Mach 2 that movable ramps really become worthwhile.

glyn · 07-21-2007, 06:52 AM

[quote=TIN MAN;389746]Interesting that the Vulcan B2 was no faster than the early B1. I thought the Olympus 301s`were much more powerful than the 201s`? What was their comparable IAS at sea level?

Sorry for the delay, but have now been able to find the time to unearth the low altitude limit info you wanted.
Victor B1 330 kts SL to 34,000'
Victor B2 350 kts SL to 19,000'
Vulcan B1 250 kts SL to 20,000'
Vulcan B2 330 kts SL to 15,000'
High altitude max speeds are unchanged in each case.

Tin Man · 07-22-2007, 12:57 PM

Thanks Glyn, you are a gentleman!

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07-13-2007, 04:55 AM	#33 (permalink)
glyn *Military Professional* Join Date: 09-15-06 Location: Penzance, Cornwall UK Posts: 6,545	[quote=pdf27;389279]Ummm... you'll have to forgive me being a little sceptical on that one. If something can do 0.95 Mach at 20,000ft there is no fundamental aerodynamic reason it isn't supersonic under the right conditions. Controllability is a minor issue, but one that I'd be stunned if they didn't fix during the flight test programme. I have the manuals here. Who said anything about M0.95 at 20,000'? Where did this figure come from? I think it is just one of those 'facts' bandied about that originated in: a) Mis-information, b) dis-information, c) a typographical error, d) a 'slip of the tongue', e) a guess, f) a boast or g) anything else! What glider were you referring to?

07-13-2007, 06:36 AM	#34 (permalink)
pdf27 Contributor Join Date: 06-05-06 Location: UK Posts: 538 Country:	Glider was a Schleichter K-8b, which can be semi-aerobatic if a g-meter is fitted. This one didn't have one fitted so is clearly non-aerobatic. Data is from some USAF publication - I'll chase down which one when I get home from work later on today.

07-13-2007, 08:21 AM	#35 (permalink)
pdf27 Contributor Join Date: 06-05-06 Location: UK Posts: 538 Country:	OK, source is "Encyclopedia of US Air Force Aircraft and missile systems, Volume II, Post-World War II Bombers 1945-1973". Author is Marcelle Size Knack and it is published by the "Office of Air Force History, Unites States Air Force, Washington, D.C., 1988". This quotes maximum speed for a variety of aircraft, and includes the various marks of B-52. That gives maximum speed as being in the range 546 to 553 Kts at altitudes from 19,800 to 23,800ft depending on mark. Some pretty simple number crunching gives a value of about M=0.95.

07-13-2007, 17:40 PM	#37 (permalink)
pdf27 Contributor Join Date: 06-05-06 Location: UK Posts: 538 Country:	Fuel flow charts tend to be a tad simplistic - L/D will vary with altitude if only for reasons of skin friction/wetted area. Peak speed being at greater than 36,000 ft is plausible unlike the 20,000 ft I quoted previously. It would be very interesting indeed to see if that's airframe or power limited, and where exactly on the transonic L/D curve the worst point is compared to aircraft performance at that point. That may be indicated by any differences given between level and diving flight or varing with all-up weight. However, I suspect that we may be getting into finger-breaking territory here given that the B-52 is still in service so I think we'd better leave the subject at this point.

07-13-2007, 18:46 PM	#39 (permalink)
Jimmy *Military Professional* Join Date: 11-16-05 Posts: 931 Country:	From what I've heard (this is in no way confirmed) there are literally tons of excess/unused wiring left in the current BUFF fleet, just left there as obsolete systems have been removed or replaced. Its fairly believable.

07-21-2007, 06:52 AM	#44 (permalink)
glyn *Military Professional* Join Date: 09-15-06 Location: Penzance, Cornwall UK Posts: 6,545	[quote=TIN MAN;389746]Interesting that the Vulcan B2 was no faster than the early B1. I thought the Olympus 301s`were much more powerful than the 201s`? What was their comparable IAS at sea level? Sorry for the delay, but have now been able to find the time to unearth the low altitude limit info you wanted. Victor B1 330 kts SL to 34,000' Victor B2 350 kts SL to 19,000' Vulcan B1 250 kts SL to 20,000' Vulcan B2 330 kts SL to 15,000' High altitude max speeds are unchanged in each case.

07-22-2007, 12:57 PM	#45 (permalink)
Tin Man Contributor Join Date: 06-02-07 Location: In the `shires. Posts: 396 Country:	Thanks Glyn, you are a gentleman!

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