Questions, technical and factual in nature, but needed for some whiffing.

[Daryl J.]

At what altitude are propellors no longer effective?  Or is there no limit?

Don't both the WB-57F and Canberra PR.9 do their thing at about 55,OOO feet?  If yes, what is the advantage of the oversized wing/tail on the Convair/Martin machine?

At very high altitudes, do winglets offer any advantages?


Hint:  Somehow,  those questions apply to the Mosquito.   


Daryl J.

[Shasper]

Dont quote me on this, but as a general rule you wont see many prop jobs above FL400 (40k ft) due to the thin air. . . regarding the winglets, I'm not sure about their effectiveness at higher altitudes (such as where the Dragon Lady prowls) but the drag & fuel savings they'll provide as you ascend to your chosen altitude would be well worth their addition.


Shas

[PR19_Kit]

Don't both the WB-57F and Canberra PR.9 do their thing at about 55,OOO feet?  If yes, what is the advantage of the oversized wing/tail on the Convair/Martin machine?

Daryl,

AFAIK the Canberra PR9 can actually get up to 65000 ft but operations are limited by the oxygen system fitted to the standard aircraft. That's a quote from the pilot of XH131 at Fairford a couple of years ago when I asked him about max. altitudes. (I was sitting in the cockpit at the time  )

I suspect, but don't know for sure, that the RB-57F carried a much larger camera than the PR9 was designed for originally. I recall a camera called a LOROP that had a huge lens that stretched along the fuselage of the RB-57F and then looked out via a rotating mirror.

In later life the PR9 later carried a camera that worked on similar principles, called a System 3 I think, but was a lot smaller with the march of technology. It needed a bulged camera bay, which I have piccies of, but it was hardly a thing of beauty! 

[kitnut617]

I've a good book which I got from the Rolls Royce Heritage Trust and written by David Birch called The RR Crecy.  It goes into quite a bit of detail about engines in general and how they lose power at extreme height, not just from the prop, which is why supercharging came all in voque.  At height though it explains that a prop powered aircraft gets a lot of it's forward motion from the exhaust thrust, a Spitfire for instance had about 150 lbs of this exhaust thrust and the exhaust stubs were designed accordingly to take advantage of this thrust.  The Crecy which was a two stroke engine was envisioned to give twice that thrust and an exhaust turbine was designed where they could inject more fuel into the hot exhaust and re-ignite it, a sort of very primitive afterburner.  Incidently one pound of exhaust thrust is about 1 hp.

Miles Aircraft were so interested in the Crecy they were concidering an aircraft which would have been powered just by the thrust of the exhaust turbine, but it fails to say how the aircraft would have got up to the height that the aircraft was to operate at as the thrust wasn't enough to get it off the ground.  Naturally it died a slow death on the drawing board

[RLBH]

To take an extreme example, the B-36 was not just a prop aircraft, but a piston one too, and some marks could operate in excess of 50,000 feet (RB-36 featherweight, 55,000 feet alluded to). Granted, those marks had auxiliary jets, but still...

In getting up to high altitudes, you need a lot of wing anyway, so you're likely to have a very long span in any case. Given that increasing span is always preferable to adding winglets where possible, you may as well have an even bigger wing. Unless you're concerned about infrastructure constraints.

Hm, there's an idea. Single-seat light aircraft, opposed-four engine, 55,000 feet. No rational reason, just because.

[jcf]

The Grob G 520 Strato 1/Egret with Garrett turbo-prop is rated to 50,000 feet and the G 850 Strato 2C with its pair of turbocharged OL-550s was to be good for up to 78,800 ft.
http://www.grob-aircraft.eu/company/legacy/high-altitude-aircraft/g-520-strato-1.html

Later versions don't have the winglets.
http://www.airliners.net/photo/Grob-D-500-Egrett/1239320/L/

http://www.grob-aircraft.eu/company/legacy/high-altitude-aircraft/g-850-strato-2c.html



Winglets basically act like an extension of the wing.

Boeing has dropped winglets on new designs, instead they are using a
swept tip as originally developed on the 767-400.

A properly designed propeller will perform at high altitude, the main problem is that as air density decreases
the blades stall more easily.

[Daryl J.]

So, rather than a winglet, the wing tips are going to this?







Daryl J., roughing out a sketch on a post-it between patients
PS:  Cool stuff on the Grobs!

[philp]

There was at least one Mosquito converted to a high altitude interceptor to go after the high altitude German Junkers Ju 86P and Ju 86R.  MP469 was converted to Mk XV status with extended wings, upgraded Merlins (61, 70, 73?), pressurized cockpit etc and according to what I can find on the web, flew to 45,000ft.
http://www.wwiiaircraftperformance.org/mosquito/mp469.pdf
http://www.historyofwar.org/articles/weapons_mosquito_XV.html

[Mossie]

I always thought the fuselage of the Vickers Type 432 high altitude fighter looked very much like that of the Mossie.  The wing was a different shape, although with a slightly longer span which makes up for the pointed wingtips.  It was only good upto about 38,000ft, but it might give some ideas:
http://www.aviastar.org/pictures/england/vickers_432.gif

[PR19_Kit]

Philp,

Amazing, that's more information than I've seen anywhere else about the Mossie XV.

Really interesting stuff in the paper, but it still doesn't answer a question I've been asking for ages. Was the pressure cabin made of wood, and if so, how? If it wasn't how did they integrate the metal cabin with the wood fuselage?

When my Dad was flying PRXIX (What else WOULD he be flying? ) Spitfires, of course, toward the end of WWII he said they would come back from ops at around 45000 ft, after dropping any tanks they had and with a light fuel load. He reckoned they could out-run anything the Luftwaffe had at that altitude (good thing too as he had no guns....) but when I asked him if that included a Ta-152H he asked me what one of them was!

[philp]

Kit,
Reading the first doc looks like they just added 2 bulkheads and the pressurization gear (see section 2.2).

I had never even heard about this variant or ever the high altitude Ju-86 versions till I saw a build article in an old Scale Modeler.  The guy painted his model in PRU Blue with the black nose.  Actually looked pretty cool so filed the data away till I saw this thread, then had to go looking on the web.

[jcf]

So, rather than a winglet, the wing tips are going to this?







Daryl J., roughing out a sketch on a post-it between patients
PS:  Cool stuff on the Grobs!

Angular on the 767-400:


Its curved and elongated on the 787-8/9. (see attached)

The 747-8 wingtip is between the two extremes.

The P-8A Poseidon also uses a raked wingtip similar to that of the 767-400.

Jon

[PR19_Kit]

Philp,

Thanks, I'll dig further into that doc. thanks, it's a pretty hefty read!

I recall something about this variant in another Forum I frequent, but darned if I can remember which one now! The Mk. XV had four bladed props as well as the two stage supercharged Merlins, and that makes it look strange even at first sight.

The Ju86Ps and Rs made some very high altitude flights over Southern UK and in the Middle East and nothing the RAF had at the time could combat them under normal circumstances. A Spitfire V that was stripped to the bone, with only two guns fitted seemingly, shot down an Ju-86P over Egypt at around 41000 ft sometime in 1942, and an even higher flying Ju-86R was intercepted overv Southampton by a stripped down and very well flown Mk IX in Sept. '42, but escaped destruction at some 43000 ft. This was the highest altitude combat of WWII apparently, and the Luftwaffe gave up the high recce flights after that.

The Westland Welkin was intended as to combat such high altitude missions too, but never saw service sadly. Now there's an aircraft full of Whiff potential! I would say that of course, anything with long thin wings gets my attention.

[philp]

Thanks for the data Kit.
There are 4 pics of WP469 at the bottom of the first doc.

Daryl, any further info on your idea?

[Daryl J.]

The idea has two parts:   Consolidated Vultee/Convair gets an order for development of a very high flying Mosquito, which they do and do a very good job of it.  So good, that they get the order later for the WB-57F.    Like the WB, the Mosquito is 95% new build and leaves behind the wooden construction in favor of a metal one.   One thought was to put wings on it that were 50 years ahead of their time, thus the winglets questions, and the other, of course, regarded prop feasibility.

The second part regards the Canberra,  but in addition to using the B-57 as a base, Convair developed a variant of the PR.9.  (Thanks Airfix!)


Thanks to everyone above for the info; it's much more than anticipated and is quite helpful.




Daryl J.