Base burning

[PR19_Kit]

Somewhere in the last few weeks I've read a bit in a book about 'base burning', the process of generating a gas flow at the blunt rear of an aircraft to reduce the drag of the aircraft.

Can I find it again, can I thump!    But I think it was in the 'Typhoon to Typhoon' book and that's many hundreds of miles away from me right now.

What I'd like to know is was there a minimum base area for such a scheme to work, because shells that use 'gas bleed', pretty much the same thing, are only 155 mm dia. so I reckon a small 'base' would still work for an aircraft.

Anyone know anything about this, or would care to postulate? 

[Gondor]

It's the whole of Appendix 2 Kit!

From a quick skim through it I don't think there was a minimum size as they were planning on testing the idea with a Phantom which is a little larger than 155mm.

The basic principle is that a cone of gas is produced at the rear of the object, which does not have to be propulsive, will reduce the amount of drag produced by the body of the odject it is emitted by.

Gondor

[perttime]

wikipedia has a little bit on Base bleed.
https://en.wikipedia.org/wiki/Base_bleed
The smallest mentioned there is 7.5 cm sjömålsgranat m/66 (7.5 cm anti-ship shell m/66)

What does it do in a fighter jet? The jet exhaust is already there at the blunt end.

[Gondor]

wikipedia has a little bit on Base bleed.
https://en.wikipedia.org/wiki/Base_bleed
The smallest mentioned there is 7.5 cm sjömålsgranat m/66 (7.5 cm anti-ship shell m/66)

What does it do in a fighter jet? The jet exhaust is already there at the blunt end.

There is a drawing or two in the Appendix showing a base burner added to a Lightning and an F-104 neither of which you would think would need them. The lightning had one on either side of the upper fuselage at the tail end and the F-104 hat one at the base of the tail fin. The thing about base burning was that it was not propulsive, it was to provide what was in effect an aerodynamic shape where it was impractical to put one, such as the base of a shell. The bulges on some supersonic aircraft to improve the area ruling would do a similar thing.

Gondor

[kerick]

Sounds like a technique to eliminate a low pressure area and replace it with a neutral or high pressure area. Would not have to be at the base just any low pressure area at the rear of the aircraft.

[Mossie]

Yep.  It conferred several advantages.  It allows a blunt rear end and increases volume available there.  You can widen the fuselage as it effectively increases the length and reduces the thrust. It also more than doubled the available thrust in trans and supersonic flight, effectively giving you the effect of a larger engine.

Sounds like wins all round but the effects were negligible at subsonic speeds.  So I assume that the wide fuselage and blunt  end would infer big penalties at low speeds and altitudes.

[PR19_Kit]

Ah yes, it's all coming back to me now, thanks for the pointers gentlemen. 

The 'base' itself doesn't seem to have to be all that large if the effect works with a 7.5 cm shell (Viz perttime's post) so my idea of such a 'base' between the jetpipes  of my Tornado F6 looks to be quite possible. It's a small flat area, maybe 2 ft x 1 ft, and if it reduces drag at Mach 2 or so that's just what would be needed during a crucial interception. 

[Gondor]

Funny you should say that Kit as there are some drawings in the Appendix of aircraft designs with a "third engine" to do exactly that, in fact on the cover of the book the artist depiction at the bottom is of aircraft designed that way.

Gondor