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|08-18-2013, 08:07 PM||#1|
Join Date: Jul 2008
Location: Cheshire, UK
Thanked 33 Times in 32 Posts
Club: A lone flyer!
A slow 'fast jet' - The Fairey Delta 2
I did achieve this with my V-1 but in some respects it is a bit of a cheat as a pulse jet has an extremely inefficient cycle with no real 'compression' so not surprisingly it has an inlet more or less equal to the exhaust.
Apart from modern ducted fans any scale 'jet' is likely to have inlets significantly smaller that the exhaust - or is it?
The Fairey Delta 2 was certainly a fast jet.
An elegant simple delta it held the worlds speed record in 1956 at 1132mph in the hands of Fairey Aviation's test pilot Peter Twiss.
Always a research plane it had a relatively small exhaust set for high speed and simple inlets with no moveable body to make use of the supersonic shock wave. As a result the total inlet area is actually greater than the area of the jet pipe.
Of course the jet pipe is nevertheless pretty small so the task is to build a relatively big plane that will fly satisfactorily with a small EDF or in other words it will have to be light, very light.
It occurs to me that the most efficient use of an EDF, particularly an out runner type, is to mount it right at the back with no exhaust duct at all. In fact the nozzle becomes an 'annulus' of exactly the fan swept area and ensures the minimum loss of the fan exit velocity.
Scaling the FD2 for a 55mm EDF as the jet pipe the numbers look like this.
The FSA is 1760 sqmm (the out runner bell occupies nearly 25% of the duct!)
The area of the 55mm duct is 2376 sqmm.
The area of the inlets (and the duct upstream of the fan) is 3400 sqmm.
This suggests the inlet velocity (and the losses) will be only half that of the outlet.
At this scale the FD 2 will have a span of 32" and be 58" long and will weigh?
Now that is the question!
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