Air intakes for jet aircraft

M

McColm

Guest
Hi,
Most jet aircraft have the air intakes either;
a) at the front of aircraft i.e. MiG-21
b) shoulder mounted i.e. F-15
c) underneath the fuselage i.e. F-16
d) along the fuselage i.e. Mirage 2000

Apart from the YF-107, has any other fighter aircraft or experimental piloted aircraft had the air intakes behind the canopy, on the upper side of the fuselage?

Or is the reason for not putting the air intakes behind the canopy, more complicated?
 
IMHO, the first jet fighter with an air intake behind the canopy, was the Heinkel He 162.
Some stealth concepts and prototypes had the intakes behind the cockpit/canopy. But with RAM,
S-duct intakes and so on air intakes behind the canopy, on the upper side of the fuselage have become obsolete.
McColm, you answered your second question already.
Major aircraft parts like radar, cockpit, avionics, weapon systems, gun, engine, APU etc. have to be easy accessible for ground crews. They don't want to use special ladders or platforms while checking or repairing the aircraft.
I bet an aircraft engineer can give more reasons for example "air flow during high alpha manoeuvres".
 
It just seems a bit daft, that's all.
The boeing proposal for the TXF (F-111) concept, looks better. The intakes would prevent F.O.D.
 
The concept of dorsal air intake was also used by the SNCASE on the SE-580 (1944, forward mounted HS-24 piston engine & horizontal radiator installed behind the cockpit) then the SE-2410/2415 "Grognard" (1946, 2 x "Nene" jet engines).
Drawings from "Les avions de combat francais", Jean Cuny, Docavia, Editions Larivière.
 

Attachments

  • SE-580.jpg
    SE-580.jpg
    75.8 KB · Views: 100
  • SE-2410 Grognard.jpg
    SE-2410 Grognard.jpg
    65.9 KB · Views: 116
fightingirish said:
I bet an aircraft engineer can give more reasons for example "air flow during high alpha manoeuvres".
Click to expand...

It's the opposite situation of having a chin inlet or something like an F-16. There, the forebody redirects the flow so that it enters the intake and the fan face in a normal direction. The goal is to have a uniform pressure distribution at the fan face.

With a top mounted inlet, not only there is nothing to redirect the flow, but you also want to avoid ingesting the thickening boundary layer due to high alpha, or worse yet vortices off the nose.

The most recent examples of top-mounted inlets meant for maneuvering fighters come from Northrop and SAAB, IIRC. In both cases the shaping of the nose was essential in guaranteeing uniform flow to the engine.
 
A dorsal intake worked fine on the Handley Page HP.115 - the strong vortices from the 75 degree wing leading edge meant that at high AoA the airflow into the intake was still good.

http://en.wikipedia.org/wiki/Handley_Page_HP.115

Pictures that give an idea of why it worked are in this:

http://naca.central.cranfield.ac.uk/reports/arc/rm/3805.pdf

Basically, the airflow for the intake rolled over the vortices and into the intake.

But if you don't want a high LE sweep to get such benefits, as the high LE sweep means a low aspect ratio wing, then you probably would not want a dorsal inlet as without vortices it is unlikely to work at more than moderate AoA's.
 
Don't forget the Boeing Bird of Prey
 

Attachments

  • bird_of_prey_17.jpg
    bird_of_prey_17.jpg
    68.6 KB · Views: 92
One of the alternative designs for what would end up as JAS 39 Gripen had the air intake on the upper side of the fuselage.

http://www.canit.se/~griffon/aviation/gripen/39altern/altdesigns.html

2107
The version most likely to compete with the canard layouts had a dorsal intake, which meant a short and straight duct. Wind tunnel tests showed that it would work well at high angles of attack and that 2107 had better turning performance than 2105. Saab judged the risks with the dorsal intake as too large.
Click to expand...
 
^problem with wing or fuselage shielded intakes is lower beta performance...

though they're not much of a concern really compared to alpha
 
I recommend reading this book...

I used to read it in the university library

http://www.aiaa.org/content.cfm?pageid=360&id=267

:)
 
Intakes on the upper side of the fuselage are good for a smooth flight on the same level, ideal for the reconnaissance. Because of that the most (stealthy) UAVs have them that way. Speaking about the experimental planes, for example Tacit Blue was not mentioned yet or from the production machines I think that B-2 counts, but its not a fighter.

Also when you are spaking about the jet aircrafts, even the ones used in the military, they can have air intakes elsewhere:

e, under the wings - Me-262, Yak-25, Canberra
f, around the tail - Tu-22
 
there are 2 reasons behind that:
1. to mask off the inlet from ground based radar
2. for payload optimization

but that's mostly according to the book I've read
 

Similar threads

Back
Top Bottom