Forum: General F-22A Raptor forum

tank_top wrote:

This is WAY out there, but has anyone thought about "directing" the excess air during supersonic flight to reduce the sonic boom. I don't know if it would even be possible or useful. Has this ever been proposed. I know they have thought about other ways to minimize sonic boom in concept aircraft. It would be cool, an F-22 silently doing 1.5 1500 feet off the ground. Question

http://www.nasa.gov/centers/dryden/news ... 07-38.html

NASA/Dryden has been playing with this issue for a while.

That's why I love Edwards AFB ... they do cool sh*t all the time!

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sferrin wrote:

Tinito_16 wrote:

Seems no one knows for sure what those doors on the Raptor do...

Not true at all. They're just what many have been saying - they spill excess air overboard. Several aircraft have had the same, they're just not as obvious. XF8U-3 had 'em as did the F-14 Tomcat. Blackbird had them too.

F-15 has a diffuser ramp. http://www.f-15estrikeeagle.com/technol ... inlets.htm
F-16 uses Bernoulli’s principle … Divergent/Convergent intake shaping, or something along those lines.
Can’t let the air go supersonic down the inlet cause bad thing will happen to the motor!

Funny diffusers are a big issue in F-1 right now! http://formula-one.speedtv.com/article/ ... rs-illegal

Aerodynamicists are some brilliant people … right up with Rocket Scientists

The F-105 had these doors. We called 'em "bleeder doors". Earliest Thud was a 1957 model. Too much air in the intakes is an old problem. Interestingly enough, the F-106 did not have any bleeder doors.

I heard in newer Raptors them doors have been eliminated. Not sure how true it is, though.

I doubt it, every photo I've seen they have it.

Here's a photo of them overpressure doors open while the Raptor is taxiing:

Apparently they also function as aux air intakes at low speed. I'm always trawling airliners.net for cool pics, and when I found that one I thought, that's the first time I've ever seen those doors open. So here you go guys Crazy Pilot

EDIT: Right click and click 'View Image' to view it in full size. If you're in IE I can't help you... Sad

Anyone know how to post the full size pic on this site?

EDIT 2: Nevermind, here's the link: http://cdn-www.airliners.net/aviation-p ... 790649.jpg

LOL

I've been eagerly devouring Raptor pics trying to find these doors open as well, so this is a nice find!

However, the more I think about it, the more I'm thinking the picture here is showing them open due to some mechanical fault. If they also function as aux inlet doors, they would be open at slow speed, max thrust situations like early takeoff roll or in the Raptor's demo program, but I've never seen them open on takeoff (or ever before this pic).

Then again, that does appear to be a later block, so maybe they modified the control software to allow them to function as aux inlets.

If these doors are aux air inlets, why do they open in the aft direction, and not fwd? Why try to suck in air you have already taxied by and not air that is coming towards you, with the added effect of ram pressure? Any thoughts?

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

jacarlsen wrote:

If these doors are aux air inlets, why do they open in the aft direction, and not fwd? Why try to suck in air you have already taxied by and not air that is coming towards you, with the added effect of ram pressure? Any thoughts?

My guess is they serve multiple purposes and the orientation of the doors matters more in flight than on the ground. There's probably also the LO properties to consider, the direction the edges face is a Big Deal.

jacarlsen wrote:

If these doors are aux air inlets, why do they open in the aft direction, and not fwd? Why try to suck in air you have already taxied by and not air that is coming towards you, with the added effect of ram pressure? Any thoughts?

Because they aren't aux air INLETS, but OUTLETS and are used to reduce pressure in the inlet, generated by the inlet itself.

Quote:

Because they aren't aux air INLETS, but OUTLETS and are used to reduce pressure in the inlet, generated by the inlet itself.

That actually makes sense given the orientation of how they open... Any idea why they might be open during taxi? Perhaps it's part of the checkout?

The Raptor wasn't moving or throttling up when the doors opened during that shot. The picture was taken just before take off at RIAT last summer. Just after line up he checked his flight controls and during that test they opened and closed a few times.

I've must have been standing really close to the guy as I have exactly the same picture Very Happy

Greetz
Rick

Forum: General F-22A Raptor forum

Overpressure doors