F-15 inlet position - looking for figures

Military aircraft - Post cold war aircraft, including for example B-2, Gripen, F-18E/F Super Hornet, Rafale, and Typhoon.
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Patriot

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Unread post02 Oct 2017, 19:43

Hi!
Does anybody have or know where to look for an actual chart/s that show by how much the Eagle's intakes move up and down in function of AOA and airspeed?
My guess is the AOA is the primary factor, speed is the secondary, rpm% would be another one I guess. I'd like to see some diagrams or figures on how it's actually programmed into the FLCS (ADC?)

This video gives me some idea but I'd like to know exactly :)

https://youtu.be/FVK49DhMR38
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sprstdlyscottsmn

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Unread post02 Oct 2017, 21:36

I will consult my copy of The Great Book of Modern Warplanes when I get home, but I am 90% sure the "nodding" feature is purely AoA based and it nods to match the AoA of the aircraft within its movement limits. Mach issues are taken care of inside the intake on the upper surface. Again, I will check this when I get home.
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sprstdlyscottsmn

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Unread post03 Oct 2017, 13:41

And the 10% got me.

The Great Book of Modern Warplanes: F-15 - Structure p.89-90

"The only examples of variable geometry in the F-15's structure are the engine air inlets on either side of the forward fuselage. Because the aircraft was designed to be flown at high angles of attack in combat, the intakes are able to 'nod' up or down to keep the aperture facing directly into the airflow in order to maintain an adequate supply of air to the engines. The intakes are pivoted at their lower ende and adjusted to angles of 4deg above or 11deg below the horizontal by the air data computer. The intake angle can also be adjusted to prevent more air than necessary being taken in, and the intake surfaces have further function in providing additional maneuvering control in a similar manner to canard foreplanes. At super sonic speeds their effectiveness is almost a third as great as that of the stabilators, whose size and weight were reduced in consequence. Immediately aft of the intakes themselves are twin mechanically linked ramps to control the shockwaves created in the incoming air."

So they nod to match the AoA (as a benefit of which it provides flow control as a canard) and also nods to reduce the intake aperture at high speed.
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Patriot

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Unread post03 Oct 2017, 14:27

Thanks m8! :)

So... it looks like the intake position is totally unrelated to thrust setting or throttle position?
It all depends on AoA and speed ( AoA as a function of speed) ?


I was hoping that there is somewhere a chart that shows something like aoa=x + speed=x = inlet pos. x degs. and so on so for any flight condition (a combination of speed and aoa) there is a certain specific pre-programmed inlet position..
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zhangmdev

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Unread post03 Oct 2017, 15:25

google

A Wind Tunnel Test of the Full Scale Boeing Multi-Functional Aircraft Inlet

There is a part about F-15 inlet cowl

"Variable geometry inlets, like that of the F-15 shown in Figure 3, have been used to improve performance
over a range of flight conditions. The ability to change shape allows the inlet to deliver the right volume of air
to the engine at the optimal velocity, which then maximizes the pressure recovery, and reduces inlet spillage,
which reduces the induced drag associated with that excess air. The engine is thus operating more efficiently,
resulting in greater performance in terms of range. Inlet capture area is one of the key parameters that can be
varied to improve vehicle performance. The F-15 is a twin-engine aircraft capable of speeds in excess of
Mach 2.5. To achieve these speeds the inlet system has five ramps that are used to condition the airflow prior
to the engine face, Figure 4. The ramps are connected to the cowl and move with it, as the cowl angle is varied
fifteen degrees. The F-15 ramp and cowl actuation is normally provided by two hydraulic actuators. The inlet
capture area of the inlet is thus varied as a function of cowl position and diffuser ramp actuator. "

Air volume depends on AoA(capture area) and air speed, so I think cowl angle (-4 , +11) setting depends on both AoA and Mach number. And those ramps inside moves with cowl.
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Snapshot 2017-10-03 22-15-27.jpg
f-15 variable geometry inlet
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sferrin

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Unread post03 Oct 2017, 17:56

sprstdlyscottsmn wrote:and the intake surfaces have further function in providing additional maneuvering control in a similar manner to canard foreplanes. At super sonic speeds their effectiveness is almost a third as great as that of the stabilators, whose size and weight were reduced in consequence.


So would that make them "Incons"? :P (T-50/Levcons)
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