McDonnell-Douglas / Boeing F-15 Eagle

KJ_Lesnick

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The F-15 was able to fly on one wing because of it's wide-fuselage, and excellent control-power. I got a question, how much of a role did the variable-geometry inlet (you know the hinged inlet lip) lip position play in the amount of lift the fuselage itself produced?

KJ_Lesnick
Was the variable-geometry inlet lip design patented by McDonnell, or could any aircraft company use it?
 
KJ_Lesnick, quoted:
"Was the variable-geometry inlet lip design patented by McDonnell, or could any aircraft company use it?"

True, in my opinion. Was this something like what you were looking for?

http://www.google.com/patents?id=WOkHAAAAEBAJ&printsec=abstract&zoom=4&dq=variable+inlet+inassignee:McDonnell&as_drrb_ap=q&as_minm_ap=1&as_miny_ap=2008&as_maxm_ap=1&as_maxy_ap=2008&as_drrb_is=q&as_minm_is=1&as_miny_is=2008&as_maxm_is=1&as_maxy_is=2008&num=50

McDonnell Douglas patented that general design. Patents are meant to be wide in scope and American ones always include a disclaimer saying that many variations are possible in any patent.

However, anyone whosoever can claim improvements to a patent and then argue it out in court if sued over it. That should be how it works internationally.
 
I thought the rule with patents was that if you modified it just a little you can get around the patent?
 
In theory, yes, minor variations in a patent should be allowable.

However, there should be either some improvement or useful benefit coming out of a patent compared to 'prior art'. That's the legal standard. Where the rub comes in is the opinion of what constitutes these virtues legally.

There's a whole field of legal specialization to Patent Law in America and all litigation is art---which really boils down to an opinion. Cultural art and legal arts are like that.
 
I know the F-15 features a moving lip that can hinge up and down depending on speed which I'm guessing is to increase capture area at supersonic-speed. It also features a porous ramp.

My question is, is the porous-ramp fixed, or does it move as well (narrowing down the throat at high-speeds) in addition to the moving lip?


Kendra
 
Arh, my friend, if my understanding of which you mean porous-ramp is right, my answer is yes.
Only lip moving, will cause a turbolent flow in the inlet, so we need an incline to conform the air-flow after the lip down.
 
rousseau said:
Arh, my friend, if my understanding of which you mean porous-ramp is right, my answer is yes.
Only lip moving, will cause a turbolent flow in the inlet, so we need an incline to conform the air-flow after the lip down.


I'm confused here exactly as to what you said.

It would seem you either said...
- 1.) Only the lip moves
- 2.) The lip moves with the ramp and the lip would produce turbulent flow in the inlet if only the ramp moves

Which one is correct?
 
Sorry, English is not my native language.
What I wanted to say is, both of them would moving responsively, not only one part moving factually. If you get a cutaway of F-15, you will find a board for release/discharge air pressure after the lip of inlet.

sorry for my clumsy express. :D
 
That's how it looks
 

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flateric,

Thank you for the drawing! It really helps when you can actually see it.


Kendra Lesnick
 
Wait...

I just checked that patent again... those were dated 2001... did they patent the 'mission adaptive' idea (droopable inlet) when the F-15 was being designed and built? Or did the only do it in 2001?


Kendra Lesnick
 
Wasn't the first such intake of that general shape flown on the North American A-5 Vigilante? If so, then how do NA's patents (I presume they had some) compare with McDD's?
 
I'm not talking about the ramps, I'm talking about the intake lip which droops at low-speed and opens up at high-speed.

Kendra Lesnick
 
Out of curiosity, was the basic inlet concept, using the moveable-lids, patented by McDonnell Douglas around the time the F-15 was developed, built and flown?

Kendra Lesnick
(BTW: I know later on in 1999, they did patent the mission adaptive inlet, but I don't know if they patented anything before that)
 
The thickness ratio varies from 5.9% at the
exposed root to 3% at the tip.


The F-15 wing development program
NIEDLING, L. G. (McDonnell Aircraft Co., St. Louis, Mo.)
AIAA-1980-3044
In: The evolution of aircraft wing design; Proceedings of the Symposium, Dayton, Ohio, March 18, 19, 1980. (A80-31001 12-05) New York American Institute of Aeronautics and Astronautics, Inc., 1980, p. 125-129.
 

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ı was about to write it was 6.6 at wingroot , thinning to 3 at the wingtip area . The source was a Klaus Huenecke book from 80s , but I guess the post by Flateric is the right one .
 
I've seen number 6% at wingroot, and *exposed* wingroot is not the same, of course. Again, here we have original MacAir sourced paper...
 
BTW, this is painful story of F-15 wing planform evolution
 

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Hi this site http://www.ae.uiuc.edu/m-selig/ads/aircraft.html gives the root airfoil as NACA 64A 006.6 and the tip airfoil as NACA 64A 203 I have always found this to be a reliable site. With NACA 64 series airfoils the last 2 whole digits give the T/C ratio. On the drawing posted by Flateric the most inboard profle given is not the actual root airfoil but the one at the inboard end of the flap, so this could be the source of any confusion here.
 
I take it the unexposed wingroot is the front of the wing-body fairing back to the tip of the booms on the back?

BTW: Just out of curiousity:
-What is that line down the airfoil (I think it looks like a conical camber thing or something, but I'm not sure)?
-The reason they deleted leading-edge devices from the design was because they were not necessary correct?


Kendra Lesnick
 
flateric , I am not doubting your source , it is just my typing . For all ı know we might be both right as ı understand wing areas are calculated to include parts what everybody would accept as the fuselage

what follows is an attempt to show how ı understand it and not an attempt to teach anything ; ı try to avoid to give such an impression even when I actually know anything about the subject ...

black lines are fuselage sides , wing area includes the yellow part inside the fuselage and my 6.6 would be at the blue line .

and the post by Weirc tells this might be the case . We are not disagreeing , just looking at the same thing from different perspectives .

about the book ; I don't understand at least %80 percent of it ...
 

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Hi, I think everybody is correct on this one. The line labled BL 0.0 on Flateric's post is the center line of the aircraft, and, if the wing were continued to this point would be 6.6 percent thick. However the wing on the F-15 is only exposed to the airflow outboard of the inner end of the flap, so the most inboard part of the wing to be exposed to the airflow does have a thickness of 5.9 percent.

The line drawn along the airfoil in this case just shows the position on the wing of where the given airfoil section was taken from. If you were to see a straight line drawn from the leading edge radius to the tip of the trailing edge this would be the cord line, if you were to see a line drawn equally distant from the top surface and bottom surface of the airfoil that would be the camber line.

Hope it's getting clearer...........
 
I have two more questions (I'm pretty sure I can't find an answer to these anywhere else and you guys know your stuff).

1.) What is the thickness of the F-15's wings at the thickest point and/or the unexposed root [/i](where it's at 6.6%)[/i], the exposed root, and around the area where the wing reaches 3% T/C?
2.) What is the chordwise length of the F-15's wings at the thickest point and/or the unexposed root (where it's at 6.6%), the exposed root and around the area where the wing reaches 3% T/C?


Also, if anybody knows these ones... (I'm not even sure you guys will know this one, but I might as well ask)

1.) What is the T/C ratio of the F-15U's (The F-15E derivative with the enlarged wings) wings?
2.) Does anybody know the chordwise thickness of the F-15U's wings at the exposed root, the unexposed root (if possible), and at the tips?
3.) Does anybody know the chordwise length of the F-15U's wings at the exposed root, at the unexposed root (if possible), and at the tips?


Kendra Lesnick
BTW: I have a good reason for why I'm asking all these extra questions... I'm actually working on a WHIF-design that is essentially an F-14/F-15 hybrid -- an "Eagle-ization of the F-14" if you will: The airplane basically is to look like a twin-seat F-15 style-design with the F-14's radome-size, the F-15U's larger wing area, the F-15A/C's wing-thickness, with droops and multiple-position flaps. Other ideas included a single all-moving vertical fin.
(I'm not trying to go off topic here... I just want people to know why I'm asking all these highly-detailed questions about the F-15 and it's wings!)
 
Hi, if you want to know the thickness of an airfoil for a given cord and you have the t/c ratio of the airfoil, it's easy to work out. Measure the cord length of were ever you want on the wing, then, divide the answer by 100, then multiply that answer by the t/c ratio and that will give the size of the thickest point on the airfoil.

Sizes on airfoils, thickness, camber etc are often expressed as %'s of the cord so are usually straitforward to work out once you have the cord length for modeling purposes measuring form a decent scale drawing, to get the cord length, should be fine.
 
weirc,

Not exactly as easy as you'd think. I can't find any really detailed 3-view drawings of the F-15U...


Kendra
 
Before I start, I am not asking a question I've already asked before... Also, I have not been able to find an answer to this question using a couple of google-searches...

With that said...

Does the F-15's listed wing-area include the wing-body fairings and such? I'm just asking because a site I just looked at said...
URL: http://www.ausairpower.net/Profile-F-15A-D.html

The very low combat wing loading of 60 lb/sq ft results in superb 14 degree/sec sustained turning, the aircraft pays a penalty though, both in rough low altitude ride and in a massive 608 sq ft wing area, a large contribution to the 1050 sq ft planform. This size problem has increased detectability and forces the use of low visibility paint, initially air superiority blue supplanted later by more effective two tone greys. The F-15A accelerates well, with a combat thrust/weight of 0.9 in military power and a full 1.3 in reheat. Fully loaded with four AIM-7F Sparrows and four AIM-9L Sidewinders it will reach up to Mach 1.78 in level flight and is allowed up to 7.33 G in combat configuration.

(bold emphasis mine)


Kendra Lesnick
 
The simple answer is to get an F-15 three-view and measure it. From an aerodynamicist's viewpoint, wing area is usually calculated by projecting the leading and trailing edges to where they meet on the aircraft's centreline, the measuring the area enclosed.
 
That approach worked well when pretty well all airplanes were cigar-and-popsicle-stick design and the projected body area included in the gross area was small and (in proportional terms) not that different from one airplane to another. How well does it work in comparing a Su-35 to an F-35A/B?
 
A good point - I suspect they have got more sophisticated in working out how much body lift to take into account. I will have to get my three-vies and squared paper out...
 
Many planforms can be resolved in terms of right angled triangles, if you're out of squared paper.
 
What, and miss colouring in all the squares then counting them, including matching all the little bits together to make whole squares? LO, you are a mean old spoilsport.

Did I say that out loud?
 
According to the book "F-15 Eagle Engaged" by Steve Davies and Doug Dildy, it states on page 19 regarding the September 1968 RFP requirements for the F-X that the fighter was among other things to be capable of achieving "Global (intercontinental) ferry range with or without aerial refuelling"

The exact passage reads as follows (It's a caption on the right side of the page)

F-X Design Requirements

The September 1968 RFP required the F-X design submissions to
provide a fighter with:


1. Wing optimized for high load factor (g) and buffet-free
performance at Mach 0.9 at 30,000ft altitude;
2. High thrust-to-weight ratio to achieve very high energy
maneuverability throughout the flight envelope;
3. Mach 2.5 maximum speed at altitude;
4. Long-range pulse-Doppler radar with look-down capability;
5. One man operation of the weapons system for all missions;
6. Advanced cockpit layout, displays, and controls, which would
allow heads-up operation during close-in combat;
7. Airframe fatigue spectrum with a life of 4,000 hours;
8. 360 degree cockpit visibility;
9. High maintainability: 11.3 maintenance man hours per flight hour
(similar to WW2 fighter requirements);
10. Significant increase in avionic and airframe subsystem component
mean time between failure (MBTF);
11. Highly survivable structure, fuel, hydraulic, flight control and
electrical subsystems in a combat environment;
12. Self-contained engine starting without need for groupd support
equipment;
13. Global (intercontinental) ferry range with or without aerial
refuelling;

14. Maximum air superiority mission gross weight in the
40,000lb class;
15. Low development risk components (engine and radar) and
airframe subsystems which had been proven in prototype,
pre-production, or production applications.



Source: Steven, James Perry McDonnell Douglas F-15 Eagle, Aero
Publishers, Fallbrook, CA, 1978.

Bold Emphasis Mine


How long, distance-wise, would an airplane need to be able to fly for the US Military to consider it intercontinental or global? Could anybody venture a guess as to whether this range would be with drop-tanks or on just internal fuel?

Was the plane able to actually meet this specification?


KJ Lesnick
 
Hi guys,
I thought you would find this interesting. I did anyway. It looks like the F-15 will be fitted out with the IRST system from F-14s.
You can check it out at Flight Global.

Also notice that the end of the article states that Boeing is near closing a deal on a risk sharing partnership for the development of the Silent Eagle.
 
Sundog said:
Hi guys,
I thought you would find this interesting. I did anyway. It looks like the F-15 will be fitted out with the IRST system from F-14s.
You can check it out at Flight Global.

Also notice that the end of the article states that Boeing is near closing a deal on a risk sharing partnership for the development of the Silent Eagle.


I hope that, unlike the Super Bug, they won't have to drop the million dollar IRST if they have to clean up for ACM.
 
F-14D said:
I hope that, unlike the Super Bug, they won't have to drop the million dollar IRST if they have to clean up for ACM.

The IRST centerline tank on the Super Hornet is not jettisonable (except I assume in an emergency jettison.) Keeping one relatively small tank going into ACM isn't going to be a major problem for a plane that big.
 
F-14D said:
I hope that, unlike the Super Bug, they won't have to drop the million dollar IRST if they have to clean up for ACM.

I too have found that decision rather questionable. If not a housing incorporated into the airframe like F-35 EOTS, wouldn't just adopting something like the Sniper XR advanced targeting pod make more sense?
 

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