Wing loading and CLMax

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

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Unread post04 Mar 2008, 07:20

Hey guys, I am curious about the 3rd gen fighters. I hear stories of x-plane out turning y-plane and I am surprised by some of them. So I was wondering if anyone had data handy on jets from the 50's and 60's with reguards to CLMax and wing loading. I am especially interested in the F-104, F-106, F-4, F-5, F-8 but anything anyone wants to share would be appreciated. These planes are all old enough that its all declassified and all that, I just dont have the data available to me. Thanks for your help!
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Raptor_One

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Unread post06 Mar 2008, 07:19

sprstdlyscottsmn wrote:Hey guys, I am curious about the 3rd gen fighters. I hear stories of x-plane out turning y-plane and I am surprised by some of them. So I was wondering if anyone had data handy on jets from the 50's and 60's with reguards to CLMax and wing loading. I am especially interested in the F-104, F-106, F-4, F-5, F-8 but anything anyone wants to share would be appreciated. These planes are all old enough that its all declassified and all that, I just dont have the data available to me. Thanks for your help!


You could probably get data on these aircraft by filing a Freedom of Information Act (FOIA) request. As you said, they're pretty old jets. Back in the early days of Falcon 4.0 flight modeling, two guys filed FOIA requests for the F-15C and A-10A. Full aerodynamic and flight envelope data was obtained for the F-15 and full aerodynamic, flight envelope AND propulsion data for the A-10. This was before 9/11/01 though. The guy who got the A-10 data filed another request for the same sort of data on the F-16 and was denied outright. He even spoke to the officer who denied his request and was told, after telling him what he'd been given in the past, that things had changed after 9/11 when it came to FOIA requests. You can find some aerodynamic data on those old jets on NASA and DOD technical report servers and in appropriate engineering journals. Even some text books have data on these older aircraft. You have to take time to look for stuff though. It's out there.
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sprstdlyscottsmn

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Unread post06 Mar 2008, 12:53

Thanks Raptor One. I will try and poke around that way.
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Unread post07 Mar 2008, 18:45

Salute!

I would say the delta wings had the lowest wing-loading. And they prolly had a very good Cl until they got slow.

When I flew the Deuce, there was no "real" stall, just a mush. If you look at the Concorde crash stuff, they talk about minimum speed, but it's more related to controllability than a stall speed. The area of reverse command is very apparent in those deltas. you can make one really good "bat turn", and then you're outta speed and falling like a rock.

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elp

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Unread post07 Mar 2008, 20:28

"Bat turn".... haven't heard/seen that term in a while. :D
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sprstdlyscottsmn

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Unread post08 Mar 2008, 10:06

I guess even if a delta had a CLmax of 1.0 with a wing loading of 45 it would turn like no tomorrow. What kind of thrust would it take to sustain those tight turns?
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johnwill

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Unread post08 Mar 2008, 18:37

More than for a conventional wing with similar CLmax and W/S of 45. With that big CLmax also comes a bigger CD than for a conventional wing.
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Unread post09 Mar 2008, 12:59

Well yeah, I dont imagine Deltas have very high e values and by their very nature their ARs are between 2-3. I looked up some documentation that shows how flow separates over portions of a delta and high alpha too, so while the vortex produces lots of lift it makes more drag too. Man I wish I had a wind tunnel around! LOL, I just got reminded of an experiment I did reguarding flutter. I made balsa models of a few wings with the same area, 6 were of fairly high AR with varying wing sweeps (aft and fore), 3 had high ARs and varying taper ratios but where straight wings, and one was a pure delta. The point was simply to measure and record the bending/twisting modes reach before failure at a given speed. The delta never even seemed to shiver at the highest speed (was still only about 110 knots give or take). Of the normal wings the .5 taper ratio straight wing did best and the 45 degree forward sweep fell apart the fastest. A little off topic I know, but I just felt like sharing my fun times.
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johnwill

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Unread post09 Mar 2008, 19:23

Sounds like fun. The reason the .5 taper straight wing and the delta did well was probably because of their long root chords. That gives them more torsional stiffness, which is the key to flutter resistance.
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Unread post10 Mar 2008, 05:05

Salute!

Welcome aboard "spurts"!

John-boy is an old GD puke, so has many war stories.

My first fighter was the Deuce, so I was born in a delta. Never flew one again, but was fun while it lasted.

The F-16XL cranked-arrow had a limiter like the basic planes had, but it really helped the pilot from yanking until he was outta airspeed, altitude and ideas all at once. I t had a super weight-carrying capability and very low drag at normal AoA.

The Deuce was amazing to me, coming outta T-33's. No real strong buffet, just a buzz at high AoA. Sucker would bleed energy like you wouldn't believe, yet remain fully controllable down to 90 knots.

If all I had to do was cruise around at high mach and high altitude, I'd take the delta any day. Ask the B-58 guys, Mirage guys, Kfir guys, etc. With a good FLCS, I still think the delta could be a player. They inherently have a low wing loading, and the shape of the airframe lends itself to bays versus external ordnance.

Good questions,

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johnwill

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Unread post10 Mar 2008, 06:31

Gums, the war stories, the memories, etc make getting older almost worthwhile. Think how dull our lives could be now without them.

Got a question about the 102. The XL on the deck over 700kt wanted to climb so much it took huge amounts of down elevon just to stay level. A 106 pilot told me once it did the same thing. How about the 102? The B-58 couldn't fly there, so I don't know about that one.

Your comment about deltas still being a player - seems to me the Raptor is close to being one, just has tails to help provide more control power in pitch and roll.
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Unread post10 Mar 2008, 16:13

Raptor certainly has a higly swept leading edge and a low AR. And the best part about deltas has yet to be discussed, they make planes look sexy!

As for the .5 taper ratio wing lasting hte longest the ratios tested were .75, .5, and .25 and all had an AR of aprox 8 so it was still kinda skinny. The delta was the only one with an AR of 2 instead of ~8. Oh yeah and the best part was that the strain gauge we had set up on it told of frequency of vibrations and we had a strobe light that we could vary the strobe speed. The computer would tell us where a large moment was, we would set the strobe and see if it was 1st bending, 2nd bending, torsion or what not. It was so much fun. Man I miss school.
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Unread post10 Mar 2008, 19:16

sprstdlyscottsmn (why don't you get a shorter name?),

If you enjoy the work you just described, you should try to get into structural flight test, either for loads or flutter. I spent 40 years enjoying going to work every day to work in the best lab of all, the sky. My speciality was loads, but I also did a bit of flutter testing.

School was indeed great fun, but for me working with the real thing was far better.
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Unread post11 Mar 2008, 05:09

Yo Ho!

John-boy, I never got the Deuce faster than maybe 500 knots on the deck, and it was O.K.

The 106 had a "hinge-moment" limit, and the sucker turned worse than the VooDoo above 1.4M or so. Didn't fly it, but a buddy told me he almost hit a tgt when zooming in at mach 2+ one night. Pulled all he could and sucker barely turned.

Not sure if the "hinge moment" problem was loading or aero. I suspect it was an aero problem, as those oblique shockwaves get tricky unless you have a "slab" versus elevons.

The XL troop I knew best (Wolfman) and one of the JTF pilots said the XL was really stable at low altitudes and 600 knots IAS. They didn't say anything about a nose-up tendency. The one thing about the XL that was really neat was it could carry a dozen 500-pounders in the submerged racks and zip along at 600 knots on the deck burning less than 10,000 lbs per hour.

gotta go,

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Unread post11 Mar 2008, 06:20

Gums,

Thanks for the comments. I remember Wolfman well, good test pilot. The XL nose-up was totally transparent to the pilots, since the computer cranked in whatever elevon was required to keep the airplane at 1g. Which happened to be 11 degrees down, using about 60% of maximum hydraulic power. The load on the rear spar was so high, we had to saw out some of the aluminum spar and replace it with steel.

"Hinge Moment" limit was likely the elevons not having enough hydraulic power to move them far enough to get the g you wanted.
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