cyclops2

When Delta winged aircraft come in for a landing at their high AOA's what are they doing to the air underneath them to give such short landing runs ?
My favorite, The SAAB Draken J-35's were noted for short takeoffs and landings on pavement or ice.

This is a -- more correctly ???--- stated question about wings and air flow around them ??

I am not intending to " troll ".

Have the moderator kill it now if it is to tough to tackle.

rmh

They are pushing the air into a big pile and then pushing that pressure bubble along .
Also they are creating a big vacuum behind which is trying to snatch the plane to a stop
Basically they create a terrific unbalance in air pressure and Mother Nature stops the plane as soon as possible to try and rebalance the pressure.
This explanation won't win any awards at a meeting of rocket scientists - (or maybe it will!)

britbrat

No award -- but dead on -- as is frequently the case.

Tall Paul

Watch the air flow out from under a shuttle when it lands.... the night shots with vapor off the tips are particularly good for this.
SR-71 also uses that bubble to land softly.

Red B.

Nice to hear from a fellow Draken enthusiast!

The high angle of attack produces a lot of drag, i.e., a lot of aerodynamic braking.
This can be used to good effect for aircraft with very low aspect ratios (wing span squared / wing area) such as the SAAB Draken double delta, because they can reach very high angle of attacks before stalling becomes a problem.
For a nice introduction to "ground effect" check out [link=http://en.wikipedia.org/wiki/Ground_effect]Wikipedia[/link].

My favourite SAAB aircraft is the mighty "Viggen" (en. Thunderbolt), which has now been retired and replaced by the SAAB "Gripen". Check out this [link=http://video.google.com/videoplay?docid=-2368660162006357802&q=viggen]video[/link] with a Viggen doing a full stop landing, a reverse U-turn followed by a take-off, all within 53 seconds. Not bad for an aircraft that first flew in 1967.

Some stats:
Landing speed: 140 mph
Landing distance: 450 m
Take off distance: 400 m
Take off speed: 195 mph (reached in 7 seconds)

/Red B.

barto

Aerodynamic braking means holding the nose off with the main gear on the ground. Just landing with high pitch attitudes is not the same. Aerodynamic braking does not work.

You are correct in saying that aircraft with low aspect ratios have a big stalling AOA. This allows them to land at relative low speeds which gives shorter landing distances.

Bart

Red B.

Holding the nose off with the main gear on the ground was a standard operating procedure with the SAAB Draken. The Draken also had a drag chute for shortening the landing run. The Viggen on the other hand used a thrust reverser for braking.

Here is an old [link=http://www.youtube.com/watch?v=Hh97ixM1fv8]Draken video[/link] for cyclops2 :-)

/Red B.

barto

I don't know any of the procedures of the Draken but my point was that if you keep the nose of the ground the landing distance will not be shorter. On top of that, with certain aircraft designs, there is a big risk of tailstrikes with aerodynamic braking.
Extending the flare is also not a good option if you try to decrease the landing distance.

Maybe there was another reason with the Draken to do this...

Bart

da Rock

I've never wondered why they can do it because it looks so kewl when they are doing it.

BTW, ain't no troll on board most delta wing airplanes..... 'cept maybe ones that fly out of Norway. Ain't that where most of them little buggers live? I used to work with The Mad Norweegin. Kjell Grotland. He flew Thunderstreaks for them long ago. Had hundreds of stories about flying off ice. Actually, he had 3 stories but would tell them hundreds of times in just one evening.

barto

Yep, it looks very nice. Did it too with small aircraft, sadly not with a fighter jet.:-)

grtz,
Bart

Red B.

Many versions of the Draken had a set of retractable tail wheels to prevent tailstrikes as you can see at the end of this [link=http://www.youtube.com/watch?v=wKQ75dyF1SE]video[/link]. If you don't want to or can't use your wheel brakes (for example when landing on ice covered Swedish highways) keeping the nose well off the ground will definitely shorten your landing run with an aircraft such as the Draken.

cyclops2

Red B.

The Saab J-35 is still held in high regard by the few American pilots who have flown them. One I met 10 years ago flew it at a desert school and said he would take it into a dogfight anyday. He ferries jets for a living. He said it is totally a pilots plane.

I have tried offering several thousands of dollars to go up in the trainer, but no such luck.
Is there anyone in Sweden or Denmark making 4' or larger kits for ducted fans ?

Thanks for the Saab boost!! Made my day.

My best wishes to you , Richard.

Red B.

I don't know of any manufacturer of Draken jet models nowadays. Som years ago the Swedish company Nauwa Models Sweden, produced a nice kit that was originally intended for ducted fans, but I have seen a couple of them equipped with turbines. Very nice indeed.

Their web page is still there so you may try contacting them. Maybe they can help you out.

Link: [link=http://home.swipnet.se/nauwa/]http://home.swipnet.se/nauwa/[/link]

/Red B.

cyclops2

Thanks Red.

Site is dead since 2000.

Tall Paul

A couple of SAABs at Mohave Airport, 20 years ago...
Used for testing and chase planes, and the Draken in commercials and movies.

rmh

years back, I read in some "military publication"-- about the specs and results for a NATO fighter -- to me --the SAAB looked like the best approach - self contained - start up - park it in a roadside bunker -land it in a cow pasture etc.. and some very impressive performance stats all around - the winner was (ta da--) The F16- which here at Hill Air Force Base made everyone happy except for the guys who went straight into the salt flats when the electronics hiccuped (whoops!)
I remember thinking that test for the "best" fighter was a bit of a sham
Reminds me of the test for a new secretary
One being the best typest
One being the best at dictation
which one do you pick?
anybody ------ drum roll------------------

da Rock

Yeah, she was the one I picked too. [sm=thumbup.gif]

da Rock

You were comparing the secretaries to the two airplanes, right?

I'd have picked the F16 over the SAAB for sure for those same reasons.

It was faster.
It was slimmer.
But it didn't have a big wide tail.
It had bigger uh.... load carrying capability.
And it was as hot as a new secretary.

BMatthews

The Draken doesn't provide the landing gear to properly use the very high AoA's possible with a delta. I've seen shots of the Convair deltas at far higher AoA's during landings.

Similarly our own Avro Arrow also had very long landing gear in order to take advantage of the high drag during very nose high landings that can slow down these craft.

Cyclops, the delta winged aircraft can do this largely because the delta wing produces lots of lift as well as lots of drag at these angles of attack from the high vortex flow out and around the highly swept back leading edges of the wing. This trait passes over to model sizes just fine from what I've heard. But you need to keep the sweep angle of the leading edges high like less than 80'ish degrees between the LE's for this to work. The Convair deltas (F102, F106 and B-50) all used around a 60 degree angle between the leading edges.

Make a hacker design and play with it. Get back to us...

iron eagel

Bruce,
did you mean the B-58 Hustler instead of the B-50 that was a prop job

cyclops2

Now that APC is making L & R props for direct drive and geared brushed 400's I have no time for single engined planes.

Change 1/2 the props on my multi's and place a big order while APC is being nice to me.

BMatthews

My bad, yeah the B58 Hustler. Very long gear. Partly for the belly mounted bomb pod but I'm sure the need for high AoA for landings had a lot to do with it as well.

Consider that a Delta wing craft can't use flaps since trailing edge flaps would act like down elevator. So what's left? Just very high angle of attack.

The Mig 21 has flaps but that one doesn't count since it's a conventional layout that just happens to have a delta planform wing but with conventional tail.

Johng

My Feedback: (4)

Aerobraking most definitely does work. Nose up, plane slows down. Is it as short as a max braking landing? no. It's not even as short as medium effort braking. Why do it? You have a long military runway and you don't want to put unnecassary wear on the brakes.


Same reason fighters used to use parachutes for landings. An F-4 would wear out set of brakes in about 10 flights if it didn't use the parachutes. Even the F-16 is fit with a parachute for the ones built/used in the Euro-partner countries, since they generally have to deal with short runways or land on roads when deployed.

Johng

My Feedback: (4)

Oh, and the original question, like with most lift - it's not what happens below the wing that's very important. It's above the wing that's critical. The delta wing actually uses the vortex that we normally would blame for drag, as a main mechanism for lift - and still drag. The rotation of the vortex pulls air over and own the top surface of the wing. Not the standard way we think of lift, but we are talking deltas not glider wings.

barto

So basically you have proven my point. Aerodynamic braking does not work, i.e. it does not give the shortest landing distance possible.

Bart