Hypersonic Deltas
 

Assuming it's not classified: Why have there been so many concepts for hypersonic planes that had highly swept delta wings? Wouldn't the shockwave be swept behind the wing, thus producing a large increase in drag and a large center of pressure shift?

this is another involved explanation I would suggests a Google search of the following....'oblique and normal shock waves' and Prandtl-Meyer Expansion wave phenomena...

because the shock wave dissipates energy upon adiabatic expansion as long as the airframe is substantially within the mach cone.
Also, it depends on whether it's a double wedge- blunt object-like a bullet or a sharp object like an arrow...however the delta wing is the best planform for mitigation of compressibility effects as around 45 degrees the maximum reduction of normal sensed true airspeed vector occurs according to the Cosine of the sweep angle. of course, the basic airfoil shape is always important, thereby alleviating drag rise with TAS increase as well as compressibility effects...one other the most difficult aspects of high speed design is the heat dissipation problems associated with ram rise

the two basic designs would either be a Double wedged or circular arc...as I had said it's a very involved topic...:\

there are folks here more qualified in high speed aerodynamics than me so apologize for any horse hooey if any

:)

I was believe that the delta wing is the best shape that give a benefit in structure term and drag due to swept angle. However after I saw the graph below I'm not sure wat is going on that cause the delta wing to produce more drag than the straight wing.
Could somebody explain this to me please?

http://i536.photobucket.com/albums/f...904/img003.jpg

Best regards

Pugilistic Animus

Yeah but at Mach 5, and Mach 6 how far back is the mach cone swept? What if the airframe is not entirely inside the cone?


Mr. Vortex

As I interpret that image, a straight wing has a lower drag coefficient than the delta or swept wing....

For ultra high Mach flight, I'd suggest you look up Lifting Body aircraft.

Landing is not all that bad, but they need a hell of a lot of runway to takeoff.

But then again, the Space Shuttle is a delta wing and it certainly does ultra high Mach speed.

Just a guess but perhaps the drag rise is due to detached shock wave as the object becomes more blunted ....no good theory exists on those complication so the empirical data posted has to be relied upon, the delta plan-form clearly has more to do with offsetting first order compressibility effects than with drag reduction... but the overall L/D ratio and more importantly the lift slope curve may be more favorable, with a specific plan form; drag/Mach data alone is insufficient to conclude anything about the relative efficiencies of the plan forms


it all then becomes very empirical as the theoretical treatment makes that assumption...:)

Pugilistic Animus

If the leading edges are sharp, as I understand from what I read in books, the shockwave will sweep behind the leading edge of the wing. Drag rise from what I understand has to do with the shock wave passing through the whole leading edge (which is actually longer on a swept wing or delta wing than a straight wing) and from trim-drag due to the fact that on a straight wing while supersonic or swept wing at the same angle as the shockwave off it's wing-root, the center of pressure shifts back to the 50% chord position.

You mean pitch down tendency and low drag when getting through Mach 1?

Out of curiosity: Anybody heard of the Kuchemann Tau?

http://img339.imageshack.us/img339/439/kuchemanntau.jpg

Basically the idea revolves around adding a sharp spatular insert (2D, sharp leading-edge) in between a delta winged wave-rider that is half the span of the delta-winged section. It effectively reduces drag considerably.

As I understand

1.) It would probably reduce supersonic drag as the shockwave is going to probably be behind the leading edge anyway, and a low-sweep has lower supersonic drag than a highly swept wing.

2.) It would probably make the inlet design simpler as it doesn't have to be wrapped around the curve as you have a 2D ramp over a 3D cone

Still, I'm wondering if a thin diamond shaped wing would be more suitable as that wing-shape works well when the shock-wave sweeps beyond the leading-edge of the wing with a spatular insert in the middle; or an ogival shape with the inboard section spatular with the sweep progressively increased from the root to the tip (like a shovel or certain mideval shields).

yes, according to those prior excerpts; however shock wvae pattern at those speeds are remarkably complex, and also due to very high altitudes the effect of 'slip' a Reynold's number effect-in the manner in which the boundary layer 'slips' relative to the wing this also changes lift characteristics and the overall L/D ratio ,lift-slope curve, pitching moments coefficient, etc...

in short the exact plan form configuration chosen by the designers is contingent upon numerous factors,...but lowered total drag may simply not be that important on a particular design compared with other aspects of the design...it really all depends and theoretical treatment is limited...but hypersonic is now very old...it's just not really important for us to do right now...but mankind has been capable a while now...:)

not necessarily...as described above


Gotta see and test it...;)
yes, it has do do the volume/wetted area-ratio one need a large value to go faster, because the geometric volume increase must be higher than than wetted area increase...as measure of effective lift...I think text on high speed aerodynamics might be overwhelming...so I don't think I'm able to expand more...:\


:}

Pugilistic Animus

I have never heard of "slip" in this context. I understand vaguely what Reynold's numbers mean in that it's a function of scale.

Which would be?

have a look at this...

Reynolds Number


thermal transfer problems..:\, stability problems, structural efficiency, volumetric space for fuel and auxiliaries...etc...

Pugilistic Animus

Just a brief glance at the page it looks almost like higher reynolds numbers would lead to the airflow at the stagnation points taking longer as you go rearwards to "de-stagnify" and go back up to normal speeds. A lot of turbulence I'm sure would ensue as well.

You mean hot spots on the plane?

How would that occur? High pressure zones occurring in key areas due to the airflow stagnating and not accelerating back up?

Well, that makes more sense as delta wings are very strong structures

Makes sense as many hypersonic concepts use low density fuels.

Still, I thought the whole purpose of a wave-rider is to produce an aircraft that can get high L/D ratios while at high mach (where it is harder to do so)

well despite the mechanistic reasons, from continuity and conservation of energy and momentum, for either laminar and turbulent flow separation...Flow separation points are very important to attempt to predict, but because of Reynold's number effects, prediction of such terms as the skin friction drag and pitching moment coefficient.

all of these items are very very difficult to predict with theory due to slip, when speaking about very high speed flight at the usual very high altitudes....Reynold's number effect and Mach number effects are intertwined in a horribly complex way...

Also,
at very very high altitudes the mean free path of the air molecules at a constant Mach or a constant dynamic pressure may exceed the span by such a factor that the boundary layer moves, continuity is lost because the boundary layer is no longer in a steady state flow respective to the wing section......slipping with the wing....even as of today theoretical treatment alone fails to make good predictions of laminar and turbulent separation points and shear effect skin friction coefficients when there is 'slip' ... not a stationary boundary layer as the theoretical treatments propose...and just as a reminder when comparing different forms it is important [due to the scale effects you mentioned] to always compare different sections and planforms at the same Rn and Mach number...otherwise the results are nonsense...

something like that...:)

Still, I thought the whole purpose of a wave-rider is to produce an aircraft that can get high L/D ratios while at high mach (where it is harder to do so)



Robyn Just like Puerto Ricans the designers have their 'reasons'...:}

I think you would have been great on a design team back in the 50's or early 60's...:)

Pugilistic Animus

http://img715.imageshack.us/img715/7...lledhst002.jpg

I drew this up. The sweep angles and stuff aren't absolute but the idea is that it has almost no sweep in the middle similar to a spatular section and progressively sweeps more and more as you go outboard. Ogival.

Can you give a simple explanation of what wetted area is?

The skin friction drag I understand -- higher reynolds numbers would mean more turbulent flow (I'm guessing stronger shockwaves, more heat produced).

The pitching moment co-efficient, is that due to high pressure spots formed on parts of the fuselage monkeying around with the center of pressure?

When you say the boundary layer slips? Do you mean that from the stagnation point the flow speeds back up at a slower rate than normal, and/or that the lower area of the flow accelerates up speed unusually slow compared to the upper layers?

I'm sure that I'm being very simplistic overall, but as a rule of thumb I generally learn best by grasping the basic concept first and then proceeding from there.

my stupid power cord pulled out, while posting earlier, I hate typing so I'll just be brief...and I'll get back to the finer points later...:)

Cthe amount of wing area immersed in effective [lift producing] flow at a given alpha

almost changes in pressure distribution due to flow separation point shifting, at different values of mach

not necessarily, stronger shock waves just very complex shock wave interactions...most of temperature rise is due to compression of the air, although frictional heating term is important too

it's more of a conceptual term, meaning the boundary layer fails to separate at points predicted assuming a constant 'flow rate'...by an amount 'eta' that eta is the coefficient of slip ---it really can't by theoretically computed---it's due to the long paths over which the air molecules must travel...

I can see how something like that would cut through and ride the waves---surfboard-like....and also a decent amount of area for the low speed regimes of takeoff and landing....I can't really say how it would do,...but you could probably get an airplane out of it---that's actually how it all really starts even the SR-71, Concorde, B757 etc...imagination :ok:



me too...:)

Pugilistic Animus

Understood

So basically the surface area of the upper and lower surfaces of the wings/fuselage and so forth not counting volume inside them? Does this factor the curves of the wing's top and bottom surfaces and the curves of the fuselage and so forth?

And pressure distributions ultimately yields center of pressure shifts

You mean interference effects?
(I was always under the impression that higher reynolds numbers meant more turbulence though)

I understand

Does it separate more towards the front of the wing/fuselage, or more towards the rear of the wing/fuselage as the reynolds numbers go up?

Wait... if it can't be theoretically computed, then how come people were able to design objects that fly at hypersonic speed?

I didn't think of it that way, but I suppose it does look a little bit like the front of a surfboard

Understood

True enough

....

I'm not entirely sure what you mean here; ... picture shooting a water hose at the wing head on - a good portion of the wing will have a steady stream flowing over it and however the back section of the wing may only catch droplets of water due to dispersion as you angle the wing up then more of the wing will catch the droplets...not entirely correct as an aerodynamic analogy though...

All Designs teams have designed planes w/o a full theoretical/computational analysis...there's always a difference between computed and actual flight characteristics...the base equations are themselves inexact...that's why there exist Test pilots and IIRC the first hypersonic X-plane disintegrated...although she went out FAST!!!

Yes,...
...more turbulence =more math chaos :\:\:\

low Rn numbers generally mean poor lift and drag characteristics... due to the laminar transition to turbulent against an adverse pressure ratio...flow separation may be delayed in at low Rn but the shear-effect drag is more pronounced.

Pugilistic Animus

I understand what you're trying to say.

Yes, but there are theoretical rules of thumb to take into account scaling differences right?

Okay

What's an adverse pressure ratio?

And what's shear drag?

http://i1080.photobucket.com/albums/...1/scan0073.jpg">">http://i1080.photobucket.com/albums/...1/scan0082.jpg">

To have a "wing" at all whilst hypersonic begs the question. Do we need a wing at all ?? Save for down low, and transition back from Bullet to Truck ??

variable geometry or retracting geometry??

The Valkyrie had a nifty feature that drooped her outer wing, moving a wing 90 degrees loses all drag due Lift, and we are left with parasite, retaining all cargo and systems volume.

bear

bearfoil

The wing didn't fold down 90-degrees. The wing could be folded down 25-degrees or 64.5 degrees on A/V-1 (On A/V-2 it could be folded down 30-degrees and 69.5 degrees due to the aircraft having a 5-degree dihedral).

Jane-Doh

I read it differently, the post does not state the B-70 had 90 degree droop, only that she can droop her tips. Read the comma ??

geometrically similar bodies must simply be compared at the same Rn and Mn, in order to fully appreciate the effects of viscosity and compressibility...

pressure increases in the direction of flow prevent laminar flow...if the pressure rise is large a flow reversal occurs...this is laminar flow separation

A synonym for skin friction drag

CliveL that diagram summarizes so much:ok:


Bear unless it's gliding - a wing is helpful for being able to develops sufficient lift to maintain straight and level of climbing flight...variable geometry wings would be ideal...if the weight increase is not penalizing
:}

CliveL

I don't understand the diagram you gave me (the one on the left side). I can read and everything, I just don't understand the significance of all the parameters and what everything means.

J-D

Sorry JD, but I am not going to be tempted to go down your road. I have watched on several threads how answering one of your "innocent" questions leads to another and another .... just like they were programmed or something

Try a good textbook.:ok:

CliveL

CliveL

Is the R = rankine?

As for the second diagram regarding temperatures of an object at Mach 25... how the hell did such a blunt object get up to 6,000 K? That's 10,340 F -- blunt objects generally achieve lower skin temperatures than do sharp objects which is why they're used. IIRC, the space shuttle on reentry reached something like 1,650 to 1,750 C

As I said, I'm not going down your road!

Okay to somebody other than CliveL, does the R mean Rankine? As for the second diagram regarding temperatures of an object at Mach 25... how the hell did such a blunt object get up to 6,000 K? That's 10,340 F -- blunt objects generally achieve lower skin temperatures than do sharp objects which is why they're used. IIRC, the space shuttle on reentry reached something like 1,650 to 1,750 C


CliveL

I know you think I'm some kind of chatterbot, or just purposefully being annoying, but I'm not a chatterbot, and I'm not purposefully trying to annoy you. I honestly am just having trouble understanding the graph and rather than help you're instead just being difficult.

it's not about the absolute temperatures it's about how fast the heat can be dissipated transfered to cooling medium such as fuel; do a pprune search for 'ram rise formula'...:)


further discussion involves too much writing about 'flow in pipes'...:\:\:\ and compressibility:\:\:\

Pugilistic Animus

I'll look for it

interesting...blunt bodies always form detached shockwaves at very high speed

I see what they are doing but I'd imagine getting an airplane out of it, as opposed to a missile, would be difficult

I wish they'd declassify the SR71's flight envelope...about as close to a functional hypersonic platform as we've come...Space shuttle excepted, too heavy and cumbersome for a plane ---and it explodes a lot...:ouch:
my guess regarding the blackbird is M 4.0 @ FL 900...:)

really, I think that Clarence just talked to space aliens...:)

msbbarratt

The air-spike they're talking about involves projecting a small amount of directed energy which effectively acts like a sharp-nose.

I don't know if that applies at all speeds. From launch to supercavitation, it definitely would use the exhaust gas to lower drag; once it's supercavitating, it is effectively riding in a stream of air/steam.

Absolutely not. You can have a wing that is not swept much yet performs well at supersonic speeds. The wing has to be comparatively thin compared to a delta, has to have a sharper leading-edge; it should either be symmetrical, or inversely cambered, with the crest at at least 50% back. The shockwave will either be split by the wing (not sure about this, but if so it would be at zero sweep) or will sweep beyond the leading edge of the wing (greater than zero-sweep).

Trim drag is often substantial once the shockwave sweeps past the angle of the wing, the center of pressure will immediately go back to the 50% chord position, but that will happen once the shockwave sweeps beyond the leading-edge of a delta-wing too. Below the speed at which the shockwave sweeps beyond the leading-edge, a delta-wing is generally better from the standpoint of trim-drag; above it a straight or trapezoidal wing is actually better. The longer leading edge of the delta will have more shockwave traversing over it than an unswept wing (the leading edge is shorter from root to tip for the same span) as well as the fact that a delta wing is of a much longer chord typically than a straight-tapered, or trapezoidal wing.

The F-104 had a wing with barely any sweep and officially it could do Mach 2.2 (in truth, it could probably cruise near that speed), and in most likely could exceed Mach 3 in a short dash; it could definitely slip through the sound barrier even at low altitudes without afterburners being used (unsure if the plane was in a shallow dive when this happened or just at high power when level -- though this did happen with some remarkably loud results :})

It's wings were effectively tapered, but otherwise considered straight. They were only 3.36% thick, had leading-edges as sharp as a knife, and other than a small degree of curvature on the leading and trailing edges, was virtually flat on top; the underside appeared to have a flared, inverse-camber (at least it appeared that way from an image a member posted on one of these forums). Trim drag appeared to be compensated for by the fact that the aircraft had a relatively large tail-surface; the basic drag of the airplane (not including trim-drag) was quite low; and the overall chord of the wing was not particularly massive relative to the length of the plane (meaning even though the CP shift was large relative to the chord, the actual shift was fairly small) and it's possible that the distribution of mass throughout the airplane resulted in very little pitch changes when transitioning through the sound-barrier.

The F-104 of course, was far from perfect; it's wings were way too small and it didn't maneuver very well unless you were flying like a bat out of hell -- oddly, it maneuvered very well when supersonic also (which seems to suggest that while L/D ratios tend to always be less when supersonic, the F-104's supersonic L/D ratio might not have been too much greater when subsonic compared to supersonic because it did so badly when subsonic and so well when supersonic :}).

The aircraft was originally designed as a dedicated light-fighter, but the USAF largely felt that if a fighter couldn't perform a nuclear strike mission, perform an interceptor role, or escort bombers (and their views on that oscillated periodically -- prior to WW2 they felt the bombers were fine on their own; then by around 1942 to 1943 they decided it would be a good idea to use planes like the P-38, P-47, and P-51 for that role, of which the P-51 was best suited; this stayed that way until the Korean War, until they switched to night-bombing, though sometimes a Navy F3D Skyknight was indeed providing escort; then they developed the XF-85 which could fly in the bomb-bay of a B-36 which had too long a range for any fighter, the XF-88 Penetration fighter which would fly escort in the traditional fashion, as well as some ideas of attaching F-84's onto the wings of a B-29 or B-50, but they changed their mind and cancelled all of them; then they decided that an escort wasn't such a bad idea after all and ordered the F-101 Voodoo, which they then cancelled. After that point they decided they'd just go supersonic, pursuing designs like the B-58 and XB-70 which due to their speed and range would not need escort -- unfortunately the B-58 was pretty expensive, and could only deliver nukes; the B-70 was psychotically expensive, costing 157 million dollars a pop had the USAF procured the 250 that they wanted resulting in it being relegated to a prototype), they didn't want to have anything to do with it. Unfortunately the USAF had this annoying characteristic of being rather uncompromising with designs (especially post Korea) and seemed to almost favor the secondary roles (i.e if you have a fighter/attack plane, they generally seemed to focus more on attack capability than they did the fighter capability) and the F-104 seemed to be designed more around the interceptor requirement than the fighter requirement (a delta wing would be far better suited for a fighter/interceptor as it would work well at subsonic/high-altitudes or supersonic) though at least it had a gun and a bubble canopy and may indeed be the first plane that could dogfight at Mach 2 :} (J/K)

The F-22, on the other hand, was designed both around agility and speed (as well as stealth): It has monstrously powerful engines which provide both good acceleration, the ability to go supersonic without using it's afterburners at all (afterburners are used to achieve the maximum dash speed, provide additional acceleration and thrust to sustain a high g-load across the performance envelope); it's wings are large, have automatically operated leading/trailing-edge flaps/flaperons to provide a good L/D ratio both when flying level and when aggressively maneuvering to provide a high degree of sustained agility; it has small strakes located just outboard of the engine inlets which produce a powerful vortex that when combined with thrust vectoring effectively eliminates any alpha limits; it's wings are more highly swept than the F-104 so it flies better at lower speeds (both subsonic and low-supersonic) and still does well supersonic; it is designed to be unstable which gives it remarkable instantaneous agility both subsonic and supersonic (which is again assisted by thrust vectoring as well); while it's missiles are carried internally for the purposes of stealth, it does reduce drag to some degree over carrying them externally.

Disclaimer: No information mentioned on the F-22 is classified


Pugilistic Animus

Yes, but they normally produce gigantic amounts of drag in the process. This effectively produces low drag by using directed energy to effectively produce a similar effect that a sharp flared cone would.

I don't get it either -- the Russians have seen what it can do after they've tried fruitlessly so many times to intercept it :} -- why not just admit the speed we knew the Russians saw it fly at?

You make it seem as if it blew up half the time! It only blew up twice.

There was this guy named Robert Widmer who worked for Convair (now works for Lockheed) and worked on the B-58 and (IIRC) the Convair Kingfish, which was the competitor to the A-12. According to what he said, the Kingfish could do Mach 6.5 and from what it would appear the A-12 and Kingfish had the same top speed. No idea about altitude but I'd guess 125,000 to 145,000 feet (Remember folks, no matter how I die, it was murder :hmm:)

Consider the following
- The General Electric X279E was rated for Mach 4. The X279E later became known as either the XJ93-GE1 or YJ93-GE1. The engine was eventually enlarged into the J93-GE3. This was briefly mentioned in a book about the XB-70; this statement was effectively validated from a statement by Walt Spivak who was either the chief designer or chief engineer on the XB-70 and said the inlets could withstand conditions at Mach 4.0 made elsewhere.
- The J58 was capable of the same mach number as the J93 and was proposed briefly as a competitor, and was retained even after the J93 won the competition in case the J93 could not perform up to expectation (some people in the USAF also preferred it's simpler design).
- The J58 used on the A-12 was almost totally redesigned from the earlier versions. It was larger in diameter (IIRC: 52.5" vs 47"); it had a substantially greater amount of air-cooling; the metallurgy was almost entirely different; it had an elaborate bleed-bypass system routing up to 65% of the airflow around the engine into the afterburner; the combustion chamber and afterburner had features which allowed the fuel-to-air ratios to be lowered at high mach.
- Paul Csysz stated that the Blackbird was made out of a high temperature titanium alloy called Beta-Titanium. It has been stated that this alloy could take temperatures of 1,000 to 1,200 C; furthermore additional data has stated that the A-12 has active cooling in it's chines.


Jane D'oH!

A la X-15 ...:)

cool stuff, I think I see why you picked 'Jane'...;)

Pugilistic Animus

I didn't create the name Jane DoH as an homage to "Jane's All The World's Aircraft". Jane DoH is basically a parody of Jane Doe, which is a fairly anonymous name pronounced like Homer Simpson saying "D'oH!"

Pugilistic Animus

And I assume some energy is re-radiated back into the air? I do distinctly remember reading that if you flew at a given mach number at two different altitudes you'd get different skin temperatures which I was under the impression at the time had to do with the thinner air able to impart less heat to the plane, and the airplane's structure naturally able to radiate away a certain amount of heat.