Cry for technical help re foward swept wings

You are right about the wing not having the control efficiency of a canard, but if you have a TVC engine you don't need a canard for tight manoevres. the joined wing though will give high lift, phenomenal rate of roll, extremely high AoA (In addition to TVC), very low landing speed and additional benefits for STOL operation, all theoretical of course until someone tries it out. The degree of controllability the joined wing+TVC+FBW+unmanned combination in this UCAV should bring ought to be unrivalled. I'd love to be able to test the theory.

As for fuel capacity, any lost capacity from the shrtened FSW wing is more than made up for by the forward wing so it should be better in this respect than a pure FSW design as there is no reason the conformal tanks cannot be simply transferred across to this design.

The alternative with aft swept outer panels would be worth investigating but what extra would they bring? If they simply extend the span then they also add weight and reducing span and weight (and thus increasing rate of roll etc) was one of the prime benefits the joined wing brought to this concept. If the benefits of the full joined wing are not realised, or turn out to be overstated (by me,lol) then your FSW version would be the next best bet imho.

I’m loving this thread.

Waynos, I can see your argument. Where I’m less convinced is transonic drag and agility. But I am the first to admit that my technical knowledge is lacking. The conformal tanks are not so easy on this configuration though. We could just make the fuselage wider?

Here’s the above illustration redrawn in light of your own illustration. The wingtip pylons would need to be stressed for 400lb (heavy for a wing-tip rail) to accommodate ALARM, Maverick, Brimstone and self-defense AAMs. The rear of launch rail could have a modular bulkhead attachment for RWR, Chaff/flair/decoy fits depending on customer.

I'm loving it too planeman! You guys are making a great team. Let me know if you need any calculations done. I'll help anywhere you need me. Just u2u!

We could do with help. Anything really –from ideas, suggestions, research, technical advice, calculations, 3D modeling, photoshop rendering….

So far we have two main ideas for a S-STOL (Super-Short Take-Off and Landing) unmanned combat air vehicle for carrierborne operations. The first was D-0013 which featured a forward-swept-wing, canards, thrust-vectoring and a lift jet. We are now refining our second idea – a closely coupled biplane with rearward-swept and forward-swept elements.

Ultimately we’ll need to have three or four general configurations to notionally evaluate and come to a single proposal (all hypothetical of course).

I don't know if I'm just overlooking it, or if you haven't posted it...but do you have performance envelope for this design?

Range
Ceilings
Speed envelope
take-off and landing distance restrictions (if I remember right, for a carrier, you need to be able to take-off and clear 50 feet within like 300 something feet, is this correct? because I'm going off of 15 year old memories right now)
are there any maneuverability requirements? bank radius, etc.

Hi,

Yep, the answer to your questions is here: www.armbell.com...

The “Jaguar/AMX/Skyhawk” performance translates as:
Max speed: Mach 0.9+ (preferably Mach 1.4 ‘clean’ and Mach 0.9 with a heavy weapons load)
Range: Around 400mile radius with two ALCMs or Anti-ship missiles
Weight: 30,000 lb or there about – 10,000 lb of which is weapons.


Guys, I knew I’d seen a basically similar configuration on a UAV before. Found it: www.uavforum.com... www.daraaviation.com...&d.htm
www.daraaviation.com...
Once again the forward wing is the lower one. I wonder why. Of note, Dara Aviation claim that the coupled wing configuration (still looking for a good descriptive term –Dara call it “Joined Bi-Diamond Wing”) allows redundancy of control surfaces (!) – an advantage worth thinking about.

Good find. Someone may correct me if I'm barking up the wrong tree here but I think I rememebr from somewhere that the lower forward wing gives better cruise efficiency but the way we've been drawing it is better for agility. Looking at the fact that Dornier was thinking of doing it 'our' way on their fighter proposal there may be something to that. Even so, a proposal with the wing positions reverse would be worth looking at.

Funny you should mention control surfaces because I actually came back here to see if you think we should employ slightly larger leading edge control devices (for manoevering not just landing - known as LEMD's) on the forward wing at around 1/4 chord and restrict trailing edge flaps and ailerons to the rear FSW wing?

I see you have doubts about this design re drag and agility, I don't think we could prove these either way without a wind tunnel but there doesn't really look to be anything inately 'draggy' about it to me, but I'm biased because I thought of it





[edit on 7-1-2006 by waynos]

We started drawing the reversed wing configuration but the result is such an ugly duckling that we only got as far as the top view:

Actually, the real reason we stopped early has to do with high angles of attack. I think that it’s accepted that S-STOL landings require slow speed high angle of attack decent –wouldn’t the forward wing mask the rear wing in this configuration? That would surly detract from all the benefits of forward swept wings (slow aileron stall speeds) that made us so interested in them in the first place.

Also, isn’t the forward wing going to be lower lift in this position?

One possible benefit to having the rear wing higher is that we could more easily incorporate twin tails if we really wanted to –but twin tails are heavier and given our less ambitious operating speeds (plus thrust vectoring),probably not that relevant.

Something we’ve also got to think about is intake design. My initial thoughts are fixed intakes with generally conventional splitter-plates. The new advanced JSF type intakes seem to offer many advantages including weight and cost(?) but I don’t know much about the subject.

Because of the downward thrust of the lift-jet (or fan) I’ve always gone for lateral intakes. Belly intakes would be very complex given the forward engine and top mounted intakes would be masked by the nose at high angles of attack and also compete with the lift-jet when it’s deployed. The only alternative to lateral intakes that I can imagine is to duct the intake around the lift-jet and have a nose intake –but I can’t see any benefits to doing this, especially since we want to have a nose mounted radar (essential for anti-ship mission).

We should look into LEMDs. Please tell me more.

Guys, something –or rather someone, who interests me. Whilst trawling the net for “diamond wing” aircraft I found the page of a Mark Stock who has written a program to model airflow over wings. One of his pictures depicts a UCAV:
(image rehosted to preserve his bandwidth. Original context: mark.technolope.org... )
If only we had that capability.

The blanking effect of a lower forward wing with any sort of positive AoA is absolutely right, if it hadn't been nearly midnight I might have realised that, lol.

How about scheming a full diamond wing (a la YF23) for comparative purposes? although I think this option is less interesting than the one we currently have.

Vahall,

To explain the take-off/landing distances…. Our outline concept is S-STOL (Super-Short Take-Off and Landing). This is dictated by our target market –light/medium aircraft carrier operators. The land based market is secondary in design terms simply because a carrier aircraft can operate from land whereas it’s not always the case vice-versa. When we say small/light carriers we are talking about ones currently viewed as V/STOL only –like those of Spain, Italy, Thailand, India and currently the UK (or in future terms whoever buys them when they are retired). We suppose that these customers will not operate the X-47 UCAVs because their carriers are too small, have no arrester gear or no catapult as well as for political and/or financial reasons. So there is a market for UCAVs able to operate from them –which with current (real) projects in development would be limited to rotary ones. What is more, when their Harrier aircraft become old, the only project replacement will be the F-35 –same cost and political issues. Spain and Italy wil buy at least some F-35s but India (small carriers to be retired?), Thailand and whoever buys the UK’s current V/STOL carriers (I predict three different countries)??? And if there was a cheaper option then even Spain and Italy would both likely prefer a mixed fleet of F-35s and less capable UCAVs.

Put yourself in Thailand’s shoes. You’ve recently brought a state of the art light carrier from Spain (HTMS Chakri Naruebet) and brought second hand (and close to obsolete) AV-8A Harrier aircraft as the first step. All of a sudden the only V/STOL strike platform in serious development anywhere in the worlds is the US F-35 which you probably won’t be able to afford.

Spanish light carrier Principe de Asturias (left with Harriers on deck) and the Thai “helicopter carrier” HTMS Chakri Naruebet:


There are also countries with ‘medium’ carriers like France, Brazil, Russia and in the future UK, India and China. Some of these carriers have ski-jumps rather than catapults (Russia, India and China) but all have arrestor gear –this may negate the S-STOL requirement but a conventional landing sub-variant could be developed.

Now, given geopolitics, we have identified the Brazil, Thailand, India, Spain and Italy as the key market. And our design (which is entirely hypothetical of course) would be the only contender for that market.

So this concept UCAV must be able to operate from a small carrier using a ski-jump take-off and non-arrested landing. So there are two obvious operating choices: a proper V/STOL platform able to hover, or a S-STOL platform able to land in like 30m without arrestor gear. The former option is the most complicated and least novel so we’ve plumbed for the second.

Inherent within a S-STOL landing are:
1) Very slow approach speeds (sub-stall for most jets). If the aircraft can approach the carrier at 50kts and the carrier is steaming into a 10kts headwind at 20kts then the effective landing speed is just 20kts(!). However, we have to be prepared for the worst case scenario which is an effective landing speed of say 20% above the designed speed (=60kts).
2) Very good slow speed and high angle of attack handling
3) The ability to make this landing with a full weapons load and 20% fuel (=10,000lb or weapons plus 2,000lb of fuel –or better).

In order to meet this harsh specification, we are looking at high-lift wing forms, thrust vectoring main engine plus some form of additional downward thrust (for take-off and as a ‘cushion’ on landing) in the form of either lift-jets, lift-fans or augmented thrust main engines.

Hope this clears things up. Thanks for the interest.

Waynos, yes we should consider all main wing plans. The main limit is wingspan which we’ve set within 10m parameters. Diamond (YF-23, X-47) and clipped-diamond (F-22, F-35) wings are generally chosen for their stealthy merits more than anything else(?). Diamond wings operate like delta wings in aerodynamic terms (please correct me if I’m wrong) so they have comparatively high stall speeds = high approach speed = longer non-arrested landing. Canards can improve this aspect of handling.

Here are two quick draw illustrations of diamond and canard-diamond configurations. Both have a 10m wingspan:


Whilst I think that these configurations are limited for S-STOL, we should acknowledge their advantages over our other configurations. The main wing would be lighter than the FSW/bi-plane and contain lots more fuel, plus have the advantage of being able to have underwing hardpoints. This configuration also makes large shoulder tanks very easy to incorporate –so overall you’d expect these configurations to hold around 30% more fuel than our previous ones(!) and have more hardpoints. Of the two the canard design offers better agility and slower landing speeds. But in order to get S-STOL performance we’d be almost entirely reliant on the additional thrust of the lift-jet and main engine TVC.

The stealth benefits of the diamond wing are inconsequential as we’d still have a far from stealthy fuselage, single tail and external weapons stations. In order to carry the same weapons internally (notably 2x anti-ship missiles) the aircraft would have to be much larger –out of the question (unless anyone has a TADIS trick up their sleeve).

If we are going to go down the ‘conventional’ wing road for option 3 (D-0015) then I think it’d be taking us towards non-diamond canard (lower stalling speeds) designs with a wide blended lifting body –almost a Draken style double-delta but with canards. Your thoughts?

Chaps, just some thoughts on the modes for the lift-jet. Rather than have a heavy fully steerable exhaust duct, we could use a cruder but much lighter and simpler external paddle to deflect thrust and act as an additional air-brake (much as the intake door does). This applies equally to both our current designs.

Sound sensible?

On the subject of engines I think we should consider smaller lift jets. My choice of the Eurojet EJ-200 main engine is based on several factors. Firstly it is very advanced, reliable (apparently) and has very good performance. It is also compact, is not subject to US export limitations (Saab Viggen anyone..) and already has a TVC nozzle which underwent lots of testing thus reducing development costs.

Still considering your other points but re the lift jet, on their 60's test beds from Mikoyan Sukhoi and Yak the Russians used steerable vanes at the base of the engine rather than a steerable nozzle, this arrangement is simple, light (even more so than the paddle) and would give enough jet deflection for our needs, will come back with my other thoughts later



[edit on 8-1-2006 by waynos]

Waynos, yes, your vanes idea seems very sensible. Unless anyone has any better ideas I say run with that.

Anyway, I’ve got an illustration of where I think the recent discussion on ‘conventional’ wings was leading:

This configuration would hold around 30% more fuel and have more hardpoints than our previous concepts. I incorporated the LEMDs although this would decrease fuel load(?). The wing tip rails also eat into the 10m wingspan restriction, again reducing wing area. We could ditch them in favor of under wing stores stations allowing a slightly bigger wing (+5%)?

Re stores stations:
D-0013 (FSW): 3 under fuselage
D-0014 (Bi-diamond wing): 3 under fuselage and 2 wing tip
D-0015 (Canard, above): 3 under fuselage, 2 under wing and 2 wingtip (or 4 under wing?)

Any refinements on the Bi-diamond wing idea? Once we have decided the layout we can start looking for someone to model it in 3D reasonably accurately (preferably AutoCAD?) and then a way of getting raytrace airflow predictions.

the solid diamond shape is a good compromise as it gives you the benefits you associate with an aft swept leading edge combined with some of the benefits of an FSW trailing edge. fully agree about fuel; capacity and weapons stations but I feel this sort of wing is less responsive than the split diamond we have been looking at, can the mission be accomplished with the split diamond wing and take the rapid agility bonus or do we need the less agile but greater capacity diamond? I don't know the answer to this, I guess its a matter of opinion. Certainly with the solid diamond the need for canards returns and so I'm not sure about any overall weight advantage in this design.

Of the designs we have considered so far my favoured one is the one at the top if this page shown with 2 ALARMS at the tips, though I think the tips should not meet in the head on view but should be separated by a small vertical section as I posted on the previous page.

Whats your favourite at the moment?

Waynos, I’ll get that design redrawn with the refined wingtip spacing and fancy colors.

My favorite? I can’t decide between the FSW one and the Bi-diamond wing one. I also like the canard one but let’s face it, it ain’t as interesting. Lol.

regarding your earlier mention of the design having three underbody hardpoints. I'm not sure how you envisage this but I have tried to think of an efficient way to mount weapons and this idea, using two wingtip and two underbody, could handle (in this instance) 8 ALARM for the SEAD role.

Worth looking at a bit more do you think?

Re hardpoints. I’m reticent to put them on the pure-FSW because of the wing loading issues. But if they were then wingtips would be the obvious place (least wing loading on a FSW). Rockwell certainly considered it for their “Saber Bat” and General Dynamics also proposed a FSW F-16 with wingtip Sidewinders. But come X-29 and S-37 people were shying away from it on FSW.

I envisaged two ‘main’ harpoints, one each side of the fuselage like on the Tornado GR1 and a secondary plumbed centerline harpoint (optional) for ferry tanks, drop tanks or reccon pods. The main hardpoints could each accommodate 2 ALARM or Maverick, 1 Storm Shadow, LGB or anti-ship missile, or 6 Brimstone (triple tandem).

On the Bi-diamond wing design I envisaged identical fuselage stores plus wingtip rails for 1 Alarm, Maverick, drop tank or Brimstone. To carry 2 ALARM on a wingtip would require 600lb stressing. Is that feasible?

It may be out of reach for the ALARM but it might be worth investigating a double wingtip rail for ASRAAM carriage.