Why no tailless delta 'stealth' fighter?

lastdingo

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Has anyone a clue why there's no tailless delta low observable aircraft design?

Think a Mirage 2000 with GE F110 engine, AESA radar, and a bit more blend between wing and fuselage (forward fuselage in typical stealth fighter shape).
The vertical tail would be no issue if the wings are not parallel (hence no 90° angles) and it might even be possible to eliminate it with 3D TVC and as backup split elevons.

The absence of a (second) vertical stabilizer and of horizontal stabilizers should reduce RCS by much.

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I understand deltas bleed a lot of energy in turning, but that could be mitigated with much thrust and doesn't matter all that much when dodging missiles (which is about the most relevant use for agility in the age of 360° lock on after launch WVR missiles). Dodging missiles rather about instantaneous turn rate than sustained turn rate.
A Mirage 2000 was pretty close in agility to a F-16 which had much more thrust, so I suppose deltas don't need to be real bad in ACM (and ACM probably don't matter much any more).
 
The straight trailing edge would be bad for stealth. You'd need to sawtooth it somehow. Mirage 2000 intakes would need major redesign.

You'd probably end up with something a bit like the General Dynamics ATF - they were unable to make a workable stealthy vertical tail design and did not finish too highly in the competition.
 

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There are a few serious designs:
Avenger II was the closest design that I can think of that was a tailless delta. X-47A Unmanned Combat Aircraft design, the original Hopeless Diamond, etc. Straight edges produce radar returns so many designs incorporate leading edge alignment to reduce the different directions in which the returns would be directed towards. Straight edge surfaces are often designed with serrated internal RCS absorbent structures, or exterior serrated designs such as the ones above in the previous post, to attenuate the radar signal.
 

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I presume the OP means supersonic tailless delta fighters. There's renewed interest in it but it's unclear
if the reduced AoA performance can be compensated for by more energetic munitions which will
tend to chew into the internal payload.
 

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Boeing X-32 doesn't count?

boeing-x32-jsf.jpg
 
Even the X-32 had a 'tail' to increase directional control for maneuverability. A true 'fighter' aircraft should have copious amounts of excess thrust, the ability to sustain high-g turn performance, and have slightly negative or relaxed static stability (often compensated for by flight control computers and stability augmentation systems).

In the past aircraft without adequate tail volume and authority would lose directional control while maneuvering. A vertical stabilizer and rudder provides an aircraft with the ability to execute a coordinated turn (i.e. no slipping or skidding). An uncoordinated aircraft will spin if it is stalled (however, its interesting to look at the X-31 tailless program and its Post-stall maneuvering programs). A tailless aircraft typically suffers from lateral instability, loss of directional control at high AoA's, and deep stall characteristics when they depart making recovery difficult.

Therefore, maneuverable fighters typically have large vertical stabilizers to maintain directional control and stability. Tailless configurations maybe more adequately suited to a high speed strike or interdiction aircraft design, or a 'straight-line' interceptor like a MiG-25 Foxbat or a YF-12. However, if you engage in Air Combat Maneuvering, then some form of positive directional control is needed.

NASA and Boeing experimented with the X-36 tailless fighter configuration and found that with thrust vectoring, 'creative' control systems, and tailored aerodynamic design the aircraft could reach good turn performance. However, against a HiMAT type design in an ACM engagement my money would be on the little guy with control surfaces everywhere.
 

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There may be tailless delta stealth aircraft flying. The thing is, when it comes to maneuverability, a tailed delta (Like the F-22) will always be more maneuverable than a tailless design, since the tailless design has to use the trailing edge surfaces for control. The tailed delta can use the TE surfaces to optimize lift (Camber) while using the tails to control pitch. If it's just a strike or interceptor design, it could be tailless. Also, don't forget Northrop's Have Blue submission basically met the criteria you''re seeking and it was rated better than the Lockheed submission.

Northrop Have Blue. I did search for a link here (at SP), but it didn't show up under "Northrop Have Blue," in the search.
 
The thing is, when it comes to maneuverability, a tailed delta (Like the F-22) will always be more maneuverable than a tailless design, since the tailless design has to use the trailing edge surfaces for control. The tailed delta can use the TE surfaces to optimize lift (Camber) while using the tails to control pitch.
Is this really true? Especially for post 80s unstable aircraft?

Manoeuvrability covers a wide range of performance characteristics e.g. Specific Excess Power, sustained turn rate, instantaneous turn rate, SEP at ITR, and into agility like pitch rate, roll rate, rate accelerations, AoA limits.

For some of these then i think its relatively easy to argue that a tailed design should be better e.g. roll rate at high AoA due to reduced control saturation from simply having more controls - but really TVC is the answer here if more performance is desired

But for other criteria e.g. SEP, sustained turn rate etc. The reduced mass and drag of the tailless configuration should be better.
 
Directional stability can be controlled by tip drag rudders.
During high angle of attack flight, these drag rudders (see Grumman A-6 Intruder) probably need an automated stability augmentation system to reduce pilot work load.
Landing flaps can be installed on pure deltas ... see the split flaps installed under the center of gravity on Armstrong, NRC and SWIFT flying wing. For true STOL performance, you probably need to augment those conventional flaps with leading edge flaps that so complicate stability and control that they also need SAS.
 
The thing is, when it comes to maneuverability, a tailed delta (Like the F-22) will always be more maneuverable than a tailless design, since the tailless design has to use the trailing edge surfaces for control. The tailed delta can use the TE surfaces to optimize lift (Camber) while using the tails to control pitch.
Is this really true? Especially for post 80s unstable aircraft?

Manoeuvrability covers a wide range of performance characteristics e.g. Specific Excess Power, sustained turn rate, instantaneous turn rate, SEP at ITR, and into agility like pitch rate, roll rate, rate accelerations, AoA limits.

For some of these then i think its relatively easy to argue that a tailed design should be better e.g. roll rate at high AoA due to reduced control saturation from simply having more controls - but really TVC is the answer here if more performance is desired

But for other criteria e.g. SEP, sustained turn rate etc. The reduced mass and drag of the tailless configuration should be better.

Yes, this is true with today's technology. The Mirage 2000 is a FBW delta, and it still can't maneuver with a tailed fighter. It has to do with the available lift and control power required to trim the aircraft at higher AOA. That's why it's replacement, the Rafale, had a canard. Using the wing to adjust camber and control pitch is a compromise. You can do one or the other, but not both at the same time. It's why the F-16XL didn't have a sustained turn rate as high as a standard F-16's.
 
Trimmed lift coefficient will likely be lower without a separate control surface, but it's total lift i.e. lift coefficient*area that matters for these manoeuvres. The tailless aircraft usually have much bigger wings which offsets the differences in trimmed lift coefficient.

Did F-16XL have worse sustained turn rate? At least from what I've seen it was similar to better manoeuvrability and agility across the board. Main performance difference was clean cruise L/D being much lower from much larger and lower aspect ratio wing - but the much larger fuel capacity and conformal carriage outweighed this in the output reach/persistence metrics
 
What about morphing wings/airframes? Still not mature enough?
It is really a question of how sophisticated you want to make morphing wings.
Indian Tejas already has leading edge flaps on the shallower-swept portion of its inboard leading edges. These LE flaps help increase both lift and drag and can be used to balance extra - landing - lift created by trailing edge controls.
It comes down to a question of how many millions of dollars you want to invest in the software that drives stability augmentation systems (aka. fly-by-wire).
 
Trimmed lift coefficient will likely be lower without a separate control surface, but it's total lift i.e. lift coefficient*area that matters for these manoeuvres. The tailless aircraft usually have much bigger wings which offsets the differences in trimmed lift coefficient.

Did F-16XL have worse sustained turn rate? At least from what I've seen it was similar to better manoeuvrability and agility across the board. Main performance difference was clean cruise L/D being much lower from much larger and lower aspect ratio wing - but the much larger fuel capacity and conformal carriage outweighed this in the output reach/persistence metrics
Yes it’s sustained turning was worse

From Red Eagles America’s secret Migs

[Red Eagle Matheny flying the MiG] “We briefed each other about our airplanes and they [Edwards F-16XL pilots] turned to me and said they would be all over me – they had a roll rate of 800 degrees per second, which was the fastest in the inventory. – I got to thinking about that and it turned out the roll rate meant nothing. The problem with that airplane[F-16XL] was that it was a big bleeder: it just bled speed like nothing else when forced to turn hard – I ate them alive in the MiG-21. The F-15E on the other hand was a pretty good performer – they resisted the urge to get slow and jump in a phone booth with a MiG. They flew around the ranges at low level trying to burn off all this gas and he still needed to burn off more when we joined up on each other”.

From John Will on F-16.net (former General Dynamics structural engineer who worked on it)

Of course. Results were mixed. XL generally had a better initial pitch rate, so could make the first turn into the target better. But, like deltas in general, it had lower sustained g capability. XL had 9g turn capability, same as F-16, but had higher rolling g capability, 7.2 vs 6 for F-16. It also had a flight control refinement which allowed the pilot to command a max roll at any g level, all the way to 9g. Roll rate was automatically reduced above 7.2g. On the F-16, max roll commands are allowed up to 6g only. The XL had a higher maximum speed than the F-16, but slower acceleration.

“The XL wing, like any delta wing, has a flatter lift coefficient curve than a wing with lower sweep angle. So for a given wing area, it takes more angle of attack to produce a given amount of lift. More AoA in itself is not a bad thing, but along with more AoA comes more drag increase. Deltas also tend to have higher takeoff landing speeds (no flaps). Canards can be added to help reduce some of the disadvantages. Deltas are best suited for high speed cruise (Concorde, SR-71, B-70, B-58) and interceptors (F-102, F-106).

The top speed of XL was higher than the F-16, but by how much, we'll never know. At high altitude, high mach the climb rate and acceleration was excellent, but airplane was limited to 2.05 mach since analysis and testing had not been done to support higher speeds.”
 
I haven't read it yet-but phys.org has a new article called "Professor demonstrates novel control method in aircraft with no tail." An earlier snake bot story also featured a wing section made from 'voxels' that warp.
 
The X-36 was tailless and explored fighter maneuverability without any vertical tails but used thrust vectoring to increase pitch and yaw performance and did perform very well from what I understand. The US tailless, blended delta-type concepts (from LMCO, NGC and Boeing) for a 6th generation fighter show configurations with no apparent thrust vectoring so these may be relegated to LO-type of interceptors for first-look, first-kill. However with that said, advanced FBW and flight control system laws may negate the requirement for any thrust vectoring. As an example in regards to no thrust vectoring, I wish the YF-23 had demonstrated it's excessive high AoA performance. Northrop did a lot of work in the design to ensure low-speed maneuverability performance at least equal to the F-22. There was no doubt that the YF-23 had much superior high-speed maneuverability and turning performance than the F-22, especially with the GE YF-120 engines.
 
Here is the article I mentioned above:
 
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