Design Challenge: Loyal Wingman / Advanced Trainer / Light Combat Aircraft

[H_K]

Starting a discussion on Loyal Wingmen and whether the same platform could be derived into piloted aircraft for advanced training or light combat missions.

- We know that the USAF wants larger, higher performance Loyal Wingmen (vs. the MQ-28 Ghost Bat or XQ-58 Valkyrie). Presumably this means transonic performance (minimum Mach 0.8-0.9), and ideally supersonic performance (Mach 1.2-1.4?) for air-to-air, penetration & interdiction missions, with good survivability and sufficient internal weapons (2x AAMs or 4x 125kg class SDBs or equivalent?). Other air forces are likely to follow the same path in order to complement their expensive 6th generation fighters.

- The USAF are willing to pay 1/3rd the cost of an F-35, i.e. $20M+... much more than the <$10M being advertised for Valkyrie and other simpler/slower/smaller platforms... so this is no longer meant to be an attritable aircraft, though high loss rates will be acceptable.

- All-in-all, this means that these Loyal Wingmen will start to overlap with manned jet aircraft, especially advanced trainers / light combat aircraft like the T-50/FA-50, in terms of performance / cost / non-attritability etc. Can one platform cover both roles?

 

[kqcke for you]

Starting a discussion on Loyal Wingmen and whether the same platform could be derived into piloted aircraft for advanced training or light combat missions.

- We know that the USAF wants larger, higher performance Loyal Wingmen (vs. the MQ-28 Ghost Bat or XQ-58 Valkyrie). Presumably this means transonic performance (minimum Mach 0.8-0.9), and ideally supersonic performance (Mach 1.2-1.4?) for air-to-air, penetration & interdiction missions, with good survivability and sufficient internal weapons (2x AAMs or 4x 125kg class SDBs or equivalent?). Other air forces are likely to follow the same path in order to complement their expensive 6th generation fighters.

- The USAF are willing to pay 1/3rd the cost of an F-35, i.e. $20M+... much more than the <$10M being advertised for Valkyrie and other simpler/slower/smaller platforms... so this is no longer meant to be an attritable aircraft, though high loss rates will be accetable.

- All-in-all, this means that these Loyal Wingmen will start to overlap with manned jet aircraft, especially advanced trainers / light combat aircraft like the T-50/FA-50, in terms of performance / cost / non-attritability etc. Can one platform cover both roles?

Should be tought having an optional unmanned jet makes probaly a lot of dead weight for the UCAV. But as the newest scaled composite Model 437 shows its likely possible/ will become possible.

 

[H_K]

To illustrate my thought process, I went back to some of the earliest small transonic fighter designs from the 1950s. These include Dassault's Mirage I/II and Etendard VI (one could pick other equivalent designs from other manufacturers, but these 2 are well documented).

What I like about these designs as a conceptual starting point is their small size, low weight (<4 tons empty), low drag, and thus their ability to fly transonically despite weak engines (5,000 - 8,000 lbf thrust). We know that today the most obvious weaknesses of these smaller 1950s fighter designs could be compensated with advanced flight controls, more powerful and fuel efficient engines, and RCS reduction measures.

So I'm postulating that one could start with the same dimensions as a 1950s Mirage II or Etendard VI and start with 2 key changes to obtain a fairly high performance 4t empty aircraft:
1) A modern engine, likely in the 9,000 - 12,000lb thrust range (either F125, Adour or AI-322F with afterburning, or dry F404/M88/EJ200 without afterburning)
2) An advanced wing, e.g. delta+Levcons, delta+canard, or YF-23-like with pelican tail

Then one would start layering in RCS reduction measures (shaping + internal weapons bay). I believe the minimum internal weapons bay would have to measure roughly 3.8m x 0.7m x 0.4m (L/W/H) or about 1,000 liters in order to fit 2x AAMs or 4x 125kg class bombs (e.g. SDB I/II, Spear 3, Spice 250ER, Smart Glider etc) or alternatively 2x 250kg class bombs - this is in fact what Airbus has shown in some of their concepts. This weapons bay would likely be impossible to accommodate on the piloted aircraft (due to the aircraft's small size), but could fit on the Loyal Wingman ahead of the engine/landing gear if the equivalent volume in fuel was moved from belly tanks to the cockpit area.

To illustrate, here is a small platform with triple delta wing + Levcons showing similar dimensions to the 1950s Mirage II and Etendard VI. Also including a size comparison to the larger Mirage 2000 and M-346 advanced trainer to show the diminutive size.

Next up... discussion of internal arrangements... how to fit engine, fuel, landing gear and weapons bay into such a tight package!

 

[red admiral]

- All-in-all, this means that these Loyal Wingmen will start to overlap with manned jet aircraft, especially advanced trainers / light combat aircraft like the T-50/FA-50, in terms of performance / cost / non-attritability etc. Can one platform cover both roles?

Yes from a technical / operstional perspective. Plenty of other historical examples too e.g. AMX, Saab B3LA etc. Internal carriage drives quite a large fuselage with volume that could be used for a cockpit.

I think the main challenge for the CCA side though is keeping the cost down by avoidance of any unnecessary creep; e.g. crewed aircraft can bring extra airworthiness requirements such as moving to multiplex electrical/hydraulic control systems. So I'm not convinced that its a "good" idea. CCAs should be low cost to get the numbers.

I believe the minimum internal weapons bay would have to measure roughly 3.8m x 0.7m x 0.4m (L/W/H)

Those dimensions start to increase quite a bit once you add the likes of launchers, hinges, latches, actuators, spoilers for flow control etc. Which flows through into quite a big impact on the fuselage size, drag, mass etc.

 

[H_K]

And here's the start of an internal arrangement sketch. I'm working off an F404 engine without afterburning and the X-29's fuselage/inlet layout in order to ensure proper area ruling. Sadly I don't have the ability to model this in 3D or to draw cross-sections in order to measure volumes to determine how much would be available for fuel*, accessories, weapons bay etc... mostly just going off existing design arrangements and extrapolating from there.

@red admiral do you have an estimate of weapon bay dimensions to accommodate 2 AAMs or 4x SDBs? I'm basing my dimensions on the Silent Hornet External Weapons Pod.

*Fuel calcs: minimum requirement for 400-550nm combat radius hi-hi-hi would be 1,800kg fuel, with as much as possible in the wing - estimate based on ~4t empty weight and 6-6.5t take off weight, with fuel flow scaled down from an F/A-18C with F404 engine.

 

[The K2]

The way UCAVs are getting bigger and more sophisticated, I wondered about the same thing: can one platform carry two roles. Saw this concept from Airbus and thought about it: https://www.twz.com/air/the-airbus-wingman-stealth-drone-what-we-learned-in-berlin

 

[red admiral]

@red admiral do you have an estimate of weapon bay dimensions to accommodate 2 AAMs or 4x SDBs? I'm basing my dimensions on the Silent Hornet External Weapons Pod.

I think you need extra height as a minimum to accommodate door (non zero thickness) + gap + weapon + launcher + room for hand access, which easily gives ~0.6-0.7m height I think. Maybe you can save a bit by havjng the SDBs on individual launchers rather than the quad pack. Length probably a bit longer unless you have a trapeze arrangement to move the AAMs out of the bay first whilst restraining movement.

I'd note that anything bigger than AMRAAM e.g. Meteor, will need more space

 

[VTOLicious]

I think you need extra height as a minimum to accommodate door (non zero thickness) + gap + weapon + launcher + room for hand access, which easily gives ~0.6-0.7m height I think. Maybe you can save a bit by havjng the SDBs on individual launchers rather than the quad pack. Length probably a bit longer unless you have a trapeze arrangement to move the AAMs out of the bay first whilst restraining movement.

I'd note that anything bigger than AMRAAM e.g. Meteor, will need more space

Have a look here...
https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-506704
...That's the minimum space required for 4x AMRAAM. The design is based on the layout of Boeing's Enclosed Weapons Pod.

 

[red admiral]

...That's the minimum space required for 4x AMRAAM. The design is based on the layout of Boeing's Enclosed Weapons Pod.

So fir 2 AMRAAMs then you could reduce the height a bit (250-300mm?), but then you can't fit in 4 x SDBs without going to individual launchers instead of the existing quad pack.

From a fuselage integration side, then almost this whole bay has to protrude out of the bottom of the fuselage in order for the doors to open. And the sides are vertical. A more sympathetic integration (e.g. canted fuselage sides) will increase the width and volume required.

 

[Basil]

... already mentioned in another thread, but if you can do without an internal missile carriage, this Swiss concept is a good starting point:

https://www.alr-aerospace.ch/publications/Bridel,%20G%20Janus%20Concept,%20SMi%20Conference,%20London%20September%202016.pdf

 

[Scott Kenny]

... already mentioned in another thread, but if you can do without an internal missile carriage, this Swiss concept is a good starting point:

https://www.alr-aerospace.ch/publications/Bridel,%20G%20Janus%20Concept,%20SMi%20Conference,%20London%20September%202016.pdf

How are you proposing to have a stealthy airframe without internal weapons?

 

[Basil]

How are you proposing to have a stealthy airframe without internal weapons?

It would not be stealthy like an F-35 but its small size has advantages in visibility.

 

[Scott Kenny]

It would not be stealthy like an F-35 but its small size has advantages in visibility.

I don't care if I can barely see it visually if I can see it from 200km away on radar.

 

[Shoes31]

How are you proposing to have a stealthy airframe without internal weapons?

One option would be each airframe being purpose built for the mission so you'd have bomber, fighter, or EW airframes. Those airframes would have conformal carriage for their payload, whatever it is. Downside is that then you have different airframes which doesn't work well for the proposed question.

Could you do conformal missile / bomb carriage where you would change out a bottom plate for the mission? Instead of purpose building each aircraft for a different mission like air interdiction or bombing, you'd build one base model aircraft and the conformal "mission" section would be changeable depending on need.

 

[H_K]

One option would be each airframe being purpose built for the mission so you'd have bomber, fighter, or EW airframes. Those airframes would have conformal carriage for their payload, whatever it is. Downside is that then you have different airframes which doesn't work well for the proposed question.

Could you do conformal missile / bomb carriage where you would change out a bottom plate for the mission?

I'm actually thinking more "single platform" with several sub-variants with a high degree of commonality, and 2 switchable fuselage sections that could be changed out during deep maintenance intervals:

- Cockpit / avionics module (1 seater or 2 seater) or extra fuel & sensors (loyal wingman)
- Ventral module with Internal weapons bay (loyal wingman or 1 seater) or avionics + fuel (2 seater)

While this wouldn't allow complete mission modularity and repurposing on the fly, it would allow a common fleet of 2-3 types: a) Loyal wingman, b) Single seater, and c) 2-seater advanced trainer (without weapons bay). With the ability to "rebuild" an aircraft from one type to another if needs change, or to smooth out airframe fatigue and flight hours.

Here is a sketch of the single-seater (work in progress), optimized for transonic performance in a small 4t empty package. The loyal wingman would see the cockpit module switched out for additional fuel/sensors but would have 90%+ commonality. And also showing several internal weapons mixes.

 

[kqcke for you]

I'm actually thinking more "single platform" with several sub-variants with a high degree of commonality, and 2 switchable fuselage sections that could be changed out during deep maintenance intervals:

- Cockpit / avionics module (1 seater or 2 seater) or extra fuel & sensors (loyal wingman)
- Ventral module with Internal weapons bay (loyal wingman or 1 seater) or avionics + fuel (2 seater)

While this wouldn't allow complete mission modularity and repurposing on the fly, it would allow a common fleet of 2-3 types: a) Loyal wingman, b) Single seater, and c) 2-seater advanced trainer (without weapons bay). With the ability to "rebuild" an aircraft from one type to another if needs change, or to smooth out airframe fatigue and flight hours.

Something akin too Gambit?

Here is a sketch of the single-seater (work in progress), optimized for transonic performance in a small 4t empty package. The loyal wingman would see the cockpit module switched out for additional fuel/sensors but would have 90%+ commonality. And also showing several internal weapons mixes.

The new Phantom Strike Radar from Raytheon would probaly bei the perfect radar for it. Also do we know how short an afterburnerless M88 would be?
On another side could one integrate some of the proposed inprovements for the M88? That could reduce the SPFC as more and increase the dry thrust.

 

[RJMAZ]

H_K this is a cool and unique design.

Building a design that is optimised for supercruise and then removing the afterburner is a great concept. The top speed is still tactically useful around mach 1.3 which is far better than the subsonic loyal wingman drones.

Subsonic cruise fuel consumption of this design would be inferior compared to a conventional wing with much greater wingspan. The low bypass ratio engine also guzzles fuel compared to the higher bypass ratio private jet engines. However the cranked arrow delta wing has enough fuel volume to compensate for some of the higher consumption rate.

If NGAD and F/A-XX will be supercruising for most of the mission then this loyal wingman variant is probably the best way to keep up. It all depends how much of the mission profile is spent supercruising. For instance if 95% of the loyal wingman mission is spent subsonic and only 5% spent supersonic then fitting a fuel guzzling afterburner to the MQ-28 type design might make more sense.

I also like the 2 seat, 1 seat and unmanned variants with high commonality. The production rate is increased which reduces the unit price. This would help hit the low price point to be considered an alternative to the F-35.

It would be interested to compare the performance of this design using the Snecma M88 without afterburner versus the TEI TF10000 with afterburner. Diameter of both engines are very similar. Removing the afterburner from the M88 would shorten the length down to around 3 metres and the weight down to 1,500lb. They are both very close in dimensions.

The TF10000 has 6,000lb thrust dry and 10,000lb wet versus the M88 with 11,000lb thrust dry. When cruising at mach 0.8 the M88 would have to throttle right back. The TF10000 would be in the efficiency sweet spot and has a much higher bypass ratio. The TF10000 would give a 20-25% range improvement when subsonic. For supersonic top speed the 10,000lb afterburning thrust will probably have higher exhaust velocity than the M88 at 11,000lb dry. So the TF10000 could probably hit a slightly higher top speed. The TF10000 would be guzzling fuel like crazy while supersonic using afterburner. If the mission profile required more than 10% of the mission supersonic then the M88 would easily be the better choice.

Historically though 99+% of the fighters have spent their entire mission subsonic. This favours a design with a straight wing with afterburner for the very occasional dash.

 

[H_K]

It would be interested to compare the performance of this design using the Snecma M88 without afterburner versus the TEI TF10000 with afterburner. Diameter of both engines are very similar. Removing the afterburner from the M88 would shorten the length down to around 3 metres and the weight down to 1,500lb. They are both very close in dimensions.

The TF10000 has 6,000lb thrust dry and 10,000lb wet versus the M88 with 11,000lb thrust dry. When cruising at mach 0.8 the M88 would have to throttle right back. The TF10000 would be in the efficiency sweet spot and has a much higher bypass ratio. The TF10000 would give a 20-25% range improvement when subsonic. For supersonic top speed the 10,000lb afterburning thrust will probably have higher exhaust velocity than the M88 at 11,000lb dry. So the TF10000 could probably hit a slightly higher top speed. The TF10000 would be guzzling fuel like crazy while supersonic using afterburner. If the mission profile required more than 10% of the mission supersonic then the M88 would easily be the better choice.

I've given this a lot of thought and my design was heavily influenced by an anecdotal story of the Jaguar prototype flying side by side with an Etendard IVM chase aircraft. On paper the turbofan Jaguar should have been extremely fuel efficient (though underpowered in dry thrust) while the turbojet Etendard IVM was gas guzzling and overpowered.

But on at least one high altitude delivery flight it turned out that the Etendard landed with more fuel reserves!

Why? Because the Jaguar burned so much fuel in reheat on take-off and climb that this almost completely negated the lower fuel consumption in cruise. Also the faster and higher they flew, the less air was available for the turbofan to do its thing relative to the "crappy" Atar turbojet.

So I'd rather have a somewhat overpowered low bypass engine that gets you to altitude very fast and allows you lots of transonic freedom of maneuver, than an underpowered turbofan that cruises a little more efficiently but runs out of oompf above 25-30k ft and constantly needs reheat boost.

Incidentally, the Tornado/RB199 is another classic turbofan combination that looked so good on paper but didn't work at altitude (Tornado ADV...)