The F-35 Discussion Topic (No Holds Barred II)

[sferrin]

This where the skill of the Lockheed engineers came into being. You're right in that from a certain distance i probably wouldn't be able to tell if i'm looking at a -B, or -A. OTOH, the X-32 definitely looks different from everything else in that chart...or anything else, for that matter.
That being said, internally there's a lot of new stuff that goes in, we can't just look at the OML.
The entrails are different, and the commonality desirement meant that compromises were made. I'm saying that the optimized structure for an A and C designed in isolation of each other is much closer than between either of them and a -B.

It's all a trade off. The F-22 could have had even better performance if it didn't have to be designed for stealth, didn't have internal bays, had 3D TVC, etc. So what? The DoD doesn't care what looks the prettiest at the airshows, it wants the best capability it can afford. If the F-35B had been it's own design there would not be one, and the USMC would be out of the fixed wing business once the Harriers were out of life. As that was unacceptable we have what we have. Just because, if we were willing to compromise in other areas, it might have been 0.2 Mach faster means what exactly? When's the last time a Super Hornet went Mach 1.8 in combat? When's the last time an F-16 went Mach 2 in combat? On the other hand the F-35 is designed for Mach 1.6 armed and with fuel. Now deck out an F-16 with all the pods to at least try to come close to the F-35's built-in capability, add the external weapons, extra fuel, etc. How fast is that F-16 going to be going now? Not Mach 2 I promise you that.

 

[Sundog]

If VSTOL was not pervasive, then you could take ANY aircraft already flying and convert it to VSTOL.
good read on the subject : Kohlman "An introduction to V/STOL airplanes"

Very true. VSTOL <i>had</i> to be the design driver. Those who think otherwise have never designed an airplane.


Also, Kohlman's book is excellent. We referenced a lot of it in my VSTOL aerodynamics course twenty seven years ago.

 

[sferrin]

If VSTOL was not pervasive, then you could take ANY aircraft already flying and convert it to VSTOL.
good read on the subject : Kohlman "An introduction to V/STOL airplanes"

Very true. VSTOL had to be the design driver. Those who think otherwise have never designed an airplane.

REQUIREMENTS are the design driver. If they weren't every VTOL aircraft would look exactly the same.

 

[donnage99]

REQUIREMENTS are the design driver. If they weren't every VTOL aircraft would look exactly the same.

Priorities of requirements is the driver. And due to little thing called physics, if VTOL is part of the requirements, it becomes the design driver of the design.

 

[SpudmanWP]

if VTOL is part of the requirements, it becomes the a design driver of the design.

FIFY & Nobody has claimed otherwise.

 

[sferrin]

if VTOL is part of the requirements, it becomes the a design driver of the design.

FIFY & Nobody has claimed otherwise.

Yep. A driver not the driver. I would say it's not even the top one. For example the over all length is not driven by it and that appears to be his biggest gripe here.

 

[bobbymike]

if VTOL is part of the requirements, it becomes the a design driver of the design.

FIFY & Nobody has claimed otherwise.

Yep. A driver not the driver. I would say it's not even the top one. For example the over all length is not driven by it and that appears to be his biggest gripe here.

Sferrin - In this and prior posts you discuss 'possible' impacts of the STOVL design on the A & C like maybe 0.2 of a Mach for top end speed for example. Do we know over the entire flight regime the total impact meaning can we say "the 'A & C' CANNOT do X because of the "B and that creates a severe shortcoming in the design?"

 

[sferrin]

if VTOL is part of the requirements, it becomes the a design driver of the design.

FIFY & Nobody has claimed otherwise.

Yep. A driver not the driver. I would say it's not even the top one. For example the over all length is not driven by it and that appears to be his biggest gripe here.

Sferrin - In this and prior posts you discuss 'possible' impacts of the STOVL design on the A & C like maybe 0.2 of a Mach for top end speed for example. Do we know over the entire flight regime the total impact meaning can we say "the 'A & C' CANNOT do X because of the "B and that creates a severe shortcoming in the design?"

Somebody does (but it ain't me ). And like I've said elsewhere, AFAIK the ONLY restriction the B imposes on the others is the overall length limit, and that's not from the STOVL requirement but the footprint on amphibious assault ships. That will effect the fineness ratio (speed, drag, acceleration) BUT given the F-35 is designed for Mach 1.6 with a full internal load it will STILL be much faster than a similarly loaded F-16/18/ Harrier.

 

[LowObservable]

You might be surprised who told me that the overall length was indeed determined by STOVL, for reasons of weight and balance. The wing span was a compromise between aero efficiency and weight (crucial for VL). STOVL made single-engine mandatory because no practical fighter STOVL system can survive engine failure in powered lift. The AF took single engine as an indicator for cost, but I don't recall any suggestion at the time that the single 40 Klb engine might be heavier and more expensive than two F414s, so the assumption was flawed.

Of course the big single engine, short overall length and lift fan drove cross-section distribution and the location and size of the weapon bays. There's only so much room.

 

[Sundog]

BUT given the F-35 is designed for Mach 1.6 with a full internal load it will STILL be much faster than a similarly loaded F-16/18/ Harrier.

I'm not so sure about that, as the F-16 could go Mach 1.6 with the two large drop tanks under the wings and the wingtip sidewinders, they just don't do it. Also, The F-35 isn't going to get very far with that internal load at Mach 1.6; I don't think the F-16 would either. Both aircraft are likely to be subsonic with that load, regardless of "capability."

 

[Abraham Gubler]

Of course the big single engine, short overall length and lift fan drove cross-section distribution and the location and size of the weapon bays. There's only so much room.

Which is why the three smartest guys in the room, working together, designed a JSF with two OTS engines (one of them big, one of them small), expandable weapons bay and no vertical tail all to reduce the frontal cross section. Vale the McDonnell-Northrop-BAe F-36 JSF. And it could have had a cool name too like “Wraith”, “Tarantula” or “Hawker”.

 

[bobbymike]

Of course the big single engine, short overall length and lift fan drove cross-section distribution and the location and size of the weapon bays. There's only so much room.

Which is why the three smartest guys in the room, working together, designed a JSF with two OTS engines (one of them big, one of them small), expandable weapons bay and no vertical tail all to reduce the frontal cross section. Vale the McDonnell-Northrop-BAe F-36 JSF. And it could have had a cool name too like “Wraith”, “Tarantula” or “Hawker”.

Was always my favorite looking of the original 3 designs

 

[LowObservable]

Another feature of the McThropBrit design was that it had RR's blocker-vectoring nozzle unit directly behind the engine (upstream of the augmentor) rather than the 3BSN. This put the STOVL thrust line further forward and meant that the engine face could be located farther aft.

 

[sferrin]

You might be surprised who told me that the overall length was indeed determined by STOVL, for reasons of weight and balance.

Who would that be, specifically? Because there's absolutely zero reason one couldn't have proper weight at balance at 56 feet vs 51 feet, if one had planned on that length early on.

 

[sferrin]

Of course the big single engine, short overall length and lift fan drove cross-section distribution and the location and size of the weapon bays. There's only so much room.

Which is why the three smartest guys in the room, working together, designed a JSF with two OTS engines (one of them big, one of them small), expandable weapons bay and no vertical tail all to reduce the frontal cross section. Vale the McDonnell-Northrop-BAe F-36 JSF. And it could have had a cool name too like “Wraith”, “Tarantula” or “Hawker”.

They should have gone with the shaft-driven lift fan instead of the separate lift jets the USMC specifically said they didn't want. They might have won. (It was my favorite of the 3 contenders as well.) Then again, it's a bit more difficult to make the lift fan as narrow as a pair of lift jets in tandem.

 

[Arjen]

You might be surprised who told me that the overall length was indeed determined by STOVL, for reasons of weight and balance.

Who would that be, specifically? Because there's absolutely zero reason one couldn't have proper weight at balance at 56 feet vs 51 feet, if one had planned on that length early on.

Based on my experience with motorbikes, may I offer this guess: rotational inertia. Concentrating vehicle mass helps to minimise forces needed to control it. Smaller forces -> lighter structure.

 

[lastdingo]

The lever is larger if the control nozzles are farther away as well, so I doubt length was restricted by STOVL requirement.
Hangar and maybe even lift designs are better candidates for supplying restrictions.

 

[Arjen]

Length of the lift fan's driveshaft?

 

[SpudmanWP]

The F-35B achieved IOC today.. Congrats to all.


https://www.f35.com/news/detail/u.s.-marine-corps-declares-the-f-35b-operational


https://www.youtube.com/watch?v=KX03lzyOVew

 

[bobbymike]

Probably has been mentioned here at SPF or elsewhere but on how many ships will the F-35B be deployed and in what numbers on each ship like the new America class LHA's?

 

[sferrin]

Probably has been mentioned here at SPF or elsewhere but on how many ships will the F-35B be deployed and in what numbers on each ship like the new America class LHA's?

I can't imagine the Wasp class won't be updated for them. That's 8 ships right there.

http://www.freewebs.com/jeffhead/worldwideaircraftcarriers/wasp.htm

And the second America (the Tripoli) is under construction. The last Tarawa is nearing retirement though.

Then there are the UK's two carriers, Italy with the Cavour, and (very likely IMO) Japan. There are other current Harrier operators that could be potential candidates as well.

 

[SpudmanWP]

Gen Davis IOC interview


http://youtu.be/kSa424EhC24

 

[donnage99]

Which is why the three smartest guys in the room, working together, designed a JSF with two OTS engines (one of them big, one of them small), expandable weapons bay and no vertical tail all to reduce the frontal cross section. Vale the McDonnell-Northrop-BAe F-36 JSF. And it could have had a cool name too like “Wraith”, “Tarantula” or “Hawker”.

Yeah, their engine approach allows for a very lean and mean aircraft. Coupled with near taillessness, thrust vectoring, novel fly-by-wire control, it would have had eye watering aerodynamic performance. However, I think it also came down to the client's confidence in each of the contractor's proposal. As with the ATF program, Lockheed probably did a great job with how extensive their proposal is as an overall package. This gave their client the confidence that they would deliver.

 

[LowObservable]

Arjen is probably right - that was a big factor, I should imagine.


As for the separate engine vs. shaft-driven lift fan: as far as I know, there was never a formal study of the relative merits and costs of the two. DARPA did not look at it because it was not in their remit (it was not new or radical enough). It would have been a wash at best on weight. SDLF might have worked out a little better for pitch trim and control.

 

[bring_it_on]

 

[SpudmanWP]

http://i.imgur.com/5uPmLt2.gifv

 

[sferrin]

Which is why the three smartest guys in the room, working together, designed a JSF with two OTS engines (one of them big, one of them small), expandable weapons bay and no vertical tail all to reduce the frontal cross section. Vale the McDonnell-Northrop-BAe F-36 JSF. And it could have had a cool name too like “Wraith”, “Tarantula” or “Hawker”.

Yeah, their engine approach allows for a very lean and mean aircraft. Coupled with near taillessness, thrust vectoring, novel fly-by-wire control, it would have had eye watering aerodynamic performance. However, I think it also came down to the client's confidence in each of the contractor's proposal. As with the ATF program, Lockheed probably did a great job with how extensive their proposal is as an overall package. This gave their client the confidence that they would deliver.

It's always amusing how often the design that wasn't picked gets blessed with "eye watering performance" trouble-free development, under budget and on time delivery, etc., etc. : And if you think the F-35 makes the flight deck warm. . .

 

[sferrin]

http://i.imgur.com/5uPmLt2.gifv

Judging by that beer gut it's definitely got an eatin' problem. ;D

 

[LowObservable]

The dual nozzles would have been further from the deck, with less mass flow and more total perimeter - hence better mixing before the deck. The front fan would have been warmer, who knows by how much - "this is not Grandma's attic fan", as a designer of my acquaintance puts it. Water under the bridge, and we got the shaft, so to speak.

 

[sferrin]

The dual nozzles would have been further from the deck, with less mass flow and more total perimeter - hence better mixing before the deck. The front fan would have been warmer, who knows by how much - "this is not Grandma's attic fan", as a designer of my acquaintance puts it. Water under the bridge, and we got the shaft, so to speak.

Given that it was a lift JET probably a hell of a lot.

http://www.secretprojects.co.uk/forum/index.php/topic,2392.msg20180.html#msg20180

 

[AeroFranz]

You might be surprised who told me that the overall length was indeed determined by STOVL, for reasons of weight and balance.

Who would that be, specifically? Because there's absolutely zero reason one couldn't have proper weight at balance at 56 feet vs 51 feet, if one had planned on that length early on.

Based on my experience with motorbikes, may I offer this guess: rotational inertia. Concentrating vehicle mass helps to minimise forces needed to control it. Smaller forces -> lighter structure.

This is an oft overlooked issue with VTOL. When hovering with zero dynamic pressure over the control surfaces, introducing such forces can only be overcome by other devices such as RCS, which just add to the weight. The Pegasus notoriously has counter-rotating spools for this precise reason. I believe the RR lift fan does as well.

 

[SpudmanWP]

Both the lift fan and F135 motor are counter-rotating designs.

 

[donnage99]

It's always amusing how often the design that wasn't picked gets blessed with "eye watering performance" trouble-free development, under budget and on time delivery, etc., etc. : And if you think the F-35 makes the flight deck warm. . .

Uhmm... why do you sound as though I combined the "eye watering performance" of a design with whether the development deliver as promised in my previous comment? My WHOLE point is that the 2 are DIFFERENT.


Not sure if you were agreeing with what I was saying or just baiting for a debate.

 

[sferrin]

It's always amusing how often the design that wasn't picked gets blessed with "eye watering performance" trouble-free development, under budget and on time delivery, etc., etc. : And if you think the F-35 makes the flight deck warm. . .

Uhmm... why do you sound as though I combined the "eye watering performance" of a design with whether the development deliver as promised in my previous comment? My WHOLE point is that the 2 are DIFFERENT.


Not sure if you were agreeing with what I was saying or just baiting for a debate.

No hidden meaning. Anytime a program has problems people start rhapsodizing about how if only the OTHER option had been selected there would be no problems, and everything would be right with the world. Grass is always greener mentality. As for the second part, the NG/MD design had a bonafied lift jet vs a "cold" lift fan and would have been a hell of a lot harder on landing surfaces. Not only is the exhaust of the F-35s lift fan much cooler, it also helps reduce the deck heat to the rear, as that cooler air mixes with the efflux of the main engine. Just look at the restrictions the Yak-41 had. Ceramic tiles on the deck for example. Mods for the F-35 are relatively tame by comparison. And the less said about Boeing's design the better. Hey, don't get me wrong, I'd have preferred the NG/MD design as well but when one ignores requirements they tend to lose.

 

[LowObservable]

It's not in the least "rhapsodizing" to play a little "what if?" The Macs design might have turned out better, it might not. However, note that the Yak-141 had pure lift jets, not a high-BPR fan, that it's the aft nozzle that causes the surface problems and that twin nozzles delivering mixed airflow will be better than a single nozzle blasting core air.

 

[sferrin]

It's not in the least "rhapsodizing" to play a little "what if?"

Wasn't just talking about here specifically.

The Macs design might have turned out better, it might not. However, note that the Yak-141 had pure lift jets, not a high-BPR fan,

Fair enough. [/quote]

 

[bobbymike]

It's not in the least "rhapsodizing" to play a little "what if?"

Wasn't just talking about here specifically.

The Macs design might have turned out better, it might not. However, note that the Yak-141 had pure lift jets, not a high-BPR fan,

Fair enough.

[/quote]
As an aviation enthusiast I can't help but imagine F-23s and the McDD/BAE/Northrop JSF flying together. ;D

 

[Triton]

Did any of the programs prior to Joint Strike Fighter (JSF), ASTOVL, SSF, JAF, CALF, JAST, consider a subsonic replacement for the McDonnell Douglas AV-8B Harrier II/British Aerospace Harrier II? It seems that supersonic was a requirement beginning with the Advanced Short Take-Off/Vertical Landing (ASTOVL) program begun in 1983. Was there any reason to believe that the STOVL variant of the Joint Strike Fighter wouldn't be supersonic?

 

[Colonial-Marine]

They should have gone with the shaft-driven lift fan instead of the separate lift jets the USMC specifically said they didn't want. They might have won. (It was my favorite of the 3 contenders as well.) Then again, it's a bit more difficult to make the lift fan as narrow as a pair of lift jets in tandem.

If I recall a lot of the Lockheed Martin JSF artwork looked "sleeker" than the actual F-35 does. I don't think it would be all that crazy to assume the McDonnell/Northrop/BAE design would have also "bulked up" a bit too.

Did their proposal have TVC?

 

[kcran567]

A direct lift system with a 3d thrust vectoring rear nozzle seems like it would have had very good stovl performance, maybe not as good as the f-35, but lower risk, less complicated, lighter, etc. and the versions without the stovl requirement could have better met the f-16 replacement need.


http://foxtrotalpha.jalopnik.com/the-f-35-cant-run-on-warm-gas-from-a-fuel-truck-that-sa-1668120726

"The F-35 channels its strong thermal loads, accumulated by the powerful avionics and sub-systems on-board, as well as the engine, into its fuel. So really, the fuel works as a giant heat sink. If the fuel is already warm upon start-up, there is less capacity to exchange the heat from their aircraft's simmering systems. Therefore the jet must shut down or risk overheating. A clever design that most likely lightens up the jet and leaves extra room for weapons and fuel, but one that may have very little room for adaptation." Quote

Sorry about the source for this story. Are the concerns valid? If the fuel is the heat sink for the systems and a hot fuel truck will cause overheat and systems shutdown, is this going to be a real problem operating in say, Saudi Arabia or somewhere in a challenging hot environment?