F-16 Co-designer's take on the F-35

[busdriver]

Could happen on any Ps curve, you are forgetting about the vertical though.

I didn't forget about the vertical, I just didn't address it as I was picking and choosing, just like the single data point that is the publicly released spec. i have no doubt that the F-35 is draggy pig however, it sure looks the part.

due to the F-35's wing size vs weight it's going to have higher than ideal wingloading which means it will bleed energy significantly under g.

But that's actually what I'm talking about, if you look at empty weights (yes I'm going to use wikipedia here, I don't have anyone's dash one available), combat radius examples from that same crappy website and a baseline 2k lbs ordnance load (ballpark 6xAMRAAM) I end up with a wing loading for the F-35 that is comparable to the Super Hornet and the thrust to weight ratio that is comparable to the legacy Hornet. While not eye watering, it ends up being right in the middle of the fourth gen aircraft kinematically. In other words, the F-35 is not an improvement in fighter kinematics, just more of the same. Is that OK given the improvement in other areas?

EDIT: Sorry I said i wasn't going this far outside of my lane, but napkin calculus and afternoon lager got the better of me.

Edited July 1, 2014 by busdriver

[xcraftllc]

I didn't forget about the vertical, I just didn't address it as I was picking and choosing, just like the single data point that is the publicly released spec. i have no doubt that the F-35 is draggy pig however, it sure looks the part.

But that's actually what I'm talking about, if you look at empty weights (yes I'm going to use wikipedia here, I don't have anyone's dash one available), combat radius examples from that same crappy website and a baseline 2k lbs ordnance load (ballpark 6xAMRAAM) I end up with a wing loading for the F-35 that is comparable to the Super Hornet and the thrust to weight ratio that is comparable to the legacy Hornet. While not eye watering, it ends up being right in the middle of the fourth gen aircraft kinematically. In other words, the F-35 is not an improvement in fighter kinematics, just more of the same. Is that OK given the improvement in other are areas?

I'm not sure if the numbers will work out that way in the end, especially by the time the final product is flying (since you know how they like to throw a bunch of weight in there). It better be at least as good as a Superhornet, and even Superhornets are not on the level of F-16s,15s, or 22s, like you mentioned. The F-35A might be rated for 9gs, but pulling that many for even a brief period of time is gonna bleed off a ton of airspeed. The Superhornet doesn't care about this as much since it's only rated for 7.6 if I'm not mistaken, and the Navy's had to work with that anyway due to the limitations of carrier ops.

I'd say at this point a better engine is absolutely necessary. As many mentioned, GE is probably up to the task. A more efficient one would be better than a more powerful one. A higher efficiency engine would probably lead to more power anyway, but most importantly, and very easy to forget, this thing burns a bit more fuel than an F-16. Global warming and pricy gas aside (and gas is more expensive than ever), that's a logistical nightmare to have to deal with in a deployed environment. Hell, if they could get an engine efficient enough to offer supercruise, they'd save a lot of face and get a lot of my respect back.

Edited July 1, 2014 by xcraftllc

[Breckey]

The problem is that the aircraft was not designed for supercruise. Getting enough thrust to push through the transonic region with the current design limitations would not work with today's materials limitations. The F135 is already using exotic materials in the turbine nozzles to withstand the high temperatures needed for the thrust. The engine is already the most powerful fighter engine (~40k lb thrust). The reason the thing is so damn loud is the amount of high velocity exhaust the thing is pushing out the back.

Unless the F135 has problems similar to the early F100-100s, the F136 program will remain dead in the water. The F-16 is the only US fighter aircraft with more than one engine option. Having multiple engines leads to design problems with the aircraft (ref early block Big-Mouth F-16s). Pratt or Allison did not complain when the thousands of F-4s only used GE J79s. The F136 was mostly a political move from the Ohio and Indiana delegation.

[matmacwc]

The Block 50 F-16 wasn't designed to super cruise but it will do it.

I think GE is ready to pounce, have multiple engines isn't a problem at all. Post block 30 F-16 had common engine bays, would accept either engine. I bet the GE engine has a non lift fan compromised model as well, that would fix the power problem right there.

[SurelySerious]

The Block 50 F-16 wasn't designed to super cruise but it will do it.

An F-16 is advantageously area ruled so it doesn't have 690% more boat tail drag than any fighter in the last 69 years and doesn't need 40k+ lbs of thrust to do it.

[Breckey]

I bet the GE engine has a non lift fan compromised model as well, that would fix the power problem right there.

Both the F135 and F136 have the requirement to have complete commonality between all airframes. The requirement for the F136 was to be able to be able to be swapped between different models with minimum modification (LRU replacement for the Nf fan and nozzle, FADEC program changes, etc). The gas generator and power turbine would remain the same. The JPO also required that the engines could be swapped in the field with only software changes. All of the aircraft connections and system interfaces were required to be identical. The only reason the F136 had more power than the F135 was that the intake and exhaust design of the aircraft was solidified prior to PDR allowing the F136 to take advantage of the increased mass flow in the design. The F135 did not have this advantage.

*Caveat: All of this was true in 2008 when I worked on the F136 program. If the JPO changed the engine integration requirements since the exclusion of the F136 then my info is outdated.

[matmacwc]

You and your facts. Here's what I know. I fly Vipers:

Pratts suck

GE rocks

Fini

[NEflyer]

Oops, fat fingered that one Gearpig. Tried to +1 the post and failed.

[busdriver]

I fly Vipers:

I guess I'll ask this then: if you lost the sustained G of the Viper but gained the high alpha of the Hornet, is that a net gain or loss in your mind?

[VL-16]

The higher alpha of the Eagle doesn't seem to help you guys avoid getting gunned. I've sustained .98M in a Block 40 (centerline bag, A/A config) just using Mil power in the 20's/30's, so I'd buy that a Block 50 is capable of ~1.0M in similar circumstances. Not that we ever try to do it, or even talk about it when it comes to tactics or our A/A game plan.

[xcraftllc]

All this talk about supercruise and engines makes me wonder what would happen if we had GE develop some nice new efficient 110 series engines for 15s and 16s.

If you take a look the 9:1 thrust-to-weight and high efficiency of the GE F414s on Superhornets, it makes you wonder what GE could do with a 110 sized engine (since engines typically get more efficient with size). I bet the fuel savings would significantly offset the development costs, and considering that the 15 has two engines, and the 16 has excellent area ruling, they'd probably both supercruise, in addition to a general improvement to their overall performance.

[Steve Davies]

That image is ass-about-face: the thing is burning money (intake), not creating it (exhaust).

[Beaver]

More alpha would help the Vipers with their gun jinks...zing!

I'd also like to know what configuration, engine, altitude, and airspeed allows a Block 50 Viper to super cruse.

Clean, wingtip aim-9s, 15,000, without even trying.

[Blue]

That image is ass-about-face: the thing is burning money (intake), not creating it (exhaust).

I think that photo was at Lockheed's facility in Ft Worth, so the pic is accurate. Jet is exhausting copious money onto Lockheed, as designed.

[Breckey]

All this talk about supercruise and engines makes me wonder what would happen if we had GE develop some nice new efficient 110 series engines for 15s and 16s.

If you take a look the 9:1 thrust-to-weight and high efficiency of the GE F414s on Superhornets, it makes you wonder what GE could do with a 110 sized engine (since engines typically get more efficient with size). I bet the fuel savings would significantly offset the development costs, and considering that the 15 has two engines, and the 16 has excellent area ruling, they'd probably both supercruise, in addition to a general improvement to their overall performance.

Fuel savings does not offset development costs for the manufacturer. Sales from countries that want the fuel savings offset developments cost. Singapore is flying F110s in their F-15s and most foreign sales of F-16s use GE engines. Fuel efficiency if fighter engines is not the performance parameter that is is in passenger aircraft. GE, Pratt, and Rolls are coming out with new high-bypass turbofans for the A320NEO and 737-MAX that are a 15% improvement over the previous engine models. The advantages of the new engines are the increased fan diameter and tuning of the compressor and turbine aerodynamics. Only one of these would work in a fighter engine. Also the new re-engine efforts are combined with a lot of aerodynamic improvements to realize the cost savings over the life of the airframe (~30k hrs or so).

A re-engine effort for fighter aircraft would not be able to achieve the fuel efficiency improvement shown in the passenger aircraft because of the engine container limitations. The AF heavy aircraft (B-52, C-135, C-5) all have had space on the wing for the engines to grow in size.

Plus a 15% fuel efficiency gain would only gain the Viper something like 69 seconds of flight time. Not enough to make it worth while.

Edited July 2, 2014 by Breckey

[Prosuper]

A re-engine effort for fighter aircraft would not be able to achieve the fuel efficiency improvement shown in the passenger aircraft because of the engine container limitations. The AF heavy aircraft (B-52, C-135, C-5) all have had space on the wing for the engines to grow in size.

707/135 aircraft have only so much room on the inboard pylon before they are scraping the tarmac, found many scrape on the inbd engines after a not so smooth landing.

[Steve Davies]

I think that photo was at Lockheed's facility in Ft Worth, so the pic is accurate. Jet is exhausting copious money onto Lockheed, as designed.

Fair play.

[Azimuth]

707/135 aircraft have only so much room on the inboard pylon before they are scraping the tarmac, found many scrape on the inbd engines after a not so smooth landing.

18-inches, which is another reason why the USAF should've bought the 737 various of the F-108's.

[SurelySerious]

18-inches, which is another reason why the USAF should've bought the 737 various of the F-108's.

The one with the accessories on the side instead of the bottom, specifically designed for a low ground clearance airplane? Too innovative for the AF.

[Breckey]

More F135 problems

The incident involved the third stage of the F135 engine built by Pratt & Whitney, a unit of United Technologies Corp, for all three models of the new warplane, the sources said. "The engine ripped through the top of the plane," one said.

Pratt seems to be continuing to have problems with their third stage low pressure turbine. Here is another article from last year summarizing the problems. This is all very reminiscent of the teething problems that Pratt had with the F100-PW-100. Unfortunately the budget climate of today is not like that of the 1980s and I doubt that we can afford or are willing to spend money on an alternate engine program.

[xcraftllc]

I like how they say "engine fire" but then say "One of the sources said the engine involved - and about six feet of debris found on the runway around the jet - were shipped to Pratt's West Palm Beach facility on Tuesday for a more detailed inspection." More like an explosion to me...

[matmacwc]

Come on Brecky, 15% of what? Full AB time or loiter time. I can fly a single bag Viper for over 2.5 if I wanted, 15% would be huge.

Edited July 15, 2014 by matmacwc

[EDDIE]

Come on Brecky, 15% of what? Full AB time or loiter time. I can fly a single bag Viper for over 2.5 if I wanted, 15% would be huge.

Is that supposed to be impressive?

[matmacwc]

Nope, just saying it would help

[xcraftllc]

15% and the ability to super cruise would actually be worth it the way I think about it, about 23 mins of station time or 200 miles of range (depending on configuration) with the option to get there supersonic. Probably even better numbers for Eagles since ours are still using pratts.

Breckey, I hear what you're saying about fan size and turbine aerodynamics, but I think they should still be able to get at least 15%. Where I'm getting that from is based on the numbers for an F414(a much smaller engine based on new tech). A 110 sized engine should be able to put out a lot more power for a lot less fuel than the ones currently in Vipers and Eagles right? I mean if nothing else, enough for super cruise like a block 50 but better.

Fuel savings does not offset development costs for the manufacturer. Sales from countries that want the fuel savings offset developments cost. Singapore is flying F110s in their F-15s and most foreign sales of F-16s use GE engines. Fuel efficiency if fighter engines is not the performance parameter that is is in passenger aircraft. GE, Pratt, and Rolls are coming out with new high-bypass turbofans for the A320NEO and 737-MAX that are a 15% improvement over the previous engine models. The advantages of the new engines are the increased fan diameter and tuning of the compressor and turbine aerodynamics.

Come on Brecky, 15% of what? Full AB time or loiter time. I can fly a single bag Viper for over 2.5 if I wanted, 15% would be huge.