Forum: F-35 Lightning II

After doing some back of the gas reciept calculations using thrust compared to empty weight of the CTOL F-35 ,would I be wrong to state that the thrust to weight ratio,and thus the Boyd curve for this airframe,blows hard chunks compared to the Viper its replacing?

Yes I realize this aircraft is meant to do lots of cool and high-tech warfighting techniques,but someone 50 years back likely said the same thing about the F-111 too.Is anyone else concerned that were potentially fielding an ACM nightmare in this advanced program?

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The jet was designed at a minimum to match the F-16's performance and based on the feedback from the test program it seems to be living up to expectations.

To be honest, I wouldn't care if the thing was as cheap as it was supposed to be. Oh well, it's all we have now.

I am breaking my rule on responding to trolls but....

Why don't you save us all the time and punch us up a power to weight and wing-loading comparison between an F-16 block 60 and an F-35A.

Thanks in advance!

hobo wrote:

I am breaking my rule on responding to trolls but....

Why don't you save us all the time and punch us up a power to weight and wing-loading comparison between an F-16 block 60 and an F-35A.

Thanks in advance!

Thank you for NOT answering the question.Really,I'm honored

Rolling Eyes

As far as cost is concerned,putting our fighting men and women iin the best hardware should be #1-and the best of anything will be expensive.I'm just not sure an aircraft with an inferior thrust to weight ratio to its predecessor meets that catetgory.

Ah, but how inferior is it?

Lets see that Block 60 comparison.

I think this is the problem of comparing fourth and fifth generation designs. Remember that most of the aircraft, not just the wings, is generating lift. Plus, the equation should be thrust to weight plus drag. The F-16's going to be carrying stuff out on the wings and will be much draggier than the F-35 carrying everything internal. So yes it will be heavy, but it doesn't have to deal with the drag issue. While it might not out-turn an F-16 in certain regimes, it seems it will be faster in all situations. And the turning won't be much worse (and I'm talking full fuel + full internal load).

Well lets see, Blk60 weighs in at 11 tons empty due to increased structure for heavier loads and the addition of CFTs. It carries some 6.5 tons of fuel. as such it weighs in (without weaponry) at 17.5 tons. As such any thrust to weight rating is decreased by 6% per ton of weaponry carried (1 heavy bomb, 4 light bombs, 2 AGMs, 6 MRM, or 10 SRM). It motor produces 9.5 tons thrust mil and 16 tons AB. It gives a T/W ratio of 54% mil and 91% AB. it also yeilds a Fuel Fraction of 37%

F-35A weighs in at 14.5 tons empty and carries 9 tons of fuel for a weapon free weight of 23.5 tons. this yields a weapon sensitivity of 4%, and thrust to weight ratios of 60%/91% in mil/AB (rated thrust of 14tons/21.5tons) and a fuel fraction of 38%

So in military power the F-35 enjoys a significant T/W advantage that only increases once weapons are added (not to mention the drag benefits of the F-35s first 2.5 tons) which when added to the 5th gen capabilities would make the F-35 an obvious choice.

silversmok3 wrote:

After doing some back of the gas reciept calculations using thrust compared to empty weight of the CTOL F-35 ,would I be wrong to state that the thrust to weight ratio,and thus the Boyd curve for this airframe,blows hard chunks compared to the Viper its replacing?

So what results did you end up with and how were they worked out?
What version/model/block of the Jets were you using?

silversmok3 wrote:

Yes I realize this aircraft is meant to do lots of cool and high-tech warfighting techniques,but someone 50 years back likely said the same thing about the F-111 too.Is anyone else concerned that were potentially fielding an ACM nightmare in this advanced program?

There are so many old threads on this already - maybe worth checking some out.

EDIT, the forum didn't keep the formatting, oh well.

The only way that the F-16 has an advantage is if it's not carrying external tanks. But if a mission with such lax range requirements were to exist, the F-35 could just fill up half way. Block 30 is lighter than 60. I'm not completely sure if the numbers are exact, but they should be close.

F-35A F-16C Blk30

Int fuel 11500 7500
# tanks 0 0
tank cap 0 300
Ext fuel 0 0
Weight 42520 27740
F frac 0.27046096 0.2703677
WL 92.43478261 92.46666667
TWR 1.011288805 1.009372747

F-35A F-16C Blk30

Int fuel 18480 7500
# tanks 0 2
tank cap 0 300
Ext fuel 0 3840
49500 31580
0.373333333 0.35908803
107.6086957 105.2666667
0.868686869 0.886637112

If you want to get hypothetical, the F-35 with 50,000 lbs thrust looks like the F-15.

I did my calculations using a loaded and empty block 40/50 Viper .I also used the thrust figures reported on Wikipedia at the time (around last November).Now ,how do you guys find the specific drag of any given aircraft?I stand corrected regarding fully loaded status,but I did my numbers using min fuel and airframe weight only,given that dogfighting aircraft jettison all externals before engaging in ACM besides air to air weaponry,obviously

sprstdlyscottsmn wrote:

So in military power the F-35 enjoys a significant T/W advantage that only increases once weapons are added (not to mention the drag benefits of the F-35s first 2.5 tons) which when added to the 5th gen capabilities would make the F-35 an obvious choice.

Thank you, that sums the situation up pretty well. (The F-35A will also compare favorably in wing loading, even without accounting for the fact that a greater percentage of its lift is generated by its fuselage.)

If you wanted to talk about adding additional capabilities like EO/DAS, a larger radar, and so forth to bring the F-16 up to the F-35's level of avionics then the F-16 will pack on more pounds it was never designed to carry. (and still could not become stealthy)

silversmok3 wrote:

I did my calculations using a loaded and empty block 40/50 Viper .I also used the thrust figures reported on Wikipedia at the time (around last November).Now ,how do you guys find the specific drag of any given aircraft?I stand corrected regarding fully loaded status,but I did my numbers using min fuel and airframe weight only,given that dogfighting aircraft jettison all externals before engaging in ACM besides air to air weaponry,obviously

Are they going to jettision sensor pods, Sniper XR, Lantirn etc? What fuel state is the F-35A in?

Remember at 50% internal fuel, the F-35A STILL has roughly 2125lbs MORE fuel than an F-16C does at full internal fuel...

Not to be a kill joy, but did anyone actually look to see when the last dog fight actually occurred that involved ACM? As missiles get smarter and more effective the chances of a dog fight occurring dramatically decreases. In fact I would say a lot technology has to fail now before a dog fight happens. So with that being the case if you are an airplane designer you now want to design your plane for speed and stealth rather then extreme maneuverability as a fighter jet fighter is going to be very hard pressed to out maneuver a salvo of advanced missiles.

So some thing like this:

If you want the real drag on a figher, you need to look up. The most basic way to estimate is through CD*A, but CD changes with the Reynolds number, and fighters go through a whole lot of Reynolds numbers. Not to mention it depends on what side of Mach 1 you're on too.

Area is pretty consistent (though as AoA changes, it might actually change), so you could compare frontal area to thrust. If you want to replicate the additional CD of external stores, give them an exaggerated area. Also remember that thrust isn't constant, so that's another source of error.

Forum: F-35 Lightning II

Boyd Curve Comparison?