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Enthusiast Joined: Dec 07, 2006 Posts: 28 Status: Offline

This is from Aviation Week regarding the F-35's first flight:

"The jet had a takeoff weight of 46,100 lb., including 15,200 lb. of fuel."

If true, then that puts the empty weight at ~+30k-lbs, and a far cry from 26k-lbs or whatever other people on this site are claiming. I understand about extra equipment for data collection, but there is not 4000 pounds of data collection on the F-35.

What gives?

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Elite 1K Joined: Jul 22, 2005 Posts: 1088 Status: Offline

Keep in mind this one doesn't have a lot of the weight saving features of the full production model.

Enthusiast Joined: Sep 27, 2006 Posts: 67 Status: Offline

AA-1 weighs around 29,000lbs empty, add in the pilot and other things and it probably comes out to over 30,000.

The production F-35A should weigh about 26,500 lbs empty, it will be plenty agile with a 43,000 pound-thrust engine, for a roughly similar SLS T/W ratio as the Rafale/Eurofigher/F-15C.

Lets say that with the pilot (gear) and gun ammunition the production model (F-35A) weighs 27,000 lb empty. Add to that it's fuel load of 18K and a full (internal only) weapons load and IMO you get a seriously underpowered aircraft.

Don't forget this is a test jet. It is most likely packed with flight test instrumentation...that stuff is not light.

Newbie Joined: Jan 07, 2007 Posts: 6 Status: Offline

correct me if I'm wrong, but the 18k weight with full fuel...will this ever be the case? I mean how likely is it that an F-35 will engage right after coming off a tanker? Wouldn't it be more likely that the F-35 would have to travel a couple hundred miles after refueling to get into the combat zone? Realistically, what would the fuel range/weight be in a real world engagement? 50%? 60%? then wouldn't you be looking more at a greater than 1:1 power to weight ratio?

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

Quote:

Lets say that with the pilot (gear) and gun ammunition the production model (F-35A) weighs 27,000 lb empty. Add to that it's fuel load of 18K and a full (internal only) weapons load and IMO you get a seriously underpowered aircraft.

Two things:-

(1) A fully fueled F-35 is heavy? Perhaps. But so is an EF Typhoon with three external tanks and full internal fuel for instance. And the EF has much worse aerodynamics so configured to boot! What is more indicative of the airframe's performance is how heavy it is EMPTY and how much thrust it has. If you just want the range of an EF in an F-35 for some mission, then load it up with the same fuel fraction. 4500 kg of fuel in a 11 ton aircraft is about 29% fuel fraction. Load the F-35 with just 4900 kg of fuel and you'll get a 29% fuel fraction. This also yields a total weight of ~16900 kg vs 15,500 kg in an EF. However you have 43,000 lbs of thrust vs 41,000 lbs in the EF. Thats not much difference in terms of thrust to weight.

However, if you do need to go the distance an F-35 with 8150 kg of internal fuel will go further than an EF with about full internal fuel (~4500kg), two 1500 litre drop tanks (~1230kg x 2 in fuel; wing carried) and one 1000 litre drop tank (820 kg x 1 in fuel; centerline). Why? Because that adds up to 7720 kg of fuel -- less than the F-35 carries internally. It adds weight from the pylons and the tanks themselves. And with 3 external tanks you now have aerodynamics that is a lot worse than a clean F-35. We haven't even talked about ordnance yet. Hang a pair of 2000 lb bombs or eight SDBs, plus AAMs on the EF and that is even more drag. Carry the same in the F-35's internal bay and you add nothing.

(2) In anycase, even with a full load of fuel the F-35A has a thrust to weight ratio of 0.96:1. Thats not underpowered at all. That is BETTER than an F-16C/D with the original 23,500 lbs engines for instance. If the F-35 lights its burner on takeoff roll, by the time it clears lifts off it is probably 1:1 and it can climb vertically if it wants to. Thats not "underpowered".

An official document of USAF released in Sep. 2006 declared that the anticipated empty weight of F-35A should be around 13,170 kg, or around 29,035 Ib.

The empty weight of AA-1 today should be around: 46,100 - 15,200 (fuel) - 220 (pilot) = 30,680 Ib

30,680 - 29,035 = 1,645 Ibs.

AA-1 will be the only JSF without the benefit from weight reduction plan, and according to the declaration of LM in 2005, the weight reduction plan will help F-35B to reduce the weight of around 2,700 Ib, and F-35A/C to reduce the weight of around 1,300 Ib.........

Enthusiast Joined: Dec 07, 2006 Posts: 28 Status: Offline

Roscoe wrote:

Don't forget this is a test jet. It is most likely packed with flight test instrumentation...that stuff is not light.

Yeah, but not 4000 pounds of test eqp. Strain gauges, accellerometers, themistors, and radio transmission eqp... Should not weigh that much to my engineering mind. Where's the room in the aircraft for the heavy stuff too? Only spare roon is the weapons bays.

Enthusiast Joined: Dec 07, 2006 Posts: 28 Status: Offline

PhillyGuy wrote:

Lets say that with the pilot (gear) and gun ammunition the production model (F-35A) weighs 27,000 lb empty. Add to that it's fuel load of 18K and a full (internal only) weapons load and IMO you get a seriously underpowered aircraft.

Underpowered just like and F-15 with FAST packs and wing tanks. Remember that the F-35 does not NEED to fly into an a2a situation fully tanked to the brim with JP. Though I am not an F-35 fan, its not going to be underpowered when loaded for a2a missions. Its got more lifting area than the F-16, a higher thrust to weight ratio (when loaded properly), and thrust vectoring capability. Though the F-35 is not the leap over the F-16 than the 22 is to the 15, the F-35 is going to be a heck of a "dog fighter" when loaded with 4 AAMs and ~10K pounds of fuel. I'll give credit where credit is due, and the F-35 is not a total waste of money. (I just dont forsee it as the replacement to the Aussies F-111 or us Americans the F-15E) I am also interested to know the airspeed limitations on the weapons bays for missile release.

dwightlooi wrote:

(2) In anycase, even with a full load of fuel the F-35A has a thrust to weight ratio of 0.96:1. Thats not underpowered at all. That is BETTER than an F-16C/D with the original 23,500 lbs engines for instance. If the F-35 lights its burner on takeoff roll, by the time it clears lifts off it is probably 1:1 and it can climb vertically if it wants to. Thats not "underpowered".

Umm... 27,000 lb plus 18,000 plus lets say a modest 2,712 (2 x 1,000 JDAM and 2 x AIM-120C) internal load you get a T/W ratio of .9/1, now that's in afterburner. The F-35 is not going to be fighting or flying in afterburner much. It's dry T/W ratio with a full fuel and weapons load (same as above) is .58/1. I don't find it convincing to rely on the F-35 always engaging with half empty tanks and a light payload while it's in afterburner.

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

<i>Umm... 27,000 lb plus 18,000 plus lets say a modest 2,712 (2 x 1,000 JDAM and 2 x AIM-120C) internal load you get a T/W ratio of .9/1, now that's in afterburner. The F-35 is not going to be fighting or flying in afterburner much. It's dry T/W ratio with a full fuel and weapons load (same as above) is .58/1. I don't find it convincing to rely on the F-35 always engaging with half empty tanks and a light payload while it's in afterburner.</i>

How much does a fighter not typically thought off as "heavy" or "underpowered" weigh when carrying 8150+kg of fuel and ordnance? How much does a Rafale weigh? How much does a Typhoon weigh? In fact, in many cases the limitations of the pylon stations prevent that kind of fuel load period, but let's assume there is no such restrictions, are they underpowered then?

The fact that the F-35 has the ability to to carry that kind of fuel load doesn't make it underpowered. Its empty weight tells the whole story. Saying that you are not convinced that the F-35A can be relied upon to fight at half load is like saying you cannot rely on the Rafale not to have to fight with three external tanks. If you are troubled by the fuel load -- and yes 18,000 lbs is A LOT of fuel. Don't carry it!

In fact, there is practically no chance that the F-35 will fight at full load. Typically, you spend about half the fuel just getting to the fight. And if you are flying an interception those burners will empty your entire tank in minutes (perhaps about 5 mins to bingo). The difference is that if you fly on burners for two minutes in a Typhoon you will be gliding home and hence you can't. Do that on an F-35 and you have over half the fuel left to fight with. In otherwords, that huge fuel load allows you to fly get to speed and altitude like other fighters cannot.

Elite 1K Joined: Aug 19, 2004 Posts: 1092

PhillyGuy wrote:

dwightlooi wrote:

(2) In anycase, even with a full load of fuel the F-35A has a thrust to weight ratio of 0.96:1. Thats not underpowered at all. That is BETTER than an F-16C/D with the original 23,500 lbs engines for instance. If the F-35 lights its burner on takeoff roll, by the time it clears lifts off it is probably 1:1 and it can climb vertically if it wants to. Thats not "underpowered".

Umm... 27,000 lb plus 18,000 plus lets say a modest 2,712 (2 x 1,000 JDAM and 2 x AIM-120C) internal load you get a T/W ratio of .9/1, now that's in afterburner. The F-35 is not going to be fighting or flying in afterburner much. It's dry T/W ratio with a full fuel and weapons load (same as above) is .58/1. I don't find it convincing to rely on the F-35 always engaging with half empty tanks and a light payload while it's in afterburner.

You're being ridiculous, plain and simple. I'm going to say it straight out. You just don't know what you're talking about. As people have pointed out already, an aircraft carrying that much fuel and weaponry will be heavy. An F-16C Block 52 with CFTs, 2x370 Gal drop tanks, 2x1,000 lb JDAMs, and 2xAIM-120 will be really heavy as well. And it will have a somewhat high drag index. And it won't have nearly as much MIL or AB thrust as the F-35. I don't think you have any idea what a realistic thrust to weight ratio is for fully loaded aircraft.

Really? So do you care to dispute the figures or are you going to reassure me again that the F-35 will always fight with half a fuel load, four internal missiles while in afterburner? Rolling Eyes

Elite 1K Joined: Aug 01, 2006 Posts: 1003 Status: Offline

PhillyGuy wrote:

Really? So do you care to dispute the figures or are you going to reassure me again that the F-35 will always fight with half a fuel load, four internal missiles while in afterburner? Rolling Eyes

I can assure you than the F-35 CAN always CHOOSE to fight with half fuel load and 4-internal missiles (probably 6 internal missiles once an appropriate AAM rack is introduced), just like I CAN assure you than an F-16 can CHOOSE whether to carry an external fuel load or or not. You can load it with half tanks if you want any time you want, or more realistically you'll simply burn it off in a couple of minutes while you get a big heap of kinetic energy in return by lighting the burners and charging at Mach 1.8.

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