F-35 internal fuel, range

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spazsinbad

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Unread post13 Oct 2017, 00:17

'Gums' IIRC the A4G 'rule of thumb' for quick mental gymnastics was 6 pounds per NM range at low altitude at 360 kannots.
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count_to_10

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Unread post13 Oct 2017, 00:36

neptune wrote:
steve2267 wrote:... I kind of doubt it... if you burned ALL your fuel, you would no longer have hydraulics. But I may be wrong.


....if you burn all the fuel, you don't need hydraulics.......OTOH you will arrive at the crash site, first!

....maybe you will alarm when the fuel quantity depletes to the minimum fueldraulic limit???
:)

Alternately, if you spring a hydraulic leak, you would have the whole fuel tank as a reserve reservoir while you tried to get back to base. All the fuel in the world won't do you much good if you lose your controls.
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Unread post13 Oct 2017, 00:40

count_to_10 wrote:Alternately, if you spring a hydraulic leak, you would have the whole fuel tank as a reserve reservoir while you tried to get back to base. All the fuel in the world won't do you much good if you lose your controls.


Heh I guess it might also be nice for emergencies. If you start running low on fuel because of a leak at least they could refuel you on the way. If you start running low on hydraulic fluid I'm not sure what they can do.
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Unread post13 Oct 2017, 03:23

Aaaah 'hydraulics'.... viewtopic.php?f=60&t=19215&p=351271&hilit=hydraulics#p351271

Damage control & testing was undergone years ago where proof obtained how the aircraft is able to fly with various damage bits & pieces. One claim is that it can fly with one tail IIRC - I'll look that up as well "...example, the F-35 can fly with one horizontal tail and one rudder missing..." http://www.aviationpros.com/article/109 ... ke-fighter

More: viewtopic.php?f=58&t=24027&p=307076&hilit=aviationpros#p307076

Good 'LIVE FIRE TEST' info: viewtopic.php?f=54&t=14199&p=221179&hilit=live+fire+test+bahdayton#p221179
&
viewtopic.php?f=22&t=16020&p=204074&hilit=live+fire+test+bahdayton#p204074
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Unread post13 Oct 2017, 04:08

Gums wrote:Salute!

Not so sure about your "analysis", Spurts.

1) I cannot find a F-16 GTOW you mention that only has internal fuel.

2) The two engine discussion is familiar to this old fart. It turns out that you can only pull the throttles back so far and you still have "x" pounds per hour, total. So in our over-powered A-37 we would have about 1500 - 1600 PPH total to maintain a good loiter AoA/speed. If we shut one down and pushed up the single engine we saw about 1300 PPH or so. The motor was running at a better point on the "curve" at a higher rpm.

The Hornet guys I first met said their fuel flow was about like an Eagle!! I discount the higher drag from more skin friction, but you could convince me.

3) I have a problem with asserting F-35 weight requiring lots more lift and associated induced drag. I'll bet that the sucker will come close to the 7 pounds per mile I saw in the Sluf and Viper, and that was total gas from climb to cruise and descent at home. e.g. RTB from 300 miles away using 2100 pounds plus reserve once there. worked every time.

Gums sends...

Salute!

My "analysis" was only to mathematically show the things that actually effect fuel burn. I will happily talk about each of your points and how they apply.

1) The HAF Blk 50/52+ -1 lists an empty weight of "about" 20,000lbs with oil, oxygen, unusable fuel, pilot, and tip missile rails with an internal usable fuel load of 7,162lb JP-8 (GE enigne, p.B1-6) giving ~27,000lb.

2)Turbine engines tend to run more efficiently the closer to a design throttle setting. Lower throttle settings will have a higher TSFC (more fuel burn). This is what you were seeing. Speed was the same, so drag was the same (maybe even a little higher with an engine out creating ram drag, unless you just idled it) so thrust was the same, so the improved TSFC for operating the one engine closer to the design point led to reduced fuel burn. Out of curiosity, was that in the manual or was that just a tricked you guys picked up?

2.5) the F404 has a higher TSFC than the F100. The F100 was a marvel in how much thrust it could make and how little fuel it could drink.

3) My actual analysis of Stubbies performance shows a greater L/D than the F-16 when clean. Not so much that it actually has less drag (I think it was on the order of 10-20% more drag), enough that it does not have to "pay" for all the extra weight with drag. I was using terms "even with a similar L/D" and "if they have the same L/D and TSFC" to show that even with pessimistic assumptions the F-35 still handily outranges the F-16. Looking back through my statements though I did not call out that these were pessimistic values. Oops. 7lb/nm comes out to ~.14nm/lb. A quick glance at the HAF -1 shows optimum cruise values not being less than .2nm/lb when clean, so I would buy .14nm/lb with climb and ordnance, no problem. My last Stubby model shows .10nm/lb from startup to approach on a 590nm radius optimum profile strike with two one-ton GPS bombs, landing with nearly 7k remaining in the tanks (can't remember if it was Col. Simms or Dolby Hanche that gave the statements I based that on).

"If the pilot took off with full fuel 2 amraams and 2 2000lbs bombs flew 590nm and came back with a 10 min weapon deployment time they would land with around 7,000-8,000lbs still in the tank."

1,180nm total for 10,500-11,500 of fuel, 0.1124nm/lb to 0.1026nm/lb fuel, heavy out, light back

Like I said, range is not one of Stubbys problems.
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Unread post13 Oct 2017, 05:36

Gums wrote:
3) I have a problem with asserting F-35 weight requiring lots more lift and associated induced drag. I'll bet that the sucker will come close to the 7 pounds per mile I saw in the Sluf and Viper, and that was total gas from climb to cruise and descent at home. e.g. RTB from 300 miles away using 2100 pounds plus reserve once there. worked every time.

Gums sends...


When a pair of F-35A's flew from Eglin AFB to Oshkosh, the AOPA story had this to say about fuel burn:

F-35 Lightning public debut shows the right stuff
by David Tulis 8 August 2015

For the quick two hour, ten minute jaunt from Florida to AirVenture, each fighter jet burned about 5,000 pounds of fuel at 270 knots. Niemi said typical approach speeds are 150 knots and strictly by a 13-degree angle of attack all the way to the ground. “It’s a real easy plane to fly and it has good powerful [air] brakes. At 100 knots it will sit down pretty good,” he said.

Source: https://www.aopa.org/news-and-media/all ... ight-stuff


The great circle calculator gives 815nm from Eglin AFB to Oshkosh, which serves as a decent 1st order swag on nautical miles flown. 5000lb for 815nm works out to 6.1 lb/nm, just a little under Gums' 7lb/mile swag. (Gums, I presume you meant nautical mile when you said "miles"?)
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post13 Oct 2017, 05:47

Gums wrote:Salute!

2) The two engine discussion is familiar to this old fart. It turns out that you can only pull the throttles back so far and you still have "x" pounds per hour, total. So in our over-powered A-37 we would have about 1500 - 1600 PPH total to maintain a good loiter AoA/speed. If we shut one down and pushed up the single engine we saw about 1300 PPH or so. The motor was running at a better point on the "curve" at a higher rpm.

The Hornet guys I first met said their fuel flow was about like an Eagle!! I discount the higher drag from more skin friction, but you could convince me.

Gums sends...


The F404 was originally called the J101 ultra low bypass turbofan. It is part of the F101/F110/F118 family, uses almost the same core as the F110. I wish I could remember who called it a turbojet with a leak. But it is very low bypass 0.34:1, verse the F110's 0.76.
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Unread post13 Oct 2017, 07:05

playloud wrote:That's why the F-35 is a little pudgy.


I prefer "curvy"... :P
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Unread post13 Oct 2017, 07:17

mixelflick wrote:In any case, it really looks like the F-35 has some great legs. You always hear about how much gas Flankers carry/great range but you never hear about how much drag there is from lugging a meaningful weapons load around. Their AAM's look to be real draggy, hung off of a draggy airframe.

The F-35 sure is impressive...


It sure is... F-35A

1. Has similar dimensions to F-16
2. Has about 2.5 times the internal fuel of F-16 or 80% of internal fuel volume of Strike Eagle with CFTs
3. Can carry 5,000 lbs of weapons internally
4. Carries advanced targeting pod, insane amount of avionics systems and extensive EW capabilities internally
5. Can do Mach 1.6, 9G and 50 degree AoA maneuvers while carrying all of the above
6. Is the stealthiest fighter jet in existence according to everybody in the know
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Unread post13 Oct 2017, 13:45

hornetfinn wrote:It sure is... F-35A

1. Has similar dimensions to F-16
2. Has about 2.5 times the internal fuel of F-16 or 80% of internal fuel volume of Strike Eagle with CFTs
3. Can carry 5,000 lbs of weapons internally
4. Carries advanced targeting pod, insane amount of avionics systems and extensive EW capabilities internally
5. Can do Mach 1.6, 9G and 50 degree AoA maneuvers while carrying all of the above
6. Is the stealthiest fighter jet in existence according to everybody in the know


Is it commonly accepted that the F-35A has a lower RCS than the F-22? Or are we discussing "total signature" to include visual + thermal? Regarding RCS, the last number I saw cited (or stated) for the F-22 was 0.0001 m^2, or the "size of a marble." Are you stating the F-35 comes in less than that number (or have read statements by "people in the know" stating or implying that to be the case)?
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post13 Oct 2017, 14:03

steve2267 wrote:
hornetfinn wrote:It sure is... F-35A

1. Has similar dimensions to F-16
2. Has about 2.5 times the internal fuel of F-16 or 80% of internal fuel volume of Strike Eagle with CFTs
3. Can carry 5,000 lbs of weapons internally
4. Carries advanced targeting pod, insane amount of avionics systems and extensive EW capabilities internally
5. Can do Mach 1.6, 9G and 50 degree AoA maneuvers while carrying all of the above
6. Is the stealthiest fighter jet in existence according to everybody in the know


Is it commonly accepted that the F-35A has a lower RCS than the F-22? Or are we discussing "total signature" to include visual + thermal? Regarding RCS, the last number I saw cited (or stated) for the F-22 was 0.0001 m^2, or the "size of a marble." Are you stating the F-35 comes in less than that number (or have read statements by "people in the know" stating or implying that to be the case)?


According to General Mike Hostage it is:

https://breakingdefense.com/2014/06/gen ... -starts/3/

The F-35’s cross section is much smaller than the F-22’s, but that does not mean, Hostage concedes, that the F-35 is necessarily superior to the F-22 when we go to war.


According to LM:
https://www.f35.com/about/capabilities/stealth
The stealth capabilities in the F-35 are unprecedented in military aviation.
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Unread post13 Oct 2017, 14:18

hornetfinn wrote:According to General Mike Hostage it is:

https://breakingdefense.com/2014/06/gen ... -starts/3/

The F-35’s cross section is much smaller than the F-22’s, but that does not mean, Hostage concedes, that the F-35 is necessarily superior to the F-22 when we go to war.


According to LM:
https://www.f35.com/about/capabilities/stealth
The stealth capabilities in the F-35 are unprecedented in military aviation.

General Bogdan also concurred...

http://www.airforcemag.com/MagazineArch ... roach.aspx
"I would say that General Hostage … is accurate in his statement about the simple stealthiness of the F-35 [with regard] to other airplanes," Bogdan said in the interview. The statement was accurate for radar cross section, as measured in decibels, and range of detectability, he said, and he scoffed at the notion that anyone can tell how stealthy an aircraft is just by looking at it.
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Unread post13 Oct 2017, 15:34

Salute!

THNX for the update, Spurts.

Gross weight? Spurts 1, Gums 0.5 I'm too old and forgot about all the weight increase as the Viper porked up over last 30 years, heh heh. Remember, I cut my teeth on the original "lightweight fighter" !!!!!

Single engine cruise? It was a standard procedure for the A-37 for at least first 6 or 7 years. We used it mostly to loiter, so I would cross my fingers and shut one down in the middle of the night over the Trail and wait for Covey or Blindbat to find a truck convoy. We hardly ever cruised to the tgt on one motor due to ordnance drag. I flew twice from Colorado to Louisiana with only two drop tanks - over 700 n.m. We had to switch motors after a half an hour or so to keep the lubrication where it was supposed to be.

Optimum engine rpm? Yep, Spurts. We're in the zone on that. Even at idle, the J85 was still using 300 - 400 pph.

I, too, saw the "leaky turbojet" comment back in 1974 or so. It was an interview in AvWeek, best I recall. I just think the Hornet was/is too draggy. Even with the pylons on the sluf, both it and the Viper were amazing descending at 300 kias and using only 500 pph. We would pull back to idle 100 miles out, 35,000 ft and put the flight path marker on the homebase TD box. We would soon get to 300 kias and maybe a bit higher.

Gums sends....
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Unread post15 Oct 2017, 19:07

Gums wrote:Salute!

Not so sure about your "analysis", Spurts.

1) I cannot find a F-16 GTOW you mention that only has internal fuel.

2) The two engine discussion is familiar to this old fart. It turns out that you can only pull the throttles back so far and you still have "x" pounds per hour, total. So in our over-powered A-37 we would have about 1500 - 1600 PPH total to maintain a good loiter AoA/speed. If we shut one down and pushed up the single engine we saw about 1300 PPH or so. The motor was running at a better point on the "curve" at a higher rpm.

The Hornet guys I first met said their fuel flow was about like an Eagle!! I discount the higher drag from more skin friction, but you could convince me.

3) I have a problem with asserting F-35 weight requiring lots more lift and associated induced drag. I'll bet that the sucker will come close to the 7 pounds per mile I saw in the Sluf and Viper, and that was total gas from climb to cruise and descent at home. e.g. RTB from 300 miles away using 2100 pounds plus reserve once there. worked every time.

Gums sends...


Fuel flow is measured in lbs/min in this aircraft. Normally 20's - mid 30k cruising .8-.92M you're burning between 85-100 lbs/min; generally figure 100 for planning but we will beat that a lot. FADEC seems to keep fuel flow pretty constant in a lot of different situations. Max endurance will generally stabilize around 85lbs/min 250-280kts. Unlike a lot of other a/c, you don't buy nearly as much during an idle descent as it seems to take a lot of fuel to keep this gigantic engine turning, around 50lbs/min.

For reference, two tanked F-18 max endurance with pylons you figure 4800 lbs/hour fuel burn. Goes up quickly with speed increase.
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Unread post15 Oct 2017, 20:58

010137 wrote:
Gums wrote:Salute!

Not so sure about your "analysis", Spurts.

1) I cannot find a F-16 GTOW you mention that only has internal fuel.

2) The two engine discussion is familiar to this old fart. It turns out that you can only pull the throttles back so far and you still have "x" pounds per hour, total. So in our over-powered A-37 we would have about 1500 - 1600 PPH total to maintain a good loiter AoA/speed. If we shut one down and pushed up the single engine we saw about 1300 PPH or so. The motor was running at a better point on the "curve" at a higher rpm.

The Hornet guys I first met said their fuel flow was about like an Eagle!! I discount the higher drag from more skin friction, but you could convince me.

3) I have a problem with asserting F-35 weight requiring lots more lift and associated induced drag. I'll bet that the sucker will come close to the 7 pounds per mile I saw in the Sluf and Viper, and that was total gas from climb to cruise and descent at home. e.g. RTB from 300 miles away using 2100 pounds plus reserve once there. worked every time.

Gums sends...


Fuel flow is measured in lbs/min in this aircraft. Normally 20's - mid 30k cruising .8-.92M you're burning between 85-100 lbs/min; generally figure 100 for planning but we will beat that a lot. FADEC seems to keep fuel flow pretty constant in a lot of different situations. Max endurance will generally stabilize around 85lbs/min 250-280kts. Unlike a lot of other a/c, you don't buy nearly as much during an idle descent as it seems to take a lot of fuel to keep this gigantic engine turning, around 50lbs/min.

For reference, two tanked F-18 max endurance with pylons you figure 4800 lbs/hour fuel burn. Goes up quickly with speed increase.

These are the considerations that got me wondering if it was possible to power the compressor by sending only a small fraction of the combuster air through the turbine, while the fuel burned in the rest of the air is varied to control thrust.

viewtopic.php?f=38&t=53008
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