Forum: F-16 Design & Construction

Hello guys

New fellow on [Link pending approval]

I would like to find a way to calculate fuel consumption depending on altitude (tables).

For example: what fuel to carry for 150nm fl250 95% rpm?

Thanks for your answer

Milan

F-16.net Sponsor

to make it simple:
if you want to fly endurance (that would be slower then "combat speed") you will be
flying about 3500-4500 pounds per hour in light configs.
5000-6000 in heavy configs.it doesn't change with altitude.
if you want to go far (range) then you should fly as high as recommended, the fuel flow will be about the same in endurance but you will be able to go further the higher you are
thats Ballpark figures
fezy.

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Huh? Fuel flow doesn't change with altitude? Oh yes it does... it changes big time. And gross weight has no direct influence on fuel flow. What it does have to do with is drag and with more drag comes more thrust to maintain a certain speed. Fuel flow is a function of airspeed and altitude, much like thrust is.

Hey Milan.I dont have a damn idea about fuel consumption but anyway welcome to the site from all the f-16.net community.Hope you enjoy here.

at a given weight the minimum drag is a relative constant at all altitudes, but the speed for it increases with altitude. L/D max doesnt change with altitude, and since you need the same L at a given weight at all alts then teh D is the same as well, but that drag value is only applicable to Max Endurance speed which is slower than max range speed.

What Raptor One is getting at is that if you want to fly at say... 600 knts, fuel flow is VASTLY higher at SL than at 30K ft. but at a given altitude 600knts will give you your new speed for L/Dmax. Flying below that speed is a waste of fuel as induced drage begins to overpower parasite drage.

thanks for these answer
to whom fly the f16 how do you calculate fuel to put inboard and that will be consumpted

thanks

milan

consumpted?

Raptor_One wrote:

Huh? Fuel flow doesn't change with altitude? Oh yes it does... it changes big time. And gross weight has no direct influence on fuel flow. What it does have to do with is drag and with more drag comes more thrust to maintain a certain speed. Fuel flow is a function of airspeed and altitude, much like thrust is.

Huh?
like i wrote, im giving a simple answer, not 2 years of flight school:
when flying endurance Fuel flow doesnt change with altitude. not big time and not small time, doesnt change- sorry.
fezy.

FEZT, I am a bit confused here! I am not a pilot so I don`t know..
Do you mean MINIMUM fuel flow doesn`t change with altitude? I think that is right.

I ment what i wrote: endurance fuel flow does not change with altitude.
endurance is the flight speed you should stay in to keep on flying the same altitude with the minimum amount of fuel used. in short its the speed to fly to stay as long as you can in the air ( not as far as you can go- but as long as you can).
this has nothing to do with altitude- whatever altitude you pick to stay in the air, the minimum fuel flow to stay in any altitude will be the same.
fezt.

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

Fezt,

Have you ever seen the fuel flow charts for an F-16? Any block mind you. I don't care what speed you are talking about... the fuel flow for both MIL and AB decrease with altitude. The trend is obvious and glaring. Are you trying to tell me that max endurance speed at 20,000 ft will have the same fuel flow for max endurance speed at 40,000 ft or sea level? Also, 1000 lbs difference in fuel flow for MIL power or less is quite a bit since at higher altitudes your fuel flow might only be 5000 lbs/hr maximum in MIL. Also, to answer the posters question you would have to go into a lot of detailed aeronautical engineering equations. There is no way around that. There is no simple answer. Notice I didn't even begin to try to answer the posters question. I may have studied aerospace engineering, but I'm not trying to be a professor here. I probably wouldn't be a very good one either.

Raptor_One wrote:

Fezt,

Have you ever seen the fuel flow charts for an F-16? Any block mind you. I don't care what speed you are talking about... the fuel flow for both MIL and AB decrease with altitude. The trend is obvious and glaring. Are you trying to tell me that max endurance speed at 20,000 ft will have the same fuel flow for max endurance speed at 40,000 ft or sea level? Also, 1000 lbs difference in fuel flow for MIL power or less is quite a bit since at higher altitudes your fuel flow might only be 5000 lbs/hr maximum in MIL. Also, to answer the posters question you would have to go into a lot of detailed aeronautical engineering equations. There is no way around that. There is no simple answer. Notice I didn't even begin to try to answer the posters question. I may have studied aerospace engineering, but I'm not trying to be a professor here. I probably wouldn't be a very good one either.

You should go back to the books, mil and burner have nothing to do with what I wrote.

Once again, endurance fuel flow is the same for all altitudes. when you are at sea level your endurance fuel flow is about 3000 for a block 10 viper. at sea level this would be kept with the throttle back and low rpm. in 20000 feet your endurance fuel flow will be exactly the same 3000, but your rpm would be higher and throttle position forward.

To sum it up. To stay in the air in the viper, for as long as you can. It doesn't matter what altitude you choose. The fuel flow endurance will be the same. And yes I have seen every chart the Viper has. I am a block 5 10 40 52 Viper driver, thanks a lot.

fezy.

PS: sprstdlyscottsmn explained it well in the first part of his post.

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

You're just wrong. I am looking at endurance fuel flow for a block 25 which uses the same engine as a block 5 or 10 and the fuel flow changes significantly with altitude. Way more than what you're quoting. For example, drag index zero and gross weight 18,000 lbs:

Sea Level, FF max endurance = 2040 PPH
20,000 ft, FF max endurance = 1670 PPH

That's a difference of 370 pph.

At 30,000 ft it's down to 1500 PPH.

Now consider max endurance fuel flow at sea level and go from clean config at 18,000 lbs GW to DI 250 and 36,000 lbs GW. The fuel flow is then 4440 PPH. That's a 2400 PPH difference! The reason for the small changes or large changes are due simply to the change in fuel flow with speed and altitude. Max endurance speed WILL change with altitude, gross weight, and drag index. And anytime you change speed or altitude the fuel flow changes. Just look at the fuel flow charts.

-Raptor

P.S. Just noted you said you are an F-16 pilot. Well... I guess this is just one of those times that engineers and pilots disagree. Smile

There is sometimes a bit of a disconnect between the two. Hehehe...

Dont have the books at home, will bring the numbers next time I'm at the Sqn.

What book are you looking at?

fezt

Elite 1K Joined: Aug 19, 2004 - 09:19 AM Posts: 1092

The block 25 -1 cruise performance charts listing, among other things, max range speed/fuel flow and max endurance speed/fuel flow. While I agree that the difference in fuel flow for the same weight may not be that great, the change with weight and/or drag index seems significant to me. But I'm the kind of guy that will quibble over 400 PPH difference, so go figure. Smile

The main thing I see is a trend towards decreased fuel flow with increased altitude, even for max endurance. Even if it's just a 100 PPH decrease per 10,000 ft. or something like that, if it's an obvious trend I see it as significant. Like I said, engineers and pilots are bound to think differently about some of the same things.

Forum: F-16 Design & Construction

Fuel consumption