Forum: General F-35 Forum

Last edited by qwe2008 on Sep 01, 2012 - 05:15 PM; edited 2 times in total

http://www.flightglobal.com/news/articl ... ed-372074/

some months ago, the record is as below

F-35B,
The F-35B has flown at altitudes over 49,000ft ,
hits speeds of Mach 1.4.
The B-model has also flown at its maximum airspeed of 630 knots and has achieved its maximum 7G limit.

F-35C,
The C-model has flown out to 630 knots, but the naval variant is required to hit 700 knots.
The C-model has also flown at 45, 000 ft and at speeds of Mach 1.4.
It has also hit its maximum 7.5G limit.

but there's no news about F-35A in the article.

Now, I think the record need update.

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The A-model has flown out to 1.6M in 2011.
It has also hit its maximum 9G limit in 2011.

But there's no news about the height record.
The latest record is less than B/C model, it's 43,500 feet by Jan-9 2012.

The next news is very surprising.
the F-35 being repeatedly pushed out to its maximum speed of Mach 1.6 and 700 KCAS fully laden with internal weapons.
If the height is more than 25,000 feet, the 700 KCAS speed will be more than 1.6M.
It means that F-35A's max speed record is much more than 1.6M?

qwe2008 wrote:

The A-model has flown out to 1.6M in 2011.
It has also hit its maximum 9G limit in 2011.

But there's no news about the height record.
The latest record is less than B/C model, it's 43,500 feet by Jan-9 2012.

The next news is very surprising.
the F-35 being repeatedly pushed out to its maximum speed of Mach 1.6 and 700 KCAS fully laden with internal weapons.
If the height is more than 25,000 feet, the 700 KCAS speed will be more than 1.6M.
It means that F-35A's max speed record is much more than 1.6M?

Well, they are really only telling us what the requirements are -- not what the real capabilities are. They could be pushing 2M and just keep it to themselves.

The F-35 is more then capable of reaching over Mach 2 if you look at it's thrust to weight ratio numbers. How ever their are two things preventing this. The first would be its Diverterless Air Intakes and second would be its stealth coatings. Also there is no real pratical need to go beyond mach 1.6 for a jet fighter as the infared signature gets so large that the aircraft becomes easy prey for an infared missile.

Then again, the F-22's top speed was given as Mach 1.8 for quite awhile as I recall; so who knows what the F-35 is really capable of. Rumor has it that the thing is quite capable of supercruise (despite its engine design), but that LM and the USAF could get into trouble if it does (Congress didn't want to pay for that capability), which why the USAF raised the standard for supercruise to the rather arbitrary Mach 1.5.

The key performance parameters (KPP) for the F-35 require higher sortie rates for the B-model at four sorties per day. The A and C models are only required to generate three sorties per day.

"So far in SDD [System Development and Demonstration], all three variants are on track to exceed their KPPs at the completion of SDD," Gardner says. "
The B looks to come in at about six sorties per day, the A at about 3.5 and the C at close to four."

http://www.flightglobal.com/news/articl ... 10-371985/

Currently, all weapons pit drop tests required for the system development and demonstration (SDD) phase, save for the 250lbs GBU-39 small diameter bombs, have been completed.
"We're just getting ready to do our first weapons separation and that'll be in the October timeframe," Schwartz says. "We're going to do a GBU-31 and an AIM-120."

http://www.flightglobal.com/news/articl ... fb-375964/

alloycowboy wrote:

The F-35 is more then capable of reaching over Mach 2 if you look at it's thrust to weight ratio numbers. How ever their are two things preventing this. The first would be its Diverterless Air Intakes and second would be its stealth coatings. Also there is no real pratical need to go beyond mach 1.6 for a jet fighter as the infared signature gets so large that the aircraft becomes easy prey for an infared missile.

Actually, I thought it was the higher bypass engine and relative inefficiency at higher mach numbers. The larger fan does not produce the required thrust offset to get to Mach 2+ flight. That_Engine_Guy might be able to shed light on the details, but basically above a certain speed, a turbofan engine will suffer stagnation "stall" if not managed properly, a compressor stall will develop, and a loud bang result.

The best record to-date? IMO doing a pretty good job at silencing critics with it's impressive performance so far.

neurotech wrote:

alloycowboy wrote:

The F-35 is more then capable of reaching over Mach 2 if you look at it's thrust to weight ratio numbers. How ever their are two things preventing this. The first would be its Diverterless Air Intakes and second would be its stealth coatings. Also there is no real pratical need to go beyond mach 1.6 for a jet fighter as the infared signature gets so large that the aircraft becomes easy prey for an infared missile.

Actually, I thought it was the higher bypass engine and relative inefficiency at higher mach numbers. The larger fan does not produce the required thrust offset to get to Mach 2+ flight. That_Engine_Guy might be able to shed light on the details, but basically above a certain speed, a turbofan engine will suffer stagnation "stall" if not managed properly, a compressor stall will develop, and a loud bang result.

If I understand correctly, the primary limiting factor is the exhaust exit velocity, which goes down as the bypass ratio goes up. Thrust is determined by how fast the exhaust gas is moving relative to zero airspeed, so an aircraft loses thrust rapidly as it approaches the relative speed of the exhaust.

count_to_10 wrote:

neurotech wrote:

alloycowboy wrote:

The F-35 is more then capable of reaching over Mach 2 if you look at it's thrust to weight ratio numbers. How ever their are two things preventing this. The first would be its Diverterless Air Intakes and second would be its stealth coatings. Also there is no real pratical need to go beyond mach 1.6 for a jet fighter as the infared signature gets so large that the aircraft becomes easy prey for an infared missile.

Actually, I thought it was the higher bypass engine and relative inefficiency at higher mach numbers. The larger fan does not produce the required thrust offset to get to Mach 2+ flight. That_Engine_Guy might be able to shed light on the details, but basically above a certain speed, a turbofan engine will suffer stagnation "stall" if not managed properly, a compressor stall will develop, and a loud bang result.

If I understand correctly, the primary limiting factor is the exhaust exit velocity, which goes down as the bypass ratio goes up. Thrust is determined by how fast the exhaust gas is moving relative to zero airspeed, so an aircraft loses thrust rapidly as it approaches the relative speed of the exhaust.

I like to think of it as giving the F-35 a lower gear-ratio than the F-22, but who knows what might be accomplished as the engine control software develops.

1st503rdsgt wrote:

Then again, the F-22's top speed was given as Mach 1.8 for quite awhile as I recall; so who knows what the F-35 is really capable of. Rumor has it that the thing is quite capable of supercruise (despite its engine design), but that LM and the USAF could get into trouble if it does (Congress didn't want to pay for that capability), which why the USAF raised the standard for supercruise to the rather arbitrary Mach 1.5.

You don't get in trouble when you exceed KPPs. KPPs are the minimum goal to be attained. By defining supercruise as M1.5 or greater, LM can still say that the F-35 doesn't supercruise, if it only reaches M1.49(not that I think that's the case) on dry thrust. It doesn't mean that it can't exceed M1 though.

Last edited by 1st503rdsgt on Sep 02, 2012 - 07:24 PM; edited 1 time in total

wrightwing wrote:

1st503rdsgt wrote:

Then again, the F-22's top speed was given as Mach 1.8 for quite awhile as I recall; so who knows what the F-35 is really capable of. Rumor has it that the thing is quite capable of supercruise (despite its engine design), but that LM and the USAF could get into trouble if it does (Congress didn't want to pay for that capability), which why the USAF raised the standard for supercruise to the rather arbitrary Mach 1.5.

You don't get in trouble when you exceed KPPs. KPPs are the minimum goal to be attained. By defining supercruise as M1.5 or greater, LM can still say that the F-35 doesn't supercruise, if it only reaches M1.49(not that I think that's the case) on dry thrust. It doesn't mean that it can't exceed M1 though.

If I were to guess, the max AB speed without the heavy A2G weapons may eventually be in the 1.8-2.0 range, with with the possibility of just nudging past 1.0 with dry thrust. Then again, I'm no engineer, so maybe not; but I do know that Jane's paper statistics don't tell nearly the whole story when it comes to aircraft performance, which is affected by a host of factors that include air temperature, air density, weight, CG, and drag from any external stores. Even a soft breeze can affect range by several miles. Heat issues can also play a part if one wants to make the planes last as long as possible and reduce maintenance costs.

In any case, the ability to carry so much weapons and fuel internally means that the F-35 will be able to use more of its flight envelope more of the time than previous fighters, which translates into better real-world performance.

The actual installed thrust of an engine also depends on how well the engine is integrated into the airframe but I'm not going to talk about that since I assume a lot of CFD work was done to ensure things like interference drag and frictional losses in the diffuser are negligible (DSI design should definitely help alleviate these issues vs. legacy inlet systems) so I'm sure F-35 is quite well off in that regard.

Count to 10 is correct in that exhaust velocity matters a lot in the realm of thrust. Performing a control volume analysis of an engine and evaluating the conservation of momentum of a gas (in this case air) will result in uninstalled thrust being essentially the equation of net thrust given in the wiki article here: http://en.wikipedia.org/wiki/Turbojet

That said with high bypass ratios there is a much larger mass flow rate of air going around the core so less fuel is burned but a lot of the mass flow rate of air at the exit of a higher bypass ratio turbofan is just bypass air that is at a relatively low exhaust velocity compared to the fuel/air combo mass flow rate from the core. As bypass ratio increases the average exhaust velocity of the total mass flow rate of everything coming out of the exhaust of the engine goes down. As a result if you go to supersonic speeds with the F-135 you will most definitely encounter the situation where the force of the exhaust is countered by what's called "ram drag" created by the fact that there's air mass flow entering the engine inlet at a very high speed (it's slowed down to subsonic via shocks and isentropic compression from the bump surfaces on the DSI structure but law of momentum conservation prevails and those shocks will hurt the performance as well) and since the exhaust isn't very high in velocity compared to the exhaust of the F-119 engine and fuel doesn't add much to the mass flow rate then you will reach zero net thrust well before, say, an F-22 does. I am neglecting drag on the airframe here for simplicity.

There's also the fact that the diverterless supersonic intakes have only been tested to about Mach 2 on the F-16 so I believe that means that if you go faster it might be too difficult for the bump compression surface to generate the sufficient pressure gradients needed to divert the increasingly thick forebody boundary layer (its mach number dependent IIRC) away from entering the inlet and therefore you might get large turbulent boundary layers separating from the bump and diffuser walls and causing enormous flow distortions on the engine face at aircraft mach numbers above mach 2. These distortions hurt stagnation pressure recovery which is a big deal since the ratio of stagnation pressure to ambient pressure is a big factor in engine and nozzle performance. Not only that but these distortions might also cause the inlet to unstart which only raises drag, lowers mass flow rates to sub-optimal levels, etc.

tacf-x wrote:

The actual installed thrust of an engine also depends on how well the engine is integrated into the airframe but I'm not going to talk about that since I assume a lot of CFD work was done to ensure things like interference drag and frictional losses in the diffuser are negligible (DSI design should definitely help alleviate these issues vs. legacy inlet systems) so I'm sure F-35 is quite well off in that regard.

Count to 10 is correct in that exhaust velocity matters a lot in the realm of thrust. Performing a control volume analysis of an engine and evaluating the conservation of momentum of a gas (in this case air) will result in uninstalled thrust being essentially the equation of net thrust given in the wiki article here: http://en.wikipedia.org/wiki/Turbojet

That said with high bypass ratios there is a much larger mass flow rate of air going around the core so less fuel is burned but a lot of the mass flow rate of air at the exit of a higher bypass ratio turbofan is just bypass air that is at a relatively low exhaust velocity compared to the fuel/air combo mass flow rate from the core. As bypass ratio increases the average exhaust velocity of the total mass flow rate of everything coming out of the exhaust of the engine goes down. As a result if you go to supersonic speeds with the F-135 you will most definitely encounter the situation where the force of the exhaust is countered by what's called "ram drag" created by the fact that there's air mass flow entering the engine inlet at a very high speed (it's slowed down to subsonic via shocks and isentropic compression from the bump surfaces on the DSI structure but law of momentum conservation prevails and those shocks will hurt the performance as well) and since the exhaust isn't very high in velocity compared to the exhaust of the F-119 engine and fuel doesn't add much to the mass flow rate then you will reach zero net thrust well before, say, an F-22 does. I am neglecting drag on the airframe here for simplicity.

There's also the fact that the diverterless supersonic intakes have only been tested to about Mach 2 on the F-16 so I believe that means that if you go faster it might be too difficult for the bump compression surface to generate the sufficient pressure gradients needed to divert the increasingly thick forebody boundary layer (its mach number dependent IIRC) away from entering the inlet and therefore you might get large turbulent boundary layers separating from the bump and diffuser walls and causing enormous flow distortions on the engine face at aircraft mach numbers above mach 2. These distortions hurt stagnation pressure recovery which is a big deal since the ratio of stagnation pressure to ambient pressure is a big factor in engine and nozzle performance. Not only that but these distortions might also cause the inlet to unstart which only raises drag, lowers mass flow rates to sub-optimal levels, etc.

+1 Informative; I Wonder if I go into too many details in posts sometimes.

The exhaust velocity is also a factor. DSIs can work over Mach 2.0 but like all jet engine intakes, has to be tuned for the airflow volume to match the flight profile and engine design.

Forum: General F-35 Forum

The best record in the flight test