The F-35 Thread

[NineLine]

L8hMqOqauz0

[TimeKilla]

Great footage SiThSpAwN!

 

:worthy:

[tflash]

Reuters: US Navy to buy fewer F-35

 

http://www.reuters.com/article/2014/03/04/lockheed-fighter-idUSL6N0M101N20140304

[aaron886]

If you have such doubt about posting it, why do it? It's definitely inciteful, but I doubt it will be removed. It's illogical, anyway, but that doesn't stop people caring.

[KillarZ]

Because I thought it was funny and wanted to share. I could care less about the "what plane is actually better debate". Some people would try to turn it into this but it's just something I wanted to share for a good laugh and move on.

Edited March 5, 2014 by KillarZ

[Chazz_BMF]

Dont know if this have been posted before, but some rather interesting views on the F-35.

 

[GGTharos]

They have been posted before, they have been debated about before, and they have been found to be bunk.

[Weta43]

Maybe his conclusions are extreme, but not everything he says is untrue.

Airforces have been saying since the Vietnam war that the era of BVR combat has arrived, and every conflict since has made the claim ‘premature’ (unless you’re prepared to wear friendly fire – which appears to have been the case in some conflicts).

 

The JSF does have a wing loading that’s between 30% (empty) and 50% (max takeoff) higher than an A-10 and 40% higher than an F-15 empty or full.

 

What does that mean ? What does a smile on a dog mean ? (it means something, maybe even what you think it does)

 

Lets assume most of the criticisms levelled against it as a strike aircraft are unjust.

 

Will it replace the A-10 at CAS ?

 

It will if that’s what it’s tasked with after the A-10 is retired, but if you assume a JSF range of 2220km ( ‘clean’ - guess where that number came from :) ), and a cruise speed of 883km/h (480 knots) that gives you a loiter time of 61 minutes & 10 minutes combat assuming a 460km combat range & 20 minutes safety margin on fuel. With the same combat range the A-10 has 112 minutes loiter & 10 minutes combat. That’s with the JSF capable of 1 gun run and a few SDB’s internally. You can carry externals and fuel, but that mean's you arent worried about stealth, in which case you could have sent the the A-10, carried what you wanted & stayed for twice as long...

The A-10’s cannon may not be the tank busting thor’s hammer it once was, but it does a lot of good CAS work. It has something like 1200 rounds of 30mm on board, and the F-35 has 180 rounds of 25mm.

 

After reading this thread (using a tramping analogy), the F-35 is a spork.

 

The spork is cheaper than a spoon and a fork bought separately. A spork is a better spoon than a fork, and a better fork than a spoon. It’s great when you can’t carry both a fork and a spoon (budgetary reasons ?), but it isn’t as good at being a spoon as a spoon or a fork as a fork.

The F-35 is a spork

That’s alright - Life’s full of compromises…

Will it go down as the F-105 of the 21st century ? I don't think it's that bad.

For the meantime its stealth & radar probably give it an advantage over most 4th generation fighters it might face in BVR, but it’s not a good 5th generation A2A fighter & if it closes with a 4th gen fighter it better hope those ASRAAMs work well..

It’s probably stealthy enough to be an effective strike aircraft against most foreseeable opponents for the next while - as long as you don’t want to strike too hard because of its limited internal stores.

You can hang stores off it if you have authority over the airspace, but if you have authority over the airspace you don’t need a stealthy delivery platform…

& it can turn its hand to CAS, but it won’t do as good a job as if you could afford a dedicated CAS aircraft.

It seems to me it’s proponents had one eye on the conflicts of the present, and one on possible future (more capable) opponents, and thought they'd better fill the export vacume for 5th gen aircraft before someone else does…

Edited March 8, 2014 by Weta43

[Eihort]

If you know Spey, you know Boyd, and then you know where they're coming from, and from that perspective, what he's saying makes a certain kind of sense.

 

The problem is, those views are 30 years old.

[wilky510]

The JSF does have a wing loading that’s between 30% (empty) and 50% (max takeoff) higher than an A-10 and 40% higher than an F-15 empty or full.

While wing loading is important to aircraft, the new crazy kid thing these days is body lift. Which has me baffled at Mr. Spreys comments about wing loading. His own aircraft, (the f-16) uses basically the same layout as the F-35, high wingloading, but massive body lift... If wing loading was the end all to be all. The F-4 should apparently fly circles around the F-16, and the MiG-29 (which has one of the highest wing loadings out there).

 

Also, if you do 2 AAM and 8000lbs; compared to other aircraft, the F-35, it has one the highest T:WR out there. The F-35 is carrying a godly amount of fuel for it's overall weight.

 

There is so much hate surrounding this F-35 Program that it's sickening, the press/media have put it in a bad spotlight that it can't seem to return from. The F-22 was put in the same spotlight, but it IMO one of the best aircraft ever built.

[Exorcet]

The JSF does have a wing loading that’s between 30% (empty) and 50% (max takeoff) higher than an A-10 and 40% higher than an F-15 empty or full.

The F-35 is good when it comes to wing loading.

 

At 29300 lbs per 460 ft^2 of wing it has as much wing as the F-16. Then it gets better with weapons because the % increase in weight is less. And after that it doesn't have to suffer a drag penalty just for carrying more than a cannon.

 

The wing loading argument is bad since wing loaded is so vaguely related to performance, but even if WL was definitive, the F-35 would beat the F-16.

[Faith]

The wing loading argument is bad since wing loaded is so vaguely related to performance, but even if WL was definitive, the F-35 would beat the F-16.

 

Wing loading is directly in the performance equations for rate of turns. Therefore the loading is not "vaguely related" so much as directly related to fighter performance.

 

In short the Radius of a coordinated turn has the wing loading in the equation so any differences will in fact affect the performance.

[Exorcet]

Wing loading is directly in the performance equations for rate of turns. Therefore the loading is not "vaguely related" so much as directly related to fighter performance.

 

In short the Radius of a coordinated turn has the wing loading in the equation so any differences will in fact affect the performance.

 

That would be "lift loading" not wing loading, unless you were talking about tubes with wings style planes that haven't been in use as fighters for a while now.

 

In the turn, if you want to sustain speed, you need to overcome drag, which for constant wing loading is impacted by factors like airfoil, aspect ratio, and wave drag (if fast enough). Outside of turns, which is still "performance", these factors still have an effect, particularly in range and acceleration.

 

Wing loading itself can be highly misleading. Despite the large WL advantage of the F-4, the following generation teen fighters are more agile. More lift despite more wing loading, more ability to overcome drag (this admittedly is partially down to powerplants being much better, but the effect is the same as significantly lowering drag).

[Faith]

That would be "lift loading" not wing loading, unless you were talking about tubes with wings style planes that haven't been in use as fighters for a while now.

 

In the turn, if you want to sustain speed, you need to overcome drag, which for constant wing loading is impacted by factors like airfoil, aspect ratio, and wave drag (if fast enough). Outside of turns, which is still "performance", these factors still have an effect, particularly in range and acceleration.

 

Wing loading itself can be highly misleading. Despite the large WL advantage of the F-4, the following generation teen fighters are more agile. More lift despite more wing loading, more ability to overcome drag (this admittedly is partially down to power plants being much better, but the effect is the same as significantly lowering drag).

 

From "Introduction to Aerodynamics and Aircraft Performance" by James F. Marchmann, III

 

Turning Radius R = [2W/(rho*g*S*Cl)]*[n/(n^2-1)^0.5]

Which is in fact "wing loading" and not "lift loading". He summarizes by saying "High wing loading (W/S) will also allow a tighter turn." Also that "It should be noted here that if a small turning radius is desired a high load factor and lift coefficient are needed and low altitude will help."

 

Could you please cite your source for your above statements so everyone can evaluate the data independently? If you are interested in the above equation's derivation I suggest reading the text.

 

The equation for rate of turn is

domega/dt = g{[(rho*S*Cl)/(2W)]^0.5*[(n^2-1)/n]^0.5}

which also features "wing loading".

 

These equations are then used to find V-n diagrams that describe your structural and aerodynamic limitations.

 

This obviously does not consider things such as thrust vectoring or flight controls, it is purely an elementary expression of the basic governing equations.

Edited March 8, 2014 by Faith

[Exorcet]

From "Introduction to Aerodynamics and Aircraft Performance" by James F. Marchmann, III

 

Turning Radius R = [2W/(rho*g*S*Cl)]*[n/(n^2-1)^0.5]

Which is in fact "wing loading" and not "lift loading". He summarizes by saying "High wing loading (W/S) will also allow a tighter turn." Also that "It should be noted here that if a small turning radius is desired a high load factor and lift coefficient are needed and low altitude will help."

Are you sure he did not say low?

 

The equation comes from the equation for circular motion where accel is v^2/R. Multiply by mass to get force. The force in this case is lift. The equation assumes all the lift is coming from the wings. It also ignores the ability to hold the turn which requires looking at thrust and drag.

 

 

Could you please cite your source for your above statements so everyone can evaluate the data independently? If you are interested in the above equation's derivation I suggest reading the text.

 

My statements aren't directly taken from text, they're my own applications of physics. For an aircraft in motion it all basically comes down to F=ma. The wing loading equations are ignoring a component (or 2) of F which is the vector sum of lift, weight, drag, thrust, and side forces.

 

If you want a source the effects of the parameters I mentioned (airfoil, aspect ratio, [you can throw in wing sweep as well]) see

 

Anderson, John D. Jr, Fundamentals of Aerodynamics (I don't have it on me so I can't give pages, but according to Wikipedia equation 5.63 matches the Wiki equation for drag including induced drag)

 

The equation for rate of turn is

domega/dt = g{[(rho*S*Cl)/(2W)]^0.5*[(n^2-1)/n]^0.5}

which also features "wing loading".

 

These equations are then used to find V-n diagrams that describe your structural and aerodynamic limitations.

As before the equation isn't enough to give you total aircraft performance on its own. It's useful in cases where you can ignore other variables (like comparing F-35 variants to each other), but is less reliable the more diverse the planes you're comparing get.

 

Now I will give you that you can use these equations to make estimates, but there is no guarantee that the ranking you get will match the ranking seen in flight envelope diagrams.

[Basher54321]

The JSF does have a wing loading that’s between 30% (empty) and 50% (max takeoff) higher than an A-10 and 40% higher than an F-15 empty or full.

 

What does that mean ? What does a smile on a dog mean ? (it means something, maybe even what you think it does)

 

 

The reason you are getting this bit wrong is that you are trying to compare basic wingloading!!

 

Over the weight range F-35A is comparable to the F-16C B50 (The F-35B/C have very different figures!) - However you CANNOT compare old airframe design concepts like the F-15 with newer like the F-35 using basic wingloading.

 

Here is why - the F-16/F-22/F-35/Su-27 derive a lot of lift from Vortex and lifting tails that the given wingloading figure doesn't take into account - this is what can give them an advantage in certain parts of the flight envelope.

 

The Sprey video is a joke - and yes people who have limited knowledge on the subject are easily fooled!.

 

After seeing the newest release its part of an agenda - F-35 still conforms to Boyds theories at the end of the day!!

Edited March 8, 2014 by Basher54321

[Faith]

Are you sure he did not say low?

 

Yes I am sure he did not say low.

 

The equation comes from the equation for circular motion where accel is v^2/R. Multiply by mass to get force. The force in this case is lift. The equation assumes all the lift is coming from the wings. It also ignores the ability to hold the turn which requires looking at thrust and drag.

 

That is technically not the correct equation for circular motion. V^2/R is the equation for centripetal acceleration, not total circular acceleration. To get the equation for circular acceleration you have to add the tangential accceleration term and sum it with the centripetal.

 

 

My statements aren't directly taken from text, they're my own applications of physics. For an aircraft in motion it all basically comes down to F=ma. The wing loading equations are ignoring a component (or 2) of F which is the vector sum of lift, weight, drag, thrust, and side forces.

 

If you want a source the effects of the parameters I mentioned (airfoil, aspect ratio, [you can throw in wing sweep as well]) see

 

Anderson, John D. Jr, Fundamentals of Aerodynamics (I don't have it on me so I can't give pages, but according to Wikipedia equation 5.63 matches the Wiki equation for drag including induced drag)

 

In Anderson's book you mentioned equation 5.63 (page 440 in the fifth edition) is

[size=4]C[/size][size=1]D[/size] = Cd + [size=4]C[size=1]L^2/pi*e*AR[/size][/size]

which is an equation for drag coefficient using a parabolic variation of CD vs CL which you cannot always assume, especially without data for the specific structure geometry.

 

As before the equation isn't enough to give you total aircraft performance on its own. It's useful in cases where you can ignore other variables (like comparing F-35 variants to each other), but is less reliable the more diverse the planes you're comparing get.

 

The equation I gave was for a coordinated turn and would be in fact enough for an F-35 since it is derived from fundamental forces and is not specific to any hardware configuration.

 

Now I will give you that you can use these equations to make estimates, but there is no guarantee that the ranking you get will match the ranking seen in flight envelope diagrams.

 

I don't think you have seen the final V-n diagrams I was referring to since they incorporate several other factors into their plots, not just the equation I gave.

 

Please include your own "application of physics" derivation so everyone can examine it instead of making claims that are difficult to verify.

[Weta43]

High wing loading (W/S) will also allow a tighter turn

 

This is true only if you are talking about applying the wing loading to the same aircraft at the same speed. A tighter turn in plane A at a given speed will result in higher wing loading on that plane than a wider turn in the same plane at the same speed.

[Faith]

This is true only if you are talking about applying the wing loading to the same aircraft at the same speed. A tighter turn in plane A at a given speed will result in higher wing loading on that plane than a wider turn in the same plane at the same speed.

 

That equation is for a coordinated turn. The W is weight, not Lift or centripetal force in a turn. I think you are confusing my statements with a high performance turn which is governed by your elevator effectiveness among other things. A high performance turn would be completely different.

[Exorcet]

-Then I must be doing something wrong, if W goes up, so does R.

 

-Well the tangential term was just zero in my case. WL can't tell you about the tangential acceleration because it knows nothing about drag directly and nothing about thrust.

 

-When does the equation not work?

 

-Right, and ranking aircraft performance by turn radius using your equation won't necessarily produce the same ranking when looking at the flight envelope because of things like g limit and stall.

 

 

Please include your own "application of physics" derivation so everyone can examine it instead of making claims that are difficult to verify.

 

I did. WL ignores thrust/drag so using it alone you can't get an idea of how the aircraft will actually accelerate.

 

What claim was hard to verify?

[aaron886]

That equation is for a coordinated turn. The W is weight, not Lift or centripetal force in a turn. I think you are confusing my statements with a high performance turn which is governed by your elevator effectiveness among other things. A high performance turn would be completely different.

 

Relatively disconnected from "elevator" effectiveness. That's hardly a problem in tactical jets these days.

[Faith]

There is no point arguing this unless you show the exact equations you are using to come to these conclusions and for the specific cases where your assumptions are valid. Aerodynamics and Flight Control are very complicated subjects and do not lend them selves well to generalities as anyone who has studied them in depth can attest.

 

I think you missed what I was specifically referring to - a specific coordinated turning maneuver case.

[aaron886]

Exorcet, I'm sorry, but it seems like you're just talking a whole lot of nonsense.

 

Faith you've done a good job finding a formula to describe turn radius, but you don't seem to understand the practical application. I get a whiff of BS when I read your posts, so you might hop off the high horse. A "high performance turn" is not completely different, it can still be approximated by the same equation you used before. Bank angle, CL, and G necessarily increase, and by including the changes to these coefficients (CL changing with a variety of factors that would require extensive testing to determine,) you can effectively describe a wide variety of turning performance scenarios.

 

It has little or nothing to do with "elevator" effectiveness (available pitch moment) in a modern tactical jet. Nothing designed with that kind of maneuvering potential is going to be limited in the heart of the envelope by control deflection, rather by deficiencies or compromises in wing loading (read: effective lift production,) thrust to drag ratio (sustained turning performance,) or structural integrity. (Think Tomcat with F110s... so much potential limited by a 6.5G airframe.)

 

The JSF does have a wing loading that’s between 30% (empty) and 50% (max takeoff) higher than an A-10 and 40% higher than an F-15 empty or full.

 

What does that mean ?

 

It means there is a potential for poor sustained turn performance, but that's not something any of us can determine. That's the stupidity of making wild conjectures about the performance of an aircraft not yet well known. The F-35 could have very effective aerodynamic performance, producing a higher coefficient of lift per square meter of wing. It most certainly utilizes some wizardry that previous generations of fighters did not. Just visually compare the design of the wings... that should be enough to tell you we don't know all that much.

[Weta43]

You're over thinking it - it's not rocket science, a little bit of thought about it will do better than pages of formulae

 

Assume an object moves at a constant speed.

The force required to turn that object around an infinitely larger circle is infinitely small (you don't need turning force to move in a straight line).

Any turn 'curve 1' tighter than a straight line needs more force than a straight line.

Any curve 'curve 2' that's tighter 'curve 1' requires more force than the first.

 

If the object that's doing the turning is an aircraft (& assuming we're not talking thrust vectoring) the 'turning' force is provided by the wings.

The wings have a fixed area.

If the force they provide ( to turn a tighter turn ) goes up, the force per unit area goes up : the wing loading goes up ...

 

Same as a puck on an air-table doing circles constrained by a string.

Same tangential speed + shorter string = more tension in the string

same diameter string + more tension = more force per unit area...

 

 

 

If you have two pucks of different masses, both with the same tangential speed, constrained by similar strings of a fixed ultimate tensile strength, you can pull the lighter object into a tighter circle before the string fails.

 

So,

 

If 2 aircraft have different mass, but are only able to generate the same maximum wing loading, the lighter one will turn a tighter turn.

 

 

Take 2 aircraft of the same mass (& speed) with the same general design and basic aerofoil design, but of different wing areas (one's wings are scaled up slightly)

Same aerofoil ~ same maximum available force per unit of wing area (wing-loading) before you stall it.

Maximum force for the turn = maximum available force per unit are * wing area.

Bigger wing generates more force.

More force for the same mass = tighter turn/

All other things being equal: bigger wing = lower wing loading for a given turn radius = tighter turn possible.

 

It's not complicated...

Edited March 9, 2014 by Weta43

[Exorcet]

There is no point arguing this unless you show the exact equations you are using to come to these conclusions and for the specific cases where your assumptions are valid.

First, what's my conclusion:

 

Wing Loading is not a direct one size fits all when it comes to aircraft performance, and this would include looking at sustained turn performance in particular.

 

For that to be true, I need to show that there are factors that would impact sustained turning outside of wing loading.

 

What's a sustained turn? Let's assume it's a turn in a 2D plane of constant radius perpendicular to gravity where the tangential velocity is constant.

 

The aircraft's acceleration is V^2/R, force is MV^2/R. The force holding the plane in the turn is lift.

 

F = L*sin(o) [o being the bank angle]

 

L = .5*rho*V^2*CL*S

 

.5*rho*V^2*CL*S*sin(o) = MV^2/R

 

R = 2M/(.5*rho*V^2*CL*S*sin(o)) = 2W/(g*.5*rho*V^2*CL*S*sin(o))

 

So according to this, low W (which leads to low W/S) makes R smaller. However V is pulled out of no where. The aircraft can only sustain V is drag = thrust.

 

CD = CD0 + CDw + CDi

 

Assume CD0 is constant or close enough to constant, let's make CDw = 0

 

CDi = CL^2/pi*e*AR

 

If S is fixed, so is CL and W/S

 

CDi goes down when AR goes up, so with constant wing loading the plane with higher AR requires less thrust to maintain the sustained turn.

 

If thrust is finite you will reach a CL or V that makes the drag overcome the engine thrust and you can no longer sustain the turn.

 

For fighters a non zero CDw is very likely, but again this can vary with constant W/S.

 

 

Now for instantaneous turn, W/S is a big factor since drag doesn't matter and you can bleed as much speed as you want.

 

 

EDIT

 

And I forgot to mention that assuming all lift comes from the wing is incorrect anyway, so wing loading without considering lift from the body isn't accurate in the first place.

 

EDIT 2

 

It means there is a potential for poor sustained turn performance, but that's not something any of us can determine. That's the stupidity of making wild conjectures about the performance of an aircraft not yet well known. The F-35 could have very effective aerodynamic performance, producing a higher coefficient of lift per square meter of wing. It most certainly utilizes some wizardry that previous generations of fighters did not. Just visually compare the design of the wings... that should be enough to tell you we don't know all that much.

So would the F-104, but looking at CDi this means more drag. In the case of the F-104 this was a fair trade for lower CDw, but the plane was terrible at subsonic flight. The F-35's main advantages could be body lift lowering the effective W/S, low sweep increasing CL vs alpha, and low CDw.

Edited March 11, 2014 by Exorcet