Forum: General F-35 Forum

Does somebody knows why the JSF wasn’t design as a low wing loading fighter, if even the AF states that low wing loading is crucial for a fighter???

F-16.net Sponsor

The wing-loading calculations for the F-35 do not include the large amount of body lift that its design has. The calculations also look at the F-35 fully fueled, which it will not be by the time it gets into combat.

That spud, is quite the relative claim.
I can't see how the F-35 include a large amount of body lift if you compair it to other aircraft design..
And your last statment also adhere to all other modern fighters, they can eighter drop, burn or vent fuel before an engagement.
So the wing load stays pretty much the same for all aircraft.

You have to compare conditions where the combat takes place, not stats standing on the runway.

As AVM Osley said:

Air Vice Marshall Osley: The design criteria of the F35 provided that it would have representative performance similar to the advanced legacy aeroplanes. When you get down to this level you need to make sure you are comparing apples with apples. For instance, with some of those figures, if you say that you want 50 per cent of remaining fuel in the aircraft, the F16 normally flies with tanks. With some of the acceleration numbers they have used a clean aeroplane with half fuel. If you had a clean F16 with half fuel, all it is going to do is accelerate, declare an emergency and land with minimum fuel, because it has almost no fuel. The F35 carries a lot of fuel internally and so 50 per cent fuel is actually more than the total internal fuel of an F16.

http://parlinfo.aph.gov.au/parlInfo/dow ... 8e/0000%22

Just for fun, it is very crude; at the pointy end:

F-35A
50% internal fuel (9200lb), 2 x amraam, wl = 85lb/ft^2

F-16C, blk30, gas bags jettisoned
100% internal fuel (6500), 2 x amraams, wl = 88lb/t^2

Seems that the F-35 should be ble to handle itself.

F-35 engine also consumes more fuel than F-16's.

And one reason for the topic question, JSF is more of a striking fighter than agile fighter. Fuel, range, 2000 lb JDAM are priority.

Interesting. That internal fuel load is probably going make a whole lot of comparative calculations look odd.

I'm no engineer, but my understanding is that wing-loading is an over-simplistic measurement for predicting the performance of modern fighters.

Airfoil, sweep angle, LERX, body lift, aspect ratio, canard vs tail...

Where does the Air Force call wing loading "crucial"?

The main thing wing loading is relevant to is making sharp turns, but other factors go into that, too. For example:

What about cruise L/D? Or did they just pack it full of gas to get range? I saw a chart showing most 4th gen around 8-10 for subsonic and around 6 for supersonic L/D. I'd like to know what the F-22 and F-35 are. It would be really neat to see the A vs the C model for both.

I've thought about this before and performed a little experiment to understand why the F-35's underside is shaped like it is even though its not ideal for all-aspect stealth.

After a spot of reading and a very rough simulation came up with this:

The underside of the aircraft in front of the centre of lift and centre of balance is a generally concave shape with lots of wide, flat surfaces. As the aircraft starts pulling a higher angle of attack, the concave shape and the angles of certain surfaces such as the bottom of the intakes cause a buildup of pressure forward of the CL.

Immediately behind the CL, the fuselage tapers off towards the back and toward the sides and the fuselage features are all convex which decreases pressure at the rear of the aircraft under high aoa.

Most other aircraft designs are not like this because many have two, smaller diameter engines and their fuselages are not as deep which doesn't allow for as much tapering toward the back. For aircraft with flat undersides under high aoa the pressure on the rear partially counters the pressure on the front and makes it more difficult for the rear of the aircraft to pivot around the CL (tailslide).
With the F-35, its centre of pressure moves forward significantly (comparitively) as the angle increases, giving the elevators more leverage to pitch the aircraft.

If you bend a piece of paper or cardboard in roughly the same shape as the F-35's underside then generate some wind at a moderate angle to the bottom surface, it wants to pull up. Think this shaping has a lot to do with why it can maintain a crazy angle of attack that has been quoted...

...but I guess we'll see when it shows its stuff at an airshow.

Probably all completely wrong, who knows.

1st503rdsgt wrote:

I'm no engineer, but my understanding is that wing-loading is an over-simplistic measurement for predicting the performance of modern fighters.

Exactly. The F-106 has a lower wing loading than the F-15, so that right there immediately discredits the notion that wing loading is the sole determining factor of how maneuverable a fighter is. In that particular comparison the low aspect ratio of the F-106's delta planform ensures that high energy losses will be incurred from induced drag as vortices on the wingtips cause flow to spill over cause and spanwise flow over the top of the wing which lowers the effective alpha. In the subsonic regime that is a SERIOUS PROBLEM! There's also the fact that any high alpha maneuver will cause flow separation on the top surface of the wing which will kill the F-106's ability to control itself as it will lose the flow circulation over the elevons at the very moment said flow separation occurs due to being inconveniently placed at the aft end of the delta planform and being subjected to the same angle of attack that the wing sees.

Of course, that comparison is quite unfair as F-106 was meant to beeline to high supersonic speed and high altitude to launch nuclear Genies at Russian bombers while F-15 is optimized for transonic maneuvering.

Allow me to use Carlo Kopp's logic against him. In an APA article Kopp stated that the Eurofighter Typhoon was inferior to the F-15 due to having an inferior internal fuel load and having an increased dependence on external fuel tanks.

With a larger internal fuel load and lack of dependence on drag-inducing tanks which all results from the design requirement for something that needs to have an outstanding mission radius while being Low Observable, the F-35, when engaged with an enemy CAP formation of, say Eurofighter Typhoons or Rafales, the F-35 will likely have burnt up a lot of its internal fuel and as such will most certainly being working with a fuel load of about 50% capacity while the Typhoons and Rafales might have just recently disposed of their tanks and as such will be working with full 100% internal fuel.

What I am getting at is that the F-35 would surely be burning a lot of its fuel away during its ingress while similar-sized fighters like F-16's, Typhoon's, Rafales, Legacy Hornets, etc. would need fuel tanks just to patrol similar sized mission radii. As such in a dogfight the F-35 will be at the advantage of not having as high of a percentage of internal fuel weighing it down due to needing tanks on the ingress. That and the lack of drag that results from not having external stores will ensure that less energy will be bled off when performing high-G maneuvers as opposed to those other fighters.

Even when energy is bled off the drop in internal fuel load will leave the F-35 with a favorable T/W ratio to get energy back. Also with a similar weapons load the F-35 will most certainly not have to crank up the alphas as much to sustain a turn as the Eurocanards thanks to being so massive relative to the payload being carried in comparison to said eurocanards. This of course means that the weight differential between loaded and unloaded weight for the F-35 wouldn't have as high of an impact on its maneuvering capabilities as the eurocanards as the increases in induced drag resulting from alpha increases needed to sustain turns won't be as bad.

I say I am using Kopp's logic against him in the sense that Kopp completely ignores these properties inherent to the F-35 when comparing the eurocanards to the F-35 while I am bringing said properties to light.

Canard's vs. Tails have their advantages and disadvantages with neither side being truly "superior" in all of actuality. To make any firm judgement on that part would be quite foolish for a soon-to-be engineer like me.

Of course there is the fact that there are various methods of energizing the flow circulation over airfoils at high alphas so as to improve control and maneuver characteristics at said high alphas. These methods must be taken into account. Like I said earlier whether they be LEVCONs or simple chines they all have advantages and disadvantages.

Having the ideal airfoil shape and sweep angle for the transonic regime is certainly a plus. After all, transonic is the regime that modern fighters are generally optimized to maneuver in anyway. It is nice to have a supercritical type wing with a decent sweep so as to reduce wave drag by weakening the normal shocks that tend to form on the surface. By smoothing the transition from supersonic flow to subsonic flow in (accordance with adjusting to the freestream air properties) via a supercritical type airfoil design wave drag can be substantially reduced and the wake doesn't become quite so turbulent so as to disturb the flow over potential control surfaces aft of the wing. That coupled with the lower freestream mach number the airfoil "sees" thanks to being swept will surely lower wave drag by delaying the freestream mach number needed to start making normal shocks form.

Essentially the point of this post is that it is VERY superficial to state that the F-35 sucks at maneuvering just because it apparently has a low wing loading. Also, bear in mind that Spudman is right. Any engineer with experience like johnwill will tell you that simple wing loading figures do not take into account the actual lift that the entire airframe generates as a whole.

Heck, just look at the time when an F-15 lost a wing and was able to safely land thanks to body lift! Certainly wing area isn't everything right?

haavarla wrote:

That spud, is quite the relative claim.
I can't see how the F-35 include a large amount of body lift if you compair it to other aircraft design..

May I refer you to johnwills post on the first page of the thread i've linked, he actually knows a thing or two about such matters.

http://www.f-16.net/f-16_forum_viewtopic-t-7491.html

calel wrote:

Does somebody knows why the JSF wasn’t design as a low wing loading fighter, if even the AF states that low wing loading is crucial for a fighter???

Because the wing loading doesn't take into account the body lift, which results in a much lower loading.

megasun wrote:

F-35 engine also consumes more fuel than F-16's.

If......the F-16 is flying clean. If the F-16 has 2 EFTs, 2 JDAMs, 2 AMRAAMS, Sniper/Litening pod, Jammer pod, HTS pod, then this isn't necessarily the case

Quote:

And one reason for the topic question, JSF is more of a striking fighter than agile fighter. Fuel, range, 2000 lb JDAM are priority.

This is also inaccurate. The F-35 will 5000lbs of weapons, has similar agility to a clean F-16.

Forum: General F-35 Forum

JSF High Wing Loading: why?