larrysogla

I have been going to military airshows since 1984 and always there will be either an F-14, F-15, F-16 or F-18 doing a very low level 360 deg.(full circle) turn with afterburners going and..........the wings are banked at 80+ deg. to 90 deg. and the jets do not fall off and nose down.................yet I seem not to see a corresponding rudder deflection to keep the nose up during the extreme banking turn. So how is it done at practically 90 deg. bank during the full circle turn?
Thanks in advance for your valuable reply.
larry

BMatthews

Lots of up elevator and G loads on the pilot.

If the bank is truly 90 then the plane would fall downwards. But at an 85 degree bank and lots of G load the residual lift downwards from that little 5 degree difference is still a lot of lift. There may be a bit of top rudder that results in some knife edge lift as well. Depends on the pilot.

rmh

What is stranger -is flying on of the new small indoor type electrics with as much effective fuselage area as wing area (sometimes ,even more ) The "g forces simly shift from wing to "fuselage"
turns are done with NO banking ,only rudder application and are smooth and as tight as wanted
the bank is seldom used ,as it accomplishes nothin on these designs.

CrateCruncher

My Feedback: (1)

As was said, even a small angle away from 90 degrees vertical can generate a large amount of vertical lift to support the weight of the plane. Can you tell the difference between 88 and 90 degrees observing from the ground. I sure can't. Remember that Lift is generated in proportion to speed squared AND angle of attack so even as the plane slows to perform a tight turn the lift generated can go way up. Often the wing will increase in angle of attack as it turns even though it's not apparent to the observer on the ground or even the pilot. Realize also, the horizontal force felt by the plane and pilot is a result of changing direction (turning) but doesn't help in preventing the plane from falling to earth. (At 90 degrees bank angle the plane will fall to earth no matter how high the horizontal 'g's get.) In fact the way to solve a turn problem mathematically is to make the vertical lift component equal but opposite to the weight of the plane, then set the horizontal lift component equal but opposite to the centrifugal force felt by the plane as a consequence of performing the turn in a separate step, then back into the total lift and bank angle by combining the vertical and horizontal components.

Horizontal Component:
L sin@ = mV^2/R

Vertical Component:
L cos@ = mg

Then divide one equation into the other and solve for the bank angle:
@ = arctan[ V^2/Rg ]

Rotaryphile

According to my calculations, keeping the nose level without top rudder during an 85 degree banked turn would require pulling 11.47G. 88 degrees of bank would dictate pulling 28.65G, which would be briefly possible for a high powered model with a low wing loading, before the resulting rather large induced drag slowed the airplane too much to allow the wing to develop the needed lift.

CrateCruncher

My Feedback: (1)

.......which makes a very strong argument for getting rid of that 180 pound sack of water in the front seat! No way could a human take more than 6 g's without severe hypoxia. Pressure suits help but there are limits. The pilot provides the inputs but the computers "fly" the aircraft making sure he doesn't pull too many g's or stall the wing during a crazy sharp turn.

I vaguely recall watching the "single" Thunderbird doing 360 degree sharp turns while the rest of the team set up for the next maneuver. I doubt if he was banked anywhere near 88 degrees though. It was probably closer to 70 or so and the computers were keeping him outa trouble.

Bozarth

My Feedback: (15)

CrateCrunch - I flew F-16s in the 1990s. The computer limited us to 9.2 g's. The computer did not "fly" the aircraft, we did. The computer made a dynamically unstable airplane feel stable. The computer did not keep us outa trouble. You could fly the airplane into the ground easily by overbanking on a low level - something we stressed alot, especially while on the range. Unfortunately, many F-16 pilots have flown their planes into the ground. How much bank did we use to make the tightest turn - I don't know, we simply looked outside and made sure our lift vector was correct. Too much bank and we descended.

Kurt

Jezmo

I understand what the OP was refering to though. From the ground it certainly looks to be 90 degs. I've also witnessed good pilots in G-suits pull over 10 g's in a 360 deg. turn without blacking out. They were flying edge 540's and if anyone watches the Red Bull air racing series those guys routinely pull around 10 g's in their turn around loops. They are in awesome shape though.

gboulton

My Feedback: (15)

You've clearly never seen the Red Bull Air Races, have you?

CrateCruncher

My Feedback: (1)

OK, I definately got that one wrong. I just Googled "human g limits" and discovered 9 g's is not uncommon for a tight turn in a fighter or aerobatic plane. But the thrust of my point was that the plane could be capable of much more if it were remotely piloted.

gboulton

My Feedback: (15)

Have to agree with you there...no question an airframe could be designed (heck, many already have) capable of withstanding far more G's than a human body could...even such highly trained pilots as fighter jocks, etc.

Then again, that WOULD kinda take something away from the Red Bull series, now wouldn't it?

(Actually...that's not a bad idea...the challenges of modeling the RBARWS in RC would be tremendous...but incredibly cool to overcome *heh*)

FILE IFR

Hypoxia is not the problem of a pilot under a high G load.

in a short description, Hypoxia is oxygen deprivation.. not blood deprivation to the brain.

Bozarth

My Feedback: (15)

Shoe

Hypoxia is absolutely a problem for pilots under high g load. Blood deprivation to the brain will quickly lead to oxygen deprivation (the oxygen deprivation isn't instantaneous because of oxygen stored in the brain tissue). Although "hypoxic hypoxia" (due to insufficient oxygen partial pressure in the lungs) is probably the type of hypoxia most people think about, "stagnant hypoxia" caused by head-to-toe g forces is also a form of hypoxia.

combatpigg

My Feedback: (3)

Without knowing the weight of the aircraft in airshow trim or knowing how much lift is being produced by the fuselage it is impossible to calculate.

BMatthews

Actually the G load for any pure bank angle doesn't depend on aircraft weight. It's simpley a function of the angle and the component vectors if we assume a properly coordinated turn. But there's no doubt that side area lift and any directed thrust will affect the "purity" of the straight G load issue.

combatpigg

My Feedback: (3)

When a plane is flying on the fuselage with no help from the wing, weight does matter ........the lighter the plane, the slower it will be able to fly the circles.

larrysogla

At a 5g turn the 30,000 lb. F-18A(with fuel) is exerting a flying load on the wings and other lifting surfaces equal to 150,000 lbs. of force. How about 10g....it would be a flying load of 300,000 lbs. on a tight turn. It is staggering the amount of load the airframe is carrying. Fighter planes are truly a marvel of engineering..............so again the question of how does the jet fighter keep flying in a 360 degree turn without losing altitude with the jet fighter practically standing on one wing almost at 90 degrees. It seems the really clear definitive answer is yet to come...........perhaps from some military fighter pilot reading and responding in this forum.
larry

HighPlains

My Feedback: (1)

The load is distributed, as is the lift. It's not the same as putting a static load on the airframe.

Bozarth

My Feedback: (15)

ANSWER: They are really not at a constant 90 degrees of bank - even though it looks like it. A sustained 84 degrees (approx.) of bank is what you need (simple sine calculation) to maintain a level 9 g turn. High Plains can provide the proof, but it will probably be on a napkin (he's knows I'm playing).

Kurt
COANG, F-16C/D, GE F110 Big mouths, Block 30
1992-1997

RosscoW

Rule of thumb is that a trained pilot can sustain 6g sustained without a G suit, around 9g with one, so an 80deg banked turn is possible WITHOUT fuselrge lift. Instantanious G loads of much higher values can be withstood (I've personally pulled 11g in a pull up in an Extra 300.)

combatpigg

My Feedback: (3)

When you are in a 80 degree turn, how do you go about telling the fuselage to provide no lift?
Do you just give it a direct order?

BMatthews

If it's a properley coordinated turn then there won't be any side slip. If there's no side slip angle then the fuselage won't be generating any knife edge or sideways lift. At that time all the lift will be with the wing and top view of the fuselage body (given that it's been estimated that something like 40 to 50% of a modern fighter's lift comes from the fuselage. The lift that is holding it from falling is that part of the lift vector that is pointed directly downwards.

HighPlains

My Feedback: (1)

Kurt, you've done things in a plane that I could only dream of. I just feel good that I helped to pay for your play.

Wasn't the C/D variant the one with the enlarged tailplane so it could carry a heavier bomb load?

And I only used napkins in bars.

HighPlains

My Feedback: (1)

A simple sketch of the g load vectors would show that for the airplane to pull 9 g's, gravity is contributing 1 g downward, and the g load due to the radius of the turn is 8.944 g's. This is derived by subtracting 1 from 81 and taking the square root of 80. Take the arctangent of the ratio of this number to one g, to arrive at the angle flown to maintain level flight at 9 g's.

83.6 degrees as Kurt said.