F-16 best glide speed

[RockyMnt1]

I was watching "Real TV" the other night and they showed a clip of an F-16 losing an engine and gliding to a landing. The airspeed was held at around 208 kts during the glide. He had some external fuel tanks hanging of the wings which he eventually dropped when he got below the cloud deck so as not to hurt anyone on the ground.

Even at 208 kts, this guy was sinking like a rock!!! Is this really the best glide speed of an F-16??

Yikes, that was a shock to this civilian pilot.

 

[FSIGRAD]

Best glide is not actually a set speed, it is an angle of attack. In training aircraft we use a standard best glide speed because the weight of the aircraft does not vary to a large extent. (The change in best glide of an arrow at maximum gross compared to 1 pax and empty tanks is only 2 knots.) The best glide in the POH is for max gross.
For something like an F-16 which carries a large ordinance load I would assume they would determine thier "best glide speed" using an angle of attack meter in the cockpit?

I'm sure some military guys on the board can give the correct answer.

 

[jetdriven]

QUOTE]For something like an F-16 which carries a large ordinance load I would assume they would determine thier "best glide speed" using an angle of attack meter in the cockpit?[/QUOTE]

if it were my F-16 I think I would dump the ordnance!![

 

[Toro]

I can't answer for an F-16, but I can throw out some info for an F-15. We don't have to worry about best glide speed like a viper does since its rare that one of our engines flames out, let alone two, and if they both flamed out we would have to eject. However, our best glide speed would equate to our best lift over drag coefficient. For the F-15, this is going to be 17-18 units of AOA, depending on altitude. The airspeed that corresponds to this is going to depend on gross weight of the aircraft (fuel and external stores) and altitude, but should be somewhere around 220-ish knots. With no thrust, this would put you somewhere around a 10 degree nose low descent. The F-16 can glide much better than us due to the fact that it's much lighter. They practice Simulated Flame Out traffic patterns quite a bit to prepare for when the engine conks out on them.

 

[PilotoHalcon]

Hey Toro, I have not flown a real high performance aircraft other then a LR35 and a C550 BUT I believe the best L/D Max as in a AOA value would be the same regardless of the weight or altitude. As far as weight is concerned the AOA would be constant, but the IAS would change to maintain that best AOA. And as far as altitude is concerned the only thing that would change is TAS. As a general rule, aircraft fly off of IAS, or better yet AOA.
j

 

[ExAF]

Flameout/SFO Landing

Here ya go...right out of the checklist (for a block 40/GE 100 engine...and out of date by a few years)

1. Stores-Jettison (if required)
2. Airspeed-210 kts (note...Increase airspeed by 5 kts per 1000lbs of fuel/store weights over 1000lbs. This equates to approx 6 degrees AOA)

Then there's a bunch of other steps until you get in the Flameout Pattern then once the gear are down:
9. Airspeed-200 kts optimum in the pattern (note...Increase airspeed by 5 kts/1000lbs of fuel/stores over 1000lbs) (Additional note...do not let airspeed to decrease below 180kts plus 5 kts/1000lbs of fuel/stores weight over 1000lbs.)

If you were doing an actual flameout landing, you would almost always jettison any external stores/fuel.

So yes, you are going pretty fast and pretty steep. If you were landing out of a straight in versus an overhead pattern, you would be starting your decent when your aimpoint was approx 11-17 degrees below the horizon. The first time you see the SFO pattern it kind of waters your eyes, but after practice, it is kind of fun. Hope this answers your question. Cheers

 

[Toro]

Reply to PilotoHalcon

Yes, in regards to AOA remaining constant with altitude and weight changes, you are right as a general rule of thumb. However, in the F-15E, it differs slightly with altitude. Above 25,000 feet we use 17 units AOA for max endurance and below 25,000 we use 18 units. Similarly, we use 14 units below 25,000 for max range and 14.5 above 25,000.
I didn't say AOA changed with weight, just airspeed. And yes, if we were trying to do some type of glide/endurance/range for gas or other reasons, we would fly AOA, not airspeed.

 

[Draginass]

I would guess that the F-15 would have considerably more drag in an engines-out glide, and hence, a worse glide ratio. Now about gliding a B-1 . . . . . not.

 

[Draginass]

Any F-4 guy will also tell you that with enough power, even a coke machine can fly.

 

[Hugh Jorgan]

Fat chicks too!

 

[Typhoon1244]

Originally posted by Draginass
...with enough power, even a coke machine can fly.

Originally posted by Hugh Jordan
Fat chicks too!

My wife flies just fine, thank you very much...


Just kidding, Honey!

 

[Draginass]

Keep that up Typhoon and the only things flying will be you s**t flying out the front door and into the street when you leave on your next trip!

 

[bigD]

Toro mentioned that if both engines flamed out on an F-15, the pilot would eject. I'm curious, if that's the case, why wouldn't the F-16 drivers do the same thing? Is the glide ratio of the F-15 so much worse that you wouldn't even bother trying to make a landing?

 

[DaveGriffin]

I once heard a Phantom jock say a coke machine glided better than his F-4 did.

I've heard Phantom drivers describe their aircraft's glide capabilities as similar to a manhole cover.

 

[Mud Eagle]

Toro mentioned that if both engines flamed out on an F-15, the pilot would eject. I'm curious, if that's the case, why wouldn't the F-16 drivers do the same thing? Is the glide ratio of the F-15 so much worse that you wouldn't even bother trying to make a landing?

It has nothing to do with glide ratios.

The difference is that in the Eagle, the flight controls are run by the hydraulics, which is given operating pressure via engine rotation. If one or more engines are windmilling above 12%, there is enough pressure to somewhat control the airplane. The problem is that it takes something near 350 knots to maintain that 12% windmilling RPM....so, when it came time to slow to land, the RPM would stop, the hydraulic pressure drops, and the airplane is uncontrollable.

The F-16, on the other hand, has the Hydrazine emergency power to make the flight controls continue to work for something like 10 minutes following an engine flameout.

 

[PilotoHalcon]

I heard the T38 had the same problem. It would loose N1 in the flare so the hydraulics would be inop. Course I never flew a 38.
j

 

[Typhoon1244]

Keep that up Typhoon and the only things flying will be you s**t flying out the front door and into the street when you leave on your next trip!

Easy! I was just kidding...a wife joke just seemed to fit the flow of the discussion.

My wife's pregnant for the third time in three years. The first ended in miscarriage early on. The second produced a wonderful little boy. The third is ongoing. This time it was an accident; it took three years for us to get pregnant at all...profound fertility problems, you know. Who knew it'd happen again so soon?

We tell each other a lot of fat jokes to ease the tension.

But I digress...you were saying, about stall speeds?

 

[Toro]

Landing with windmilling hydraulics

I heard the T38 had the same problem. It would loose N1 in the flare so the hydraulics would be inop. Course I never flew a 38.

Mud Eagle was right on with why the F-15 can't land with dual engine flameout, which, as you correctly heard was the reason a T-38 can't land with dual engine flameout. The difference is that maintaining windwilling engine RPM on a T-38 requires much less airspeed than an F-15. Mud Eagle pointed out that you need about 350 knots to do it in a Strike Eagle - well, you only need around 150-ish knots in a T-38. In a T-38 won't get insufficient airflow to windmill the engines until the aircraft flares for landing - I've always been told this is when the jet would lose control. Personally, I didn't think losing hydraulics 2-3 feet in the air at touchdown would send the jet out of control. At most, you would lose the authority in your horizontal stabilizer and have a hard landing, but nothing worse than the average beginner T-38 student. I tried landing a T-38 in the sim with dual engine flameout and it landed just fine...doesn't mean I'd necessarily trust it to do the same in the jet, though.

 

[AlbieF15]

Toro,

CPUs (Cockpit units) approximately equal to true AOA + 10...ie...18 units AOA is 8 units true. This gets to be a factor when you talk to Hornet guys, who can REALLY generate the AOA. I believe when they talk AOA it is in true vice CPU units.

For T-38s, the problem with running out of hydraulics 2-3 feet off the ground is the only thing providing resistance on control surfaces is airloads and actuator friction. Put an assymetrical load on the flight controls (rudder or stab) and you might get a yaw or pitch that would put you in a terrible spot in about 2 heartbeats. Not a lot of time to grab handles if something starts to go wrong, and in likely the MOST critical phase of flying at that!

FYI...I give Vipers guys grief sometimes, but I have personally flown with 2 guys who bailed out of Eagles when an engine failed catastophically to the point of taking out the other engine. Two other guys I know (1 an F15E 229) had engines shell and pieces go out the top and side of the jet but not go through and take out the other engine. A former Holloman Eagle Squadron Commander (buddy of mine's boss) used to say "every moment is an ambush". I love flying the Eagle...swear by two engines....but I still preflight the ACES II every flight.

Fly safe!

 

[bigD]

Ah - thanks for the explanation guys! That makes a lot of sense.