Author Topic: Question for ex military pilots... (Read 303 times)

jigsaw · « **on:** April 01, 2004, 06:23:13 PM »

Hanging out at the school today a couple of us were shooting the breeze when a mig (15 or 18 not sure) took off. After I made an obligitory joke about it running out of fuel by the end of the runway, someone brought up an interesting question on turbine planes.

On turbine singles like the F-86, F-16, etc., did you guys have any turning tendencies from torque?

On turbine twins, is there a critical engine?

Toad · « **Reply #1 on:** April 01, 2004, 07:29:00 PM »

No there's no "torque" on a centerline single.

There can be on a multi, it depends on the engine mountings. For example, a T-38 with two turbines is still considered "centerline thrust", IE: it really doesn't yaw much if you lose a motor.

OTOH, with wing mounted engines there usually is a varying degree of yaw when you lose one. It depends on where it's mounted.

For example, on a four engine 707 type, losing one of the outboards is much more noticeable than losing an inboard. In fact, we used to counter loss of an inboard simply by pushing up the corresponding outboard a bit. Rudder really didn't change much. That wasn't true if you lost the outboard.

Hope that helps.

Golfer · « **Reply #2 on:** April 01, 2004, 09:50:52 PM »

I'm not military but have Single, Multi and Instrument ratings.

The definition of 'critical engine' is the engine which, if failed, will most adversely effect the flying of the airplane.

This is important on piston twins and turboprops (not so much for reasons we will get into later) that have conventional engines which means both props spin the same way. If the engines have counter-rotating props (P-38, Piper Seneca) then one engine is not worse than the other, thus no critical engine.

The reason behind the critical engine is because the descending blade creates more thrust than the ascending blade and that means the arm between the Center of Gravity and the point of max thrust is further on the right engine than the left engine (we're talking conventional twins, where the prop spins clockwise when viewed from the cockpit) because the descending blade on the right engine is farther away from the CG than that of the left. That makes the left the critical engine because if it fails, then the right engine can really whip that airplane around and it is harder to fly than if the left engine fails.

Turbine engines don't have this problem because there is no windmilling propeller. Turboprops such as a King Air 350 and damn near every other one these days have an 'auto feather' which if an engine fails, all the oil is forced out of the hub and the prop feathers automatically without any input from the pilot...this is handy because if you lose an engine above V1, you want to continue the takeoff.

Turbine engines also don't have any problems with torque, in fact some jet engines have compressor fans that rotate opposite one another.

By the way...where do you go to school so that you can see MiG's taking off...I wanna go there

Sandman · « **Reply #3 on:** April 01, 2004, 10:08:32 PM »

Quote

Originally posted by Toad
No there's no "torque" on a centerline single.

There can be on a multi, it depends on the engine mountings. For example, a T-38 with two turbines is still considered "centerline thrust", IE: it really doesn't yaw much if you lose a motor.

OTOH, with wing mounted engines there usually is a varying degree of yaw when you lose one. It depends on where it's mounted.

I'm not a pilot, but I did intercept control in the Navy. The F-14 has enough space between the engines for asymetric thrust if an engine fails... or at least the F14A did. I assume that nothing changed on the D model.

SunTracker · « **Reply #4 on:** April 01, 2004, 10:17:48 PM »

F-14 had a design flaw with engine thrust. If it entered a spin, one engine would usually stall, and it was impossible to recover from the spin.

I remember watching a video of a F-14 fall from 20,000 feet all the way to earth in a flat spin.

Munkii · « **Reply #5 on:** April 01, 2004, 10:24:38 PM »

Quote

Originally posted by SunTracker
F-14 had a design flaw with engine thrust. If it entered a spin, one engine would usually stall, and it was impossible to recover from the spin.

I remember watching a video of a F-14 fall from 20,000 feet all the way to earth in a flat spin.

We all saw that.. Goose died.

jigsaw · « **Reply #6 on:** April 01, 2004, 10:42:26 PM »

Thanks for the feedback gents. We couldn't come to a definitive answer on the singles during the hanger flying. Some theorized the having torque effects from the rotors. I just resigned to "I don't know, but I know a place I can ask."

Quote

Originally posted by Golfer
By the way...where do you go to school so that you can see MiG's taking off...I wanna go there

I'm an instructor at DVT. We get quite a few interesting planes in transit. The guy with the MiG is local, but I think he flys out of SDL more often. There's a group of Yak trainers on field that do a lot of formation flying. Lot of L-39s in the area.
We had a B-17 drop in for a few days last year. He'd no more gotten to the ramp when the crowd had descended on him.
When a certain radio personality was in the local rehab, his Gulfstream was parked on the ramp. The C-123(?) from Operation Dumbo Drop is perma parked on the north side ramp. I bought a cheapy digital camera a while back to try and catch some photos for the next time something cool drops in.

We practice in Luke AFBs area a lot. Interesting to have approach tell you "Traffic x o'clock flight of F-16s" and watch them zip by. If it's a slow day for them, can ask for a buzzing and the viper pilots will wave as they fly by a few hundred feet away.

Since we use Seminoles for our multi training, our definition of critical engine is "The one still running."

Sandman · « **Reply #7 on:** April 01, 2004, 11:45:36 PM »

Quote

Originally posted by SunTracker
F-14 had a design flaw with engine thrust. If it entered a spin, one engine would usually stall, and it was impossible to recover from the spin.

I remember watching a video of a F-14 fall from 20,000 feet all the way to earth in a flat spin.

We lost a plane near San Clemente island... engine stalled on approach and the asymetric thrust caused the aircraft to yaw/roll.

Golfer · « **Reply #8 on:** April 02, 2004, 01:05:33 AM »

Quote

Originally posted by Sandman_SBM
We lost a plane near San Clemente island... engine stalled on approach and the asymetric thrust caused the aircraft to yaw/roll.

I had the examiner from hell on my multi checkride. I flew my patterns a little wide (i believe they were referred to as 747 patterns) and on downwind just turning base he asked 'could you glide to the runway if you had to'. That phrase is the most sinister of evil phrases you can hear on your checkride (thinking back to my power off 180s...at least i was expecting those on the commercial ride!) I reply to the affirmative and byebye goes my good engine, I was in a piper apache and my left engine was the one that was dead via mixture control so I'd already hand pumped the gear down. Made the approach and made the first taxiway at Wood County (Bowling Green, OH) then fired up the left engine and taxi'd in...a new multiengine pilot. That was for a VFR only add on too as I'd not yet had an instrument rating...what a day that was

At any rate, the power settings on approach are already quite low, and I dont see how an engine conking out would have any effect, worst case scenario in a military jet (lots of extra power) like an F-14, a little extra juice and a little rudder. Heck, even a go-around is an option. In a prop plane its your typical Mixtures-Props-Throttles to the wall, identify verify feather...get that done in about 5 seconds and you still have options. I cant see how that would be a problem, let alone have enough adverse yaw to spin the airplane without the pilot knowing what was going on.

I wasn't there though...