CO1404 off runway at DIA

[flyingcheesehead]

Well, I am not into the aerodynamics, but it doesn't make sense that a windmilling turbine would create little or no drag. I mean, a windmilling prop creates a ton of drag.

Be that as it may:

I DO know that with a twin, you have a BUNCH of excess thrust both engines running as opposed to a 4 engine airplane with all engines running.

Aha! Maybe THAT is why the B-36E video I was just watching shows an abysmal climb gradient! They'd only lose 10% of their thrust with an engine out! (Assuming, of course, that the ones that are turnin' have the same thrust as the ones burnin' which is highly doubtful.)

BTW Greg, I must admit that I gave Scott the answer at dinner tonight, and he still didn't believe me.

 

[TMetzinger]

Well, I am not into the aerodynamics, but it doesn't make sense that a windmilling turbine would create little or no drag. I mean, a windmilling prop creates a ton of drag.

Be that as it may:

I DO know that with a twin, you have a BUNCH of excess thrust both engines running as opposed to a 4 engine airplane with all engines running.

Work is definitely being done to turn the engine when it's windmilling, as it's not frictionless. While that may not be as much work as turning over a piston engine, it still is work and it still causes drag.

I _think_ that in turboprops where the prop is freespinning - like a PT6, the drag when windmilling is much less than that of a turboprop where there is a gearbox. But it's definitely not zero.

 

[RotorAndWing]

Work is definitely being done to turn the engine when it's windmilling, as it's not frictionless. While that may not be as much work as turning over a piston engine, it still is work and it still causes drag.

I _think_ that in turboprops where the prop is freespinning - like a PT6, the drag when windmilling is much less than that of a turboprop where there is a gearbox. But it's definitely not zero.

When a PT6 loses oil pressure the prop goes to feather, so in an engine failure it would feather itself.

On a Garrett powered aircraft they have NTS, "Negative Torque Sensing" which drives the prop to 97% feather, just a slow windmill. When the pilot pulls the stop and feather knob it completes the feather.

 

[ScottM]

A transport category airplane is required to be able to get off the ground with AN engine failure. One. Lose one on a 4 engine plane and you have lost only 25% of your thrust. Lose one on a 2 engine plane and you have lost HALF the thrust. A two engine plane needs that extra thrust on takeoff in case one fails. The remaining engine needs to be able to get the airplane off the ground. That is why a two engine airplane will seem to have more pep than a 4 engine plane of the same weight. That is because it DOES have more pep.

I am not following your logic here.

Lets assume similar weights for the aircraft.

The 4 engine aircraft still has 75% of it's total power while the 2 engine version would only have 50% of it's available power. So if total power is the same between the two aircraft, isn't the 4 engine aircraft with it's 3 remaining engines able to produce 50% more power at any given time over the 2 engine plane's remaining engine?

 

[ScottM]

How does that non-producing engine now creating more drag than thrust figure into the equation?

Well if it is on a treadmill......

 

[ScottM]

Scott, what you propose goes against EVERYTHING we as pilots have been trained to do. There just isn't enough time at that point to analyze the situation and decide to go or not. That decision HAS to be made just before V1. Any later and the airplane goes off the end at a high speed. Not good. you can Monday Morning Quarterback that all you want, but the crews had no choice but to continue the takeoff.

I think I figured out why we look at this differently.

It is the way we have both been trained to think of situations.

Your a pro-pilot, an operations guy. You are taught to think and react with what has worked and is proven to work giving you the best odds at success. You given proceudres that have been designed and calcualted to give the best odds.

I am a design guy. I taught to look at things and see how if there are different better outcomes and then to design systems that would make that outcome a reality. IOW I paid to think 'what if....' While you are paid to think, 'this works...'

This occurred to me last night as I was driving home form the PoA gathering. We had been discussing so technical wireless things and I my mind was drifting towards filling some of that input to a problem I am working on at work. We were also discussing the 2-engine comment you made.

 

[RMCN172RG]

I am not following your logic here.

Lets assume similar weights for the aircraft.

The 4 engine aircraft still has 75% of it's total power while the 2 engine version would only have 50% of it's available power. So if total power is the same between the two aircraft, isn't the 4 engine aircraft with it's 3 remaining engines able to produce 50% more power at any given time over the 2 engine plane's remaining engine?

Invert this Scott,

Plane A(4) and plane B(2) both need 10000 LBs of thrust for takeoff.

With one engine out 10,000/3 each engine on plane A only needs to produce 3,500 LBS of thrust to takeoff with a one engine failure and small safety margin. Plane B requires each engine to produce 10,000 LBS to be able to take off with one failed.

So with all engines working plane A has 14,000 LBS of thrust and plane B 20,000 LBs. Zoom Zoom!

 

[ScottM]

Invert this Scott,

Plane A(4) and plane B(2) both need 10000 LBs of thrust for takeoff.

With one engine out 10,000/3 each engine on plane A only needs to produce 3,500 LBS of thrust to takeoff with a one engine failure and small safety margin. Plane B requires each engine to produce 10,000 LBS to be able to take off with one failed.

So with all engines working plane A has 14,000 LBS of thrust and plane B 20,000 LBs. Zoom Zoom!

Ah, see I was just looking at it from a thrust with engine failure standpoint. Not total available thrust with all engines working.

 

[Everskyward]

Work is definitely being done to turn the engine when it's windmilling, as it's not frictionless. While that may not be as much work as turning over a piston engine, it still is work and it still causes drag.

While it isn't frictionless, the fan on a jet engine is easy to spin, unlike a prop on a piston engine which is physically connected to the parts of the engine that drive it. It only takes a light breeze to get the fan spinning on the airplane I fly although I don't know if that's true on airliner sized airplanes.

 

[Greg Bockelman]

So if total power is the same between the two aircraft,

Ray already answered this. But I never said that the POWER was the same. Only that the weigh is the same. From this point on, I would be repeating Ray so I won't go on.

 

[Greg Bockelman]

It only takes a light breeze to get the fan spinning on the airplane I fly although I don't know if that's true on airliner sized airplanes.

Well, it takes just a little more than a light breeze to get a 777 engine spinning, but not much more.:smile:

 

[Greg Bockelman]

I think I figured out why we look at this differently.

In other words, I look at it from a human point of view in the here and now, and you re looking at it from a technology/hardware point of view in the future.

I can live with that. But what you are talking about is just one more step in the direction of designing the pilot out of the cockpit. Maybe that is the direction we are going. I don't know. I don't know that you can program the technology to cover enough variables to be foolproof. I have lived with the technology we have long enough to know it isn't foolproof.

If the time ever comes that we have pilotless commercial passenger airplanes, I will move far away from a commercial airport and never step foot in a commercial airplane again.

 

[Steve]

I've seen 'em stick broom handles in C-5A engines to keep them from rolling in the breeze while on static display. I'd say that was a near-airliner sized airplane.

Just big 'ol windmills.

I often hear Citations and the like clicking on the ramp.

While it isn't frictionless, the fan on a jet engine is easy to spin, unlike a prop on a piston engine which is physically connected to the parts of the engine that drive it. It only takes a light breeze to get the fan spinning on the airplane I fly although I don't know if that's true on airliner sized airplanes.

 

[ScottM]

In other words, I look at it from a human point of view in the here and now, and you re looking at it from a technology/hardware point of view in the future.

I think that is a fair interpretation.

I can live with that. But what you are talking about is just one more step in the direction of designing the pilot out of the cockpit. Maybe that is the direction we are going. I don't know. I don't know that you can program the technology to cover enough variables to be foolproof. I have lived with the technology we have long enough to know it isn't foolproof.

I do not know if designing the pilot out of the cockpit is the answer. I see a lot of computing power in most humans heads that cannot be replicated by technology at this point in time. I would say that I would look at solving some problems by trying to figure out how to get the right information to the pilot in a timely fashion for them to make the decision. Perhaps somethings can be automated perhaps not.

If the time ever comes that we have pilotless commercial passenger airplanes, I will move far away from a commercial airport and never step foot in a commercial airplane again.

I am with you there.

We are already doing intelligent highway development that can take drivers out of the picture ala Will Smith in I, Robot.

And trains can already run without engineers in them.

 

[Greg Bockelman]

And trains can already run without engineers in them.

True. Case in point, the people mover at O'Hare. Granted that is a Short Line.

But the variables are manageable in a deal like that. Three dimensions, weather, wind and on and on increase the variables more than exponentially.

 

[TMetzinger]

While it isn't frictionless, the fan on a jet engine is easy to spin, unlike a prop on a piston engine which is physically connected to the parts of the engine that drive it. It only takes a light breeze to get the fan spinning on the airplane I fly although I don't know if that's true on airliner sized airplanes.

But that's only the fan, on the ground. In flight, the air would also be driven through the high-pressure section, which would be a different proposition.

Depending on the engine and the bypass ratio, the drag will vary.

My point really is that there IS drag from a windmilling jet engine, as compared to no engine there at all, or the engine at neutral thrust.

 

[RotorAndWing]

But that's only the fan, on the ground. In flight, the air would also be driven through the high-pressure section, which would be a different proposition.

Depending on the engine and the bypass ratio, the drag will vary.

My point really is that there IS drag from a windmilling jet engine, as compared to no engine there at all, or the engine at neutral thrust.

The drag is negligible and not even considered.

 

[TMetzinger]

The drag is negligible and not even considered.

Reference, please? That fan is as much a prop as the one in the front of a PT-6. Why do we feather the prop in front of the PT-6?

 

[RotorAndWing]

Reference, please? That fan is as much a prop as the one in the front of a PT-6. Why do we feather the prop in front of the PT-6?

OK, please show me in ANY manual on ANY jet powered aircraft where the discussion is on "engine out" drag produced by the engine?

 

[AWACSEng]

Without data to support it, my thought would be a seized jet engine will provide more drag than a windmilling one. I think this because depending on the engine, a certain amount of thrust is produced by the bypass fan air. With that engine turning, a certain amount of thrust will be produced. I agree that this thrust is negligable, but it still is being produced. Just splitting hairs here. And you will not find drag data in any book on the operator level. Maybe the designers have it, but not us.

Back on topic here, Greg K., any updates on your DIL-to-be's quest to regain idenity?

 

[TMetzinger]

Ah... I apologize - we're back to the ops/engineering thinking. I'm not aware of the drag of the windmilling engine figuring into airplane ops manuals, but it does appear to me to be considered in FAR 25, 25.149, which clearly does not apply only to airplanes with props.

25.149 Minimum control speed.
(a) In establishing the minimum control speeds required by this section, the method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service.
(b) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative and maintain straight flight with an angle of bank of not more than 5 degrees.
(c) VMC may not exceed 1.13 VSR with -
(1) Maximum available takeoff power or thrust on the engines;
(2) The most unfavorable center of gravity;
(3) The airplane trimmed for takeoff;
(4) The maximum sea level takeoff weight (or any lesser weight necessary to show VMC);
(5) The airplane in the most critical takeoff configuration existing along the flight path after the airplane becomes airborne, except with the landing gear retracted;
(6) The airplane airborne and the ground effect negligible; and
(7) If applicable, the propeller of the inoperative engine -
(i) Windmilling;
(ii) In the most probable position for the specific design of the propeller control; or
(iii) Feathered, if the airplane has an automatic feathering device acceptable for showing compliance with the climb requirements of § 25.121.
(d) The rudder forces required to maintain control at VMC may not exceed 150 pounds nor may it be necessary to reduce power or thrust of the operative engines. During recovery, the airplane may not assume any dangerous attitude or require exceptional piloting skill, alertness, or strength to prevent a heading change of more than 20 degrees.

Now, back to the engineers perspective. The drag, however small, is NOT zero. And whatever it is, it must be considered and the rudder must offer enough authority to deal with both the large moment change of the functioning engine, and the moment change of the inop engine. That engine may have a failure mode (bearing failures) where that big fan does NOT freewheel. Perhaps in that situation the pylon is supposed to fail and shed the drag, I don't know.

So, I believe that pilots don't need to think about it, because the FAA and the manufacturers already have. Make sense?

 

[Greg Bockelman]

OK, please show me in ANY manual on ANY jet powered aircraft where the discussion is on "engine out" drag produced by the engine?

Maybe the fact that there isn't a DAMNED thing a pilot can do about it may factor into the lack of documentation.

 

[AWACSEng]

Tim, I see your point and I realize many engine failures will not be simple flame outs that allow the engine to rotate. I do, however have first hand experience that when and engine completly fails during the takeoff run to rotate phase that the mighty E-3 will indeed climb on the remaining 3. So, yes either the designers figured that into the data, or we just completed the final stage in flight testing. Either way, the data is predicated on OEI period. It does not specify windmilling or not, just a failure.

 

[AWACSEng]

Maybe the fact that there isn't a DAMNED thing a pilot can do about it may factor into the lack of documentation.

Exactly. Thats why when this happened to us, we continued the takeoff and climbout just as we had practiced in the sim hundreds of times. Thank you, Boeing and P+W for making a fantastic product.

 

[maddog52]

The drag is negligible and not even considered.

Depending on the aircraft and engines, I wouldn't call it neglidgible. Case in point:

A friend of mine was takeing off in his B-52 when he lost the numbers 3 and 4 engines (inboard left pod). When I said lost, I mean the engines departed the aircraft! After the appropriate checklists were done and they had burned down to landing weight, they shot a six engine approach. Should not have been a big deal since we practiced 6 engine approaches all the time.

Well, when they pulled the throttles back for the flare, the aircraft started drifting right at a good rate. They went around and tried to figure out what went wrong. Two IPs went over to the simulator and ran some approaches and determined that the drift was probably caused by the drag on all the right side engines at idle being signifigantly greater than only two engines at idle on the left.

Armed with the new info, the crew lined up slightly left of centerline and made an "uneventful" landing. I was lucky in the fact that I was supposed to fly that aircraft earlier but had been given the spare instead. A lot of people in the squadron were campaigning for the chance to fly it back to Boeing for the repairs.

 

[RotorAndWing]

As far as the discussion concerning the "drag" produced by an inoperative jet engine and the effects, below are pictures of B747's with the spare engine slung under the wing for transport.

 

[Greg Bockelman]

As far as the discussion concerning the "drag" produced by an inoperative jet engine and the effects, below are pictures of B747's with the spare engine slung under the wing for transport.

Neat pictures, but what is your point?

 

[TMetzinger]

Neat pictures, but what is your point?

Yeah, no way can you tell me that there's no drag in those cases - only that the drag is manageable.

 

[RotorAndWing]

Neat pictures, but what is your point?

Lots of surface area there dragging under the wing, however Boeing felt it was adequate to use that area for transport. I'm sure there is a performance degradation to figure in for the extra engine.

I guess the point I'm making is there is enough available thrust that this "drag" is easily overcome and not an issue for the flight crew.

 

[Greg Bockelman]

I guess the point I'm making is there is enough available thrust that this "drag" is easily overcome and not an issue for the flight crew.

But I guarantee that there is a flight manual supplement of some sort that covers the operation.

 

[RotorAndWing]

But I guarantee that there is a flight manual supplement of some sort that covers the operation.

Absolutely.

 

[RotorAndWing]

Yeah, no way can you tell me that there's no drag in those cases - only that the drag is manageable.

That's what I posted originally.

The drag is negligible and not even considered.

 

[gkainz]

Back on topic here, Greg K., any updates on your DIL-to-be's quest to regain identity?

Thanks for asking - the last word we have is they (Continental) was talking with the Ecuadorian consulate to assist in replacing her passport without requiring her to travel to Los Angeles or Chicago for a face to face meeting - the normal requirement. They also are working with someone (State department?) to replace her green card, I'm told.

We heard that carry on (and maybe checked?) bags have been recovered from the aircraft, are being assessed, inspected, cleaned (?) and hopefully they can begin to return salvageable belongings to the passengers soon - perhaps as soon as next week.

 

[TMetzinger]

That's what I posted originally.

Manageable <> Negligible, at least to an engineer like me:smile:.

Do you jet jocks even mention Vmc in your training? If not, then my guess would be that the airplane is designed with enough rudder that the wings stall first, and like you say, it's a complete non-issue operationally.

 

[RotorAndWing]

Manageable <> Negligible, at least to an engineer like me:smile:.

Do you jet jocks even mention Vmc in your training?

Can't speak for the guys that fly the twins, but a B727 is pretty much center line thrust although not technically qualified as such. On a pod engine out rudder input is not significant. So to answer your question, no mention of VMC for the B727.

 

[Greg Bockelman]

Do you jet jocks even mention Vmc in your training?

We don't in any of the planes that I have trained on at UAL. Of course it is a severely bad thing if you stall a transport category airplane, so everything is done to try to avoid that situation.

 

[RotorAndWing]

We don't in any of the planes that I have trained on at UAL. Of course it is a severely bad thing if you stall a transport category airplane, so everything is done to try to avoid that situation.

"Ladies and Gentleman, If you look out the left side my FO has decided before we land to practice a few departure stalls. Flight attendants take your seat please...."

 

[TMetzinger]

We don't in any of the planes that I have trained on at UAL. Of course it is a severely bad thing if you stall a transport category airplane, so everything is done to try to avoid that situation.

That makes sense - in your airplanes you probably can't run out of rudder authority with one engine failed before you are below flying speed anyway.

 

[AWACSEng]

Tim, here's what our (E-3) book says about Vmcg and Vmca.

Critical Field Length (CFL) is the total length of runway
required to accelerate on four engines to V​

​

​

​

1, experience an
engine failure and then continue the takeoff or stop. If V1 is
equal to VCEF the CFL is a balanced critical field length,
because the distance to continue the takeoff is the same as the
distance to stop. When VMCGis greater than VCEF (increased
V1), the CFL increases to the VMCG accelerate-stop distance.
When V1 is based on VMCG, the runway required is
unbalanced because the distance to stop is greater than the
takeoff distance. In this situation the takeoff distance does
not exceed the CFL computed without crosswind. For a safe
takeoff, CFL must never exceed runway available.​

AIR MINIMUM CONTROL SPEED (V​

MCA)​

Air minimum control speed, V​

​

​

​

MCA, is the minimum airborne
speed at which an outboard engine can fail, and with no
change to the thrust of the remaining engines, the airplane
can be kept on a straight flight path with rudder boost ON and​

no more than five degrees of bank away from the failed engine.

 

[AWACSEng]

Thanks for asking - the last word we have is they (Continental) was talking with the Ecuadorian consulate to assist in replacing her passport without requiring her to travel to Los Angeles or Chicago for a face to face meeting - the normal requirement. They also are working with someone (State department?) to replace her green card, I'm told.

We heard that carry on (and maybe checked?) bags have been recovered from the aircraft, are being assessed, inspected, cleaned (?) and hopefully they can begin to return salvageable belongings to the passengers soon - perhaps as soon as next week.

Didn't realize she wasn't a US Citizen. Sucks that you have to involve multiple gov't agencies. Good luck!