Boeing 727 Question

[Mr.Vortex]

Hi all,


I have been reading the B727 FCTM and it said that the B727 can't
recorver it self from the dutch roll condition at high speed & high altitude.
Is that true? What make the B727 unable to damping the dutch roll?
Small rudder surface of B727? or large swept wing angle?

Also, does any of you have ever firewalling the throttle? Is it increase the
thrust significantly more than the takeoff rating?

Thanks for all of your reply

Best regards

[MarkerInbound]

I've hear it's the sweep of the wings. I've seen it cause the sim to shutdown due to the violence. If it gets started, the 727 is dynamically unstable. Meaning it will just get worse and worse. Recovery is a standard maneuver on checkrides. However the simple solution is to just slow down. The problem goes away below about .75 mach.

Define the TO rating. I can think of 6 different engine dash number combinations. At an airport 5000 feet up with a temperature of 40c, a dash 7 engine won't give rated thrust and your takeoff numbers will reflect it. At sea level on a 5c day, a Super 72 with a 219-15-219 engine mix will have some more EPR to give you.

[Jane-DoH]

Mr. Vortex,

I have been reading the B727 FCTM and it said that the B727 can't
recorver it self from the dutch roll condition at high speed & high altitude.

You mean the pilot can't recover the plane, or it simply will get progressively worse (dynamic instability) without any pilot intervention

Is that true? What make the B727 unable to damping the dutch roll?
Small rudder surface of B727? or large swept wing angle?

I think it has to do with the combination of wing sweep-angle, and the T-tail configuration.

Also, does any of you have ever firewalling the throttle? Is it increase the thrust significantly more than the takeoff rating?

I'm not a pilot, but I can tell you that during virtually all commercial airliner takeoffs are not done at 100% power; they are done at a reduced power settings which still allow the airplane to get airborne, and climb purposefully, yet increase engine service-life (as well as reduce noise).

Fire-walling will push the engine past 100% RPM -- it is a setting only used in emergencies such as a stall, or in windshear. Being that the engine is pushed past its normal maximum operating RPM, an inspection is generally done after something like this is done.

[JammedStab]

Try using speed brakes in such a scenario. Really damps out the Dutch Roll.

[Mr.Vortex]

To Jane DoH

Yes. I mean without pilot input.

Also, another question is what is the usual descent target speed? I've
readthe previous thread in this forum and is said the speed is about
the barber pole. Is that the common for all other airline too or it is
depeneds on the airline SOP.

Thanks to all reply.

Best regards

[Jane-DoH]

JammedStab,

Try using speed brakes in such a scenario. Really damps out the Dutch Roll.

Logical enough


Mr. Vortex,

Yes. I mean without pilot input.

Understood

[18-Wheeler]

Try using speed brakes in such a scenario. Really damps out the Dutch Roll.

My father used to fly 727's and he has said a few times that the speed brakes are the fastest way to stop Dutch Roll in them. It is possible to do it with the conventional controls only (had to be demonstrated in the old TAA sim during a check) but it's difficult to do.

[Mr.Vortex]

That's interesting!!. I've never heard about using the speedbrake to stop
the dutch roll. Does anybody have an experience to share with.

[MarkerInbound]

We'd hold the same mach as we were cruising at and switch over to 300-310 knots. Waiting to start down at .88 or .89 increases the fuel burn. Book says to switch to 280 knots but that seemed so slow. I'd adjust for the headwinds and tailwinds, glider flying has some uses.

[trimotor]

It's been a while, but the 727 has issues between lateral (high) and longitudinal (low) stability. Don't think the T tail has much, if anything to do with it, though get too much yaw (11° is the magic number in the back of my head) and the tail will reputedly come off.

The 727-100 will depart if Dutch Roll is left unchecked (you'd have to be dead not to notice it), though the 727-200 is pretty-much neutral (longer, and more directional stability), but obvious i.e. it won't recover itself, but won't get worse.

18-Wheeler is correct: initial actions include extending the speedbrakes - very effective - lessens the lateral stability. Hand flying the recovery (the only way) is difficult, especially in the -100, as it's easy to get out of phase with the roll and make it worse. The recover is ideally a 2-person job with the other guy checking to see that you have the correct inputs - mostly an input timing issue.

The aircraft has significant MEL restrictions relating deispatch with inop yaw dampers.

[By George]

Obviously slowing down using any means helps but the best way to recover is as the 'down' wing starts to rise apply full into down wing aileron and back to neutral. Wait for the wing to go 'down' again and repeat the action. After about four cycles the rolling motion begins to dampen out and normal roll control becomes effective. If you're good you can work both wings but it requires very good co-ordination. During my initial Command training we had to be familiar with Dutch Roll recovery but only in the Sim. If my memory serves me correctly in the early days they lost a 707 trying it in the aircraft. Quite a strange aerodynamic event the first time you see it. Good to know the limits of the envelope we don't seem to 'explore' this enough these days.

[411A]

If my memory serves me correctly in the early days they lost a 707 trying it in the aircraft. Quite a strange aerodynamic event the first time you see it

Yup....and the early 707's were much the same, divergent dutch roll was a definite possibility, if not handled correctly. Later models with series yaw dampers were much more stable.

[aterpster]

trimotor:

The aircraft has significant MEL restrictions relating deispatch with inop yaw dampers.

It's been a long time, but my recollection is that at least one had to be operative. And, it was two operative unless at a non-maintenance station. The altitude restrictions were significant, just as they were if one became inop enroute.

The -100 was far worse than the -200, thus more restrictive if memory serves me.

[Jane-DoH]

Marker Inbound,

We'd hold the same mach as we were cruising at and switch over to 300-310 knots.

You typically would be cruising around M=0.84-0.85 right?


trimotor,

It's been a while, but the 727 has issues between lateral (high) and longitudinal (low) stability.

I never heard anything about the plane having poor longitudinal stability, I guess you learn something new every day.

Don't think the T tail has much, if anything to do with it, though get too much yaw (11° is the magic number in the back of my head) and the tail will reputedly come off.

11-degrees of sideslip?

The 727-100 will depart if Dutch Roll is left unchecked (you'd have to be dead not to notice it)

Of course, the plane rolls and yaws back and forth all over the place.

the 727-200 is pretty-much neutral (longer, and more directional stability)

I thought a shorter plane had more directional stability (at least that's why I was always under the impression that the 747-SP had a bigger tail) than a long plane

The aircraft has significant MEL restrictions relating deispatch with inop yaw dampers.

Was it's dutch roll characteristics worse than the 707?


By George,

Obviously slowing down using any means helps but the best way to recover is as the 'down' wing starts to rise apply full into down wing aileron and back to neutral.

I assume if you were getting dutch-roll, the yaw-dampers would be dead, would you use small rudder inputs with the ailerons, or just the ailerons alone?


411A,

Yup....and the early 707's were much the same, divergent dutch roll was a definite possibility, if not handled correctly.

I assume the 707 had worse dutch-roll characteristics than the 727 because of it having a higher wing-sweep?

[MarkerInbound]

No, we'd normally be at long range cruise around .80. It make a big difference fuel wise between .80 and .85.

Braniff lost a 707 on a delivery flight with Check Airman, Feds and Boeing pilots on it. We had a 727 Check Airman who was old Braniff and you knew every time he was giving the check you'd see Dutch Roll as the flight control malfunction. I have seen so many pilots get out of sync playing whack-a-mole on the rising wing. You don't want to add any rudder inputs.

MEL for both the -100 and -200 just says to comply with the AFM restrictions. Can't remember the -100 but the -200 is a max 270 kts at 30,000 and a sliding scale to 310 at 26,000 and then it jumps to 350 at 25,000 and below.

[CaptainSandL]

As Dutch Roll in the 707 and 727 were tricky to handle without a yaw damper, the 737 prototypes were originally fitted with two YDs due to anticipated MEL restrictions. Once they flew it, it was proven to be a pussycat and the second YD was removed. There is also no MEL restriction if the YD is inop.

In my experience in both 737 Classics and NGs if you induce a Dutch Roll at cruise alt & Mach it will decay to zero in about 6-8 oscillations with the YD off, or just 1.5 with the YD on - both figures are without any pilot input.

S&L

[By George]

'Jane-Doh', Your question has been answered by 'MarkerInbound' I was taught to use aileron only and yes for the exercise the Yaw dampers were off.

[Jane-DoH]

By George,

'Jane-Doh', Your question has been answered by 'MarkerInbound' I was taught to use aileron only and yes for the exercise the Yaw dampers were off.

Understood

[JammedStab]

Originally Posted by By George

Obviously slowing down using any means helps but the best way to recover is as the 'down' wing starts to rise apply full into down wing aileron and back to neutral. Wait for the wing to go 'down' again and repeat the action. After about four cycles the rolling motion begins to dampen out and normal roll control becomes effective.

The sharp aileron input seemed to be the basic recovery manouver as taught to me but speedbrakes seem to be much more effective.

With the sharp aileron input, as said above, you did it into the rising wing. So choose a wing and then each time it is rising, apply aileron input quickly and then back to neutral. You could screw it up though. If you look at the ADI and after having chosen a particular wing to apply aileron against, you do it 180° out of sync because you mistook the rising horizon on the ADI as the rising wing. Oops.

We practised it in the sim but did it in the real aircraft on a post maintenance check. Yaw Damper off and then a small kick in one direction of the rudder starts the cycle. Real plane seemed to handle like the sim.

Here is the kind of strange part. Initially the wings tended to dip more or less equally on either side of wings level(call it the neutral point). But, after some aileron recovery inputs you can end up with a new neutral point such as, for example, 15° right bank being the new neutral point and equal wing dips from that point. Happened in the sim and on the airplane.

[Old Fella]

Dutch roll

Never operated the B727 and do not know if it is less susceptible to Dutch rolling than the B707, but would think there is more to it than a 3 degree difference in wing sweep. (B707 35 degrees - B727 32 degrees). I remember induced Dutch Roll and recovery certainly grabbed our attention. FL150 over Bass Strait when converting to B707 and being trained by Qantas. Interesting exercise to say the least. Why did we do it in the aircraft and not the Sim? Because the Qantas Sim was dismantled and sent to Aer Lingus as soon as we completed the Sim training phase of conversion.