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speedracer1407
Topic Author
Posts: 330
Joined: Fri Dec 24, 2004 4:19 pm

707 Flight Controls

Fri Jul 21, 2006 4:28 pm

I seem to recall reading on this forum and elsewhere that the 707's Flight controls were not hydraulically assisted (or atleast some of them weren't). Some of you may recall my curiousity about the DC-9 family's control tabs, and my question here is roughly the same.

If such a relatively large aircraft's flight controls were not hydraulically assisted, how in the world did pilots produce the strength to control the plane, especally during, for example, landing situations where quick shoves might be needed to keep the thing level? Obviously, the thing works, but I'm curious as to how a pilot can input a few inches to the yoke, and end up with the necessary movement of ailerons and elevators acting against airflow over those surfaces.

I tried a quick search, both of this forum and elsewhere to see if Douglas-style control tabs were employed, but failed to find any pertinent information. Thanks for your replies, folks,

O
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
VC-10
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RE: 707 Flight Controls

Fri Jul 21, 2006 8:32 pm

Only the Rudder was hydraulically controlled.

The Ailerons & Elevators were manually operated via servo tabs and in addition there were 'balance panels' attached to the control surfaces that gave aerodynamic assistance to movement.
 
DH106
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RE: 707 Flight Controls

Fri Jul 21, 2006 8:35 pm

Quoting VC-10 (Reply 1):
The Ailerons & Elevators were manually operated via servo tabs and in addition there were 'balance panels' attached to the control surfaces that gave aerodynamic assistance to movement.

Not meaning to be pedantic, but I thought servo tabs WERE panels attached to the control surfaces that gave aerodynamic assistance to movement? They effectively use the airflow to give 'power assist'
...I watched c-beams glitter in the dark by the Tanhauser Gate....
 
arluna
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RE: 707 Flight Controls

Sat Jul 22, 2006 1:03 am

Hello folks,

VC10 is correct, there are servo tabs on the external flight controls to assist the pilots. The balance panels you mention are actually located inside the trailing edge of the wing in sealed bays called balance bays. I was never exactly sure how they worked but they did. We seldom saw the panels because there was no reason to open the bays except during phased inspections when they were looked at for corrosion control.

Jerry
(Retired KC-135 crew chief)
 
boeingfixer
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RE: 707 Flight Controls

Sat Jul 22, 2006 1:11 am

To add a bit of detail, the elevators have two tabs each. The outboard tab is the servo tab while the inboard tab is connected to the horizontal stab and operates to keep the elevators in an aerodynamic neutral position to the stab.

Cheers,

John
Cheers, John YYC
 
411A
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RE: 707 Flight Controls

Sat Jul 22, 2006 9:13 am

Ailerons and elevators had balance panels
In addition to ailerons, differential spoilers were used for roll control, flaps up or extended, and of course, were hydraulically actuated.

Ailerons.
Inboard and outboard.
The inboards were used at all times, the outboard ailerons were locked out with flaps retracted.

Balance panels, as mentioned, were used for control surface assist, and were indeed contained in bays at the trailing edge of the wing and horizontal stab, and were connected thru a clever arrangement of push/pull tubes and bellcranks.

Caution was advised however.
Careful examination was required before flight if the airplane had been landed on a slush covered runway previously, as snow/slush could accumulate in these balance bays, thus rendering the balance panels unserviceable.

The Convair 880 also had balance panels, of a similar design to the Boeing system.

Were the controls heavy on the 707?

The answer is yes (especially in the roll axis), and lighter guys soon developed muscles accordingly.

However, caution again advised.
IF heavy forces were applied to the elevators, the motor that supplied motive power to the horizontal stab, could become stalled, thus rendering the stab unable to be trimmed.
NOT a good scenario, to be sure.
The correct answer, was small amounts of stab trim applied constantly, rather than trying with large amounts, all at once.
 
speedracer1407
Topic Author
Posts: 330
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RE: 707 Flight Controls

Sat Jul 22, 2006 2:42 pm

Thanks for your replies, folks.

I'm a bit confused about what these mechanisms are that help reduce effort in roll control, however.

Here's what I AM familiar with, just to clarify and simplify any potential replies: Control tabs, as on DC-9s and spoilerons for roll control assist.

Quoting 411A (Reply 5):
Balance panels, as mentioned, were used for control surface assist, and were indeed contained in bays at the trailing edge of the wing and horizontal stab, and were connected thru a clever arrangement of push/pull tubes and bellcranks.


What are these balance panels? I imagine some sort of counterweight that "balances" the aileron in such a way as to eliminate the added force needed to overcome the wieght of the control surface itself, but that's just a total guess.

Quoting VC-10 (Reply 1):
he Ailerons & Elevators were manually operated via servo tabs

What are servo tabs? Are they control tabs or something different?

The helpful poeple who have replied to my inquiry all suggest that these mechanisms "assist" in control surface movement, but aren't the primary mechanisms. Is this the case, or is it just a matter of semantics? If the former, does that mean that the 707 has three different mechansims on each control surface, each working towards a cumulative effect on control surface movement?

Quoting 411A (Reply 5):
The inboards were used at all times, the outboard ailerons were locked out with flaps retracted.

Do I understand you correctly that in climb and cruise phases of flight, in clean wing configuration, the outboard ailerons are locked? How strange! Atleast compared to my understanding of pretty much every other big jet (unless my understanding sucks ofcourse).

And finally, I"m a bit surprised by the lack of hydraulic controls on the 707. I suppose weight savings and perhaps a lack of reliability/refinement in hydraulics in the 50s MIGHT be part of it. But I seem to recall that even the Comet had hydraulic controls, the lack of "feel" of which may have contributed (even if slightly) to some of the over rotation accidents in its early days. So what was the design philosophy behind the 707's controls given the fact that all subsequent (and smaller) boeings employed hydraulics for all control surfaces?
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
vc10
Posts: 1429
Joined: Thu Nov 15, 2001 4:13 am

RE: 707 Flight Controls

Sat Jul 22, 2006 7:54 pm

speedracer,

Try the following web site as it also has pictures, which are always more valuable than words

http://selair.selkirk.bc.ca/aerodynamics1/controls/Page2.html

little vc10
 
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Starlionblue
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RE: 707 Flight Controls

Sat Jul 22, 2006 10:59 pm

Quoting Speedracer1407 (Reply 6):
Quoting 411A (Reply 5):
The inboards were used at all times, the outboard ailerons were locked out with flaps retracted.

Do I understand you correctly that in climb and cruise phases of flight, in clean wing configuration, the outboard ailerons are locked? How strange! Atleast compared to my understanding of pretty much every other big jet (unless my understanding sucks ofcourse).

Your understanding sucks  Wink

On the 777 the outboard ailerons are also locked out, although I think it's speed related instead of flap related. IIRC it's over 200-220 knots but I could be wrong.

AFAIK the 310 doesn't even have outboard ailerons.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
arluna
Posts: 95
Joined: Thu Jun 01, 2006 12:28 pm

RE: 707 Flight Controls

Sun Jul 23, 2006 9:29 am

If I'm not mistaken (and I could very well be) the reason the outboard ailerons are locked out when the flaps are retracted is because of the twisting effect they would have on the wings at higher speeds. The wing is much thinner and narrower toward the tip and is much less resistant to torsional loads. I would think there would be some very interesting results if this were true.

Help me out here and tell me if I am wrong.

Arluna
 
474218
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RE: 707 Flight Controls

Sun Jul 23, 2006 10:33 am

Quoting Speedracer1407 (Reply 6):
Do I understand you correctly that in climb and cruise phases of flight, in clean wing configuration, the outboard ailerons are locked? How strange! Atleast compared to my understanding of pretty much every other big jet (unless my understanding sucks ofcourse).

Of the "modern" airlines only the L-1011 uses the outboard aileron in all flight conditions. All the others lock-out, null or don't even have an outboard aileron. They do this to reduce the bending of the outboard wing.
 
411A
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RE: 707 Flight Controls

Mon Jul 24, 2006 3:45 am

474218 is indeed correct about these ailerons on the L1011.
The A300-600 for example, eliminated the outboard aileron, and a few pilots that I personally know that fly this airplane, complain just a bit about the rather slow roll control of this model, as compared to the A300B4, which did have an outboard aileron.

Just to expand a bit about the B707.
It had two hydraulic systems, the utility and the auxilary.

The utility system was pressurized from the engine driven hydraulic pumps, and supplied the following systems...

Landing gear.
Nose wheel steering.
Brakes.
Some spoilers.
Flaps.
*Flaps could also be extended electrically, wing leading edge devices were extended pneumatically.

The auxilary system was pressurised by two electric pumps, which operated at all times, and provided hydraulic power to the following systems...

Some spoilers.
Rudder.

The two systems could be interconnected on the ground, but not in flight...EXCEPT on those aircraft that were delivered to PanAmerican, which did provide interconnect while airborne, for one very good specific reason.
PanAmerican operated very long non-stop sectors with their B707's and wanted utility-auxilary interconnect while airborne, so as to provide an alternate method or retracting the landing gear, in the event of MLG trucks not completely level.
This enabled flight continuation without fuel dumping and return to destination, and also provided an alternate hydraulic supply for the brakes, after landing.

The L1011 of course, being a much more modern design, had four hydraulic systems, with engine driven pumps, pneumatic air driven hydraulic pumps, power transfer units, and DC electric pumps...and a ram air turbine.
A very well thought out, and redundant design, with hydraulic fusing built in direct from the factory, quite unlike the earlier B747's and DC-10's.
All things considered, a quite superior design, compared to its contemporaries of the day.
 
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Jetlagged
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RE: 707 Flight Controls

Tue Jul 25, 2006 6:44 am

Quoting Speedracer1407 (Reply 6):
What are servo tabs? Are they control tabs or something different?

Servo tab is the usual name for what you are calling control tabs. They certainly aren't exclusive to Douglas designs. The BAe 146/Avro RJ is another modern example using servo tabs.

There are many different types of tab, for different purposes, but they all work by changing the hinge moment of the control surface.
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speedracer1407
Topic Author
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RE: 707 Flight Controls

Tue Jul 25, 2006 5:33 pm

Thank you all for your posts, I learned a lot. I'd though I had the fundamentals down for basic things like attitude controls; turns out I didnt.

One question though:

Quoting 474218 (Reply 10):
Of the "modern" airlines only the L-1011 uses the outboard aileron in all flight conditions. All the others lock-out, null or don't even have an outboard aileron. They do this to reduce the bending of the outboard wing.

What about planes that don't have inboard ailerons, like the A320, 737, MD-80, etc.? Or were you referring to modern airliners that have both, like almost every widebody, and thus the option of locking out the outboards.

Jetlagged, thanks, I was waiting for that clarification.

O
Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
 
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Starlionblue
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RE: 707 Flight Controls

Tue Jul 25, 2006 8:36 pm

Quoting Speedracer1407 (Reply 13):

What about planes that don't have inboard ailerons, like the A320, 737, MD-80, etc.? Or were you referring to modern airliners that have both, like almost every widebody, and thus the option of locking out the outboards.

Airliners with only outboard ailerons use those in all phases of flight.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
474218
Posts: 4510
Joined: Mon Oct 10, 2005 12:27 pm

RE: 707 Flight Controls

Tue Jul 25, 2006 11:22 pm

Quoting Speedracer1407 (Reply 13):
What about planes that don't have inboard ailerons, like the A320, 737, MD-80, etc.? Or were you referring to modern airliners that have both, like almost every widebody, and thus the option of locking out the outboards.

How about "modern airliners with more than one aileron per wing"?
 
miamiair
Posts: 4249
Joined: Thu Jul 15, 2004 9:42 pm

RE: 707 Flight Controls

Wed Jul 26, 2006 12:51 am

Quoting 411A (Reply 5):

Rudder also has balance panels, as the rudder and it's tab are balanced assemblies.
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