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# Can you point me to "turning with elevator" online info?

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# Can you point me to "turning with elevator" online info?

18th Oct 2020, 23:49

Join Date: Jul 2012
Location: Raleigh
Posts: 19
Can you point me to "turning with elevator" online info?

Hey all, I'm a long time GA lurker and I don't post much because I know so little..

However my nephew came to me, the aviation guy, and asked me a question that I not only can't answer, I can't even figure out where to find the answer and know you guys can help me out.

When I describe a banking turn it includes balancing rudders with aileron.

However he has learned from military jet simulators that he can roll 90° and then pull back on the yoke and make a much tighter turn than the bank turns I'm familiar with.

Can someone explain the terminology to me and point me to online resources that I am likely to understand?

19th Oct 2020, 00:33

Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 3,072
Elevators cause the aircraft to rotate around the pitching axis, nose up or nose down. If the aircraft is at 90 deg bank, then this pitching axis is making the aircraft turn. But at 90 deg bank, you are headed for the ground, none of the generated lift is pointed upwards, so the weight wins. (But you still needed aileron to roll to 90 degrees).

In any turn, you will be using a little back stick anyway, as you need to generate more than 1g worth of lift whenever the lift vector is not vertical. 60 deg bank, 2g, and then 72(I think) for 3g and then tear the wings off as the bank angle increases. You need infinite g at 89-89.99999 degrees.
19th Oct 2020, 02:09

Join Date: Feb 2006
Location: Hanging off the end of a thread
Posts: 18,205
The FAA do some very good free online books such as these engineering ones

https://www.faa.gov/regulations_poli...uals/aircraft/

for all things aircraft see

https://www.faa.gov/regulations_poli...uals/aviation/

RAF jet wise these are the manuals to look through... I can't help thinking some bits have been dumbed down over the years though.

I suggest book 1 although the full set is online.

AP3456 The Central Flying School (CFS) Manual of Flying

https://www.gov.uk/government/public...tent=immediate
19th Oct 2020, 02:30

Join Date: Dec 2006
Location: The No Transgression Zone
Posts: 2,346
Knife edge flight works because the fuselage itself is an airfoil at 90 degrees but the wings produce no lift.

If you want to know how much 'g' per bank angle it's 1/Cos (phi) or sec (phi), with phi in degrees

Edit rudder takes the role of the elevator, they switch roles

Last edited by Pugilistic Animus; 20th Oct 2020 at 00:41.
19th Oct 2020, 11:04

Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 3,072
but the wings produce no lift.
Actually the wings are producing lift, but none of it is vertical to oppose weight. It is pointing horizontally.
19th Oct 2020, 16:28

Join Date: Dec 2006
Location: The No Transgression Zone
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Originally Posted by Ascend Charlie
Actually the wings are producing lift, but none of it is vertical to oppose weight. It is pointing horizontally.
Indeed!.....
19th Oct 2020, 17:23

Join Date: Sep 2008
Location: Dark Side of West Wales
Age: 81
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Most of the "how" is well explained in posts above. The "why" is a different matter. In high speed fighter jets of the 1950's and later the rudder was not powered assisted in the same way as elevators and ailerons were, thus when the speed got above about 250 knots the rudder started to become in operative due to the force of the air passing over them. In my experience the Hawker Hunter was a good example of this.
19th Oct 2020, 23:40

Join Date: Jul 2012
Location: Raleigh
Posts: 19
Thanks!

I haven't had a chance to read yet, but if I understand correctly, this kind of turn is called "knife edge"?
20th Oct 2020, 02:02

Join Date: Oct 2013
Location: UK
Age: 38
Posts: 419
A knife edge would normally be described as straight line flight with an angle of bank of around 90 degrees. As pointed out, if you wish to maintain level flight you have to do something to replace the lift vector now not opposing gravity - so you end up with the fuselage having to have its angle of attack (with respect to straight and level flight) increased - by yawing usually.

What your nephew is doing is a banked turn with an extreme angle of bank (certainly compared to a lot of GA). It is usually not a balanced turn as GA teaches it, and it is necessary to pull positive G (considerable amounts) in order to maintain height as well as change heading.

Fast Jets are required to have considerable capacity for rate of change of angle about all of their axes to do their work (for example evading missiles or Radar Lock or flying at low level). This is best achieved by rotating the aircraft angle of lift towards the direction you wish to go with t/ailerons, and then pitching to change heading.

A lot of the time rudders don't feature in a lot of fast jet flight (or in a lot of aircraft). When I flew Bulldogs the pilots would tell me off for trying to coordinate turns after having it (rightly) drilled in to me when flying Vigilants! For the most part there are much lower structural limits on vertical tailplanes than on wings. Partly this is due to a lack of requirement for Yawing at high speeds - I think the Harrier has a Yaw limit of 7 or 11 degrees for example above certain speeds. Someone here may remember. I didn't work on Harrier - I didn't want to live around Farnborough. Therefore you can't generate the turning moment about the aircraft CofG to change heading fast enough even if you wanted to, and obviously it doesn't make sense to 'skid' around a turn at any speed using yaw only as its very inefficient and potentially dangerous.

The downside of high G banked rolls is that you lose energy very quickly, and this has to be replaced during the turn using throttle to balance the massively increased drag (multiple sources) and to also accelerate away after exiting the turn. Depending on the loading state of the aircraft the G you can pull can be severely limited too, thus modifying what you can do with the aircraft.

You can explore these situations in RC aircraft.

A simple 3-channel powered aircraft will usually have a throttle, a rudder and elevator channels. This type of RC aircraft changes direction using rudder and aircraft configuration (usually high wings with a marked amount of dihedral) to take advantage of the secondary effects of control of yaw to induce bank. This is further controlled using pitch to assist with maintaining level flight.

A standard 4-channel aircraft will use throttle, rudder, elevator and aileron for control and can perform efficient balanced turns. If configured correctly it can also perform highly banked turns with aileron, assisted with pitch.

You can also operate an aircraft on 3-channel controls using throttle, elevator and aileron. These are more commonly known as 'Bank and Yank' aircraft after what you need to do to turn them.

This is a massively complex topic that I'm butchering but that is the dirty basics.
20th Oct 2020, 09:00

Join Date: Apr 2009
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Originally Posted by unmanned_droid
What your nephew is doing is a banked turn with an extreme angle of bank (certainly compared to a lot of GA). It is usually not a balanced turn as GA teaches it, and it is necessary to pull positive G (considerable amounts) in order to maintain height as well as change heading.
Maybe not a balanced turn as taught for GA in the sense that rudder is generally not consciously applied by the pilot, but in all of the FJ types I've flown it would be expected that the ball stayed roughly in the middle under the action of stability augmentation systems (yaw dampers and the like) so the practical outcome was a balanced turn. I never flew the Jag, but understood that it was particularly prone to departure from controlled flight under pitch-yaw coupling...
20th Oct 2020, 09:20

Join Date: Apr 2000
Location: EGDC
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I never flew the Jag, but understood that it was particularly prone to departure from controlled flight under pitch-yaw coupling...
There used to be e very good video of a Jag departing controlled flight and tumbling end over end with fuel coming out of the intakes. ISTR it was a TP at the helm and he eventually deployed a drogue chute to get it pointing down in order to restart.
20th Oct 2020, 09:52

Join Date: Feb 2006
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Jag film starts at about 3.22

20th Oct 2020, 11:01

Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 3,072
That Mirage BEZU ball was having a hard time keeping up with the spin
20th Oct 2020, 13:10

Join Date: Oct 2013
Location: UK
Age: 38
Posts: 419
Originally Posted by Easy Street
Maybe not a balanced turn as taught for GA in the sense that rudder is generally not consciously applied by the pilot, but in all of the FJ types I've flown it would be expected that the ball stayed roughly in the middle under the action of stability augmentation systems (yaw dampers and the like) so the practical outcome was a balanced turn. I never flew the Jag, but understood that it was particularly prone to departure from controlled flight under pitch-yaw coupling...
I consciously decided to leave SAS and 'carefree handling' out of it but knew someone would have something to say about it.
20th Oct 2020, 22:05

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Anyone got Reynolds mobile number?
20th Oct 2020, 22:34

Join Date: Sep 2007
Location: Wiltshire
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Originally Posted by oldmansquipper
Anyone got Reynolds mobile number?

this rings a bell ........... 1.460×10−5

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