timz
Posts: 6102
Joined: Fri Sep 17, 1999 7:43 am

Some Elementary Flight-control Questions

Thu Apr 03, 2003 10:33 am

In order to roll a C172 into a 60-degree bank, do you turn the wheel right, then center it as you roll, then turn it left to stop the roll at 60 degrees, then center it to hold that bank? Or do you need right aileron to maintain the bank? What about rudder?

If you're in the bank, trimmed for level flight (whatever that means), and you release the controls of the C172 (and reduce power to that needed for level flight?), what will happen and how long will it take to happen?

Would the answers be different for a 30-degree bank?

 
jhooper
Posts: 5560
Joined: Thu Dec 13, 2001 8:27 pm

RE: Some Elementary Flight-control Questions

Thu Apr 03, 2003 10:40 am

In general, you apply aileron control pressure to establish the aircraft in a bank while also using coordinated rudder.. Once you reach the angle of bank desired, neutralize the ailerons. Up elevator would need to be used to compensate for the loss in the vertical component of life (the wings still need to support the weight of the aircraft as well as the centrifugal force). To roll the wings level, apply opposite aileron input and then neutralize the ailerons once the wings roll level. If you trim the aircraft for level flight in a turn, the turn should continue indefinitely at a medium bank turn. In a shallow bank turn, the (lateral?) stability of the aircraft would cause the aircraft to tend to return to straight flight. In a steep bank, you may notice an overbanking tendency since the outside wing travels farther throughout the turn and hence generates more lift. I hope this helps.

[Edited 2003-04-03 02:41:48]
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Woodreau
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Joined: Mon Sep 24, 2001 6:44 am

RE: Some Elementary Flight-control Questions

Fri Apr 04, 2003 9:19 am

If after you're established in the steep turn, you trim the aircraft properly, you can let the controls go and the aircraft will stay in the steep turn in level flight.

One of my instructors demonstrated this, got into the steep turn, trimmed out and let go of the controls. We just kept going around and around. It'd get bumpy as we flew thru our wake.

Cheers  Smile
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A330
Posts: 688
Joined: Wed May 19, 1999 12:31 am

RE: Some Elementary Flight-control Questions

Fri Apr 04, 2003 6:55 pm

If you are properly trimmed and cut power, the plane will descend, and with about 100ft per 100 rpm less! Try it!
Shiek!
 
Guest

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 2:29 am

Small amounts of bank: You will have to hold aileron pressure to keep that bank angle, to counteract the effects of dihedral.

Medium amounts of bank: You should be able to maintain that angle of bank with no aileron pressure.

Large amounts of bank (aka steep turns): You will have to hold some opposite aileron pressure to maintain that bank angle to counteract overbanking tendency. Use rudder pressure to correct for adverse yaw.


'Speed
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 6:35 am

Hi guys.

> Timz, here's a little info in response to your words..... trimmed for level flight (whatever that means)

A pilot can trim an aircraft for level flight (to maintain his current altitude), via the use of a "trim tab" which is attached to the aircraft's elevator. In a C-172, the pilot controls the trim tab by rotating a small wheel that's located on the cockpit's center console (below the throttle).

Once the pilot has trimmed the aircraft for level flight by deflecting the trim tab into the relative airflow at a certain angle, which in turn holds the elevator at an angle needed by the pilot (this involves aerodynamics which myself or another member can explain to you), the pilot can then remove his hands from the control column, rest them on his legs, behind his head, in his pockets, wherever ........ and the aircraft's nose won't pitch up or down.

The trim tab is used to "fine tune" an aircraft's pitch untill the Vertical Speed Indicator (VSI) is holding a desired rate of climb, descent, or level flight, which allows the pilot to remove his hands from the controls, so he can relax his arms.  Big thumbs up

In this photo you can see the black trim tab wheel below the throttle & to the left. If you rotate this wheel down towards the floor - you'll be adding Nose Up trim. If you rotate it up towards the windscreen - you'll be adding Nose Down trim. When doing so, a gauge to the left of the wheel shows how much trim imput you've added for a pitch setting above or below neutral -- the takeoff setting.


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In these photos you can see the long trim tab on the trailing edge of the right side of the elevator.


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PS, a 60 degree bank causes 2 G's of force, regardless of airspeed.

Chris  Smile
"Just a minute while I re-invent myself"
 
ThirtyEcho
Posts: 1409
Joined: Tue Jan 01, 2002 1:21 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 7:01 am

A little word about using that trim gauge alongside the trim wheel; you're about to find out why the Cessnas have a rear window. Having once spotted a trim tab that was substantially "nose up" when the gauge indicated neutral, I now make it a practice to roll the trim to neutral by holding the elevator up and actually LOOKING at the trim tab through the rear window. I then look back at the gauge to see if it is also showing neutral. I do this after the runup and then give the nose trim a little flick nose up so I can nail the proper climb angle right after liftoff without effort. I'm lazy.

Also, if you look in the autopilot manual it will tell you how much altitude you will lose with runaway nose down trim. The "thumb trim" can operate even if the autopilot is offline. While you can overpower it, the last C172 POH I looked at said that you could lose up to 250ft with runaway nose trim before recovering. I always disconnect the "thumb trim" before takeoff.
 
ThirtyEcho
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Joined: Tue Jan 01, 2002 1:21 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 7:17 am

"PS, a 60 degree bank causes 2 G's of force, regardless of airspeed."

I think that I found a way around the laws of physics, then. When I was young and foolish, I liked to give my instructor gray hairs by rolling into a 60-degree bank turning from base to final but also adding substantial forward force onto the wheel so that there was NO additional G load. All you have to do is turn slightly before you get to the runway centerline.

Later, I began to wonder if this wasn't the entry to the "Czech Death Spiral" or something. But there sure as hell wasn't anything beyond 1G all through the 60-degree turn.
 
PPGMD
Posts: 2398
Joined: Sun Sep 30, 2001 5:39 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 7:36 am

30E I think he means if you want to stay at the same altitude.
At worst, you screw up and die.
 
XFSUgimpLB41X
Posts: 3960
Joined: Fri Aug 25, 2000 1:18 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 8:20 am

he was talking about a level 60 degree turn.... a 70 degree level turn is 3.


And yes, 30E... if a student did that with me in the cockpit turning on final, they may have some bruises around their neck when we get on the ground unless i had good warning and we were goofing around a bit.
Chicks dig winglets.
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 9:53 am

Hi guys.

Yes, I was talking about a 60 degree turn during level flight.

I must admit I was surprised when my flight instructor told me that you feel 2 G's of force during a 60 degree bank ......"regardless of airspeed"!

I instantly thought of a fighter jet banking into a 60 degree turn while flying around 700 mph, and couldn't figure out why the pilot wouldn't feel higher G forces. Then, after poping through a couple of mental blocks, I figured out that at such a high airspeed, a fighter jet's 60 degree banking turn would have a diameter of miles apon miles before 360 degrees of heading were finished ....compared to a Cessna 150's tiny little 360 over the ground. So, airspeed and distance covered during the turn became relevant to me with regards to the 2 G's being pulled. So I just accepted that 60 degrees = 2 G's.

I fighter pilot simply has to start pulling back on the stick during a bank to increase G forces.

I don't know if I figured it out in my head properly or not. I never bothered to start messing around with fancy math .... that would only confuse me more!! Big grin


Chris  Smile
"Just a minute while I re-invent myself"
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Some Elementary Flight-control Questions

Sat Apr 05, 2003 10:53 am

Hello again.

>ThirtyEcho, the method of visually cross-checking that your trim tab & the trim gauge in the cockpit agree with each other by actually looking through the back window is exactly how I was trained for my PPL back in 1987. I hope today's Flight Schools still have that technique as an item on the checklist somewhere between the ground and takeoff.

For myself, it's an item on the pre-taxi part of the checklist.

After checking that my flight controls are "Free and Correct", I pull the yoke all the way aft so I can get a good look at the elevator & trim tab. Then I roll the trim wheel through it's whole range of travel (both Nose Up & Nose Down), while watching the tab move, and cross-checking it's position with the cockpit's gauge. Then I return the tab to neutral. Doing this lets me know that the trim tab cable isn't jammed somewhere.

I also add a little nose up trim during my pre takeoff checks. I bet a lot of pilots do.

Chris  Smile

"Just a minute while I re-invent myself"

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