Author Topic: Combat Trim?  (Read 3303 times)

Offline Traveler

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Re: Combat Trim?
« Reply #30 on: January 12, 2012, 04:36:52 PM »
Just made a paper aeroplane, gave it elevators and gave it trim tabs on the elevators.  It loops up faster with trim tabs deflected up and elevators deflected up. :banana:

 :old: when lacking a full explanation, experimental evidence helps, on occasion.


 :D

if it was to scale, yes, I’d agree with you, however, I would not stake my life on it.
 I've run across more then a few students pilots  who found it difficult to accept the correct answer even when it was pointed out by many that they were just wrong in their thinking.  With them it’s easy, I just point out that they have to take the FAA written pilot exam and they can’t take it without my signoff.  And I don’t signoff on students that don’t understand basic concepts. 

Some even go so far as to parrot back the correct answer for signoff but then go put down the wrong answer on the test.  There the very best of the special students.  I enjoy them the most.  The first written test is free, but re-test is $150.00 and of course there is ground school, additional flight lessons at $175.00 a pop.  I call those student “Money in the pocket”.  Like my Dad told me once, “Can’t fix stupid”.   
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Offline FLS

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Re: Combat Trim?
« Reply #31 on: January 12, 2012, 04:44:52 PM »
Midway a better experiment would be to time your max performance turns with and without the trim tab up.

The basic mistake you're making is thinking that turn rate is limited by elevator deflection. Since you can already stall or black out with max deflection there is no need to increase it. Turn rate is limited by speed and AOA. Elevators are designed with more than enough deflection to provide max AOA. Exceeding max AOA just stalls you.

If you scale your stick then trimming might make it easier to control your AOA near the critical stall point but it won't increase your max turn rate.
« Last Edit: January 12, 2012, 04:50:37 PM by FLS »

Offline FLS

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Re: Combat Trim?
« Reply #32 on: January 12, 2012, 04:47:44 PM »
Ah, I think I see. I'll give it a try, thanks FLS.

Since required trim changes with speed it won't be exact but it lets you get close while keeping your eyes outside the cockpit.

Offline hitech

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Re: Combat Trim?
« Reply #33 on: January 12, 2012, 05:19:39 PM »
Traveler: Excessive lift does not = climb ( i think I saw you write this) when wings level , excess lift = pitch up. In a steady state climb I assume you know you need less lift then when in level flight.

As to Midway's strange question of will full down trim when holding full back stick give you better turn performance.

First the question poses many unknowns and assumptions.

1. Unless you were very slow there are not many planes you could have full trim and have enough strength to move the control full opposite  direction.
2. If full elevator already stalls the more aoa/elevator will  not help your turn.

So on to the real question. Does full down trim when the elevator is fully deflected up , increase the AOA.

My guess is , it would increase the AOA if it could be done.

In AH it does not.

HiTech

HiTech




Offline SectorNine50

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Re: Combat Trim?
« Reply #34 on: January 12, 2012, 06:03:41 PM »
Plus, the trim tab is so small I don't think it would add a noticeable amount to the deflection anyway.  The only reason it's as effective as it is at it's job is because it's at the end of the elevator, where it has a mechanical advantage.
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Offline Traveler

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Re: Combat Trim?
« Reply #35 on: January 12, 2012, 06:24:47 PM »
Traveler: Excessive lift does not = climb ( i think I saw you write this) when wings level , excess lift = pitch up. In a steady state climb I assume you know you need less lift then when in level flight.


I did write it and I didn’t want to confuse Midway with the different components  of lift, I was speaking in the terms of the sum  total sum of all upward forces of lift, frequently, much of the difficulty encountered in explaining the forces that act upon an airplane is largely a matter of language and its meaning. For example, pilots have long believed that an airplane climbs because of excess lift. This is not true if one is thinking in terms of wing lift alone. It is true, however, if by lift it is meant the sum total of all “upward forces.” But when referring to the “lift of thrust” or the “thrust of weight,” the definitions previously established for these forces are no longer valid and complicate matters. It is this impreciseness in language that affords the excuse to engage in arguments, largely academic, over refinements to basic principles.

Having no idea of Midways background or education in aviation matters I chose to use and speak in terms that had a long standing understanding by the general public, if somewhat imprecise I thought he would understand the concept.

No matter what words we use or what we call it, it still comes down to Newton’s third law, right.
« Last Edit: January 12, 2012, 06:30:03 PM by Traveler »
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Offline Midway

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Re: Combat Trim?
« Reply #36 on: January 12, 2012, 07:42:14 PM »
Midway a better experiment would be to time your max performance turns with and without the trim tab up.

The basic mistake you're making is thinking that turn rate is limited by elevator deflection. Since you can already stall or black out with max deflection there is no need to increase it. Turn rate is limited by speed and AOA. Elevators are designed with more than enough deflection to provide max AOA. Exceeding max AOA just stalls you.

If you scale your stick then trimming might make it easier to control your AOA near the critical stall point but it won't increase your max turn rate.

 :O  This I understand!  Thank you, FLS.

You're saying that turn rate is limited by stall/blackout and you can get there using just elevators, adding trim tab deflection to get to that AOA is pointless since you can get there with the elevators alone.  :aok

I understand now.

Forgive me, my education in things aerodynamic is very very limited and I tend to keep pushing the bounds of my idea until I get an answer that I can comprehend.  I understand this one and HiTech's comments above reinforce it.

Thank you gentlemen for helping this aerodynamically uneducated AH pilot comprehend this.   :salute :rock

 :cheers: :bolt:


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Offline Midway

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Re: Combat Trim?
« Reply #37 on: January 12, 2012, 07:48:44 PM »
if it was to scale, yes, I’d agree with you, however, I would not stake my life on it.
 I've run across more then a few students pilots  who found it difficult to accept the correct answer even when it was pointed out by many that they were just wrong in their thinking.  With them it’s easy, I just point out that they have to take the FAA written pilot exam and they can’t take it without my signoff.  And I don’t signoff on students that don’t understand basic concepts. 

Some even go so far as to parrot back the correct answer for signoff but then go put down the wrong answer on the test.  There the very best of the special students.  I enjoy them the most.  The first written test is free, but re-test is $150.00 and of course there is ground school, additional flight lessons at $175.00 a pop.  I call those student “Money in the pocket”.  Like my Dad told me once, “Can’t fix stupid”.   


I would never do this.  I would keep pushing you or research on my own until I comprehend the concepts.  The key for me is to understand why I'm wrong, not just that I'm wrong.  I was pretty sure I was wrong since you all are experts and I am not (in this field), but I didn't want to change my view of it because somebody told me to (ACK ACK), I want to change it because I understand it.  Which I now do.

Thank you, sir, for trying to help me.  I learned something today.  Nice.  :aok

 :old: :airplane: :joystick:


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Offline MK-84

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Re: Combat Trim?
« Reply #38 on: January 12, 2012, 08:06:28 PM »
So how do the ailerons on a zero work?

Offline Traveler

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Re: Combat Trim?
« Reply #39 on: January 12, 2012, 09:00:00 PM »
I would never do this.  I would keep pushing you or research on my own until I comprehend the concepts.  The key for me is to understand why I'm wrong, not just that I'm wrong.  I was pretty sure I was wrong since you all are experts and I am not (in this field), but I didn't want to change my view of it because somebody told me to (ACK ACK), I want to change it because I understand it.  Which I now do.

Thank you, sir, for trying to help me.  I learned something today.  Nice.  :aok

 :old: :airplane: :joystick:

Everyone tries to be helpful, but you might have been better served to have just stated in plain English, I don’t understand can someone explain it to me, instead of continually stating an incorrect concept as being the correct choice.
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Offline SectorNine50

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Re: Combat Trim?
« Reply #40 on: January 12, 2012, 11:42:43 PM »
So how do the ailerons on a zero work?

What do you mean?  Do they have a unique design?
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Offline Midway

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Re: Combat Trim?
« Reply #41 on: January 13, 2012, 12:11:09 AM »
Everyone tries to be helpful, but you might have been better served to have just stated in plain English, I don’t understand can someone explain it to me, instead of continually stating an incorrect concept as being the correct choice.

Ah, but I was correct that full down trim, deflecting trim tabs up, would raise the nose further adding to what up elevators are doing assuming you had the required muscle or hydrolic power.  In other words AOA would increase.   It is just not necessary since you can achieve stall or blackout with just the elevators.   So the concept was correct, just not doable except at very low speed where a stall would likely occur before the trim tabs add to AOA.  I do understand this is an odd way of looking at it due to my lack of any flight school experience.

Anyways on my original question, I have an answer that makes complete sense to me now.  Trim tabs offer no increased slow speed turn performance in AH, which differs from what someone told me in AH   Elevators will take you to the stall or blackout limit.

 :)

« Last Edit: January 13, 2012, 12:23:24 AM by Midway »


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Offline Midway

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Re: Combat Trim?
« Reply #42 on: January 13, 2012, 12:54:33 AM »
Just to take this one step further.  Given that trim tabs can add to AOA, if the elevators froze in a neutral position and could not move for some mechanical breakdown reason, then dialing elevator trim tabs down (deflecting them up) would be a way to get your nose up, although it would only do so slowly due to the small size of the tabs.

Correct? :pray


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Offline hitech

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Re: Combat Trim?
« Reply #43 on: January 13, 2012, 10:15:47 AM »
Just to take this one step further.  Given that trim tabs can add to AOA, if the elevators froze in a neutral position and could not move for some mechanical breakdown reason, then dialing elevator trim tabs down (deflecting them up) would be a way to get your nose up, although it would only do so slowly due to the small size of the tabs.

Correct? :pray

That would be my guess.

HiTech

Offline Midway

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Re: Combat Trim?
« Reply #44 on: January 13, 2012, 10:18:10 AM »


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