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Effects of Flaps and Ailerons on Pitch Trim
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jimpuglise(at)comcast.net
Guest

Posted: Mon Apr 12, 2010 11:08 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

As I remember my aerodynamics, the center of lift is always slightly aft of the center of gravity, causing a tendency for the aircraft to pitch down if the elevator is discounted.  The elevator therefor exerts a small downward force on tail of the aircraft.  This situation is reversed in a cannard, which is why they are a little more efficient.  Neither of these relates in any way to the positon of the trim tab on the elevator.  I'd probably agree that the tab would cause less drag if it were in line with the rest of the elevator when at cruise speed.  (I think this is the same thing Peter is saying.)   

  

Jim Puglise A-283 

---

mikenjulie.parkin(at)btin
Guest

Posted: Mon Apr 12, 2010 12:28 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

I suppose where the confusion comes here is the fact that there are 2 things

going on here..... a trim system overlaying an anti-servo system.  In a

conventional trim system the trim tab will retain its offset position if

that is where you leave it. Not so with an all flying tail where the neutral

is effectively changed  - with the trim system in the europa.  In a powered

all flying tail, the feel system is often used to move the effective

neutral.



Regards,



MP



Do not archive.

peterz(at)zutrasoft.com
Guest

Posted: Mon Apr 12, 2010 3:22 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

Hi Glenn,

that was my understanding as well - but when trimmed for cruise, wouldn't the anti-servo/trim-tab be required to portrude *downwards* to drive the trailing edge of the tailplane *up* to result in the equivalent of pulling back on the stick,  to have the tailplane produce the required downward force on the tail?

All the pics I've seen show the trimtab portruding *up*, ie, trim  = foward stick..... no?

Still confused,

Pete

A239

 On Mon, Apr 12, 2010 at 2:41 PM, Glenn Crowder <gcrowder2(at)hotmail.com (gcrowder2(at)hotmail.com)> wrote:

 	  Quote: 	
		   --> Europa-List message posted by: Glenn Crowder <gcrowder2(at)hotmail.com (gcrowder2(at)hotmail.com)>

 The airfoil of the wing of any aircraft with a non symmetrical section will produce a negative pitching moment (-cm) around the aerodynamic center of the wing.   This means that without the tailplane producing an equal but opposite moment the acft will pitch over into a vertical dive.  The all flying tailplane on the Europa has no fixed angle of incidence so to produce an opposing positive torque moment to the wings negative one the trim tab must be held out of plane.  At higher speeds then the tailplane must provide greater downforce then requiring even more trim tab offset.  We have to pay a small drag penalty to achieve a level trim condition in cruise flight.   This penalty can be reduced somewhat by loading the acft towards the aft cg limits requiring less trim tab offset reducing the downforce the tailplane must produce to maintain level flight.

   The tailless flying wing derives it's pitch stability due to the outer portions of the wing being reflexed up to produce that necessary positive pitching moment but also introduces that small drag penalty again.  There is no free lunch in aerodynamics!  Every desireable aerodynamic quality (like pitch stability) has a price that must be paid.

                                    Glenn

 Fred Klein <fklein(at)orcasonline.com (fklein(at)orcasonline.com)> wrote:

 >

 >On Apr 12, 2010, at 6:24 AM, david miller wrote:

 >

 >> I think that for most efficient flight the incidence of the wing and

 >> tail should be such that at cruise there is no up or down trim on

 >> the elevator or all flying tail.

 >

 >Fascinating discussion...as a non-aerodynamicist, I can't resist the

 >temptation to add a comment...

 >

 >I've always understood that the elevator or an all-flying tail

 >(horizontal tail plane) has a "job"...namely, to exert a force, either

 >up or down, in order to balance the lift of the wing and stabilize the

 >flight path of a normally configured aircraft (i.e., not a canard

 >type). To do this "job" requires "work"; the tail plane is never

 >neutral.  And w/ our Europae...with it's trim tabs acting in

 >opposition to the all-flying tail plane thru a direct mechanical

 >connection...whenever the tail plane is doing its job (at whatever

 >angle of incidence), the trim tabs will be doing their job as well

 >(that of counterbalancing forces on the tailplane), and will

 >necessarily be raised or lowered w/ reference to the tailplane.

 >

 >Of course if this explanation is correct, one might ponder the

 >aerodynamics of my tail-less biplane...pix below.

 >

 >Fred

 >

 >

 >

 >

 ========================

  target="_blank">http://www.matronics.com/Navigator?Europa-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

-- 

"A man is not old until his regrets take the place of his dreams. "

  [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Mon Apr 12, 2010 4:29 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

On 04/13/2010 01:19 AM, Peter Zutrauen wrote:



 	  Quote: 	
		   that was my understanding as well - but when trimmed for cruise,

 wouldn't the anti-servo/trim-tab be required to portrude *downwards* to

 drive the trailing edge of the tailplane *up*


	


Read again what you just said. If the trailing edge of the tailplane

moves up, the trim tab moves up even more. It *always* goes back to the

same stabile position, regardless of trim setting. The only difference

is that this stabile position is achieven by a different tailplane

incidence. This is how it works: you trim it down, it drives the

tailplane up, this will take the trim tab up even more, counteracting

what you just did... and the nett effect is that the tailplane's

trailing edge has moved up. This is how a anti-servo tab works.



 	  Quote: 	
		   to result in the

 equivalent of pulling back on the stick,


	


Pulling back on the stick is not the equivalent. If you pull on the

stick, the trim tab won't revert to its stabile aerodynamic position...

and that is why you need to keep pulling on the stick, to counteract the

forces on the trim tab.



 	  Quote: 	
		   to have the tailplane produce

 the required downward force on the tail?


	


Actually, it is not a trim tab, but an anti-servo trim tab. It works

differently.



 	  Quote: 	
		   All the pics I've seen show the trimtab portruding *up*, ie, trim  =

 foward stick..... no?


	


The *only* conclusion you can draw from the trimtab protruding up, is

that its stabile position is upwards relative to the tailplane. This

will remain the same for all trim settings. If you change the trim, the

only nett effect is that the tailplane will move to a different

incidence... but the trim tab will remain at the same position. Play

with it on the ground, until you see what's happening.



Frans

fklein(at)orcasonline.com
Guest

Posted: Mon Apr 12, 2010 4:34 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

Gentlemen,



Help me wipe the egg off my face...delete my last post...w/ our  

Europas, we're talkin anti-servo tabs, not trim tabs...my apologies  

for riffing on trim tabs before engaging my brain...



Fred

gcrowder2

Joined: 09 Jan 2006
Posts: 136
Location: Golden, Colorado USA

Posted: Mon Apr 12, 2010 5:53 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

Peter Zutrauen <peterz(at)zutrasoft.com> wrote:



 	  Quote: 	
		  Hi Glenn,



that was my understanding as well - but when trimmed for cruise, wouldn't

the anti-servo/trim-tab be required to portrude *downwards* to drive the

trailing edge of the tailplane *up* to result in the equivalent of pulling

back on the stick,  to have the tailplane produce the required downward

force on the tail?



All the pics I've seen show the trimtab portruding *up*, ie, trim  = foward

stick..... no?



Still confused,

Pete

A239



On Mon, Apr 12, 2010 at 2:41 PM, Glenn Crowder <gcrowder2(at)hotmail.com>wrote:



> 

>

> The airfoil of the wing of any aircraft with a non symmetrical section will

> produce a negative pitching moment (-cm) around the aerodynamic center of

> the wing.   This means that without the tailplane producing an equal but

> opposite moment the acft will pitch over into a vertical dive.  The all

> flying tailplane on the Europa has no fixed angle of incidence so to produce

> an opposing positive torque moment to the wings negative one the trim tab

> must be held out of plane.  At higher speeds then the tailplane must provide

> greater downforce then requiring even more trim tab offset.  We have to pay

> a small drag penalty to achieve a level trim condition in cruise flight.

> This penalty can be reduced somewhat by loading the acft towards the aft cg

> limits requiring less trim tab offset reducing the downforce the tailplane

> must produce to maintain level flight.

>

>  The tailless flying wing derives it's pitch stability due to the outer

> portions of the wing being reflexed up to produce that necessary positive

> pitching moment but also introduces that small drag penalty again.  There is

> no free lunch in aerodynamics!  Every desireable aerodynamic quality (like

> pitch stability) has a price that must be paid.

>

>                                   Glenn

>

> Fred Klein <fklein(at)orcasonline.com> wrote:

>

> >

> >On Apr 12, 2010, at 6:24 AM, david miller wrote:

> >

> >> I think that for most efficient flight the incidence of the wing and

> >> tail should be such that at cruise there is no up or down trim on

> >> the elevator or all flying tail.

> >

> >Fascinating discussion...as a non-aerodynamicist, I can't resist the

> >temptation to add a comment...

> >

> >I've always understood that the elevator or an all-flying tail

> >(horizontal tail plane) has a "job"...namely, to exert a force, either

> >up or down, in order to balance the lift of the wing and stabilize the

> >flight path of a normally configured aircraft (i.e., not a canard

> >type). To do this "job" requires "work"; the tail plane is never

> >neutral.  And w/ our Europae...with it's trim tabs acting in

> >opposition to the all-flying tail plane thru a direct mechanical

> >connection...whenever the tail plane is doing its job (at whatever

> >angle of incidence), the trim tabs will be doing their job as well

> >(that of counterbalancing forces on the tailplane), and will

> >necessarily be raised or lowered w/ reference to the tailplane.

> >

> >Of course if this explanation is correct, one might ponder the

> >aerodynamics of my tail-less biplane...pix below.

> >

> >Fred

> >

> >

> >

> >

-- 

"A man is not old until his regrets take the place of his dreams. "

dustinclowser_1014(at)YAH
Guest

Posted: Mon Apr 12, 2010 6:47 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

304.904.3850



 

   From: Glenn Crowder <gcrowder2(at)hotmail.com>

To: europa-list(at)matronics.com

Sent: Mon, April 12, 2010 9:36:43 PM

Subject: Re: Europa-List: Effects of Flaps and Ailerons on Pitch Trim



--> Europa-List message posted by: Glenn Crowder <gcrowder2(at)hotmail.com (gcrowder2(at)hotmail.com)>



Peter Zutrauen <peterz(at)zutrasoft.com (peterz(at)zutrasoft.com)> wrote:



 	  Quote: 	
		  Hi Glenn,



that was my understanding as well - but when trimmed for cruise, wouldn't

the anti-servo/trim-tab be required to portrude *downwards* to drive the

trailing edge of the tailplane *up* to result in the equivalent of  pulling

back on the stick,  to have the tailplane produce the required downward

force on the tail?



All the pics I've seen show the trimtab portruding *up*, ie, trim  = foward

stick..... no?



Still confused,

Pete

A239



On Mon, Apr 12, 2010 at 2:41 PM, Glenn Crowder <gcrowder2(at)hotmail.com (gcrowder2(at)hotmail.com)>wrote:



> --> Europa-List message posted by: Glenn Crowder <gcrowder2(at)hotmail.com (gcrowder2(at)hotmail.com)>

>

> The airfoil of the wing of any aircraft with a non symmetrical section will

> produce a negative pitching moment (-cm) around the aerodynamic center of

> the wing.  This means that without the tailplane producing an equal but

> opposite  moment the acft will pitch over into a vertical dive.  The all

> flying tailplane on the Europa has no fixed angle of incidence so to produce

> an opposing positive torque moment to the wings negative one the trim tab

> must be held out of plane.  At higher speeds then the tailplane must provide

> greater downforce then requiring even more trim tab offset.  We have to pay

> a small drag penalty to achieve a level trim condition in cruise flight.

> This penalty can be reduced somewhat by loading the acft towards the aft cg

> limits requiring less trim tab offset reducing the downforce the tailplane

> must produce to maintain level flight.

>

>  The tailless flying wing derives it's pitch stability due to the outer

> portions of the wing being reflexed up to produce that necessary positive

> pitching moment but also  introduces that small drag penalty again.  There is

> no free lunch in aerodynamics!  Every desireable aerodynamic quality (like

> pitch stability) has a price that must be paid.

>

>                                  Glenn

>

> Fred Klein <fklein(at)orcasonline.com (fklein(at)orcasonline.com)> wrote:

>

> >

> >On Apr 12, 2010, at 6:24 AM, david miller wrote:

> >

> >> I think that for most efficient flight the incidence of the wing and

> >> tail should be such that at cruise there is no up or down trim on

> >> the elevator or all flying tail.

> >

> >Fascinating discussion...as a non-aerodynamicist, I can't resist  the

> >temptation to add a comment...

> >

> >I've always understood that the elevator or an all-flying tail

> >(horizontal tail plane) has a "job"...namely, to exert a force, either

> >up or down, in order to balance the lift of the wing and stabilize the

> >flight path of a normally configured aircraft (i.e., not a canard

> >type). To do this "job" requires "work"; the tail plane is never

> >neutral.  And w/ our Europae...with it's trim tabs acting in

> >opposition to the all-flying tail plane thru a direct mechanical

> >connection..whenever the tail plane is doing its job (at whatever

> >angle of incidence), the trim tabs will be doing their job as well

> >(that of counterbalancing forces on the tailplane), and will

> >necessarily be raised or lowered w/ reference to the  tailplane.

> >

> >Of course if this explanation is correct, one might ponder the

> >aerodynamics of my tail-less biplane...pix below.

> >

> >Fred

> >

> >

> >

> >

-- 

"A man is not old until his regrets take the place of his dreamsp; -->                    -Matt Drall============


	


         [quote][b]

gcrowder2

Joined: 09 Jan 2006
Posts: 136
Location: Golden, Colorado USA

Posted: Mon Apr 12, 2010 7:55 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

OK Pete - the tailplane is ALWAYS pushing down at all airspeeds but at higher airspeeds the wing is at a very low angle of attack.  As the airspeed goes up, the

aerodynamic forces on all control surfaces (ailerons, rudder, tailplane) go up by the

SQUARE of airspeed.  This is why you cannot give full control deflection at VNE, the

control surfaces will depart the aircraft.  So when the wing goes to a very low angle

of attack, the tail must also.  The tail is still flying at a negative angle of attack but

it is very small.  However this small negative angle of attack is generating a lot of

positive CM because of the high airspeed.  To get this slightly negative angle of attack

at a high airspeed requires a lot of force and this is generated by the UP position of

the trimtab forcing the trailing edge of the tailplane DOWN.  The trim tab controls the

angle of attack of the tail (always negative but less negative at high speed), the

anti servo system keeps the tail at the set angle of attack.  Other factors come into

play here such as the angle of relative airflow from the wing downwash.  The tail

may look as though it has a positive angle of attack but because of the wing downwash, the relative airflow is actually hitting it from above.  This angle becomes less at high speeds but the forces go up with the square of airspeed.  

at high speeds

Date: Mon, 12 Apr 2010 19:19:06 -0400

Subject: Re: Effects of Flaps and Ailerons on Pitch Trim

From: peterz(at)zutrasoft.com

To: europa-list(at)matronics.com

Hi Glenn,

that was my understanding as well - but when trimmed for cruise, wouldn't the anti-servo/trim-tab be required to portrude *downwards* to drive the trailing edge of the tailplane *up* to result in the equivalent of pulling back on the stick,  to have the tailplane produce the required downward force on the tail?

All the pics I've seen show the trimtab portruding *up*, ie, trim  = foward stick..... no?

Still confused,

Pete

A239

On Mon, Apr 12, 2010 at 2:41 PM, Glenn Crowder <gcrowder2(at)hotmail.com> wrote:

The airfoil of the wing of any aircraft with a non symmetrical section will produce a negative pitching moment (-cm) around the aerodynamic center of the wing.   This means that without the tailplane producing an equal but opposite moment the acft will pitch over into a vertical dive.  The all flying tailplane on the Europa has no fixed angle of incidence so to produce an opposing positive torque moment to the wings negative one the trim tab must be held out of plane.  At higher speeds then the tailplane must provide greater downforce then requiring even more trim tab offset.  We have to pay a small drag penalty to achieve a level trim condition in cruise flight.   This penalty can be reduced somewhat by loading the acft towards the aft cg limits requiring less trim tab offset reducing the downforce the tailplane must produce to maintain level flight.

 The tailless flying wing derives it's pitch stability due to the outer portions of the wing being reflexed up to produce that necessary positive pitching moment but also introduces that small drag penalty again.  There is no free lunch in aerodynamics!  Every desireable aerodynamic quality (like pitch stability) has a price that must be paid.

                                  Glenn

Fred Klein <fklein(at)orcasonline.com> wrote:

 	  Quote: 	

On Apr 12, 2010, at 6:24 AM, david miller wrote:

> I think that for most efficient flight the incidence of the wing and

> tail should be such that at cruise there is no up or down trim on

> the elevator or all flying tail.

Fascinating discussion...as a non-aerodynamicist, I can't resist the

temptation to add a comment...

I've always understood that the elevator or an all-flying tail

(horizontal tail plane) has a "job"...namely, to exert a force, either

up or down, in order to balance the lift of the wing and stabilize the

flight path of a normally configured aircraft (i.e., not a canard

type). To do this "job" requires "work"; the tail plane is never

neutral.  And w/ our Europae...with it's trim tabs acting in

opposition to the all-flying tail plane thru a direct mechanical

connection...whenever the tail plane is doing its job (at whatever

angle of incidence), the trim tabs will be doing their job as well

(that of counterbalancing forces on the tailplane), and will

necessarily be raised or lowered w/ reference to the tailplane.

Of course if this explanation is correct, one might ponder the

aerodynamics of my tail-less biplane...pix below.

Fred

========================

target="_blank">http://www.matronics.com/Navigator?Europa-List

http://forums.matronics.com

le, List Admin.

="_blank">http://www.matronics.com/contribution

-- 

"A man is not old until his regrets take the place of his dreams. "

_________________________________________________________________

The New Busy is not the old busy. Search, chat and e-mail from your inbox

peterz(at)zutrasoft.com
Guest

Posted: Tue Apr 13, 2010 3:02 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

Hi Frans etal,

OK, ok,  I believe I have figured out what's going on with the upward trim tab in cruise.

The when the anti-servo trim tab is *trimmed* out of the neutral position, then the 'zero stick force'  angle of incidence of the tailplane wrt to the airflow is changed. When the trim tab is protruding *up* (thus driving the trailing edge downward),  I had thought this configuration was providing *lift* to the tail.  It was this simplistic interpretation which was confusing me. My bad. 

So, how does the following sound to all the aerodynamicists out there?  When one considers the tailplane&trim tab combination as a "symmetrical airfoil wing with flap", then moving  the trimtab off-center is effectively adding camber to the tailplane 'wing' and making the airfoil no longer symmetrical. In fact, moving the trimtab *up* results in an inverted camber (traditional wing upside down), thus generating a downward lift vector - and the stars are again all in proper alignment.

The faster one cruises, then the more camber is required to provide more downforce to counter-act the main-wing lift pitch, thus more trim tab.

I was/am not speaking of the anti-servo function of the tab, which I agree fully is driven in the same direction as the stick to augment/provide the (otherwise negligible flying-tail) stick forces to give proper speed-related feedback and make the tailplane less prone to flutter - that function is easy to visualize.

Cheers,

A happy that things now make sense again,

Pete

A239

On Mon, Apr 12, 2010 at 8:28 PM, Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)> wrote:

 [quote]--> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>

On 04/13/2010 01:19 AM, Peter Zutrauen wrote:

 > that was my understanding as well - but when trimmed for cruise,

 > wouldn't the anti-servo/trim-tab be required to portrude *downwards* to

 > drive the trailing edge of the tailplane *up*

Read again what you just said. If the trailing edge of the tailplane

 moves up, the trim tab moves up even more. It *always* goes back to the

 same stabile position, regardless of trim setting. The only difference

 is that this stabile position is achieven by a different tailplane

 incidence. This is how it works: you trim it down, it drives the

 tailplane up, this will take the trim tab up even more, counteracting

 what you just did... and the nett effect is that the tailplane's

 trailing edge has moved up. This is how a anti-servo tab works.

 > to result in the

 > equivalent of pulling back on the stick,

Pulling back on the stick is not the equivalent. If you pull on the

 stick, the trim tab won't revert to its stabile aerodynamic position...

 and that is why you need to keep pulling on the stick, to counteract the

 forces on the trim tab.

 > to have the tailplane produce

 > the required downward force on the tail?

Actually, it is not a trim tab, but an anti-servo trim tab. It works

 differently.

 > All the pics I've seen show the trimtab portruding *up*, ie, trim  =

 > foward stick..... no?

The *only* conclusion you can draw from the trimtab protruding up, is

 that its stabile position is upwards relative to the tailplane. This

 will remain the same for all trim settings. If you change the trim, the

 only nett effect is that the tailplane will move to a different

 incidence... but the trim tab will remain at the same position. Play

 with it on the ground, until you see what's happening.

 Frans

[b]

peterz(at)zutrasoft.com
Guest

Posted: Tue Apr 13, 2010 3:09 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

Further to my previous post, if one were to optimize the airfoil of the flying tail to minimize drag (which I had incorrectly presumed Don D had done), then the tailplane would have had a very slight inverted camber, calculated such that no trim-tab offset would have been required at the "target" cruise speed.

Cheers,

Pete

On Tue, Apr 13, 2010 at 7:00 AM, Peter Zutrauen <peterz(at)zutrasoft.com (peterz(at)zutrasoft.com)> wrote:

 	  Quote: 	
		   Hi Frans etal,

OK, ok,  I believe I have figured out what's going on with the upward trim tab in cruise.

The when the anti-servo trim tab is *trimmed* out of the neutral position, then the 'zero stick force'  angle of incidence of the tailplane wrt to the airflow is changed. When the trim tab is protruding *up* (thus driving the trailing edge downward),  I had thought this configuration was providing *lift* to the tail.  It was this simplistic interpretation which was confusing me. My bad. 

So, how does the following sound to all the aerodynamicists out there?  When one considers the tailplane&trim tab combination as a "symmetrical airfoil wing with flap", then moving  the trimtab off-center is effectively adding camber to the tailplane 'wing' and making the airfoil no longer symmetrical. In fact, moving the trimtab *up* results in an inverted camber (traditional wing upside down), thus generating a downward lift vector - and the stars are again all in proper alignment.

The faster one cruises, then the more camber is required to provide more downforce to counter-act the main-wing lift pitch, thus more trim tab.

I was/am not speaking of the anti-servo function of the tab, which I agree fully is driven in the same direction as the stick to augment/provide the (otherwise negligible flying-tail) stick forces to give proper speed-related feedback and make the tailplane less prone to flutter - that function is easy to visualize.

Cheers,

A happy that things now make sense again,

Pete

A239

On Mon, Apr 12, 2010 at 8:28 PM, Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)> wrote:

   	  Quote: 	
		  --> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>

On 04/13/2010 01:19 AM, Peter Zutrauen wrote:

 > that was my understanding as well - but when trimmed for cruise,

 > wouldn't the anti-servo/trim-tab be required to portrude *downwards* to

 > drive the trailing edge of the tailplane *up*

Read again what you just said. If the trailing edge of the tailplane

 moves up, the trim tab moves up even more. It *always* goes back to the

 same stabile position, regardless of trim setting. The only difference

 is that this stabile position is achieven by a different tailplane

 incidence. This is how it works: you trim it down, it drives the

 tailplane up, this will take the trim tab up even more, counteracting

 what you just did... and the nett effect is that the tailplane's

 trailing edge has moved up. This is how a anti-servo tab works.

 > to result in the

 > equivalent of pulling back on the stick,

Pulling back on the stick is not the equivalent. If you pull on the

 stick, the trim tab won't revert to its stabile aerodynamic position...

 and that is why you need to keep pulling on the stick, to counteract the

 forces on the trim tab.

 > to have the tailplane produce

 > the required downward force on the tail?

Actually, it is not a trim tab, but an anti-servo trim tab. It works

 differently.

 > All the pics I've seen show the trimtab portruding *up*, ie, trim  =

 > foward stick..... no?

The *only* conclusion you can draw from the trimtab protruding up, is

 that its stabile position is upwards relative to the tailplane. This

 will remain the same for all trim settings. If you change the trim, the

 only nett effect is that the tailplane will move to a different

 incidence... but the trim tab will remain at the same position. Play

 with it on the ground, until you see what's happening.

 Frans

-- 

"A man is not old until his regrets take the place of his dreams. "

  [quote][b]

raimo.toivio(at)rwm.fi
Guest

Posted: Tue Apr 13, 2010 5:26 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

Glenn,

  

 that makes sense.

  

 That is why when flying faster pilot have to push stick  forward to keep altude.

 Tailplane´s trailing edge is moving then down and  tailplane´s negative AoA goes slightly smaller.

 Tab´s anti-servo function moves tabs even more down to  generate (more) force to the pilot´s hand. To eliminate  that force pilot trims "nose down" = trim tabs move a little upp to keep  tailplane´s trailing edges down = where they should be to keep to maintain level  flight.

  

 Without anti-servo function I assume there would be still  pitch forces but only about 1/3-1/2 (look at the torque tube position in  relation with tailplanes)?

  

 When cruisíng levelled and with power lever in  it´s fore position, XRT needs almost full nose down trimming. 

  

 Raimo OH-XRT

 [quote]   ---

gcrowder2

Joined: 09 Jan 2006
Posts: 136
Location: Golden, Colorado USA

Posted: Tue Apr 13, 2010 11:59 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

  Hi Pete - yes, it is totally valid to think of it that way.   With the trim tab set to neutral, the tailplane is designed to maintain a negative angle of attack sufficient to balance the negative pitching moment of the wing at typical "in the pattern speeds".  This angle corresponds to the matching fillets molded into the fuselage sides at the tail.



   At low to moderate airspeeds, the tailplane needs a sizeable negative angle of attack to create enough downforce at the tail to force the leading edge of the wing up to it's required angle of attack.  Without the tail pushing down thus raising the wing leading edge up, the wing becomes lazy and does'nt want to fly, trying to reduce the angle of attack.  This is that negative pitching moment that all non symmetrical airfoils have. This is easily noticed in a stall situation, with nearly all the UP elevator being required to hold the high angle of attack.  

  

   Now when we want to go fast, requirements start to change.  We want the wing to assume a very low angle of attack because as the speeds go up, the lift

 on the wing goes up by the SQUARE of airspeed.  Reducing the angle of attack

 reduces the lift of the wing and also the induced drag.  But since we are going

 much faster, the wing is creating the same amount of lift sufficient to maintain a

 steady cruising altitude.  But at this higher airspeed the tailplane is still trying to maintain the high negative angle of attack it was designed to maintain at low to moderate airspeeds.  So now we have to do something to reduce the extremely high downforce the tail is trying to generate.  This is achieved by reducing the negative angle of attack of the tailplane.   We needed a large negative angle for takeoff and pattern work but now we need a much smaller negative angle.  

  

   To reduce this negative angle of attack we then apply DOWN trim which raises the trimtab UP, which then forces the trailing edge of the tailplane DOWN, which then reduces the negative angle of attack to a much smaller value, reducing the downforce generated by the tailplane.  It is still producing a large amount of downforce though as the high airspeed is creating a lot of force with only a small negative angle of attack (the airspeed squared thing).

  

   The aircraft COULD have been designed to maintain this high speed slightly negative angle of attack with neutral trim tab to minimize drag.  However if this had been done the design would have required HUGE trimtabs trimmed DOWN at lower speeds to then force the trailing edge of the tailplane UP that would then create a large negative angle of attack on the tailplane required to balance the wing at lower airspeeds.

  

  Date: Tue, 13 Apr 2010 07:08:34 -0400

Subject: Re: Effects of Flaps and Ailerons on Pitch Trim

From: peterz(at)zutrasoft.com

To: europa-list(at)matronics.com



Further to my previous post, if one were to optimize the airfoil of the flying tail to minimize drag (which I had incorrectly presumed Don D had done), then the tailplane would have had a very slight inverted camber, calculated such that no trim-tab offset would have been required at the "target" cruise speed.



Cheers,

Pete



 On Tue, Apr 13, 2010 at 7:00 AM, Peter Zutrauen <peterz(at)zutrasoft.com (peterz(at)zutrasoft.com)> wrote:

  	  Quote: 	
		  Hi Frans etal,



OK, ok,  I believe I have figured out what's going on with the upward trim tab in cruise.



The when the anti-servo trim tab is *trimmed* out of the neutral position, then the 'zero stick force'  angle of incidence of the tailplane wrt to the airflow is changed. When the trim tab is protruding *up* (thus driving the trailing edge downward),  I had thought this configuration was providing *lift* to the tail.  It was this simplistic interpretation which was confusing me. My bad. 



So, how does the following sound to all the aerodynamicists out there?  When one considers the tailplane&trim tab combination as a "symmetrical airfoil wing with flap", then moving  the trimtab off-center is effectively adding camber to the tailplane 'wing' and making the airfoil no longer symmetrical. In fact, moving the trimtab *up* results in an inverted camber (traditional wing upside down), thus generating a downward lift vector - and the stars are again all in proper alignment.



The faster one cruises, then the more camber is required to provide more downforce to counter-act the main-wing lift pitch, thus more trim tab.



I was/am not speaking of the anti-servo function of the tab, which I agree fully is driven in the same direction as the stick to augment/provide the (otherwise negligible flying-tail) stick forces to give proper speed-related feedback and make the tailplane less prone to flutter - that function is easy to visualize.



Cheers,

A happy that things now make sense again,

Pete

A239  

 



 On Mon, Apr 12, 2010 at 8:28 PM, Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)> wrote:

  	  Quote: 	
		   --> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>

 On 04/13/2010 01:19 AM, Peter Zutrauen wrote:



 	  Quote: 	
		   that was my understanding as well - but when trimmed for cruise,

 wouldn't the anti-servo/trim-tab be required to portrude *downwards* to

 drive the trailing edge of the tailplane *up*


	




Read again what you just said. If the trailing edge of the tailplane

moves up, the trim tab moves up even more. It *always* goes back to the

same stabile position, regardless of trim setting. The only difference

is that this stabile position is achieven by a different tailplane

incidence. This is how it works: you trim it down, it drives the

tailplane up, this will take the trim tab up even more, counteracting

what you just did... and the nett effect is that the tailplane's

trailing edge has moved up. This is how a anti-servo tab works.

 

 	  Quote: 	
		   to result in the

 equivalent of pulling back on the stick,


	




Pulling back on the stick is not the equivalent. If you pull on the

stick, the trim tab won't revert to its stabile aerodynamic position...

and that is why you need to keep pulling on the stick, to counteract the

forces on the trim tab.

 

 	  Quote: 	
		   to have the tailplane produce

 the required downward force on the tail?


	




Actually, it is not a trim tab, but an anti-servo trim tab. It works

differently.

 

 	  Quote: 	
		   All the pics I've seen show the trimtab portruding *up*, ie, trim  =

 foward stick..... no?


	




The *only* conclusion you can draw from the trimtab protruding up, is

that its stabile position is upwards relative to the tailplane. This

will remain the same for all trim settings. If you change the trim, the

only nett effect is that the tailplane will move to a different

incidence... but the trim tab will remain at the same position. Play

with it on the ground, until you see what's happening.



Frans

  

 



	




	


-- 

"A man is not old until his regrets take the place of his dreams. "

 	  Quote: 	
		  



 	  Quote: 	
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ww.matronics.com/contribution



	
 		 	   		  The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail.  Get busy.  [quote][b]

grahamsingleton(at)btinte
Guest

Posted: Tue Apr 13, 2010 1:35 pm Post subject: Effects of Flaps and Ailerons on Pitch Trim

Maybe I can add a bit more confusion?

In fact the tail plane pivot is not at the neutral point, it's slightly forward I think (Mike?) You're right that the tab is anti balance.

With symmetrical sections aerodynamic centre doesn't move, that's why all flying tails are usually symmetrical. (afaik) Add the effect of the displaced tab and you have camber so the section will now provide lift at zero AoA. ie tailplane in trail?  This lift is just enough to balance the wing pitching moment. Increase speed and you get more lift so nose will pitch up. Speed reduces again etc. 

Graham

From: Frans Veldman <frans(at)privatepilots.nl>

To: europa-list(at)matronics.com

Sent: Monday, 12 April, 2010 19:51:09

Subject: Re: Effects of Flaps and Ailerons on Pitch Trim



--> Europa-List message posted by: Frans Veldman <frans(at)privatepilots.nl (frans(at)privatepilots.nl)>



On 04/12/2010 08:06 PM, Peter Zutrauen wrote:



The only thing I'm troubled with is that the stable rest position of the

tailplane plus trim tab is not when they are perfectly lined out in

relation to each other.



Maybe, just maybe, this may have something to do with the fact that the

hinges are on the upper side of the tailplane, rather than in  the

center. The forces acting on the lower side have more leverage than the

forces acting on the upper side, hence the stable position of the trim

tab where all forces are cancelled out, is slightly up.



The more I think about this, the more I think that this is the reason

why we always see a trim tab up position.



Any comments about this hypothesis?



Frans

 

  [quote][b]

rparigoris

Joined: 24 Nov 2009
Posts: 785

Posted: Tue Apr 13, 2010 2:21 pm Post subject: Re: Effects of Flaps and Ailerons on Pitch Trim

Another contributing factor to necessary stabilator force required is engine angle. An easy check would be to trim for normal cruise speed with engine running, note trim position and measure precise location of stick (string or ruler). Then kill engine, prefer if you can feather prop, but stopped prop is sufficient, then with trim in same location and stick brought to precise location see what speed you achieve. If speed is greater than engine on cruse speed you don't quite have enough down engine angle (prop end not down far enough)  for most efficiency and vise versa (less speed and too much down engine angle).

On models and full scale having a slight positive nose up pitching is not a bad thing.

BTW similar technique can be used to dial in CG on a model, motor off trim for a few MPH over stall, then dive to maneuvering speed and put stick in exact position it was to achieve trim a few MPH over stall, if it pitches wildly up you are too nose heavy for most efficiency. Again a slight nose up pitching is desirable

Ron Parigoris

jan(at)thesambrooks.net
Guest

Posted: Wed Apr 14, 2010 12:29 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

How do I change my husbands e mail - all this europa info comes to me and it

should go to Martin Sambrook martin(at)thesambrooks.net,

Thanks Jan



--

loboloda(at)execulink.com
Guest

Posted: Wed Apr 14, 2010 5:01 am Post subject: Effects of Flaps and Ailerons on Pitch Trim

Jan,



You can go to the matronics web site and cancel. hubby will then have  

to re-enlist with his address



Dave



do not archive

On 14-Apr-10, at 4:27 AM, jansambrook wrote:



[quote] 

 <jan(at)thesambrooks.net>



 How do I change my husbands e mail - all this europa info comes to  

 me and it

 should go to Martin Sambrook martin(at)thesambrooks.net,

 Thanks Jan



 --

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