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LarryM

Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL

Posted: Thu Jan 10, 2008 5:57 pm Post subject: How to increase lift on horizontal stab?

Would anyone know or be able to direct me to someone/where....



   I want to increase the lift of my flat surfaced horizontal stab.  It can be done by increasing the span, or by putting airfoil shaped ribs on the underside.  Any ideas on which would have the greatest effect for the amount of work needed?  The ribs would be quite simple, but how does one estimate the benefit?



Thanks,

larry



Ps I already have vg's.  They helped incredibly, but I;m on a quest for even more!

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Thu Jan 10, 2008 9:36 pm Post subject: Re: How to increase lift on horizontal stab?

 	  Quote: 	
		  Ps I already have vg's. They helped incredibly, but I;m on a quest for even more!

	




What did you gain and on what model ?  

What is your stall characteristics now  ?



I have used differnt Vgs with some benefit but not huge like many claim.



I tried a few years ago some VGs on bottom of horiz stab just ahead of the hinge line  to try to get more elevator control while on amphib floats so that I could rotate easier.  I did have a negative AOA with wheels down and it was hard to rotate and lengthy.  I never found they helped. 

What I did was to redesign the nose wheels casters and raiser the nose about 1 " high giving me about 1 degree +  now.   On water I sat about 3 to 5 degrees + and was never an issue.

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LarryM

Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL

Posted: Fri Jan 11, 2008 8:24 am Post subject: Re: How to increase lift on horizontal stab?

Dave check this link in the archives.

It's an Avid Mk4, STOL wing



http://forums.matronics.com/viewtopic.php?t=25907&highlight=cci+vgs

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Fri Jan 11, 2008 10:11 am Post subject: Re: How to increase lift on horizontal stab?

 	  Quote: 	
		  However; in the normal cruise range with a cruise rpm of 5400 yielded 84 mph with the vg?s on the tail. Without the vgs, the same rpm yielded 74mph. This is explained by the efficiencies of the tail. 

	




Larry,   that is quite a gain.  I t hink everyone should go out and try this.



I have VGs on my wings and have not been in any hurry to take them off.  Certainly I did not see and gains like you did BUT i never put on tail yet.  How far ahead of Hinge line did you place them ?  and what spacing? I have several kinds of Vgs in stock here that I can try with.  



One drawback that I did notice is that there is less buffeting felt prior to stall. On power on stalls you can go from flying to abrupt stall and most times a wing drop.  I think mine are at about 10% of chord. My  Wing is not under cambered like your either if that matters

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Jan 11, 2008 10:22 am Post subject: How to increase lift on horizontal stab?

I think I'm missing something here...  If you increase the lift on your HS

then you will put the nose down.  I expect you want to increase down

pressure generated by the HS to lift the nose up.



One thing to try is gap seals... With your vg's that could be a big asset.

The next thing to try is aerodynamically shaped foils... finally all thee;

vg's seals and foils.  Past that you are stuck with larger surfaces, the

increase in weight and change in balance that occurs.



I expect the greatest drag will be caused by the vg's.  Foils and seals

should only make the airflow more efficient.



Noel

Mod III-A



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

clint_bazzill(at)hotmail.
Guest

Posted: Fri Jan 11, 2008 10:24 am Post subject: How to increase lift on horizontal stab?

I read his article.  Very well written and I will have data for the laminar flow wing on the Kitfox shortly along with horiz data also.  Clint

[quote] Subject: Re: How to increase lift on horizontal stab?

 From: dave(at)cfisher.com

 Date: Fri, 11 Jan 2008 10:11:21 -0800

 To: kitfox-list(at)matronics.com

 --> Kitfox-List message posted by: "dave" <dave(at)cfisher.com>

 > However; in the normal cruise range with a cruise rpm of 5400 yielded 84 mph with the vg?s on the tail. Without the vgs, the same rpm yielded 74mph. This is explained by the efficiencies of the tail. 

 > 

 Larry, that is quite a gain. I t hink everyone should go out and try this.

 I have VGs on my wings and have not been in any hurry to take them off. Certainly I did not see and gains like you did BUT i never put on tail yet. How far ahead of Hinge line did you place them ? and what spacing? I have several kinds of Vgs in stock here that I can try with. 

 One drawback that I did notice is that there is less buffeting felt prior to stall. On power on stalls you can go from flying to abrupt stall and most times a wing drop. I think mine are at about 10% of chord. My Wing is not under cambered like your either if that matters

 --------

 Rotax Dealer, Ontario Canada

 Flying Videos and Kitfox Info

 http://www.cfisher.com/

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=157487#157487<===============

   	  Quote: 	
		  [b]

clint_bazzill(at)hotmail.
Guest

Posted: Fri Jan 11, 2008 10:43 am Post subject: How to increase lift on horizontal stab?

Balance your elevator with springs.  Use gap seals, put vortex generator on bottom of stab.  As good as it gets.  Clint

 	  Quote: 	
		   Subject: How to increase lift on horizontal stab?

 From: CrownLJ(at)verizon.net

 Date: Thu, 10 Jan 2008 17:57:02 -0800

 To: kitfox-list(at)matronics.com

 --> Kitfox-List message posted by: "LarryM" <CrownLJ(at)verizon.net>

 Would anyone know or be able to direct me to someone/where....

 I want to increase the lift of my flat surfaced horizontal stab. It can be done by increasing the span, or by putting airfoil shaped ribs on the underside. Any ideas on which would have the greatest effect for the amount of work needed? The ribs would be quite simple, but how does one estimate the benefit?

 Thanks,

 larry

 Ps I already have vg's. They helped incredibly, but I;m on a quest for even more!

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=157357#157357

===========

[quote] 

   	  Quote: 	
		  [b]

LarryM

Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL

Posted: Fri Jan 11, 2008 6:52 pm Post subject: Re: How to increase lift on horizontal stab?

The tail does have seals - did nothing.  I do want more lift at the horizontal stab to push the nose down.  I have too high of an attitude at slow speeds causing the tail to hit way too soon, and I still have lift left in the wing when it partially stalls, with the stick full aft.  I figure any increase in lift at the tail will help both situations.

When I hold the stick aft to the limit, it simply raises the nose, then drops the nose, then raises, and so on.  In fact if I do an extreme slip and with the stick full aft, it will not even "break" like a stall, but just comes slips down like a lead sled.  I do not spin it, as the wings will not remain stalled and a spiral is instantly is generated and can quick exceed the normal speeds.

  The VG's are spaced about an inch forward of the hinge line and about 1" apart.  The apparent speed gain was realize with the VG's installed only on the tail.  I now have some on the wing at about 6%, and I can't "see" difference in slow speed, and the OAT has changed since testing before, so an apples to apples comparison can't be made right now.  I did plan on moving them to several locations to see whats best, but haven't moved them since  I put them on last year.  On the slow speed end, I can't rightfully comment on the effectiveness, as the elevator is the weak link for now - the wing has more lift than I can extract.



  Has anyone put an airfoil under the stab?  



Thanks,

larry

LarryM

Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL

Posted: Fri Jan 11, 2008 7:04 pm Post subject: Re: How to increase lift on horizontal stab?

Noel,

  What I'm thinking is that as the angle of attack is increased, the center of lift moves forward, hence the attitude of the airplane is increased.  If I could get the same angle of attack without the cp moving so far forward (which we can't with a given airfoil) then I could have a flatter attitude with for the same angle of attack.  Since the cp can't be kept back, that only leaves changing the contribution that the tail makes to lower the nose at any given AoA.  The overall desire result is slower speed due to the elevator being able to generate the higher AoA, and having a shallower pitch angle so I don't slam the tail on before the mains.  What do you think?



larry

jcorner(at)shaw.ca
Guest

Posted: Fri Jan 11, 2008 9:05 pm Post subject: How to increase lift on horizontal stab?

Larry



I think the only way you are going to get the flying characteristic that you are looking for is to move your  cg forward.  Doing this may result in a slight  decrease in cruise speed.   Where is your cg now?

Jim

 What I'm thinking is that as the angle of attack is increased, the center of lift moves forward, hence the attitude of the airplane is increased.  If I could get the same angle of attack without the cp moving so far forward (which we can't with a given airfoil) then I could have a flatter attitude with for the same angle of attack.  Since the cp can't be kept back, that only leaves changing the contribution that the tail makes to lower the nose at any given AoA.  The overall desire result is slower speed due to the elevator being able to generate the higher AoA, and having a shallower pitch angle so I don't slam the tail on before the mains.  What do you think?

larry



 Jim Corner

Model 2, 582,. Ivo med !FA, 1100 hrs

Model 5 under construction

Calgary, AB

 



 [quote][b]

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Jan 12, 2008 3:16 am Post subject: Re: How to increase lift on horizontal stab?

 	  Quote: 	
		  I want to increase the lift of my flat surfaced horizontal stab. It can be done by increasing the span, or by putting airfoil shaped ribs on the underside. Any ideas on which would have the greatest effect for the amount of work needed? The ribs would be quite simple, but how does one estimate the benefit? 

	




Ok well why  not put in ribs that are more curved on top so it would be like a wing?  instead of a horiz stab made out  of 1/2' tube  make it like the Kitfox model IV  1200

propellerdesign(at)tele2.
Guest

Posted: Sat Jan 12, 2008 3:17 am Post subject: How to increase lift on horizontal stab?

Larry,



You can not have a higher AoA at shallow angle (to the ground) without 

increasing the sink rate. (or moving the wing relative fuselage)



You can increase lift without increasing the AoA with effective flaps.



VG's on wing don't increase lift it self, it make the wing tolerant to 

higher Alfa (AoA)



Lift is linear to Alfa up to near stall.



With a high camber wing and forward/normal CG the tail don't produce lift, 

but negative "lift"



This negative lift needs to be lifted by the wing. (increasing the induced 

drag)



The wing is said to have center of lift at about 24-25% of cord. then it is 

said to have a moment around the 25%

with a highly cambered airfoil it have a negative moment, that want to lower 

the nose.



The CG is somewhere from 15-30% on most airplanes.

meaning if it is ahead of 25% it add to the  nose lowering moment, if behind 

25% it reduce the moment.



To be able to control the airplane this moment need to be compensated, that 

is the task of the horizontal tail plane.



If we have a (we do in most cases) negative moment around the wing's 25% We 

need a force pointed down on the tail to balance the negative moment.



If we wants a higher Alfa we rise the elevator (increase the camber on the 

tail) this increase the negative lift, until the increased Alfa (wing and 

tail's lift and moment) balance this moment out again



If the elevator don't produce enough negative lift, we can lower the leading 

edge of the horizontal, so we can get the Alfa needed to stall the wing, but 

that is best don with a in the air moveable horizontal, others we have to 

push hard on the stick in high(er) speed.



Problem is if the tailplane stall before the wing, that can happen if 

negative moment is high and or CG is far a head. meaning you can't stall out 

the plane when landing

Even worse if CG is so far behind that the horiz. tail have so much positive 

lift that it stall, a situation that can trip that stall is if slowing down 

for landing pulling flap, and compensating the increased wing lift with down 

elevator, The airplane will flip nose up, standing as a cross in the sky, 

and you will soon have a cross with your name on it on ground too.



Rule Nr 1 on all airplane is the have the most forward wing to stall first, 

canard or 3-surface or "normal" configuration,



If we make the forward wing more effective we might need to do something at 

the rear end too!



If VG's isn't enough in front of hinge line at bottom, maybe VG's on the 

leading edge of top surface can help? making the air follow the front fixed 

part of horizontal to the up deflected elevator.



If the tail wheel hits ground first the landing gear need to be higher! if 

you want to land short.



Jan Carlsson

JC Propeller Design



---

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Jan 12, 2008 3:27 am Post subject: Re: How to increase lift on horizontal stab?

 	  Quote: 	
		  If the tail wheel hits ground first the landing gear need to be higher! if 

you want to land short. 



Jan Carlsson 

JC Propeller Design 	


Jan this is what I have been saying that I would like to do.  Extend my main gear 6 to 10"  longer.  Have you seen my videos how my tail hits first ?

http://www.youtube.com/watch?v=itqyBYxU0lU

dave

Joined: 22 Sep 2006
Posts: 1382

Posted: Sat Jan 12, 2008 3:28 am Post subject: Re: How to increase lift on horizontal stab?

Jan, Another point on VG placement , what about on the underside of an uncamber wing ?

KITFOXZ(at)aol.com
Guest

Posted: Sat Jan 12, 2008 5:06 am Post subject: How to increase lift on horizontal stab?

In a message dated 1/12/2008 6:18:37 A.M. Eastern Standard Time,  dave(at)cfisher.com writes:

  	  Quote: 	
		  

Ok    well why  not put in ribs that are more curved on top so it would be like    a wing?  instead of a horiz stab made out  of 1/2' tube  make    it like the Kitfox model IV  1200 	
  Changing the hor stab's airfoil for more lift will be even more effective  at higher air speeds!  I think Larry simply has a tail heavy bird.  I  would experiment with a more forward CG first.



  

  	  Quote: 	
		  

    

   John P.    Marzluf (John Z.)

Columbus, Ohio

Series V Outback (Out Back In The    Garage)

20% Complete, Not Currently Building

Do Not    Archive

	


Start the year off right.  Easy ways to stay in shape in the new year. 

  [quote][b]

propellerdesign(at)tele2.
Guest

Posted: Sat Jan 12, 2008 7:30 am Post subject: How to increase lift on horizontal stab?

Hm, it might reduce drag at high speed, if thinking of airfoil with concave 

underside. with VG's close to leading edge! It need to be tested Dave.



Thinking of STOL plane, some have the horiz. stab. plane with a upside down 

airfoil to be able to stall the wing.



Was Re-reading what Larry said,



But



The Center of lift isn't moving forward with increased Alfa, it is the 

opposite, or more aerodynamically correct speaking  that the negative moment 

is increasing with higher Alfa, The Alfa is increasing because the negative 

lift is increased at the tail. The elevator have to both overcome the 

increased neg. moment and the fixed part of the horiz tail's increased lift 

from the aircrafts increased angle.



If center of lift was moving forward you would be needed to reduce up 

elevator at high Alfa.



Jan

---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Jan 12, 2008 9:09 am Post subject: How to increase lift on horizontal stab?

Now I see what you want...



Increasing the lift of y9ur tail at slow speeds is as easy as letting the

stick go a bit forward of full back.  But then you have the problem of a

faster sink rate and of course an increase in speed.



These planes are well known for landing tail first at slow speeds.  The

consensus so far is to get around that put on higher gear of something like

the Kingfox tires.



Redesigning the gear higher can make your plane slower and more ungainly on

the ground.  The taller tires have been used by a bunch of guys on the list

with great results.  Me I like floats...  not enough strips around here but

thousands of water. 

Noel Loveys

AME Intern, RPP

Kitfox III-A, 582,B box

Ivo IFA, Aerocet 1100 floats



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Jan 12, 2008 9:16 am Post subject: How to increase lift on horizontal stab?

The AOA you would want to increase to accomplish what you want to do is the

AOA of the wing not the elevator.  Increasing the AOA of the horizontal stab

will cause you to have to fly with a lot of pressure or trim put into the

elevator to compensate.  



Sorry I don't know any easy way of increasing the AOA of the wing so you

will have a better slow speed attitude for landing.  That is of course short

of a lot of redesigning cutting and welding.  I could be done though.  If

you tried it you would probably feel like you were flying downhill at

cruise.



I still think taller tires would be the first thing to try.  Just remember

higher stance = higher CG = more tippy on the ground.



Noel 

--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

LarryM

Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL

Posted: Sat Jan 12, 2008 3:23 pm Post subject: Re: How to increase lift on horizontal stab?

Ok.  I need to retract a lot of what I said.  It might be just as easy to ask to erase everything, and Iâ€™ll explain what should be.  When I spoke to the designer I mis-communicated what I was trying to achieve, therefore we were not talking about the same thing.  Please accept my apologies.  (Though I still wonder if anyone has experience to which would be more effective; airfoil stab or increased length?)

 

   I spoke to him again today and simply asked â€œhow can I achieve a lower aircraft attitude at a high AoA?â€  His responses were: adjust the flaperons down to  just above the point of aileron reversal when fully deployed. (reversal will come around 25-30 degrees) and; to increase the chord of the flaperons and; to raise the angle of incidence of the wing and to adjust the horizontal stab to keep the same relationship.



  To increase the stab was to answer elevator effectiveness, as was the airfoil.  I had already employed his other recommendations of gap seals, increase elevator size, and VGâ€™s.  



  Again, I apologize for my gross miscommunication and I tank everyone for their inputs.



  I plan to ensure max flaperon deployment and perhaps enlarge them as suggested.  I am also going to extend the gear 6â€, and take the wash out out of the wing.



larry

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sat Jan 12, 2008 5:41 pm Post subject: How to increase lift on horizontal stab?

Be very careful when adjusting wash out of the wings.  It is there to make the aircraft controllable at slow speeds.  You don't want to get up only to find you have to land at 80+ mph.



I always think to KISS... Keep It Simple S...  So I would try the biggest tires I could put on first.  Check ATV shops and see if you can have the lugs ground down to keep rocks from perforating your wings.  Your take off speed may be in excess of 40 mph but you are only there for a second or so.



If you find you still need another inch or so then think about taller gear.  Then flapperon extension and after that washout. 

Noel Loveys

AME Intern, RPP

Kitfox III-A, 582,B box

Ivo IFA, Aerocet 1100 floats





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_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

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