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Author Topic: Tapered Flaps/Elevator??  (Read 2640 times)

Offline Jerry Bohn

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Tapered Flaps/Elevator??
« on: May 07, 2007, 11:26:14 AM »
I am at the final stage of assembly of both a profile and full body Oriental.
I was wondering weather to taper the 1/4" flaps/elev, or just leave flat.
What are the flight manuvering problems of flat control surfaces, if any?
I have built planes with both and have not noticed a big difference in doing it either way.
None of my previously built planes,Twister, Barnstormer, Accentor to mention a few, have been high zoot pattern planes.
Jerry Bohn


Offline Leester

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Re: Tapered Flaps/Elevator??
« Reply #1 on: May 07, 2007, 03:38:05 PM »
Jerry: If the side view of the wing on the plans doesn't show them tapered I'd leave them flat.
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Offline Jim Oliver

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Re: Tapered Flaps/Elevator??
« Reply #2 on: May 07, 2007, 03:59:05 PM »
Jerry,

Of the few Oriental ARF's I have seen, none had flaps/elevators tapered.  Just rounded off on the trailing edge.

After I crashed one of my Oriental ARF's, I rebuilt it and since the flaps are fairly thin did not taper them or the elevators.  Seems fine for my limited flying skills.

Cheers,
Jim
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Offline Jerry Bohn

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Re: Tapered Flaps/Elevator??
« Reply #3 on: May 08, 2007, 12:29:07 PM »
10-4, Will leave well enough alone.
Thanks for the tips on looking for taper on the plans. Always wondered about that. Makes getting to finishing stage a bit quicker, weather is getting ripe for flying more and building less.
Still have Ares to finish also. Soon it will be sanding and painting extravagansa.
Jerry Bohn

Offline phil c

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Re: Tapered Flaps/Elevator??
« Reply #4 on: May 08, 2007, 08:11:51 PM »
Rounding the trailing edge of the flaps and elevator kind of invites vibration/flutter.  It is best to leave them square, with no more rounding than you'd get ironing on covering or sanding down a silkspan finish.
phil Cartier

Offline Bill Little

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Re: Tapered Flaps/Elevator??
« Reply #5 on: May 09, 2007, 07:25:42 AM »
Rounding the trailing edge of the flaps and elevator kind of invites vibration/flutter.  It is best to leave them square, with no more rounding than you'd get ironing on covering or sanding down a silkspan finish.

Hi Phil,

I am reminded of Lou Andrews' demands on leaving the TE of the stationary flaps "SQUARE" on the Barnstormer.  He was adamant about that.  Do you *think* it was because of possible "flutter" or something else??

Thanks
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Offline Larry Renger

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Re: Tapered Flaps/Elevator??
« Reply #6 on: May 11, 2007, 05:35:17 PM »
Leaving the TE square results in the LEAST turbulence because of the clean cut-off.  Round TE lets the air try to follow it, and generates more turbulence, thus less lift and more drag.  In race cars, it was called a Kamm tail, and was used by both Porsche ( 904? 905?) and the infamous Ford "Bread Van".
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

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Offline Jerry Bohn

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Re: Tapered Flaps/Elevator??
« Reply #7 on: May 12, 2007, 03:19:53 PM »
Good tip, gotta try that, can always go back and round it if It goes sour. At my level of flying it I may never notice the difference, but it's good to have in my repitiour of helpful hints.
Jerry Bohn

Online Fredvon4

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Re: Tapered Flaps/Elevator??
« Reply #8 on: May 01, 2017, 01:50:09 PM »
Preparing  several F. Twister builds ...all with great advice from searches on this forum

I have always made both the TE and LE of Stab and Elevator (hinge line) 45s and rounded the entire edges of Rudder, TE Flap, TE Elevator, either tapered or rounded

Leaving all the aft surfaces Square would greatly reduce work...But I assume the LE edges like for Rudder or Stab should still be airfoil profile or rounded

Do I have this right?

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Offline Howard Rush

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Re: Tapered Flaps/Elevator??
« Reply #9 on: May 17, 2017, 01:01:40 AM »
I agree with Larry and Phil (and a couple of world champs).  You might search here for a piece Gary James wrote awhile back on combat airfoils.  A less lazy person than I could calculate the frequency of the vortices coming off a rounded TE and see if the vibration would be a bother.

That said, I've been tapering mine and rounding them off with a 1/32" radius.   
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Online bob whitney

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Re: Tapered Flaps/Elevator??
« Reply #10 on: May 17, 2017, 08:01:33 AM »


  I built a Scorpio with a 3/8 in  flat stab and elevator with rounded leading and trailing edges. worked on it for a year and could not get it to Groove either up rite or inverted.
 finally
 tapered the elevator to about 3/16 trailing edge and made a new plane out of it. it now grooves great
rad racer

Offline Ted Fancher

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Re: Tapered Flaps/Elevator??
« Reply #11 on: May 17, 2017, 04:41:28 PM »
Sure, flat flaps and elevators with square trailing edges on lifting surfaces are obviously the way to go since all the full scale aircraft manufacturers use them to keep the cost of passenger barf bags at a minimum...

Oh....wait...

Never mind.

Offline Howard Rush

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Re: Tapered Flaps/Elevator??
« Reply #12 on: May 17, 2017, 05:59:01 PM »
Sure, flat flaps and elevators with square trailing edges on lifting surfaces are obviously the way to go since all the full scale aircraft manufacturers use them to keep the cost of passenger barf bags at a minimum...

I think the TE radius on a 737 wing is sharper than my flap TE, and my flap TE is sharper than most.
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Offline Ted Fancher

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Re: Tapered Flaps/Elevator??
« Reply #13 on: May 18, 2017, 11:13:02 AM »
I think the TE radius on a 737 wing is sharper than my flap TE, and my flap TE is sharper than most.

I'm with you, Howard.  I can't argue with the success some have claimed for "flat surface, squared off, control surface trailing edges (Les McDonald is one who seriously kicked my butt on more than one occasion) but, if nothing else, they are an aesthetic abomination.  Shoot, my skin crawled a bit just typing this.

 ::) ::) H^^

Ted

p.s. at the risk of shooting myself in my nether regions, didn't the X-15 vertical stabilizer have a straight tapered airfoil starting with a sharp leading edge and ending up with a very wide and flat trailing edge????  If so, I 'm sure you can explain why.  If not, forget I said anything.  ~^

Offline David Hoover

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Re: Tapered Flaps/Elevator??
« Reply #14 on: May 18, 2017, 12:32:20 PM »
Like this?
Life is simple. Eat. Sleep. Fly!
Best, Hoovie

Offline Brent Williams

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Re: Tapered Flaps/Elevator??
« Reply #15 on: May 18, 2017, 01:02:53 PM »
The wedge shape was for stability at hypersonic speeds.

https://history.nasa.gov/SP-60/ch-3.html


"A phenomenon is encountered in which the vertical tail loses ability to stabilize the airplane and the nose tends to yaw. Indeed, the only previous airplanes that had been flown to Mach numbers above 2 - the X-1A and X-2 - had experienced such large decreases in stability that the pilots lost control (disastrously, in the case of the X-2) when they maneuvered the craft to angles of attack of only 5 or 6 degrees. Yet the reentry maneuver of the X-15 would normally require it to operate at an angle of attack of 20 to 25 degrees.

The initial solution, proposed by NACA, was found in the large, wedge-shaped upper-and-lower vertical-tail surfaces, which are nearly symmetrical about the aft fuselage. A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds. A vertical-tail area equal to 60 percent of the wing area was required to give the X-15 adequate directional stability.

A disadvantage of the wedge shape is high drag, caused by airflow around its blunt aft end. This drag force, when added to the drag from the blunt aft ends of the side fairings and rocket-engine nozzle, equals the entire aerodynamic drag of an F-104 jet fighter."




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Offline Ted Fancher

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Re: Tapered Flaps/Elevator??
« Reply #16 on: May 18, 2017, 03:17:23 PM »
Thanks, Brent.  That info sounds familiar.  Probably yet another example of advancing old-timers memory.

Wonder if you could slip your C-172 in behind it and draft for a few miles?  It would take exquisite  timing I expect. y1 y1

Ted

Offline Matt Spencer

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Re: Tapered Flaps/Elevator??
« Reply #17 on: May 18, 2017, 09:22:05 PM »
Quote
In race cars, it was called a Kamm tail, and was used by both Porsche ( 904? 905?) and the infamous Ford "Bread Van".

Thats a Faroary Bread Van , by Drago. Not a Ford .

http://www.autoblog.nl/archive/2008/03/21/bizzarrini-kicked-ass




Though Somebody Did Have a 51' Ford Bread Van , back in the Ground effects Era . The Sub Floor inverted Wing at the rear, combined with the frontal Slopes
Had It pull itself onto the bump stops past 60 mph . Handle of ' exocete ' as it felt like it was about to expolode at 90 .2 Litre Capri engine . HA Front & discs .



The S. Hurricane 30 , By O. Hara , has flat flaps & Tailplane , and is a doozy to fly . A bit like a Farmall .

though the elevators are tapered ' V ' aft .







Offline phil c

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Re: Tapered Flaps/Elevator??
« Reply #18 on: May 21, 2017, 04:43:52 PM »
Leaving the TE square results in the LEAST turbulence because of the clean cut-off.  Round TE lets the air try to follow it, and generates more turbulence, thus less lift and more drag.  In race cars, it was called a Kamm tail, and was used by both Porsche ( 904? 905?) and the infamous Ford "Bread Van".

What Larry said.  It doesn't look as sleek pretty, but flat flaps with a square trailing edge and light carbon fiber matte are stiffer than tapered flaps with CF matte.  Basic engineering- the average beam thickness is substantially more for a flat sheet flap.  Airliners and other larger planes have different design criteria, plus much better Reynolds numbers than models.  Every excess pound of drag means more fuel and less profits.  Airlines hate to buy fuel.

From practical experimentation, on a 10-13 in. wing chord a half inch high trailing edge is probably a bit too much.  Anything less than 1/8 is probably too little. Tapering the flap to a near point is very finicky on a flapless wing but does reduce level flight drag(speed and team race).

The trailing edges should be as sharp a corner as possible.  There was one obscure flap tried in the 1930's which was thing sheet mounted vertically on the trailing edge(or somewhat forward of it) and extending 1-2% either below the wing(Zaparka or Guerney flap on race cars)  which was as about effective as a much larger split flap.  Another one(I forget the inventors name, sorry) extended above and below the wing so it worked for aerobatics.  The drawback was substantial drag all the time.  Zaparka patented a retractable version of his design.
phil Cartier

Offline Howard Rush

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Re: Tapered Flaps/Elevator??
« Reply #19 on: May 21, 2017, 09:26:02 PM »
From practical experimentation, on a 10-13 in. wing chord a half inch high trailing edge is probably a bit too much.

I've made 3"-high flap trailing edges. That was probably a bit too much.
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Offline phil c

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Re: Tapered Flaps/Elevator??
« Reply #20 on: May 25, 2017, 07:05:29 PM »
I've made 3"-high flap trailing edges. That was probably a bit too much.
AS always Howard, if some is good too much is better.
I was referring to the height of a squared-off trailing edge in the middle of the previous post.
phil Cartier

Offline Ted Fancher

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Re: Tapered Flaps/Elevator??
« Reply #21 on: May 28, 2017, 09:58:34 PM »
The wedge shape was for stability at hypersonic speeds.

https://history.nasa.gov/SP-60/ch-3.html


"A phenomenon is encountered in which the vertical tail loses ability to stabilize the airplane and the nose tends to yaw. Indeed, the only previous airplanes that had been flown to Mach numbers above 2 - the X-1A and X-2 - had experienced such large decreases in stability that the pilots lost control (disastrously, in the case of the X-2) when they maneuvered the craft to angles of attack of only 5 or 6 degrees. Yet the reentry maneuver of the X-15 would normally require it to operate at an angle of attack of 20 to 25 degrees.

The initial solution, proposed by NACA, was found in the large, wedge-shaped upper-and-lower vertical-tail surfaces, which are nearly symmetrical about the aft fuselage. A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds. A vertical-tail area equal to 60 percent of the wing area was required to give the X-15 adequate directional stability.

A disadvantage of the wedge shape is high drag, caused by airflow around its blunt aft end. This drag force, when added to the drag from the blunt aft ends of the side fairings and rocket-engine nozzle, equals the entire aerodynamic drag of an F-104 jet fighter."






Hmmm.  Sounds a lot like that old CG/NP/static margin conundrum doesn't it. 

I've no idea about where drag/shock waves etc. are located with respect to the vehicle itself at such speeds but if it is aft of the vehicle itself it probably wouldn't contribute to the static margin of the vehicle...or not.  Maybe the wedge and resultant Kamm effect aft of it produces the necessary vehicle drag in a location that restores the static margin. Beats the baloney out of me.  Any rokit scientists out there with the real skinny?

Online Paul Smith

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Re: Tapered Flaps/Elevator??
« Reply #22 on: May 29, 2017, 05:25:00 AM »
The subject was wings & tailplanes, not rudders. The X-15 did have shape TE's on the horizontal surfaces.
Paul Smith

Online Brett Buck

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Re: Tapered Flaps/Elevator??
« Reply #23 on: May 29, 2017, 12:50:37 PM »
Hmmm.  Sounds a lot like that old CG/NP/static margin conundrum doesn't it.  

I've no idea about where drag/shock waves etc. are located with respect to the vehicle itself at such speeds but if it is aft of the vehicle itself it probably wouldn't contribute to the static margin of the vehicle...or not.  Maybe the wedge and resultant Kamm effect aft of it produces the necessary vehicle drag in a location that restores the static margin. Beats the baloney out of me.  Any rokit scientists out there with the real skinny?

   The real story is that the wedge tail for Mach 3+ flight stability (causing abundant normal pressure from LE to TE compared to a flat or conventional airfoil along with MASSIVE base drag (as noted)) has very little relationship to a 50 mph stunt plane, aside from the drag. For sure, stability was a severe problem for airplane above Mach 2 at the time. Chuck Yeager almost killed himself at about Mach 2.4 when the X-1A became unstable due to inertial coupling effects, and Mel Apt died in the X-2 when it got it to Mach 3.2 or so and tried to turn. The X-15 was stable out to full speed (and beyond, designed for Mach 6 but went Mach 6.7 once with drop tank and larger internal tanks, but came *very close* to melting despite being painted with a very thick ablative coating for the effort, and never flew again). Interestingly, it was more stable with the ventral rudder removed.


The Kamm effect does have some relevance to stunt, reducing drag and weight assuming you are constrained in terms of overall length - which we are not in any practical way. A square trailing edge where you could use a taper (without changing the dimensions otherwise) does not provide any aerodynamic advantage that I am aware of, and the people who started using it for flaps didn't do it for strictly aerodynamic reasons.

     Brett

Offline Howard Rush

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Re: Tapered Flaps/Elevator??
« Reply #24 on: June 03, 2017, 09:56:22 AM »

A square trailing edge where you could use a taper (without changing the dimensions otherwise) does not provide any aerodynamic advantage that I am aware of, and the people who started using it for flaps didn't do it for strictly aerodynamic reasons.

I cannot dispute either of these, although the second may not apply to all those people.
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