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Author Topic: Stiletto tail size  (Read 748 times)

Offline Dietmar Morbitzer

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Stiletto tail size
« on: January 20, 2018, 11:36:48 AM »
Hello stunt pilots,
I've started to build a Stiletto 660. The tail size is under 20%
of the wing. I've learned that the tail shout be in the range of 25+%
of the wing. Does somebody have experience with a bigger tail
on a Stiletto and in which direction should it grow?
Dietmar


Online Brett Buck

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Re: Stiletto tail size
« Reply #1 on: January 20, 2018, 02:12:10 PM »
Hello stunt pilots,
I've started to build a Stiletto 660. The tail size is under 20%
of the wing. I've learned that the tail shout be in the range of 25+%
of the wing. Does somebody have experience with a bigger tail
on a Stiletto and in which direction should it grow?
Dietmar

      At least around here, that will make it not legal for Super 70s/Nostalgia 30, if you care about that.

     I will preface this with  - I probably wouldn't do this for a variety of reasons, but if I was, and the only option was to add to the existing tail, I would add it entirely in chord and only to the stabilizer. That will reduce the aspect ratio and reduce the stabilizer/elevator split. If I was going to replace it entirely, I would design a tail with about a 4.25:1 aspect ratio, a 65/35 split, and about 25-26%

   Brett

Offline Matt Spencer

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Re: Stiletto tail size
« Reply #2 on: January 20, 2018, 09:06:56 PM »
Perhaps youd better let Les McDonald Know. He might want to change it before He starts Flying It . :) ;)




Offline Target

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Re: Stiletto tail size
« Reply #3 on: January 20, 2018, 11:25:22 PM »
Les himself told me that in later years the following mods were popular on the Stiletto 660:

Make the cord 1/4" wider on the stab.
Make the cord 1/4" wider on the elevator
Both of the above is for the full span.

Make the outboard flap 1/32" wider.

Hope that helps you.

R,
Target
Regards,
Chris
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Offline Target

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Re: Stiletto tail size
« Reply #4 on: January 21, 2018, 09:52:03 AM »
That's what he told me....
Take it or leave it.

Puts the precision in precision stunt.
« Last Edit: January 21, 2018, 03:32:00 PM by Target »
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Chris
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Online Brett Buck

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Re: Stiletto tail size
« Reply #5 on: January 21, 2018, 02:05:14 PM »
1/32" on the flap?  One less stroke of the sanding block & use a good micrometer.

 You had darn well be able to build to much better than this sort of tolerance if you want to have any sort of predictable results.

     Brett

Offline Dietmar Morbitzer

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Re: Stiletto tail size
« Reply #6 on: January 22, 2018, 01:04:12 PM »
      At least around here, that will make it not legal for Super 70s/Nostalgia 30, if you care about that.

     I will preface this with  - I probably wouldn't do this for a variety of reasons, but if I was, and the only option was to add to the existing tail, I would add it entirely in chord and only to the stabilizer. That will reduce the aspect ratio and reduce the stabilizer/elevator split. If I was going to replace it entirely, I would design a tail with about a 4.25:1 aspect ratio, a 65/35 split, and about 25-26%

   Brett

Thank you all for answering.
Because we only fly F2B and a little OTS around here I don't have to care for being legal in Nostalgia.
If I add the chord on the stabilizer should I also lenghten the hinge line flap to stab-elevator, if so how much?
What advantages can I get from split stabilizer/elevator size instead adding stabilizer and elevator the same?
Dietmar

Online Brett Buck

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Re: Stiletto tail size
« Reply #7 on: January 22, 2018, 01:46:34 PM »
Thank you all for answering.
Because we only fly F2B and a little OTS around here I don't have to care for being legal in Nostalgia.
If I add the chord on the stabilizer should I also lenghten the hinge line flap to stab-elevator, if so how much?
What advantages can I get from split stabilizer/elevator size instead adding stabilizer and elevator the same?
Dietmar

   If you are not concerned with replicating the original, with all due respect to those involved, why not just copy the Impact or Trivial Pursuit and put a Stiletto fuselage on it? 

   Adding to the stabilizer is intended to get your desired area while reducing the aspect ratio of the tail, and moving the ratio of stab/elevator to be more linear. The very high aspect ratio tails are *very* sensitive and also non-linear - a little elevator deflection does a lot, a little more does a lot less.

      Overall, if you are willing to change this much, definitely put an Impact or Infinity stabilizer on it, make the tail moment 18-18.5" and move on. Also, make the flaps removable so you can change them later if necessary (probably to have less taper and possibly smaller, depending on the weight).

     Brett

Online Howard Rush

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Re: Stiletto tail size
« Reply #8 on: January 22, 2018, 09:50:56 PM »
The very high aspect ratio tails are *very* sensitive and also non-linear - a little elevator deflection does a lot, a little more does a lot less.

Why’s that?
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Offline Target

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Re: Stiletto tail size
« Reply #9 on: January 29, 2018, 08:32:38 PM »
Yes, why IS that, or why ISN'T that??
Brett and Howard-
Whatever the answer is or isn't about the high aspect tails, please pass that along, I would like to know your thinking.

I was always told that in sailplanes, the same tail area at the same moment arm was more effective with a higher aspect tail plane.
But there was always the asterisks next to that statement to warn of the lower Reynolds Numbers when the chord was too small.
Personally, with the sailplanes, I have seen them BOTH work pretty well; but to me, the designs with the greater tail volume trumped everything for control, but not for speed.

Thanks gents!

R,
Target
Regards,
Chris
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Offline Ted Fancher

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Re: Stiletto tail size
« Reply #10 on: Yesterday at 05:46:59 PM »
Tails are lifting surfaces just like wings and in most respects act just like wings with respect to their "jobs"...which in both cases is to produce lift.  Higher aspect ratio lifting surfaces develop less drag per unit of lift than lower aspect ratios and as a partial result result in less drag while producing those "units" of lift.  They also produce a given unit of lift at lower angles of attack.  Thus sailplanes have long wings (high aspect ratios) commensurate with achieving prolonged flight with no visible means of thrust! They also provide the variations in lift necessary for various stages of flight through extremely modest angle of attack changes.

High speed aircraft are pretty much the opposite of that using low aspect ratio surfaces to minimize form drag and great mechanical thrust to attain and maintain high speeds while maneuvering despite much greater angles of attack...and, therefore, drag...developed to support the much greater wing loading under such aerodynamic distress.

The profound configuration differences between sailplanes and fighter planes are the result of their grossly different missions.  Most "normal" airplanes...like stunt ships...fall somewhere in the great middle ground between those two extremes.  The effects of aspect ratio of the lifting surfaces for such airplanes is somewhat broader than for the previous two extremes and useful variations can and have exhibited comparatively modest variable with respect to lifting surfaces for their missions.

The fundamentals of lift/drag development still, however, impact the performance of aircraft utilizing varied aspect ratios and those impacts are obvious to the lay person (your "average" stunt flyer") and verifiable and quantifiable by the cognoscenti amongst us (the less average Howards, Igors, Bretts etc.)

Among those observable and verifiable differences due to aspect ratio is the fact that higher aspect ratio wings and tails on stunt ships will produce greater lift per unit of angle of attack increase than will lower aspect ratios and will produce less drag while doing so.  (Note that the wing's angle of attack is driven by the lift generated at the tail which drives the angle of attack at which the wing strikes the ambient air mass.  The tail, on the other hand, in order to drive that wing A of A must reshape itself so as to produce--for instance--negative lift to drive the wing to a positive angle of attack and, as a result any angle of attack achieved by the tail must be "greater" than the angle at which the aircraft is changing its overall angle of attack.  You might have to cogitate on that for a bit.

The effect of aspect ratio on a tail trying to drive the ship in the opposite direction of the lift that tail is producing is significant.  Remember that a high aspect ratio surface of a given "area" produces a given amount of lift at a lower angle of attack than a low aspect ratio surface of the same area.  Inasmuch as "X" amount of lift must be produced to drive the wing to an A of A necessary to support the lift required for the pitch change (think "corner") the high aspect ratio tail will accomplish that at a lower angle of attack and with less resultant drag than will a much lower aspect ratio tail.

If you can find a picture of it, check out the tail of Bob Baron's spectacular flying Humbug design way back in the dark ages of stunt.  A flapless triple boom operation with a tail aspect ratio of 10 to one which turned absolutely incredible corners (and more than a few of other competitors heads) when it had the highest flight scores way back at the 1966/7 (or so) Nats.  It's also instructive to read the issues Bob (and designer Wild Bill Netzeband) encountered trying to develop a control system that was insensitive enough to fly competitive round maneuver while still maintaining the ability to fly the Humbugs trademark "where'd it go" corners!  The very high aspect ratio stab/elevator were an important component to the aircraft's well remembered response!

Of course, I could be wrong.  I don't build much anymore but I would be interested in the results of someone building a ship with the ability to mount stab/elevators with a variety of tails of the same area with A/Rs ranging from say 3 to one up to 8 to one or so both with say 60/40% split stab to elevator all of which would be attached at the same location with respect to the location of say 25% of their average chord.  The CGs should be adjusted to be in the same place for all of the tails.  My guess is you could tell the difference.  Both in the feel at the handle (high load with low aspect ratio and low with hight aspect ratio) and in the response of the airplane (brisk with high aspect ratio unresponsive with the low).


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