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Jun 28, 2020, 07:17 PM
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Discussion

vtail rebuild advice


So last time I rebuilt this glider I used a V tail whose surface area was all nicely calculated. At speed it handled better than the original crucifix tail on yaw. The problem was there is quite a bit of tail waggle on the roll axis on any but the least control input. This means slow speed maneuvering is very sketchy. I built this plane to float so I'd like to correct this. I miss having fun flying low and slow.

The boom is an 8 mm wrapped carbon tube I'm pretty sure that the individual tail members weren't flexing I isolated and could tell that the boom was just flexing rotationally along its 14" length.

I have a nimbus pro tapered boom ive been wanting to use I'm wondering if there will be less rotational flex.

I'm looking for advice on how to solve this rotational flex problem I thought of putting 2 mm carbon rod between the 2 tail members but that wouldn't solve the problem at all
Last edited by skydaddy413; Jun 28, 2020 at 07:19 PM. Reason: typo
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Jun 30, 2020, 12:34 AM
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Yes, I've run into the torsional rotation of the boom issue as well.
The only "real" solution I could find was to use a boom tube with significantly thicker wall thickness or of different material altogether.
Of course, there are many factors here. Here are a few factors affecting the outcome:
Length of boom
Wall thickness of boom
Material boom is made of
Force exerted by tail surfaces (which varies with flight conditions)

Of course, it is nearly impossible to predict in advance just exactly the right combination you'll need. Experimentation is the only practical way.

In one case I decided to simply go with a shorter boom of very hard wood.
An aluminum tube with decent wall thickness would almost certainly solve the rotational issue...
Jun 30, 2020, 11:36 AM
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OK well I'm thinking that the walls of this tapered boom are thinner in fact I know that they are then my 8 mm non tapered sky shark P 400X.

Now im tossing around either rebuilding with same dimensions or go with a shorter 8mm and recalculate the surface area of the tailfeathers to compensate

Hm this would further reduce the amount of ballast in the nose wouldn't it? At what feels like maximum wing loading it is perfectly balanced with a 3500 mah battery all the way forward in the nose but anything smaller I have to add a significant amount of ballast in the nose
Jun 30, 2020, 11:39 AM
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Wait what I said is wrong isn't it? longer tail means less counterweight in the nose.
Jun 30, 2020, 01:26 PM
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birdofplay's Avatar
Use a Building Jig to get things correctly aligned
and the correct angle of attack.

110 deg - 55 deg left 55 degree right
Jun 30, 2020, 02:31 PM
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Quote:
Originally Posted by birdofplay
Use a Building Jig to get things correctly aligned
and the correct angle of attack.

110 deg - 55 deg left 55 degree right
I googled 95゚ angle held a piece of paper up to the screen and traced it with a straight edge transpose that to a piece of 3 mm pvc and used that as the jig. I just use gravity to align the whole tail feather assembly perpendicular at the correct angle to the fuselage
Jun 30, 2020, 02:32 PM
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Good old plastic and dangle method
Jun 30, 2020, 03:52 PM
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I need to make an angle of attack jig for wing inclination
Jun 30, 2020, 06:48 PM
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I'm sure it will not make much of a difference.

5-10 deg aint a big deal.

Here's another you can easily measure ...

https://static.rcgroups.net/forums/a...th%20props.JPG

Or this Fouga Glider at 106 deg . see pic
it was my 1st 2 channel RC back in 1969 !
Last edited by birdofplay; Jun 30, 2020 at 06:53 PM.
Jun 30, 2020, 10:23 PM
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I put numbers in endlessly into this sheet: http://www.tailwindgliders.com/files...May%202016.zip

Have been having a ton of fun with these calculators.

if i recall 110 degrees gave me a bit pitch authority but my geometry had tons of that and 95 gave more yaw authority which i prioritized with a no aileron design.

I'm sure the two wouldn't have had noticeable difference flying
Jun 30, 2020, 11:02 PM
Laughs at un-boxing videos...
basicguy's Avatar
I have done the calculations a few times and never was really satisfied with the way that the v tails have handled. Tried them from about 90 to 140 included angle.

Not sure of the reason exactly but the answer that went with was that that rudder control would induce an adverse roll. Something that I didn't notice with conventional tail surfaces.

Mind you they flew but all are in derelict status now.

The last 4 or so years I have just removed the horizontal stabilizer and flown planes with wing and vertical stab. It is all you need. But that isn't the answer you were looking for.
Jul 01, 2020, 12:49 AM
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Quote:
Originally Posted by basicguy
Not sure of the reason exactly but the answer that went with was that that rudder control would induce an adverse roll.
True, there is some minimal adverse roll - but, that will pale in comparison to the effect of a not-stiff-enough boom that is torsion rotating in flight.
By the way, one reason why some do an inverted v-tail is to avoid the adverse roll you mention. Of course, the inverted v-tail has its own set of disadvantages.
This stuff is always a game of trade-offs

https://www.youtube.com/watch?v=2X0bgEoqkQk
Jul 01, 2020, 08:17 AM
Sokol
JureZ's Avatar
Quote:
Originally Posted by basicguy
...
The last 4 or so years I have just removed the horizontal stabilizer and flown planes with wing and vertical stab. It is all you need. But that isn't the answer you were looking for.
so, your latest planes are like Bill Evans' Simitar , or along the style of flying planks ?
Ultimate simplicity and elegance ! I like it !
Latest blog entry: Weasel-EVO
Jul 01, 2020, 10:03 PM
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I like that adverse roll tendency on A tails is more like a conventional tail than a V tail however I don't know why but on landing the V seems safer as far as damage goes although I am still dragging the root of each winglets, covered in some pvc. I was thinking of making a 60" span twin boom yank and bank thing, it might be time to try an A. what is there between booms to keep them from flexing, ruining that peak angle? Perhaps just 2mm carbon rod between the booms at base of A tail winglets
Jul 01, 2020, 10:05 PM
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I've decided to just cut a less expensive 8mm boom to reduce the amount of material there is to roll torsionally. add on bonus less nose ballast


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