Measuring incidence on a v tail

[rorywquin]

Can anybody tell me how to measue the incidence on a v-tail. I have a Robart incidence meter and with the wings at 0 the tail should be -1.5. This is a v-tail glider and the fuselage was broken between the wing trailing edge and the tail. I have since rejoined the two halves and would like to check the incidence!

Thanks

Rory

[Sparky Paul]

About the only way I can think of is to set the tail 1/2way between two level and parallel blocks, and then measure the wing/fuselage angle to the blocks.

[rorywquin]

Well if you don't know how to do it, then I am stuck!! ;)

[Salto]

On one of my V tail gliders with a removable tail I do a quick pre-flight check of the tail alignment by looking from the front of the model at the tail surfaces and checking that they are aligned straight along the fuselage. I can see when the surfaces are pointing straight at my eye, and if my sight line is running along the top of the wing and on the centre line, then I know the tails have seated correctly.

Maybe you could use a variation of this method, defining a sight line at your -1.5 degrees, and aligning the tails by eye.

Graham.

[rorywquin]

On one of my V tail gliders with a removable tail I do a quick pre-flight check of the tail alignment by looking from the front of the model at the tail surfaces and checking that they are aligned straight along the fuselage. I can see when the surfaces are pointing straight at my eye, and if my sight line is running along the top of the wing and on the centre line, then I know the tails have seated correctly.

Maybe you could use a variation of this method, defining a sight line at your -1.5 degrees, and aligning the tails by eye.

Graham.

Cheers Graham- This is for my Mini Graphite - I have been thinking about it and as it is a removable tail, I will block the plane up without the tail - if I then set it up so that a spirit level is at 0 degrees on the tail mounting surface....I can then measure the wings, with my incidence gauge, which should be -1.5 degrees (I need +1.5 on the tail .....my earlier post was incorrect). I assume a positive incidence is leading edge below trailing edge or is it the other way around!!

[Salto]

rorywquin,

To answer your last question we would need to know what kind of airfoil you have, particularly what % camber. If it is near flat bottomed and a usual thin glider type airfoil, then your required 1.5 deg. would be LE of wing higher than TE of wing relative to a line at 0 deg. to the tail. If it is a very highly cambered airfoil then the 1.5 deg may be TE higher, but this would be an unusual airfoil to find on this kind of model.

Graham.

[rorywquin]

The spec says that the Wing is MH32 and the v-tail is NACA63 A007.

Will my described method work - ie I need 1.5 deg. positive incidence on the v-tail. This cannot be measured directly so if I set up a spirit level so that the tail is exatly level, I can put an incidence meter on the wings and they should read 1.5 deg negative incidence if the tail is correctly set!!

My only other question is what is positive or negative incidence - I had assumed that a positive incidence will have the leading edge of the wing as the pivot point (ie LE below traileing edge).

[Salto]

With that airfoil, when the tail mounting surface is horizontal, the wing LE should be higher than the wing TE.

Graham.

[1nk]

This is a difficult problem, and is the reason why I hate V-tails.

[jofo1]

...flat and level surface (dining room tables work great), block the wings level (zero incidence), put a torpedo level on the incidence meter to "calibrate the position of the bubble at zero incidence, put the torpedo level on the fuselage where the v-tails mount (top side), raise or lower the tail of the fuselage until the level reads level, note the angle of the incidence meter on the wing (that's your tail incidence).

In order to mount the v-tails with the correct incidence, you simply have to now reference a point (orientation) to the tail of the fuse. In the end you still are eyeing the v-tail in to mount it, but doing it with less margin of error, basically establishing a datum (line of reference) between the wing and the tail of the fuse.

I used this method on my 3M F3F, flew with zero required trim.

jofo