Tailboom length vs. Tail Volume

[target]

I'm wondering what the differnce in flight characteristics would be between two similar sailplane designs with equal "tail volume". One would have a longer boom, with a smaller stab and vertical. The other would have larger tail surfaces, with a shorter boom. Wings would be identical.

Structural pro's and con's also?

Thanks,
Target

[yoyoML]

I'm wondering what the differnce in flight characteristics would be between two similar sailplane designs with equal "tail volume". One would have a longer boom, with a smaller stab and vertical. The other would have larger tail surfaces, with a shorter boom. Wings would be identical.

Structural pro's and con's also?

Thanks,
Target

If you know the classic example of a mass-spring-damper system...

The tail volume corresponds to the spring constant; the whole plane's pitch/yaw moment of inertia is the mass. Then, the longer boom with a smaller stab/vertical means just higher damping.

Would you like the math?

[target]

I'm not too interested in the "math" answer to my question. I would be quite happy to get a real world explanation, though.

Thanks,
Target

[histarter]

If you know the classic example of a mass-spring-damper system...

The tail volume corresponds to the spring constant; the whole plane's pitch/yaw moment of inertia is the mass. Then, the longer boom with a smaller stab/vertical means just higher damping.

Would you like the math?*
Unfortunatly the math does not deal with all the nuances such as boom rigidity and its torsional resistance, moment of inertia, along with induced circular error overviewed by a realistic range in airspeed. :rolleyes:

*[Unless you are talking about a blackboard full of calculus!!] :eek:

Basically slow thermal flight seems to like large tail surfaces for small angular control changes for rapid responce with little error induced by circular flight; whereas fast flight wants small tail surface with reduced responce for small angular changes and is not concerned with circular error. I like simplicity, so I concentrate on short coupled since my prime interest is in hound-dogging low thermals efficiently. :D

[target]

Thanks, Histarter.

I should have stated that I'm thinking primarily about F3F slope racing, where a blend of straightline speed and 180* turns with energy retention is needed.
I like the stability of the longer tailboom on most models, but I am wondering what, if any negative effects the long tailboom has on scrubbing off energy on a 180* reversal.

Thanks,
Target

[Ollie]

The long tail moment arm makes the plane groovier. It settles down quicker from a gust or nervous thumbs on the sticks.

In a DLG launch, the yaw needs very large damping so the energy is for height rather than wiggle. So the best DLG's have long tail moment arms and large vert. tail areas.

[nauga]

I'm not too interested in the "math" answer to my question. I would be quite happy to get a real world explanation, though.
At the most general level and with all other things being equal the two layouts would have roughly similar characteristics, with the longer boom having less tendency to oscillate (wander, wobble, hunt, whatever you want to call it) in and out of turns and hard pulls.

Longer booms are (often but not always) harder to deal with structurally and generally heavier, and shorter booms result in larger tails which have higher drag and require more surface throw for a given response.

Helpful?

Nauga,
comfortable with the math

[target]

I definitely seem to prefer the longer tail booms on my planes for running the 180* turns...Probably has to do with the way they seem to go where pointed at the exit.
Thanks to all who answered.

T

[histarter]

I definitely seem to prefer the longer tail booms on my planes for running the 180* turns...Probably has to do with the way they seem to go where pointed at the exit.
Thanks to all who answered.

T
My short tails for thermalling have one trick for making them run on rails for speed. The stab carries about 1.5% MCL inverted.

This idea gave me an extra spar to stiffen my Legionair stabs tremendously, and help my Legionair go through the F3B speed runs. F3B was not my expertise, and I needed all the help I could get. :rolleyes:

[As speed builds up so does adverse pitch thus the stab definitely has a down load. The profile yields the least drag for the amount of download.] :D