flight characteristic questions

[fixwingagain]

what are the flight characteristics of a model with a horizontal stabilizer that is to large and a model with a horizontal stabilizer to small ?

[batman]

If the stabilizer is extra big it won't effect the flight of the model except to maybe make it a little more stable in the horizontal plane. If it is too small, however, the model will not be as stable and will not have as good response to control input in the horizontal plane. Better overly large than too small.

[fixwingagain]

Is there a rule of thumb here ?

How about T-Tails ? They seem to be far smaller than a standard horizontal stabilizer.

Sorry for the questions just trying to figure out some stuff for a scratch build of my own design.

Thanks

[FFFlier]

I generally use 20% wing area for the tail area (10% rudder, 10% stabilizer). You can think of the fuselage as a lever between the wing and the stab, and the stab as the force to move the lever up and down. If you have a long lever, you can lift more weight with less force (less stab area) and if you have a short lever, you would need more force (more stab area) to lift that
same weight.
My fuse lengths are about 3/4 of the wing's span with the length
between my wing, tail about 1/2 the wingspan.

[Mark Wood]

This will probably get more in-depth answers in Modeling Science.

mw

[Ollie]

Almost anything can be made to fly, big tail, little tail or even no tail if the thrust is adequate, the controls are powerful enough and the CG is very near to or ahead of the neutral point.

Most people want their design to fly well. Trainers, aerobats, pylon racers, etc. each have a different definition of what "fly well" means. So design starts with a general objective which is then analyzed into particular sub objectives and priorities in order to begin to pick wing spans, wing loadings, stalling speed, power loadings, top speeds, airfoils, aspect ratios, tail moment arms, tail areas, etc., etc. that harmonize with each other to meet the general design intent and priorities. Very often design objectives conflict with each other so that priorities are required to deside where the balance should fall between conflicting objectives. Without sufficient background information there is no context in which to judge the quality of each interdependent design decision.


For example: The tail area affects the tail weight. The tail weight affects the weight budget. The weight budget affects the wing loading and wing area. The wing area together with the tail moment arm, wing chord and CG location affect the tail area. Oops, we are back where we started. This example just illustrates the point that design is not so much deterministic as artistic. Yet some aspects of design can be highly technical.

In another example, the tail area affects the tail drag which is part of the drag budget. The drag budget affects the thrust requirement to meet the top speed objective. The thrust requirement affects the power loading. The power loading affects the gross weight. The gross weight affects the wing loading and wing area. Some of the affects are very weak and some are quite strong. Some of the affects are weak in one configuration but stronger in another.

[fixwingagain]

Sorry about the delayed reply.

The model that I am trying to design is a small electric wing span under 24" Fuse under 18" motor will be an IPS "A" with prop size under 9*7. Batt 7 cell 370 mah NIMH under 2 oz. total weight with batts will be around 8 oz. 2 PICO servos. Constructuion will be balsa.

The design is around the IPS and Batt Pack. I need the airframe to support the above equipment.

Thanks for your info.

[Ollie]

It sounds like you are designing a park flier. Assuming an aspect ratio of 6 with a span of 24 inches, you would have a wing area of 2/3 of a square foot and a wing loading of12 ounces per square foot. This is kind of a heavy wing loading for a park flier of this size. The wing average chord would be 4 inches. With a fuselage length of 18 inches and a short nose length, a tail moment arm length of about 12 inches should be practical. A horizontal tail area of about 15 to 18 % of the wing area will give reasonable pitch stability with a CG location at about 33% of the average wing chord. A horizontal tail area of about 16 square inches would work well for an experienced flier. A slightly larger horizontal tail area of about 20 square inches would be better if you are an inexperienced flier. Give the wing about 8 to 10 degrees of dihedral on each side if the plane will not have ailerons. The vertical tail area could be half the horizontal tail area.

The above set of suggested dimensions will result in a plane of average appearance and average handling characteristics but faster than normal for a park flier. It is by no means the only thing that will work or even the best for a particular flying style. If you specify the speed range, climb rate and any pecular handling characteristics, then an airfoil can be chosen and the above configuration modified to get closer to your objectives.

I arived at the suggested configuration by applying certain formulas but it could just as well have been arrived at by the "that-looks-about-right" method. If you want to know what the formulas are, just ask.