whatwheel

What would hapen to the flight characteristics of a GB tiger 60 if you shortened the tail moment about 4 inches?
Any in put?
Thanks, Sparky.

BMatthews

Maybe nothing or it may cause some problems with stability and lack of grooviness in the turns. A slightly more forward CG can help with the first problem and some tip plates on the stabilizer or a larger dorsal fin can help with the last if needed. You'll know if you need more fin area if the tail tends to hang low in the turns, if it swings the wrong way when using ailerons or if it tends to wag the tail back and forth in a low throttle climb. The desireable CG range will all shift forward by about 5 to 8% depending on how touchy you like your pitch settings. Also that's a lot shorter a tail. You'll probably want to shorten the nose an inch as well so you don't need to add much if any tail weight to make the model balance.

It may also show up some odd pitch problems when the speed slows down like near the stall. Watch for that.

But most of all it'll really start to look odd. It's a nicely proportioned design as is and with a shorter tail it'll look odd.

whatwheel

Thanks Bruce, I must have a bad dream .

Thanks for your reply.

Glenn.

Ben Lanterman

I have to ask, why do you want to shorten the tail. The pattern guys have been happy with long tailed airplanes.

whatwheel

Hi Ben, Well i have been thinking about getting a tiger 60 kit but keep reading post about all the things they try or do to fix the
``tail heavy problem,, .
I have a plane with the same span and a shorter tail so i just thought ???? thinking by me can be hazardous.

Glenn.

w8ye

My Feedback: (16)

As has already been said, the Tiger 60 is a very smooth pattern style plane. You will destroy the smoothness of the flight characteristics.

Typically, when you shorten the wing-tail relationship, you need to enlarge the tail surfaces.

It would be a lot less involved and change flight characteristics less drastically to adjust the nose length slightly to change your CG problem?

What about making the rear of the plane lighter? That wouldn't change the flight characteristics at all except for the less overall weight involved which would be good?

Put a 4 stroke in it?

Enjoy,

Jim

whatwheel

Thanks Jim, it just so happens that i have a new OS 91 fs surpass II , I will leave plane alone. Thanks again to every one, this sport and the people in it are great.
Glenn.

Ben Lanterman

Let's look at it from a different direction then and based on what a friend of mine has done. Think about a normal pattern ship and a flying wing with symmetrical airfoils. Both can be made to fly nicely. My friend built a model that was inbetween. He had a fuselage that was normal length for a .60 size engine (nose moment and tail moment/vertical/rudder was normal) and he put a horizontal tail that was about twice the normal size halfway between the trailing edge of the wing and the normal aft position. The airplane flew fine.

What we can't tell by flying however are things like pitch response and damping of the kind that would be perceptable to a pilot flying in the airplane. But that doesn't bother us from a model standpoint.

So assuming we can keep control (the reason I brought up the two extremes in the first paragraph) and arn't trying to maintain the precision of pattern flight with the absolutely dead beat damping that they have after a snap maneuver there isn't any reason that you can't shorten the tail that much. Most models are build on a "that looks about right" process including the pattern airplane designers. Truthfully there isn't a nickel's worth of difference between any of the top 50 used in contests today. It's all pilot.

So if that is the case changing the tail length and not changing the tail sizes probably won't make much difference. If this were full size where they have worked to shave off every ounce of structural weight then Bruce's advice is good. But were it is all guesses, not a big issue.

What would be better perhaps would be to lengthen the nose a little as was noted above. If you go too far you might want to enlarge the vertical tail some more. However again go back to pattern designs. We used to fly small nosed designs with big vertical tails and they flew beautifully. I just saw a design that had a huge amount of side area in front of the CG and not much at all in the back and the vertical was so tiny as to look all out of proportion. Totally strange. But it flew fine also.

There would seem to be a lot of variaton in model designs available because we tend to design so conservatively. But again not so with full scale.

I should add that I have a Tiger 400 that ended up with a much bigger electric motor and it flies really nice. The basic design responds well to more power.

whatwheel

Thanks Bill, for putting it in away that i could understand it. Boy i hope someday i will be able to do more than ask questions ,and help others out.
Thanks again , Glenn.

rmh

What is not obvious--is that we can -in models , use powerplants which are far lighter for power developed - than full scale .
Imagine what designers could have done in full scale with these power to weight setups
Much of the work at streamlining - attention to lift/drag profiles -- could have been tossed out the cockpit .
Now before anyone feels slighted - remember the P51 - a design "masterpiece" which was a dud until more power was crammed into it.
In the exploding marketplace of electric models the old rules for good stable design can be skewed to extremes -simply because of the super light -super power available
On the CG Tiger -a more simple mod , increases aerobatic performance and -increases stability - just shorten the wings 4" per panel.
I know --Blasphemy

Ben Lanterman

Well Dick you don't know Blasphemy if you see it ....... true the Tiger would be a little more to my liking especially with more power but the reason it seems more stable is ........ It has more than enough wing area and the higher wing loading will make it "feel" more groovy/stable but the real longitudinal stability won't change enough for us to see.

rmh

Not after higher wing loading - what the clip does is make the roll rate faster --
makes the yaw stability better - at low speeds - this improves as the span to tail moment is reduced.
Maybe you don't agree but we have seen solid results.

We started doing these mods on all the models with wings much longer than the overall fuselages - it improves all of em .
However -If you don't do aerobatics - you don't see the change.
I was not the first to do this
it goes back to the 30's 40's on air show craft - clipped Cubs - Clipped Tcraft clipped Monocoupe etc..

Ben Lanterman

I was thinking longitudinal stability and you are talking lateral-directional stability. I do agree with you on that.