Build up tailplane.

[rebell]

What do you think of a build up, ribbed tailplane and fin on a 900mm span Extra 300 instead of a flat sheet? What is the advantage of it? I think that as it is a proper airfoil, it will give better control characteristics, especially at low speeds.

[vintage1]

No aerodynamic advantages really at the sorts of speeds we fly at, but a lot lighter, which will help the models dynamics..

[downunder]

I build up the tailplane, elevator and fin on my models. The tailplane is quite thick (1" at the root tapering down to 5/8" at the tip) and given a symmetrical wing section. The ribs are usually 1.6mm (1/16") and it's then covered with 1mm sheet followed by dope shrunk tissue. You won't believe the lightness, strength and rigidity compared to a flat sheet :)

Ever since going to an airfoiled section tailplane I've found I can reduce the elevator throw considerably. One hint though, keep the leading edge of the tailplane quite sharp because this helps keep the model flying level (the downside is it's easier to damage).

[Sparky Paul]

I like the built-up surfaces because of the aerodynamic shape, which improves the elevator authority. As downunder mentions, you need less elevator for the same manuverability.

[Aio_1]

Flat plate tails work quite well at low reynolds numbers.
I think a thicker aerofoiled tail should produce slightly smoother increase in pitch response with increase in deflection but I'm not sure if this will be noticable. An aerofoiled tail will produce less drag and can be stiffer and lighter.
They also look nicer!

At small sizes up to about 1m span I would probably just use a flat plate for simplicity. There are some advantages to a thicker aerofoiled tailplane (and fin/rudder) but at smaller sizes I think the advantages are small and to me it's really as much about simplicity and appearance as performace. I'm lazy so simplicity often wins!

Aidan

[rebell]

Thanks everybody,

I think I will still go for the build up tailplane and fin for the looks of it. If there is a aerodynamic advantage, it is a bonus. I like the building process and it gives me much pleasure if something looks good.

[HELModels]

Flat plate tails work quite well at low reynolds numbers.
I think a thicker aerofoiled tail should produce slightly smoother increase in pitch response with increase in deflection but I'm not sure if this will be noticable. An aerofoiled tail will produce less drag and can be stiffer and lighter.
They also look nicer!

At small sizes up to about 1m span I would probably just use a flat plate for simplicity. There are some advantages to a thicker aerofoiled tailplane (and fin/rudder) but at smaller sizes I think the advantages are small and to me it's really as much about simplicity and appearance as performace. I'm lazy so simplicity often wins!

Aidan

people throw around reynolds number. I am of the school that thinks models typically fly below 100,000. I'm terrible at visualizing metric, so what might a 900mm span Extra have for chord? Chord is one key to reynolds number.
Knowing what speed an Extra flies at is the other.

Would a flat plate be suitable anywhere below 100,000? I'm fairly lazy too, so no hearing advantage to built up tail reinforces me, but I've seen built up tails on .020 sized freeflights. .020 freeflights are around 30" span or less maybe, so pick a minumum chord of around 4 inches.

[Aio_1]

people throw around reynolds number. I am of the school that thinks models typically fly below 100,000. I'm terrible at visualizing metric, so what might a 900mm span Extra have for chord? Chord is one key to reynolds number.
Knowing what speed an Extra flies at is the other.

Would a flat plate be suitable anywhere below 100,000? I'm fairly lazy too, so no hearing advantage to built up tail reinforces me, but I've seen built up tails on .020 sized freeflights. .020 freeflights are around 30" span or less maybe, so pick a minumum chord of around 4 inches.

Reynolds number is not a fixed quantity for a given plane at a given speed. The Reynolds numbers at the tip of a tapered wing will for example be lower than the root and the tailplane will generally be much lower still. I'm not suggesting that there's a critical reynolds number at which suddenly a flat plate is just as good but rather that as the Reynolds number decreases (i.e. small planes and especially those that don't fly terribly fast) the difference is less noticable. I agree that Re=100000 is in the range where the wings of many smallish planes would operate but some are much lower, some are much higher and tailplanes can be considerably lower!

There's 25.4mm in 1 inch.
900mm = 35.4"
Without checking I'll guess the aspect ratio of an Extra is around 6.5 :confused:
That would make the mean chord 5.45"

Aidan

[davecee]

I'm no expert, not even close. I will say that my VK Cherokee Babe with a symmetrical airfoiled horizontal stabilizer was, without any shadow of a doubt, the smoothest flying plane of that general size that I've ever owned. I've been told by people who should know that the airfoiled stab was a significant contribution to that plane's abilities.
Dave

[Sparky Paul]

I was using airfoiled horizontals on my FAI Team Racers back in the early '60s. These planes would almost fly hands-off, and remain manuverable enough in traffic, and for the all-important rapid landing.

[HELModels]

Reynolds number is not a fixed quantity for a given plane at a given speed. The Reynolds numbers at the tip of a tapered wing will for example be lower than the root and the tailplane will generally be much lower still. I'm not suggesting that there's a critical reynolds number at which suddenly a flat plate is just as good but rather that as the Reynolds number decreases (i.e. small planes and especially those that don't fly terribly fast) the difference is less noticable. I agree that Re=100000 is in the range where the wings of many smallish planes would operate but some are much lower, some are much higher and tailplanes can be considerably lower!

There's 25.4mm in 1 inch.
900mm = 35.4"
Without checking I'll guess the aspect ratio of an Extra is around 6.5 :confused:
That would make the mean chord 5.45"

Aidan

I dont doubt your expertise or education. I'm an aerohack and know enough to say it wrong most of the time.

They keep screwing with my computer, proving they control it or something.
I always know it when the keyboard sticks, makes it near impossible to type a rudimentary thought. no, I'm not paranoid.

[rebell]

Something I would like to know. If an airfoil vs. flat plate does not make much of a difference at very low RE#, why do micro indoor freeflight flyers go through all the effort to use airfoil?

[downunder]

Something I would like to know. If an airfoil vs. flat plate does not make much of a difference at very low RE#, why do micro indoor freeflight flyers go through all the effort to use airfoil?
Because they're crazy :)
But I guess no matter what the Reynolds# then an airfoil must be better than a flat plate. Microfilm models must have the lowest # of anything (man made or natural) that can fly and they're simply fascinating to watch. Maybe unbelievable is a better word! They're the only form of competition modelling that has a minimum weight...1 gram for something that has a wingspan of over 20". Work out the wing loading on that :)

[Aio_1]

Something I would like to know. If an airfoil vs. flat plate does not make much of a difference at very low RE#, why do micro indoor freeflight flyers go through all the effort to use airfoil?
An aerofoil is always the optimum for performance (Lift/Drag). Small differences in the best glide angle are not going to be noticed on a small aerobatic or sport plane but they will on a highly optimised performance oriented plane like a pylon racer, inddor freeflight plane or perhaps a high performance glider.
Also I think (don't hold me to it) that most indoor free flight planes use very large lifting tails which basically means the plane is a tandem and the tailplane is nearly as important as the main wing.
There are also lot's of other considerations when you get to REALLY low Re. numbers but let's not go into that or I'll have to go look things up.

Aidan

[Sparky Paul]

We just had an indoor fun fly at a local school..
The task was to build an AMA Thermal Dart, and compete for longest flight time.
I built mine to spec...... except for covering it with Jap tissue.
I had to launch it down by the floor, as it easily outclimbed all the stock planes.
Kept running into the rafters though, which spoiled the flights. :(