tail sections: flat or airfoil???
 

Hey guys,
I'm desighning a 50 sized 3d biplane and i want to keep it light and to make a sectioned elevator and rudder would mean making them foam core which i've heard is hevier. how much diference is there in flight with a flat section plate? :confused:

tail sections: flat or airfoil???
 

I don't think it really matters with a small airplane...

One way to look at it, most if not all of the full scale aerobats (Ultimate, Edge 54) have flat tails.

I think a flat tail is more responsive right around center. I can't remember why I'm saying that though...

When I was flying a Seduction Freestyle with an Airfoiled tail, I started wondering if there actually was an advantage. Seems like the only advantage was being able to tell everyone at the field I've got an airfoiled tail!! :)

tail sections: flat or airfoil???
 

thanks for the fast reply!! i'll probably go for the flat tail.

tail sections: flat or airfoil???
 

if you have an airfoil tail section, it would be a fast model. i think you would have controlability problems on takeoff and landing.. more so than with a flat foil.

tail sections: flat or airfoil???
 

Why Jim?

Not sure I understand the faster part OR the take off part...

tail sections: flat or airfoil???
 

thanks again for the very fast replies! definately the flat section then.

tail sections: flat or airfoil???
 

For 3d you probably won't notice the difference between flat or airfoil tail feathers.

An airfoil tail will "fly"better (I think it's to do with boundary layer separation at high angles of attack),and try to keep the tail where it should be- ie behind the pointy end.

Much more important on pattern type models, I think.

tail sections: flat or airfoil???
 

Most modern day, non-biplane aerobatic airplanes have airfoiled tails, including the Edge 540. The Edge did start out with a flat welded tube tail though.

The biggest advantage of the airfoiled tail is if designed correctly, it eliminates the need for flying wires.

At these reynolds numbers however.. you will be unable to tell the difference.

tail sections: flat or airfoil???
 

i prefer it thought because airfoiled tails look a lot better.

tail sections: flat or airfoil???
 

A flat tail section should not be more responsive in flight. Actually, it feels like you have some exponential on your transmitter. An airfoiled tail section will be more precise due to being rock solid in center. Sloppy servos and linkages will be more apparent with an airfoiled stab and fin.

Structurally, the airfoil gives a big advantage but you know a flat tail is easy to build and repair if you ever have to...

I am not so sure that airfoiled stabs are heavier since you often need flying wires to hold in place flat tails. With flying wires come glitch if they are metal wires...

I would lean to airfoiled tail sections.

tail sections: flat or airfoil???
 

Why does an airfoil tail eliminate the need for flying wires?

tail sections: flat or airfoil???
 

flat plates are very poor performers for bending loads (low moment of inertia) whereas the airfoiled section would be significantly thicker at the center of pressure (approx spar location if there was a spar). Therefore, most airfoiled sections would have a higher moment of inertia to resist the bending loads.
Or something like that :confused:

tail sections: flat or airfoil???
 

I've been flying small electrics for a while with just flat plate wing sections for the size of the planes and the speeds that they are flying at an airfoil is pointless.

tail sections: flat or airfoil???
 

When you have a flat tail I have found that the plane doesn't do the 3d as good as an airfoil tall. With flat tail surfaces the stab are not producing that much lift. However with an airfoil tail section the surfaces are producing lift for the back of the plane.

James

tail sections: flat or airfoil???
 

Actually the difference in lift created by a flat plate vs a normal airfoiled section is very small. The biggest difference is the flat plate will stall more quickly than the airfoiled section. This is noticed mostly at 3D deflections where there airflow doesn't stay attached as well.

tail sections: flat or airfoil???
 

OK Doug, that I can understand. My next thought is if what you say is true, sheeted wings perform better than ribbed wings because the airflow has a better chance of staying in contact with the surface. Is this correct?

tail sections: flat or airfoil???
 

Generally sheeted wings will perform better yes since the airfoil has a better chance of remaining true across the entire wing planform. That depends upon building quality of course.

Now.. as to how much of a difference, and whether you could tell? I don't know honestly. I doubt it could really be felt.

tail sections: flat or airfoil???
 

Someone once told me that the airfoiled tail gives the aft end more lift and allows you to increase tail moment with no adverse effects on C.G. I am not sure that this person is right, but they generally are. For a .50 size, I would go with a flat tail surface b/c it makes things a lot easier to build. Im pretty sure it would make the model lighter anyways. I have also heard that a Bipe is usually a little more tail heavy anyways (thats why everyone use to say "this heavy motor would be good in a bipe") by adding the additional weight with the airfoil design you could have trouble balancing the model. The best 3D bipe I have ever seen was a Barnstormer Ultimate (1.20 size). It had a flat tail and would do anything that chip hydes TOC bipe would do.

tail sections: flat or airfoil???
 

yea, by Chip Hyde!

tail sections: flat or airfoil???
 

Actually I think the bipe was created by the Barnes family in Kentucky. I talked to the guys selling it and I found it it was $$, but I guess you get what you pay for.

tail sections: flat or airfoil???
 

this is getting a bit hard to choose

tail sections: flat or airfoil???
 

I've been told that the aerofoil sections dont make much difference over flat sections until you get to about 120 size and up. It comes back to reynolds numbers and such again.

On a 50 size, I would go for the flat plate simply because it is easier to build.

tail sections: flat or airfoil???
 

Go for flat right now, you need something to make the MK.2 different from the prototype.

Where in Australia are you from ?

tail sections: flat or airfoil???
 

brisbane. looks like i might go for the flat plate.

tail sections: flat or airfoil???
 

May I add, avoid flying wires at all cost. They add much more weight than a little more wood and can always loosen up due to vibration.

As a side note, it always amazes me when somebody say that a particular design, say a Cap 232, is, by design, tail heavy. Not that they are wrong, my Cap is tail heavy as well as about every Cap I have seen from 40 size to 40%. What really amazes me is seeing designers come up with another tail heavy Cap. What if somebody would finally lengthen the nose by one inch or something like that. I am not so sure that it will be that apparent when finished. OK it will look more like an extra but hey, we can still make a difference comparing a Ford Taurus and a Monte Carlo in Nascar racing.

Why can't we design a naturally balanced airframe?