Originally Posted by Quick61

While were talking DLG wings, I was looking for something else and came across this cute little guy.

And what i was looking for was this thread here - http://www.rcgroups.com/forums/showthread.php?t=1412503 Don't know if you have seen it Kent, but it might be worth a look. Of note is the way the fin is done.

Mark

Now that first one is nice!
Is the thinking behind the fin design to keep the drag "lower"?
Stuart

Originally Posted by Stupot46

Now that first one is nice!
Is the thinking behind the fin design to keep the drag "lower"?
Stuart

Yea, I kind of liked that first one my own self. As to the fin, on SAL and DL type gliders, there is a lot of force being put on the fin/rudder during launch. I have blown off more than a few tails when I started in building DLG's, that and cracked tail booms. From the looks of the tail Kent has drawn, to hard of a discus launch will put a lot of stress on the joint where the fin meets the boom. That's why you see the vertical tail surfaces on DLG's above and below the boom in almost a balanced side loading. With all the surface on top, it has to be very, very strong or it will fold over like a wet noodle or twist the boom till it cracks.

Mark

Originally Posted by Quick61

Yea, I kind of liked that first one my own self. As to the fin, on SAL and DL type gliders, there is a lot of force being put on the fin/rudder during launch. I have blown off more than a few tails when I started in building DLG's, that and cracked tail booms. From the looks of the tail Kent has drawn, to hard of a discus launch will put a lot of stress on the joint where the fin meets the boom. That's why you see the vertical tail surfaces on DLG's above and below the boom in almost a balanced side loading. With all the surface on top, it has to be very, very strong or it will fold over like a wet noodle or twist the boom till it cracks.

Mark

Thanks Mark.On the first two you showed the tail area is horizontal rather than vertical,I presume to get around the problem.Less efficient than the same area vertical?
On that last pic it looks as though it could be vulnerable on a less than perfect landing.
Regards Stuart.

Originally Posted by Quick61

Of note is the way the fin is done.
Mark

That fin is a good design. Same as the Alula uses. It's a very light ship.

I plan on bungee launching this one on a regular basis and at 26 oz. AUW it will not be light. I like the idea of a strong tail to serve as a handle for launching. Also, I do better with more durable gliders. I'll be using a short fiberglass tube for the tail boom and will draw some carbon tow through it to give both strength and flex.

I'll be sure to get some video of the DLG launch so we can see if that top heavy fin is flexing. Who knows, maybe a wing mounted key chain camera is in my future.

Kent

Originally Posted by Stupot46

On that last pic it looks as though it could be vulnerable on a less than perfect landing.
Regards Stuart.

Mark's photo of the typical DLG tail shows how far this type of glider has developed. All carbon. Very strong, rigid and light. These planes are so light that many landings are hand catches. Hard crashes are rare for these "floaty" birds.

Kent

Originally Posted by Knoll53

Mark's photo of the typical DLG tail shows how far this type of glider has developed. All carbon. Very strong, rigid and light. These planes are so light that many landings are hand catches. Hard crashes are rare for these "floaty" birds.

Kent

How large a dia. tube are you going to be using Kent? The trouble I have had with both CF and fiberglass tubes / rods is their inability to handle torsional loading because all but the most expensive ones are made with uni fibers. either rolled or die extruded. Pulling epoxy soaked CF rovings through the tube will help, especially it you twist them. If it's in your budget, I might suggest instead of, or in addition to the tow filled center, cover the outside with some biaxial sleeve Or maybe even better yet, roll your own boom with layers like, 2 layers uni CF, then cover with biaxial FG/CF.

Another thing you could do if not wanting to go to the trouble of making your own boom or ordering new materials would be to spiral wrap the FG boom with CF tow. Wrap in the direction of the expected torsional load so it tightens on loading. (the direction of the wrap is determined by whether you are right or left hand launching)

This information was borne from weeks of research I did while looking into building a tail boom that would stand up to the torsional loads of a V tail on a little pod and boom glider called Eclipse that is on my "someday" list.

Mark

EDIT: This thread - http://www.rcgroups.com/forums/showt...hlight=mandrel - has info on rolling your own tail booms if your not familiar with the process. There are many others on here as well as some youtube videos.

Great Mark. Good idea!

I'm using .231" diameter fiberglass filament wound epoxy tubing. I could easily wrap it with some kevlar cloth at 45/45 to add torsional strength and rigidity. Because the tail boom is so short, the torsional deflection should be small. I'll start off with the solid CF core version. I wouldn't imagine that I'll be able to get much rotational force on the fin with the discuss launch with such a big wing. I'd think that using the fin as a handle for bungee launches would induce more bending on the tail boom. So strong and flexible looks attractive at this point.

I fully expect that this tail boom is the most vulnerable to damage part of this plane. We will know soon enough.

Kent

Kent,

Like the new plank If you keep your centre fin but add a strake that runs from somewhere halfway back on the root chord to the fin LE AND run the elevons in to the root, when you apply a roll input the lateral shift in the centre of pressure gives the fin an apparent angle of attack and thus a positive yaw interaction.

The dear old Vulcan had such a feature...

Also, as a bonus, the strake adds useful strength.

Regards,

Richard
(not getting any flying OR building done atm)

Hi Richard,

Thanks for your comments. Although I could tape on additional fin parts, the wing is "set in stone" at this point. Or to be more accurate, lite ply. I hope to get parts back from the laser cutter this week.

Kent

I should be able to build this balanced fin strong enough to withstand a landing or two. There will be no touch and goes with this tail. The moment the bottom of that tail touches some thing firm, it will send the nose into the dirt. It's my automatic landing tail.

Kent

I wouldn't worry too much about digging the nose in the dirt. You will probably be hand catching the thing more than letting it land on its own.

ha ha ha....You give me too much credit. I think the last time I hand caught a plane was 1982. We'll see. I give it a try. This might be the heaviest DLG on the planet.

Kent

Originally Posted by Knoll53

ha ha ha....You give me too much credit. I think the last time I hand caught a plane was 1982. We'll see. I give it a try. This might be the heaviest DLG on the planet.

Kent

Methinks you'd better start exercising that throwing arm!
Stuart

After building so many Hortens, I'm eager to build a fin. This is a shaped 1/4" balsa plank, stained and glass with light cloth. I found some thin mylar looking material so I waxed it up and vacuum bagged it. Like it. Should hold up well for light duty.

25gm for the fin

This is the mylars coming off.

Plank 101 fin - out of the bag (1 min 18 sec)

Kent

The spars just showed up. This is a 1/2" diameter carbon tube from Goodwinds.com. Stiff and light. Testing with 8 kg. Equvilant to about 12 G's with full ballast. Currently thinking that 16 oz. of ballast will be plenty for the windy days. A proper test would have the spar supported at the MAC, not the tips...but I'm looking for trouble.

Kent