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Old Jul 20, 2004, 07:52 PM
Bubble Head SSN 762
LexTalionis's Avatar
Austin Bergstrom, Texas, United States
Joined Apr 2004
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SS V-Tail angle poll...

I'm about to mount my V-Tail on my SS fuse and I've got two balsa mounts ready, one that's 120 degrees and the other is at 90 degrees.

Which should I go with? What are the pros and cons of each, with regard to control and stability?

Thanks,
Lex
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Old Jul 20, 2004, 08:12 PM
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Neither. 110 is the right angle. With 120 you'll have too little yaw stability and too much adverse roll. With differential rudder travel you'll get pitch coupling. At 90 you may run out of elevator authority at slow speeds. If you can't change the angle, I'd go with 120.

I stopped by the LHS today, which has changed their hours and were closed (grr...), but I did see a huge stack of Slow Sticks through the window. I might have to scrape up the loose change in the couch and buy another one to build with a v-tail and spoilers. I even have a reciever, servos and ESC sitting around already. Ok, I have a plan now My wife hates it when I have a plan...

Steve
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Old Jul 20, 2004, 08:57 PM
Bubble Head SSN 762
LexTalionis's Avatar
Austin Bergstrom, Texas, United States
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Quote:
Originally Posted by SFT2
My wife hates it when I have a plan...

Steve
Thanks! I thought I read somewhere on the forum that 110* is the official angle from the areonautical engineering gurus. I'll try to bevel sand the balsa side to the fuse such that I approach as close to 110* as possible.

Thanks!

BTW, Roger that one the above quote

Lex
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Old Jul 20, 2004, 10:21 PM
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Why would you do this? (I hate V-tails!)
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Old Jul 21, 2004, 01:14 AM
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Less drag, less weight, something different, use another gizmo in the transmitter (which is likely smarter than me). I love v-tails myself.

Steve
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Old Jul 21, 2004, 06:45 PM
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Picked up another SS today and started fiddling. Noticed that they've greatly improved the wheels since my first SS. Maybe these won't fold over by the time I get to the field (5 minutes). Stuck some 3/8 square and 1/8 sheet balsa together and ran it through the scroll saw at 55 and have a v-tail mount. Just need to split the stabilizer and elevator, epoxy on a spar, and add about a mile of strapping tape. Should be done tonight and hopefully I'll be able to sneak out to the field tomorrow.

Steve
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Old Jul 21, 2004, 07:28 PM
Bubble Head SSN 762
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Austin Bergstrom, Texas, United States
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Steve,

Post a picture when she's done. I'm taking a bit more time on mine, plus I've got lots of distractions going on now. I got 110* after some sanding. Too bad I don't have a scroll saw ;-)

Lex
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Old Jul 21, 2004, 07:30 PM
Bubble Head SSN 762
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Austin Bergstrom, Texas, United States
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Quote:
Originally Posted by Bob HSG
Why would you do this? (I hate V-tails!)

Though I haven't flown a V-Tail modified SS, I hear it maneuvers much better...tighter loops, etc.

Lex
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Old Jul 21, 2004, 08:23 PM
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Have fun. You'll be flying your stock stick again after 3 flights. Once the novelty wore off, I couldn't switch back fast enough.
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Old Jul 21, 2004, 08:24 PM
You're a nerd.
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That came out sounding pretty crappy. It's a fun mod that's easy to do, but I didn't like it. It felt too twitchy.
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Old Jul 21, 2004, 08:25 PM
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Double post.... I'm dumb
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Old Jul 22, 2004, 02:08 AM
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Twitchy is easy to take care of. Move the CG forward a hair and reduce throws. Exponential rates are good, too. I've flown v-tailed sailplanes for... over a decade now and honestly I can't tell any performance difference with any type of tail. However, the v-tail is just as good as a T-tail on landings. The stab tips aren't as close to the ground and don't grab stuff sticking up. The v-tail is substantially stronger and lighter than a T-tail, though.

Wing is done. Fuselage is done (ok, so that's a 1 minute job). Need to epoxy the stab halves to the saddle, solder the spreader wire to the gear, and install the electronics. Since I cotter pin my gearboxes to the fuselage I decided it would be nice to have a way to drill them in the same spot every time, so I whipped up a quick jig out of the scraps from the stab saddle. I'll take a pic of the jig when I take a bunch of pics later.

Steve
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Old Jul 22, 2004, 07:21 AM
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Quote:
Originally Posted by SFT2
Neither. 110 is the right angle. With 120 you'll have too little yaw stability and too much adverse roll. With differential rudder travel you'll get pitch coupling. At 90 you may run out of elevator authority at slow speeds. If you can't change the angle, I'd go with 120.
Well 110 is a good rule of thumb.

The Charles River website (a site for glider design - http://www.charlesriverrc.org/articl...tailsizing.htm) has a lot of good discussions about V-tails and they suggest using the Mark Drela formula which is:

To convert a conventional tail into a V-tail:

A_vtail = A_vertical + A_horizontal

angle = arctan[ sqrt( A_vertical / A_horizontal ) ]

Notes:

1. "A_vtail" is the area of both halves together, rotated flat. "angle" is the V-tail's dihedral angle from the horizontal.

2. These formulas are strictly correct only for large tail aspect ratios, since they do not account for the local interference and lift cancellation at the V-tail roots during yaw or "rudder" application.


Which may produce an angle moderately different to 110 (my experience suggests anywhere from 100 to 130 depending on the application)

I'd agree about going with the 120 - just keep on your toes.

Just my 2c


Digsy
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Old Jul 22, 2004, 03:54 PM
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Ok, I didn't get finished last night thanks to a computer game I'm hopelessly addicted to, but I'm getting there. ESC (20a for a Speed 400. Overkill, but it was handy) is soldered in and heat shrinked to the fuselage, servos (HS-55s instead of Futaba standards, I'm going for light this time) are in, radio is programmed, tail is mounted, gear is soldered, motor is on, wing is built, just need to hinge the tail, fix a toe-out problem on the main gear, mount the Rx (a huge Futaba for the time being, need to pick up a 6 ch GWS), clean up the wiring, and set the CG.

In other news, totally unrelated to Slow Sticks, the brown truck brought me a box with a 60 amp ESC. The battery and motor wires look like jumper cables. It's going in either a Mosquito with a pair of Speed 480s or a Sea Fury with an Endoplasma. Either way it's 10 cells and no chance of keeping the thing over the school I fly at. Just way too fast.

Now back to slow, sane projects...

Steve
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Old Jul 23, 2004, 05:07 AM
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Finally got some pics taken. She wasn't quite finished yet, but close enough. I still needed to mount the receiver and mess with the CG. I wanted the longest tail moment possible, so I move the wing as far forward as possible and shifted stuff around until the CG was right. I added a bit of dihedral so I need to add some shims to the mounts. Figured out the perfect way to hinge the surfaces. Strapping tape just didn't want to stick so I spread some GWS glue on the spots where the tape goes and mashed the tape down to get it into the glass strands in the tape. Works great. The ESC is held on with heat shrink like my first SS. With the huge 8 cell 1600 mAH AA pack in the pics she weighs 18 oz. The stock SS with a similar pack is almost 22 oz. (big servos, that's my windy day plane). Hopefully I'll be able to sneak out to the field tomorrow and fly them both back to back. And give a real opinion.

Noticed some interesting things with this one. My first SS was from very shortly after they came out and some things have obviously changed:

-New wheels are VASTLY better. The spokes are about twice the thickness and they don't want to fold over every time you look at them.
-Tailwheel wire is much stiffer. The first SS wants to sit on her elevator. No problem with the new one. I twist the wire 90 degrees and leave the wheel off, personally.
-Spar joiners are made of much thicker tubing. I still replaced it with 6" long brass tubes and CA'ed the spars in, though. They aren't breaking.
-Something is different about the motor, but I'm not sure what. Could just be marked different.

Next I'll be putting spoilers on the old wing and adding a sheet of foam to make it a flat bottom airfoil.

Steve
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