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Author Topic: Transition of an 8 inch CLG  (Read 493 times)
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Sailaway
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« on: June 24, 2018, 08:19:29 PM »

Hello ,
Can you please help me understand this phenomena that my 8 inch CLG is displaying.
It weighs 5.6 grams. I launch it almost straight up. I also launch it to the right of the occasional breeze. It goes very scary high. The climb is just around 100 degrees as seen from the ground.Then beautifully drops the left wing to make the CLG level. Now it always wants to circle to the right. No loops, no dives, good transition. I do have left rudder, visually confirmed, left. Tried putting weight on the left wing, does funny things so took it out as the transitions were not consistent. I do have a 1/32 tilt on the stab, left side high from rear. Both wings are of equal weight as balance CLG upside down on the fuse. No heavy right wing. No wing warps either. Slight wash-in on the left wing and very slight washout out on the right tip.

Couple other odd things. First I had to make the fuse of bass as that is all I had that was hard enough. the Second most weird thing is that when I launch it straight up , the twist for a consistent transition is at past 90 degrees on the wings.

It glides well, and because of the right turn stays on the field but cannot figure this out. What should I be learning from this? 
I do get 50 seconds on a cloudy late evening but why would it not (after flopping level in the transition) turn left?

Thanks in advance for all your input.
Regards,
Sailaway
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frash
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« Reply #1 on: June 24, 2018, 08:54:38 PM »

Congratulations, Sailaway. Your CLG is good, even it happens to like indoor cat glider trim rather than outdoor trim.

Usually cat glider trim for outdoor is right-left, but I am left-handed so usually left-right for me. However, for indoor, flight pattern is usually right-right or left-left because the flying site is not large enough to allow the S-turn transition. This is particularly true if one flies (or mentors) the Science Olympiad Elastic Launch Glider event in school gyms.

You probably know all of this, but I recommend posting on the  Indoor Cat Glider section also. The experts there may help.

Fred Rash
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OZPAF
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« Reply #2 on: June 24, 2018, 09:08:04 PM »

As this glider is flying Ok regardless, I would leave this one alone.

I can only advise what I think may help to understand what is happening. The asymmetrical  tip washout on the right wing tip could be overpowering the rudder on the glide, particularly as is most likely, the rudder is primarily sized to control the glider during the high speed of the climb.

The wash in on the left wing is also generating a right roll on the climb which is balancing the left roll from the rudder producing your straight climb. This would be more noticeable on gliders with low dihedral, as the yaw induced roll of the rudder would increase with dihedral.

To achieve a left transition  I feel that you would need to first add equal washout to the left tip to balance the roll effect of the right tip or not have any washout on either tip.

I would then use a lot more tail tilt - up to double what you have.

Check hand glides then should at least indicate a left turn tendency. If not add a slight bit more left rudder.

The rudder then should be checked during the launch. It helps if the tail tilt is the primary source of the glide turn and rudder is only used to adjust the climb and transition.

More dihedral would possibly help as well.

John


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Hepcat
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« Reply #3 on: June 24, 2018, 09:18:51 PM »

Sailaway,
Wash in and Wash out ARE wing warps.  As you describe them they will make a glider turn to the right. You should reduce them or use more left rudder. I think tilted tailplanes are an unecessary complication on a catapult glider.
John


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Sailaway
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« Reply #4 on: June 25, 2018, 07:47:08 PM »

Thank you so much for your quick response.
I was looking for unwanted wraps on my CLG. But realize now that intentional Washout and wash-in are also wraps, that combo making it go Right glide overriding the tail tilt and left rudder. Wow, never imagined that. I built in the left side washin as it almost always needs it. But to get a  slow level flight I had to give a very slight tip washout on the Right tip.
Talking about rudder left. Too much left rudder always gives me a spiral down. Either have to reduce it or more up elevator. How much left rudder do you guys use. I am at 1/32 plus a bit more.
Thanks again
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Hepcat
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« Reply #5 on: June 25, 2018, 10:46:01 PM »

My reply in #3 was too brief. I dont use tilted tailplanes on my CLGs but I have done on plenty of other models and they are often the correct solution.  However I am averse to trying to sand wash-in or wash-out onto solid balsa wings; it is difficult to do accurately and much more difficult to change if wrong.  I usually trim my CLGs with left rudder and Gurner strips under the left wing trailing edge.
 Just to round off what I  do and don't do; I don't ever recall using weight on a wing tip for turn - perhaps I should try it sometime!
John   
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OZPAF
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« Reply #6 on: June 26, 2018, 05:26:23 AM »

Quote
Talking about rudder left. Too much left rudder always gives me a spiral down. Either have to reduce it or more up elevator.

Actually this is why I use tail tilt to provide most of the left turn. Rudder is far more effective at high speed then during the low speed of the glide, thus it is best to just have enough to roll the glider into the left glide turn during the climb. It needs to be enough to start the left glide - but no more.

I have approx. 1 deg offset of the whole rudder for left turn. However this is a starting point and I often need to reduce this by adding a bit of right rudder, when trimming the climb.

It's not a good idea to add more elevator to overcome too much left rudder as this will only hurt your climb - causing it to arc towards a loop.

When you have a glider climbing close to the vertical - it means that the pitch stability is low and it will not generally tolerate getting it's nose down and speeding up.

Tail tilt I have found has next to no effect on the climb but is effective on the glide. How much you will need depends on the geometry of the model - it's tail size ( more accurately it's tail volume).

These comments are all based on trimming the CLG for a right/left "S" type pattern.

I agree with John's(Hepcat) comments re sanding in wash out. I have never actually used wash out.

John has a much broader experience than I do and most of my CLG and HLG experience is with different sizes of the one design. I also don't use tip weight much although I do have a very slight offset of the wing on the fuselage - I doubt whether it does much though.

John

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Rewinged
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« Reply #7 on: July 04, 2018, 12:25:01 AM »

I'm late to this thread, but I want to address the subject of accurately putting washout in a solid balsa wing.  There are 2 good ways I know of, both best done after shaping the wing:

The easiest is to simply cut the tip dihedral joints at a slight angle.  This should be very slight; without checking plans it should be a few degrees.  If you do this for both wing halves at the same time, you can match them up after cutting and sand until they are equal.  The angle should be such that the cut is closer to the fuselage centerline at the TE than at the LE.

The second way is to cut the tip dihedral joint straight--parallel to the fuselage.  Then, tip section a wedge out of the tip section.  The cut is such that you remove no material at the LE, but you remove enough at the TE that the wedge angle is about 8-10 degrees.  Cut a similar wedge out of the TE to make the TE straight again from the main panel to the tip panel.  This will leave you with TE thickness increasing from the minimum (e.g. 1/32 to 1/16) at the joint to thicker at the tip.  Sand the bottom of the tip to again get the TE to constant thickness.

The second method is preferred for optimum performance, since it gives a gradual washout rather than putting the whole tip at the same angle.

--Bill
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