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Old Oct 10, 2012, 03:33 PM
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United States, CA, Tehachapi
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CG does affect launch. That doesn't mean you have to tune your CG for launch, however. I tune my CG to get the best flight characteristics and then play with launch settings, much like Austin described. However, your CG will affect your launch. With a more forward CG, the higher speed at launch will tend to cause the plane to pitch up, so you will probably have to add some down trim to get it to follow a straight trajectory on climb. Then you may want a second speed mode for flying because the down trim on your "launch" speed mode will make it more difficult to fly efficiently. I personally prefer a near neutral CG, which allows me to use the same speed mode for launch as for coming home from downwind without any elevator compensation.

And yes, i do use an elevator preset to rotate vertical right after release.

Brandon
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Old Oct 10, 2012, 03:44 PM
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You are correct. Cg does affect launch but should not be used to tune launch.
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Old Oct 10, 2012, 04:30 PM
Launch high. Fly low.
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There's absolutely nothing wrong with a forward cg. It's better flying IMHO.

Soar!
Jun

Quote:
Originally Posted by Scrib View Post

I have my DLGs setup with a forward CG (cause I suck at flying) making them a bit more stable in pitch, this also requires carrying a bit more up elevator trim to maintain a reasonable flight speed. The up elevator trim at high speed (launch speed) is enough to pitch the plane into a nice ascent angle.
I'm also a little on the tall side and tend to throw more upwards than some do (I can get away with a little more up angle without tip strikes), requiring a little less pull-up from the plane to get into launch...
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Old Oct 10, 2012, 04:45 PM
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Originally Posted by jcats View Post
I always use it. Always.

Soar!
Jun
I do as well however when in winds over 12mph I'm on the switch for about 1/4 second.
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Old Oct 10, 2012, 05:38 PM
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I also fly a forward cg. This my ships require a few clicks of down trim for speed mode.

I think one of the things that confuses inexperienced pilots about the preset is exactly what David said. The preset is engaged for fractions of a second. Then speed mode takes over.

Austin
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Old Oct 10, 2012, 05:47 PM
launch low, fly high
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I experimented with a launch switch in the very early days of dlg, and found that I was not competent enough to operate a launch switch. I'd rather have my right thumb supply the required elevator to rotate to the climb attitude. Works for me, but this solution doesn't work for many people... If mode 2, ya gotta be a lefty.

From my perspective, all you right handers are laterally impaired, and have to use a switch to compensate!
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Old Oct 10, 2012, 05:57 PM
or F, J, K, or even TD
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Yeah, no fair flying your model through the rotation!

I use a preset, and have experimented with NOT using one. Not using a preset does require a more upward launch angle, and does risk a tip strike (ask me how I know) but does yield good results. Not any better than with a preset, but in some cases penetrating upwind on the launch is best handled by a more shallow climb angle than your preset may be tuned to.

If windy, and I wanna be upwind, I will throw without a preset. But really, who wants to be upwind anyway

Mike
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Old Oct 10, 2012, 06:05 PM
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Quote:
Originally Posted by Joe W View Post
I experimented with a launch switch in the very early days of dlg, and found that I was not competent enough to operate a launch switch. I'd rather have my right thumb supply the required elevator to rotate to the climb attitude. Works for me, but this solution doesn't work for many people... If mode 2, ya gotta be a lefty.

From my perspective, all you right handers are laterally impaired, and have to use a switch to compensate!
Or simply fly mode 1 works for me used to do like Joe but after working with launch preset for awhile i like the preset.
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Old Oct 10, 2012, 08:38 PM
Fly, tinker, fly, tinker....
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From the perspective of another DLGer with noobness, I thought I'd offer my experience with a launch preset thus far. I use it. I have it setup on my trainer button (momentary on DX8 relocated to back left). I have programmed it to almost a barely perceptible amount of up elevator, no rudder offset, and timer start. It works great for me. I'm an absolutely horizontal thrower, and the time I hold the button determines my angle of climb. If I'm launching in still air, a longer hold gives a great climb, and a simple tap to start the timer is sometimes all I need in windy conditions. Again, I'm a newer DLGer, but this has worked well for me.
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Old Oct 10, 2012, 09:01 PM
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I started flying DLG with a Hitec Flash5 Tx, pre-set was not an option. Get the cg right and it went right up.
That said, I've got a lot more options now with my SD10G, which lets me optimize other flight regimes as well as the launch mode.
Dave
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Old Oct 10, 2012, 10:24 PM
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CG doesn't affect the launch. It affects the trim you have the rest of the time, which needs to be changed to neutral in launch, at least in the speed part. One of these days I need to fiddle with my radio a bit to get another mode. If I use the speed mode that I use for flying around fast, it still pulls up slightly.

I suspect that optimal climb angle in a wind will actually look like the glider is slightly over on its back. If you have a 10 mph wind, and the dlg is ascending straight up through that air, it will end up downwind of where it rotated on launch.

If the average speed of the throw is 50 mph (initial speed 100 mph?), and you launch to 200 feet, the glider will be 40 feet downwind of where it rotated!
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Old Oct 10, 2012, 11:34 PM
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All the Arrow family including the Legend and Ghost do not "need" any presets for rotation to climb. This is all in the decalage, CG and airfoil.
I like to keep it simple.

Dave
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Old Oct 11, 2012, 12:22 PM
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This assumes you have an elevator trim setting that has the DLG pulling up when at speed in launch mode. If the ship was trimmed neutral there would be very little rotation.
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Old Oct 11, 2012, 01:00 PM
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The CG position (static margin) affects pitch stability. It determines the strength of the airplane's pitch response to return to trim speed if the airplane is flying faster or slower than trim speed.

If you have the glider that is trimmed for a "normal" glide speed in speed mode, if the CG is forward it will pitch up on launch; if the CG is near the neutral point it will not pitch up on launch. The CG position (stability) determines how much the glider pitches up to return to trim speed.

If you trim for launch speed in speed mode (high speed), then with the CG forward the glider will not pitch up on launch, but it will try to go launch speed all the time in speed mode.

If the CG is near the neutral point, you can basically set the flight speed by the airplane attitude, and the airplane does not change it's pitch angle to return to a trim speed.

You can use these characteristics to adjust the pitch up on launch. If you have the CG slightly ahead of the neutral point (perhaps a 5% static margin), and trim it for a reasonable glide speed in speed mode, the glider will pitch up at the higher launch speed. The pitch up will die off as the speed bleeds off during the launch. If you get too much pitch up, move the CG slightly aft and re-trim your your speed mode. This will give less pitch up during launch. Do the opposite if you have too much pitch-up during launch: move the CG aft, and re-trim your speed mode.

Unfortunately, adjusting the CG position will affect your trim speeds in all your other modes as well, and the pitch rate in response to elevator; More forward CG require more elevator deflection, aft CG position requires less.

Another drawback of the method of trimming the launch pitch-up are that it will pitch up more as the wind speed increases, which is the opposite of what you really want. You would have to adjust the CG position and your trims for all your modes as the winds speed changes.

When the CG gets near the neutral point, many other small factors effect the stability margin. such as dihedral angle, wing height above the CG, tail position relative to the wing wake, etc. This can result in different response to speed changes with different airplanes with small static margins.

Kevin
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Old Oct 11, 2012, 05:53 PM
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Momentary lapse: Kevin can you shoot me a PM or E-mail I would like to ask you some questions. Thanks, Paul

Now back to launch fine tuning,

Oh, I have tried both and had one plane set up so I needed the pre-set in no to light breeze and didn't use it in the wind.
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