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Old Oct 11, 2012, 07:15 PM
turn, turn, turn.
Athol, Massachusetts
Joined Oct 2005
10,290 Posts
Like Mike, if I want to go upwind, I won't use one... but I usually need a read to go upwind.

I don't know if anyone's mentioned it, but to do a turn and burn, I will hold my preset just a tad longer... this will rotate the plane towards inverted, and then I'll roll it over level and head downwind.
Anywhere between those 2 points of extreme preset, will give me any trajectory I choose to go on launch.

I don't have any rudder in my preset.
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Old Oct 11, 2012, 10:49 PM
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1900 Driver's Avatar
Denver CO
Joined Mar 2009
610 Posts
I launch to around 160 to 180 and have never used a preset, I just have a slightly forward cg. I really need to stop fighting it and switch my momentary over (hitec aurora)!

Brandon
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Old Oct 12, 2012, 12:34 AM
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Congress, AZ
Joined Sep 2001
4,907 Posts
For those of you who say it's the CG that effects the climb, do a simple test. Add 10 g to the nose and throw. The plane climbs the same. The glide of course will be effected by the weight.

Now add some up elevator. The glide will smooth out, the throw will go over the top.

It's the elevator that controls the climb. If not, then our pre set would move the cg.

Agghhh. It's sort of like chicken and egg.

I'm surprised that Phil Barnes hasn't chimed in by now.

Gary

Sorry, it's a completely un-necessary post.
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Old Oct 12, 2012, 01:50 AM
Sure it'll work
Flyextreme's Avatar
United States, CA, Torrance
Joined Nov 2005
4,272 Posts
I suppose I should give some the reasons for the original question.

1). I have yet to find a button I like to install on the left side, or the the time to relocate the momentary switch or install a button.
2). I have been trying to keep it very simple so I can concentrate on launch form (or lack of).
3). I was wondering if people looking at me like I had 3 heads when I told them I didn't have a preset was normal.

From the responses here, it looks as though I can get by without a preset for a while. However, setting up a preset as soon as I'm more confortable, would be better.

At this point, I have my flight conditions set on my left slider because that's what I am used to, and it's easier right now. I intend to get everything set up the way most pilots have it, then I may have to relocate a few switch functions to suit.

Another factor is that I have two bum arms. My left arm is partially paralized, and I've lost about 75% of the strength in the right bicep. This makes the way I do some things a bit more challenging to say the lest. It even looks like I may have to try and find a way to make my TX tray/strap work because it's hard to hold the radio very long.

I will get it figured out one way or another. I may have to achieve the same results by a slightly different way of using my TX.

Bill
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Old Oct 12, 2012, 02:04 AM
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JamesCH's Avatar
Thailand, Bangkok
Joined Oct 2011
70 Posts
Quote:
Originally Posted by Flyextreme View Post
At this point of my noobness, not having alot of time at the field, not yet getting things completely dialed in, and not having relocated my momentary switch to the left side, I have not been launching with a preset. Also, I've been thinking at this point to keep it as simple as possible so I can concentrate on keeping the plane in the air, and in one piece. It seems to be working fairly well so far.

I've been launching 3 different planes, and each launches a little different from the other.

Just to keep my question simple........

Does anyone "not" use preset?

Thanks, Bill
FWIW, I use some sort of launch preset, but it is not on a momentary switch. My plane is rudderless and I use the rudder stick -with reduced rate- to control the elevator on launches. So from the pic, I first hold the stick to the left, giving proper amount of up elevator -providing a great grip to the Tx as well-. Then when the plane has pitched up to a satisfied attitude I release the stick back to neutral. Then I start the pushup by pushing the stick to the right. This a very natural and with analog control throughout the launch process.
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Old Oct 12, 2012, 02:13 AM
turn, turn, turn.
Athol, Massachusetts
Joined Oct 2005
10,290 Posts
You can spring load a switch with a rubber band.

Hook the switch, run the rubber band around the back of the radio and hook it on any protrusion.
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Old Oct 12, 2012, 02:20 AM
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JamesCH's Avatar
Thailand, Bangkok
Joined Oct 2011
70 Posts
On a rudder ship however, a launch switch is needed. When the switch is pressed, it does:
1. kills the rudder control on the rudder stick
2. authorizes elevator control on the rudder stick - with reduced rate of course -
3. mixes rudder stick at each stage to different wing cambers
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Old Oct 12, 2012, 04:34 AM
Team Hong Kong F3K
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Hong Kong
Joined Sep 2010
3,071 Posts
JamesCH, I understand point 1, but why would you need points 2 and 3?
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Old Oct 12, 2012, 04:37 AM
Team Hong Kong F3K
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Hong Kong
Joined Sep 2010
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FWIW, I use a preset as well, although I've lowered the rate a little bit since I've begun to throw at a higher angle.
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Old Oct 12, 2012, 08:41 AM
Registered User
United States, CA, Tehachapi
Joined Jun 2011
3,207 Posts
Quote:
Originally Posted by GaryO View Post
For those of you who say it's the CG that effects the climb, do a simple test. Add 10 g to the nose and throw. The plane climbs the same. The glide of course will be effected by the weight.

Now add some up elevator. The glide will smooth out, the throw will go over the top.

It's the elevator that controls the climb. If not, then our pre set would move the cg.

Agghhh. It's sort of like chicken and egg.

I'm surprised that Phil Barnes hasn't chimed in by now.

Gary

Sorry, it's a completely un-necessary post.
I can tell you with absolute certainty that a more forward CG causes pitch up on launch IF THE ELEVATOR IS TRIMMED FOR A FLAT GLIDE AT NORMAL SPEEDS. Yes, the theory is sound. Yes, I have experienced it. 1 year ago I was flying DLG with a TX that was incapable of programming a launch preset. I was able to make up for it by using a more forward CG. I often had to manually give slight down elevator at about half to three quarters of the way up the climb to keep it from going inverted, but it worked. Once I got a better transmitter, I moved the CG back to where I really liked to fly it and I set up a launch preset. With the elevator trimmed for a flat glide, the DLG would go straight in whatever direction I pointed it on launch. I didn't measure it, but my launches seemed to be higher, too. Note that that last statement was purely subjective. My perception of higher launches could be completely false. However, CG certainly did affect the behavior of the plane on launch.

If your momentary switch is on the wrong side and you don't feel like doing surgery on your TX to move it, you can do like I did and use a rubber band to hold the switch you use in the off position. I still use this method today. Just make sure you change the rubber band frequently. I've had one break, leaving the launch preset turned on during launch (it'd been on there for like 3 months). Scared the bejeezes out of me.

Brandon
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Old Oct 12, 2012, 09:08 AM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
United States, NY, Plainview
Joined Aug 2005
8,091 Posts
Let me understand something here.

Those who have a forward Cg and not using a launch preset.

1. If you trim the plane to a normal speed mode or cruise mode, will that not be much slower than the speed on launch?

I would think - yes even if you are running from sink, why waste altitude needlessly. You can always add down elevator if you need to go faster still.



2. If a plane has a more forward Cg, it is positively stable. If a plane flies faster than trim or slower than trim, won't the plane desire to regain trim speed?

again, I would think - yes. If it is flying faster, it will pitch up until the speed has bled off and may oscillate up and down or just settle into the trim speed by some manner.



3. If after you launch, the plane pitches up. Isn't there drag being caused by the desire to go to trim speed?

again I would think - yes. any deployment of a control surface to cause a change in pitch , yaw or roll adds drag. In this case none are deployed but is there trim drag causing the pitch up ? I would guess yes.



4. If you throw too hard, couldn't the plane loop over?

I would think - yes. If this could happen, you might need to add elevator which will add drag until the plane has attained trim speed. I would think it would take longer to attain the speed one has trimmed the plane to in speed mode than the pbrief time to turn off a launch preset.



I would think the desire on launch is to have the least control inputs nec. to get the plane to the greatest altitude. If your plane is setup neutral in stability, It will not pitch up or down with changes in speed. a preset is necessary. If you are only slightly positively stable, I would wonder if the rate of pitch up would be slow such that too much altitude be lost? I susopect this to be the case.

Does the ability to have a plane pitch up in speed mode, could this suggest too slow a speed mode?

Should one be able to fly slowly in speed mode?

Is speed mode set so that the plane is neutral at launch speeds or can it be trimmed slower than that? Should speed mode be so neutral that it should be neutral and hold whatever velocity and pitch it is set to?


I do not know.....


Based on control input added drag, I opt for a neutral plane and a launch preset. Any control input on launch should reduce launch height.

IMHO.....


Frank
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Old Oct 12, 2012, 09:42 AM
Registered User
United States, MD, Baltimore
Joined Feb 2007
660 Posts
I agree with Frank. "speed mode" trimed for level flight will give a reduced launch height on positivley stable CG air craft as the trim slows the plane to the set trimmed speed. Along with reduced launch height in my mind there is no reason to trim a speed mode that will recover on a dive test, the whole point is to RUN. If it is trimmed to slow down to level flight you are not getting the "speed" out of it. In circumstances you would use a mode like this you should then be using cruise mode as this will give a more favorable sink rate.

So yes CG determines how an aircraft recovers and is more pronounced at high speeds eg. launch. However an aircraft with ANY CG can and should be (IMHO) trimmed for straight flight during launch. You may chose to have a seperate Launch and Speed mode but I do not see the advantage in that.

As for the momentary swith. yes it is convenient but it is not necessary I know pilots that simply use the most comfortable 2 posistion switch. Use 1 position for rotation and after that is complete just flip the switch to end the "preset." then Fly in speed mode until push over. It is a simple mix that almost any computer radio sold can do and once again IMHO will provide higher launches than without preset. YMMV

Austin
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Old Oct 12, 2012, 10:00 AM
or F, J, K, or even TD
FLY F3B's Avatar
Joined Jun 2007
2,912 Posts
Simpy put, and simply executed:

Trim AND CG the model for glide

THEN,

Trim for launch preset(s) to get rotation and straight climb trajectory. Do NOT CG for Launch.

It's as simple as that.

If you can't or don't want to use a preset, then simply adjust your trim slightly so that after release you get an up ward arching trajectory. It is NOT opitimum, but it does work.

Mike
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Old Oct 12, 2012, 10:08 AM
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United States, MD, Baltimore
Joined Feb 2007
660 Posts
^^^
Yes.

Thank you Mike.

Austin
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Old Oct 12, 2012, 10:52 AM
Registered User
United States, CA, Tehachapi
Joined Jun 2011
3,207 Posts
Quote:
Originally Posted by FLY F3B View Post
Simpy put, and simply executed:

Trim AND CG the model for glide

THEN,

Trim for launch preset(s) to get rotation and straight climb trajectory. Do NOT CG for Launch.

It's as simple as that.

If you can't or don't want to use a preset, then simply adjust your trim slightly so that after release you get an up ward arching trajectory. It is NOT opitimum, but it does work.

Mike
+1

Leaving my CG forward on that plane ensured it would pull up on launch, but it didn't fly as well as it could have. I was new to RC as well, so I welcomed the added stability at the time. Now I would never use CG to trim my launch.
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