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Old Dec 02, 2012, 05:59 AM
Canadian Bacon
flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
12,914 Posts
Both handlaunches were so badly botched, it wouldn't have mattered where the trim or CG were. If he could have gotten down elev and right ail or rudder, something might have saved but I don't think anyone has that quick of reflexes to do it.

Gord.
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Old Dec 02, 2012, 08:52 AM
Not always grumpy!!
insomaniac45's Avatar
UK, Eastleigh, Eastleigh
Joined Jul 2010
555 Posts
i agree a decent hand launch makes all the difference, but even a bad hand launch is recoverable on a flyable plane.

as some one has mentioned before, make sure it glides first. if it glides, it will fly. do a simple chuck test into the long grass to see if it wants to glide. if it just goes up (with all trim set to neutral) then your cog is way off, and should be addressed immediatly. if it glides nicly into the grass, then it should be able to fly as is. i dont have any motor offset, or trim on my wings set to counteract torque roll, but then thats all about motor placment and wing size. i would add a bit of right offset at least (put a washer under the right hand mount point (as you look directly at the motor) this will help counteract torque roll.
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Old Dec 03, 2012, 02:37 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,767 Posts
Quote:
Originally Posted by insomaniac45 View Post
im a bit of a noob my self, but have tried to build a few models in the past, with mixed sucess. i have however noticed no one has said about COG?

it could just be too tail heavy, causing the rising nose, then stall.
a plane like this does need a bit of speed to generate stability from air passing over the wings.
No one said tail heavy because in his opening post he said it was balanced, if anything nose heavy. Of course he could;d have been mistaken but a few posts back he said that he changed the prop for a larger one and now it flies ok. So that pretty much confirms the problem was being under-powered, possibly a reversed prop also?
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Old Dec 04, 2012, 07:50 PM
Space power
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United States, IA, Hampton
Joined May 2012
307 Posts
Here's how I see it. On the launch it is thrown from well behind the CG and this can lead to a down force on the tail as the wrist flicks down. At the speed that it is flying just after launch it is near stall and with the added problem of the sudden down force from the wrist flick you have a stall. As stated it has a lot of power, so in this stalled condition the motor torque will cause a slight roll to the left and P-factor will cause a severe yaw/roll to the left as seen in the video. He was throwing with his left hand so his right hand was on the controls. This means that his immediate response to the left roll would be to roll ailerons to the right. This will cause the left wing to stay more stalled than the right and continue the roll into the ground, no matter how much throttle you give it. If indeed it has enough power to hover it should be launched at a lower throttle setting and add in more after you have a stable climb.
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Old Dec 05, 2012, 09:01 AM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,428 Posts
Quote:
Originally Posted by cfircav8r View Post
Here's how I see it. On the launch it is thrown from well behind the CG and this can lead to a down force on the tail as the wrist flicks down. At the speed that it is flying just after launch it is near stall and with the added problem of the sudden down force from the wrist flick you have a stall. As stated it has a lot of power, so in this stalled condition the motor torque will cause a slight roll to the left and P-factor will cause a severe yaw/roll to the left as seen in the video. He was throwing with his left hand so his right hand was on the controls. This means that his immediate response to the left roll would be to roll ailerons to the right. This will cause the left wing to stay more stalled than the right and continue the roll into the ground, no matter how much throttle you give it. If indeed it has enough power to hover it should be launched at a lower throttle setting and add in more after you have a stable climb.
I'll buy THAT for a dollar!
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Old Dec 06, 2012, 06:24 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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Quote:
Originally Posted by cfircav8r View Post
Here's how I see it.
Isnt the time for speculation past given the fact that he fitted a bigger prop and that solved the problem
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Old Dec 06, 2012, 07:11 AM
Space power
cfircav8r's Avatar
United States, IA, Hampton
Joined May 2012
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Prop wasn't the problem, the larger one just made it more forgiving. You can't learn from your mistakes unless you know what they are.
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Old Dec 06, 2012, 08:44 AM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,428 Posts
I agree. That first launch made anything but a grossly overpowered plane guaranteed to crash. Changing the prop COULD make that kind of difference, but unless it was grossly wrong to begin with, I have my doubts.

He didn't say what he started with for a prop so that's all speculation. But the fact is that the plane would have flown had it been properly hand launched with the motor off. We don't know what the new launch looked like. Fixing that alone would result in a plane that flew well.

And we don't know even if the new prop is appropriate for the plane and power system. The only piece of info that we have is that the plane flies.
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Old Dec 06, 2012, 09:10 AM
Space power
cfircav8r's Avatar
United States, IA, Hampton
Joined May 2012
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And actually, upon rereading, he said he went to a faster prop not a bigger prop. This either means he went smaller diameter and higher pitch, which would reduce some of the problems I wrote about, or he did go bigger and just doesn't understand how props work. Either way he could still learn something from my post.
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Old Dec 07, 2012, 06:31 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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His actual words were "bigger speed" whatever that's supposed to mean Either way what he said was that he changed the prop to one that was 'bigger' in some way and it's now in flies fine.
Personally I suspect the original prop was on backwards. The lousy throw didn't help either I agree.
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Old Dec 07, 2012, 06:35 AM
Canadian Bacon
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Kingston, Canada
Joined Jun 2004
12,914 Posts
Your right. He probably figured out how to throw it properly.
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Old Dec 14, 2012, 02:09 PM
Registered User
FlyBoy20's Avatar
United Kingdom, Wales, Swansea
Joined Aug 2012
698 Posts
I'm just a noob with many similar launch disasters, but it looks on the first try to be tail-down launch and the inevitable stall. The second looks like he imparted a left-hand twist as he let go?

Looks a lot like this one...

Mini Cub J3 bites the dust (0 min 6 sec)


BTW the plane was also underpowered, has he check the watts/lb?
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Old Dec 14, 2012, 06:37 PM
Space power
cfircav8r's Avatar
United States, IA, Hampton
Joined May 2012
307 Posts
Being under powered will not make a plane harder to control. Aircraft setup, design, launch technique, and control inputs are the reason for launch problems. Under powered planes just won't climb or hold altitude, but will still be fully controllable, although many people believe that if it won't climb vertically then its under powered. The best thing to do is to learn what forces are involved in the hand launch and the techniques and control inputs needed to control, and/or work with those forces.
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Old Dec 14, 2012, 08:12 PM
Rocket Programmer
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United States, AZ, Mesa
Joined Jul 2007
25,419 Posts
You don't throw a plane like a football, which is what happened with the blue Cub. The important part is to give the plane a little speed and get it going level. With trainers like the one in the video, usually you don't even throw it forward at all... just throttle up, push it forward out of your face, and let it fly out of your hand. If it's trimmed right, most trainers will fly down a bit, gain speed and pull up without the need to apply any elevator. So, your only task really is to keep the wings level. With planes that accelerate more slowly, it's still the same, you just need a harder toss. I hear a lot of crazy suggestions like putting uptrim on your plane before launch, but really I think people just need to learn to keep the plane level all the way through the launch.

And yes I agree with the comment above. The problem is usually not power... the electric standard used to be 50 watts per pound, and a Cub will still fly great on 30 watts per pound, but at those power levels, technique and setup is more critical. That blue Cub in the video was going way more than fast enough immediately after it left his hand. He just didn't have enough control authority to correct the nasty twist he put on it.
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Old Dec 14, 2012, 10:37 PM
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United States, CA, Ridgecrest
Joined Aug 2007
518 Posts
Got to get the nose into the wind..
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