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Hi-Performance and Sailplanes RC hotliners, electric pylon racers, F5B, F5D, sailplanes and gliders

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Old 07-16-2014, 06:00 PM   #1
bargainbin2
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Default 2x4 I think

I think this old glider was named 2X4 from many years ago. Any way I placed an electric motor on it to get her up to soaring height and it works great. That is as long as you go slow. Under full power it noses up sharply and could be a hand full if you do not reduce power. It has a small 8 inch prop and a 1300 lipo battery. Yes it has down and right.

What is it doing to me it soars great.
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Old 07-16-2014, 09:32 PM   #2
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Originally Posted by bargainbin2 View Post
I think this old glider was named 2X4 from many years ago. Any way I placed an electric motor on it to get her up to soaring height and it works great. That is as long as you go slow. Under full power it noses up sharply and could be a hand full if you do not reduce power. It has a small 8 inch prop and a 1300 lipo battery. Yes it has down and right.

What is it doing to me it soars great.
This is all quite normal. Remember gliders are made to glide, and thermal gliders do it slowly. If you have your trim set for slow gliding speed speed and then apply power in level flight, the glider will nose up and want to climb. It can also loop on takeoff, or at least fall over on its back.

What you have to do is drop the nose as you add power and then once you get to your desired speed, re-trim. That is how airplanes fly.

Gliders are not optimal for powered flight. Those of us who use electric thermal-ling gliders use the motors only to gain altitude in lieu of the high-start. Once we get to altitude, we shut off the motor and look for lift.

Before I fly my Radian I do a couple of power off hand launches to make sure my trim hasn't changed since the last time I've flown it. From experience I know that the plane will glide to a perfect hands off landing when things are right. Then my custom is to hand launch without power and smoothly add power while holding the nose in climb attitude until I get to about 80%. When I hit my altitude I smoothly back off the throttle while lowering the nose to level flight.

In order to help things along I have dual, even triple rates set for rudder and elevator. I use the lowest rate and maximum expo during the launch and climb phase, high rates for thermal-ling, and a medium rate for landing.

It is also possible that you used a motor that has too much pep for the plane. In that case you might want to change it or use a lower pitch prop. You could also just leave it alone and use less power. But do consider the dual/triple rate approach.

my 2cents

cliff

PS I do not change my trim for takeoff. Don't see a point in doing that since the climb phase is less than a minute.
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Old 07-17-2014, 08:46 PM   #3
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Just what i thought, I just hold back on the throttle and hold the nose down as best I can it is a rough ride but only last a fed seconds. I just want to make sure I am not missing something.

Thanks
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Old 07-17-2014, 09:15 PM   #4
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Originally Posted by bargainbin2 View Post
Just what i thought, I just hold back on the throttle and hold the nose down as best I can it is a rough ride but only last a fed seconds. I just want to make sure I am not missing something.

Thanks
The effect is actually all quite normal and obvious if you give it some thought. But I know where you are coming from. When I first started flying gliders I tried all kinds of things to prevent or lesson the effect. Then it finally dawned on me. Duhhh

I strongly recommend the dual/triple rate approach and don't be afraid to try plenty of Expo. After awhile you will find that you won't even notice anything unusual.

At some point also consider moving your CG much further back, but if you attempt that, do it in small increments, with several flights between changes so that you get used to the new location. Each time you move the CG back you will have to add down trim to compensate. Ace glider pilots fly with the CG close to or at the neutral point. Moving the CG to the rear will also lesson the pitch up tendency under power because you will have less built in up trim.

As an example, Parkzone recommends that the Radian's CG be located 2 1/2 inches from the leading edge. I fly at 3 3/8. It's a whole different plane at that point. It took me about a dozen flights to get there, plus a few more to feel comfortable. Once you find your sweet spot you can adjust the decalage so that you can take the trim out and clean up the elevator. Paul Nation has an excellent free video on modding the Radian. He talks about the problem of forward CG and its cure. His idea can be adapted to any airframe. Track it down. It is very informative.
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Old 07-18-2014, 12:09 AM   #5
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Most all of those old designs have a lot of decalage built in to the design. That means there is a significant angle between wings angle of attack and the stabs angle. This is, in effect, UP elevator that is permanently built in. They also were designed with the CG pretty far forward compared to how modern sailplanes are flown.

The science of sailplanes has progressed a good bit in the last 30 years

You can get rid of a lot of that pitch UP just by moving the balance point (CG) back and re-trimming the model. I fly my 2x6 with the CG set a full inch behind the recommended location and it flys much better there.

Try moving the CG back in very small steps and re-trim the model after each change.

You will find, as you move it back, that the model begins to respond to control inputs much better. It will have a wider speed range. It will feel livelier in the air and it will indicate lift much better and it will land slower and it will not pitch up with power on nearly so much.

Try it. You will like it

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Old 07-18-2014, 09:54 PM   #6
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I have electric powered 2X4 and to cure some of the climb with power on I shimmed the rear of the wing about 1/16inch. Also as stated above the CG was moved back about 1/2 inch. But when I transistion to glide I still have to give it 3-4 clicks of up elevator for a good glide. Fun little plane, I put a Key Fob camera on it, mounted on the left side of the wing at the dihedral point. Not a real good thermal bird, but a handy size to throw in the trunk of the car for evening flying....

Bob M.
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Old 07-19-2014, 12:09 AM   #7
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Shimming up the trailing edge of the wing removes some of the decalage I was talking about. Its the same effect as adding down elevator trim - but looks better

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Old 08-21-2014, 06:59 PM   #8
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And the decalage on the HOB 2x4 and 2x6 gliders was extreme. They had no penetration at all and when I owned one I wasn't knowledgeable enough to fix it. As designed they were absolute pigs to fly. Should be a minor fix to make 'em good.
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Old 08-21-2014, 09:10 PM   #9
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Give the motor 5 degrees of down thrust, set the wing and stap. incidence to as close to 0 - 0 as you can, the down thrust will help to load the wing and prevent it from wanting to climb under power to a good degree so its more manageble

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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