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Glider cradle causes tow plane instability

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Glider cradle causes tow plane instability

Old 07-20-2006, 08:09 PM
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tenacious101010
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Default Glider cradle causes tow plane instability

We are working on a cradle to use to carry a glider up for release. We started by flying the Alpha trainer with just the cradle installed and found it very unstable. We suspect the cradle is causing turbulence around the vertical stabilizer, the plane lacks lateral stability that gets worse as the speed increases.
To test our theory, we used our G3 simulator, modified the Alpha trainer by reducing the size of the vertical stab and the rudder. We were delighted that the simulator modified alpha flew jusr like the real alpha when the cradle was installed. I was impressed. I have just finished adding two vertical stabs on the ends of the horizontal stab, they are about half the surface area of the existing stabilizer. Has anyone had a stability problem similar to this and if so what did you do to resolve it?

1. The cradle is mounted solid and square to the fuselage.
2. The cradle looks very similar in size and weight to the great planes cradle.
3. The center of gravity of the plane is the same with or wiothout the cradle installed.
4. This is a 40 size Alpha trainer with a 60 Super Tiger installed.
5. The plane flies perfectly before and after the flight with the cradle.

Thanks, Denny
Old 07-20-2006, 08:23 PM
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Flyfalcons
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Default RE: Glider cradle causes tow plane instability

In the seaplane world we often add additional vertical fin area when installing floats. Any vertical surface forward of the CG will cause lateral instability, and you can compensate for that by adding more vertical area behind the CG.
Old 07-20-2006, 10:17 PM
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Tall Paul
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Default RE: Glider cradle causes tow plane instability

You're probably correct about the turbulence.
Mine looks like this.. no adverse effects..
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Old 07-21-2006, 04:42 PM
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Default RE: Glider cradle causes tow plane instability

Heres some pics of the current setup, hope to test fly it very soon.
Denny
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Old 07-21-2006, 05:13 PM
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Default RE: Glider cradle causes tow plane instability

Heres a couple more pics with the glider sitting on top.
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Old 07-21-2006, 08:11 PM
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Tall Paul
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Default RE: Glider cradle causes tow plane instability

More photos..
The wing supports prevent the second plane from banking on the cradle, which affects the flight path of the combination.
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Old 07-23-2006, 09:07 PM
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Default RE: Glider cradle causes tow plane instability

There's quite a bit of side area in those cradle sides and much of it is forward and low where the brackets are quite solid looking. I don't doubt that it may well need the extra fins.

So how did it manage with the added fins?
Old 08-01-2006, 07:53 PM
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Default RE: Glider cradle causes tow plane instability

The additional vertical stabs worked great, I was very happy with the results. Finally got this contraption including the glider into the air. It was the scariest/most fun thing I have done in a while. We had 2 sucessful flights. I didnt take it up to the altitude I had hoped for and both times released the glider before making the first turn.
I think next time I will take off a bit slower and use the glider and tow plane rudder to make the turn. After takeoff, the way our field is set up, I needed to make a left turn but I now realize using the ailerons on the tow plane is not the way to go, next time we will use the rudder of both planes. I think I was way too fast when I took off, I can easily slow down for takeoff and climbout. Both flights the left wing of the glider lifted, I believe I was putting in slight left aileron inputs that may have been a factor in the left wing of the glider lifting. Out of inexperience, fear and safety concerns, I took off at max power, next time I will throttle back a bit. Got some great video and best of all, my son and I had a fun time figuring out how to make this work and working together as a team. Thanks to all here that have given inuts to help us make this happen.
Denny
Old 08-01-2006, 11:24 PM
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da Rock
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Default RE: Glider cradle causes tow plane instability

Good deal that yours works.

One of the guys at our field cobbled the rig shown in the attached. I flew as the glider pilot on the 2nd round of test flights and we had to have the glider rudder working in the turns.
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Old 08-26-2006, 01:33 PM
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Default RE: Glider cradle causes tow plane instability

darock, I love that glider, is it a kit? Does it have ailerons? We found the same thing you did, we need to use the glider rudder to make turns and I use the elevator on the tow plane to control pitch. We loved exploring this so much we decided to see what else we could do with our Alpha, now known as the "TRUCK" since we haul so much junk into the air with it. We made a pod that attaches underneath so we could carry things aloft. We dropped a fairly large parachute with it , some plastic easter eggs filled with baby powder and some water ballons, what fun ! The plastic eggs were visually great when the hit the runway. We are going to grind up some colored chalk to give them color next time. Was funny, every time someone took off or landed we saw a cloud of baby powder and smelled it too. Made the flying field smell like a nursery, well, exceot with out the bad odor part. Heres some pics of the setup. I made it based on a cardboard tube, it actually turned out to work quite well and was simple to make. Now I am thinking of what else I can drop from it, we thought of a candy drop for the open house. I am thinking for the open house I would like to do a fly-by releasing a banner that says " WELCOME TO THE TRAC OPEN HOUSE !", has anyone tried anything similar to this? For some reason I keep having this thought of taking it way up and dropping a framed picture of my mother-in-law and watching it drop, not sure whats up with that. I am open to any other ideas of fun things to do with this plane, anyone have any ideas? I will take some detailed pictures of the pod in case anyone wants to make something similar using what I made.
Denny
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Old 08-26-2006, 03:45 PM
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da Rock
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Default RE: Glider cradle causes tow plane instability

Hey Denny,
The glider was bought at a swap meet I think. I've flown RC gliders since the late 70s and it was a surprise to me. I've never seen one before. The owner (guy in middle) said he bought it because the seller promised that it was an excellent thermal soarer. Yeah...

That bomb bay thing is kewl. Looks like a great setup. Why didn't I think of that..... chuckle
BTW, I'd would suggest that although it's probably in an area of very messy airflow, that the airplane would probably go AT LEAST 40-50mph faster (maybe even MORE) if you glued half of one of those Legg's eggs to the front to streamline it. Heck, the reduction in drag from that modification ought to double your payload too. At least.... grin..... maybe more.....

Darn what a kewl idea.... cardboard tube you say..... heck, just paint on some epoxy and the fibers would soak it up and it'd be strong enough for just about anything that'd fit in it.
Old 08-26-2006, 05:38 PM
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Default RE: Glider cradle causes tow plane instability

I really like that glider, it looks like a scale replica of a WW2 era US military glider. I will be looking for one, I really like the looks of it.
You guessed my next modification, a nose cone. I will probably make one from foam and caot it with epoxy and more yellow dope. I used some model dope to coat the tube and wood, mainly since I was planning on dropping water balloons. A good thing I did, today we had one burst in the pod as we started the engine, looked like the plane had peed it pants, was kinda funny.
I think I am getting a bit weird with making things to take aloft. I had been thinking of all kinds of entertaining things to do with this plane and had the idea that I could make a bubble maker. I was at Wally mart and saw a battery powered bubble machine, its gonna get attached to the plane soon. We also found some rainbow foil conetti, I see a mess coming. We are also planning a candy drop. All this is for our upcoming open house, oh I also bought supplies to start making a banner to be towed at the field. I really dont have this much time on my hands, I just cant stop being a kid. here are some close up pics in case anyone wants to make something similar.
Denny
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Old 08-26-2006, 05:44 PM
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Default RE: Glider cradle causes tow plane instability

oops forgot to explain how it works, in case it is not obvious. When the servo is actuated it pulls the rod, releasing the rubber band that holds the doors closed. I do need to make a provision for retaining the rubber band, as it is now I lose one every time I drop something. It installs easily, a pin retains it in back and 2 screws in front. then just hook up the plug that I use for my actuation switch channel. I can use this mounting for all my hang on toys.
Denny
Old 08-26-2006, 06:03 PM
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Tall Paul
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Default RE: Glider cradle causes tow plane instability

I use this mailing tube to drop 6 ping-pong balls, one at time, from a Yard Stick.
The release servo is on channel 5.
The ball to be dropped rests against the release wire.
When the servo moves that wire out of the way, another wire gets pushed between the ball to be dropped and the next ball in line.
When the ball is dropped, and the servo returns to 0, the wire that held the next ball is removed, and that ball moves into the drop pocket for the next drop.
Without the air vent, the balls tended to stay in the tube until I climbed the airplane.
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Old 08-30-2006, 10:49 PM
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Default RE: Glider cradle causes tow plane instability

I love both the ping pong ball brop and the standard bomb drop. But I really would dig the bubble machine if it would work on the plane. I have used my trainer both for bomb and or parachute drops as well as a glider tug. I have used a cradle or I have used a tow wire. The tow wire was a little more fun because the glider pilot has to fly his bird up to altitude instead of being just long for the ride.

I have also crashed with a glider on my cradle. Although I thought I could handle a cross wind it completely overpowered my rudder commands. Immediately after take off I was pushed into a strong right turn. I followed it around only to make a 359.5 degree turn whereby I released the glider as both planes were headed for terra-firma. It was hilarious because of a couple of reasons:

First. Everything was safe and well away from any other planes and or course, pilots.
Second. The ground was soft and did not damage either aircraft.
Third. I called out release as both planes were headed down (and only about six feet from the ground)
Fourth. Both planes hit like syncronized lawn darts....thunk..thunk![X(][X(]
Fifth. My friend and glider pilot just looked blankly at me after the crash...whereby I exclaimed "Didn't you hear me yell release???"
Sixth. The calm pause of astonished confusion on the face of my friend until I burst out in laughter.

Both planes were flying again the next weekend....albeit on a less windy day!

Dan
Old 08-31-2006, 08:58 AM
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Default RE: Glider cradle causes tow plane instability

danmilo,
Dang, I wish Oregon was closer to Nawth Ka'lina. Your field sounds like a fun place to fly.

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