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Feb 21, 2010, 09:33 PM
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Chlorinator's Avatar
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Hydrogen Wedgie


RTL (ready to launch).

Have been wanting to try this for a long time. added a 20 oz. water bottle rocket to a M&M Glider Tech Wedgie. Has been test flown by hand lauch.

Water powered launch tests will depend on the nxt weeks wheather.

Have seen some of the other threads on water lanches so hopefully this plane will not encounter problems. But the tests will tell.

Keith
Last edited by Chlorinator; Feb 21, 2010 at 09:40 PM.
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Feb 22, 2010, 12:19 AM
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Wow, that'll be some CG shift!

Good Luck!!!

Feb 22, 2010, 08:59 AM
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Chlorinator's Avatar
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CG Shift


Thanks Dt56,

My thinking is the bottle is over the middle of the wings cg.
However the thrust line is the same as the powered thrust line. So under power, the wings cg will not matter. Only if too much water is left after power launch the cg will change.

OH BOY.
Feb 22, 2010, 01:47 PM
An itch?. Scratch build.
eflightray's Avatar
Looks fun

Couldn't the bottle be the 'rocket booster', and fall away once it runs out of push ?
Feb 22, 2010, 02:33 PM
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Chlorinator's Avatar
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Quote:
Originally Posted by eflightray
Looks fun

Couldn't the bottle be the 'rocket booster', and fall away once it runs out of push ?
Neat Idea. But I did not want to mess with an xtra servo and releaseable mounting system just yet. One thing at a time. A mech system activated by full up or down would not require a third servo but still just want to see if I can get full launches first.

Just the bottle alone would travel for 10 seconds under power. Anxious to see how high the bottle will boost the wing.
Feb 22, 2010, 05:09 PM
www.scotiarc.co.uk - OMP Helis
Smoggie's Avatar
There will be some unpredictable pitching moments to deal with. On initial acceleration from launch your gonna get a strong 'nose down' pitching moment because the thrust line passes well above the vertical CG (that is vertical when the plane is orientated horizontally in glide mode)

Once you get up to speed, acceleration reduces and aerodynamic forces come into play the pitching moment due to the wing's trim will then tend to cause a strong pitch 'nose up'.

Either or both of these pitching moments could conceivably be very pronounced, perhaps even uncontrollable. A gyro on the elevator may be a solution if it does prove to be a big problem. Ideally the thrust line of the rocket should be arranged to pass through the centre of gravity, this would mean the rocket would have to be 'buried' into the wing.

Steve
Feb 22, 2010, 05:52 PM
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Chlorinator's Avatar
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Quote:
Originally Posted by JetPlaneFlyer
There will be some unpredictable pitching moments to deal with. On initial acceleration from launch your gonna get a strong 'nose down' pitching moment because the thrust line passes well above the vertical CG (that is vertical when the plane is orientated horizontally in glide mode)

Once you get up to speed, acceleration reduces and aerodynamic forces come into play the pitching moment due to the wing's trim will then tend to cause a strong pitch 'nose up'.

Either or both of these pitching moments could conceivably be very pronounced, perhaps even uncontrollable. A gyro on the elevator may be a solution if it does prove to be a big problem. Ideally the thrust line of the rocket should be arranged to pass through the centre of gravity, this would mean the rocket would have to be 'buried' into the wing.

Steve
Similar to jato assist rocket on jet planes.

Wished I had gone to school and become an aeronautical engineer (rocket scientist.) Excellent input. Having been built at the ACME Rocket Design Institute Wiley Coyote would be proud.

Not able to calculate the thrust but quessing, I did add about 2 degrees up thrust to tail cone of rocket. At launch I will be switching on launch mode adding a slight amount of up elevator?

Great suggestion on gyro. I have one left from the dlg days. I think that will be very helpful.
Last edited by Chlorinator; Feb 22, 2010 at 10:45 PM.
Feb 23, 2010, 04:22 PM
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Bilbobaker's Avatar
Love it, be sure to take some videos.
Feb 23, 2010, 06:11 PM
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Chlorinator's Avatar
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Pressure Test


Pressure tested up to 60lbs. Oring on launcher did not hold. Had to reset a second oring.
Held presure then I releaved pressure to 10 lbs and pulled pin while holding the launcher horizontal. Plane accelerated straight out then nosed into the ground.

Test was encouraging till the nose dive. No damage but then realized I had forgot to install battery. Very tail heavy with out battery installed.

Looks like rain the next couple of days. Definately will take video.

Keith
Feb 23, 2010, 10:16 PM
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Bilbobaker's Avatar
Cool, can't wait.
Feb 24, 2010, 02:10 AM
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Quote:
Originally Posted by Chlorinator
Pressure tested up to 60lbs. Oring on launcher did not hold. Had to reset a second oring.
Held presure then I releaved pressure to 10 lbs and pulled pin while holding the launcher horizontal. Plane accelerated straight out then nosed into the ground.

Test was encouraging till the nose dive. No damage but then realized I had forgot to install battery. Very tail heavy with out battery installed.
Looks like rain the next couple of days. Definately will take video.

Keith
The receiver battery?
Feb 24, 2010, 08:32 AM
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Chlorinator's Avatar
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Quote:
Originally Posted by DT56
The receiver battery?
The plane has two HS80 servos for the elevons, and the reciever is buried inside the nose of the wing. The battery pack is located externally on the underside of the nose.

I will have total control and be able to use presets for launch and glide with the flick of a switch.

I was charging the rx batteries when I was pressure testing the stand and bottle rocket. When I had pulled the pin holding the whole assembly horizontal the plane shot straight out about 10 ft under power. But like you said, aero dynamic forces then came into play and being tail heavy nosed over because the airfoils cm(?). Right?

It's raining today.

Keith
Feb 24, 2010, 09:25 AM
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vintage1's Avatar
should get about 100ft out of it. I used to make water rockets as a kid. Take about 200psi maybe. Be careful and wear waterproofs. Don't think about nosing onto glide mode till all the water is out.

Using a nozzle restrictor gets a slightly longer and less explosive 'burn' - the commercial rockets had about 1/4" diameter nozzles.
Feb 24, 2010, 10:31 AM
Herk
HerkS's Avatar
Chlorinator, Two factors will tend to cause the nose over.

The first is that the thrust line is somewhat high. That puts the thrust above the overall CG of the model creating a nose down moment during acceleration. Initially, there is a lot of water weight in the bottle. The situation will get worse as the water is expended making the effect of the aircraft weight effect more significant.

The other factor is the fact that the thrust line is above the drag vector of the wing. That is the drag of the wing is below the trust of your water rocket. The as the plane accelerates the drag increases making the effect stronger.

The CM of your wing should be positive due to the normal trim position of your elevons. Positive Cm is necessary in order for a flying wing to fly in a stable manner.

Initially the model is probably quite unstable due to the aft location of the weight of the water. Once the model starts to pitch either up or down for any reason, the inertial moment of the water weight will likely cause the pitching rotation to accelerate. Get the water out of there as fast as you can and hope that you will have time to recover if an extreme divergence develops. Adding the gyro is probably not a bad idea at all
Feb 26, 2010, 06:28 AM
Registered User
Another option could be to add some stabilizing fins to the "booster" and detach them once the launch is completed. Actually, a two stage design would probably work better, with the wing riding along with the booster until the thrust is exhausted, and the booster bottle returning to earth with a small chute, to ensure it will land nose first at a moderate speed and to be reused later. Yet another approach would be to have the bottle in the nose, and either the nozzle just above the wing or a tube to bring the nozzle at the back. If the acceleration is sufficiently large being nose heavy in the first few seconds should not be a problem. And the tube will allow you to adjust the thrust vector


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