Conversion of Hacker Pin to Rocket Glider

I was getting some gear from the LHS and came across this Free Fight Glider kit and figured a B motor would save the trouble of making a towline to launch,

So far.I have almost finished the construction of the basic model as per the instructions

I'm thinking a slot to be cut in the pod to fit a B something motor, Then got to wondering about thrust lines and incidences, So i now wonder if there is a knowledgeable soul out there that could assist with improving my chances of getting a successful boost.

Got this far today. I hope to finish tomorrow and if the wind dies down will maybe get a few hand launches in to test the rigging and trim.

Weight is to be around the 75 gram mark. There is also a substantial amount of incidence on the wing mount and wonder if that needs to be reduced a little

See https://estesrockets.com/wp-content/uploads/Educator/2266_TR_4_Boost_Gliders.pdf but it may not be super-helpful.

Probably your best bet is a pop-pod arrangement. You could try making it a rocket glider (motor/pod stays on the glider) but I think it would be harder to get trimmed.

Here is a photo showing my intended layout. The motor is the only one I have the right size to show layout.

With the motor positioned here, there will be little CoG change with motor burnout

Basic construction is finished, wings and tail plane are held with elastic bands to give me some chance to adjust incidences on both wing and tail surfaces,

I did a couple of test throws in the warehouse at work and I am very happy with the glide so far but will need to set a turn into the glide, probably using weighted wingtip method.

I'm curious, do you have a method for adjusting the trim after boost? Usually it is necessary to shift the CG, or pop up an elevator to transition from a straight boost, to a glide.

Thanks for your interest Marten. The idea here is that the motor burn should not affect the centre of gravity which I believe is an issue with a lot of boost gliders, that being the reason for trim tabs on that type of glider

If you have the CG where it wants to be for stable glide, then it will almost certainly be unstable during boost. But by all means try it, just make sure you're prepared for instability.

Thank you Mike,That is the feed back I was looking for. I am wondering if that instability could be corrected with down thrust in the motor.

I understand the Phoenix RC glider was a similar layout to my scheme but of course that had RC to assist on the boost

I've flown an S8E RCRG and I think the chance of trimming one to both boost and glide with no control and no change in elevator trim at burnout is very, very low, if it's possible at all. And that's with fairly low-thrust motors.

mikec said:

I've flown an S8E RCRG and I think the chance of trimming one to both boost and glide with no control and no change in elevator trim at burnout is very, very low, if it's possible at all. And that's with fairly low-thrust motors.

Click to expand...

Yes, I think aerodynamics prevents it.

You'll need to either kick back the CG, kick up the elevator, or some combination of things to reconfigure the flight trim. It may be possible by directing the thrust in the right direction, but I'm not sure. I think you would want the thrust to result in a nose down torque. But if you motor is at the CG, you won't get much torque.

I think you would have much more likelihood of success with either a pop pod design or a motor eject design along the lines of the Astron Falcon

Thank you very much gentlemen.

I guess I can spend my spare time re thinking this project.

Thanks again for all your input

It's a beautiful looking glider, keep us updated with your results. I think that a pop pod idea is a good one, the motor could be in front of the glider's CG to move the overall CG forward for rocket boost. Then, when the motor burns out, it pops off allowing the glider to fly unhindered.

You will need to protect the Fuselage from the engine exhaust. Otherwise, it will be damaged by the heat.

Dave F.

Hi All, this one has stalled a bit as I saw something shiny the other week and am getting that done. I have done the test gliding and I can say it flies. Have to figure out how to go some sort of launch system,

Pete

I would take the positive incidence out of the wing and make it 0-0 degrees......the CG during boost must be in front of the leading edge of the wing. During boost and a lesser degree during coast, the motor is losing mass since the propellant and delay train are burning and the cg will shift a little towards the back. So lets say with a full engine it balance 1/2" in front of the leading edge of the wing.....this might reduce to 1/4" or less from the leading edge.....with the entire weight of the motor gone, it then shifts backwards even more to it's glide cg

For glide stability, the CG is usually somewhere between 60% and 75% of the wing chord......measured from the leading edge

I would check the boost balance point with an engine installed.....and then balance it with an expended engine for glide..... that will be your boost-glide cg shift range

With the motor mounted below the wing you risk looping your glider into the ground during launch. I agree about removing the wing incidence. That incidence would only add to the looping problem. Instead put the incidence in the tail, a about 1 degree negative to pull the nose up at ejection an transition. Pop pod mounted on the topside at the nose would be your best bet. Drops weight at ejection but keeps CG far enough forward for a stable launch.

You may find this information helpful . . .

https://www.rocketryforum.com/threads/glider-design-trimming-library.155758

Dave F.