ScrewBall in side pocket, reverse stability

[BABAR]

well, first rendition isn’t quite working right.

maybe trying to do too much with one rocket.

looking for something marketable (not that I am ever going into business, but one of my “dreams” is to come up with a design that gets picked up by Odd’l Rockets, FlisKits (is @jflis even doing new designs), Semroc, ERockets, Estes, Apogee)

obviously something different and funny.

cheap (hence the ping pong ball nose cone, since I have read that nose cones are the most expensive part of most low power kits, although with question of worldwide balsa shortage that may change)

low power

i like asymmetric fin rockets that corkscrew, I consider corkscrew flights entertaining as well as a way to keep altitude low with flight time high, kind of like saucers with a literal twist.

also was hooooooooopppppping that could achieve backslide recovery, that may be too much.

anyway, I don’t know how to use open rocket (I know, I should just use it), but I am also in doubt of the Accuracy of Sims for a ping pong ball nose cone. I also suspect the CP Effect of a ping pong ball nose cone is partially dependent on the size of the tube it is attached to. Big tube you essentially have a hemispherical cone, little tube you literally have a ball.

anyway, I did @lakeroadster ‘s swing test, and it WAS stable…….backwards. Consistently backwards.

for those that want to play with this.

ping pong ball is 4 cm diameter, mine weighs 2.6 Grams although per Google it should weight 2.7 grams.

tube is standard BT-5, 18” long.

ring fin is BT-60, 1.5 inches long.

with an A10-3T total weight is 20 grams, and the CG with 1/4 of motor hanging out the tail is 6” from tail of BODY tube, which ends lined up with the ring fin.

i have a paper straw launch lug on inside.

i am pretty sure I am going to need a bigger diameter ring fin.

i am TRYING not to add nose weight as I am hoping for Back Spin recovery.

ideas anyone?

once I have a workable design I will poke holes in the ping pong ball, the launch rod will go THROUGH the ball.

 

[neil_w]

looking for something marketable (not that I am ever going into business, but one of my “dreams” is to come up with a design that gets picked up by Odd’l Rockets, FlisKits (is @jflis even doing new designs), Semroc, ERockets, Estes, Apogee)

As someone who has tried this and failed miserably, let me say: good luck to you sir.

An alternative is to submit a design to Apogee for inclusion in a PoF newsletter.

 

[BABAR]

Swing test was WITH A10-3T motor, btw.

 

[Cape Byron]

Swing test was WITH A10-3T motor, btw.

It may seem counter-intuitive, but I've had things that swing test backwards consistently and flew beautifully.

That said, bung some nose (Ball?) weight in there and swing again.

 

[BABAR]

That said, bung some nose (Ball?) weight in there and swing again.

You are quite right, I COULD easily fix it for STABILITY with nose weight.

I am still hoping to be able to do backslide recovery. Too much nose weight would bung that up!

 

[Cape Byron]

You are quite right, I COULD easily fix it for STABILITY with nose weight.

I am still hoping to be able to do backslide recovery. Too much nose weight would bung that up!

Good point. Okay, load 'er up!

 

[teepot]

I use balls and domes a lot. I just make sure that the fins are big enough to keep the CP far enough back to be stable. Also base drag helps keep it pointed up. Here are a couple of pictures. Yes, that is a real plunger. Wooden stick and rubber bell. Flies fine. I have used styrofoam balls too. I put the nose weight in a coupler bay under the ball. I also have used large Christmas ornament light bulbs. That rocket flies like any other rocket. The only downside of the plunger, is because of the stick there is no recovery device, It's a one and done. Out in the desert is the first one I made. I heard it come down but haven't found it, yet. Swap the stick for a BT and your good to go. One rocket has a big plastic bowl as fins. And before I get flamed. The plunger went up with just me and my wife watching and about a square mile of empty desert around.

 

[BABAR]

. That rocket flies like any other rocket. The only downside of the plunger, is because of the stick there is no recovery device, It's a one and done. Out in the desert is the first one I made. I heard it come down but haven't found it, yet. Swap the stick for a BT and your good to go. One rocket has a big plastic bowl as fins. And before I get flamed. The plunger went up with just me and my wife watching and about a square mile of empty desert around.View attachment 557334View attachment 557335View attachment 557336

the plunger one would be fun to do with a Stick colored body tube and a loNg white streamer, say bout 4 inches wide and cross hatched transversely with little black lines every 4 inches. Be great to see it stick the landing!

 

[teepot]

I have a secret rocket I'm going to show you all someday. There is a story too.

 

[Cape Byron]

I have a secret rocket I'm going to show you all someday. There is a story too.

Tease.

 

[jqavins]

anyway, I don’t know how to use open rocket (I know, I should just use it), but I am also in doubt of the Accuracy of Sims for a ping pong ball nose cone. I also suspect the CP Effect of a ping pong ball nose cone is partially dependent on the size of the tube it is attached to. Big tube you essentially have a hemispherical cone, little tube you literally have a ball.

I think you place too little faith in the software. In RS, I can simulate a ping-pong ball nose with two pieces, and I expect the procedure and results are the same with OR. Start with an elliptical nose cone, and set the length to half the base diameter; that gives you a hemisphere. Follow that with an elliptical transition from the nose cone diameter down to the body tube diameter, again setting the length to half the diameter. To be really perfect about it, take a little off the length to account for what would dip inside the top of the tube, but that will be so little that I wouldn't worry about it. The software will not have any trouble accurately simulating that configuration, since there's really nothing outside the scope of normal parts.

As for nose weight, I bet the ping-pong bass is extraordinarily light compared to the molded plastic cones one usually sees. Food for thought: weigh a "regular" plastic cone, and I just bet it'll be a gram or two heavier. You could add that much to the top of the rocket without being any more top heavy than most designs. And as long as that rocket is pretty tall (compared to its other dimensions) just one or two grams might be all you need. You could test taping or gluing small weights to the bottoms of some balls to try out. (A US dime is just about 2¼ grams but, unfortunately, won't fit inside a BT-5.)

 

[teepot]

The ball I used on the plunger rocket was full of BB's and epoxy. Needed a bunch of nose weight to get the CG in front of the CP.

 

[lakeroadster]

View attachment 557284
well, first rendition isn’t quite working right.

maybe trying to do too much with one rocket.

looking for something marketable (not that I am ever going into business, but one of my “dreams” is to come up with a design that gets picked up by Odd’l Rockets, FlisKits (is @jflis even doing new designs), Semroc, ERockets, Estes, Apogee)

obviously something different and funny.

cheap (hence the ping pong ball nose cone, since I have read that nose cones are the most expensive part of most low power kits, although with question of worldwide balsa shortage that may change)

low power

i like asymmetric fin rockets that corkscrew, I consider corkscrew flights entertaining as well as a way to keep altitude low with flight time high, kind of like saucers with a literal twist.

also was hooooooooopppppping that could achieve backslide recovery, that may be too much.

anyway, I don’t know how to use open rocket (I know, I should just use it), but I am also in doubt of the Accuracy of Sims for a ping pong ball nose cone. I also suspect the CP Effect of a ping pong ball nose cone is partially dependent on the size of the tube it is attached to. Big tube you essentially have a hemispherical cone, little tube you literally have a ball.

anyway, I did @lakeroadster ‘s swing test, and it WAS stable…….backwards. Consistently backwards.

for those that want to play with this.

ping pong ball is 4 cm diameter, mine weighs 2.6 Grams although per Google it should weight 2.7 grams.

tube is standard BT-5, 18” long.

ring fin is BT-60, 1.5 inches long.

with an A10-3T total weight is 20 grams, and the CG with 1/4 of motor hanging out the tail is 6” from tail of BODY tube, which ends lined up with the ring fin.

i have a paper straw launch lug on inside.

i am pretty sure I am going to need a bigger diameter ring fin.

i am TRYING not to add nose weight as I am hoping for Back Spin recovery.

ideas anyone?

once I have a workable design I will poke holes in the ping pong ball, the launch rod will go THROUGH the ball.

Can you show a photo, or give spec's, or both, as to how you, @BABAR, attached the ring fin to the BT on your rocket shown above?

What diameter is the vent hole at the top of the BT?

Thanks!

 

[BigMacDaddy]

Maybe try to move that ring fin back - get it [mostly] behind the body tube so engine pulls in air and pushes it through the ring tail. Probably wont burn the ring tail...

 

[BABAR]

some good ideas.

i think ho

Can you show a photo, or give spec's, or both, as to how you, @BABAR, attached the ring fin to the BT on your rocket shown above?

What diameter is the vent hole at the top of the BT?

Thanks!

Trick I use on all my single ring “corkscrew” rockets.

draw line for launch lug.

glue launch lug (I use paper straws, a bit oversize but they work) in place, hold with hair pins while drying.

this is an easy joint to line up.

i then use the launch lug as. “Cheater” to line up the body tube. The combo also provides (I theeenk) a much stronger joint (kind of important with one big round fin), partially hides the lug as well, which is cosmetically nice.

in BT-20 and larger, I use a standard hole punch for vent. Can’t fit it into a BT-5, so I literally took a stab at it with an 11 blade and drilled it. Measures about 5/16”, I was shooting for 1/4.

I haven’t glued on the body tubes yet. My “mindsim” guesstimates that the BT-60 would be too small, but I figured I’d try it.

as opposed to @Daddyisabar ‘s solution of nose weight and more power (which certainly do work), because I am hoping for Back Slide recovery, my go to solution at least at first is to add more tail fin, so I am going up from 1.5 inch long BT-60 to 2.0 inch long BT-80. I will tape this on and try a swing test tonite.

the ratios of ring fin to billiard table pocket are closer here to realistic, the ping pong ball wouldn’t even fit into BT-60, it is much closer to realistic with the BT-80.

my best backsliders have used the really thin competition style nose cones that weight just about nothing. Backslide recovery relies mainly on looooong body tubes to provide enough nose weight (or at least forward weight) to achieve boost stability at near zero angle of attack, but lots of surface area to achieve INSTABILITY at apogee with major off-0 angle of attack. So I really am loathe to add any kind of nose weight to this bird.

on the other hand, this just begs for the NEXT rocket, which will be a parachute recovery, where I use a real golf ball, a ring fin about 4.25” wide and 4” long (i think that’s the standard for a golf hole), and name it something like “Eagle” or ”Hole in One.”

 

[lakeroadster]

some good ideas.

i think ho

Trick I use on all my single ring “corkscrew” rockets.

draw line for launch lug.

glue launch lug (I use paper straws, a bit oversize but they work) in place, hold with hair pins while drying.

this is an easy joint to line up.

i then use the launch lug as. “Cheater” to line up the body tube. The combo also provides (I theeenk) a much stronger joint (kind of important with one big round fin), partially hides the lug as well, which is cosmetically nice.

in BT-20 and larger, I use a standard hole punch for vent. Can’t fit it into a BT-5, so I literally took a stab at it with an 11 blade and drilled it. Measures about 5/16”, I was shooting for 1/4.

I haven’t glued on the body tubes yet. My “mindsim” guesstimates that the BT-60 would be too small, but I figured I’d try it.

as opposed to @Daddyisabar ‘s solution of nose weight and more power (which certainly do work), because I am hoping for Back Slide recovery, my go to solution at least at first is to add more tail fin, so I am going up from 1.5 inch long BT-60 to 2.0 inch long BT-80. I will tape this on and try a swing test tonite.

the ratios of ring fin to billiard table pocket are closer here to realistic, the ping pong ball wouldn’t even fit into BT-60, it is much closer to realistic with the BT-80.

my best backsliders have used the really thin competition style nose cones that weight just about nothing. Backslide recovery relies mainly on looooong body tubes to provide enough nose weight (or at least forward weight) to achieve boost stability at near zero angle of attack, but lots of surface area to achieve INSTABILITY at apogee with major off-0 angle of attack. So I really am loathe to add any kind of nose weight to this bird.

on the other hand, this just begs for the NEXT rocket, which will be a parachute recovery, where I use a real golf ball, a ring fin about 4.25” wide and 4” long (i think that’s the standard for a golf hole), and name it something like “Eagle” or ”Hole in One.”

Hmm.. not sure I understand? Do you glue the launch lug to the body tube and to the ring fin and just leave the ring fin off center?

 

[jqavins]

 

[lakeroadster]

View attachment 557663

Thanks Joe

 

[lakeroadster]

.... for those that want to play with this ....

Open Rocket says she stable... maybe overly stable.

I put a streamer in the rocket that weighs nothing. I did that so the simulation will show velocity at deployment... so we would know what speed the rocket is traveling when the motor ejection charge fires.

 

[Daddyisabar]

At least the motors and fin are at the back of the rocket, where they should be! Non RSO frightening. Silly embedded, canted tractor motors with no fin would work, but are just too scary. Rocket Science rules so don't use a magic 8 ball to get answers. My old RSO would tell me that thrust and nose weight are just a crutch for an inherently poor design. Then he would ask for the Rocsim, cardboard cut out or swing test video.

A pool que, wood grain veneer and leather handle paint scheme on the body, maybe with some green felt just beneath the eight ball.

 

[teepot]

The only rocket that I had back slide was one with grid fins. Lots of drag.

 

[BABAR]

Open Rocket says she stable... maybe overly stable.

I put a streamer in the rocket that weighs nothing. I did that so the simulation will show velocity at deployment... so we would know what speed the rocket is traveling when the motor ejection charge fires.

View attachment 557705View attachment 557702View attachment 557701

Thanks for doing what I am probably simply too lazy to do, learn OpenRocket.

you got the livery down pretty close too, I was thinking a black 8 ball, although I might try a drunken smiley face instead of the 8.

the tube is a brown pool cue, the outside of the ring is the green of the table, might do the inside in black.

well, I have the tubes and rings and a pack of 6 ping pong balls, so I may build both the BT-60 1.5” ring and the BT-80 2” ring, and see which one earns its paint.

lining up the holes on the ping pong balls is going to be a bit of a challenge, I was thinking of heat the tip of a launch rod (with the rest of the rod in the lug), eyeballing the line up and melting it through.

i could also probably just use the rod to mark the hole in the tail end of the ball, then pass the rod through that hole and since ball is translucent may be able to see where it touches the forward end of the ball.

have to do this before painting, though.

definitely the smaller ring will be a heads up launch. Nice thing is that even if fecal turbine interaction occurs, unlikely to hurt anyone with a ping pong ball.

 

[jqavins]

lining up the holes on the ping pong balls is going to be a bit of a challenge, I was thinking of heat the tip of a launch rod (with the rest of the rod in the lug), eyeballing the line up and melting it through.

i could also probably just use the rod to mark the hole in the tail end of the ball, then pass the rod through that hole and since ball is translucent may be able to see where it touches the forward end of the ball.

IF you have access to a drill press, I suggest the following:

• Place a piece of scrap on the table.
• Drill a blind hole (i.e. a counterbore) of roughly 10 to 20 mm diameter.
• Nudge the scrap by the required offset then clamp it in place.
• Hold the ball in the counterbore and drill all the way through, i.e. both holes, in a single go.

The only potentially tricky bit is nudging the scrap by the correct amount. Other than that, perfection is assured.

(Note that I did not condition this on having a drill press, but merely having access to one.)

 

[BABAR]

IF you have access to a drill press, I suggest the following:

• Place a piece of scrap on the table.
• Drill a blind hole (i.e. a counterbore) of roughly 10 to 20 mm diameter.
• Nudge the scrap by the required offset then clamp it in place.
• Hold the ball in the counterbore and drill all the way through, i.e. both holes, in a single go.

The only potentially tricky bit is nudging the scrap by the correct amount. Other than that, perfection is assured.

(Note that I did not condition this on having a drill press, but merely having access to one.)

Appreciate the ideas. Sounds do-able IF I had access. I do not. An electric hand drill and a dremel knockoff make up my power tools. The nice thing about it is however that for the most part I can do my rocket building in the house watching TV with my wife and yellow lab (well, I don’t know that Lucy watches, but her idea of heaven is just being in the same room with both here “peeps”.)

I am also living my teenage fantasy climbing into bed with two blondes every night!

I managed to line up the holes in the Tank Killer toilet float, this can’t be much harder.

 

[BABAR]

Slide the ring with the lug up to the tube-ball joint

Inked up a dowel, slide through lug to mark ball at edge.

Eyeballed where center would be just lateral to edge

Carved/drill hole with #11 blade (drill would have been challenging as ball already glued onto tube)

Checked with dowel slide through, made minor adjustments.

Slide dowel through lug on ring and through hole in ball. Dowel tip black, with translucent ball can see where it would “come out”. Marked with ink.

Again carved-drilled second hole, passed dowel a few times to adjust to center.

I think I am pretty close. I will need to put a rod through both holes and launch lug before gluing lug/ring fin to body.

 

[BABAR]

Pics are out of order, should go 3-1-2-4-5

 

[lakeroadster]

Easy Peazy. Forest Gump Tested.... Forest Gump Approved.