The Challenge is On!!!

Here is the statement:

Phil: "You don't need to design a rocket to make one that will fly. It will not fly optimally. But it will fly."

Milo: "No you can't."

Phil: "I bet you can."

Milo: "Prove it."

So the challenge is on. I'm betting that I can take a toilet paper tube and an engine and make a flyable rocket with no design help. So, I will report on the progress from time to time.

Any feedback? Am I crazy? Is Milo crazy?

hehe... Hey BillyBob, watch this!

I'm guessing it will tumble or spiral outta control. Or the rocket will be so small the design errors that show up in larger rockets will not present themselves as much in a smaller rocket.

Anybody want to help me build a launch bunker?

Oh, I'm not guaranteeing that no animals will die during the launch. I bet you could do it with larger rockets but the risk gets higher. Think about an H engine in a toilet paper roll. Will it fly? You bet your butterknife. Will someone die. Probably....

What I'm thinking is that the more powerful the engine the higher the risk and the greater the desire that designing comes into play. But it is possible to put that all aside and go for it.

BTW: My Roll Rocket will not be recoverable in one piece. I said fly, not land.

Just like every other bet we've made, you are already changing the rules so that you will be right. By your definition of "fly" I can attach an M to a brick, light it off and say it flew. But is the brick really flying? Or is it just hurling along because it has no choice?

Still taking applications for bunker builders.

Well, I guess I should clarify. The rocket has to go up, with minimal spiral. That is flying.

... and no tumbling.

And another thing... there is a stipulation that design tools can't be used. I consider the members that are experts in design on this forum as a design tool. So no hints or help from members.

Members: You may predict what the rocket will do but please do not suggest why you think it will do this. That may clue Rocketman Jr. here on how to build his rocket.

You two are spooking me!!!

Why don't you peal the spiral tube apart, wrap it around a 54mm K1100 casing with some duct tape, light the fuse and call it a life!

We will name the rocket "Gene Pool Remover"

I would send flowers

You don't actually think I am going to be there for the launch do you?!?!? I'm going to make him film it for proof.

I will be safely tucked away in my basement 60 miles away. I figure I will be safe there.

But it appears that one expert agrees with me (so far).

I say the name should be "Darwin I". Of course, there'll never be a "Darwin II" but, what the heck its got a certain ring to it.

Nose cone: Aquired
Body: Aquired
Fins: working...
Motor Mount: working...

Airline Ticket: Acquired

Cardboard Paper Towel tube: $0.95
Plastic Nose Cone: $1.05
Balsa Wood for fins: $2.00
Rocket Engines: $5.00
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Watching your friend blow himself up to satisfy a silly bet: Priceless.

PGerringer's hero is that guy the Rocketman in England trying to become the first commercial space voyager.

Two peas in a pod....

Well, I'm offended...

Ok Guys, I saw this on the LRDS 20 page. It is basically a cable reel or cable spool. No wings no modification except motor retention and parachute. Here is the on the pad picture link: https://www.ldrs20.org/pics/rockets/pages/jds0121.htm and here it is going up: https://www.ldrs20.org/pics/rockets/pages/jds0124.htm. I was told that it went straight up and was a great flight. I suppose that anything with enough motor behind it would go straight up.

Amazing! That is what we used to say about Soviet aircraft. Big enough engine and anything will fly.

Oh man!!! There is no way I could compete with that. I was thinking A engine so noone gets killed. Well, I will continue with my experiment just for uniqueness. I think I won the argument though.

Thanks for the links, bikeboy.

What have I told you about "thinking". You know that gets your little pea hurting.

I don't think you have won the argument yet. I think those pictures prove the "brick with engine" theory.

Wasn't the "brick with engine" theory the arguement. Yeah, cause I said you can make a rocket without designing it and it would fly. Not optimally, but it would fly. They proved that using a spool as the rocket.

That was soooooo cool. I wonder what else we could launch?

If you put the engine straight up, it's gonna lift off, yes, but...

Happened to me once. Never try that again...

Oliver

Anyone who has built a rocket will automatically build in some things that will make it work. When you think "AH...I will put fins here" that thought did not spring like Athena...

Where you get into trouble is when you _design_ a model.

I was Pad Manger one day at the recent NARAM- a guy comes up with his kid to launch an altitude bird. They were using an Apogee 10.5 mm motor. It looked a little hinkey to me so I asked the guy if he had thought the thing out.

He told me he had used all the software available and had also string tested the model...it was safe. I asked him if he had string tested the model with an empty motor. "Nope...sims says it will work".
Very Gruffly he asked for his pad.

I told the LCO to announce "heads Up!". The father got a little irate...then we launched the bird. It flew up about 10' and went crazy.

The guy asked me how I knew. "Simple...the long motor changes the CD as it burns."

A simple test...test with a full motor and a burned motor would have prevented these folk from a DQ. But they had the latest design software...

How would a motor change the CD (as in coefficient of drag)? It sits inside the motor tube and doesn't do anything to the airflow around the rocket, except for it shoots a little gas out the back. Then, CD doesn't affect stability of the rocket...

If it was CG (as in center of gravity) yes, it changes, but if a motor in the back burns the CG moves forward, which would make the rocket more stable. Except for when the loaded motor's CG is forward of the complete rocket's CG, then the burning motor would indeed shift the CG aft and make the rocket unstable. Was that the case? This is indeed difficult, because an empty rocket, without even a burnt motor would have the CG forward, and only moved back by the weight of the motor casing in the back.

Oliver

Yes, I meant CG.

Not only did it affect the one fellow, I saw...but was not involved in....at least three other such pinwheeling min. dia. A altitude models. Some of the clubs had been passing this shortened design around.

I believe that the stability problem is from a shifting CG in relation to the CP. My Apogee altitude models require the use of a load of tracking powder in the _nose_ to fly correctly. I push a little baggie down over the streamer with the edges outside the tube and pour in about 1/4 oz of powder, then put in the NC. This keeps the weight in the nose. None of the models I saw DQ used any powder weighting in the nose.

Without that 1/4 oz the model is unstable during flight. Or I can add about three inches to the length. Which then more closely mirrors the Centrix design but is still longer.

The problem is that you can make them over stable by increasing the length, but that increases mass, and drag. So it does seem to be a function of aspect and a shifting CG. One that doesn't seem to quite fit in with some of the software.

I suspect that the same thing will happen with the new E motors if people fly them in min. dia. short tube designs.

Actually, no matter what kind of motor you're using, the CG will always move forward, or at least not backward in relation the fully loaded CG location. So the rocket cannot become unstable due to CG shifting. Except for you show me the measurements (mass, dimensions) of both rocket and motor so I can figure it out myself.

Or perhaps shifting of CG was not even the problem, but there was a gust of wind that shifted the CP of the marginally stable rocket (so it would not be affected by winds that much) to a point where the rocket became unstable?

Oliver

All I can tell you Oliver is that the model is marginally stable. I have flown similar models in all sorts of weather. Dead calm and windy. I can tell you that it is my eyewitness observation that the model will go unstable if you shorten it even a tad and do not increase the nose weight.

Despite what the sims say.

I have also upscaled the model for both 13mm and 18mm. It does not act the same way.

The Apogee B2 motor is 10X86 mm. The A2 is 10x 55 Very long and skinny.

I say it is the shifting CG, which despite the fact that a CG forward of CP should increase stability...it does not in this design. OTOH, if you fly the very same model with a 1/4A it does not act the same way, it flys stable.

Furthermore, all motors do not affect shifting CG in the same way. A core burner will not have the dramatic affect that a long skinny end burner will have. A core burner will shift differently beacuse the mass is decreasing evenly along the length of the motor. An end burner will have the weight of the unburned propellant still at the front of the motor.

It may be that because the fins are the smallest that can be put on and not be unstable, that the shifting CG causes the model to wobble and the fins cannot compenstate.

What is the correct answer? I don't know...I do know that the design does not act the way the sims say. I am not the only one to notice this. The only way I have been able to trim the model is to swing test it with a unburned motor and with a burned motor and adjust the nose weight so that it remains stable.

YMMV.

Originally posted by PGerringer
Here is the statement:

Phil: "You don't need to design a rocket to make one that will fly. It will not fly optimally. But it will fly."

Milo: "No you can't."

Phil: "I bet you can."

Milo: "Prove it."

So the challenge is on. I'm betting that I can take a toilet paper tube and an engine and make a flyable rocket with no design help. So, I will report on the progress from time to time.

Any feedback? Am I crazy? Is Milo crazy?

Click to expand...

So, what is the status of the challenge rocket?

Well.... I was wondering when someone was going to ask. I have the pieces for 2 non-designed rockets. They are in a box waiting for assembly but too many other, more interesting things have been going on. After the A4, the launch pad. After the launch pad, then the yet bought Mustang. And the wife keeps reminding me about the many home projects still unfinished in the home. Too many projects too little time. Hopefully soon.

I know this thread is reaaalllllyyy old, but it's just too delicious to let Phil off the hook! Has the rocket been built, and the bet been won?

Loopy

LOL... The rocket was made... but I was too chicken to launch it. It looks very, very unsafe...