Mega Rebel from Arkansas [Rocketarium] - Phase 1

[Crawf56]

Gluing the upper tube into the Nosecone. Using the cowl to a Zero fighter, that I happen to also be working on.

 

[Crawf56]

Here is the main body of the Mega Rebel. Same assembly procedure. Make sure the holes in the disks are aligned!

 

[Crawf56]

Adding fillet to the base of the tube.

 

[Crawf56]

The instructions for this model are very good. This is my first Rocketarium kit, and I will purchase other Rocketarium kits in the future.

 

[Crawf56]

Well, I am pretty much done.

Note that I left it unpainted, since that will help the Monokote adhesion in the future.

 

[kuririn]

Nice job. looking forward to Phase II.

 

[BABAR]

Showing the side profile. Note that disk #9 is shown to the left, but NOT glued to the Nose. #9 is used for alignment.View attachment 402082

View attachment 402083

Edited, overcome by events.

Hoping for a good flight!

 

[Crawf56]

I contacted Rocketarium about the CG location, which is not given. Their response was that, they assumed I was talking about the CP, and that a CP was not found. The design was developed by trial and testing.

Ok, let me go through this again.

CG = Center of Gravity, which is the mass balance point of the rocket. Adding nose weight moves the CG.

CP = Center of Pressure, which is the sum of forces acting on a body (?); a calculation based on physical dimensions, not component density.

So, for a stable rocket, the CG should be in front of the CP. (CG closer to the nose.)

NOTE: The instructions suggest TESTING the Mega Rebel with a D12-3. They also state that painting the model will add more weight than the D12-3 can handle.

So......I will need to gather CG information BEFORE I apply monokote.

 

[Crawf56]

Test

 

[Crawf56]

Work on finding the balance point, or Center of Gravity [CG] of the Mega Rebel.

I tested the rocket balance with an Estes D12-5 and an Aerotech E15-4W. For both motors, I found the balance point to be 7-1/2 to 7-3/4 inches from the base of the fins. This is roughly at the 3rd disk, as measured from the bottom. (Disk #6.)

Next task is a test launch!

 

[neil_w]

I'm looking forward to seeing exactly how you're going to attack Monokoting that thing.

 

[David Schwantz]

Monokote will not stick well to the laser cut edges. If you sand the burn marks off it will at least be better. Post pics when done. Good luck.

 

[BABAR]

I kinda thought the raw wood look was part of the charm of the kit!

 

[DuaneW]

I don't know if anyone mentioned this, but if you add a skin (Monokote) to this design, then all bets are off as to where the CP will be. There's a lot of induced drag being created by having those centering rings open to the air in flight. Covering them will change the CP location. Where? Probably forward, but that's just a guess.

Good Luck!

 

[Sooner Boomer]

I don't know if anyone mentioned this, but if you add a skin (Monokote) to this design, then all bets are off as to where the CP will be. There's a lot of induced drag being created by having those centering rings open to the air in flight. Covering them will change the CP location. Where? Probably forward, but that's just a guess.

Good Luck!

I *hate* to be contrarian, but...the CP is not a great unknowable quantity. The easiest way to calculate the CP of a rocket is to make a cardboard cutout of the silhouette of the rocket and find the balance point. It's probably in one of the Estes Technical Manuals about how to do this. Here's what NASA says - https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/rktcp.html

edit Estes Technical Report TR-1 "Rocket Stability". https://estesrockets.com/wp-content/uploads/Educator/2845_Classic_Collection_TR-TN.pdf

 

[neil_w]

I thought the monokote was going to be on the surface of the wood, not skinning the whole thing like a stick-and-tissue airplane.

CP of the open frame would be pretty much impossible to determine with anything short of a CFD model, due to all the drag and turbulence in there.

 

[DuaneW]

I *hate* to be contrarian, but...the CP is not a great unknowable quantity. The easiest way to calculate the CP of a rocket is to make a cardboard cutout of the silhouette of the rocket and find the balance point. It's probably in one of the Estes Technical Manuals about how to do this. Here's what NASA says - https://www.grc.nasa.gov/WWW/k-12/VirtualAero/BottleRocket/airplane/rktcp.html

edit Estes Technical Report TR-1 "Rocket Stability". https://estesrockets.com/wp-content/uploads/Educator/2845_Classic_Collection_TR-TN.pdf

That technique doesn't work so well for rockets of this shape. The Estes Tech Report was written years ago and is a bit simplistic in its assumptions for anything that doesn't look like a typical Estes kit. It especially doesn't take rockets of this profile in to account. Open Rocket or RockSim would provide a better estimate.

 

[Crawf56]

I plan to start a separate thread on covering with monokote. First, let's get a successful launch...…...which may be easier said than done.

 

[Crawf56]

So, had low winds, so I went for a launch......and got a CATO.

I am not sure exactly what happened. The motor went THROUGH the rocket. Using a Estes D12-3.

 

[Crawf56]

Even though the motor nozzle was not damaged, the thrust does not look right.

 

[Crawf56]

Motor keep going up and over.

 

[Crawf56]

Post blast analysis...

Shock chord in two; showed signs of melting. Parachute was attached to eye on nose; some melting with torn string.

EDIT: Shock chord NOT in two.

 

[Crawf56]

The lower half of the rocket, still on the launch pad. Was not binding with the launch rod.

 

[Crawf56]

A closer look at the motor mount. Or what is left of the motor mount.

 

[Crawf56]

Well, the shock chord did NOT break. Here it is, attached to the nose...…..and the front half of the motor mount.

 

[Crawf56]

Motor mount tube.

 

[kuririn]

Engine CATO.
Bad luck.
Not resulting from a rocket design problem.
Has anyone flown this successfully? Please comment.
I have yet to maiden mine.

 

[dhbarr]

Sad, but epic. MESS report?

 

[BABAR]

Weird.

Looks like the motor did what IT was supposed to, generating thrust going up and up and up.

I thought CATOs either blew out the front and/or back and/or side(s.)

Could this be a motor mount failure, where motor just went straight up through the rocket and kept going?

Sorry about the rocket. Is it fixable?

 

[kuririn]

Could this be a motor mount failure, where motor just went straight up through the rocket and kept going?

Don't think so. Second picture shows a fireball and flaming bits of motor.
Good news is the plywood is rugged. Check for cracks and repair with thin CA and clamps.
Replace the motor mount and maybe the central tube. New kit = $$$. Rebuild = motor mount + maybe new tube.
Make her better, faster, stronger.
THE BIONIC REBEL.