Cadet Cruiser In Open Rocket

Before anybody complains, 
I don't have much experience plotting model parts into Open Rocket. Still, I gave it a shot.
I took the RockSim simulation for the Sky Eagle off the Apogee website and dropped it into Open Rocket. I made a few small corrections based on the parts I had in the kit.
The engine mount tube is only 2 25" long and the kit did not have an engine block.
The engine hook does extend 3/4" out the back end of the fin can. I couldn't get the engine to extend the final 1/4" out the back. The above Sim is with an Estes A8-3 engine.
Enlarge the picture above and you can see the CG/CP are right on top of each other.

Below is the B6-4 simulation.

This is without the .30 oz. of clay nose weight I added and the engine moved 1/2" forward.
After adjustments, you should add .45 oz. of nose weight to get it stable with the heavier C6-5 engine. But - don't go by my results. Please do your own simulations.

A commercially available kit should fly stable without adding this much nose weight.

What's With The Blog Header?

Maybe I'm making light of a bad design?
The MPC Cadet Cruiser kit was a bad move from the start.

• The kit box lists an engine that doesn't exist. 
• The box estimates the maximum altitude at 260 feet. Mine never got nearly that high! If it were stable, a C6-5 engine should have reached at least 500 feet.
• The 18" parachute is cute, but way too large for a model this size.
• If built by the directions, the engine mount extends 3/4" out the back end of the model.
• The the front half of the fin root edges "float" above the body tube. Only the rear half is locked into the fin can.

I had flown it twice with a A8-3 and B6-4 engines. Both flights were unstable.

The engine mount was moved forward so only 1/4" of the engine extended out the back.

.30 oz. of clay weight was added to the nose cone. Both of these changes should have helped stability.

A third flight with another B6-4 showed it to be only marginally stable.

There had to be thousands of these kits produced. Were there ever any test flights before distribution?

Luckily I paid very little for the kit. That might be the reason so many are on sale.

I hate to trash a kit, but that's where it ended up!

MPC Cadet Cruiser FIX! Part 2

Here's a dry fit of the improved mount.
The BT-20 sticks out the back by about 1/8".
This puts the engine about 5/8" forward from where is was before.

With the engine hook farther up it doesn't move enough to allow the engine to slide in easily.
I filed the shallow notch to allow more engine hook movement.

Here's the tail end fix.

The hollow plastic nose cone got .30 oz. of clay nose weight.
It was tamped in place with a dowel.
This thing will fly stable!


EDIT: Now stable? Nope!
After these fixes - On February 7, 2015 another flight with an Estes B6-4 proved it was only marginally stable. The model was thrown away! I saved the 18" Porky Pig parachute.

MPC Cadet Cruiser FIX! Part 1

After two unstable flights of the MPC Cadet Cruiser I decided to make it work!
Built from the kit instructions, the engine sticks 3/4" out the back!
That alone could throw off the C/G position. I'll make a new mount where the engine only extends by 1/4".
The fin can and engine out came cleanly off the air frame tube with a little wiggling.

The shorter kit engine tube was glued in pretty well. From the rear the tube was grabbed with needle nosed pliers. Some twisting broke the tube sides off the plastic fin can.
From the top the engine block was grabbed and twisted.
The old tube was slid out the top.

The new engine mount tube is a standard 2 3/4" long BT-20.
The kit engine hook was thrown away, it wasn't spring steel and prone to bending.
The hook was held with a wrap of Scotch tape. Electrical tape would have been too thick.

MPC Cadet Cruiser, Finished

The model is cute and the colors bright. It should be a decent B6-4 or C6-5 model.
The instructions were vague with too many mistakes.
The box says "Flies up to 260 feet!
A C6-5 should take this one closer to 600'.
The B8-3 engine does not exist.
The shock cord was too short, the parachute WAY too large.
The nose cone shoulder took a wrap of tape for a good fit.
Look at the rear end picture and you can see how the front half of the fins "float" over the tube. The earlier MPC Enterprise fins were similar. There is a gap between the upper root edge and body tube.
I don't know why, but the engine sticks out 3/4" beyond the end of the fin can.
It is interesting to see how model rocketry is done in China.

Am I complaining? Not really, just observations. Heck, I only paid $4.80 for the kit.
I doubt these models will be around long, some vendors are clearing them out.

Launch in less than an hour? The model took an hour and a half to finish.

MPC Cadet Cruiser, Part 5, Launch Lug Gluing

The copy positions and the drawing positions for the two launch lugs don't match up!
The copy says 3 3/4" and 7 3/4" from the rear end.
In the same step the drawing shows 2 1/2" and 8" from the rear.
I went with the drawing positions.

One of the two lugs was opening at the seam.
It was glued shut.

The lugs are a glossy card stock wrap.
I roughed up a gluing side at the wrap seam end.

Mark the body tube for the lugs on the opposite side of the Porky Pig graphics. the instructions don't mention to do this.

The printed body tube wrap is also gloss stock.
After marking the lug positions, scrap away some of the gloss and print for a better glue bond.




Again the instructions don't say anything about it -

Sight down the body from the rear to be sure the lugs are in line.
This goes without saying for anyone who has built a few rockets.
These kits are made for first time builders who may not know to line up the lugs.

I assembled the 18" parachute but won't use it on a model this size.
The porky Pig graphics look great but I'll use a standard 12" chute.
A longer elastic shock cord was tied to the Kevlar.

MPC Cadet Cruiser, Part 4, Fin Decor and Gluing

Stickers are supplied for fin decor.
It's easiest to lift them off the sheet with your knife. Leave them on the knife for placement on the fin sides.
I applied the stickers before gluing the fins into the fin can slots. you can better center the stickers with the fins free, off the model.

 Again the directions are vague about how to glue the fins on.
"Slide each fin from the bottom up into the slots in the fin can and secure in place with model glue."
Plastic glue would be too messy so I applied a drop of thin CA to the top and bottom letting the glue run down the joint.
TIP: Always have a paper towel in hand when using CA to pick up any runs or drips.

The nose cone eyelet was closed. The instructions make no mention of opening it up.
I used my knife tip to clear the plastic flash.
A #11 X-Acto would be a better choice over my break off blade knife.

MPC Cadet Cruiser, Part 3, Fin Can & Parachute

Here's an illustration from the instructions -
Don't apply glue to the fin can shoulder. You would have glue squeezing out to the outside of the model.
Apply the glue inside the tube and slide the fin can into place. the glue remains inside the body tube.
Note the engine hook (and engine) extends 3/4" out the back end of the model. If I were to build another one of these, I'd cut a new longer engine mount tube and set the hook so the engine only extends 1/4" out the back.

Before gluing the fin can in place, center the rocket name graphics between two fin locations.
It'll look better (and with the launch lugs on the opposite side) and photograph better on the launcher.
Plan ahead with some pencil marks to line it all up.



Here's another mistake in the instructions:

"Pass the ends of the lines through the eyelet on the Clear Payload Tube . . . "
What clear payload tube? Obviously this copy block was copied from another kit and that sentence stayed in.

MPC Cadet Cruiser, Part 2 Engine Mount & Fin Can

"Launch in less than One Hour!" We'll see.
I normally take more time building than most.

The engine hook isn't spring steel.
The bent ends seem a little long.
The ends were trimmed back easily with some small wire cutters.

The instructions say to "Tape ove the hook with a piece of clear tape".
I went with electrical tape and found it too wide to slip into the fin can opening.
I ended up using a wider piece of Scotch tape than the instruction illustration showed.

The vague instructions said to "Slide it into the fin can. Glue both ends with model cement."

I layed down a line of plastic cement in the fin can hole, slid in the mount flush with the end of the plastic can. The instructions don't say how far in to glue the engine mount tube.

A fillet of plastic cement was added around the top.

There is no engine block ring.
I cut a 1/4" long piece from a used engine casing.

I didn't want to use the thin paper tri-fold mount.
The block was notched and a line of 135 lb. Kevlar tied on.
The block was glued in the top of the tube over the top of the engine hook bend.

MPC Cadet Cruiser, Part 1 Parts

Here's another of the MPC Round 2 kits.
These are not the older MPC rockets from the late 1960s but relabeled Sky model rockets from China.
Sky also makes the engines imported and relabeled by Quest.

I bought this one on Ebay, a "Buy It Now" for $4.80, too good to pass up. I was a big Looney Tunes fan and thought I'd give it a shot. This'll be a quick build.

The package box is bright and seems small considering the rocket when built is over 17" tall.  

Check out the "Compatible" engines - Estes or Quest
A8-3, B8-3, C6-5
I've never seen a B8-3 engine.

This looks to be the same model sold through Apogee as the Sky Eagle with Porky Pig graphics. CLICK HERE

Here's the parts - 
Four plastic fins
Pre-wrapped graphic on a convolutely (not spiral) wound tube.
Convolutely wound is like the old BT-30 or how you might roll a tube from a sheet of paper around a dowel.
A too short elastic shock cord
A very thin paper tri-fold mount
A BIG 18" parachute, too large for this sized model
Fin stickers
Instructions and a NAR membership flyer

Parts of interest:
The engine mount tube is just 2 1/4" long, also convolutely wound.
It's thin like a BT-20 but stiffer and stronger.

The fins are thin! The inset picture was taken outside to be back lit. You can see the light through the thin outside edge.






The nose cone is blow molded plastic.
The surface is smooth but with a "pebbled" texture.

The model is shades of purple with a yellow fin can.