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!
It has a picture of a Looney Tunes character on it, what did you expect?
ReplyDeleteBut seriously, you built it according to instructions and then used your experience to adjust it to make it more stable and it STILL failed. I can't help but wonder about the potential danger to the kids out there buying this kit who are not experienced.
I think you did a good deed by building and testing this rocket and now warning others.
Hi Lonnie,
DeleteI don't like to do bad reviews. I feel for the vendors that are stuck with these things.
I also wonder about how many other unstable models are out there.
I'm guessing that the model in question is based on the Sky Eagle kit from the Chinese manufacturer Sky Rocketry ( http://www.apogeerockets.com/Rocket_Kits/Skill_Level_1_Kits/Sky_Eagle_Rocket_Kit ). If I'm not mistaken, many of the recent MPC rocket kits with special decoration are based on Sky kits -- which makes me wonder what sort of differences were introduced in the course of creating a special decoration version, as I've not heard too many tales of problems with those kits.
ReplyDeleteI've heard of situations where you've got to be careful when using certain motors from Quest as there may be differences in the thrust-time curves which might cause problems with heavier models.
http://www.rocketryforum.com/showthread.php?15568-Estes-vs-Quest-Engines
Hi Naoto,
DeleteThe MPC Cadet Cruiser is a relabled Sky Eagle kit.
I used Estes engines, one A8-3 and two B6-4 engines.
One thing that I just noticed about the listing for the Sky Eagle kit on the Apogee site -- it only lists the Quest A6-4, Estes A8-3 and Aerotech D10-7 a recommended motors.... I wonder if running simulation under RockSim might shed light on the problems you were having?
ReplyDeleteHi naoto,
DeleteI can't speak for the recommended engines listed on the Apogee website. The Cadet Cruiser kit box lists "Estes or Quest A8-3, B8-3 and C6-5."
Yes, that B8-3 is printed on the box.
This post has me concerned for my own rocket now. I recently purchased the Star Trek trio, and the Klingon Bird-of-Prey uses the same nose cone, fin can, and body tube size(colored, of course). The fins look bigger than on the Cruiser, and the body tube is about 2.5 inches longer.
ReplyDeleteI am thinking that Naoto Kimura's suggestion to do a RocSim build before starting actual construction might be a good idea.
Hi Lester,
DeleteCheck the following blog post. I got the RockSim information from the Apogee website and dropped it into Open Rocket.
It comes up unstable. It seems there is just too much weight in the fin can and the fins might be too small.
If your Bird-Of-Prey is 2.5" longer it might be okay? Try a simulation using the Apogee info as a start.
Your blog inspired me to try to find a way to make it stable. I think the launch lug positions are bad in the kit instructions, and could contribute to the instability. I put one at the CG and one on the BT as far back as possible. The idea is to get a few more inches of guidance. In addtion, the fin can ridges interfere with the rod, so I put the lugs on making sure the rod would sit between two ridges to avoid the ridges dragging on the rod. I tried to do your engine mount mod but only got it 1/4" forward, so it is 1/2" out the back. I downloaded the trial of Rocksim which shows the CP a bit further aft than your open rocket sim. I added clay weight to the nosecone to move the CG to 12.1" from the nose which gives a bit more than 1 caliber of stability with a C6-5 loaded, in Rocksim. I finished the rocket the night before a very calm launch day and was rewarded with two arrow straight flights on B6-4s. Other than the launch lug issues, other problems with the kit were the shroud lines were different lengths, the nosecone requied several wraps of tape to fit the tube, and there was some wrap adhesive both inside and outside my tube. Thank again for doing the blog, it allows others to make changes to fly straight.
ReplyDelete