The Nimbus is a 54mm minimum diameter rocket from PML that is designed for extremely high altitudes. PML claims that this rocket has reached over 13,000 on a K motor. It consists of a phenolic airframe, PML's CPR 3000 dual recovery system , G10 fiberglass fins , and a plastic nosecone. It has a 36" nylon main chute and a 144" nylon streamer for a drouge. PML recommends that this kit be fiberglassed and they offer a fiberglassing kit for this purpose.
The Nimbus is a very well engineered kit employing PML's CPR 3000 recovery system. This is one of the best dual recovery systems I've seen and I have used the design in my other rockets as well. For more information on the design of this system, visit PML's website.
The instructions for this kit are very complete and easy to follow. Even a person with limited experience building high power rockets should be able to handle this kit. Drawings are included and are clear and easy to understand.
The parts of this kit fit perfectly the first time. I did not have to sand a single piece. I built this kit straight from the instructions with one exception. I had an accident while epoxying the upper ejection tube into the airframe, the assembly dropped and the airframe cracked and the centering ring set inside the tube. Result-- I had to order a new section of 54mm tubing from PML. (by the way I received it the next day via priority mail). Since this was a full 36" piece I decided to use the whole thing instead of cutting a 15" piece off. This resulted in a very tall rocket which is now probably over stable. I would not recommend this as a modification. Although it flew perfectly on a Kosdon J280 in 15MPH winds I will probably cut it back to the designed length .
The good features of this kit are the well fitting parts, the "dado slots" used for surface mounting the fins and the design of the CPR 3000 system. This is the 3rd minimum diameter rocket that I have built and the "dado slots" work great. They involve cutting slots about 1/4 to 1/2 thru the airframe and setting the fins in these slots. The only change I make to PML's instructions which tell you to epoxy them in place is that I set the fins with medium viscosity CA and then apply epoxy fillets to the joint. I have yet to lose a fin. On my modified VB38 the main chute separated and the rocket came down very hard on just a streamer and there was no damage to the fins.
The remainder of the construction is very straight-forward and does not need to be discussed here.
One feature that I have not mentioned is the piston system used to deploy the main chute and drouge. Being new to the hobby I asked a lot of questions at our launches at Whitakers N.C. We have a lot of very experienced people in this group and most of them recommend leaving the pistons out. I started to do just that but decided to try them anyway. (the only piece of advice that I have not used). The result - The pistons have worked great and I will probably keep using them . Like PML says in the instructions-- Just make sure they slide freely. They should fall out when the airframe is turned upside down.
Now for the bad part. I hate PML's phenolic tubing. It is too brittle, hard to cut without chipping, and has deeper than normal spirals to fill. About the only thing I would use this stuff for is as a mandrel for fiberglassing. I am not good at fiberglassing so I use Hawk Mountain or Giant Leaps filament wound epoxy fiberglass tubing for high stress applications. My next project is going to be an exact copy of this kit using Giant Leap's 54mm tubing and replacing the Nimbus fins with a 54mm Acme fin canister and flying on a K700.
Finishing was done using basic finishing techniques. I filled the spirals with Elmers wood filler. It took three heavy coats but it worked. I then applied two coats of Krylon white primer and finished in with Krylon purple and Krylon brass colored metallic paint.
Construction Rating: 4 out of 5
So far I only have 1 flight on this bird. It was a perfect flight on a Kosdon J280. This was my Level 2 cert flight and it was very windy that day so I decided to go with the smaller J instead of the K185 that I had planned to use. The Kosdon pushed this lanky 5 lb plus (loaded) bird through a 15MPH wind straight as a arrow . The PML CoPilot made by Missile Works deployed the streamer right after it arc'd over and the main came out at about 400ft . Exactly as planned. The rocket was recovered about several hundred yards away all laid out in a straight line.
The CPR 3000 works great as does the PML CoPilot. This altimeter is essentially the same as the RCC2 from Missile Works. The instructions are easy to follow , the altimeter is easy to prep and every flight has worked to perfection. I also use this on my VB38 which I modified for dual recovery. With the exception of one flight in which I put too much BP in the ejection charge a blew apart my homemade screw on coupler. The altimeter was in the part that came down hard under streamer only. No damage and I have had a couple of nice flights with it since then . Including the Nimbus flight.
Flight Rating: 5 out of 5
Great looking kit . Get rid of the phenolic tubing. CPR 3000 is the best, easiest to use dual recovery system I've seen so far.
Overall Rating: 4 out of 5
UPDATE 6/01: Just like to add a follow-up on the phenolic tubing. Apparently PML's phenolic gets more brittle with age. I went to Orangeburg for the June launch. I had the rocket prepped except for the motor and propped it up against the back of my vehicle while I went to purchase a motor. When I came back the rocket had fallen over and cracked the tubing in 2 places. Result- I took a hammer to the airframe pieces and cracked the airframe away from the CPR 3000 components and they are going in a all fiberglass version. Moral - Either fiberglass this kit from the start or better yet - start with all fiberglass tubing. PML - find a better grade phenolic.