Thursday, December 16, 2010

Review: Madcow AQM-37 Jayhawk

My review of the Madcow  AQM-37 Jayhawk is below the page break.  You can also find out more about this kit by following the tag at the bottom of this post. Enjoy!


Brief:
This is a nice scale model of the Navy's AQM-37 Jayhawk. It features high quality components and flies on 29mm motors. The kit has recently been upgraded with a plastic nose cone.  I love this rocket!


Construction:
The parts list:

* Plastic nose cone and screw eye
* Balsa tail cone
* Pre-slotted 2.6" body tube
* One plywood centering ring
* 29mm motor tube
* Laser-cut fins, winglets, and canards
* 1/8" dowel
* Combination of Kevlar® and nylon shock cord sections
* 9" x 9" chute protector
* 30" Nylon chute
* ¼" launch lugs
* Waterslide decal set


The kit came with 7 pages of instructions. These are not as extensive as some but are more than adequate for even relatively inexperienced builders. Even though the design is somewhat exotic, the precision components made this a relatively easy build. I used 5-minute epoxy everywhere but on the fin/winglet interface.

You start with the motor mount, which consists of the tail cone, motor mount, and a forward centering ring. I decided that I wanted to add positive retention so I attached all-thread atop of a thin spacer to the motor mount. This required that I notch the tail cone but this was easily accomplished.

The Kevlar® portion of the shock tether is tied around the motor mount and epoxied to the centering ring. It fits in a notch on the ring and is tied to the nylon cord. The main trick up to this point is to not obstruct the fin tabs.

The motor mount and fin installation was straightforward, due in a large part to the precision laser cutting. The issue here is the attachment of the side winglets. Madcow warns that they tend to snap off on landing and offers two options. One is to attach them lightly so they will snap off easily and without damage. The other option is to try to make them bulletproof. I thought about using a larger chute (and probably will anyway) but decided the snap away idea is the way to go. I was afraid that the thin pointy tips would take a beating even if the fins stay on. You could glass them, but I didn't really want to.

The nosecone build was interesting. Due to the problems associated with attaching parts to the plastic cone, the canards employ a unique mounting technique. You drill holes in the cone and insert the provided dowel (cut in half). These dowels mate with slots in the canards so the structural support is independent of the bond with the plastic. I had two problems but neither affected the results. First, the dowel provided was warped and if you cut it to the specified lengths they are about 1/8" short. I contemplated buying a replacement but just made it work.

The instructions provide the target CG and instructs you to add nose weight to move the CG to a point 19" from the nose cone's tip. They recommend adding the weight to the shoulder section as weight in the tip is subject to coming loose. I first determined the amount of shot by placing it in a sandwich bag and draping it over the rocket at the rear end of the cone's shoulder. I then added lead shot and epoxy through a ½" hole drilled in the cone's shoulder. My completed model weighs in at 25oz. I noticed this is a little heavier than the other reviewer's model and quite a bit over the quoted number.

Finally, I added two orange colored buttons from railbuttons.com in lieu of the provided lugs.

Finishing:
I first sealed the wood parts and filled the thin spirals with Elmer's Fill 'n' Finish. The instructions referred to newer plastic primers for the plastic cone. I'd had never used any and thought I'd try Rustoleum Plastic primer. I initially painted the nose cone tip with Krylon H2O black. H2O over plastic primer seemed like a good idea. After that had dried, I masked the tip and shot Plasti-Kote primer on the canards and over the plastic primer on the base. Primer over primer? This worked OK and saved masking the base of the cone. I then shot Testor's Competition Orange on. So far so good. Then, however, the Frog Tape that I used to mask the tip lifted 50% of the H2O off. I removed the rest and repainted with the only other black I had on hand--Rustoleum Hammered Black. I sprayed this into the plastic top from a pack of Estes engines and brushed it on. The cone actually turned out OK.

The body was more straightforward with Plasti-Kote primer and Testor's Competition Orange. The kit comes with a lot of decals and they are good quality. I did a lot of repositioning and the only problem was one small corner folded under. As I was trying to unfold it, the edge broke off. Barely noticeable.

I rate this build a 4. The canard dowels were not perfect but everything else was top notch.

Flight/Recovery:
Flight #1  -  I flew the Jayhawk at MDRA's Red Glare V launch. All the recommended motors are Fs so I opted for an F42-4 EconoJet for the maiden flight. The -8 seemed too long and I'd rather see the delay too short than too long. I used a tape thrust ring in lieu of the F42's cardboard ring and added a small washer on the retention bolt. I upgraded to a 42" chute and added the provided one to the range box supply. The boost was very straight in the perfectly calm winds and, as typical for "winged" sport rockets, performed a slight wiggle after burn out.


Ejection was early and, because the cone is so heavy, the body slammed into it. Luckily, no fins were stripped by the impact but the balsa tail cone had a nice divot that looked like it might have been made by the screw eye in the base of the cone. This seemed a little odd since it was on a surface tapering away from the body.

Despite the bigger chute, the fillets on both winglets both had stress cracks in their fillets. Although not totally unexpected, I thought the bigger chute and soft plowed ground would have spared them.

I won't fault the kit for the impact as this was user error and the cracks in the fillets were due to my chosen build technique. However, my general sense is that this kit is more subject to landing damage unless you went hog wild in its construction.

Flight #2 - The second flight was at Red Glare VI on a G78-8.  It swooped like crazy under boost and after, but remained in a solidly upward direction. Ejection was nosecone-down and it recovered with zero damage. 

Flight #3 - The third flight was at ESL-148 on a G64-7.  It was a really high flight and I didn't see where it ejected.  It gave us a long walk...luckily my son and daughter in law did said walking!


Summary:
PROs:

* This is an awesome looking kit.
* Despite its unique looks, it is quite stable.
* Precision cut parts/quality recovery components.
* Nice method of attaching the canards to the plastic cone.
* Nice decals.

CONs

* Winglets are asking to snap off.
* Chute is undersized.
* Should provide motor retention.