Kitbash: Mini Viper IV from Estes Hornet

[brewster_rockit]

One of the rocket plans that's been sitting on my build pile for a while is John Viggiano's Mini Viper IV, a roughly 1/2 downscale of the classic cluster model from LOC. I had an "a-ha" moment when I saw the Estes clearance special on the Monarch, Cosmic Explorer & Hornet bundle, since all three models were BT-55 based. Sure enough, my kits arrived today and the Hornet has the perfect body tube for the project: a single piece, 14 3/16" long!

Due to the worldwide balsa shortage (apparently due to the use of balsa in wind turbines,) all three kits come with plastic PNC-55AO nose cones (the shape dating back to the Estes Goblin.) To my eye, the PNC-55AO is a better match for the Viper IV's nose cone than the Arcas-style PNC-55AC that the original plan calls for. Not posessing a Viper IV to inspect though, it's hard to tell. Thoughts? I do have a pair of PNC-55AC's on hand...

In any case, I intend to order some BT-5 soon and get started. i'll post pics as the project progresses. It'll be interesting to see how the four BT-5's fit inside the BT-55. It will probably require a bit of sanding where the BT-5's join with each other, and where the BT-5's touch the inside of the BT-55. The project would probably be a bit easier if I substituted a BT-56 / Centuri Series 13 for the BT-55, but I intend to work with the parts on hand.

 

[Joe_Shockcord]

I regret not having taken advantage of that last sale, as the PNC-55AO is one of my favorite shapes. It's perfect for a 55 downscale of a Red Max, Mean Machine or Citation Patriot. I knew that the Monarch had a plastic cone but I was unaware that the other two models now had plastic as well. The last time I saw them they still had balsa. Bummer. This is exactly what I was talking about when I suggested to Mr. Boren that Estes should expand their offering of bulk plastic nose cones, as this shape is not available in plastic from any other manufacturer. A bulk pack could really fill that need.

 

[TopRamen]

Any progress???

 

[brewster_rockit]

I've got the fins cut but I'm awaiting the BT-5 that I just ordered from BMS. Only open question is what I'll use for a motor retainer. The original plan calls for a single nylon screw post (used to bind photo albums) between the motor mounts. I was thinking that a screw anchor with a metal screw and a washer might be a better choice though, especially because I have screw anchors already.

Pics to follow soon!

 

[brewster_rockit]

After studying the fin template provided in the plans, it appears that the fin shape is quite at odds with the real shape on the full-size Viper IV. I was able to find
the correct fin template in a YORF thread, so I'm currently correcting the fins I've already cut.

I've also realized that to do a true 1/2 scale Viper IV, none of the readily-available nose cones is a close match. The BT-55 V-2 nose cone from BMS seems to be the best fit for the length and shape, plus a 15" BT-55 to match the original kit's 30" tube. I'm using a longer cone (PNC-55AO or AC) and a slightly shorter piece of BT-55.

 

[brewster_rockit]

How's this for a progress pic? It's not flight-ready yet, and it'll probably take a few coats of sanding sealer and a few coats of paint before I'm calling it finished. But the basic airframe is complete. There was little issue with getting the motor tubes to fit into the BT-55 after I sanded the motor tubes along all gluing surfaces.



I'm also attaching my .ork file if anybody wants to build their own Mini Viper IV. While I used a 14.125" BT-55 and a PNC-55AO, a closer approximation of the real Viper IV's proportions would use a BNC-55F (Estes original V-2 nose cone, available from BMS) and a slightly longer piece of BT-55. The full-size Viper IV has a 30" body tube and 9" nose cone.

View attachment mini viper iv.ork