Model Rocket Building Blog
Estes Sprint XL BackgroundThe first K-49, BT-50 based Estes Sprint was introduced in 1970. It was advertised as "The First True Competition Model". To see the catalog page, CLICK HERE Very few models had boat tails back then. The Sprint sported a low drag parabolic nose cone and fin shape. It used 18mm engines, streamer ...[Read More]
Estes Sprint XL #7224 Build, Part 2, Tail ConeYou could cut through the nose and tail cone with a razor saw but I used my break-off blade knife. Repeated scoring and the plastic was separated. The tail cone needs the most work. When first broken off the slot for the engine hook is very narrow. GOTCHA: Trust me, do a dry fit (no glue yet) of ...[Read More]
Estes Sprint XL #7224 Build, Part 3, Tail Cone FitFirst up you'll have to widen the low end hole. 200 grit was wrapped around an 18mm casing. Constantly check the fit of the BT-50 engine mount tube. The engine hook slot was widened with a small diamond coated file. Even though the slot was wide enough at the back, the hook was still getting ...[Read More]
Estes Sprint XL #7224 Build, Part 1, PartsWell, I screwed that up! This post should have gone up yesterday after the first "Background" post. Here it is, I'll fix the order later. I've wanted to build this one for a while. I picked up two in the Estes clearance sale. I had an Astron Sprint in the early 1970s. It was considered high tech ...[Read More]
Estes Sprint XL #7224 Build, Part 4, Engine Mount & KevlarLook close at the ends of the tail cone. There is a slightly raised molding lip. I used my sanding block with 220 grit to straighten out the sides. The engine block sits inside the end of the engine mount tube. Use a D engine casing to set the block so it won't be glued in at an angle. The ...[Read More]
Estes Sprint XL #7224 Build, Part 5, Fin ShapingIn the original Sprint kit you had a choice to either airfoil the fins or round the edges. These new instructions say to round just the leading edges. That didn't make much sense given the shape of the fins. I decided to round it all - the leading edge, outside tip and trailing edges. The ...[Read More]
Estes Sprint XL #7224 Build, Part 6, Lugs and Primer FillThe launch lugs have to be cut in two. The original smaller Sprint had two lugs only 1/4" long. The lug ends were cut at an angle. This lug is simply cut in two. To get a straight cut, wrap some tape around the lug at the halfway mark. Slide a dowel inside to support the lug, otherwise it could ...[Read More]
Estes Sprint XL #7224 Build, Part 7, Fin GluingWith the lugs glued on the fin marking guide is wrapped. Line up the LL line with the lugs already in place. The engine mount hasn't been glued in place yet. TIP : With the tail cone removed, extend the fin line over the lip end of the tube. With the fin even with the end of the tube the gluing ...[Read More]
Sprint XL and Long Tom Builds on EbayFor the next few days, both the finished Sprint XL and Long Tom builds are up for auction on Ebay! The Sprint XL is HERE , The Long Tom is HERE Stop by, make a bid and support the blog![Read More]
Estes Sprint XL #7224 Build, Part 8, DecalsThe fin grain still showed on two fin sides after the first light white coat. I rubbed in some CWF with a fingertip. The coat was thin so there wouldn't be much sanding. These are all the decal you get! The original Sprint kit had two sheets for two different decors. The big "meatball" decal is ...[Read More]
Estes Sprint XL #7224 Build, FinishedAn interesting, easier build. I missed the extra decals that were included in the original BT-50 based Sprint kit. On the right is the catalog version I put together years ago. The cleaner decor is okay, just a little too plain for me. I probably could draw and print it up but home print black ...[Read More]
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