Scratch - Hawkeye (BT-50) {Scratch} Original Design / Scratch Built

Contributed by Geoffrey Kerbel

Manufacturer: Scratch
(Contributed - by Geoffrey Kerbel - 09/01/08) (Scratch) BT-50 Hawkeye

This Hawkeye is a 1.79x upscale of the Estes original which was based on a BT-5 tube. It is a single stage larger version of the "mini" rocket that used a 13mm engine. Due to the size, a parachute is used for recovery.

The components used were:

  • Estes instructions for the original Hawkeye (used to see where and how all the parts go together) from JimZ's site
  • BT-50 body tube x 10.75" in length
  • BT-50 x 1" tube x 2 for the wing tubes
  • A PNC-50 YR nose cone or equivalent
  • 3/32" balsa for fins (two wings, two small fins and two vertical fins
  • Standard Estes 18mm motor mount or 2.75 length of BT-20 with 3 CR-2050 mounting rings, 1 520 engine block and standard Estes motor hook or short length of wiper blade side steel bent to form an engine hook.
  • 8" of 100# Kevlar® for shock cord anchor
  • 30" of 1/8 elastic for shock cord
  • 12" plastic chute
  • 1" piece of 1/8th" launch lug
  • Glue
  • Full sheet sticky back label paper to paper fins
(Scratch) BT-50 Hawkeye

Construction starts with the motor mount. Take the BT-20 tube and make a pencil mark 1/4" down from one end and another mark 1" past the first. Take the short length of Kevlar® and make a small end loop on it. Place the loop around the engine hook and place the hook with the short end into the slit on the tube. Pull the Kevlar® towards the front of the motor mount. Above the 1" mark, wrap the tube and hook with about three wraps of masking tape to hold the hook in place. Take one CR-2050 and slide it down from the top to the slit. Take another CR-2050 and slide it from the opposite end to the tape. Place glue fillets on both sides of the CRs and a generous amount on the tape. Make sure the Kevlar® loop is also glued to the mount at the hook slit. When this has dried, take the third CR and cut a notch in it so that when you slide it on the mount it is deep enough for you to pull the hook out enough to get the engine out. Slide it onto the mount and place it right at the bottom edge of the mount with the notch aligned with the hook. Apply a glue fillet to this CR but don't allow the glue to get on the hook. Set aside the mount.

I used my scanner to upscale the fin patterns onto 110# paper. After cutting them out of the paper, I then transferred the paper patterns to the balsa sheet. First give the balsa sheet a good flat sanding with fine grit paper then transfer the patterns. Make sure the balsa grain is parallel with the leading edge of all the fins. Once the fins are cut out, stack like pieces together and sand the edges flat to each other and give the leading, tip and trailing edge a good rounding. This small step is a bit of a chore but it will always make your rockets look and fly better. Leave the root edge flat.

At this point, I paper the fins on both sides with the sticky back label paper, however, you can use whatever method you prefer or do nothing at all. Some people do the balsa sealing after the fins are mounted, some do it before. I have found the papering methods so much faster and easier, that I just about do it to all the balsa pieces I use before I mount those pieces on the body tube. After the balsa pieces are papered, I use thin CA to seal the edges of the paper to the balsa except on the root edge. Use the regular glue on the root edges very thinly for the first of the double glue method of fin attachment.

Using your favorite fin marking method, make marks on the BT-50 x 10.75" tube for four fins 90 degrees apart from one another and two more 120 degrees to either side of the upper fin. Extend the marks at least half way down the tube. I started fin attachment with the vertical fins first since I could use the popsicle method of keeping them straight to each other and aligned vertically with the body tube. See the building tips section for this. Once they had set up, the side wings were added. All four of these fins are placed with their root edges even with the back end of the body tube. Make sure they are perpendicular with the tube! The two small fins are added last on the 120 degree lines with their back edges even with the front of the wings. The upper "conduit" piece is then glued to the tube in line with the upper fin and right up to the front edge of that fin. Glue the launch lug on the lower joint line of one of the small fins.

Let all the fins set up and then add your glue fillets to all the joints. Do this before you glue on the small BT-50 tubes or you will not be able to get to some of the joints. When the fillets are set up, glue the small tubes to the upper part each of the wings even with the back ends of those wings and touching the body tube.

Last thing to do is glue in the motor mount. Test fit the mount into the body tube with the Kevlar® coming out of the front of the body tube. Make a mark on the Kevlar® where you will place another end loop. You want the loop to be just inside the body tube. Make sure the engine hook is not in line with the launch lug. I placed the hook on mine almost even with the other small fin up front. Pull the mount out to make that loop and put it back in to check if the loop is where you want it. If everything is OK, pull the mount out again and put the Kevlar® back through the mount to get it out of the way. Place a ring of glue inside the body tube where the upper CR will be, slide the motor mount about halfway in and add another glue ring to the inside of the body tube. With one smooth push, move the motor mount all the way into the body tube so that the back end of the mount is flush with the body tube. When the glue had set up for the mount, add a thin ring of glue to the body tube and lower CR where the two touch. Keep this fillet very thin so it looks good and the motor will still fit into the mount.

Take the 1/8" elastic and tie one end to the Kevlar® loop. Pass the elastic through the mount and out the front of the body tube. Pull the whole thing through.

Wait to tie the elastic to the nose cone until after the rocket has been painted if the cone is already white. Otherwise tie the two together, add the chute and the rocket is ready for flight or finishing.

Finishing of this rocket is really quite easy! The color scheme is a white nose cone with the rest all gray. Nice! If your nose cone is already white (mine was) that is done! If there is no nose cone on the front of the rocket, place something into the tube so that the inside does not get paint on it otherwise the nose cone will not fit back in later. After sanding and two coats of primer (sanding in between coats) the paint job was done. I used gray primer. It doesn't get much easier than that. Since I wanted a dull coat for the gray color, the primer was perfect as is. Just make sure the final coat is put on fairly "wet" so that it is nice and smooth when dry. If you have to sand yours to smooth it out, just use a dull top coat to finish it off.

I have a decal set from Excelsior to put on but because of the use of the primer for a finish coat, I will take a small piece of the decal paper he uses to test whether it will stick properly. Sometimes decals will not stick to non-glossy coatings. I haven't done the decals yet so that is yet to be determined. If they don't I will have to gloss clear coat the rocket first, add the decals and then use some dull coat to get the finish I want. You can always spray gloss gray on yours and be done with it.

There are no real "gotchas" except that the instructions for this rocket are not really for this size rocket. However, this is a fairly simple one to construct and upscaling should pose no challenges. Always test the balance when doing this kind of upscaling with the largest motor you plan to use. This one balanced perfectly even with a C6-7 motor in it which I most likely will not use. I like to get my rockets back! I get plenty of exercise jumping to conclusions...

While I was making this upscale, I was also building the Mega Hawkeye, a BT-20 size Hawkeye and a clone of the original BT-5 one. The scaling bug hit me just like it does to my good friend Moe Bertrand. Once he gets going on a rocket, almost every size body tube is used to make the others, sometimes leading to four, five or more different sizes of the same rocket. Wow! I like this one because I knew the finishing was going to be easy no matter what size it was to be.

Before all the finishing was done, I had the chance to fly this and the other Hawkeyes at one of our monthly meets.

First flight was with an Estes B6-4 and the entire flight was textbook. The delay was almost right at apogee and the 12" chute brought the rocket down fairly fast but there was no landing damage even on our hard packed desert.

I have been using the Estes B4-4 in our local park launches on most of my smaller rockets and have been very happy with their performance. This was the same with the next launch of the Hawkeye although the height was slightly lower (I think) and the delay just after apogee.

After some more flights of my other rockets, the last flight for me was this Hawkeye on a C6-3 motor. This one really got up there and the delay was a bit short. The walk, however was not! Even with the small chute, once the wind came up, I was taking a good hike to get it back.

The Kevlar® to elastic shock cord was holding up just fine. The chute, although small, was doing its job nicely and the rocket was flying straight and true. What more can you ask for?

I didn't start out building this for the 2008 EMRR Challenge contest. I started with the Mega Hawkeye kit. But for some reason I liked the look of this one and was quite surprised at how small the original was. At that point I decided to make the scratch upscales and there was my contest entry.

The Mega Hawkeye kit was a snap to build, I had all the parts I needed to do the other size ones, and things just happened. If you are interested in doing an upscale of your own, you might just take a look at the Hawkeye. It was fun to build and flies with the best of them.

comment Post a Comment