Brief:
Rear engine type mini-motor powered boost glider. Designed to imitate the appearance of the SR-71 spyplane.

Construction:
According to a note in the kit, Apogee had a supply problem with the nose cones. So as to not delay delivery any further Apogee vacuformed their own nose cones as a substitute. The note went on to say that the vacuformed nose cone probably wasn’t durable enough and nicely included a coupon to replace it with a proper nose cone for free with my next order. More on this in the flight report.

The kit is simply packaged and the important little parts are thankfully sealed in separate bags. A nice thing I noticed also was that the kit came with spares for the little (easily lost) rubber bands that actuate the elevons. The instructions are very clear (except for one thing mentioned below) and the illustrations are excellent. The first thing I did was to apply balsa fillercoat to the balsa fins while they were still in their sheets. I do this because I find it easier to apply the fillercoat and even sand to a nice finish while its still safely in one big sheet instead of a dozen tiny pieces. Later I round the edges, usually after its been glued to the model. The instructions don’t say to do it that way, it’s how I like to do it. I’d also like to take a moment to advocate the use of Sig brand dope and fillercoat. Our hobby shop normally carries only Pactra products, which I hate. The Sig stuff seems to go on better, provide a nicer finish and the label even tel! ls you what kind of chemistry is compatible (butyrate, nitrate, etc...). The templates in the kit work well and the die cutting on the balsa was very sharp.

My only complaint about the instructions was in step 22. This regards the placement of the rubber band hooks for the elevons. Instead of a drawing, a photograph is used to illustrate the installation. Unfortunately, the photograph reproduces almost completely black in the critical area. I scratched my head a while and figured it out, but it would be nice if that were changed. I include a picture of the area on my model for other builders to consult.

Finishing:
Finishing is straightforward since the paint scheme can’t get any easier – flat black everywhere! My only reservation in this area is the lack of decals. I know a secret spyplane should have no markings, but decals are always the last cool touch to any model. Lets face it, our models spend 99.9% of their time on the bookshelf. They really are displays that fly once in a while. On the other hand, the model is a bit on the small side anyway and frankly looks great.

Construction Rating: 4 out of 5

Flight:
I made three flights, all using Estes A10-3T motors. Tim’s micro motors aren’t available in California for some reason. I would really like to try one. You load a motor into the boost pod, fold up the boost pod streamer, and insert the pod in the body of the SR-72. The pod has tabs that keep the elevons straight during boost. Boost was straight and with an A10 motor this thing really leaps off the pad. Wadding isn’t required.

Recovery:
On each flight, right after core ejection the model went immediately into a flat, fast, non-porpoising glide. I had a friend press the button while I waited with the binoculars, but the transition took place so fast I didn’t have time to watch it. Here in the desert we have mostly dirt and gravel, but there was no damage to anything on any of the landings. This is surprising since I expected the ventral fins to suffer.

I went to the launch site that day with several very skeptical model airplane building friends. I have to say we were ALL very impressed with the flight performance of this model. Completely reliable and with a remarkably flat, fast glide. I was really expecting this to perform like other cool looking delta wing rockets, which is to say I expected it to fall in a flat attitude instead of glide. I think I owe my success on this model to two things: light weight and correct c.g. position. Here are my weights:

Glider only, no paint, no ballast: 21.7 gm
Boost pod only, never painted: 8.4 gm
Glider only, painted, ballasted: 26.3 gm

Please look at the picture I included comparing my c.g. to the plans c.g. I did a lot of tests and my c.g. ended up about 1” behind the plans c.g. You should do your own tests. I’m sure Apogee did a lot of tests and they found the correct c.g. for them. Not much is said in the plans on how to test glide a model like this. I think this is very important! Grip the model where the chines meet the main wing. Throw it like a javelin at a 45 deg. angle as hard as you can. There is no other way to get enough speed or altitude to get a realistic view of how it will perform in actual flight! Many attempts are needed to average out the effects of asymmetrically releasing the model. Check the trim of the model. If it looks straight but turns hard you are probably not releasing it smoothly. Tim’s fear about the temporary nose cone I got turned out to be correct. I replaced mine with a spare balsa cone from Balsa Machining Service. Since it was balsa I could carve a little shovel effect into the nose thereby blending in the windshield a little better. This was slight and may not be visible in the photos.

Flight Rating : 5 out of 5

Summary :
My main cons are: 1) the illustration of elevon hooks, 2) the need for a more detailed discussion of how to test glide the model, 3) decals would make a great kit into a classic!

The pros: Overall this is a great kit and a great flier. Tim has done an excellent job of designing the kind of kits that got me excited about rockets back in the 70's.

I can't ever say the name of this kit without smirking. I always think of that scene in Spinal Tap where the amplifier "goes to eleven". It's an SR-72. That's one better now isn't it?

Overall Rating : 4 ½ out of 5