Interview with Tim May

Artem Kaznatcheev:

Well now, let’s start off with some basic questions. What would you recommend for young rocketeers to start off on their first rocket?

Tim May:

I suggest you go get a kit rather than trying to scratch build. Because there are certain things you need to know about balance and getting the fins right and whatnot. Hobby stores are really good for getting kits. There’s a couple of good names out there. There’s also in town right now a rocketry club to help you figure things out. If you can join a club, that’s fun too.

Artem Kaznatcheev:

What if your teacher tells you, you can’t build the rocket from a kit?

Tim May:

Engines, you don’t want to mess around with. Because it’s just too much trouble otherwise. If you’ve gotta’ buld your own rocket, the best thing to do is to get plans off the internet. If you try doing your own design, you’re going to fail.

Comes off the launch rod, spin around and just won’t fly right. So my best recommendation would be to go out and find a pre-made plan that can fly. There’s just too many calculations you’ll have to go through as a beginner to figure out the center of gravity and such.

Artem Kaznatcheev:

I went on the internet and looked up nose designs and there are different designs for different speeds. The lowest coefficient of drag is for a dome design which is used only for sub-sonic flight. My question is: Why are the designs with more drag used for sonic and supersonic speeds?

Tim May:

For rocket launching you want to get the shape right so that you have the best launch and flight characteristics. For certain levels of flight, you get more concerned about those shapes. When you get to the high levels of rocketry and supersonic speeds, where you are breaking the sound barrier, then the nose design becomes really important. For beginners it’s really not a big deal.

At low levels of speed the friction is different then when a rocket approaches the sonic barrier. The characteristic of air flying past a surface can change dramatically.

Artem Kaznatcheev:

Have you built many rockets?

Tim May:

Yeah, mostly from kits. Building from scratch takes too much work, figuring out where the balance is and stuff.

Artem Kaznatcheev:

What do you prefer for the number of fins on a rocket?

Tim May:

I would stick with three and four fins, because you want to get the stability. It’s a lot easier to come up with a jig that will split a circle into three or four parts. Balsa wood is a really good material for fins, but some people use stiff cardboard or plastic. The most important thing is how you glue things together, construction and such.

Artem Kaznatcheev:

For a beginner, what would be the best recovery system?

Tim May:

It’s fun to put out a parachute because it’s fun to watch it sail down. Unfortunately, if there is a lot of wind your rocket will get dragged really far. It really depends how much you want to run around. I prefer streamers. Just a couple of pieces of fabric to slow down the rocket. It makes it comes down much faster and closer to where I am.

Artem Kaznatcheev:

For us the hardest part was building the engine mount. What would you recommend for engine mount construction?

Tim May:

If you’re doing scratch build, some people will just take a used engine tube to get the spacer just right. Others take cardboard and just wrap it around. It really depends on the difference between your tube size and your engine size. If your tube’s much bigger, then it gets kind of complicated with all the spacer rings and such. Just remember to always have a hole on top.

That lets the secondary charge and the gases escape and push the parachute out.

If it’s a really big motor then get some metal clips to hold it in, because sometimes it’s too big and too heavy and just pops out of your rocket.

Artem Kaznatcheev:

For A to C engines, how long would you want your rocket?

Tim May:

You can make them as long as you like. I know some people that have small rockets that are 3 feet tall. Ostensibly, it will fly faster, but you have more weight on it. The bigger concern is the center of gravity moves up. And you want the center of pressure and gravity not to get switched around. If it’s flipped then the rocket just tumbles and that’s the number one problem with building from scratch.

Artem Kaznatcheev:

In general do you want the center of gravity towards the back or front of the rocket?

Tim May:

That’s where the center of pressure comes in. When you launch a rocket or an arrow, you want the drag at the back to keep the nose flying straight. You have to have that center of pressure working behind your center of mass properly. It really matters where the center of gravity is in relation to center of pressure. That’s where you don’t want those two to get flipped. You can pretest by adding a string to the middle of your rocket and swinging it around.

Artem Kaznatcheev:

Now more space related questions: what do you think of the DEEP impact mission?

Tim May:

I heard of it. They fired a copper slug into a comment. It was a pretty impressive challenge to get a rocket up there and have it point in there and blast. There were a lot of people watching it from earth to see what kind of change happened in the comet. It got quite bright, actually. They were actually taking spectra of what came of the comet. They actually got some new information from it. It was like a giant snow drift.

Artem Kaznatcheev:

What do you think of SpaceShipOne?

Tim May:

Spaceship one is a tremendous achievement. They did a marvelous job designing the White Knight and then it launched from it. I think it’s a great thing for rocketry in general. Maybe space tourism one day. We had some people in the same race, saying that they would launch from Kindersley. They say they are still going to do it. It would be great to go down and watch that go up.

Artem Kaznatcheev:

What do you think of the Chinese space efforts?

Tim May:

They want to have a presence in space. They want to compete with U.S and Russia. They’ve got the economy to do it. I thought they were going to try a mission to the moon.

Artem Kaznatcheev:

What about the United States goal to reach Mars by 2020 or 2025?

Tim May:

I have never been that excited about missions to Mars. I think… well… the politics are weird these days. I think eventually it would be great to get people out colonizing the planets. I would expect it would be easier to work with colonizing the moon first. Learn how to really run a base in a vacuum and such on a heavenly body like the moon, before trying to Mars. It’s a heck of a long trip up to Mars. A couple of years people flying up there to bring stuff back. Already with have several great robots up there and some satellites to take pictures. I think remote silence is really great, good value for the money. I think we should work it over on the moon first and then send people to Mars. Keep all that money for keeping some of the satellites up, like the Hubble.

Tim May:

How long did it take you to make the rocket?

Artem Kaznatcheev:

Our rocket actually…. It took longer then we expected it would. But it was around basically a day or two to make it. We had two successful launches. The first launch was very successful and the rocket went high. The second launch wasn’t as good. Our engine malfunctioned and both the primary and secondary charge fired at the same time.

Tim May:

Did you make your own launch pad and everything?

Artem Kaznatcheev:

No, no, no we were provided one by the teachers. Basically, four rods together and everything. One, Two, Three and launch.

Tim May:

For sure, want to have a countdown

Artem Kaznatcheev:

How long should the parachute strings be in relation to the length of your rocket?

Tim May:

It’s more a matter of how big the bonnet is on the parachute. Usually when I use a parachute I cut a hole in the middle to make it go down straight. The line length is not as critical, but the tie length from where it connects to the rocket and the nose is important. The elastic should be about the length of the rocket.

Artem Kaznatcheev:

How tight do you want the nose cone?

Tim May:

You want it to be, basically something you can basically pluck off with two fingers. You don’t want to jam it in there, because that’s too tight, the secondary fire isn’t strong enough. It won’t come off. You don’t want it rattling around, it is helping your rocket. If you can take your rocket and turn it upside down and the nose cone stays in place then it’s good.