Faaaaark! - Model rocket build.

Afternoon all.

I've just sketched a model rocket design in a (ratehr dull!) meeting at work this morning, and thought you might like to see the development from sketch to first flight? I'll post the concept sketch, the CAD design, the build and the flight/setup video too.

Anyway, the idea was for a rather small little rocket that weighs next to nothing, and is nice and quick to build. being so small and light, it won't really fly off the launch pad, instead it will seem to explode off it instead! Obviously it is going to be going up quite high, especially when used with the bigger motors. I want to to be reusuable, and land in the same county as the launchpad, so it will be recovered using a streamer. All will become clear when I post the sketches/design images

I need to find a scanner now

Cheers
Andy

Right, it was that simple, I bypassed the design sketches, and went straight into CAD!



Estimated weight is coming in at around 18 grams, plus the motor on top of that (approximately 40 grams or so, depending on the rating of the motor). Some quick calculations on the back of a cornflakes packet give the following numbers (all assuming the use of a C6 motor):

Weight = 58grams
Motor impulse = 9Newton-seconds
Motor burn time = 1.5seconds
Average thrust = 6 Newtons (in reality the thrust has a very high peak at the beginning, and it tails off towards the end)
Maximum velocity = ~270 mph
Altitude at motor burnout = ~120 metres
Motor Delay (from when the motor thrust ends until receovery parachute is deployed) = 6 seconds
Maximum altitude acheived = ~470metres (~1500feet!)

So, I think it should get off the deck prety quickly, going from 0-270mph in about 1.5 seconds! The only problem is, that model is only about 300mm high (12 inches), and 18mm diameter, so keeping sight of it, is going to be tricky

Cheers
Andy

can't wait

sounds like you need to employ the services of a radar tracking station!

I managed to get the parts cutout for it this morning before work. It only took me about 25 minutes, and that included trimming a body tube to length (cardboard tube froman online supplier: http://www.modelrockets.co.uk/shop/index.php ), trimming the flash off the plastic nose cone (also from the shop above) , finding a bit of reasonably hard 2mm balsa and cutting/sanding the fins to shape.

All I need to do now is assemble everything, and get it painted! Fingers crossed I'll be bale to glue up the fins this evening. This is quite straightforward, although it is VERY important to get things lined up properly. The last thing you want is an unstable rocket moving at speeds of over 200mph! My method is to mark the body tube out carefully, then use medium CA to tack the fins in place. I then build up a fillet of epoxy/milled fibres around the root of the fin, and leave that to cure overnight.

If I wanted a really nice paint finish on a rocket, I would normally go over the parts with some filler/sanding sealer before assembling, but I'm not fussy, so I won't bother with this build. In fact, a slightly rough paint finish may help slow the rocket down a bit, and increase the chance of it landing in the same county as it was launched!

I'll get some pictures tonight.

Cheers
Andy

you need a jig for the fins andy. used one when i was a kid making these things. my dad made it from a few bits of ply worked a treat.

You know, I have just this minute been sat here wondering if I can knock something up to act as a gluing jig for fins.... I need a "Friday Morning Meeting" project to sketch out/design, or I run the risk of falling alseep infront of all the managers whilst they talk billhooks for a couple of hours

Hmmm. A universal jig to accomodate all sorts of body tube sizes, and all common fin layouts (120° , 90° etc)..... Sounds like a good project to me!

Cheers
Andy

Here's a pic of the parts ready for assembly. Nothing too complicated really!



Cheers
Andy

Finally, a picture of the progress from a few weeks ago:



The fins have been glued on using CA, and a small fillet made using epoxy and milled fibres. I just need to paint the thing now, so I'll be doing that tomorrow morning all being well....

Incidentally, the "wet" looking bit of the body tube, is where I have wicked in some thin CA. The nosecone gets inserted in here, so a bit of wear resistance is always good

Cheers
Andy

Just a little bit more work on this today. The fillets around the roots of the fins have been increased in size using some epoxy mixed with microballoons (a really stodgy mix, just enough epoxy to hold the microballons together, the aim to reduce weight as much as possible). I have also glued the launch lug on (a 3mm ID mylar tube).

The next thing I did, was prepare the recovery device. This is an orange streamer, about an inch wide, and 18 inches long. This is held onto the rocket using an 18" bit of kevlar cord (the cord going between the nose cone, and the inside of the body tube, with the streamer attached in the middle). The idea is that when the rocket reaches apogee, the nose cone pops off, the streamer comes out, and it comes back to earth pretty quickly, but not so quick it will damage itself.




The kevla cord is just tied onto the nose cone (it has a moulded in hoop) and bonded to the inside of the body tube, using a folded bit of paper to spread the load.










Finally I have given the tube a light sanding with 600 grit sandpaper, ready for paint. The only thing now, is to decide what colour! Any suggestions?

Cheers
Andy

Oh, I popped it on the scales too. Ready to fly (but without pretty paint) it is coming in a hefty 11.1grams. That's less than half an ounce!

It is currently more than 6 grams less than the design estimates, which is a 10% reduction. That is going to mean some pretty big performance increases, hopefully it will be sufficient to break the 300mph barrier

Cheers
Andy

I've just re-run the numbers based on an empty mass of 15g (so I have 4g for paint!), and I get the following numbers:

Weight = 34grams (inc motor)
Motor impulse = 9Newton-seconds
Motor burn time = 1.5seconds
Average thrust = 6 Newtons (in reality the thrust has a very high peak at the beginning, and it tails off towards the end)
Maximum velocity = ~310 mph
Altitude at motor burnout = ~135 metres
Motor Delay (from when the motor thrust ends until receovery parachute is deployed) = 6 seconds
Maximum altitude acheived = ~405metres (~1200feet!)

The Speed has actually gone up, and should break the 300mph barrier, especially on a warm day (air density drops, therefore drag reduces). To get to over 300mph in less than 2 seconds is quite some acceleration!

Interestingly, the lower mass, means it slows down a lot quicker in the coast phase (same drag force, less mass), resulting in a lower maximum altitude. In order to design a rocket to reach the maximum altitude (rather than speed, which was the aim of this design), it is a careful matter of juggling minimum weight to get the speed up, adding weight to increase the distance travelled upwards once the motor has burnt out, and of course, minimising drag.

Roll on launch day!

Cheers
Andy

Another busy day at work Andy.

Royb.

Indeed!

Calculations like that only take about 20 min on paper, or about 30s if you have created an excel spreadsheet with the formulae in

I've also been sketching another rocket design... Something that is at the opposite end of the spektrum to this build. Something big and heavy that flies low and slow with maximum smoke and noise!

Cheers
Andy

he loves his numbers. will this one crumple by the fins like the last one? like u said andy thats some acceleration u should multi stage it that would be a sight to behold

Hopefully not This one is a lot shorter than the black one with the cranked fins. That suffered from crumpling because of the length of the body tube (acting like a lever under acceleration).

Plus, I have used a longer insert in the body tube that acts as a motor stop. This spreads the load from the motor out a lot more.

Multi-staging, this one would probably not be stable with two motors on the back end. It would need a fair bit more fin area aft of the CG to get it stable under boost. That said, it should be quite easy to glue some basic fins to the 1st stage motor... Hmmmm. Some quick number crunching, and that is going to push the burnout velocity up around 400mph! The only issue might be tracking the thing. It is going to reach around 650m (~2000feet)!

The next rocket on the drawing board is a cluster. 3 * 24mm motors (D class) all ignited at the same time

Cheers
Andy

And you thought I had forgotten about this one! Well, the paint is finished, and it is ready to fly. Or disintegrate spectacularly!





The colours were chosen especially to aid recovery in long grass, and the best bit is that it has only added 3 grams to the airframe weight. That means the total is ~14g, and the performance should mean a burnout velocity of over 300mph!

Maiden this afternoon? I think so! I'll try and capture the thing on video too...

Cheers
Andy

It's flown!

There was a bit of breeze to contend with yesterday down at the RDMFC firing range, something that proved to be a bit of a problem!

The first flight was on an A8-3 engine, and it didn't half shift of the deck! It flew great on the motor, just canting into the wind slightly (indicating it was a bit over-stable), but it landed about 50 yards from the launchpad. The next flight was on a B6-4, and this was great. Not quite as quick of the deck, but a much higher flight. It tracked nice and straight, but drifted quite a long way down wind when the streamer was deployed at apogee.

Finally, a flight on a C6-5 was attempted. This proved to be only marginally stable, indiciated by a slight wigglyness under power. I lost sight of it way before the streamer was deployed, and never saw it again! Despite an extensive search of the field, nothing was found, so it seems it reached orbital velocity, and is still up there!

If any finds a bright orange rocket, about 11" tall, keep hold of it for me please! (regardless of the condition!).

I'm uploading a video now



Andy

And here's the video: https://www.youtube.com/watch?v=pjjxIccxREg

It is available in HD by clicking the little button at the bottom right of the window labelled, er, HD!

Cheers
Andy

Thats a great vid andy, nevermind design you have a future directing. I hope it turns up somwhere was a little monster

great video,Andy hope you find the Rocket

Afternoon all.

I'm putting a reward up for anyone who can recovered the Faaaaark! I don't mind what state it is in (I expect a Cow has munched at it or something), but it would be nice to get it back again....

Oh, the reward is a free press of the "launch" button to fire the next rocket I launch

Cheers
Andy

Ive had another couple of walks round but cant see it, maybe your right non of us saw it come down so it may still be up there

We had the video reconnaisence out this evening. Rich Badham kindly affixed his FlyCam to my glider, so hopefully, the eye in the sky will spot something orangey on the ground somewhere.

And if that doesn't work, then it is quite obvious that it never did come down, and it actually managed to acheive a low Earth Orbit velocity

Methinks the next model rocket build should be something that flies loud, low and slow, instead of fast and high!
Onwards!
Andy

TO INFINITY AND BEYOND - BUZZ LIGHTYEAR!!