Orsus-Lite

Wingnut · **Posted:** Tue Jan 29, 2008 11:35 pm

I've just completed my first scratch design, which I've been working on since early January. I've named this rocket "Orsus" (i.e. "a beginning").

My objectives with this project were:
** Cheap to fly
** Apogee at 400ft on small-ish motors
** Diameter large enough to carry a timer or altimeter (i.e. 40mm)
** Trial a design for strap-on boosters
** Trial recovery deployment by electronic timer

I intend to build two versions of Orsus. This one – which I've named Orsus-Lite – is a light-weight prototype (115grams dry), 725mm long and flies on a 24mm motor.

The second version will be more robust, powered by an F or G motor and carry a timer or altimeter. Orsus-H will have pretty much the same dimensions as this rocket but will use stronger materials and thus weigh more.

Orsus-L began life in RockSim as an Estes BT-60 airframe. There's really nothing special in the design after that; maybe just separation mid-tube and piston ejection. Orsus-L can accommodate two strap-on boosters, powered by ½A3-2 mini-motors. They have their own ejection pistons and streamer recovery. Actually, the boosters have more scratch built components than Orsus: I reshaped conical balsa nose cones and made my own bulkheads, pistons, streamers and tube couplers. The strap-on's won't increase apogee altitude very much. I'm mainly experimenting with lugs to attach the strap-on's to the main airframe. I have a future project in mind that will need functional strap-on boosters. Hey Bones, that's where those BT-20 tube couplers will be going.

As you can see, I'm yet to paint the strap-on's. And fortunately, you can't see the dodgy paint job on the fins. The gloss coat wasn't compatible with the black and it got badly crazed. Then black dust "smudged" into the white when I re-sanded. Anyhow, it still came-up OK... Provided you're standing back far enough.

Orsus-L will make its maiden flight on a C11-5 motor. I originally intended to use a C6 motor, but in the later design phase I discovered that 6-Ns average thrust wouldn't be enough to reach 45ft/sec before leaving the launch rod. If she boosts OK and survives her maiden flight, I'll trial the strap-on boosters at the QRS launch on 10th Feb.

Any feedback and suggestions – especially regarding the strap-on boosters – will be greatly appreciated.

Bye,
Mike

matthew · **Posted:** Wed Jan 30, 2008 8:17 am

Cool looking model. I understand strap on boosters are quite a challenge, so you've certainly jumped in with both feet.

For your gloss clear coats, call into Woollies and pick up a bottle of Pledge One Go from the cleaning products aisle, and never look back. It's the Aussie equivalent of Future Floor Polish. It just works.

memberr · **Posted:** Wed Jan 30, 2008 8:51 am

Very nice.

I am keen to see how these strap-on boosters go

Rhodes · **Posted:** Wed Jan 30, 2008 11:28 am

Nice rocket Mike, I will be interested to see how your project progresses, the strap on boosters are very interesting.

astroboy · **Posted:** Wed Jan 30, 2008 5:53 pm

Hey Mike, very nice looking rocket. Strap ons are very much a challenge. member had an awesome non optimal flight with them back at our old site.
have you done a stability analysis on rocksim or launch for this design?

Scoop1261 · **Posted:** Wed Jan 30, 2008 6:10 pm

This..........I like!

.......But a C11???? Bah.... where is your sense of adventure??? .....Stick a D up it!

Bones · **Posted:** Wed Jan 30, 2008 6:50 pm

I dig the design a lot. That's some nice work on the spirals as well....

I see you have sanded around the spirals, dig you fill them with something or just let the undercoat do its job?

Wingnut · **Posted:** Wed Jan 30, 2008 6:55 pm

Well, after of those "encouraging" comments, I'm dying to see if my strap-on's actually do work. I probably should have built a dummy airframe and done a "static test", but I couldn't get any ½A3 motors before I started construction.

I've thought about what could go wrong. Here's some scenarios, starting from the bad end of the scale:

(1) One of the boosters could separate upon ignition; the asymmetrical thrust from the remaining booster causing Orsus-L to CATO. Kiss a month's work good-bye! Not a good look at my first club launch, and no more flying for me that day.

(2) The boosters could rip the lugs off the main airframe. This would mean a few hours of repair work. The boosters would be relegated to the spare parts box. However, Orsus-L will fly perfectly well without them.

(3) The booster lugs could prove "unreliable". If so, I will have a couple of options: (a) glue the boosters to the main airframe; (b) design some new lugs; or (c) just continue to fly Orsus-L without the boosters.

(4) The boosters could work perfectly... separating at T+ 2.3 seconds, while Orsus-L continues to boost majestically for another full second on the E9 motor, then coasts for six seconds, popping the chute right on apogee (~1,500ft).

Now guys... Where's your confidence in the abilities of a fellow rocketeer?

Astro, I checked the stability in RockSim. Static margin is still 1.6 with an E9 motor and no nose weight. The tips of the booster nose cones are 10-20mm behind the CP. I haven't done a simulation with the booster motors attached as yet, to see if I'll need to add nose weight.

Scoop, the C11 is just for initial flights. The target of the Orsus-L is to fly on E9's. I'd ideally like the main motor to still be burning when the boosters pop, and E9's will give me three seconds.

Mike

air.command · **Posted:** Wed Jan 30, 2008 7:13 pm

Mike I like the idea for the separation of the boosters. Very clever.

Just from observation, how tight is the fit between the nosecone and the main part of the booster? It seems if there is a little movement in the nose cone away from the main booster body, even a couple of mm then the booster could fall off sideways. This movement might be caused by vibration.

The design could be modified so that you have little tubes attached to the main rocket body instead of the lugs and have equivalent "pins" sticking out from the nosecone of the booster and pointing down, and same sort of thing on the bottom of the booster pointing up. That way the concept stays the same but you have a lot more vertical movement margin, as well as a lot of lateral strength.

If you are concerned about the booster lugs breaking off, you can test them by knowing what your maximum force will be on them based on the motor you use, and then turn the rocket upside down and just hang an equivalent weight (or a little more) on the lugs and see if they stay on. If they do then no problems.

Quote:

(1) One of the boosters could separate upon ignition; the asymmetrical thrust from the remaining booster causing Orsus-L to CATO. Kiss a month's work good-bye! Not a good look at my first club launch, and no more flying for me that day.

... but can you imagine how impressed they will be if it works! ... give it a go!

astroboy · **Posted:** Wed Jan 30, 2008 7:49 pm

Excellent work Mike. Sorry if I sounded a little pesimistic, by I approach my own projects with the same jaded eye, usually launching new design ideas with only a few people around. It wont usually be something that you think that goes wrong, it is usually something you never thought of.

i am gonna love to watch it all go to plan (all digits crossed!!) :lol:

Perhaps it would be best if we can organise to launch it either first thing or last thing. I have a glider design that needs testing without the crowds around so perhaps we can both do it at the same time.

Wingnut · **Posted:** Wed Jan 30, 2008 10:22 pm

Hi Bones, I filled the spirals with water-based wood filler called "Timber Mate" (white coloured) which I bought at Bunnings. I thin it right down with just a couple of drops of water. I let it dry for a couple of hours and sanded it back with 400 and then 800 grit sandpaper. You risk warping balsa fins if you use water-based filler on them. I have some fine acetone-based car body filler for balsa parts.

AirCommand, I've seen some pin/tube style booster lugs before. I was worried that they will bind if the booster gets slightly askew. So I mimicked the idea but used wedge shapes instead of "pins". The weight test is a great idea, just to help my confidence levels. Thanks! The maths is easy: divide Ns thrust by 4.448 to convert it to pounds. Multiply lbs by 453.59237 to convert it into grams. The booster nose cones fit tight and the coupler shoulder is 10mm long. I pulled it apart a little just for the photo... so you could see how the lug is attached to the nose. I did a "shake test" the other day. The boosters came off after a 3-4 seconds of vigorous shaking in the vertical plane. I did some horizontal shaking too, but I can't remember the result. All the same, I'll paint the couplers to make them fit a little more snug.

The lugs are wedge-shaped in two dimensions (see pictures below). Each set of lugs was cut with razor saw and labeled, so that they match perfectly. Under thrust, the rear lug should shelf-tighten. Well that's the plan. Vibration is my main concern.

Astro, a little healthy skepticism is OK. I was hoping to do the maiden flight this weekend, but I'm yet to finish building my launch controller. So I'd love to do an "experimental session" first-up on the 10th Feb, as long as there’ll be a ¼ inch launch rod available. Maybe that should be a regular feature of the QRS club launch days. 7:00am start with "Experimental rockets" and only a limited number of pre-arranged participants allowed on-site, then the public launch starting at something like 8:00am.

Hi Shane, I haven't really started on the rail. I asked for a quote on some aluminium welding in Dec '07 and guys still haven't got back to me after 2 follow-up calls. So I need to find someone else to do the welding but I just didn't have enough time to get around to it. However, my rail should be finished very shortly after I get the welding done.

Ciao,
Mike

Guppzor · **Joined:** Sun May 20, 2007 5:58 pm **Posts:** 455

I have a ¼" launch rod that I will bring on the 10th...

Kryten · **Posted:** Thu Jan 31, 2008 9:14 am

Mike wrote:

Maybe that should be a regular feature of the QRS club launch days. 7:00am start with "Experimental rockets" and only a limited number of pre-arranged participants allowed on-site, then the public launch starting at something like 8:00am.

That sounds like a good idea for all clubs. If the flight is somewhat dubious, the best place for this to happen is at a large site rather than a local park.
Any model for which flight characteristics may be suspect, the smaller number of people in attendance the better

astroboy · **Posted:** Sat Feb 02, 2008 11:53 am

Fine finish on that Mike, very nice indeed.

It would be nice if a few more of us made something like this to move development along on the seperation mechanism, I am yet to see anyone fly a successful clip on booster design. When I get the time I want to make a Bloodhound or English Electric Thunderbird like the one on the forum header. Hopefully you have some joy, and I can incorporate some of your design to make mine work.