ScottMcLeod

I need some design software to help me work out the design for a physics project i'm doing at the moment.

Basically what i'm building is a glider that launches vertically via the use of 2 C-sized rocket engines, then from the top of it's flight, glides down to the ground.

FYI, i've gotten the approval of the rocketeer that's come to the school to help us with the project, so don't lecture me about using RC on rockets.


I'm trying to design something I can cut out of foam, and mount everything into. The shape, I figgure, is going to be delta-like, with not too much wingspan.


My second question is what's a cheap way of building a foam cutter...? Any ideas?

tiggerinmk

Some time ago back in the UK, I had an Eestes starter kit with a foam model space shuttle.

If I remember correctly, the shuttle was just made of white foam with a hollow centre in which was placed a card roll. The card roll held the rocket motor and the parachute.

The shuttle was launched from a standard rocket launcher supplied with the kit. When the motor burnt out, the ejector charge would shoot the card tube from the shuttle which would descend with the aid of the parachute while the shuttle glided back to earth (at least that was the theory).

I believe Eestes did once sell an R/C rocket aircraft, I saw one once on ebay. I don't know if you can still get these.

Looking into both the Eestes shuttle and R/C rockets should give you some ideas of what's possible, of course using multiple rocket motors adds more complication to an already interesting project....

BMatthews

Actually the problem is the other way around. It's against the rules to launch rockets FROM the RC models.....

Anyway, there is a recognized class for RC rocket boost gliders. Most of these look like slightly small discus/hand launch gliders. But for some reason I can't find much about it picture wise on the net just now.

I'm not sure what you mean about software to help you design your model. We mostly sketch up something based on the basics and then choose an airfoil based on what we want the model to do.

I suspect you're going to find that the delta planform doesn't glide all that well if your goal is to catch thermal. Too much drag at high angles of attack.

ScottMcLeod

The goal is ultimately just to land the damn thing, and do it with a bit of style.

I've got a microreceiver (9 grams), and i'm getting servos soon... (2 servos + elevon mixer)

-Scott

Couch-pilot

Boost gliders... lotsa fun!

Search the web for Estes "Strato-blaster", "Astro-blaster", or "Sweet-Vee". 3 great kits they used to make. These would be a great starting point as they're tried and tested. Oh, they're not deltas either - deltas usually glide like bricks...unless they're big.

If I can dig out my kit, I'll see if I can scare up a 2-view/3-view.

ScottMcLeod

Ugh. I've just realised that I may be in over my head on this one.

I need a material that I can cut easily, that's strong enough to survive boosted flight, and I need some kind of straightforward plan to implement this crap into.

I've got the radio equipment solved, now for the plane :-(

5 weeks... I wonder if it can actually happen.

Couch-pilot

Relax, bud! Balsa and white styrofoam!

Should take you a week tops...

tiggerinmk

"The goal is ultimately just to land the damn thing, and do it with a bit of style. "

"deltas usually glide like bricks.."

Falling with style, that sounds exactly like the Estes shuttle I had, it usually made it to the ground before the rocket motor pod.

Personally I'd ditch the on board mixer in favour of a Tx that has basic mixing functions to save a bit of weight. just my 2p....

R. C. Day

My Feedback: (7)

Scott,
I have five different hot wire cutters, all use the same power source, a 10A battery charger. The cutters are a section of wood (your choice of length) with two pieces of fiberglass exiting at a angle with a wire stretched between them.

I use a dimmer switch to control the temperature of the wire by changing the battery charger output.

I would hot cut the design and cover it with a 50%/50% mix of white glue/water and brown paper bag. How much cheaper can you get than that? You could vary the thickness/weight/strength by using wrapping paper instead of paper bags.

Wrap all of the design at once, don't want the paper to shrink unevenly and create warps.
Pic one, dimmer/charger
Pic two, wire bow

Questions?

R. C.

R. C. Day

My Feedback: (7)

Pic two, Wire (cutting) bow

mulligan

Regarding your "physics" question... which is actually an aerodynamic question:

For an object to be propelled by rocket, it must be fairly slender- launching a normal glider configuration with high aspect ratio wings would break apart and/or ascent would be wildly unstable.

For an object to glide well, it should have a relatively high aspect ratio wing.

Note the Space Shuttle is NOT a glider. Of course it must endure the violence of launch, so the wings are quite stubby. When landing, although said to be gliding, it is actually falling like a brick until it pulls up just before it hits terra firma. If this is all you need, the Space Shuttle is a good form to follow.

Otherwise, you will need to invent some pop-out wings that are triggererd either by rocket eject charge or RC servo- that would certainly add time to your project.

- George

tiggerinmk

A couple of things spring to mind:

1. Use a form more like Concorde. Fuse just large enough diameter to hold motor with large wings but still in delta form.

2. Look around at rocket sites for ideas:

How about the Transwing glider?
http://www.estesrockets.com/products/product166.html

Or the Nightwing?
http://www.estesrockets.com/products/product261.html

Bear in mind that for the most part we are not rocket people here, you may get more response from some of the many hobby rocketery sites around. I guess all you really need is a rocket incorporating some wing like those above that can carry the 'payload' of radio gear...

fly300s

I remember a few years back I built a glider that had an optional foliding wing. It was a flat bottom wing where the tips folded under to the root creating a half span symetrical wing. A servo could be used to pull a pin and unfold the wing. It was basicaly a "space shuttle design" that the wings could double in lenght at the flip of a switch for gliding. The only thing is that I had never flowen it, don't know what I did with it, or remember who made it.

ScottMcLeod

That's brilliant... I might try to use that.

BUT...

Great comment from Tiggerinva about the "Nightwing" (aka Concorde style)...

It's very do-able... light and probably wouldn't glide so badly.

tiggerinmk

Looks like a possibility....

http://cgi.*********/ws/eBayISAPI.dl...&category=2567

Couch-pilot

Scott, here's your baby...

ScottMcLeod

Out of aerodynamic newbieness, "high aspect ratio" meaning...? I'm slowly trying to learn aerodynamics between my other classes... :-P

Couch-pilot

Like a glider - long thin wings for high lift.

They tend to get torn off at high speeds - remember, this thing's going to accelerate to about 250-300 mph (note - MILES!) by the time it reaches the end of the launch rod (3ft.) on an E engine.

That's why the only "live" payloads you can use in model rockets are bugs - they're about the only thing (short of a well-packed egg) that can survive the acceleration.

Oh, and build it straight....REAL STRAIGHT! Otherwise you end up with an uncontrolled cruise missile that can go anywhere...

Have fun!

ScottMcLeod

So if my rocket/glider starts humping other manly-looking rockets, i've got a problem?

Couch-pilot

Put it this way, you'll be under the car with the rest of your buddies/class waiting for that E engine to burn out...

mulligan

Aspect Ratio (AR) = b^2 / S

b = wingspan
S = wing area

High AR means high wingspan, low area (long and skinny), which provides higher lift/drag ratio, but is structurally inherently weaker.

- George