# Launching an airoplane using a mouse trap

hey, i have just recieved an assignment from school, in physics. we have to build a plane out of wood and figure out how to launch it using a mouse trap. we also have to keep a log book about it. i have a couple ideas already but otherwise i am stuck and i was wondering would anyone have some suggestions for me. i would greatly appreciate it. thanks.

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Danger
Gold Member
gangsta_jme4 said:
i have a couple ideas already but otherwise i am stuck and i was wondering would anyone have some suggestions for me.
How about you post your ideas first, and we'll have a nice little round-robin critique to decide if they're practical or not. Anything that you do for a project should be your own idea, but folks here will be happy to help you fine-tune it. One tip though: don't use ironwood or oak for the plane, or you will need one honkin' huge mousetrap.

Well, i was thinking of doing a type of catapult thing, using a piece of string to hold down the the catapult, and a piece of elastic to move the catapult. The mouse trap should be set off and detach the string, and because the elastic is pulled really tight it pulls the catapult arm up into the air, where the plane is then shot forward.

The plane is going to be made out of balsa wood.

Danger
Gold Member
Welcome back; I thought that my previous response had killed yet another thread.
I didn't realize that extra components such as elastics were allowed. It seems to me, though, that the things you have mentioned are actually decreasing the efficiency of the launch. If your plane has a small hook under the nose for a launch attachment, then anything that can get the string moving quickly in a shallow take-off angle will work. My initial thought before you mentioned extra materials was to just have the string tied to the the trap arm. If you're allowed extras, might I suggest that you use the elastic to supplement the original spring in the trap, so that it has far higher release energy? If the aeroplane design isn't mandated, try to make actual airfoil shapes for the wings rather than just flat balsa. That's where the lift in a real plane comes from, and it will greatly extend the flight of your toy bird. Also test various trim configurations to get the flight path the way you want it. (ie: if your plane tends to pitch downward, add a touch of positive elevator. If it pitches up, add negative elevator. If it veers to either side, tweak the ailerons.) It's also a good idea to have some significant weight in the nose, such as a clamp-on fishing sinker.

I thought that we were aloud to use extra components, but found out that we aren't. I like your idea about the airfoil shape wings, that will help alot with the lift. We have kind of changed the launching material, and i would love to tell you but it is really hard to describe at the moment because we haven't fully worked it out yet. But having a hook under the nose, wouldn't that cause parasectic drag and slow the movement of the place down. I would have a picture attached but I don't know how to do it.

Danger
Gold Member
gangsta_jme4 said:
But having a hook under the nose, wouldn't that cause parasectic drag and slow the movement of the place down. I would have a picture attached but I don't know how to do it.
It should be unnoticeable. 'Hook' was kind of a sloppy word to use. I just meant some quick-release attachment point under the nose of the plane where the launch cable (string, whatever) fastens on. Best would probably just be a small screw not quite screwed all the way in. If the plane is light enough (I don't know how big it is), the screw could also be used as your nose weight in place of a sinker or such-like. Also, if you're not allowed even a string, a screw would give a good solid grab directly to the trap wire without binding on release.
If they don't specify the model of mousetrap, get the biggest rat trap you can lay yours hands on. Some of those suckers could launch a small Cessna.

thank you heaps for your help. if i need anymore i'll put out a new post. THANKS HEAPS.

Danger
Gold Member
gangsta_jme4 said:
THANKS HEAPS.
You're more than welcome. Good luck with it. Let me know how it turns out.

saltydog
Homework Helper
Well, I wanna know too. Two suggestions: Get two mouse traps: detach the spring on one of them and carefully study the motion of the arm in order to adapt it's motion to your design. Also, the sudden jolt of the trap releasing will put strain on the plane which may cause damage. You'll need to provide some sort of "absorbing" mechanism to handle this I would think.

Danger
Gold Member
saltydog said:
You'll need to provide some sort of "absorbing" mechanism to handle this I would think.
What?! Balsa can't handle 100 g's?!
That's a good point, Mr. Dog. The simplest solution in that regard might be to use a semi-elastic cord as the 'tow-line' (perhaps a fabric type such as is used for the waistband in trousers). Elsewise, the nose hook could be screwed into a chunk of soft rubber that's firmly attached to the plane.

saltydog
Homework Helper
I'm thinking if I had a mind to, I could get one to go about 50 feet. However, I believe it's possible with the right talent working on it to go up to 300 feet on a calm day, with a aerodynamically efficient design as well as a optimized launch mechanism (get it high in the air and just glide the rest of the way).

Edit: Oh yea, I mean a rat trap, not a mouse trap. You know the difference: rat trap would break your finger. A mouse trap would just hurt it.

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saltydog
Homework Helper
I wish to revise my estimates: I feel using a regular house-hold rat trap, I can get a plane 100 feet but I think the maximum distance would be around 200 feet. Of couse that depends on the size of the rat trap. With a large enough one, I suppose I could strap two wings on my pick-up truck and fling it 300 feet. Thus there must be a lower limit. One could pose the question: Just how large would a rat trap have to be to send a normal size model airplane 300 feet?

I've come up with what I think is an optimum launch design which captures the full motion of the spring: Build a ramp as some angle. Mount the trap on the vertical wall at the end of the ramp, and attach a catapult spring to it, a roller at the edge and a hook to attach to the plane. This is similar to, except the rat trap, to what's used in an aircraft carrier right? Now one needs to figure out what is the optimum angle and the best aerodynamic design.

Consider trying to launch a javelin by hitting it with a hammer.
However hard you hit the javelin the hammer remains in contact with it for only a small amount of time - therefore not much energy is transferred and the javelin won't go very far. It's better
if you apply a long slow accelerating force - like a throwers arm/hand.

The mouse trap launcher is similar. You need to slow down
the energy release.

At the start the energy is in the trap's spring - Potential Energy.
You need to transform that energy into kinetic energy - in the plane.

You also need to consider the velocities.
The plane's kinetic E is = m . v . v / 2 ( m is mass of plane )

You must match the final velocity of the launch mechanism to
that of the plane. This requires some sort of "gearing" or "leverage" of the mouse-trap arm so that it releases its energy
at an appropriate rate.

The Physics I leave to you...

saltydog
Homework Helper
Gotta' work. Down there.

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Danger
Gold Member
saltydog said:
Gotta' work. Down there.
You might want to inset that top pulley to just above the ramp, there, Salty. Elsewise the plane's going to smuck right into and kill the pilot. :tongue:
Great design otherwise, though.

for my interest, does the plane has to be in a shape of a plane, i thougth that some small and light, some thing close to a ping-pong ball or something smaller and lighter could work better. it is very hard to imply the real lift and make a real nice plane which glide on most occasion.

multiple mouse trap, that sound very pleasing to me

saltydog
Homework Helper
ArielGenesis said:
for my interest, does the plane has to be in a shape of a plane, i thougth that some small and light, some thing close to a ping-pong ball or something smaller and lighter could work better. it is very hard to imply the real lift and make a real nice plane which glide on most occasion.

multiple mouse trap, that sound very pleasing to me
Really Ariel, I'm thinking washing machines, TVs, microwave ovens, toilets, kitchen sink too. We'd need a much bigger moust trap of course. The only requirement is that it should have wheels, wings, and a nose cone. I mean with a large enough one, Danger could help me build some light-weight wings for my old pick-up truck. I'd spray-paint on the side of it, "PF POWERED!"

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Danger
Gold Member
saltydog said:
I mean with a large enough one, Danger could help me build some light-weight wings for my old pick-up truck. I'd spray-paint on the side of it, "PF POWERED!"
Love it, man! Some aluminum, some rivets, a couple of Brewnog's surplus Rolls-Royce Olympus engines... use the mousetrap to trip the starter switch... :rofl:

Danger
Gold Member
Something else dragged itself up from the dark depths of my memory. A few decades ago some engineering students were trying to make a more efficient paper airplane. They found that an abrupt step down on the lower side of the wing about 1/3 - 3/4 of the way back, which increased the thickness by about 50%, drastically improved the glide distance. It might work on your model as well.