Gravity Mechanisms - In flight
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- Опубликовано: 12 сен 2024
- This video shows a couple of common mechanisms often used as a basis for designing parachute deployment mechanisms for water rockets. We demonstrate how these behave in actual flight and why they can't be used reliably to detect apogee.
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See previous experiment with mercury switches (Jan 2010)
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When we first started out in rocketry we too thought about a similar system. It is very counter intuitive when you see the mechanism work perfectly well on the ground.
Thanks Ruben. :) Tinkering with designs is one of the fun things in rocketry. :) Tomy-timers are definitely one of those nice simple solutions that tick all the right boxes. Cheap, light, small and effective.
Hi DogLover, I think the best kinds of mechanisms are that detect apogee either barometrically, magnetically or using accelerometers. This way the parachute is always deployed what ever the flight profile is. They tends to be a little more expensive though.
This is a great question. The thrust phase is really stretched out with foam. We haven't tried it yet, but would like to. I think it will still happen when thrust gets lower than the drag force but may happen at double the altitude.
Dean Wheeler's Simulation predicts about -1.6G after burnout. Yes, a smaller nozzle would increase the burnout delay. It may be interesting to see what happens with foam with a much more gentle acceleration/deceleration profile.
Now this would've saved me a lot of tinkering in my days.... I knew by the end the trigger fired at burnout, so short flights! I got the best results with the tomy-timer models. Thanks! Great informative video!
I agree, a lot depends on the rocket and how long the boost is. It can take a second or two also before the parachute is fully out and fully inflated. By this time the rocket can be getting close to apogee and look like the system worked.
Very nice and informative George, as always.
If you get a bottle, and a tube that fits loosely outside it, attach the tube to the top of the rocket, and use the bottle as nosecone/parachute bay. It will open from side ways drag and centrifugal force (aka rotational inertia)
Thanks bruba95, we had fun doing this experiment. :)
I used to just put a golf ball in the top of mine and have the nose cone with the parachute inside friction fit on to the rocket. That seemed to work pretty well, at least for smaller rockets.
We use a barometric logging altimeter that samples at 10Hz and has 1 foot resolution. We just download the data from the altimeter to plot it.
This is a cool experiment, George. Do you know how many negative G's after burnout? Maybe a smaller nozzle would keep it from triggering too early?
What kind of a rocket do you fly your mechanism on? Do you have video of your rocket in flight?
That's exactly the point of the experiment. Mechanisms similar to these can often deploy at max velocity. :(
How did you get the graph, was it by estimation through the camera or do you have electronic and software device to detect altitude with precision?
Nice experiment. :) But after I saw experiment I was confused. I use a simple circuit with "free weight inside a tube" as apogee detector and it always open the parachute immediately after apogee. So why my result is different from yours?
How would it react with a foam launch? Did you try that?
No, i don`t have a video with rocket in flight :( . It is (as configuration) Polaron VIIIx but , as I said, I use a simple circuit to open the parachute door and it does its job well. I almost finish Acceleron V and should I change the circuit system to a more precise or "safe"?
After the earlier question on another video, now I ask you about the magnetic apogee detectors (read on a comment to NDogLover). How do they work?? Thanks again!!
They sense the direction of the Earth's magnetic field. When the rocket tips over at apogee the direction of the magnetic field flips in relation to the rocket and you detect apogee. They are pretty neat bits of kit. :)
I imagined soething like that but man! the compass must be quite precise for not making a false positive detection due to rocket vibration, right? I guess it's a digital compass?
DoNotPushHere It's quite robust as the magnetic field lines actually aren't parallel to the ground but they are more perpendicular over the majority of the Earth. The closer you get to the poles the more vertical they are. The detector can deal with rocket spin as well as the rocket flying in an arc. Depending on your launch location and the angle of the magnetic field with the ground, the sensor will be able to detect the rocket tipping over differently in different directions. For example the rocket may need to go through 100 degrees East- west, but perhaps 110 degrees North-South before it will detect the flip.
Perfectly clear now. Thanks for all!
I tried something like this and the parachute came out right at burnout altitude but the rocket came apart and I thought that is what made the rocket deploy.
This is interesting... I am trying to make a mechanism to tell my parachute to open on a HAB (High Altitude Balloon). I am unsure on leaving it under the Balloon in case of entanglement, but I'm not sure if a mercury switch will work... (I have a small budget).
+Sorted Science Interesting problem. I would imagine a balloon near apogee could potentially go up and down a few times before it bursts, and deploying a parachute too early could be a problem.
+AirCommandRockets Thanks for the reply! This is what I'm worried about... I can't think of a good way to ditch the balloon and pop a chute, yet I don't want to use mini computers.
+Sorted Science Are you flying a phone on it? You may be able to use its on-board accelerometers to sense when you begin free fall.
+AirCommandRockets I hope so. Great idea. But I'm not sure how I will link the phone to the 'detacher' and 'deployer' as I have not much experience with programming.
+AirCommandRockets I just thought of the airflap method... would that be any good?
Those switches already exist and are cheap and small,lightweight so brobably not worth the effort to make them yourself,still good to think about different systems.
Sure, this approach would also work.
Thanks for posting! I thought myself about a mechanism like this, but now I know it will not work =)
But if your flying with water only, you probably wouldn't want the parachute to be deployed at burnout. I don't want the think what would of happned it the parachute came out at that speed. :)