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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Speed flap versus Tommy timer

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Braaainz
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Speed flap versus Tommy timer

Post by Braaainz » Wed Aug 08, 2018 11:57 am

Working up my first Tommy timer rocket, but love the idea of a speed flap.

I noticed that most seem to prefer Tommy timers. Is this just because of ease of construction? Or are speed flap really unreliable?



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anachronist
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Re: Speed flap versus Tommy timer

Post by anachronist » Wed Aug 08, 2018 2:19 pm

A speed flap will deploy your parachute when the rocket slows down sufficiently. It could still be going up, or be right at apogee. This is useful if you want to extend the parachuting time. There are contests for that, in fact there's a record here on WRA2 for longest duration flight.

Otherwise, if you aren't interested in maximizing parachuting time, a timer can be timed so that the parachute deploys on the way down. The lower you can deploy the chute, the less chance that the rocket will drift into a tree on the way down.



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Terranoid Labs
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Re: Speed flap versus Tommy timer

Post by Terranoid Labs » Fri Aug 10, 2018 11:21 pm

I tried the flap system for my first real rocket and didn't like it because it seemed difficult to get it to deploy in a reliable way. I also had a gut feeling that there was a bunch of added drag, so I switched to Tomy timers. I had instant success on my first iteration, so that's the road I'm headed down at this point. That being said, the 2.0 version of the Tomy timer deployment is 1 for 4 this week, so I'm kind of sitting here scratching my head and questioning my decision making. I know for sure that one of those failures was operator error and another was from not learning a thing from the previous launch fail, so I still have faith in the Tomy.

Side note - I started out looking at my local thrift shops for wind ups and found many of them are either broken or low quality. In my area there is a Party City store that carries wind up toys called Z Wind Ups that have very nice timers in them and they seem to be very robust. They go for $3.99 a piece, so not exactly as inexpensive as the stuff you'll find on Amazon or Ebay, but I haven't broken one on a crash yet.



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anachronist
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Re: Speed flap versus Tommy timer

Post by anachronist » Sat Aug 11, 2018 1:47 am

Terranoid Labs wrote:
Fri Aug 10, 2018 11:21 pm
In my area there is a Party City store that carries wind up toys called Z Wind Ups that have very nice timers in them and they seem to be very robust. They go for $3.99 a piece, so not exactly as inexpensive as the stuff you'll find on Amazon or Ebay, but I haven't broken one on a crash yet.
$3.99 isn't expensive compared to a deployment altimeter and servo mechanism. I recall spending $50 on launcher parts alone.



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Terranoid Labs
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Re: Speed flap versus Tommy timer

Post by Terranoid Labs » Sat Aug 11, 2018 5:12 pm

Ha, that is true. I'm trying to do this on the cheap, but it adds up pretty quick.



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addstogether2
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Re: Speed flap versus Tommy timer

Post by addstogether2 » Wed Aug 15, 2018 7:02 pm

Hi I also had problems when I started using tommy timers.
I totalled my first one as I was setting the delay for too long.

The best way is to use the simulators and then work out where to set your timer position based on how long you require.

Then trial and error for the fine adjustment.

Al


Life is like riding a bicycle. To keep your balance you must keep moving.
"Albert Einstein"

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retrotec29
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Re: Speed flap versus Tommy timer

Post by retrotec29 » Sat Aug 18, 2018 1:18 pm

I will second using a simulator as the first step in a successful tommy timer flight. I kill dinosaurs to.
IMG_20180607_195955552_HDR_1534612449879_1.JPG
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No matter where you go, there you are. Buckaroo Banzai

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addstogether2
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Re: Speed flap versus Tommy timer

Post by addstogether2 » Sat Aug 18, 2018 5:50 pm

Those Tommy timers look massive in the photo.


Life is like riding a bicycle. To keep your balance you must keep moving.
"Albert Einstein"

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retrotec29
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Re: Speed flap versus Tommy timer

Post by retrotec29 » Sun Aug 19, 2018 9:26 am

A little bigger than most. The gearing resists the winding of the rubber band well.


No matter where you go, there you are. Buckaroo Banzai

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