Bottle Rocket B

User avatar
Toms_42
Member
Member
Posts: 143
Joined: November 17th, 2012, 6:57 am
Division: Grad
State: PA
Has thanked: 0
Been thanked: 0
Contact:

Re: Bottle Rocket B

Post by Toms_42 »

THE_ACE_ wrote:If a component opens. and nothing comes apart. is it considered separation. :D
I would be wary of it changing shape in flight intentionally. I don't have a B rule packet, but it used to be it could not change form in flight. I would file an FAQ if you are still unsure.
Image
chalker
Member
Member
Posts: 2107
Joined: January 9th, 2009, 7:30 pm
Division: Grad
State: OH
Has thanked: 1 time
Been thanked: 56 times

Re: Bottle Rocket B

Post by chalker »

Toms_42 wrote:
THE_ACE_ wrote:If a component opens. and nothing comes apart. is it considered separation. :D
I would be wary of it changing shape in flight intentionally. I don't have a B rule packet, but it used to be it could not change form in flight. I would file an FAQ if you are still unsure.
I don't see anything in the rules that says anything like that....;)

Student Alumni
National Event Supervisor
National Physical Sciences Rules Committee Chair
User avatar
Toms_42
Member
Member
Posts: 143
Joined: November 17th, 2012, 6:57 am
Division: Grad
State: PA
Has thanked: 0
Been thanked: 0
Contact:

Re: Bottle Rocket B

Post by Toms_42 »

chalker wrote:
Toms_42 wrote:
THE_ACE_ wrote:If a component opens. and nothing comes apart. is it considered separation. :D
I would be wary of it changing shape in flight intentionally. I don't have a B rule packet, but it used to be it could not change form in flight. I would file an FAQ if you are still unsure.
I don't see anything in the rules that says anything like that....;)
Oh, nevermind then! I think it used to be a rule in 2012/2011, but I can't remember. I guess a break-apart recovery is viable!

EDIT: nevermind
Last edited by Toms_42 on December 14th, 2014, 12:43 pm, edited 1 time in total.
Image
joeyjoejoe
Member
Member
Posts: 142
Joined: December 27th, 2012, 12:56 pm
Division: C
State: GA
Has thanked: 0
Been thanked: 0

Re: Bottle Rocket B

Post by joeyjoejoe »

I think I see where you are going chalker but I checked with a division B coach and there seems to be some blurb about the rocket not changing shape or deploying any type of recovery system.
chalker
Member
Member
Posts: 2107
Joined: January 9th, 2009, 7:30 pm
Division: Grad
State: OH
Has thanked: 1 time
Been thanked: 56 times

Re: Bottle Rocket B

Post by chalker »

joeyjoejoe wrote:I think I see where you are going chalker but I checked with a division B coach and there seems to be some blurb about the rocket not changing shape or deploying any type of recovery system.
Correct, there is a prohibition against changing shape, I missed that in the rules.

Student Alumni
National Event Supervisor
National Physical Sciences Rules Committee Chair
goodcheer
Member
Member
Posts: 155
Joined: October 27th, 2012, 7:09 am
Division: B
State: KY
Has thanked: 0
Been thanked: 1 time

Re: Bottle Rocket B

Post by goodcheer »

sciolympiad wrote:Hello, I know that parachutes are not allowed in Bottle Rocket but are wings?
Yes, Rule 3b speaks of using tape to attach fins and other components (like the nose, 3e).
SOCoach
Member
Member
Posts: 117
Joined: January 16th, 2003, 6:08 am
Has thanked: 0
Been thanked: 0

Re: Bottle Rocket B

Post by SOCoach »

I have a question that has been a mystery for me for several years.

I have coached Science Olympiad for years and done bottle rocket both as an event and also in my classroom. I have seen numerous back-slider rockets built by students over the years, usually consisting of three or four fins, a long cardboard tube (wrapping paper tube) and some sort of Ping-Pong ball or Easter egg at the end. On the first flight they perform beautifully . . backslide just like they are supposed to and land in one piece. On the second flight WITH NOTHING physically changed on the rocket they nose dive and destroy the cardboard tube. Why do they work on flight one but not on flight two, when nothing about the rocket has changed? At least nothing observable. I've seen this happen numerous times. Students build a rocket, test it once and it performs great. On the second flight . . . . it ends up like a lawn dart. What changes between flights? Anyone have any insight as to why this happens?
chalker
Member
Member
Posts: 2107
Joined: January 9th, 2009, 7:30 pm
Division: Grad
State: OH
Has thanked: 1 time
Been thanked: 56 times

Re: Bottle Rocket B

Post by chalker »

SOCoach wrote:I have a question that has been a mystery for me for several years.

I have coached Science Olympiad for years and done bottle rocket both as an event and also in my classroom. I have seen numerous back-slider rockets built by students over the years, usually consisting of three or four fins, a long cardboard tube (wrapping paper tube) and some sort of Ping-Pong ball or Easter egg at the end. On the first flight they perform beautifully . . backslide just like they are supposed to and land in one piece. On the second flight WITH NOTHING physically changed on the rocket they nose dive and destroy the cardboard tube. Why do they work on flight one but not on flight two, when nothing about the rocket has changed? At least nothing observable. I've seen this happen numerous times. Students build a rocket, test it once and it performs great. On the second flight . . . . it ends up like a lawn dart. What changes between flights? Anyone have any insight as to why this happens?
I haven't personally observed this, but can guess as to a couple reasons:

1. Upon landing the first time, the nose or fins are knocked slightly out of alignment, and in the rush get ready and launch a second time the students don't notice that
2. The first launch and landing weakened the fastening materials for the nose / fins. While not readily observable while setting up for the second launch, the force of the second launch is the proverbial 'straw that breaks the camels back'
3. Pure coincidence / luck with regards to winds. Again, due to time, students are careful to wait for the right moment for the first launch, but then rush the second one
4. The air tank supply isn't given enough time to get up to full pressure, thus there is reduced air pressure available on the second launch
5. The water from the first launch coats all the rocket components somehow, adjusting their weight and hence the center of gravity of the rocket

Student Alumni
National Event Supervisor
National Physical Sciences Rules Committee Chair
retired1
Member
Member
Posts: 676
Joined: July 25th, 2012, 5:04 pm
Division: Grad
State: FL
Has thanked: 0
Been thanked: 0

Re: Bottle Rocket B

Post by retired1 »

Actually, it is the bottle slightly changing shape and loosing much of its elasticity. We are not having the nose dive, but times drop several seconds on the second launch.
joeyjoejoe
Member
Member
Posts: 142
Joined: December 27th, 2012, 12:56 pm
Division: C
State: GA
Has thanked: 0
Been thanked: 0

Re: Bottle Rocket B

Post by joeyjoejoe »

I've seen this once or twice before (nothing like what you are seeing) and I always attributed it to air currents.
In order to understand my argument, suppose you were holding a 2ft long stick in your open palm against the current of a creek with the force of the current holding it against your hand. As long has you hold the stick perpendicular to the current, it would most likely stay that way due to the uniformity of the forces being applied across it's length. If, however, you placed it a bit off from perpendicular or if the current increased on one side for some reason, it would tend to point in the direction of the current, leaving your hand and float down the creek.

With a backslider, the CLA is typically a bit in front or coincides with the CG (see my previous post for definitions if necessary) and, as such, should fall sideways. If, for any reason, the nose is pushed down or the fins are pushed up, it is likely to nosedive - and once it starts, it will typically continue.
The probability of this is proportional to the weight in the nose cone and (I said I'd never give the secret up but, here goes) inversely proportional to the lateral area (shadow) of the nose cone- at least regarding the "coneys" or rockets with FTC between the nosecone and the pressure chamber (the latter is my favorite).
You see, increasing the nosecone weight increases the moment arm about the rocket's CG and increases the likelihood that it will tip downward if given a nudge by the atmosphere. This can be countered, however, by adding resistance to these forces in the form of a bulbous* (yet still aerodynamic) nose cone. This will obviously move the CLA up which is typically necessary on a good backslider anyway. In fact, it is possible to build such a backslider with absolutely no added nosecone weight at all. My last build was around 3ft long, 102grams with average 6oPSI launch times of 18s.

Remember, falling gracefully is much more delicate a chore than being forced to fly gracefully.
An F16 is proof that, given enough power, a rock can fly beautifully but just cut the engines and it gets ugly real quick!

* Google "guppied nose cone". Takes some practice to get right.
Locked

Return to “2015 Build Events”

Who is online

Users browsing this forum: No registered users and 4 guests