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Fibreglass Bottle reinforcement - Initial Failures

Discussions about water rocket powered cars, sleds or boats.
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thampson
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Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Tue May 03, 2011 9:50 am

We had our first attempt at fibreglass wrapping a 2L bottle and quickly found out that its very easy to mess it up. We decided to document it on our website in quite a bit of detail as a how-not-to do it .. LOL

Lessons learned included -

Lesson 1: We have since learned that its a good idea to use tape along the lines to be cut, this stops the fraying
Lesson 2: Make the bottle holder so that the bottle can spin without touching it
Lesson 3: Try not to touch the fibreglass when its wet
Lesson 4: Use a rotisserie to rotate the bottle as it drys

Here are some pics of how it turned out.
fibreglass-attempt1 003.jpg
fibreglass-attempt1 004.jpg
There is a more detailed writeup on our website for those interested in the gory details :D
http://wrocket.hampson.net.au/?p=1485

We will try again and see how the next ones goes and share our progress

-todd-
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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by RaZias » Fri May 06, 2011 2:10 pm

I see your are aiming for high pressures with a 2 nozzle car, it makes me wonder if there will be needed a total upgrade of the stabilization system and therefor a massive weight increase.

Your car achived 48 km/h (I think), will the new achive 80 km/h or will it stay at 60 km/h due to the weight? Only the tests can tell...

-------- Now making some futurology about the WR-cars:

Since you have a 230 psi pump (I think) and a stronger pump will be harder to get, and more expensive will be the reinforcement the future of WR-cars will be the nozzle and volume increase, so at each record bigger and bigger the car will be...maybe one day we will se a 2 meter "beast" with wheels.

-------- About the speed record

For a speed record do you think a FTC WR-car would have more advantage since not too much volume is needed ?


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Sat May 07, 2011 12:53 pm

HI RaZias,

The next car will have 3 nozzles all 15mm ID. We will increase the size of the rear wings slightly but not massively, we are designing a stronger chassis which should be about the same weight as the previous car. So the power to weight ratio will be much higher than the current car.

Yes the last car achieved 48km/hr but we have designed the new one with 100km/hr as our target speed :) You are right, we will have to test to see how it goes.

With regards to the pump pressures our pump does go to 230psi, but we have been researching 2 stage pumps and some people in the spud gun community have achieved around 800psi out of 2 manual hand pumps in series. So you can get the high pressure with manual pumps but at these high pressures you dont pump much volume. So it will be interesting to see which way the development of the cars go .. maybe back to 1 or 2 bottles and very high pressures may be an option ? or as you say, the cars get bigger launching at 200 - 250psi range ?

Its interesting to see if someone will attempt an FTC car, I did see one that was similar to an FTC car a while ago but it was very unstable, even r/c steering wouldn't have helped. Its certainly a challenge to a) keep the water rocket cars on the ground, b) get them to go relatively straight ..

Any very light car will want to get airborne if the thrust to weight ratio is too high, then you have to look at adding wings to provide downforce to keep in on the ground :)

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by U.S. Water Rockets1 » Sat May 07, 2011 10:27 pm

thampson wrote:HI RaZias,

The next car will have 3 nozzles all 15mm ID. We will increase the size of the rear wings slightly but not massively, we are designing a stronger chassis which should be about the same weight as the previous car. So the power to weight ratio will be much higher than the current car.

Yes the last car achieved 48km/hr but we have designed the new one with 100km/hr as our target speed :) You are right, we will have to test to see how it goes.

With regards to the pump pressures our pump does go to 230psi, but we have been researching 2 stage pumps and some people in the spud gun community have achieved around 800psi out of 2 manual hand pumps in series. So you can get the high pressure with manual pumps but at these high pressures you dont pump much volume. So it will be interesting to see which way the development of the cars go .. maybe back to 1 or 2 bottles and very high pressures may be an option ? or as you say, the cars get bigger launching at 200 - 250psi range ?

Its interesting to see if someone will attempt an FTC car, I did see one that was similar to an FTC car a while ago but it was very unstable, even r/c steering wouldn't have helped. Its certainly a challenge to a) keep the water rocket cars on the ground, b) get them to go relatively straight ..

Any very light car will want to get airborne if the thrust to weight ratio is too high, then you have to look at adding wings to provide downforce to keep in on the ground :)

-todd-
It looks like you have not been resting since your world record runs! Cool!

A couple of suggestions: when you wrap your bottles you can make a holder by screwing a cap onto a wooden dowel. The bottle cap threads onto the bottle and you use the dowel as a handle. The bottle cap is made of LSE plastic, so even if you get glue on it, it will not stick to the cap, so the cap won't get stuck on and it protects the threads from getting gummed up.

It's really unlikely that anyone would get an FTC water rocket car to be successful, since the FTC tube does not hold much volume per foot, so the car would need to be 8 feet long just to hold the same volume as a 3 liter bottle. This does not seem like a practical design.


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Wed May 11, 2011 9:20 am

Thanks for the suggestions USWaterrockets :)

We are keen to get the next car operational and there are some challenges with some new tech for us to get our heads around .. all part of the fun :)

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by RaZias » Thu May 12, 2011 2:10 pm

I liked the idea of Red Bull 7 F1 car, I think they send accelerated exhaustion gas towards the rear wing to increase downforce.

I don´t know if a small wing (with mininal needed openings to let the nozzles connect to the launcher) that would catch the air release would increase ground effect.

In fact this reminds me to ask a question: why you quitted the horizontal rear wing tipical from dragsters cars ? It made no difference ?


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by Spaceman Spiff » Fri May 13, 2011 5:37 pm

RaZias wrote:I liked the idea of Red Bull 7 F1 car, I think they send accelerated exhaustion gas towards the rear wing to increase downforce.

I don´t know if a small wing (with mininal needed openings to let the nozzles connect to the launcher) that would catch the air release would increase ground effect.

In fact this reminds me to ask a question: why you quitted the horizontal rear wing tipical from dragsters cars ? It made no difference ?
I thought the wings on the back of cars was there to give the rear wheels more traction, so they would not slip and start spinning free. Once you break them loose they just start burning rubber and you go nowhere. The rear wing is not needed on a jet car I suppose.


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Sat May 14, 2011 8:00 am

Hi RaZias,

We took off the horizontal rear wing because I dont think we were going fast enough for it to produce any significant downforce. It was just adding weight. Looked good though :)

Thats why we went back to the corrugated plastic wings to reduce weight, we also tried out the 45 degree wing to see if it worked. IT seemed too, but I dont think it will be suitable for 100Kmhr+ of the car we are building now.

Adrian Newey is an aerodynamic guru, I will need to look into the RB7 a bit more to see what he is doing. We did try a an exhaust deflector on the last run of Green Hornethttp://wrocket.hampson.net.au/?p=1424

See the link above. I dont have any feel for how it performed, didnt seem to make a great difference, but again I havent really tested it out very well, so some additional development in this area may yield some additional downforce as you suggest.

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Sat May 14, 2011 8:08 am

Spaceman,

I have seen that a rear horizontal wing is not visible on any recent world and speed record cars, usually just a vertical fin for yaw stability. The rocket cars usually dont need a rear wing anyway as the wheels are not driven, unlike F1, and the body design is taking advantage of all the air going by to push the entire car down anyway.

For our previous cars we were having issues of the rear wanting to swap ends under hard thrust conditions and so we were trying to push the rear wheels onto the ground, as you suggest, by using a horizontal wing in order to give more rear grip. It did have limited success, but previously we had success with vertical fins stopping the rear swapping as well, so i dont think we have drawn any conclusions yet which is the best way to go.

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by U.S. Water Rockets1 » Sat May 14, 2011 10:45 pm

thampson wrote:Spaceman,

I have seen that a rear horizontal wing is not visible on any recent world and speed record cars, usually just a vertical fin for yaw stability. The rocket cars usually dont need a rear wing anyway as the wheels are not driven, unlike F1, and the body design is taking advantage of all the air going by to push the entire car down anyway.

For our previous cars we were having issues of the rear wanting to swap ends under hard thrust conditions and so we were trying to push the rear wheels onto the ground, as you suggest, by using a horizontal wing in order to give more rear grip. It did have limited success, but previously we had success with vertical fins stopping the rear swapping as well, so i dont think we have drawn any conclusions yet which is the best way to go.

-todd-
Todd,

Do you think that a large vertical fin would prevent the car from swapping ends in your design? It is not likely that your thrust is scaled down as small as the car from a true dragster, so you may be doing a small scale test on what amounts to a full size dragster with 10 times the thrust over a shorter time. That might not be so good in full size either... especially if you are scaling the gravel up to the size of golf balls.


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by RaZias » Sun May 15, 2011 6:54 am

I totaly suport the idea of a large vertical fin.

It seems that the WR-dragster follows the rules of a water-rocket and not from a car with wheel traction.

The WR-dragster is in fact a WR with a lower aceleration...and what happens to a WR with low accelaration ?...it doens´t create enough aerodinamical force to allow the wings to stabilize him, see the difference between a 22mm and a 9mm WR, the 9mm has a curved trajectory.

So since the WR-dragster has a lower accelaration than a vertical WR, the WR-dragster needs bigger wings compared to a vertical WR.


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Sun May 15, 2011 11:07 am

USWaterRockets,

When we started with the water rocket cars we had a 1 bottle car that we could consistently get to swap ends, 1 x 2L bottle 140psi ... too much thrust and around it would go. When we added some vertical fins it stabilised the rear of the car and it wouldnt swap ends, still wouldnt go perfectly straight, but generally in the direction we wanted it to go.

Also on our first two bottle wrocket car when we managed to control the swapping ends using vertical fins.

we tried it on the 3 bottle car I think but they may have been too small or the thrust too much as they didnt do much, so we tried the horizontal wing, then the 45 degree wings both of which had some success.

I think there is merit in the vertical fins, its a question of how big to make them and the weight of them. We really just need to size them appropriately to the thrust the car develops and the speed it is doing. Not terribly scientific more of a try it and see what works kind of exercise ... we will see what we get with the next car as the thrust will be approx 9 times more than our previous car .... and the weight we are oping for no more than 150% of the current car.

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by thampson » Sun May 15, 2011 11:27 am

RaZias,

thanks for the comments and your view on the merit of vertical wings. Its good to get the mind thinking and discuss the pros and cons with others. There is definitely merit in what you are saying, although I dont think its quite that easy.

We thought this as well and tried to get the car to behave more like a vertical rocket by letting the fins at the back straighten the trajectory of the car. A vertical water rocket when its flying through the air column vertically (y axis) doesnt need much force to straighten the rear of the rocket in the x axis as there is only the friction with the air column itself. With the car, to get the fins to straighten the rear of the car the force needs to overcome the friction of the rubber tyre on the road to push the rear of the car sideways back into alignment with the front of the car.

We tried to reduce this friction and make it easier for the rear of the car to move sideways by removing the rubber from the rear tyres. Theory being that now it takes less force to straighten the car which in theory could be achieved at lower speeds. In reality what happened was that the thrust just overpowered the rear grip (nearly nothing) and the car fishtailed and would have swapped ends if not for the r/c steering to save it.

The test was worth doing but it didnt turn out as we thought. So the water rocket car still does require the traction on the wheels and we cant eliminate this variable from the wr car equation so easily, well not at the speeds we have been going anyway.

When we up the speeds to 100kmhr+ we will be getting closer to vertical water rocket speeds and the force of the air on the wings will be more noticeable.

I think you are right that at slower speeds the car needs bigger wings but for them to work as well as a vertical rocket, they need to be very big (heavy) or the car just needs to go faster :)

We are working on the latter ;)

-todd-


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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by Freezy » Sat Mar 17, 2012 11:03 pm

OT: OT: But, how heavy is a reinforced bottle compared to a normal bottle.



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Re: Fibreglass Bottle reinforcement - Initial Failures

Post by U.S. Water Rockets1 » Sat Mar 17, 2012 11:13 pm

Freezy wrote:OT: OT: But, how heavy is a reinforced bottle compared to a normal bottle.
The answer depends on a lot of factors:

- The desired pressure
- The reinforcing material
- The diameter of the bottle
- The workmanship of the build

It is impossible to know the weight without knowing the details.


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