Thảo luận tên lửa tách tầng

[huynh_ngoc_long_88]

Trong tất cả các loại tên lửa, thì tên lửa tách tầng ( 1 tầng dùng để bay, khi đạt đến độ cao nhất định, tầng này sẽ tách ra, và tầng trên sẽ đưa tên lửa bay tiếp) là khó nhất...>"<.

Nên mình mở Topic để các ban thảo luận hướng giải quyết và chế tạo.:sm (2):

[huynh_ngoc_long_88]

Đây là tài liệu tiếng Anh trên mạng, dạo nì mình hơi bận nên chưa dịch kịp ra tiếng Việt cho các ban.


Water Rockets - 2 Stage Rocket

The 12 litre rocket was originally intended to be a 2 stage rocket but I couldn't find the parts that I needed for the stage mechanism. After over six months of looking around, have come up with a working alternative (in size - not design) to Bruce Berggren's staging mechanism. The rest of the rocket is pretty much the same as for the 12 litre rocket.

Just to make this rocket a little different to the others, I decided to make it entirely from green bottles (I am not a heavy drinker by any means and getting the 3 litre bottles (only 3 litre cider bottles of a particular brand were suitable at the time) took some time to collect)

Construction
Putting bottles bottom to bottom is the same as with the 6 and 12 litre rockets which I will not repeat here (see the 6 litre rocket for details).
I made the fins for the sustainer in the same way that the fins for the 12 litre rocket are made, only making them slighly narrower. Each one has a slight twist at the bottom so that a spin of one to two turns per second is induced so that any error in the angle of the nozzle cancels out during the 'burn' (around 3 seconds for the water part of thust).
Each bottle join uses a skirt and with the exception of the 2 - 3 litre join, they are all made from the side of an appropriately sized bottle. The join between the 2 litre and 3 litre bottles was made from the side of a 2 litre bottle and the top of a 3 litre bottle. I marked out and cut the hole in the top of the 3 litre bottle and cut it to length as in the diagram on the left.
The idea behind the double support like this is that the 2 litre skirt supports the weight of the top 6 litre section, taped (or glued) at the skirt's top (being the same diameter), and resting on the shoulder of the lower 6 litre section; and the 3 litre skirt, is taped to the lower 6 litre section (being the same diameter) and supports the side of the 2 litre skirt, hopefully reducing any tendency of the rocket to bend. Unlike the 12 litre rocket, the top section just sits on the bottom section and is free to separate. I taped all of the skirt joints that needed taping but there is no reason why you should not use glue instead.
Note. Before you cut the inter-stage skirts to length, you should first make the Stage Mechanism
Once you have done this, cut the length of the 2 litre bottle diameter skirt so that the nozzle of the sustainer goes into the booster part of the mechanism far enough for it to be able to grip but with a sufficient gap for the one way valve to operate without being jammed against the end of the sustainer nozzle. Start by making it slighty too long and then trimming it as this cannot be done if you make it to short. If you do make it slightly too short, you can increase the gap again by adding extra Blu - Tack to the seal in the sustainer nozzle.
Recovery
Booster: As the primary objective of the booster is to get the sustainer moving as fast as possible and then to fall away thus allowing the sustainer to continue on its ascent, I decided to have a go at making a booster without fins. The booster only affects the flight of the sustaner while it is thrusting and during all of this, the thrust is axial. Fins on the booster would not have any significant effect on the sustainer. Without fins and without the sustainer, the centre of mass (COG) of the booster is roughly in the same place as the centre of pressure (Cp) and therefore there is no reason why, once it has finished its thrust and jetisonned the sustainer, it should point in any particular direction. If it is pointing sideways, it will fly a lot slower than end on so the booster should just tumble to Earth.
Sustainer: If the sustainer was to hit the ground after falling from 400 - 500 feet, it would do serious damage to itself, therefore it needs some type of recovery to reduce this velocity. With such a long duration of ascent - using a restricted nozzle for a long burn - the rocket has a good chance of going too fast for an NSA deployment method to deploy. One thing is for certain, however, and that is that if the rocket is stable, it will be pointing downwards during the descent.
With the recovery method chosen here, the water that makes the rocket stable during ascent, pours out of the rocket when it tips over and, as the rocket loses weight at the front, the centre of gravity moves rearwards, soon making the COG and the Cp fall within 1 rocket diameter and therefore become aerodynamically unstable and, hopefully start to tumble, hitting the ground a lot slower than it would without (24m/s for straight descent and a lot slower for a tumbled descent).
I managed to make the sustainer have the COG and Cp in the same place (coincidence I assure you). The recovery is simply the top 5" (12.5cm) of a bottle with the neck cut off with a soldering iron. This is taped to the top of the sustainer and water is added when it is in posisition at the launch. The rocket empty (apart from a small amount of water in the top bottle, representing what would be left after a launch) weighed around 200g. to move the COG forward by 1 body diameter, I found that I needed aproximately 75g of water making a sustainer weight of 275g.
Water
Pressurising to 6.5 BarG (95 psig) the amount of water required is approximately 2.25 litres in the booster and 1.15 litres in the sustainer. This should get it (with a 5mm nozzle) to around 450 feet. The water runs out at around 180 feet and it gets to apogee just before 6 seconds. If the recovery fails, it hits the ground at least 6 seconds later at a speed of 32 m/s or less (the deviation from these figures depends on how much weight it has lost by shedding the nose weight). Staying in the air for such a long time (over 12 seconds without tumbling or weight loss means that it has to be launched on a very calm day or great distances may have to be travelled.
On the way up, during acceleration, the water is forced away from the opening in the nose. During decelleration during ascent and during descent, the water goes towards the opening but during ascent, (hopefully) the water will tend to stay inside, only emptying when the rocket is inverted.
This is what was planned. Have a look at the pictures to see what actually happened (I think I'm beginning to get old :-)

To the pictures . . .

Stage Mechanism

This is an adaptation of Bruce Berggren's Crushing Sleave Staging Mechanism which can be found at http://www.geocities.com/wrgarage/stage.htm .

I have adapted it so that it can be made with the materials that I could find in the UK. There seems to be a lack of materials that are suitable for the making of water rockets in the UK so here is what I came up with (after searching the shops and everywhere else for over six months).

For computer modelling purposes, it has a Stage Mechanism Diameter of 15mm and a release differential pressure (with one hose band) of around 45 psi or roughly 3 Bar. The latter can be increased by using extra or wider bands.

Materials

To make one of these, you will need:

• Two bottle tops - the type with a thin, plastic sealer in them;
• around 1" of 21.5mm PVC Pipe (just normal overflow pipe);
• around 5" of 15mm PVC Pipe (this stuff is pretty neat (it is made from three layers - picture on the right) but it appears to be standard. It is marked with the following - "Speedfit 15mm B-PEX to BS7291 : Part 3:1990 Class S 12 BAR 20ºC - 4 BAR 82ºC - 3 BAR 92ºC 9927/0609/279");
• around 4" of 20mm o/d transparent, flexible PVC Hose (garden irrigation type - it fits snuggly inside the 21.5mm o/d PVC tubing);
• around 1/2" reinforced Garden Hose cut into two pieces around 4mm wide;
• 22mm Tube Inserts (Speedfit J158 for polybutylene pipe (see15mm pipe above));
• 15mm Tube Inserts (Speedfit J157 for polybutylene pipe (see15mm pipe above));
• two Paper Clips;
• a Plastic Bead;
• some Blu Tack or similar - epoxy resin may do this instead for the bead - see construction details below;
• some PET plastic from the side of a bottle; and,
• some 4mm to 5mm i/d plastic pipe (keep your eye open for this stuff - lolly handles, child's balloon sticks (a balloon on an adaptor on a hollow stick - the type that they get given as a store promotion when you are out shopping and they quickly become a liability as the balloon bursts and the little dear wants another one:-).

Construction
Nozzle

1. Make good the end of the 15mm pipe using a pipe cutter. This pipe will cut okay but once you have got through to the blue plastic (which is very ductile and will stretch instead of cut) you have probably weakened the inner part of white plastic enough to finish the job off with a sharp knife. Make sure that the end is flat but DO NOT get rid of the burr on the inside of this end.
2. Using the same cutting technique, cut the other end giving you a tube around 11cm long. Remove the burr at this end (the water will flow into the pipe through here so it needs to be reasonably smooth).
3. Get one of the 22mm Tube Inserts and ram the inlet end of the 15mm pipe into the end without a flange (as per the picture on the right). Use a small hammer but don't hit it too hard or the 22m Tube Insert will split (it may not do this straight away so if you have hit it too hard, you may not know until it is too late). It is tight enough when you can't pull it off the tubing using a similar force to that of the pressure in the rocket during the flight.
4. Cut a hole in the centre of a bottle top so that the Tube Insert just fits through if and then a hole in the centre of the bottle top seal that is just smaller than the Tube Insert. Put the seal into the top and slide them onto the pipe.
5. Get one of the 15mm Tube Inserts and roll up a strip of bottle side PET (around 20mm wide x 20cm long). Pull the PET strip over a sharp edge to make it curl and then roll it up so that the hole in the middle is as small as you can make it. Trim the PET strip so that it will roll up small enough to get into the flange end of the 15mm Tube Insert (you may have to trim it so that the external diameter is small enough to do this) and then tap it home with a small hammer.
6. Cut approximately 25mm of the 4.5mm i/d tubing, making sure that the ends have no burrs. You may find that this will fit snuggly into the hole in the rolled PET but I found that there was enough room to insert another layer of PET. Roll the PET up (you want enough to go around the outside of the 4.5mm i/d tubing - the PET that is already there is a spiral so get the outer end of the new piece to butt upto the inner end of the outer piece thus forming a tight continuation of the spiral. I found that one layer was enough), put the 4.5mm i/d tubing in it and carefully tap that into place.
7. Using a sharp knife, cut a smooth, tapered inlet to the 15mm Tube Insert nozzle that you have just made. The water has to flow into the nozzle throught this so it should be smooth and conical (get that k nozzle factor as low as possible).
8. Push the tube insert nozzle into the end of the 15mm tubing - this should be a tight fit and the burr should make it more so. Be careful not to damage the end of the 4.5mm i/d tubing. Using a sharp knife, take off any burrs that have formed - a burr on one side will push eht jet over to one side and make your rocket loop in the air instead of flying straight.
9. Take some Blu Tack and role it into a small cylinder (around 6mm diameter) and cut off around 5cm of this. Roll around the 22mm Tube Insert below the flange, forming it into a seal, so that it is slightly narrower than the internal diameter of the bottle neck.
10. To fit into the bottle, push the flange with the Blu Tack seal into the neck of the bottle so that the seal is below the end of the nozzle. Screw on the bottle top and then pull then pull the nozzle so that the flange slides towards the top, squashing the seal and making it it seal. The flange and the hole in the bottle top will keep the nozzle aligned - this is why it is important to get the hole central. This is effectively a removable, watertight seal.

Crushing sleeve

1. Get the cut-off end of a pop bottle (the nozzle and a few inches of neck) and push through, from the neck end, some 21.5mm o/d plastic overflow pipe so that around 5cm protrudes through the nozzle end.
2. Heat up the very end (around 1cm) using a cooker or a candle - the surface will change its texture - and pull the tubing back into the bottle so that only around 4mm protrudes. Push the end down onto a flat surface, being careful to make sure that the end is square. The aim of this is to flare the end of the tubing so that it is slightly larger than the end of the bottle neck - the bottle neck that you are using will help to keep the PVC tubing in shape. Don't press too hard as you may flare the end unevenly. Once you have done this, it should have around 1mm of PVC pipe that should not go through the bottle neck (that doesn't mean that you have squashed all 4mm into just 1 mm though - it tends to slide as you are pushing it).
3. Cut the pipe using the pipe cutter around 25mm from the flared end. Do not remove the burr - this will help to grip the flexible PVC tubing when the system is not pressurised. You should now have a short length of pipe that will not go completely into a bottle and should be fairly easy to remove from a bottle neck.
4. Cut around 15cm of 20mm o/d clear flexible PVC tubing making sure that both ends are flat and square. Push one end into the length of 21.5mm o/d pipe that you have just made so that the end of the flexible PVC pipe is flush with the flared end of the 21.5mm o/d pipe. The burr on the outer pipe should help to hold the flexible pipe in place.
5. Cut a piece of 15mm o/d pipe around 15mm long, leaving the burrs. Push a 15mm Tube Insert into the pipe leaving around 5mm gap between the flange and the end of the pipe (see bottom of diagram below).
6. Get a paper clip and straighten it out. Bend around 6mm of the end back on itself, using a pair of pliers, so that it is a tight fit in the hole in the plastic bead. Push the straight end of the paper clip through the hole in the bead and pull the bent over end into the hole so that it is a tight fit.
7. Push some Blu-tack into hole to seal it (it is only going to have any serious pressure along it for a fraction of a second) or, as an alternative, fill the hole with epoxy resin, using a flatened piece of Blu-tack as an end to the mould formed by the inside of the bead (when the epoxy is set, remove the Blu-tack).
8. Put the paper clip in the bead through the 15mm Tube Insert and bend the end over so that it won't come out. remember to leave a few millimetres of travel so that it can act as a valve.
9. Push the 15mm Tube Insert into the end of the 20mm o/d clear flexible PVC tubing so that the ends are flush.
10. Cut two rings of garden hose and fit them in the positions shown on the diagram. To get them over the PVC tubing, you will need to stretch them first. I did this by putting the handles of two table knives into the hose rings and twisting them to stretch the rings. After a few minutes the rings shrink to their original size. I found it necessary to put a ring at position 2 (not seen in the original US design) because the flexible tubing I could find in the UK was not a close enough fit - without some initial seal such as that provided by this extra ring, too much air escaped during pressurisation. This works like a dream.
11. Straighten out the other paper clip and wrap it once around the 20mm o/d plastic tubing, twisting the two ends together using pliers. Cut off the excess and bend the twist down so that it is flat to te side of the tubing (remember that this assembly has to pass through the neck of a bottle).
12. Cut a hole in the centre of a bottle top so that the 15mm o/d PVC pipe fits through and then a hole in the centre of the bottle top seal of the same size. Put the seal into the top. Be careful to make sure that the 15mm PVC pipe will fit smoothly by making sure that the hole is central. One way of doing this is to put the flexible sustainer end into the end of a bottle and to make the hole in the bottle top (being careful not to cut the flexible PVC) in situ - passing the 15mm PVC through the hole close to finishing to make sure that it is aligned properly. A tollerance of 0.5mm is okay here as the seal is made by the end of the PVC pushing against the bottle top seal.
13. To fit into the bottle, wet the garden hose rings (they are a tight fit) and push the assembly into the bottle as shown in the diagram. The 21.5mm PVC pipe should stop short of going all of the way in. Screw the top down and the 21.5mm o/d PVC pipe and the 20mm o/d flexible PVC tubing should fit flush to the seal. The pressure in the bottle will push these harder against the seal for an air tight seal in use.

Operation

Filling

1. With the booster end of the Stage Mechanism in place on the top of the booster, fill the booster to the appropriate level and mount on the launcher. Beware of the tendancy for the booster to empty if the one-way valve is not in place (this shouldn't happen but it is as well to be aware of this in case it does).
   An alternative method is to put a normal bottle top on the top of the booster, fill the booster with the appropraite amount of water, place it in position on the launcher and, when it is water tight, take the top off and replace it with the crushing sleeve mechanism.
2. Fill the sustainer (second stage) to the appropriate level.
3. Push the sustainer nozzle in, along with its Blu Tack seal, screw on the top and pull the nozzle up so that the seal fill in the space. If the hole in the top is central, the nozzle will be straight.
4. Put the sustainer onto the booster. The one way valve (the bead) will stop the water form flowing into the top of the booster.

Pressurisation

1. Before pressurisation, water flow into the booster from the sustainer is stopped by the one way valve and the sustainer is held in place by its weight.
2. When pressurisation commences, the pressure at a increases, forcing air past the one-way valve into b. Air does not pass to atmosphere at 2 because of the light pressure seal caused by the garden hose. Note that the pressure from the garden hose is never enough to hold the 15mm pipe in place.
3. As the pressure increases, the pressure in a, forces the flexible tubing at 1 onto the surface of the 15mm PVC tubing (displacing the air that was in this space to atmosphere - c) which provides a sufficient grip to stop the PVC tubing from being released. This force also pushes the tubing against the Cap Seal and enhances its seal. The more the pressure, the more the gripping force, the more the seal.
4. Once pressurisation has been completed, the pressures in a and b are equal. The one-way valve only has the hydrostatic pressure of the water in the sustainer on it as it did before pressurisation commenced and the pressure from the paper clip at 3 is sufficient to hold it in place.

Release

1. When the rocket is released, the water is ejected from the booster and the pressure in the booster decreases. The whole rocket is accelerated to maximum velocity. The one-way valve holds the water and the pressure in the second stage of the rocket and the pressure on the flexible tubing holds the second stage nozzle pipe in place.
2. Once the water has finished, the air escapes from the booster and the pressure carries on falling towards atmospheric pressure. The restraining pressure on the flexible tubing diminishes until the pressure at the end of the second stage nozzle (between 2 and 3) - still at the initial pressurisation pressure - is suffucient to overcome both the reduced grip on the nozzle and the lower acceleration from the booster.
3. At this point, the nozzle, lubricated by a small amount of water from the sustainer, is forced out of the flexible tubing and the second stage is released - still at the initial pressurisation pressure.

During the depressurisation of the booster, two things happen:

• The force holding the sustainer in place reduces as the acceleration falls - trying to force a release when the force that is a result of the pressure on the area of the end of the nozzle (15mm diameter in this case) exceeds the force from accelerating the mass of the sustainer with its water; and,
• The pressure in the booster falls by the amount required to release the grip on the side of the nozzle.

Note that this pressure is the difference between the pressure in the booster and sustainer and is not relative to the pressure between the inside of the booster and the outside air. This is because the pressure on the inside of the tubing is derived from the sustainer via the end of the sustainer nozzle because the one-way valve (the bead) prevents the water from flowing into the booster.
As a result of this, it is possible to measure the release pressure by putting the sustainer nozzle onto a spare bottle (a 1 litre will do) with a little water in it (not to weight too much) and putting the booster release mechanism onto a bottle that can be pressurised (two bottles bottom to bottom like the 4 litre rocket or one with a tyre adapter in the base) and pressurising the base bottle in 5 psi steps, releasing the pressure each time to see if the release mechanism releases. I found that it did this for this mechanism at 45 psi. It is not unreasonable to assume that it will release, dropping from, say, 100 psi, when it gets to 55 psi if the acceleration makes the force on the nozzle from the sustainer fall below the force from the end of the nozzle (100 psi x 0.27 square inches = 27 lbs force or 122 Newtons). The numbers that you put into the computer model for 2 stage optimisation are 45 psi and 15mm.






(nguồn : http://ourworld.compuserve.com/homep...2oRocketR8.htm)

[earthmen]

Loại tên lửa này phải dùng nhiên liệu lỏng, hoặc thuốc nổ mới bay được. Nhưng nghịch mấy thứ này phải có những yếu tố an toàn cao. Dân amateur Việt Nam chưa có điều kiện làm.

[fairydream]

Đang bàn đến tên lửa nước mà bạn, nước nhưng bay cao hàng chục m là thường

[huynh_ngoc_long_88]

Mình nghĩ giải pháp về áp suất và cách tách tầng tên lửa cần đc kiểm soát ngay từ dưới mặt đất.

Tức van khí sẽ kết hợp cả 2 loại, loại dùng ma sát và bong bóng + Một khoá an toàn....^^

Khi phóng thì khoá này mới mở, nhưng lúc này, tầng dưới có vtốc lớn hơn nên đẩy tầng trên (tức dính với tầng trên) khi vtốc và áp suất tầng duới bé hơn tâng trên, tên lửa sẽ tách ra...^^

[fairydream]

Bài của bạn huynhngoclong (long không vào diễn đàn được)
Loại 1:
http://ourworld.compuserve.com/homep...2oRocketR8.htm




This is an adaptation of Bruce Berggren's Crushing Sleave Staging Mechanism which can be found at http://www.geocities.com/wrgarage/stage.htm

Nguyên Tắc:
Khi bơm khí vào bình 1. Khí sẽ qua van 1 chiều a, đi vào ống b.

Đoạn dây ống nước ở 2 sẽ giữ ống của màu vàng nối liền với bình phía trên (đóng vai trò tạo lực ma sát).

Khi áp suất tăng, áp suất bình 1 tăng, tạo 1 lực áp vào ống màu xám, từ đó sẽ tạo tăng lực ma sát giữ thanh màu vàng để khỏi trượt ra. (Các lực ma sát , chỉ giữ đc đến 1 áp suất nào đó thôi)

Lúc này, p1=p2, v1 =v2 (với p1,v1: áp suất và vận tốc bình dưới ; p2,v2: vận tốc bình trên)

Lúc phóng: p1<p2 , v1>v2 (vì do ma sát)

Đạt đến 1 độ cao nào đó:
p1<p2 , v1<v2 => Tên lửa tách tầng

Loại 2: Gary Ensmenger:
http://www.h2orocket.com/topic/hose/hose.html


http://www.h2orocket.com/topic/deploy/deploy.html



Khí sẽ đi qua van 1 chiều

Sau đó khí sẽ qua lỗ ở giữa ống, làm lớp bong bóng phồng lên => giữa tầng trên lại.

Khi áp suất tầng dưới thấp hơn tầng trên sẽ làm bong bóng xẹp xuống => tên lửa tách tầng







Loại 3: Phương pháp Huỳnh Ngọc Long


(các bạn Load về rồi zoom coi cho rõ)

Với hệ thống dây rút nối giữa tầng trên và dàn phóng, giúp ta giữ đc tầng trên đến áp suất mong muốn

[fairydream]

Anh có chút chưa hiểu ở mô hình cải tiến của Long các ngàm của dây rút mở ra bằng cách nào ?
Nếu kéo ống ngay lúc phóng thì từ trên xuống tầng trên sẽ bay ra trước. Anh không đọc rõ chữ nên chưa hiểu hay là em lợi dụng quán tính để tự kéo ống xuống khi phóng ?

[huynh_ngoc_long_88]

Trong lúc bơm khí, thì tầng trên được giữa lại bằng : Dây rút nối với dàn phóng, lực ma sát trong van nối giữa 2 tầng 1 và 2 do áp suất(giống loại 1), khối lượng của tầng trên.

Khi giật ống có d=41mm, ngạm của dàn phóng sẽ bung ra, đồng thời ngạm nối tầng trên với dàn phóng cũng bung ra.

Nhưng lúc này, tầng trên sẽ không tách ra được vì:
gia tốc của tầng trên nhỏ hơn gia tốc của tầng dưới

Lực đẩy của tầng trên bé hơn tầng dưới (do còn có lực ma sát giữa 2 ống ở van áp suất) và khối lượng của tầng trên sẽ lớn hơn tầng dưới

[haianh_zeee]

chúng ta có thể dùng đến cái ống to hơn đc kô .Cái ống to bằng miệng chai đó chứ anh Long dùng cái ống như ở trường Minh Khai thì bé wá ,e rằng kô bay đc nhiều . Và anh nhớ lắp thêm cái nệm trên ống nối tầng ngoài nữa để ngăn kô cho kô khí chạy ra ngoài

[huynh_ngoc_long_88]

Um...thất bại hồi sáng là do khí tháot ra tại chổ nối wá nhiều...>"<