totalitor

If the first weird voice was some part separated from rocket and the second was that part hitting the pad? Time between those voices is about 2 s so that part came down from 20 metres. What is on that location?

The speed of cooling liquid should be the same from nozzle to exit point and to maintain the same speed cooling flow area should be the same. But there is that de laval nozzle. In my design smallest diameter of the outer skin combustion chamber would be 6 mm (about 2,5 mm inside is the throat diameter). Elsewhere diameter would be 8 mm. Instead of curving outer cooling tube, what if I fill that curve with copper? I would have 3 mm layer of copper there instead of tube thickness 0,8 mm. The engine would be easier to make becouse no curving of outside cooling tube would be needed. What would happen?

ap0r - that equation no 25. There is a number 6430 on that example. Where does it come from? I GOT IT! 100 psi is 14400 lbs/ft^2 ... had to convert it.

Calculating...tell me if I go wrong. Expected thrust 2 lb. I use the same book and formulas that ap0r uses. Isp using gaseous oxygen and 75 % alcohol about 240 so total mass flow 0,00833 lb/sec. Mixture ratio 1.25, chamber pressure 300 psi, so fuel flow 0,0037022 lb/sec and oxygen flow 0,0046278 lb/sec. Pressure on throat 169,2 psi, Throat area 0,0043913 inch^2. This was hard. Need info about molecular weight of gas. Diameter of throat 0,0747741 inch (1,8993 mm so my first RUD-1 throat is too big). Guessing value L? Make a guess between 50-100? I make 50 so chamber volume is 0,219565 inch^3. Diameter of chamber should be 3-5 x throat diameter. I use value 3,37 so chamber diameter is 0,25197 inch (6,4 mm) Lenght of chamber is 4 inch (10,16 cm). Looks weird. RUD-1 is too small I guess. And hole for fuel injector 0,0113232 inch (0,28761 mm) and if I want two holes even smaller...a big problem. Oxygen hole 0,0432435 inch (1,0984 mm) - no problem.

You are exactly right. Still, I do it my way...

I use "How to design small rocket engines" book for insructions. I took there example and made 1/10 size of that (chamber lenght is just guessing). Example engine thrust is 20 pounds and chamber pressure is 300 psi. I don't know how those scale, maybe thrust in my engine is 2 pounds but I don't know about chamber pressure. Maybe that is the same? Fuel and oxygen flow rates will also be 1/10. I will make different versions becouse fabrication is so easy, one day for an engine. And it is not expensive.

Thank you for advice A Fuzzy Velociraptor. So let me introduce my first rocket engine : RUD-1 http://imgur.com/h6KLaIJ Showerhead/ film cooling injector system Combustion chamber diameter: 6,4 mm Combustion chamber lenght including nozzle area: 50 mm Nozzle throat diameter: 2,5 mm Oxygen hole diameter: 1 mm. Fuel hole diameter: something (two holes) Planned propellants: gaseous oxygen and 75 % ethanol Cooling liquid: water Cooling gap between tubes: 0,8 mm 100 % copper (excluding brazing material) Firing day: unknown I don't know will this work. This is how I made it: http://imgur.com/a/ko9WJ

If I keep thickness in the annulus same all the way from nozzle area to injector area, does the velocity of coolant on nozzle throat increase? Have I understood correctly it is a good thing considering cooling? I am just wondering should I keep outer tube straight or follow inner tube curve. A straight version would be easier to do.

On page three on this topic there is a picture about small rocket engine (at the end). There is a cooling gap but on the throat area the gap is a lot wider. According the book "Design of liquid propellant fuelled engines" : "Abrupt change of flow direction and sudden expansion or contraction of flow areas should be avoided". In that picture cooling gap is not the same all the way. How important is to keep cooling gap uniform?

Nozzle is really like triangle. Bad craftmanship that's all. Should be round. Fuel and oxygen feed - what would you recommend? Oxygen from side? Or oxygen from behind parallel to fuel? Or a little angle? What is the best?

Me? I'm following instructions of that book " How to design small rocket engines". I study ways to put parts together only by brazing. Exact calculations later. Now I am wondering how to do injector. Combustion chamber has only 6.4 mm diameter and there should go fuel and two oxyxen holes. How to drill three 1 mm holes to that? I am planning to attach oxygen inlets not to injector plate but to the sides of the engine. Look at the last pictures and say would this work? http://imgur.com/a/X7HPo

Hi! I am calculating dimensions but I get weird result in combustion chamber lenght. Becouse of materials I have, combustion chamber diameter would be 6,4 mm, throat diameter 2 mm. I am planning to use gaseous oxygen and 75 % alcohol. Combustion chamber would be between 10-21 cm (including converging section) according a book "How to design small rocket engines".. Sounds a little long. This rocket never flies and it doesn't need to be efficient but am I calculating wrong that chamber lenght?

Hi! New picture in imgur album. I tried to braze copper tubes together and it went well. I'm reducing chamber diameter to 6,4 mm, cooling gap would be 0,8 mm. Learning new skills, interesting.

Hi! Here are some pictures what I have been doing. Well, I don't have a lathe so I have to do parts some other way. I made de Laval nozzle by using only ball pen hammer. I know, it's quite clumsy but I had to try. Look at the pictures, you get the idea. Give comments please. http://imgur.com/a/X7HPo

I tried to make a bridge to island. Part count is killing me.

Landing is now almost routine...but never boring!

Could someone explain advantages and disadvantages of using single big rocket engine or using multiple small rocket engines?

Hi! I guess you know http://copenhagensuborbitals.com/ If not, there are good videos how to make a rocket engine.

I try to do SSTO working with deadly re-entry mode. Getting back on one piece is the hardest part. Anyone succeeded?

How about using volfram? Melting point 3683 K. Does it need cooling at all?

But those fire on engines? Is it normal?

That was impressive!

One more point why reuse rockets: used boosters drop to the sea (when launched from USA). Reducing garbage everywhere is good to do. Even if it will cost more! Right?

Let me show my Enterprise. All stock. Looks nice far away but take a closer look...not so nice. It has 690 parts and weight 151 t. Yes I can use rockets and steer it, but it can go nowhere becouse it has no power!

In near future there may be a simple way to deorbit satellites. This spring or summer Spacex is launching a lot of cubesats, including Finnish satellite Aalto-1. It will demonstrate electrostatic plasma brake, details can be found here: https://directory.eoportal.org/web/eoportal/satellite-missions/a/aalto-1#launch