Téma:

Hi Andrej,

regarding your first question, the maximal ceiling of our rockets is generally up to 1km. The biggest reason for that is the area of usable launch sites and we like to watch the entire flight as well. Even though we use a dual-deployment. For our rockets we are not using so much metal parts because of the safety (based on the Tripoli safety protocol), weight and also that for our required performance it is not necessary.

That's for the beginning. In case of any other question, don't hesitate to write it down here and enjoy this website

Best regards,
Michal

Thank you for all your replies. I will try to answer all the questions.

I wonder function lighters, what is full and what amount?
Or as individual grains stěsnit fuel between, on the one hand, the motor is fixed to the nozzle and the second fixed lighter?

This igniter works as a small rocket motor. Electric match ignites a small block of sugar propellant (36 grams). This block burns out in about 0,2 seconds. Hot gas shoots down the motor core through four nozzles. This igniter is very efficient and it also makes sure that the motor doesn't pressurize to quickly which could lead to cracking of the propellant grains. As you probably noticed the igniter is placed at the top and the flame propagates from the top end towards the nozzle.

can you please post there any additional information about your rocket and motors?

Regarding your rocket model 100 mm diameter , what is starting mass (weight) fo rocket ,
total lenght , what is the material for fins this model?
I suppose, you use engine N-3535 for this rocket?

And also weiht and dimension for your 50 mm rocket with this engine charakteristics - thrustcurve of this engine. I allow me make any calculations to better understand this models.
I´m pretty suprised yours models and engines - it looks as any Slovenian "Mini sugarshoot"!

Lift-off weight of the rocket was 18,3kg, total lenght is 1887mm. Fins are made from a 4,0mm thick aluminum plate and TIG welded to a short piece of tube that screws to a motor casing. N-3535 motor was used for this flight.

50mm rocket is about 180 cm long and weighs 4,7 kg. Propellant is potassium nitrate/mannitol. Max. chamber pressure is 100 bar. Bellow is a thrust curve and a static test of this motor:

About N-3535:
Your Mannitol is really near our Sorbitol sugar. Isp= 1372 Ns/kg is pretty high.
Our people using also fuel SX81 - it is like KNSB , but there is 9 % Sulphur instead Sorbitol.
KNSB motors have Isp from 1000 to 1100 Ns/kg , for SX81 it is to 1280 Ns/kg.
According picture your fuel grain there is core diameter about 28-30 mm and burn rate about 10-11 mm/sec!! Itś quite high burn rate.

What is weight of casing for N-3535 and weight complete motor?
How high pressure is in this engine?
What do you use as ignition mixture for quick and reliable ignition this relatively long motor? What do you use for sealing between fuel grains - rubber O-rings ?

Such a relatively high specific impulse is a result of a high chamber pressure (average pressure is about 75 bars) and of optimized nozzle. 50 mm motor that I already mentioned, runs at even higher pressure and measured specific impulse was 1420Ns/kg.
Complete N-3535 motor weighs 13,2 kg, propellant weight is 7870+/-30 grams. N-3535 is ignited with a pyrogen igniter as I explained before. For ignition of smaller motors I use pyrotechnic charge made of black powder/ magnesium powder mixture (50/50). I use no seals between propellant grains, in fact it's good to have a small gap between grains, so the gases can penetrate quickly between the grains and the casing wall. That way the pressure is equal on all sides of the grains which prevents cracking. I use rubber O-rings only to seal a nozzle and a forward bulkhead.
I hope I answered most of your questions. If not, don't hesitate to ask.
Right now I started working on a new project. Simulations show that altitudes approaching 15 km are possible. Rocket will be a boosted-dart type rocket. Motor is 84mm in diameter with a 11kNs total impulse. Casing is not aluminum but filament winded fiberglass to reduce weight. Motor will boost the rocket to Mach 2,5 in 2 seconds after which a small unpowered dart will separate and coast to apogee. Launch is planed for end of April. If everything works OK I will post some pictures here.

Andrej

Hello Andrej ,

Thanks for your response.
To ignition of N-3535. What is for shape and dimensions this 36 grams ignitors grain ,
to acquire burn time 0,2 sec burning time ?
This four holes are arranged to guide flame directly to core surface , no to the core center – its nice and effective.
Very important is also your notice about not too quick pressurize engine chamber !!
Perfect ignition , his technology and his pressure curve is basic condition to have succesfull and also reproducible thrust curve of motor!!

It is not so easy for different motors with wide range chamber lenght and core diameter.
Special kind is motor with very long chamber and relative small web thickness os propellant grain - for instance your 50 mm engine!

Some people use for ignition Sorbitol and SX81 core engines special 2 or 3 step ignition.
Mixture used for first or second step are produces small quantity of gases (for lower pressure) and make temperature activations propellant surface. Second mixture get more gasez and heat to run and maintenance burning process.

Thanks for information about chamber pressure , for 75 bar this burn rate and Isp perfectly response.
Very ineresting is your notice using hot gases pressure outside propellant graines to reduce forces on grain and prevent cracking of propellant graines!!
It is very important for engines with so high chamber pressure as in your engines.
Our sorbitol engines use more low pressure to 30-40 bar.

Your 50 mm rocket is also very interesting and his shape and mass concentration to small diameter ie effective to get high fly. Long burning motor will be better , but shape , dimensions and propellant charakteristics limited our possibilities.
100 bar pressure is pretty high.

For this engine i guess Ic=2500-2600 Ns , and max. acceleration this rocket about 46 G!!
Itś really gunshoot and electronics part , other components in this rocket has heavy conditions to survive!

Your new project is nice. Can you post there also booster lenght., diameter and lenght of second – dart part? Total weight and lenght od this model?

Non metallic body is good way.

I have any idea for your dart stage to raduce his drag.
Get to bottom side this stage any cylindrical propellant grain in low pressure casing – as source hot gases aftes afted dart separation. This hot gases can stronly reduce aerodynamic drag this shape and help to get higher!! It is not worked as rocket engine, but it reduce turbulent flow around bottom part!!
This method is used in active-reactive artillery shell to get shoot to distance 40 km ( 155 mm shells).

I hope that our discussion ( and not only discussion) will be continued …

Mirek

To ignition of N-3535. What is for shape and dimensions this 36 grams ignitors grain ,
to acquire burn time 0,2 sec burning time ?

It's a tubular not-inhibited grain (all surfaces are burning). Propellant is KN/Dextrose doped with 1% of iron oxide- Fe2O3. Iron oxide increases burn rate for about 20%.

Your new project is nice. Can you post there also booster lenght., diameter and lenght of second – dart part? Total weight and lenght od this model?

Booster motor is 84mm in diameter and the casing is 1310mm long. Total motor lenght with the nozzle is 1426mm.
I haven't designed the dart yet. It will be about 1 meter long and about 25-35mm in diameter. Total lenght of the rocket will be about 260 cm and expected lift-off weight is about 17 kg.

I have any idea for your dart stage to raduce his drag.
Get to bottom side this stage any cylindrical propellant grain in low pressure casing – as source hot gases aftes afted dart separation. This hot gases can stronly reduce aerodynamic drag this shape and help to get higher!! It is not worked as rocket engine, but it reduce turbulent flow around bottom part!!
This method is used in active-reactive artillery shell to get shoot to distance 40 km ( 155 mm shells).

Yes, this is called base bleed. It would work but that would require quite some development time to get consistent results. For minimizing dart base drag I will use a boat tail, like the one in the photo bellow:

I hope that our discussion ( and not only discussion) will be continued …

I would really like to come to one of these launches in Czech republic to talk to other rocketeers and launch some rockets (and drink some beer ). Are there any launches organized in the summer or autumn? Where in Czech republic are these launches?

Best regards
Andrej

Ahoj
Andrej je asi pořádnej šoumen.Akorát pro nás kdo neumí emericky je škoda , že z toho moc nemáme.
Nějaká dobrá duše (Mirek) by mohl udělat překlad .Aspon těch technickych dat .
Dík Mirku máš u mě novou hlavici pr. 80mm co budu odpoledne zkoušet odlévat,
Forma a model mě stály 2 litry tak se to snad povede.
Honza

Hello Andrej ,

thanks for your answers, informations are very interesting. Now it get me better vision about this emgines and models!

At Czech republic we have several years tradition to organize so called "meetings of builders big rockets".
Itś three meetings at year.

1.) Meeting : near village "Svojek" at northern part CR.
thereś any older flyer with map: www.raketovemodely-jp.wz.cz/novy/akce.pdf

contact person : Jan Plecháč , email:Jan.Plechac@seznam.cz
date of meeting : 3-5. May 2013

2.) Meeting : at ModelPark Suché - at modellers airport
web pages for rockets of this club: www.mkchlumec.cz/rakety_hl.htm
GPS and map: www.mk-severka.cz/mapa-letiste.html
contact person : Karel Jeřábek , email: Tato e-mailová adresa je chráněna před spamboty. Pro její zobrazení musíte mít povolen Javascript.

3.) Our main and biggest meeting: at modellers airport Koprník near Knežmost
letter of invitation from year 2012: www.rmkpraha.cz/koprnik2012pozvanka.pdf
organizer web: www.rmkpraha.cz/
contact person : Petr Vysloužil , mail: Tato e-mailová adresa je chráněna před spamboty. Pro její zobrazení musíte mít povolen Javascript.


If you need any orher information which I forget, pls don´t hesitate to contact me there, or
on my email: Tato e-mailová adresa je chráněna před spamboty. Pro její zobrazení musíte mít povolen Javascript..

Meet you there will be very interesting and also our discussion at this web ....


Mirek