It's unusual - especially with these size rockets - to actually carry a
(heavy) solenoid valve on the rocket/engine. You need heat/energy/reactive
radicals to initiate N2O decomposition and O+F reaction anyway, so
typically, the generation of such is also used to open the flow of N2O into
the combustion chamber.
Examples:
U/C valve: where the filling hose to the tank is fed through the nozzle and
CC into either an olive or press-in connector that also can act as an
injector. A small solid propellant preheater slug is typically placed next
to or around the hose at the injector end that (upon ignition) acts to both
open the flow by burning through the hose, preheats the surrounding fuel
grain and heats the incoming flow of N2O to begin the *exothermic*
decomposition. 2 MPa rated nylon hose is generally employed for this fill
hose which will actually hold the typical 5-7 MPa N2O feed pressured but
will reliably burst at a touch under 8 MPa. So the hose (very elegantly)
acts as (1) a fill hose (2) an "on" valve and (3) a pressure reliving
device.
Pyrovalve: a slug of solid propellant is used to block the injector flow
(ie. typically directly aft of the injector). Sometimes a thin layer of
plastic or polymerized resin or whatever seals the solid propellant from
direct exposure to the N2O. Similar concept to the above except the tank
requires filling from the top thereby requiring a check valve (typically)
and some method of disconnection (hose cutter/mechanical disconnect) of the
fill hose.
To initiate the engine, the solid propellant is ignited from the CC end
and proceeds to regress to the point where it mechanically fails and allows
N2O flow though. Again (as with the UC valve), the solid propellant
preheater grain also needs to preheat/decompose some of the fuel and
initiate N2O decomposition as it flows though.
The advantage with this method over the UC is it allows for a broader
range of injector geometries and there's less chance of over pressurising on
ignition. The downside (as mentioned) is it require separate valving and
disconnection of the fill hose.
Kline/Pooley? Valve: used for the Hypertek commercial range of hybrids of
the late 90s-2000s era. This system required more ground support equipment
but required no solid propellant it was a totally pyroless ignition system.
Basically, a coaxial stainless steel fill spike is inserted up the nozzle,
through the CC with the inner (longer) spike inserted all the way up into an
o-ring recess just aft of the (interchangeable) screw-in injector. The base
of this spike is also attached to a plate that is used to act as anchor
points to tie the motor down via plastic cable ties which is to stop the
rocket from popping off the fill spike upon filling. N2O is fed up in the
centre spike into the tank and when the rocket is ready to fire, gaseous O2
is fed up the (shorter) outer jacket tubing into the CC to create a very
reactive zone between the solid (plastic) fuel and GOX within. Some 2 core
speaker wire is generally taped to the outer sleeve/tube and when ready, a
high voltage arc is passed between the ends of the wire thereby igniting the
wire's insulation and subsequently the exposed fuel in the GOX filled CC.
Upon enough thermal reaction, the cable ties holding the nozzle (retainer)
down to the plate will melt through and let go, thereby allowing the rocket
to rise and the N2O to start flowing into the CC as the spike clears the
o-ring sealed recess. and off we go.
There's probably a hundred more methods, but these 3 are the most elegant or
practical especially for the size hybrids being discussed here.
As for non pyrotechnic recovery. There are systems - I've been doing non
pyro recovery for over 10 years, but it's a really challenging project to
develop your 1st hybrid engine AND do non pyro recovery.
A local club presentation I did back in 09. It's a bit dated, but provides
more detail on the methods I just described. I've posted this link before
here.
www.propulsionlabs.com.au/hybrid/TRAAU Hybrid Propulsion Systems
Presentation.ppt
<http://www.propulsionlabs.com.au/hybrid/TRAAU%20Hybrid%20Propulsion%20Syste
ms%20Presentation.ppt>
Cheers,
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of SAI WAI PHYO
Sent: Friday, 12 March 2021 6:37 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Hybrid High Powered Rocket
Hi all!
I am want to design a hybrid high powered rocket which uses nitrous oxide
as the Oxidizer and 3d printed ABS as fuel. I need help on the design
process of the certain aspects of the rocket such as:
1. What should be appropriate amount of total impulse that I should
set for the motor? My target altitude is 1km.
2. What size should the airframe be? I am aware of the different sizes
of airframes but since I am making a hybrid, I need an airframe that can fit
a solenoid valve that has a pressure rating fit for nitrous operation and
can have a large range of fitting choices.
3. Are there any non-pyrotechnic recovery methods that I can look into?
I do not plan to make this yet, I just want to learn the design process of
a high powered rocket .
Regards,
Sai Wai Phyo
Student | Diploma in Aeronautical Engineering
Singapore Polytechnic
500 Dover Road, Singapore, 139651