Autogyro pre-rotation Project
AUTOGYRO ROTOR PRE ROTATION WITH HYDROGEN PEROXIDE ROCKETS
PROJECT REPORT 1
A project to install hydrogen peroxide rockets on the rotor tips of an autogyro has been initiated.
Autogyros are easy to fly and to land. They can land on a very short runway, just by shutting off the propeller motor! The weakest point of performance is the long and tricky start. Throughout autogyro history there has been a strong incentive and many attempts to spin up the rotor to high speeds before start - close to the lifting speed - and make an easy so called "jump start" possible.
Most pre-rotation systems in use today are mechanical. The propeller motor is equipped with a link shaft that drives the rotor shaft, with a belt drive or a cogwheel drive. These systems have their limitations:
* The tough mechanical conditions make it unpractical to speed up the rotor to a high velocity.
* The torque has a tendency to make the autogyro framework rotate in the opposite direction of the rotor.
The best mechanical system in use in Sweden today is capable of spinning the rotor to a maximum of 300 rpm. This autogyro - A Sportster owned by Mr. Seth Hedström - is taking off after about 70 meters on the runway at a rotor speed of about 350 rpm. Most other autogyros need a couple of hundred meters to take off.
Our main goal is simply to install a system with better performance than the present mechanical systems. We believe this should be possible, because the driving forces from the hydrogen peroxide rockets are applied on the rotor tips instead of on the shaft. There should be no problems with the momentum forces.
As flying autogyro is only a spare time amusement hobby for most users, it is also a goal to create an easy to handle and affordable low cost system.
A third goal is to create a low weight system that can be used on ultra light autogyros.
The project team is as follows:
Morgan Lång is the owner of the autogyro on which we will install the system. His autogyro is called Humlan, the Bumble Bee, and was designed by Mr. Helge Svensson in the 1970's. Morgan damaged the rotorblades at a start attempt this summer. He needs to install new aluminium blades. That is one of the reasons why our project and Morgan's plans fit so well.
Ivan Tuelstrup is the supplier of Morgan's new rotor blades and installation kit.
Helge Söderman is chairman of the Swedish Rotorcraft Flyingclub. He is probably the most experienced and knowledgeable person in autogyro technology in Sweden today. He is a retired teacher in aerodynamics and aviation. Helge is our senior technical advisor in the project.
Roland Stenlund is a teacher at the Aviation School in Västerås. His specialty is jet engines. Important for our project is that he is also a brilliant and hands on mechanic. Roland has volunteered to make the mechanical installations and work shop fabrications in the project. He is also authorised by the Swedish aviation authorities to be an official auditor for projects like ours.
Morgan's Humla is presently parked on the Flight Aviation Museum Hangar in Västerås, close to Roland's home and close to the workshops at the hangar and at his school.
Nils-Gunnar Ohlson was previously a professor at the department of material sciense at the Angstrom Laboratory at Uppsala University. He is now the manager of the material science department at Alfa Laval. He is also a Humlan owner and has taken part in several autogyro building and reconstruction projects. Nisse has offered to make mechanical strength calculations for the project and to give technical advice.
Erik Bengtsson. My own input is that I will suggest a basic design of the rocket system and provide the hydrogen peroxide fuel, the decomposition catalyst and the key mechanical components.
The basic design of the system is illustrated in the flow sheet at the top of this page. In the flow sheet a comparison is also made with two other systems, namely the Bell Rocket Belt and the Intora Firebird helicopter.
The design is still preliminary and only a couple of the components have been acquired at this time, namely the hydrogen peroxide tank and the control valve.
The hydrogen peroxide tank is a composite construction with an inner lining of aluminium.
Weight 2.9 kg.
Volume 8.5 liters.
Design Pressure 140 bars.
There is no fuel pump. Instead the fuel tank is under pressure. I believe the pressure holding system is unique. At least I am not aware that it has been used for this application before. It works as follows:
The tank is first filled with 7 liters of hydrogen peroxide and then topped up with liquid carbon dioxide, CO2, until the tank is completely full, 8.5 liters. Some of the CO2 will dissolve in the peroxide, but most of it will be a separate liquid phase floating on the top. The pressure will be 55 bars at 20 oC.
When the control valve is opened and the tank is gradually emptied, the liquid CO2 will start boiling and the tank will gradually be filled with gaseous CO2 in equilibrium with the remaining liquid CO2 phase. The nice thing is that the pressure will remain constant, 55 bars, until the tank is completely emptied.
I have already tested this system. It works very well! You can read about it in the April/May development report. I couldn't describe the system in detail back than, because we had some thoughts of filing a patent.
People have wondered why the pipes does not freeze, like you can see if you evaporize CO2 in a pipe. The explanation is that the CO2 is in direct contact with a big volume of liquid HP, which has a big enough heat capacity, for the system to cool down only a few degrees, because of the heat of evaporation.
One other beauty of the system is that no mechanical components are needed for pressure holding, which makes the system simple and saves cost and weight.
The system also has some other benefits:
* Part of the CO2 is dissolved in the HP. This will lower the pH and contribute to stabilising the HP at storage.
* The dissolved CO2 will release when entering the rocket and will then help to atomise and distribute the liquid HP.
The piping is 3/8" stainless steel.
The control valve is a 3/8" needle valve. The stem is not rotating when moved up and down, so it can either be controlled by rotating a handle directly on the valve or removing the handle and connecting the stem to a gas wire and a gas handle.
The fixed part of the piping ends with a standard type rotating sealing 3/8". This sealing has not been purchased yet. The most interesting candidate is a sealing from Duff-Norton. Stainless steel 3/8". Weight 560 grams. Sealing surfaces are ceramic/carbon. Can run 500 rpm and 57 bars without leaking. Can run dry without being damaged.
The part of the piping that rotates with the rotor is run through the hollow centre of the rotor head and inside the rotor blades out to the rotor tips. To allow for tilting and flapping movements, the stainless steel pipe is replaced with flexible high pressure Teflon hoses 3/8" before and after the rotor head.
So far we have only made sketches on how to modify Morgan's existing rotor head. Nisse has suggested that we could make a test assembly on the original prototype rotorhead made by the Humlan designer, Helge Svensson, in the 1970's. Nisse made a failure strength test on this rotorhead and he has kept it since then! (He hasn't found it when I write this report, but he believes that he will eventually.) Most rotor head component are undamaged by the strength test.
The rockets that are going to be placed on the rotortips are calculated for a thrust force of 10 kgf each. The excel program previously described on this web site has been used to calculate the dimensions:
D, catalyst chamber 35 mm
L, silver catalyst pack 25 mm (50 screens)
L, catalyst chamber, total 60 mm (the extra length is spare for lower active catalyst)
D, nozzle throat 4.6 mm
D, nozzle exit 10 mm
The plan is to screw the nozzle to the rocket body so that we can make tests with different rocket thrusts.
Calculated weight of each rocket body is 1.0 kg including the catalyst pack.
The two rockets are calculated to consume 6.6 liter HP/minute (3.3 liter/minute each) at full load. The tank will then last a little over one minute at full load.
It is still a question how fast one can speed up the rotation with these rockets. My best estimate (after having studying some similar tests made by Armadillo Aerospace) is 15 seconds to the lifting speed of 400 rpm - but I wouldn't bet on it! If I am right, the tank would be large enough for 3 to 4 jump-starts.
The project idea first came up at the Swedish Rotorcraft Flyingclub's annual meeting in Valbo on May 30.
We had our first project meeting in Väterås on September 6 2003. At this time we tried to be open minded on what design to go for. We brainstormed around different solutions.
One idea was to install the tank in the centre above the rotor and let the whole system rotate with the rotor. The valve would be radio controlled. Finally we disregarded this design, because we believed that it would be very difficult to solve the problems with the aerodynamic pulsating drag forces from the tank, that would be transferred to the rotorblades and to the stick.
One other fascinating idea that came up was to use the hollow blades as storage for the hydrogen peroxide. At rotation the centrifugal forces would make the rotor blades work as a centrifugal pump! This idea was also judged to be too complicated for us at this stage, but we concluded that the idea is interesting enough to work with in the future. It would be interesting to hear if someone else has been working with this idea!
At this time it is the design described above we are going for. The suggested detailed installation solutions are still open and the next step for us is to scrutinise all details, make stress calculations, approve them and make them final.
After this, but before doing any installation on Morgan's autogyro, I have suggested that we (i.e. Roland) fabricate one of the rocket bodies, so that I can test run the propulsion system itself in my test bench.
As soon as these tests work out fine we can go further and make the autogyro installations and test runs.
The goal is to have everything ready before the next summer season, when Morgan needs to be ready to fly with his Humlan.
The ambition is to publish progress reports on this site.
Status Report Oct. 03
This article was updated on November 30th, 2006