Tip Rocket Propeller
Project report 1, April 2005
I have built a propeller with hydrogen peroxide tip rockets. The intention is to demonstrate that tip rockets can be used for driving a propeller in the same way as a rotor for a gyroplane, which has already been demonstrated. I can see several possible applications for this very light propeller engine, like lifting of sailplanes and for light back-pack helicopters. The total weight of the whole system, including the fuel tank, the propeller and the rockets is 8 kg. It could probably be made even lighter, because my propeller hub is quite heavy.
The propeller thrust can be very high according my calculations , despite this low weight. With the pitch I have now (+ 2 degrees) on my 70 inch propeller, the calculated thrust is estimated to be around 1000 Newton (~100 kgf, ~220 lbf) at 2500 rpm. This should be more than enough for lifting a glider airplane, which I think is the most interesting application. The propeller thrust could be much higher with a higher pitch. To drive such a powerful propeller with a conventional gasoline engine, would require an engine weighing much more than this tip rocket propeller.
The blades are made of glued laminate pine wood. This Gallery shows how I made the propeller, step by step. The profile is called GAW1. This profile gives a low drag. At the same time it is rather thick, so there is room for the embedded fuel pipe and catalyst chamber, without the need of a very wide chord. The chord is 156 mm and the blade is 26 mm thick. The GAW profile starts to give a lift already at -5 degrees pitch. The pitch I have chosen is +2 degrees.
The rocket system is the same as for gyroplane rotor blades. The pressure in the tank is low. The pressure at the propeller tips is much higher thanks to the centrifugal force at rotation. The propeller is working as a centrifugal pump. See calculation . Part of the high tip pressure is lost in the propeller embedded catalyst chambers. This is because the chambers have to be long and narrow to fit inside the blades. This price is worth paying, because there is very little drag because of the rockets.
I have just about started to test run the propeller and I have not yet been running any near full capacity. This is because I want to be sure I will not break anything, so I intend to increase the power in small steps. So far, I estimate I have been running with maximum about 1000 rpm for a short moment, even if I have no higher registered reading than 600 rpm on the tachometer (no continuous measurement). The fuel valve has just been barely open so far and for very short periods. Other wise the speed would be much higher than I want it to be at this stage. My first impression is I will need to switch to smaller nozzles to avoid ”over speeding” the propeller by mistake or I can make the propeller with higher pitch and thrust.
A movie is showing the first test here
I say on the movie, that the prop was not well balanced. I fixed that problem by adjusting the amount of silver screen catalyst, until the weight of the two blades was exactly similar
One of the things that were most critical was how hot the wood would be because of the heat from the rockets. Luckily enough the wood temperature has not been very high so far -knock on wood! This is because there is a sheet of glass fiber fabrics between the rocket body and the wood. There is also silicate putty in between that can stand 1000 C and is a good insulating material.
The next step is to gradually increase the propeller speed and measure the maximum performance. I need to complete the test stand so I can measure the thrust.
I have a lot of work right now, so please do not expect the next progress report until a couple of months or so.
At last a few potential applications for the tip rocket propeller:
See Mr. Schoeffmann flying his heli here
The standard concept for a helicopter is to have the rotor on top of the craft, but on the Hiller Flying Platform two counter rotating rotors were placed under the pilot. One would think this craft would not be very stable, but in fact it is!
A flying platform with rotor tip rockets, would only need one rotor and it would be simpler, lighter and more powerful.
Demonstration movie of the Hiller Flying Platform
UPDATE, May 28, 2005
Finally I found time for more testing.
The first thing happeneing was I got a leak of peroxide inside the propeller! The leak started a fire in the wood!
You can see the damage on the two thumbnails below.
Front side of the blade
Back side of the blade
The leak was at the welding of the pipe to the rocket. The leak has most probably been there all the time. It just needed some time to leak through the surrounding silicate putty.
Fortunatelly it was possible to repair the welding. New silicate putty was applied and the propeller was re-balanced, by adjusting the weight of the silver catalyst.
I made several tests, but I never managed to adjust the speed to a reasonable level. Instead the propeller accelerated to a very high speed and vibrated a lot. When I tried to throttle down the peroxide flow, the flow stopped completally.
Two movies shows one of the tests.
The first movie shows the test right before I had to throttle the flow because of too high speed/too much vibration.Here
The second movie shows the test right after throttling Here
My conclusion is that the propeller tips accelerate to sonic speed, or higher, because the rocket thrust is too high for the propeller. I believe I have two options:
* Eather I install smaller diameter rocket nozzles,
* or I increase the blade pitch.
The option I have chosen is to increase the blade pitch with 4 degrees. This will increase the propeller thrust to around 180 kgf at a speed of about 2000 rpm with the present rocket nozzles, according my calculations.
This thrust would be more than enough for a strap on helicopter!
I will report when the modified propeller is ready and has been tested.
Update June 4 2005
After having increased the blade pitch, the propeller speed became more proper and there was less vibration. The thrust increased a lot. I could feel the strong wind from the propeller!
Instead I ran into a new problem: The decomposition was not complete. I have seen this problem coming. The reason is that I have used the same silver screen cartridges for a long time. I took them from the prototype gyroplane rotor, I worked with last winter. They are no longer perfectly cylindrical, so there is a leak between the catpack walls and the cartridge.
I will correct this problem and make a new test, but not now, because I am too occupied with other things right now.
I will have to put the propeller on the shelf for a while. I feel I have already prooven the concept of the peroxide tip driven propeller though. It can really be done!
Update September 29 2005
I said in the last update I was quite occupied with other work. I still am, but a couple of days ago a customer ordered a rotor tip rocket system and he wanted to have his silver catalyst cartridges tested before delivery, so today I finally brought myself together and installed his cartridges in the tip rocket propeller and made a couple of test runs.
This time the rockets were running clean! The exhaust was visable, but this is common and normal at weather conditions like today. There was no peroxide smell or any wet exhaust.
As last time I could notice the rocket thrust is in better balance with the propeller thrust after the blade pitch was increased, but the rockets are still too powerful. Even though the tank pressure was low, 15 to 20 psi, the throttle valve could not be fully opened, without the propeller tending to over speed -at least this was my impression -I failed to get a valid reading of the rpm. I frequently closed the throttle valve completly to avoid over speeding.
I wrote already last time, I thought I had proven that the principle works - the tip rocket propeller concept really works! I felt I confirmed this with this short test, but I will test next time with a smaller diameter rocket nozzle that is in better balance with the propeller. The reason the present rockets are too powerful is because they are standard designed for gyroplane and helicopter rotors. See SHOP page I definitly also have to find a better rpm -meter!
Even if this is not a big job I am afraid this new test will have to wait for a while because of other priorities.
The test from today can be seen on this movie (28 Mb): Propeller test with fresh catalyst, September 29 2005
UPDATE, January 28, 2006
I installed new catalyst cartridges and new rocket nozzles with 4 mm throat diameter.
The propeller was running just butiful! It reached a high but constant speed! This is in oposite to the previous tests when the propeller accelerated to a too high speed so the fuel flow had to be throttled or shut off to avoid "over speeding".
I was very happy to feel the strong propeller wind and the nice performance for about 20 seconds, but than the propeller started to vibrate - again!! When i stopped I found out why: One of the blades had taken fire at the tip. See thumbnails below:
Detail of burnt propeller
It is only the burnt area closest to the tip that happened this time. The other damages that can be seen on the pictures happened in May 2005 -se earlier uppdate.
I believe the fire was because of a leak from the flange connecting the nozzle with the catalyst chamber.
My conclusions from todays test are:
* The 4 mm nozzle trhoats are close to optimum for this propeller with D=1.8 m and aerodynamic pitch = 11 degrees (Geometric pitch = 6 degrees).
* The propeller works very efficiently as a fuel pump! The fuel pressure is probably well over 100 bar (=1500 psi) at the tips!!
This is proven by the fact that quite small nozzle diameters are needed for a certain propeller thrust and also by the fact that the rockets tends to leak in flanges and other weak spots.
The high pressure saves fuel.
* The tip rocket propeller concept works!!
When I have chance I will make a test with even smaller nozzles and an aluminium propeller. It would be nice to work together with a partner from now on. Please write me a mail if you are interested!
This article was updated on July 29th, 2007