ptwizz

The exhaust system of a 2 stroke is very much part of the engine. The wrong exhaust can make a huge difference to power, or even make the engine impossible to start. That said, there is a great deal in common between many of the engines used in paramotors. Many of them are derived from kart engines and many of the kart engines are essentially copied from one another. If you can find an exhaust from a similar engine (similar capacity, power, rpm) then you should be in with a good chance.

We DO NOT have an artificial way to generate lift. The motor generates thrust, which may be translated to lift by a correctly functioning wing. The addition of thrust to a wing whose drag is increased will generate a greater angle of attack, bringing the wing closer to stalling. Any disturbance of airflow over the upper surface will also promote stalling, by causing the flow to detach from the surface. We may have the advantage of greater wing loading and therefore greater flying speed. I have been caught in drizzle once, free flying from tow. My lightly loaded wing felt like a brick and I landed quickly. I would suggest that there is more value in learning to read the weather and avoid the issue altogether, rather than theorising as to how one might deal with it. Weather forecasting can be practiced every day whatever you are doing.

There will always be some people who will hate anything, whether it's paramotors, motorcycles or cats. They're just wrong.

Ethanol in fuel is a hot topic among classic bike and car owners and has been the subject of much research and discussion. Some of the basics about Ethanol: Ethanol is hygroscopic, which means it attracts water. It draws in water from the air, which then sits inside your fuel system and corrodes parts which would normally be protected by their immersion in fuel. The combination of water, alcohol (i.e. ethanol) and dissolved oxygen will attack most of the materials used in traditional fuel systems, including steel, copper, brass, rubber and Mazak (carburetor bodies). Some of the plastics used in fuel systems are attacked and form a translucent, gummy deposit which is near invisible when immersed in fuel. I have dismantled petrol taps which have been entirely filled with this stuff. Ethanol increases the octane rating of petrol. Some brands of 'premium' fuel contain more ethanol than the non-premium fuel of the same brand. Ethanol has a lower energy content than petrol, so the reduction in power may provide some limited protection from overheating.

If you google "Octane compression ratio chart" you'll find plenty of data. Predetonation is not 'all or nothing'. Predetonation will begin to occur as the temperature (generated by compression and residual heat in the engine) reaches the auto-ignition temperature of the fuel. Higher octane gives a higher auto-ignition temperature. In normal operation, the spark plug ignites the fuel at the correct time, then the flame spreads through the combustion chamber at a speed determined by the heat and pressure generated. This process takes a finite time, so ignition is timed to occur before the engine reaches TDC and peak pressure occurs at or after TDC. When auto-ignition occurs, most of the fuel will ignite and burn at the same time and the combustion process will be much faster. If this happens significantly before TDC, then you get a knock as it briefly tries to turn the crank in the wrong direction. It follows that a low octane fuel may auto-ignite after the spark has fired but before the flame front would normally have spread through the combustion chamber. This causes peak pressure to occur earlier and is similar to running slightly over-advanced ignition. You won't notice a power loss and your engine will probably put up with it, until you are climbing flat out on a hot day.

You might get away with lower octane fuel for a limited time, but it's not a good thing. When you were running 91RON (Relative Octane Number) fuel, it may well have been pre-detonating when running at full power. During your first few weeks with the new motor, you may not have noticed this. Note that when running with the throttle partially closed, the effective compression ratio of the engine is reduced, as the throttle restricts the volume of fuel / air mix which is admitted to the cylinder. Thus the effects of low octane fuel will not become apparent until the throttle is opened and the effective compression ratio is increased to a value at which pre-detonation occurs. The lower the RON, the lower the compression at which pre-detonation will occur.

The size of an engine alone is no guide to fuel economy, neither is its maximum power. Any engine may be tuned for maximum power, torque or efficiency at a particular RPM, but there will always be a compromise. To win an Eco Challenge, an engine should be running at its maximum efficiency at cruise. This could equally be an 80cc engine at 8000rpm or a 200cc engine at 4000rpm. A 2 stroke engine is most efficient at its resonant frequency, when the airbox, porting and exhaust pulses combine to get almost all the exhaust gas out of the cylinder and almost all of the intake charge in with minimal losses. If that frequency (i.e. rpm) coincides with the cruise power setting, then you will be getting the best efficiency from that engine. However, tuning for maximum efficiency at cruise will not give maximum power at full throttle. There is also the complication of torque/power curves. If the engine can make 20HP at 10,000 rpm, but only makes 10HP at 8,000 rpm, it won't have enough torque to get the prop past 8,000, so it will never achieve it's full power. It quickly becomes apparent that it is necessary to balance the engine characteristics, drive ratio and prop to make sure that both the engine and the prop are used effectively.

I have caused myself a further delay to the build, this time by deciding that the Russian valve rockers are just too crap to tolerate. When I came to assemble the pushrods, I checked the lengths of a few in situ only to find that the clearances were all over the place. On investigation, the variation turned out to be in the rockers. I have designed aluminium rockers with roller tips and improved geometry. I have turned the blanks for them (fourteen 75mm diameter billets, 42mm long) and started milling. When they are finished, I'll be back to where I thought I was 2 months ago.

Rotate the image 90° anticlockwise. It's clearly a 'Space Invader' from the original video game.

My Ozone Indy has 2 loops. As I understand, these are for use with high an low hang points. I have high hang points, so I use the upper loops. I'm not sure how a paramotor and wing can be statically trimmed to fly straight at all power settings. All torque applied to the prop must be reacted through the risers and lines. Changing the balance of loads across the risers causes a turn (all other factors remaining equal). This is the same whether the load change comes from torque or weight shift.

There are many reasons why you might have a slight turn to one side: Are your trimmers set to exactly the same position? Do you keep equal pressure with both feet on the speedbar? Are you perfectly central and symmetrical in your harness? Do you have a side mounted reserve? Do you have asymmetric weight (e.g. all your right side pockets full of keys, change, spanners etc? Even with the high hang points of the Bailey 175, I can offset any yaw tendency either with the trimmers or asymmetric pressure on the speedbar.

It's been quite some time since I've had anything to add to this blog. Whenever permitted by work and weather, I've been furthering my training towards NPPL(M). I am now flying the microlight solo and expect to have my license in the next few months. I also have a single seat project under way. As you might imagine, this has not left much room for paramotoring, which has been limited to an occasional local flight, just enough to remember the procedures. I can't see that I would become a more frequent paramotorist in the future and I think it unwise to fly it once in a blue moon, so I am likely to sell up the trusty Bailey and Ozone Indy which have served me so well through training and 4 years of sporadic flying. I'm not letting the kit go just yet. There's a couple of places I'd like to fly from before I hang up my harness, but in the next few months there will be a Bailey 175 paramotor, Ozone Indy 29.5m wing, Apco Mayday 18 reserve in front container plus flight deck bag, all will be advertised here first. Ideal beginners kit, provided the beginner is comfortable with a 35kg motor.

For a 2 stroke with 10 hours on it, that looks pretty reasonable. The absence of black deposits on the insulator (white bit in the middle) indicates that the plug is a 'hot' enough grade to avoid fouling. The electrode (bent over bit) appears to have a slight brownish deposit, like the middle row of Nielzy's chart, indicating correct mixture. Most of the charts available are for 4 stroke engines. A 2 stroke plug will always show some degree of soot from the oil which is burnt with the fuel. So long as the soot is not staying on the electrodes or the insulator, it's OK.

I don't see why the paramotor wouldn't travel inside the caravan / camper?

Apologies for my no-show. Our dog's on her last legs and clearing off for the weekend would have gone down like a bag of poo with the 'management'. Good to hear all went well.

Idling the engine once it is warm is not so bad, but warming it by idling is an invitation for trouble: The cold plug is more likely to foul. Fuel (and lubricant) is more likely to condense on the inside of the crankcase, causing lean running and reduced lubrication. Condensed fuel and oil may enter the cylinder when the throttle is opened, with the potential to cause plug fouling or stalling.

Warming a 2 stroke at idle is not good practice. I believe the ROS has a clutch? If so, the engine will tick over with a prop fitted, without the prop turning. To warm the engine properly, it should be under load (driving the prop). With the paramotor on your back and after checking the area and thrustline are clear, start the engine and run at a little more than idle (enough to engage the clutch and turn the prop) until it runs smoothly. This allows for it to clear any excess fuel from starting. Next, slowly increase throttle so that the engine builds RPM smoothly until you are at full throttle and, as you say, hold it there for a few seconds. You can close the throttle more quickly, but best not to just 'snap' it shut. Closing the throttle quickly means that the engine is still spinning fast, but drawing against a closed carb. The engine only gets its oil with the fuel, so high RPM plus closed throttle equals insufficient lubrication. It can also cause you to lose balance as the torque and thrust drop away. With the engine at idle, prepare yourself for a burst of thrust and torque, then open the throttle quickly. If all is well, the engine should pick up smoothly. Hesitation or stalling indicates either an insufficiently warmed engine or an issue with its set-up. At the heart of all this, the key is to warm the engine evenly. Too fast and the parts will expand at different rates, leading to leaks and possible seizure. I have had an occasional momentary loss of power, which I soon traced to accidentally hitting the kill switch (on the throttle grip).

... and I mis-spent too much of my youth repairing other peoples RD's. That is why I fly a 4 stroke Bailey.

Thanks for the compliments gents. I should say again, I am only copying the work done by pioneers over 100 years ago. I am quite happy with 'slow burn' projects. As I tell my wife, if I said I'll do it, I'll do it. I don't need reminding every year. It's all a matter of perspective. To my mind, mechanical stuff is simple. I can see how the parts work together and get a reasonable feel for the loads involved, so when a calculation or test goes wrong, i have a good idea what to look for. I am learning about electronics as I go along, so i can make my own ignition module, which will later be expanded to engine monitoring and possibly fuel injection. When a PIC doesn't do what I expect, it doesn't give me any clues (or more likely I have no idea where to start looking).

There's more to that map than just airspace categories. For example, the QNH zones are simply the areas over which pressure at sea level is considered to be constant, so everyone operating in that area is using the same QNH setting. The categories you need to be aware of are detailed in this document https://www.caa.govt.nz/rules/Rule_Consolidations/Part_071_Consolidation.pdf

I use Gaggle (which is free) to log my flights. Before each flight, I start Gaggle and put the phone away in a zipped pocket. Gaggle has a live display which can show a moving map or live data (altitude, ground speed, heading, etc.) but I only get it out occasionally to check altitude if I'm near anything sensitive. For navigation, I use the traditional method of studying a map and planning a route before leaving the ground. The map folds up so that the area of interest is visible and goes in the side pocket of the harness, but I've never yet needed to get it out in flight.

Hi Hann, toolmaking is all part of the fun of engineering at home. I have a collection of tools which were made by my grandfather, and a few made by my uncle, to which I am adding as projects progress. I have modelled the whole engine in CAD and produced drawings for all the parts. To establish the cam timing, I first measured timing from a camshaft from the same engine that the cylinder heads came from. This was then translated to the ring cam, using a spreadsheet calculation. The cam timing / lift spreadsheet is relatively simple when compared to the one I created to calculate the dynamic balance of all the moving parts. That is a huge, rambling set of iterative calculations (which i suspect may have become self-aware). Each cylinder head has it's own pressurised oil feed, with a spraybar arrangement to ensure that the valve guides and the exhaust port areas of the heads are liberally supplied. Most of this is for cooling rather than lubrication. The upper cylinders will drain via the pushrod tubes into the timing chest, then via the lower cylinders pushrod tubes into the lower rocker boxes. The lower rocker boxes will have drain tubes to a collector tank, where a scavenge pump returns drained oil to the main oil tank, via an oil cooler and filter.

Whether the shed wall material is tough enough depends on what level of security you want. In the relatively small panels required for a paramotor trailer, it will have no problem standing up to the wind at towing speeds when supported on a rigid frame.

I can bring it to this years fly-in, but there's not a lot more to see than last year unless you're an engineering anorak. I'm guessing about another 18 months before noise happens.

Looks just like plastic or aluminium sheds. The extent of the supporting structure would be sufficient for either material.