ptwizz

Your equations are correct, but based on stoichiometric mixture being the norm and lean burn being an excess of oxygen. The reality is that a rich mixture is the norm and 'lean' refers to a mixture which is probably almost stoichiometric.

The rate at which air and fuel flow through the carb is not so simple. What you adjust is the ratio of fuel to air, whether by adjusting a fuel restrictor or an air restrictor screw. The total flow rate is influenced by what happens in the combustion chamber, especially so in 2 stroke engines. The exhaust system is designed to use gas momentum to draw the next charge into the cylinder. A hotter burn and higher cylinder pressure will create higher exhaust gas velocity and draw more air/fuel mixture into the cylinder. This is only one of the factors at work, there are others

Thus the fuel mixture cannot be considered in isolation.

I also fly with a reserve. I've done the 'Big Fat Repack' a couple of times, which involves deploying the reserve on a zipline before repacking it.

The experience of deploying the reserve is very valuable. They send you down the zipline, in your normal harness (not with the frame and motor!), wearing your normal kit including gloves and helmet. They also give you a bit of a swing / spin so you have to find the handle, pull it and throw the parachute in the correct direction.

I was surprised at how effectively the parachute deploys. At a mere 15mph or so on the zipline, I was expecting a gentle event, followed by some slowing down. The reality was an almost instant stop as the parachute opened.

I can easily see how a low altitude deployment can make a huge difference to arrival speed. If I were in trouble at low altitude, I can't see any reason not to throw the reserve.

The term 'lean burn' is relative to the 'normal' condition which is slightly rich. In the rich condition, the reaction does not complete to CO2 throughout the charge. Some of the reaction results in CO, with an attendant reduction in heat output.

The effect on the engine components is the result of both the additional heat of the lean burn, and the additional oxygen which remains after combustion. This combination promotes damage to parts, notably the piston crowns of 2 stroke engines. It is easy to see how this is perceived as simply more heat.

...and made a radius turning attachment for the lathe, so i could turn the ball ends for the pushrods:

Another hiatus in the engine build while I restored my wife's bike:

I was referring to energy density in terms of mass rather than volume, because mass is (mostly) the limiting factor in relatively slow flying machines.

It is of course true that IC engines are limited to around 30% efficiency (2 strokes even less). While electric motors can be 95% efficient, I'm not sure that the brushless motors and their inverters are quite up to that.

I'm not against electric flight, but I fail to see any significant advantage. It's no quieter than a 4 stroke engine, it's always going to be heavier, you need either spare batteries or charging equipment to fly more than once each trip out and it's expensive. The 'zero emission' argument is marred by the production processes of both lithium batteries and rare earth magnets and by the fact that we are still using fossil fuels to top-up our generating capacity.

As I understand it, graphene has the potential to approximately double the power density of lithium polymer batteries. Graphene is simply a thin carbon carrier which replaces the polymer carrier. The battery chemistry remains the same, it's just the packaging that is reduced. This still leaves the battery at 1/25th of the power density of petrol.

WRT noise, yes, prop noise is unchanged. A Bailey 4 stroke motor is almost inaudible over the prop noise and you still need ear protection.

With regard to electric powered vehicles, be it cars, bikes or paramotors, the common theme is "we just need the batteries".

There are some fundamental limitations of physics which just aren't going to go away. For a battery to be rechargeable, it must retain all of it's matter during discharge. This means it can't release much energy, certainly nowhere near that which can be released by combustion. It also has to carry all of it's 'fuel' even after it is discharged.

Petrol has about 50 times the energy density (kWh / kg) of the best modern lithium ion batteries. There is a theoretical lithium oxygen battery which could get closer to the energy density of petrol, but there is a lot of development needed to overcome the somewhat explodey nature of the prototypes.

I think you'd soon find that the mechanisms needed to adapt the motor to each application would be so heavy and bulky that any advantage would be lost.

At the very least, you would need a quick release engine mount, a quick release power connection, an electrical connection and a fuel connection. That assumes that the exhaust system stays attached to the engine and can be accommodated in all applications.

I can imagine how a specially designed engine module could be arranged to 'plug in' to a concentric mount with a splined crankshaft connection and fuel / electrical connections built into the mount, but the mount mechanisms would be more complex than the simple 2 stroke engine. The engines are already cheaply mass produced and it would be difficult to produce a mount / adapter mechanism that would be cheaper than the motor.

The state of tune of these small 2 strokes is probably similar for the above mentioned applications. Paramotors, scooters and small outboards are all operated at or near full throttle for long periods. The more regular checks on paramotor engines have more to do with the problems associated with an engine failure.

As an example: At the Oxfordshire Fly-in several of us were flying low, chasing each other round a coppice of trees in an adjacent field. The nearest persons, livestock or structure were in the camping field, probably 400 yards (1200 feet) away.

500 feet is a surprisingly short distance if you're not used to judging imperial units from the air. As a rough guide, the 'countdown' markers before road junctions are at 100 yard (300 foot) intervals, so 2 markers = 600 feet. Not very far at all, even at 25 kts.

I had thought about the built-in golf caddy thing (as the pilot of a 35kg Bailey might).

I had envisaged a pair of tubular legs with light plastic wheels. The legs would be pivoted so they can swing back out of the way, rotating about an axis across the bottom of the frame, so that in the 'retracted' position the legs are horizontal, stabilising the paramotor when left on the ground. Retraction would be by a pull-cord with a toggle to lock into either position.

Note the wheels would not be for launching or landing, where they would probably result in a face plant.

Another useful addition would be a 5V regulated USB socket (assuming the motor has a generator) located somewhere convenient and accessible when clipped in. GPS drains my phone battery in an hour or so and it seems silly to carry an extra battery when there is already a generator behind me.

All together again. At the first attempt to fit one of the heads with the pushrod tubes in place, I struggled for several minutes and couldn't get everything to play nicely. When I finally stepped back and let go of the head, it dropped into place on it's own!

It's amazing how much more easily things go together when you already know that they fit. The other 6 assemblies were a breeze.

Next job is the pushrods, which will be from 8mm aluminium tube (pre-anodised from Wickes of all places!) with hardened silver steel tips.

Assembly of tappets. All 14 swinging tappets are identical and interchangeable. The cam ring will be gas nitride hardened - one of very few operations that I can't carry out in my workshop. I could have salt bath nitrided it, but it's a little difficult to get hold of the cyanide salt (and there may be some health and safety whining).

Pushrod tubes. From Stainless steel tube with separate collars machined and pressed on. Large chamfers at the ends are for insertion into the O ring seals at the heads and at the tappet ring.

A family of swinging tappets. Each has bronze bushes pressed in and machined to finished size in-situ. The roller cam followers are off-the-shelf items. Alongside the tappets are the silver steel pushrod cups which will be hardened and pressed into the tappets.

Christian,

no, I don't have another motor. I do have many other demands on my time, some of my own choosing and some not. Many of these demands conspire directly with the weather to minimise my air time.

"Meteorology for pilots" by Simon Westmore immediately has at least one customer.

However many times I read through the chapter in Cosgrove (and other sources) I fail to see how I am going to remember enough to pass an exam.

Approximately half of what the weather does is non-intuitive and I can't remember which half!

If it's "Meteorology for Dummies" (i.e. written like C for dummies) then you will have a ready market.

If you make up a pack of 6 lead acid cells, that is a direct replacement for the original battery.

If you make a Lithium pack, it will need a charge and balance control circuit, or you can simply disconnect the charging lead from the bailey generator and recharge the battery with a commercial charger on the ground.

If you go for the on-board charging option, the battery should be made up with the charge control as part of the package, so it plugs in directly to the unmodified wiring of the paramotor.

The battery is only used for starting, the engine generates its own ignition.

I've had my Bailey for 4 years and have put less than 40 hours on it in that time.

Hi Joe,

I also have a Bailey 175. Just before I bought it (used) it had been back to Bailey for an 'upgrade'.

If I remember correctly, this included a new crankshaft and seals to address a known issue.

I've had little reason to need support, but had prompt service from Bailey when I contacted them for minor spares (battery connector).

I did inquire about a Li-Po replacement battery last year. The replay from Paul Bailey was that they no longer use electric starters, so they have not moved with the times to offer lightweight upgrades.

I have 3 of the original Bailey battery packs, but they're all getting quite tired. I will eventually replace them with Lithium batteries with a suitable charge controller.

If you're not comfortable with Lithium, simply make up a pack of 4.0Ah sealed lead acid cells as a direct replacement.

Sounds like a plan, Simon.

The fact that most of the response has been resistant to change would suggest that you've already got most of it right

Long may it continue.

I doubt that any prospective members think in terms of reasons NOT to join.

I use a number of engineering reference websites which offer limited free access, then ask me to subscribe. I have never subscribed to any of them. I am not put off by the (usually small) fee and I fully understand that they need to raise funds to maintain the site. It is simply an inconvenience. When I've used (e.g.) Efunda to run a few calculations and the site prompts me to subscribe, I just go to a different site.

I chose to subscribe to the PMC because Simon's efforts and those of other members gave me reason to want to support the club.

The default position is that people don't subscribe. They need positive reasons to do so. The argument that there is no reason not to won't convince anyone.

Morgy is a good example here, he has the experience, knowledge and contacts to offer useful advice, but sees little to gain by becoming a full member. I would argue that he is a nett asset to the PMC, but unlikely to be persuaded to subscribe by the proposed mechanism.

Again, my opinion.

I'll stick my metaphorical neck out and say that I disagree.

As Simon points out, most posts are by paid members, so there is little to gain financially.

The present 'open to all' nature of the PMC site reflects well on the nature of foot launched flying and I believe it should remain so.

If it means raising the annual subscription by a few quid, I would be happy to pay it to keep the site open to all, just as I would happily help another pilot on the field, whether or not they are a member of my club.

This is the spirit that I found first among motorcyclists and more recently among pilots. There will always be a few who will abuse the generosity of others, but I will not allow those few to degrade that spirit.

My opinion.

You're barking up the wrong tree here, we're paramotorists.

/mumble/ Judean Peoples Front /mumble/

This looks silly now that you've edited the subject.

OK with me Simon. It is my assumption that anything I post on the forum is in the public domain and anyone can do as they like with it.

So, what's the subject matter of the book? PPG? Helicopter? Film making?

I feel the 'race' thing has added some responsibility to the project. If I don't make progress, you have nothing to race against.

Another weekend of making small uninteresting parts. Another step closer to the sound of 7 cylinders on open exhaust stubs.

Machining the cylinder heads for pushrod tubes with proper seals.

The original Russian design has steel pushrod tubes which are shoved into the rough bored holes in the head casting, presumably by a stalwart Russian woman (I've seen photos of the factory - all the stereotypes are based in fact!).

Much time has been spent recently machining unimpressive parts (pushrod tubes and collars, bushes etc).

Fairly soon I should be in a position to assemble all the valve gear and make a short video with the engine turning over slowly to illustrate the motion of the cam, followers etc.