ptwizz

You're on the internet!... where do you think I get my information from?

The picture shows vapour trails behind each turbine. Under some humidity and temperature conditions, vapour trails can be generated by relatively small pressure changes, such as occur where the moving air contacts the turbine blades. What the vapour trails show is very little disturbance of the air behind the turbines. If there were any significant turbulence in the lee of the turbines, they would have to be staggered to maintain the efficiency of the second and subsequent rows. There are other good reasons for keeping clear of wind turbines.

To arrange a 2 stroke engine that doesn't burn oil requires that the air does not go through the crankcase (with the exception of experimental dry ceramic bearing engines). In most cases, this means driving a supercharger. The key to getting power from the engine is volumetric efficiency. The action of the expansion pipe can increase the mass of fresh air in the cylinder at the moment the ports close. Ideally, the returning pressure pulse from the pipe not only pushes air back into the cylinder, but also some exhaust. In carburetted engines, this reduces or eliminates unburnt fuel exiting through the exhaust. In a direct injection engine, the mass of fuel injected is still limited by the mass of air in the cylinder. In both cases, when the engine is operating in its peak range, the result is the same. Direct injection comes into its own when the engine is used for much of the time at below peak output. At lower RPM and gas flow rate, the expansion pipe returns its (weaker) pressure pulse substantially before the exhaust ports close. This allows some of the fresh air to flow out of the cylinder and into the exhaust. In a carburetted engine, this air is already mixed with fuel, so some fuel is wasted. The YPVS valve was intended to adjust the timing of the exhaust port to take advantage of the expansion pipe over a wider RPM range. I have some ideas of my own on the subject of cleaner, more effecient 2 stroke design. These ideas involve a hypocycloidal crank and double acting piston(s). I already have too many projects in my workshop, but I would be happy to discuss with anyone who fancies building a prototype.

The expansion chamber is an element of the tuned pipe (i'm ignoring silencing for the moment). The list of pros and cons would suggest you are proposing not only direct injection, but a supercharged 2 stoke like the Commer TS3, Napier Deltic etc. While this engine design does away with the oil in the fuel, it is not the lightest solution by a long way, especially as a small displacement single cylinder engine.

Why does direct injection do away with the expansion chamber? As I understand, the expansion chamber uses exhaust gas energy to improve scavenging and volumetric efficiency.

This is a big plus of the system.. and only those who 'misbehave' fear or argue with it.... The other main advantage is that pilots are trained to a defined standard, and there is a record of who actually flies... 1) A system with the capacity to identify individual pilots in no way prevents public/media perception of their actions being applied to the whole community, any more than is true of the stereotypes applied to, for example, white van drivers. 2) I wholly reject the argument that "only those who misbehave fear or argue with it". There is massive historical precedent for the misuse of this fundamentally flawed argument which could be used to impose any and all kinds of regulation, however inappropriate or diproportionate.

Getting back to engine requirements for flying: 1) Reliability. 2) Reliability (again, because in most powered flight, it is REALLY important.) 3) User friendliness (easy to operate, service and diagnose issues.) 4) Power/weight and other performance characteristics. I believe this is a reasonable order of priorities for most of our flying. For some types of competition, performance may come higher up the list.

Really? This is an aftermarket big bore kit, the like of which marked the demise of most of the small 2 stroke bikes owned by my friends in the 70s and 80s. Is this suggested as an alternative, or is this what is supplied as part of the original paramotor?

That is a very nice engine - and it looks like a proper one! (i.e. 4 stroke). I guess its actually a poppet valved 2 stroke. Makes me come over all unecessary

While you're waiting, you could do worse than get yourself a book or two covering meteorology and air law.

Presumably, if the companies in question choose to ignore the sentiments expressed in the petition, the next stage would be for individuals, schools etc. to boycott those companies. I don't know the relative volumes of business with Dell vs. rest of the world, but I can only imagine that most suppliers would prefer to lose Dell's business rather than, perhaps 10% of the rest of their business. Does anyone have a good reason not to sign the petition?

Amusing to see Dell respond to the petition under the name "Helix decision maker", but refer to himself in the first person Duly signed.

Here's one... http://www.ebay.co.uk/itm/Yamaha-XS750-XS-750-0287-Middle-Drive-Bevel-Gears-/360328498415 Might be bigger than you want. Perhaps something from one of the recent batch of 400cc super scooters?

Some bike engines (eg. XS750) had a bolt-on 90° drive at the gearbox. I wouldn't recommend using a diff. with one side locked. Running like this, the differential gears are doing far more work than they are designed for.

The dog fighting thing appears to be a hoax. Much as Dell is deserving of such things, we should not be dragged down to his level by perpetuating hoaxes. We should stick to the facts while Dell sticks to his lies.

It's not any special ability, just the product of: 1) A healthy curiosity coupled with an inate desire to pull things apart to see how they work. 2) Age, providing decades of opportunity to indulge (1). 3) The good luck to get away with (1) over the course of (2) Working in engineering manufacture and design for 30 years has also offered opportunity to pick up the odd thing or two.

I can see nothing wrong with your method for static balance. Also worth looking at is tracking (you'll probably recognise this from RC helicopters). With the prop fitted to the engine and the plug cap removed, turn the prop by hand, noting the distance from each tip relative to the frame in the for-aft direction. If the prop wobbles in this plane, the engine mounts will be unduly stressed. To correct wobble, cut semi-circular paper shims to fit between the prop and the face of the prop driver. Once you have the right thickness of shims, they can be glued to the appropriate side of the prop.

I once had a lawnmower which had exactly the same problem. At a certain engine RPM, orbital vibration drives the starter pulley to rotate against the spring tension, allowing the starter cord to run out. The fibre washer fix adds friction to the system, absorbing some of the vibration energy. Unfortunately, friction is affected by heat, oil, humidity etc. so it might work one day and not the next. The usual fix for resonant vibration problems is to change the resonant frequency of the part. The objective is to increase the frequency to one higher than the engine frequency. In practise this means either making the pulley lighter or making the spring stiffer. Note that 'stiffer' is not the same as more preload. The spring would need to be made from thicker material. An alternative fix might be to fit a collar to the cord where it passes into the pulley housing, with a magnet to latch the cord in place there. This won't prevent the pulley from unwinding as described above, but it would keep the loose cord contained and out of the prop.

The NHGPC at Beeston fly mostly paragliders, from a 2000ft tow. There is also some hang gliding, some paramotoring and a couple of powered hang gliders. I'm based near Attleborough and looking for a local site to fly from (Beeston is near an hour's drive away). I'd be happy to come and fly with you when the gods of weather and domestic commitments permit.

Hi Henry, I'm also in Norfolk, a BHPA member and did club pilot (power) last year, now heading towards pilot. I did the training and exam with Airways Airsports who are based in Derbyshire, but come to Norfolk every year to do some training. I was signed off as club pilot in Norfolk. Our local club is Norfolk Hang Gliding and Paragliding Club, flying some north Nofolk coastal sites and a tow / power field at Beeston (between Swaffham and Dereham off the A47). I purchased training as part of a package deal with Airways. The exams for club pilot are not difficult, to the extent that an individual who couldn't pass them really shouldn't be flying. With flying experience, you should need assessment only, rather than training. There is a nominal charge for exams. Best to contact NHGPC directly for details.

Ah, yes. I must admit to approx 5 stone weight advantage.

Congratulations Pat. Re. the power before launching thing: I've heard of this technique, but never found it necessary. I've always (so far) found that, even in nil wind, so long as I keep forward pressure on the harness, the wing inflates evenly and comes straight up. 'Forward pressure on the harness' means moving forward (or attempting to move forward) right from the start. As soon as the wing is overhead, I look up once to check all is as it should be, while simultaneously squeezing the throttle and building thrust. If all is well, full throttle and a few paces of RLF results in a clean launch. Most, if not all of my failed launches have been caused by my own hesitation. The key is to keep the wing moving through the air fast enough that it can fly properly. I look forward to flying with you in the future.

I have a Wouxun kg uv6d radio (same as the baofeng) and a motorcycle helmet headset fitted into the peltier cups of my paramotor helmet. I bought an adaptor with the correct plug to fit the radio and cut off the other end. I also cut the original plug off the headset cable. A bit of fiddling with a multimeter soon identified which wire was which from the headset, and the wiring for the Wouxun radio socket is available in the web. Some slightly fiddly soldering and some heat shrink tube resulted in a tidy lead of appropriate length to connect to the radio in a top pocket. Anything can be made to work if you fiddle with it enough.

I did my training at Airways and I have only good things to say about them. I started in January and was able to take advantage of the still winter air. There's generally enough going on that the cold weather is not a major problem. For details, see 'Pete's Progress' in the Training Blogs section of this forum.

I have some thin (probably pigskin) gloves from Govt. Surplus, marked as NATO Driving Gloves. Warm in winter, windproof and can feel detail well through them (line checks etc.) Also, I can operate touch screen devices while wearing them. Not expensive (£10 to £15)