21.08.08: The is the ‘low hang point’ hang test demonstrated by Sam. The ‘bar’ is at a little bit of an angle as we had adjusted the set up for me and Sam is 2 stone lighter than me. Also, the hang test didn’t allow for the weight of the cage and fuel as both items were not fitted (an additional 9kg). We might move the wing maillons back one hole to alleviate the problem. Now then, ……………… are there any more problems to overcome before our first test flight?
Archive for August, 2008
16.08.08: I would like to take this opportunity to thank all of you who have offered advice and information so far. I have even appreciated the negative comments too as I do understand that I have chosen a very rocky path in my pursuit of flight autonomy. The ‘community’ of which I now feel a part off is a selfless and supportive one which can only help to develop the novice and expert alike.
16.08.08: In the evening Sam and I took the motor onto the back field for a test run with the larger carb jet fitted. The engine didn’t like it, it must have been far too rich for it so we fitted the original one back in and ran it some more.
I remembered that only a week or two ago on the ppghomebuilt group that Bill Kerr had posted about the variation in thrust on different days (i.e. different weather conditions). I say this because on past test runs the engine would normally give us 8300-8400rpm (28 thrust kg) but yesterday evening we struggled to get 8100rpm !?!?!? The wind was gusty again though but only 5-10mph. We tried nitrous and got a peak of 9120rpm (36kg) but as usual this soon drops as the bottle gets freezing cold while delivering the gas. If I did adopt a professional style N2O system (Sneeky Pete type) in order to deliver the necessary power then I might have to consider some sort of heating system utilizing the exhaust (obviously not too much heat otherwise the pressurized bottle would explode).
I really need to loose more weight in order for the eggmotor to be a viable option for me. I could live with the engine dropping to 8100rpm occasionally because even 26kg would be enough for a lighter pilot to float around on while hanging from a decent 1-2 modern motor wing. If I could market the motor at some point in the future then I think 13 stone (83kg) would have to be the max pilot weight. Plus, I would have to market it as some sort of ‘Sky Cruiser’ as oppose to a true paramotor. I just hope that the cheaper value of my ‘egg’ is enough to tempt those pilots who wouldn’t normally consider paramotoring due to higher costs.
16.08.08: Yesterday, Sam and I wanted to go to Pontefract Park in order for our first test flight. I had hoped that the velcro straps we had would have fitted nicely around my Sup-air Moovy harness. Unfortunately this wasn’t the case. In the end we’ve decided to modify the frame to include mid-way hang bars. The top of the engine frame is already attached to the harness using eye bolts and triangular maillons on the reserve loops.
Today while Sam had some spare time at work he fabricated the necessary parts. 2 x hang bars and 2 x thread bolts to attach the bars to the frame. So the wing will attach to the bar in one of the several holes drilled along the bar’s length to find the balance point and the harness will connect to the front end of the bar. This set up will prevent the need to alter the brake line length. The bars are going to be allowed to rotate up and down so the pilot can apply weight shift if required.
11.08.08: I’ve adjusted my Supair Moovy harness to as upright a position as possible ready for the first test flight. The motor has webbing straps that we’ve criss-crossed so they can securely be fitted over the harness. Sam and I have tried the engine on our backs using the straps and the motor has very little movement or play in it.
We just need a decent day to test. Pontefract Park has a small slope half way down that has a WNW-NNW into wind direction. Unfortunately the UK doesn’t get much wind from this direction and neither do we get many High Pressure systems overhead.
Summer 2008: During testing I thought that the standard carb looked a little restrictive so again I turned to the internet. There was a Walbro style carb plus mounting kit on ebay for £15. I ordered it immediately and fitted it the day it arrived. Luckily the weather was fine that evening so Sam and I went onto the back field for some testing. We followed the tuning set up religiously but we couldn’t get the power we got from the standard carb. 28kg of thrust is enough for an average weight person to comfortably climb on a decent modern wing but it wasn’t going to be enough to break the bonds of Earth (unless you weighed 10 stone).
I was just about stuck for squeezing any more power out of the this small engine but could I temporarily get a bit extra just for take off? The answer was to add Nitrous Oxide injection. Many people on the net warn you that nitrous would burn out your engine but then others were stating that you are only increasing the amount of oxygen in the cylinder just like super/turbocharging. I thought it was worth a gamble. I ordered a kit off ebay and promptly fitted it to the motor. This particular kit is quite restrictive and so only lets the nitrous out slowly. Sam and I tested it and the revs climbed from the normal 8330rpm (28kg thrust) to 9240rpm (37kg thrust). According to the data sheet the nitrous adds an extra 1.5hp. If you run too much nitrous without additional fuel then the engine will run lean and over heat greatly increasing the risk of it seizing. I think 1.5hp increase is a safe level. I’ve ordered a larger carb jet to give us a smidge more power and to make more efficient use of the nitrous.
The 16gm cartridge is good for about 30+ seconds. I guess a typical take off would involve running as fast as possible with the engine at full throttle and only then applying the nitrous.
Summer 2008: So after the last test it seemed that we were only getting half the thrust I would have hoped for. I searched again on the net for an engine with the same phyiscal dimensions but with more oomph!!!!! A chap was selling a ‘Stage 3’ engine on ebay for £130 and confirmed to me that the power output was around 6hp. If that was true then 40kg thrust was in easy reach. So without delay I brought a unit off him.
Thinking we were near then end of our journey, I asked Sam if he could help build a steel frame and cage to take the increased power and provide an airborne test bed. After several designs, we chose the simplest we could and Sam and his contacts set about the construction.
The rev counter showed peak revs at 8330rpm. This equated to 1660 prop rpm and 28kg thrust. Sam was very pleased with the amount of thrust being developed but I was unhappy, I wanted more.
A tuned exhaust had come as part of the package with the uprated engine and because we had to modify it to fit the frame I suspected we might have affected its power potential. We tried some flexible exhaust hose to lengthen the header section again but no advantage was gained. We welded the exhaust back to how we had originally modded it.
So, what’s next I thought?????