John Stainforth
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Posts posted by John Stainforth
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6 hours ago, Mike T said:
I disagree a bit with the 'neutral CG' notion. If, in order to fly inverted you have to put a little, continuous forward pressure on the stick to remain S&L, its a constant reminder that, in this scenario, 'forward = up'.
I fly a foamy 'F3A' practice aircraft which is CG neutral and (to me) flying inverted seems uncomfortable if I'm not leaning on the stick a bit.
Also, as a general rule, if you get 'spooked' while inverted, always roll out!
I agree with you here. All the models I have flown inverted, even those with the CG quite far back, have required a little push on the elevator stick. I say "push, push, push" to myself when inverted. If I get too close to the ground I just push harder. That works well for me.
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Looks like flutter.
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2 hours ago, EvilC57 said:
A warning for anyone who has, or is thinking of building this model.
I built the EDF powered version last winter, and had two successful maiden flights with it recently.
Unfortunately during a third flight yesterday it suffered a major (and quite spectacular) structural failure.
I had completed one fast low pass, and had just gone around for another one when the whole model seemed to blow apart in the air.Studying the recovered remains on the ground afterwards, it became evident that the fuselage had failed just forward of the wing. I suspect this to be due to a potentially weak point at the rear of the PLA skid where it joins to the carbon fibre tube on the bottom of the fuselage. During flight the weight of the heavy lipo battery with additional g-forces is effectively cantilevered from around this point. I would suggest strengthening the area by glueing CF strips to the inside of the fuselage, and/or soaking the area with thin cyano, as Planeprint suggest for other areas in the model which need local reinforcement. Despite carefully following their instructions regarding print settings and Cura profiles to ensure sufficient adhesion between the LW-PLA layers, I suspect the stresses in the area which failed were just too great for the material.
The failure point was around the area I’ve marked build instruction extract below, and not at the joint between parts.
During its short life the Jetwing flew beautifully and I feel deprived now of the fun I could have had with it in future, so if I do decide to build another one I shall certainly be paying more attention to strengthening the structure where it seems it’s needed, and suggest that anyone else building the model do the same.
Looks like flutter.
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I think there is a lot of anti-American sentiment being expressed here that is not well-founded. Having been in a southern US model club and several UK clubs, I would say that the general competence level in the US club was very high and that we, in the UK, could actually learn quite a lot from them in practically all areas, from club organisation, to safety and to model flying and set up. All the senior members of the US club were very fussy about the set-up of their models, such as fuel mixes and prop sizes. There are several differences between US and UK clubs; here I am generalising. Generally, the weather in the southern US allows vastly more flying time than the UK, the temperatures are way hotter and the humidity higher, and the noise restrictions less. In 2010, I brought a bunch of planes over from the US to the UK and was very surprised how much less well they seemed to perform here. Several factors were at play: (1) the altitude, (2) the fussier noise restrictions, and (3) the lousy fuel I bought here. The last item I changed out for another brand with similar specifications and the difference was like chalk and cheese - I suspected the first batch of fuel had nowhere near the nitro content stated, and probably none at all (that's when I started weighing and doing volumetrics on the fuel I was buying here to check the nitro content). The altitude and air temperature/humidity difference between here and the US club also made a surprisingly big difference - one that was hard to justify theoretically. I found I could partly correct for that by changing prop sizes by an inch or so. Finally, the US club was not so fussy about the noise limit (there was an enormous shooting club next door, that made such I racket you'd think WWIII had started there, which drowned out the noise of model planes). So everyone took the baffles out of their silencers, which probably gave about 10% more power - and may be one of the reasons why higher nitro fuels worked better there. I personally did lots of tests on different nitro fuels and found my Saito 4-strokes and OS 2-strokes definitely ran better and more powerfully on the higher nitro (12 to 15%) fuels. Another thing that surprised me was that I did not find the higher nitro fuels were more expensive to run; the opposite in fact: they seemed to be very economic. This was a bit baffling, but I think it was because the engines ran at greater power at given throttle settings, so I was probably throttling back more with the higher nitro fuels.
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Sorry to spoil the party, but I had one of these and I was underwhelmed. Probably the worst value for money I have ever bought in aeromodelling - it looks like about 20 quids worth.
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I think assembling ARTF's is an excellent way to getting into building models. This assembling actually requires as much care as the final stages of building a model from scratch. I found that it would typically take me about 30 hours to put together an ARTF. Assembling ARTF's actually got me back into building from scratch. The more effort one puts into the hobby the more one gets back. This is why buying off-the-shelf RTF foamies gives me very little satisfaction; those in my collection are the models that I have the least respect for.
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10 minutes ago, Andrew McKelvey 1 said:
I have just reinvested a healthy chunk of money in buying some new li-po batteries in the belief that the old ones I have may no longer be up to it. aka 4cell 3300mAh 60C as compared to the same with 20C and being about 6 years old or more.
The comparison using my wattmeter with fully charged batteries in my plane setup gives nearly a 100 w difference , ie a difference of about 6 - 8A draw at full throttle and the older battery being about a volt or more down on the new one. I know this is down to internal resistance of the battery which has worsened with age and I could do comparison checks of my older battery's against new one but I am reluctant to do a load of testing with an 12x6 prop wizzing round at full chat just to provide the load plus the wind factor isn't good in the model room.
The questions!
1 How do you test an battery for capacity and obtain comparative results
2 If you manage to compute the internal resistance of said item how do you determine a pass or fail
3 Is there a method or a bit of technology I can use that will mean I am not holding down my plane and applying full throttle and trying to read the numbers on my wattmeter.
Your thought please will be gratefully received, I have more than enough electrical test equipment to do the measurements I just dont know what the results mean other than the old battery makes the plane unflyable and the new ones make it a pleasure to fly.
Six years for a LiPo! Is that common? I've not achieved anything like that.
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3 hours ago, Don Fry said:
What is the frontal width of a 200 V. That’s the distance between the outer edges of the cooling fins of the cylinders.
I've just grabbed a ruler and measured it. Looks like almost exactly 160 mm. That's the absolute maximum width between the outer extremities of the cooling fins.
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Bucks-composites, Kingfisher Aviation and FighterAces are amongst the best in the UK for providing glass fibre and suitable resins. Phil Clark at FighterAces also provides very useful advice; and FighterAces are the UK distributors for the excellent, but expensive Klass Kote epoxy paints.
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I have an OS 115 alpha - excellent engine.
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6 hours ago, Jon - Laser Engines said:
I hadnt seen a photo of the big revolver before. It so much better looking than the small one.
There were actually two smaller ones: the 46 size and the 65 size. Both look pretty similar to this larger one and the 65 size virtually identical. The 46 was the most fun RC model of its size I have had, flew like a bomb (with OS55AX) and was great on windy days. 65 (with Saito 125, I think) flew more sedately, but nice in its own way. I wish these were still available.
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3 hours ago, Jon - Laser Engines said:
What i would suggest is to fire it up, get to full power slightly rich and just keep leaning it off until it stops. You only need to do it once, but keep going at the rate of one needle click a second and just listen to it. It will get faster, faster, faster, no change, no change, maybe sound a little harsh with a crackle sound, revs drop, dead.
Open the needle and go again but this time you have that sound change profile in your head and you stop short of the crackle and certainly short of the rev drop.
I know its a 4 stroke, but this video shows me tuning up a 150 laser and the principal is exactly the same. You can hear the rev drop clearly as i pass the peak and how the engine responds when i dial it back. setting a needle is that fast, no need to take any longer. I also faff about with the slow run after that but you can ignore that part. Start at about 1 minute 18 seconds to skip all the starting and warmup.
Jon, great video, but I waited in great anticipation of seeing you throwing the tacho away. Somehow I missed that!
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To this tired and lame "thought puzzle" I say R.I.P.
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6 hours ago, Jon - Laser Engines said:
Its true that high nitro fuel offers a wider tolerable range of tuning, but that makes it all the more strange that they drop the rpm. If you have peak rpm set, and use the larger tuning range of high nitro fuel to wind on maybe 1/4 turn rich with no ill effect on revs, why do you then need to go even further and run it 200 rpm slower than that? It makes no sense.
These high nitro/run rich recommendations are at least partially responsible for the thinking that glow engines are expensive to run, thirsty, and very messy. High nitro means richer mixture, running rich on any fuel means higher fuel consumption but its worse on high nitro, more fuel consumption means more oil on the model and clearly more expense. Its one big snowball. They are also partly responsible for reliability problems as rich/cold engines do not run reliably as the glow plug needs to stay hot to keep the thing going.
There are exceptions though like i mentioned before. Nitro cars, and boats, heli's and ic ducted fan models too might need to run high nitro/rich mixtures to cool the engine and prevent burning of the piston crown. As you know when you spill some, methanol is cold due to its evaporation and running rich in those engines cools them by using the fuel as a coolant but high nitro allows no loss of performance. But if you look at it, all of those applications are tuned 2 strokes running at high and often fixed rpm with very marginal cooling. So these engines face different challenges to a bog stock 2 stoke pottering along at low revs (vs a 20000+ boat or car) with ample airflow and cooling so need to be run in a different way.
Saito are very keen that one does not "over-rev" their engines with too small a prop: "Over-revving of a 4-stroke engine can cause internal damage to the engine". That might be one of their motives for encouraging slightly rich settings in general. Another reason may be that Saito exhaust pipes tend to become undone and fall off, if you run their engines too hot and lean! The OS recommendation to back off the needle setting by 20 to 45 degrees from the peak rpm setting seems even more extreme. They too are very keen on the user running the engines rich whilst breaking them in. "During subsequent flights [after the long-drawn out process of running in], the needle-valve should be gradually closed to give more power... after a total of ten flights, the engine should run continuously, on its optimum needle-valve setting, without loss of power as it warms up"
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Jon, many thanks as usual for your expert clarification. Now that I think about it, I actually do more or less as you say and back off the needle valve from the max revs setting only slightly - and nowhere near the amounts suggested by OS and Saito. The only justification I can think of, for the amounts suggested in the American manuals, is that the Americans used to run their engines with much higher nitro contents than in the UK, which gives a considerably wider range of tolerable tuning adjustment than lower nitro fuels. With lower nitro fuels the adjustments are finer and more critical (in my limited experience).
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19 hours ago, Jon - Laser Engines said:
If you use the laser 5 fuel i recommended before and tune your engine up properly even a 2 stroke is not that messy. It will be considerably messier than a 4 stroke, but it isnt horrendous.
Just ignore anyone who tells you to tune the engine 'a bit rich for safety' and also ignore any advice to wave the nose of the model around in the air. Its dangerous and serves no purpose at all despite claims to the contrary. Running the engine rich will increase fuel consumption, increase the mess, decrease reliability and increase the chance of corrosion within the engine. None of which is helpful.
Jon, should I ignore the advice in the manuals for Saito 4-strokes ("The peak rpm should be obtained and then reduced by approximately 200-300 rpm by turning the high-speed needle valve counter-clockwise (richen)"), and in the manuals for OS 2-strokes (which show diagrams with the "practical best (optimum) needle-valve setting" 20-45 degrees back (rich) from the maximum rpm setting ("Lean")). I've always done this. Or do you mean something else?
Also, like Engine Doctor, I do the nose-up test at the start of a new session to check the integrity of the fuel tank plumbing.
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8 minutes ago, john stones 1 - Moderator said:
Wife ordered a baby, gave us a date of December 12th, Christmas day when it arrived, can't get good service these days. ☹️
Well you are in Good company: Christ Himself got it wrong. He was meant to have arrived also on Christmas day but was (reputably) many months out!
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7 hours ago, Frank Day said:
Hi Chris,
Lets start up a business, its all legal as long as the the buyer pays. I have some US and EU addresses available we could alternate buying and selling.
The item must be Used, New will get delivered - probably!. I checked before offering international postage, IC model engines aren't on any prohibited list.
I have a terrible but "highly desirable" OS40 going at a very reasonable £299.00. No careful owners etc no service history, although a Priest was the first owner.
The strange issue is that they wont send it back because of the imaginary danger and they wont let the seller personally go and collect it.
Of course there's nothing else that could possibly catch alight on a ship or plane, like someones cigarette lighter!
This is an official item:
Absorbed liquid and butane lighters are limited to one lighter per passenger in carry-on or on one's person. When a carry-on bag is checked at the gate or at planeside, any lighter in the carry-on must be removed from the bag and kept with the passenger in the aircraft cabin.!!!!!!!!!
Confirmed, they don't carry out any test
Ha! £300 for an OS40. I see that Leeds Model Shop is selling both the OS46AX and OS55AX for £128 pounds, which I think is a real bargain given the brecciated pound etc. That must be about the greatest bangs for the buck in UK aeromodelling at the moment (and way better than the cost of batteries for leccy models, IMHO).
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22 hours ago, Jon - Laser Engines said:
I think this point is key as the issues i have experienced with 'difficult' full size pilots learning models is they consider them toys and trivialise the skills of their instructors paying their advice no attention at all. This is a problem as, in many respects, models are more difficult to fly.
In the US there is a higher proportion of model flyers who also fly full size planes, so this got discussed a lot. The consensus was that those who flew model planes before full-size were superb model aircraft pilots, whereas those who flew full-size first found model flying really difficult. It was not about them trivialising models, but it really was difficult for them because flying in the same direction as the aircraft is so ingrained that they find it very hard to unlearn that and reverse controls when the model and pilot are facing in different directions. (Unlearning ingrained bad habits is one of the top reasons for not learning bad habits in the first place, in anything.)
One of the things that I find interesting is that practically all beginners to model flying fly their models in a very similar way: with vast overcontrolling, and find it much more difficult than they expected (because they are "good drivers", or something). What varies enormously is how quickly beginners come up their learning curve. Youngsters usually seem to learn model flying skills much faster than oldies. This may be partly because many of them are already trained in computer games that require fast reactions.
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The situation a couple of years ago was clear-cut. Unless the transmitter has a genuine CE sticker it is not legal in the UK. RC transmitters in the US are allowed a higher power. I was going to bring a couple of Spektrum transmitters over from the US to the UK a few years ago, but did not because I was advised it was illegal.
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10 minutes ago, Jon - Laser Engines said:
I dont think the world could handle two of me even if one was at reduced scale.
Don't be so sure. Chuck gliders are very easy to handle and it's surprising how far one can throw them!
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I don't think Jon is using the words "cheat" and "lazy" in an offensive sense. Indeed ours is not (ostensibly) a competitive pastime, so we are not cheating others by our own approaches to model flying. What Jon is talking about is "cheating" ourselves, i.e., making ourselves seem more accomplished than we are by using various aids that hide our deficiencies. The ultimate is autopilot that flies a plane very well but teaches us little or nothing about flying.
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Kim,
Thanks for posting the excellent top and side views. All looks fine. The distance between the tank and the carb also looks fine and rather ordinary - certainly not excessive.
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Kim,
I am having some difficulty interpreting the relative levels of tank and engine in your perspective drawing. The tank and the red line appear to be angled downwards towards the front, and the engine and firewall give the impression of being set up with a very large amount of right thrust, which (in the angled view, rather than side view) also makes it difficult to tell the relative levels. Maybe these effects are just optical illusions.
First taste of the sky
in Beginners
Posted
Do you use a simulator? When I was learning I found a really good way to get more stick time was to use a simulator to more or less mimic what I was doing with the actual model. The Real Flight simulator I was using allowed one to adjust the properties of the computer model until they were very like the actual model.