John Stainforth

Don, I think you should tell me what does not impress you about my first paragraph, in which I have stated the facts as accurately as I am able to. One has to assume that the stated proportion of oil is correct. In the case of the Optifuel I mentioned, the content of both the oil and the nitromethane have to be right up to the full amounts stated by the supplier in order to explain the weight of the fuel. The nitromethane content would only be seriously in error if the suppliers had inadvertently added a lot more oil than stated, which is unlikely. The weights are easily measured on digital scales that are accurate to fractions of a percent. The estimate of the volume of water (via weight and density of water) is accurate to within a few cc's in 5 litres, i.e., parts per thousand. The densities at standard temperature and pressure are obtained off the internet. The whole measurement procedure only takes a few minutes. With the assumptions above, only three measurements are necessary: the weight of the fuel+container, the empty weight of an identical container and the weight of the latter filled to the same level (as the fuel) with water.

Please elaborate on what does not make sense to you. I may have expressed myself badly. (I am living an alcohol-free existence!)

This is your imagination. The majority of model flyers in the southern US use glow fuel with 18% oil and between 5 and 20 % nitromethane, depending on the engine and personal preference. The oil is typically synthetic or a blend of 80% synthetic and 20% castor. One of the most popular fuels there is VP PowerMaster, which uses the latter blend of oil. I have no idea what the benefit of 20% castor is meant to be; all I can say is engines using that blend did not gum up after 10 years of use. One thing to watch out for on both sides of the pond is lousy fuel that does not contain what is says on the label. This may have contributed to the idea that nitro make no difference to power. I routinely check the fuel I buy by weighing it and doing a simple mass balance of methanol, nitromethane and oil, given the densities of these three ingredients. The first thing to check is the volume of fuel you've been sold, and the easiest way to do that is to weigh an identical container filled to the same level with water and subtract the weight of the dry empty container. The last batch of Optifuel I bought here in the UK (12% nitro, 18% nitromethane) passed this test with flying colours. Not only did the mass balance suggest the fuel contained exactly the proportions stated on the label, but the volume of fuel was very generous! My own findings (in the US) re fuel consumption with different nitro percentages are at odds with some of the views that have been expressed on this site. I realise that the climatic conditions there, and the low altitude, and the fact that we took the baffles out of silencers to give the engines more power, were different to typical conditions in the UK. (I am very surprised by how much difference even modest differences in altitude make, but those can be largely compensated for by using propellors with different pitch or diameter.) I highly respect the views of Jon on this site - and follow all his advice wrt Lasers - so I intend to do some new tests myself in the UK in the coming year with different blends of fuel, particularly regarding fuel consumption.

Continuing off topic, all pre-1950's planes and ships were designed and built using slide rules and log tables. The standard tolerance on the airframes of the Schneider trophy racers was 1/16th of an inches. The airframe dimensions were all in given in "tables of offsets and sixteenths" with respect to the fuselage stations, buttock lines and waterlines.

Yes, Aero Modeller Of The Year!

Best wishes for a rapid recovery! If it's any consolation, I would vote for you as the AMOTY!

I'm another fan of Optifuel 12. Frank, have you tried your OS55AX on 10, 12 or 15% nitro?

Jon, it's easy for you to say that, as the world's expert in the language of Laserspeak! Most of us are still struggling with the basic vocabulary.

Air intake too close to firewall?

Quite an easy solution that stays fixed is a tailor-made wooden box to house the lead (or more user-friendly alternatives). One can even use lead shot in one of those.

Paul, I think I got the flexipipes (called bendy pipes) from Mick Reeves Models. (I don't seem to be able to access that site to check, because my server says it has potential viruses!) Several short videos of the first two flights of my S6b, piloted by Ian Redshaw, appeared on (the dreaded) Facebook on Sept 12th, two courtesy of the British Waterplanes Association (one of engine tuning, second of first take-off) and one from Seaplanes Scotland of some fly-pasts on the second flight. I, and several other people, also put some photos Members New Models forum on this site.

The flexipipes that I put on the Laser 200V in my S6b worried me a bit, because they are quite close to the fuel system. However, they seem to have worked out fine, in practice. The pipes are protected by thick silicone tubing where they pass through the 3D printed nylon engine fairings (which have a pretty low melting point). The first picture is with the engine running. This second picture shows the proximity to the tanks:

I'm a big fan of Optifuel. I bought a couple of gallons of Optimix 12 Sport fuel a few weeks ago for 19.58 pounds per gallon from Nexus modelling supplies, who provide an excellent rapid delivery service. Actually, the volume is nominally 5 litres, which is more than a UK gallon (= 4.5 litres), and it's a very generous 5 litres at that. (I measure the volumes and weights of the glow fuels I buy, to check the nitromethane content. Optimix contains what it says.)

But only just!

The promise of Laser engines is mouth-watering indeed!

The weight of engine is crucial, and I like to work out roughly what this should be from the get-go, using simple static balance calculations. For a scale model, it is usually possible to obtain the manufacturer’s data of the weight of the full-size plane, the weight of its engine and the position of its CG. From these one can calculate, using moments, where the CG of its airframe is relative to the CG. If one then makes the assumption that the CG of the total plane and the CG of the airframe should be in the same scaled positions in the model as in the full-size, one can then make further moment calculations to estimate the required weight of engine to balance the model exactly. One also has to make an assumption about the target weight of the complete model on the basis of its size, and for this I use a desired cubic wing loading. I also include in the moment calculations any components in the model that are not in the same corresponding positions as in the full-size, such as fuel tanks and batteries. Then I search around for a model engine of the suitable weight, bearing in mind that its scaled CG is usually not in the same place as that of the full-size engine. Also, one has to be careful to include all the clobber on the engine, such as exhaust and ignition systems, propellor and spinner. Manufacturers of model engines often to not include these “extra” items in their quoted weights. If one has the physical engine to hand it is best to weigh it with all the clobber and estimate the position of its CG at the same time. There is a tendency to want to use a model engine that is lighter than the desirable weight, so that its clunky shape can be more easily accommodated in the fuselage, but this will then require extra ballast. This approach can only be taken so far, because the lighter the engine, the more underpowered the model and the more ballast it will need - which is actually the last thing an underpowered model needs! As others have said, the position of the CG can be checked as the building proceeds. Bear in mind, though, that sheeting a model airframe will tend to move the CG backwards a little (because the sheeting is roughly distributed around the airframe CG and not the total CG). The same is true of finishing (glassing and painting).

So Laser might have run on their engines and need to up their production!

Ron, please can you tell us what the different coloured lines are showing. I think it's: Green - throttle, pink -aileron, yellow - rudder, magenta - elevator. (The resolution on my computer screen is not good enough to read the captions, so I can't be sure.) If I am right, there is a lot of elevator coming in after you start your turn on to finals, but I don't know whether this is up or down elevator. Did the spin start immediately you turned on to finals?

For me, the flying scenes were the high point of this movie, but how high is a question for some debate as we have seen in this discussion. There is no doubt, too, that the movie gave a big boost to the warbird restoration industry: that is well documented. But the movie did not do very well when it came out (I think it lost money), particularly outside the UK, mainly because of its thin, jingoistic, cliche-ridden script. Roger Ebert, the film critic of the Chicago Sun, gave it 1* for this reason. On balance, I would give it 3* There are very few war movies that have really worked for me: Saving Private Ryan was one, and Das Boot another.

Some hope! They're all members of Ethanol Anonymous.

CH3OH burns to to give CO2 + 2H2O, so ~32 g of methanol will produce ~36 g of water. The density of methanol is ~0.8 g/cc, so 40 volumes of methanol will produce about 36 volumes of water, so (as you say) pretty similar to burning petrol.

I tend to go with what the manufacturers say. So I listen to John re Lasers, but refer to the relevant manuals for other engines (e.g., I laboriously follow the procedure recommended by OS for their two strokes). Raises the question as to what really is "best practice".

No, twins are good!

The Spektrum website actually recommends using several batteries in parallel as a best practice: "DO USE A SECOND BATTERY ON YOUR MOST VALUABLE AIRCRAFT. While all Spektrum 9-channel-and-above receivers have multiple battery ports, you can actually put multiple batteries into any Spektrum receiver. Simply choose two batteries of the same size and capacity with two switches."