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Awful_Charlie last won the day on March 27 2013

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About Awful_Charlie

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    1998 M20M

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  1. Awful_Charlie

    Fuel leak

    You don't say where on the wingwalk the stain is appearing, but if it is on the inboard edge (and no trace on the outboard edge), then you will probably have to remove the wingwalk to get access. To do that, you will likely need a good quantity (a quart or so) of MEK or similar, and some sort of squeeze bottle, and a plastic scraper that tolerates MEK. If you have TKS, spend time to make sure you fully (and maybe double!) protect the near panel(s) as MEK will destroy them Of course you'll need replacement material too - mine is My leak turned out to be a single screw on the reinforcing bracket for the panel under the wingwalk: removal of that screw, a dob or PR and replacement (new!) screw sorted that one out
  2. Awful_Charlie

    500 Hour past TBO Rocket gets OH

    Is it being run with a test prop/club, or with the flight prop? If the latter, what static RPM is it supposed to make? Most aircraft with a CS prop have a max static RPM that is lower than the max RPM in flight. As the prop has been out for overhaul, it is possible the low pitch stop has been incorrectly set and it might need a tweak to allow it a little finer which will then increase the RPM
  3. Awful_Charlie

    MP vs RPM for % power.

    Except engines don't idle at 0" MP! I guess you've got the range of about 12-30 to play with at sea level They also don't make a great deal of power sub 1000 RPM, but I agree for RPM in the narrow operating band we use, it's close enough
  4. Awful_Charlie

    Long Body Market?

    Factory Lycoming comes with turbo, controls & exhaust, but starter and alternators are excluded (had to do this earlier in the year )
  5. Awful_Charlie

    Fuel efficiency in headwinds

    I already did this somewhere in times past: It's tailored for Bravo PoH figures and UK wind charts, but easily changed. It used Ed Williams aviation formulae, so has macros in it Put in the wind: (using SW UK in this example) and the desired track Read off the best/worst speeds and mpg
  6. Finally dug out the bits and got round to taking some photos: From left: Bulb with sticker & leads removed, bulb with leads but sticker removed, bulb with sticker and lead removed, new uncut bulb with box behind ($3 from ebay) Two old bulbs and the new from the front - note that theold are trimmed off asymmetrically
  7. Awful_Charlie

    My Engine Heater

    Thought I'd add to this, as thanks to the original idea, I went ahead on one of these. The only power I have at my home 'drome is via a generator, and I wanted something I could take with me too, as hangars for visitors can be quite difficult when touring. I also wanted something that could be used to eg heat a tent, or even potentially for working in the hangar. Things I wanted over Bob's original design were less protrusions on the exterior, able to be left as well as used outside (less susceptible to rain), and possibly a greater autonomy. If it could be more rodent-proof that would be an advantage, as would making it resistant to spills (I think the smell of diesel/jet fuel/heating oil in a confined space particularly nauseating) After getting the bits and starting to assemble, I wish I'd done more research before! In Europe, heaters like these are frequently found in boats and motorhomes, and sometimes the long distance trucks. They're often known by the trade name "Eberspacher" where a D5 model equivalent from ebay could be had for less than USD250. The D5 uses up to 0.6 liters (a litre is near a dammit a quart) per hour foor a 5500W output After the heater itself, a tool box from a local DIY store (expensive - this is Switzerland!, but at least I could see what was inside etc before buying), fuel tanks, batteries, charger and some odds and ends from a model shop (batteries for an RC model were more like the load profile than a motorcycle battery I thought), and a couple of evenings with a drill and knife. Result: Fairly standard looking toolbox from a distance (Oil cans for scale!) On left, exhaust, charging socket and master switch, heater supplied control panel in the middle, thermometer stuck on the right Air inlet is via hundreds of small holes drilled below the drip line of the lid that continue round the tool box Hot air outlet All the gubbins: By routing the exhaust inside of the box I expect some slight additional heat recovery! Fuel tank vents to felt air filter incorporates a non-return valve, but hoping that the loops in the vent lines will prevent the stuff getting that far - has bee tested in the roll 90 degrees either way about the long dimension. No so visible is the aluminium plate between the heater and the batteries - the idea here is to get some heat to the batteries (after all, it is being used in the cold!) to improve the capacity With exhaust extension (just visible extending out of the hangar door - I expect to put a hole in the wall at a suitable position in due course) and duct extension (short black length is what will be used to go up the cowl flap for engine heating) for use in the hangar: Autonomy at minimum heat is in excess of 18 hours which is more than I needed. At maximum I'm expecting more than two hours, which should be more than enough for an engine pre-heat - maybe another report after the cold sets in (it has remained remarkably warm so far this autumn - maybe making a heater is going to give us a mild winter!!)
  8. Awful_Charlie

    M20M LOP Discussion

    In addition to Dave's pieces, I'll try to add a bit: Let's have a quick look at torque and power before we get too far: Torque you are probably familiar with via the use of a torque wrench. Is is a measure of how hard you can turn something, and the typical example is one of a bucket in a well, where the drum on which the rope is would has a diameter, and the handle with which to wind also has a length. It doesn't matter about the diameter or the length of the handle for the amount of torque required to hold the bucket in one position, and to hold it stationary required no power, you have to apply so much force over a lever of a length which is why the unit is lb/ft or kg/m - like a see-saw used in the CofG calculations, you can apply half the force at double the distance for the same effect. If you want to move the bucket up, you need to exert not only torque, but maintain this over a period of time. So you could have a "low geared" well lift, where you wind the handle lots of times to move the bucket up one foot, or a "high geared" one when maybe only a fraction of a turn is required, but in the latter case you would need to apply a lot more torque. Power comes from multiplying the torque (which is already a product of the force and the lever length) and the rate of rotation, so consequently something at 0 RPM is making zero power, but back to the well, a tiny motor with very little torque but running through a reduction gearbox maybe able to lift the bucket - however a big motor at low RPM may have the torque to lift it without the gearbox. At the end of the day, if they lift the same weight bucket over the3 same distance in the same time, then they are making the same power. You can put a torque wrench in the vice and hang a few bags of sugar on it, and you can get a torque reading, but there's no power being produced! One way you can get power by burning fuel. You can burn fuel in a variety of ways, many of which are terribly inefficient, but if you want to extract more power (at a given efficiency) in a normal IC engine, there are two ways to do it: a) turn the engine faster (so it draws in more fuel and air) - as long as the torque doesn't diminish to much, as power=torque x more RPM ie more power (lift the bucket up faster) b) Ram more air and fuel in - this will (should!) give us more torque, so again power=more torque x RPM ie more power again (lift a heavier bucket up in the same time) Problem with a) is we need to keep the prop tips sub-supersonic (or the prop goes very inefficient) There's loads of reading out there on this too, but in summary, we need to keep the tips below about 0.85 mach or so. As the speed of sound is dependant on temperature (not air pressure!), then at high altitudes (in the cold), the speed of sound is lower, and a 75" dia prop (as we have on the Bravo), with a high TAS (which adds to the tip speed) we can get quite close even at 2400RPM. If you get up in the (very!) cold you can try this by setting max power at 2400, and then trying 2575 - if the tips get over the critical mach then you will actually slow down. (Obviously I hope, race/consumer engines for cars/bikes etc have different constraints) Problem with b) is you can only ram in so much with the compression before detonation comes a problem. The effective overall compression ratio is not that terrible, just some of the compression has taken place outside of the cylinder. A NA engine at FL180 only gets half the ambient sea level pressure, but a turbo'd one can get sea level or more, so that 10:1 ratio N/A is effectively 5:1 at FL180. In a turbo'd engine you can get the whole sea level pressure, but you're constrained by all sorts of other stuff such as the incoming charge temperature that it is principally the engine designers job to manage. With all that out of the way, we could over simplify things to say that if you burn fuel in the most efficient way possible (ie about 25-50 LOP) in an IC engine, for rotating shaft output, then the amount of power is dependant on how much fuel you lob in, hence the figures in Don's spreadsheet. Problem we have is primarily cooling and the speed of combustion, and to manage these the designer has specified an overly rich mixture at high power settings. This means we don't burn the fuel efficiently - we are putting extra in to cool the combustion and get a burn speed that allows us to get more power, albeit at an efficiency cost. Conversely, at low power, we are still making all the ancillaries and internals do their work, and these have an overhead (eg, take all the spark plugs out of your engine and spin it over by hand - hard work isn't it! Now spin it at 2400RPM and see how much power that needs!) That power is gone no matter how much fuel you put in. This is one of the factors the engine designer copes with for the idle speed - the engine might be making 10 or 20% of maximum rate power from the fuel ingested, but so much is used to internally before there is any to spare - if he makes the idle any slower, then there is not enough power to run the internal before we get anything useful for the prop, and hence the engine stops. The graph can be converted into BSFC (Brake Specific Fuel consumption), which is a measure of efficiency - how much power do you get from each pound of fuel. (Lots of reading out there on this too is you are interested) Really efficient engines (diesels) get down to maybe 0.35, gasoline engines rarely do better than 0.38, and even then only at a very controlled output. By converting the units in the graph we get a peak efficiency in the AF1A/B of about 0.45 or so which is pretty rubbish, but it is an abysmal 0.6 at max power, and over 0.5 below 50% power. The "sweet spot" for efficiency in that graph is thus in the 175-215BHP area, and outside of that it is starting to drop off Some of the good gas aero engines are getting to about 0.41 - 0.42 or so, only 0.04-0.03 difference, but this does represent 10% Hope that helps! Ben
  9. Awful_Charlie

    JPI Oil Temperature Probe Question

    Mine is where you have re-located yours too - good job :-) Wire routes with the unconnected prop heater underneath the barrels to go through the firewall on the starboard side with the starter cable (and the rest of the JPI leads) Not a great picture - EGT and cylinder probes are on the stand-offs with the lower HT leads, Oli temp just visible at the back
  10. Awful_Charlie

    M20M LOP Discussion

    Note the limits from the fuel and Compression ration in Don's sheet above, but also read it in conjunction with the Lycoming PoH "Lean Limit" curve 13490: Note that when you get over 220BHP or so (75%) the BSFC is getting substantially worse - this is around the 16.5GPH. Unfortunately the Lycoming curve has nothing about the surrounding parameters, of which the likely most significant is RPM, so as they say, YMMV!
  11. Awful_Charlie

    JPI Oil Temperature Probe Question

    My oil temp probe for the JPI is installed as per the JPI manual - no problem with unbelievable readings (#3 CHT is unfortunately not the same - problem solving TBD) Why people decide to install probes in non-approved locations bewilders me - for instance this case was an expensive lesson!
  12. Awful_Charlie

    Altimeter vs manifold pressure gauge

    RTFM!!! The JPI one! There's a table in there as it is *not* directly readable from the altimeter
  13. Awful_Charlie

    Paint or interior first

    I'd go with Matt above, but one that no-one has added yet is tanks - whether it be bladders or re-seal, get them done before paint
  14. Awful_Charlie

    An Absolutely Horrible Day!

    Well, if it is any consolation Don, I sent my first run core back to Lycoming in June, so they most likely have one on the shelf!
  15. Awful_Charlie

    Leaking exhaust

    Another good reason for LOP