AussieMozzie

Discussion in 'Hangar Flying' started by Head in the clouds, Jul 21, 2012.

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  1. Dec 3, 2012 #161

    Head in the clouds

    Head in the clouds

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    Hi Jim,

    Yes I made the prop extension according to the 912 manual, page 122. Max length is given as 120mm so that's the length I made it to.

    Cheers,

    Alan
     
  2. Jan 22, 2013 #162

    pylon500

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    G'Day Alan,
    Just came over to have a look, haven't been here for a while.
    My, you have been busy.
    Been having a think about your cooling outlet, and the comments being made about effectiveness, prop interference/noise, and would like to suggest the following;
    Having the outlet close to the prop will help 'suck' the air through the system, you don't need it when the engine is stopped, so the size doesn't need to be too big.
    As for noise, it is fortunate that you have decided to use a Bolly prop, the scimitar shape will cut down on pulse noise as the prop passes the vertical 'stern'.
    To that end I have depicted in the attachment,making a horizontal to vertical duct to go around the muffler, but suggest that it terminate as a skewed outlet, angled against the sweep of the blade thereby crossing the outlet in a sweeping motion as opposed to a single 'pulse' pass.
    Arthur.
     

    Attached Files:

  3. Jan 23, 2013 #163

    Head in the clouds

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    That's nice thinking Arthur, thank you. I'll have a look at it.

    I need cooling for the muffler as well of course but am in the midst of making a louvre pressing tool so those may well be sufficient for the muffler.

    I've also gone with a belt and braces approach (got chicken) and bought a Davies Craig fan to install on the upwind side of the rads. It's only a 10" but it really puts out. I was mainly concerned about sucking air in for/during the compulsory 3 min WOT run for C of A.

    Thanks again, Cheers, Alan
     
  4. Apr 23, 2013 #164

    Aircar

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    G'day Allan,- just happened by my computer repair and internet cafe and found your post to Hugh Lorimer and the link to here --been curious as to how you are progressing and looking for an update..... Still have no internet at home and sundry other impediments so only possible to check in on HBA occasionally.

    Hope all is going well
     
  5. Nov 24, 2013 #165

    Head in the clouds

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    It's hard to believe that it's been the best part of year since I got any work done on the Moz.

    Due to several work related and other distractions and interruptions I've just not had time to devote to it but at last I got everything else under control about three weeks ago and was able to poke my head out onto the verandah where I've been walking past the project regularly with eyes averted and trying not to feel too guilty about the neglect.

    First job was to clean out the cobwebs and get rid of the dust on the top surfaces, and treat a few areas of minor corrosion, we're very close to the beach here and although the southeasters provide us with lovely breezes, when the sea-breeze kicks in as well in the afternoons we get a salt covering on everything and cars, houses, tools and machines all get covered in rust unless they have constant care.

    A good example is all the clecos. I don't know whether the copper coating that provides the colour-coding for the 1/8 clecos reacted with the aly - I can't see how it would because copper and an aly boat in seawater results in corrosion to the aly not the copper - but anyway the clecos all lost their copper coating and are covered in deep rust pitting. Gladly that's about the worst of it, except the propshaft extension which is really annoying. That was machined from 7075 and now wish I'd used 6061 because the 7075 corrodes dreadfully and it has surface corrosion on the top surface even though I had it greased. Soon I'll be able to remove the engine cowling and then be able to get at the extension to remove it and see how bad it really is. I certainly don't want any stress risers in it that might encourage the prop to depart company, especially it being between the two tail-booms. It doesn't look too bad from what I can see so I hope to be able to machine the surface again and clean it up.

    The next big endeavour was working out where I had got to and finding any bits I'd made for the next stage, any bits I'd cut out but not formed and any templates I'd already made because I didn't want to double up. I don't like this ageing thing I can tell you, my memory used to be really good, well I think it was ...

    The next big stage to complete is the top half of the engine cowling, because when that's done I can remove the top and bottom halves and pull the engine out again so that I can get at the area under the engine and finish the cooling ducting and inlets, and hook up the oil and water radiators, oil tank and all that.

    Finally I got to cutting, filing, forming and drilling again and over the last couple of weekends I've got one side of the cowling completely finished and just three panels left to make for the other side, so it should be 'in the can' by the end of next weekend - sadly I have to work during the week, bugga!

    Here are some pics, the first shows the surprising number of parts required to make just one side of the top half of the cowling. The next two pics show the space they will cover and the last two show the parts all riveted in place.

    SDC11577.jpg SDC11579.jpg SDC11580.jpg SDC11582.jpg SDC11583.jpg
     
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  6. Nov 25, 2013 #166

    Aircar

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    Greetings Alan, --just noticed your update and good to see you are at it again on the OZMOZ . Is that the water cooled head Rotax ? if so do you have a separate water cooler and cooling for the barrels etc ? (probably that was answered a long time back but too lazy to re read ..) It reminds me of my Sunbird installation --later converted to Stiletto but for this purpose the same general geometry of pod and engine/prop . There will tend to be a pressure drop created by the prop which is greatest at about the 3/4 prop diameter position (close to your apparent exhaust outlet ) -this acts counter to the pressure recovery on the aft body but is more powerful when power is high eg low speed climb ,which helps with the critical cooling case ,and diminishes in cruise . All good; --with the Stiletto I had NACA ducts positioned just ahead of the cylinder head and even on static run up the induced airflow was enough to keep it from overheating (I had a borrowed temp sensor that worked off a special spark plug washer --a thermocouple ) - Sander Ve Enstra was present when I did the initial ground tests and expected it to cook itself and was surprised to see the reverse (and tufting the inlet even showed the 'concorde like' vortices that are created by the sharp edges of the NACA inlet and make them work ) --keep that set up in mind if you have any temp issues if you like.

    All the best, Ross.
     
  7. Nov 25, 2013 #167

    Head in the clouds

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    Hi Ross, all good thoughts, thanks again. Yes, it's the liquid cooled heads thing and I have the radiator below the engine and below an oil cooler both of which vent to the sealed compartment aft which houses the muffler. I also have a powerful thermatic fan that will force feed the radiators as required. I'll be installing a pair of 'NASA ducts' (or a P51 scoop?) in the lower surface of the wing under the engine and they will be one of the air inlets, the wheel fairings also act as scoops to direct air into the open bottom of the wheel well, in line with the tail-booms. That air then traverses into the void below the engine via the large lightening holes in the inboard wing ribs. I've initially left the fuselage sides forward of the cylinders sealed because I'm hoping for enough flow from the inlets mentioned but if they don't prove to be sufficient I can add ducts such as you described at a later stage. It is with those in mind that I have shaped/curved the surfaces of the blisters that house the cylinders, so I have some options I think. Have tried not to paint self into corner anyway!

    It'll be good to get the cowling finished so I can pull the engine and be able to post some pics of what we have in there, and get folks' thoughts.

    I had never realised that the NASA ducts relied on l/e vortex principle to make them work, I always imagined it was just the low pressure caused by the depression - live and learn ta.gif
     
  8. Dec 17, 2013 #168

    Head in the clouds

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    The last couple of days' worth of work on the engine cowling typically turned into nearly a month, not that I've had that much spare time just lately.

    I got the second side of the upper cowling finished and that provoked a sigh of relief, I'm really and truly over the finicky work involved in all that, next time it'll be a GRP cowling I think. At least it turned out quite well and looks better in the flesh than the photos indicate due to some odd reflections.

    I was about to rivet the whole cowling out when I recalled that I needed to add louvres to the lower section of the removable cowling to get rid of the exhaust manifold heat, and also add louvres to the fixed fuselage sides below the cowling, to add to the air outlet area from the radiator, oil cooler and muffler. I'd been putting that job off deliberately I think as the only bloke I know who has a press-tool for making louvres is in Brisbane 100km (60 miles) north and his tool presses a set of 16 small slots suitable for a sports car bonnet (hood) and he charges about $500 per pressing. I'd have needed 6 pressings and I wasn't sure they'd be quite the right size and I don't think his die is modular.

    That meant I'd have to make a small press-tool myself and the main problem there is that I sold my milling machine a while back because it was too large for the small work I do these days and I haven't come across a small one yet at the right price. So I had to make do with the bandsaw and files. To keep the toolmaking time down I decided to just make an aly tool. It might not last long and only pressed single vents at a time, but I only had to make 46 of them so I hoped that it would do. It didn't turn out too bad in the end although I did have to spend a while experimenting with the draw depth, at first it just cracked or tore the metal but after about a dozen adjustments they started to turn out acceptable.

    Next I had to make a new blade for my Monodex shear for cutting the slots for the vents because the standard blade was too wide (3mm but I needed 2mm). I made that up from CRMO sheet but it didn't last long enough so I had to heat treat it. I just did a quick job on that, cherry red with a blowtorch, drop in a bucket of water and then temper to straw, all done in a matter of a minute and it worked fine after that.

    I set out the pattern in the lower cowling (did it about six times in fact before I got it how I wanted it) and pressed those vents, all worked out fine.

    Then I set out a pattern on the lower fuselage side so that the first two rows of the lower were aligned with the last two rows of the upper and cut the slots in the panel. That's when I realised I'd made a really stupid mistake because if I just pressed the vents into the fuselage side and then riveted the side up I wouldn't have any access to the muffler and elevator control horn/torque tube attachment. Typically it was only seconds after I'd cut all the slots that I realised this. I really wished it had been seconds beforehand instead. I then had to work out a new pattern of slots that allowed me to cut out a large access hatch each side and also keep the vents aligned for aesthetic reasons. Then the next hurdle surfaced, I only had enough 0.025" sheet left to make an access panel for one side. So that bit of sheet would have to be used to replace the area in the side where I had already cut the slots, but on the other side I'd have to use the piece I cut out as the hatch panel. So - how to cut out a panel from the fuselage side with a 1mm (0.040") slot all around? I couldn't drill holes at the corners to start a cut with snips ...

    I ended up making a guide for the corner radiused cuts out of thick aly and using a 1mm diameter dentist drill as a cutter in a Dremel and hand milled the curved slots at the corners, then made another new blade for the Monodex shear, this time out of 0.040 sheet CRMO, hardened and tempered that as before and cut the straight parts of the slots with that. It was a bit nerve wracking but worked out well - it's the starboard side panel in the pics below. I just hope I don't need any more 0.025" sheeting on the rest of the project but it should be OK, I previously cut out all the required panels I think.

    Then I had to make the framing for the access panels, fit the DZUS fasteners and hinges blah blah, it seemed to just go on and on. At last I was ready to finish the cowling riveting and pull the engine out and get access under it, which I've been waiting to do for ages. But not quite, I still had to clean and etch prime the edges of the panels where they'll meet face to face when riveted, and I don't want an inaccessible area for corrosion later so I had to start peeling off the plastic sheet covering from the fuselage panels.

    That's when I discovered I'd fallen into a trap I was fully aware of and had been actively avoiding all along. We all know we mustn't leave the plastic protective sheeting on plexiglass and expose it to the sun or you'll never get it off, so I guessed the same might apply to the protective sheeting on the aly. Since I'd had a long delay in the work on this project I had been very carefully checking the state of the protective sheeting by peeling a little every month or so, from a panel that is well exposed to sunlight. And it never showed any difficulty to remove it. Imagine my chagrin to find that the sheeting on most of the fuselage sides and front was stuck solid and also very brittle so it was impossible to remove anything more that a scrap at a time by scraping with a fingernail. the piece I had been testing regularly was fine, so what was the difference? Well it turned out that only the protective film on the 0.025 sheeting was stuck, all the other films on the other sheet thicknesses was fine. Unfortunately most of it was 0.025". I spent a very miserable day and a half and removed about a square yard/metre before giving up with hands blistered and bleeding.

    I slept on it and gladly came up with an idea that worked even if a bit tedious. I cleaned the film surface well with methylated spirit and then covered it in strips of packaging tape which I rolled down firmly with rubber laminating rollers, with the aid of a plastic scraper and very careful and slow peeling I got the rest off in a day. See pic.

    So - at last I really am ready to pull the last few rivets in the lower cowling and work on the air inlets, oil tank and thermatic fan then it should be time to get onto the tailbooms, a change in scenery that I'm looking forward to. I'll do the doors and the rest of the instrument panel later.

    Here are some pics, if you've managed to wade your way through the above you'll maybe recognise what some of them show -


    SDC11584.jpg SDC11585.jpg SDC11588.jpg SDC11592.jpg SDC11594.jpg SDC11595.jpg SDC11599.jpg SDC11600.jpg SDC11601.jpg SDC11602.jpg
     
  9. Dec 17, 2013 #169

    BBerson

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    Those louvers look good to me. I think as we age simple tasks seem to get complicated and take ten times longer to complete.

    Do those multiple small louvers create the needed negative pressures as well as one big ugly lip? Anybody know?
     
  10. Dec 17, 2013 #170

    Aircar

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    I can sympathize with the film stuck-on problem Alan, used to run a plastics molding shop and found we needed some long lost old stock of some peculiar colour or thickness with frequently intractable covering,usually paper, stuck fast -- sometimes a little heat can loosen it and judicious rolling back over itself stop tearing into smaller bits . On metal you could soak rags in MEK or acetone or similar and see if that softens the bond and lets you peel it off (sometimes nothing bloody works!)

    I recall seeing a 'clever' way to make louvres in a hot rod magazine way back but can't remember the details --maybe a local hot rod guy could find it (if I recall rightly it was something like the way to do a jog )

    With louvres I thought that the only function was to exit the exhaust air parallel to the surface -like a shark's gills, but BB might be right about a pressure drop from the camber of the next downstream bulge.

    Is "Mosquito season' too far away up there ?

    (and a PS _ I haven't been back in touch about any memorial get together for Werner --let me know if your other mate organizes anything please.)
     
  11. Dec 20, 2013 #171

    Head in the clouds

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    The oil tank is fitted and gladly there was just enough space to have it at the Rotax approved height and distance from the pickups.

    Another squeeze though, yet again demonstrating the increased difficulty of a pusher configuration over tractor. A bit disappointed that Rotax don't supply a standard bulkhead mounting bracket for the tank since they nearly all get to be mounted this way and it's a bit tricky due to the ring clamp and flange at the top so the bracket has to be made to stand the tank off the surface. Typically I made the first bracket with too little stand-off so had to do it again. I think someone mentioned that building your own design means you've built two or three by the time you're done ...

    SDC11607.jpg SDC11611.jpg SDC11613.jpg SDC11614.jpg
     
  12. Dec 20, 2013 #172

    Head in the clouds

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    LEARNED HELP WANTED

    LEARNED HELP WANTED -

    I'm reasonably satisfied with the cooling air outlets now, with the open tailcone and louvres in the lower section where the radiators exhaust and the large upper outlets where the cylinder cooling air exhausts, and the powerful fan to force air through the radiators when required during taxy and climb perhaps.

    My attention is now on the cooling air inlets. The aft part of the wheel fairings will act as air scoops when the wheels are either down or retracted, and the air they direct will provide positive pressure to the tailbooms forcing air to traverse through the lightening holes in the centre section wing ribs and move into the area under the engine from where it can feed the radiators and/or the upper section to cool the cylinders. However I don't think that's enough inlet area and it's a mildly tortuous path so I've always intended to have a scoop or NACA ducts in the bottom of the engine bay which is under the wing so will be in a high pressure area so they should work efficiently.

    The preferential path for all of that inlet air though would be through the radiators since they are set low (nearest to the inlets) and will at times be fan forced and I'm assuming a fair bit of lowered pressure for that zone caused by the downstream effect of the louvres' form and also the effect of the prop. So my main concern now is being sure I have enough air fed directly to the front of the cylinders from where I imagine it would prefer to exit via the large upper outlets after doing its job on cooling the cylinders. It's all a bit hit and miss because I do not have the luxury of internal baffles and the Rotax isn't set up for them due to it being an engine that is predominantly cooled by having liquid cooled heads. Even so, I don't want hot cylinders so I want to get some extra air feed up higher.

    I could put NACA ducts in the top of the cowling but doubt that's a good idea for several reasons - the air would probably bypass the cylinders by going over the top of them direct to the outlet, rain would get in if the plane is parked outside but most importantly the top of the fuselage should be a low pressure zone so they would probably suck rather than blow ...

    I could have a couple of ducts in the forward fuselage area but that would mean long sections of SCAT tubing and there's little enough room to accommodate them already, let alone the inefficiency of them if they were long, so they would have to be of large diameter and so take up even more room. I had to give up on that idea or have them below the seat backs and then I'd lose half my baggage area.

    So - I've modelled them into the CAD model in the place where they suit best and are closest but my present dilemma is that they would be located behind the widest part of the fuselage where the fuselage is narrowing again, the question is - will they still work there? I don't want to have to re-model the whole thing in Solidworks to use the CFD facility (and haven't learned that part yet anyway) but may have to. Instead I thought I'd ask for some opinions or folks' previous experiences with these ducts first?

    62 NACA 01.jpg 62 NACA 02.jpg 62 NACA 03.jpg 62 NACA 04.jpg 62 NACA 05.jpg 62 NACA 06.jpg 62 NACA 07.jpg 62 NACA 08.jpg
     
  13. Dec 20, 2013 #173

    Jay Kempf

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    Re: LEARNED HELP WANTED

    One very I think pointed observation. You never need cooling when you are pointed downhill. You need cooling when you are pointed uphill. So if you put cooling duct inlets above the wing behind the leading edge you are putting them in the low pressure zone when you need them meaning you actually might be scavenging them instead of charging them. So that then points toward your under wing inlets. Those will always work when you need them. NACA ducts can be finicky. Do you really want them? What about belly inlets in front of the leading edge that aren't NACA style? How about just scoops? With slashed inlets? That way when you are grinding uphill consuming fuel madly and generating BTUs severely then you are ingesting pure laminar high pressure cold air only.
     
  14. Dec 21, 2013 #174

    Head in the clouds

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    Good thoughts Jay, thanks.

    Not sure what you mean by a 'slashed' inlet and I guess that a scoop would be more draggy than NACA ducts but perhaps more guaranteed to work. I'll model something up for comments. Whatever it is it has to be aft of the leading edge i.e. between the spars because that is the bottom of the engine bay. Anywhere forward of that requires big holes in the spar web or loss of much of the baggage space and I don't want either of those.
     
  15. Dec 21, 2013 #175

    Jay Kempf

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    What I mean by a slashed inlet is like an F-15. The slash goes from high front to low rear of the forward pointed rectangle. So when you are at extreme angles of attack you are not blocking the inlet to the relative wind. Make sense?
     
  16. Dec 21, 2013 #176

    Head in the clouds

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    Ah, thanks again Jay. Interestingly that is just how I imagined it, partly for looks and partly because it's minimalist in terms of material for the scoop. I'll model it shortly, cheers.
     
  17. Dec 22, 2013 #177

    Aircar

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    Alan, just opened this from your PM --I'll reply on the duct thing and return to the rest after . The NACA duct operates exactly like the Concorde wing only in the 'mirror image' sense --the SHARP edges of the fore part of the inlet trip the flow and start the vortex that pulls in outside air past the boundary layer and sends it into the interior (and also note that a NACA inlet is not JUST the 'cavity' - it also has a cambered lip to the 'straight across' ending (the ';trailing edge' of the Concorde wing ) --this adds to the induction by the airfoil and venturi effect . What Jay says is correct --you will always get a higher ram pressure from a 'pitot' type inlet but that might not suit your structure or other arrangements , the further back on a wing or fuselage a NACA duct is the bigger it will need to be to get flow from outside the thickening boundary layer but always better to be on the lower side -- the only exception might be if the wing loading was very low and you were flying at such a low CL in cruise to get separation from the underside of the wing --some gliders encounter this.

    With the Stiletto I had it on the rear fuselage and also in a converging shape but with the influence of the prop (doing 7000 RPM ) just behind the pressure recovery and drop due to the prop itself (pitched all the way to the hub as Sander's props did --the trailing edge of one side merged into the leading edge of the other --it acted as a good extractor --in any event I lucked out with it (and a few years before did the same on Bob Jane's Monza --they are pretty easily seen on the photos )

    That's about all I can add --Bede did a 'how to' series that included the published NACA info on calculating the size of a NACA duct --if you can't locate it let me know and I will ferret in my files for the info (the NTIS one will have it for sure )

    Back to your PM ,
     
  18. Dec 22, 2013 #178

    Jay Kempf

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    OK, on further though before you get too far into modeling. There are two ways to think of dragging air through a ducting system. The first is to ram it through. The second is to extract it from the exit. If you are having trouble with providing a ram inlet or you think you might have too much drag involved then you need to look at modes where you are generating low pressure somewhere in the mode where you need max cooling. I think you were already on that tack with locating the cooling exits near or at the inlet flow boundary layers of the rear fuselage by the prop. The problem with most pushers is that the flows are converging at the aft or pointy end. So if you really want to induce a flow in a duct you almost need to have the cooling exit VERY close to the prop with enough area to really create the flow you want. This would be much like having a carb inlet right behind a tractor prop only in reverse. Not sure of overall drag of such a thing but I think it could be designed to work in all power producing regimes quite well. Blade passing frequencies could be a beeeattttchhhhh though (thop, thop, thop).

    As far as using NACA ducts. Hasn't it been proven that mostly they are hard to get right and especially hard to have one fixed size one feeding engine cooling be adequate across all RPM, heat extraction, and power need regimes? Also, hasn't it been proven that say a P51 style inlet is not overly draggy even when it is stagnant?
     
  19. Sep 14, 2014 #179

    cluttonfred

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    Any word on the OZMOZ?
     
  20. Sep 18, 2014 #180

    bmcj

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    It was physically identical to the California mosquito, but identified by its Australian accent. :gig:
     
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