Turbo

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Everything posted by Turbo



  1. Turbo added a post in a topic Another Forced Landing - Mine   

    Glad you're o.k..  So sad to hear about your bird.  When I bought mine, the previous owner had put a paper fuel filter behind the seat, between the wing tank and header tank.  When I took it off I discovered a small amount of water trapped there by its higher surface tension relative to fuel.  Had that filled with water the fuel flow would have stopped, as Leni will attest.  The proper place for any fuel filter is downstream of the header tank, as it really is a huge gascolator!  I hope this wasn't your problem.
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  2. Turbo added a post in a topic "The Raven" a kitfox avid clone!!!!!   

    I.P. theft is really tacky.
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  3. Turbo added a post in a topic My idle thoughts on 582 cooling system   

    I for one am not convinced that the mk4 cheek rads are any less draggy than a well-sized bellyrad.  One plus: the bellyrad slows the airflow over the landing gear struts tucked up against the belly, reducing their drag contribution.  These LG struts are not streamlined like the wing struts, so their contribution is likely not negligible.  FWIW.
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  4. Turbo added a post in a topic The unquenchable EGT   

    Great idea, Dusty!  Enjoying the late spring/summer "down under"?  It's just getting darker & colder way up here!
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  5. Turbo added a post in a topic The unquenchable EGT   

    I reckon i'll go visit the local welding wizard tomorrow to get the old holes closed up.  The probes are very close to a numbered drill size, so I can drill the new holes for minimal clearance & leakage.  I have drilled out a few #10 nuts to use as spacers, along with a few ss washers.  Thanks, Vance,, for digging into this issue to such depth.
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  6. Turbo added a post in a topic The unquenchable EGT   

    Measured off the 38mm and yowtza!  That's a big difference!  Does this look right to y'all?  The pencil marks are where the new holes will go.

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  7. Turbo added a post in a topic The unquenchable EGT   

    Looking into this same issue, and not because my EGTs looked particularly weird, I found the exact same situation Vance did.  It's just that I would like to trust my EGT readings vis-a-vis the database for what keeps these engines alive.  It seems the manufacturers of these probes thought they ought to be 1"long, which sho-nuff puts the probe tip over by the opposite wall of the Y-pipe.  It's like they just decided to market the same probe for the 582 that was being used for some other engine with a 2"diameter round exhaust pipe.  (O.K., Turbo, enough whinging!)  I'm still not sure how to proceed: Buy a new pre-drilled Y-pipe and threaded probes, or try to drill new holes in the proper location, and re-use the old ones.  With the latter approach, I need about 1/2" worth of spacers, putting much of the probe's length outside the Y-pipe in a much cooler environment.  Will this give artificially low readings due to heat conduction along the probe?  If only the necked-down probe tip is where the thermocouple is, with the relatively low thermal conductivity of steel, I am thinking not.  On the other hand, I am not too keen on my current EGT gauge setup.  Still pondering this one.
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  8. Turbo added a post in a topic Gas cap part number   

    Have you checked any antique car parts suppliers?  These things sure look like what was common on old cars.
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  9. Turbo added a post in a topic Avid Flyer Speed-wing Checklist, Limits and Airspeeds   

    You either have a model C or a D (mark 4).  The C has a slight starboard incidence on the fin to compensate for the left-turning prop's P-factor, which puts the thrust center to port on taildraggers when moving forward on the ground or when flying at high AOA.  The mark 4 does not, and has elevator trim, as well as an external baggage door.  There are many other differences, although small.  
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  10. Turbo added a post in a topic MK IV Aerobat speedwing spar gouge/repair   

    Many of us fly the STOL version with spars everywhere thinner-walled than likely your scratch goes down to.  It would be nice to validate, maybe with a straight edge to span the scratch.  The highest stress is likely at the strut junction, in bending; the rest of the spar is wasted strength, really excess weight due to the design simplification of using a tubular spar.  With the speedwing this bending moment is much less than with the STOL.  The likely next highest stress is roughly midway between root and the strut attachment, where it wants to bow upward and is helped a little by compression of the spar, essentially reacting the tension of the main wing strut.  The cabane struts don't add much stiffness at all to the wing spars.  They're only there to protect the main struts in negative G conditions., to stabilize them against column failure.  Like the others with engineering backgrounds are saying, just dress out the scratches, and patch over the fabric, and you'll be fine.  I say this with confidence as an ex-professor of aerospace engineering, and designer of a couple of my own hang gliders with tubular spars, where it was my butt on the line.  The Avid (even the STOL) wings are quite strong.  My STOL wing, with me flying alone, is good to better than 6 Gs based on Avid's static test.  I nust admit I have not analyzed, so don't know about the H-stab, though.  I don't know if anyone has bent one as yet, though, but I doubt it.  Oh yeah - but it's not my butt...
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  11. Turbo added a topic in Two Strokes   

    The Mikuni oil injection pump
    I was curious to know how these pumps work. Looking on the internet I found very little information, so I took one apart. Rotax cautions us to not do this, but due to a friend's generosity I ended up with an extra.  In taking it apart, I lost an important retainer clip, so I must side with Rotax here. My impression? The pump is a robust and clever design. Bathed in clean oil at all times, the pump should have a long service life.
    Picture #1 shows the pump, minus the two banjo fittings on the outlet lines. The banjo fittings contain one-way ball valves that keep oil from being forced backwards thru the pump.  The oil inlet tube is part of the steel cap on top of the pump.  Both ends have steel caps held on with 4 screws.  Pic #2 shows the pump body with inlet tube off.  Oil comes in, and goes part way down the pump body, where it enters the center cavity through a hole.  One can see the bleed nut on the side of the pump body, which is used for initial priming of the pump.  Pic #3 shows the input drive shaft, driven by the plastic gear. Note the worm gear machined into its shaft. This worm gear drives a pinion, as seen in pic #4. This pinion rotates a cylindrical sleeve that serves as both the piston pump's outer cylinder and valving Pic #5.  Pic #6 shows the view from the other end of the cylinder.  The aluminum button serves as a bearing as the top of this cylinder is held under spring compression against the top of the pump body, pressing against the steel cap, where the inlet tube is.  Holes in the side of the cylinder act as valves to let oil in and out of the cylinder's interior at certain rotational positions, where they line up with holes in the pump's outer body.A simple spline transmits rotational torque from the pinion gear to the cylinder, while the spring tends to push the two pieces apart. The pinion shaft is actually the piston which pumps the oil, shown in pic #7.  Next to the gear you can see the two ears of the spline.
     O.K., so this thing turns!  How does it pump?  Pic #8 shows the bottom end of the cylinder with gear.  Note that with the spring & spline, this end can move up and down with respect to the rest of  the cylinder.  Note the cam surface around the end, and the button in the center.  Pic #9 gives a clue.  The cam slides on the concentric cylindrical surface of the shaft below with the eccentric machined in the middle. Pic #10 shows the parts assembled.  This cam drives the pinion gear & piston full stroke if the eccentric does not contact the central button.  This eccentric is controlled by the lever connecting to the Bowden cable.  At 50:1 the eccentric just kisses the button; but if less oil is required, it presses on the button, limiting the downward travel & hence stroke of the piston, returned by the spring. What's really clever about this design is that, if the Bowden cable should break, the cable-arm's return spring moves the eccentric to a position allowing maximum piston stroke, so the engine will not be starved for oil. Getting the desired oil ratios may require some adjustment of the Bowden cable, however.
     










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  12. Turbo added a post in a topic A simple, but worthwhile hack   

    Ski pole handle for the grip on the stick?  3/4" or 19mm stick diameter is same as many ski poles!
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  13. Turbo added a post in a topic rigging flaps   

    I've got to admit that I don't know where my flaperons are rigged with flaps "zero" in the cruise configuration.  My flap friction disc is unreliable, and the flap setting can change if I sit in the wrong spot on the seat.  My solution to this was to use cable ties to fix the flap handle relative to the control tube.  It flies fine, with crisp roll authority.  I have not experienced any of the sensitivity others claim to have felt at or near the cruise setting.  I have not used the flaperons as flaps so far.
    Manu, I wouldn't get too worried about the exact cruise flaperon angle, especially with your unique wing section shape.  Your optimal value could be different, and you will likely need to explore its contribution to pitch trim in flight test.  In addition, your CG position will play a role.
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  14. Turbo added a post in a topic rigging flaps   

    Per aerodynamics convention, positive flap deflections are trailing-edge-down.  I conjecture that Dean used an asymmetrical airfoil shape for the flaperons,  consistent with their use as flaps, but with the side benefit that the flaperons' aerodynamic moment would eliminate play in the linkages. 
    I believe that these birds are overendowed in the wing-camber department, so fast-cruising with 3 deg trailing-edge-up flaperons makes sense as a way to undo some of that excess nose-down wing aerodynamic moment due to all that camber.  It is apparently better to do this with the large-span flaperons, despite their short lever arm, than carrying the additional downforce on the H-tail.
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  15. Turbo added a post in a topic Mk iv or C?   

    I have no explanation, but my Avid C has serial number 1027.  I have the rounded rudder, but an offset fin and no trimtab or luggage compartment door.  Could there have been a time period in which one could order either model??
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  16. Turbo added a post in a topic Cabin Heat   

    Perhaps just speculation on my part,  but since a 2-stroke has much more strongly pulsating flow through the carbs, it may be that any ice starting to form would be savagely ripped away and ingested early on, rather than accumulating as it would in the carb of a 4-stroke, with its much less pulsatile inlet flow.   I think of multi-cylinder 2-strokes as individual single-cylinder engines sharing a crankshaft, since each cylinder must breathe independently.  Often, as with the 582, they are individually carburated as well.
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  17. Turbo added a post in a topic Picture of your pedals   

    Jeepers, I can't do my mag check at 4krpm, the brakes are so weak.  Stock setup, and dry disks.  Probably a good thing in my case, though, as it keeps me out of trouble!
    JimChuk - Great panel layout!  Is that an MGL FLT-2 in center?
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  18. Turbo added a post in a topic Is this worth 5K?   

    I wondered about the small offset in my model C's fin.  It's to the right, ostensibly to counter the P- factor of a left-turning prop.  I presume the AOA at which this was set is that of taxiing with the original taildragger gear, but with so many possible LG variations, along with the possibility of using other engines, some driving right-turning props, and different prop diameters to boot, it makes sense that this offset was discontinued in the Mark 4.  There's plenty of rudder authority in any case.  Still, I'd advise putting the stiffer tailwheel spring on the side of the downward-moving blade, as this side will be where the center-of-thrust is while taxiing with the TW configuration.  By the way, the use of different stiffness springs on different sides of the tailwheel is a way to eliminate shimmy, as the two sides would have different resonant frequencies.  But y'all likely already knew that.
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  19. Turbo added a post in a topic Reduced Dihedral   

    The dihedral serves a couple of functions.  It helps keep the fuel flowing in turbulent air when fuel level is low, and helps stabilize the airplane in roll when stalled.  As a side benefit, it allows you to cruise hands off, once trimmed up, using rudder only.  The dihedral and wing twist were designed in to protect us from ourselves, i think.  A Stinson -style monster fin might have also been a good call, since so many Avids get damaged in groundloops.
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  20. Turbo added a post in a topic Huston! We have a problem!   

    FWIW, my down-elevator control stop is simply a screw-on hose clamp placed on the elevator control rod behind a ferrule.  This is very simple & easy to install.
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  21. Turbo added a post in a topic Cutting off the motor mount   

    The motor mount bolts on to the front of the firewall, at least that's how they came from the factory.
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  22. Turbo added a post in a topic Avid Flyer Seats   

    Fisher's upholstery, 661 Beacon Light Rd, Eagle, Idaho, 83616 tel:208-939-6513 made the sling seats for the Avid.  They still have the patterns and can make one up for you.  Dunno the price, though.
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  23. Turbo added a post in a topic Manu's Avid C   

    Good point on trim vs stick-force mitigation.  My concern regarding trim setup comes from realization that elevator is not balanced - all area is behind the hingeline.  If your trimtab is too small, deflection for landing approach trim may be large, or you may be unable to trim to final approach speed with CG fully forward.  Of course, more trimtab span is available if what you have is insufficient.  I expect that you will be o.k., as I believe the mark 4 tab is bigger than it needs to be.   If your setup is successful I might just do something similar.  
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  24. Turbo added a post in a topic Perfoming oil injection delete on Rotax 582?   

    In answer to Chris' question: I have so far only flown with pre-mix, and have only recently put the OI system back in play.  My wet plugs problem was solved with the longer-tipped plugs, thanks to Fred.  One other issue relative to this question of OI vs premix is that of adequate mixing when buying avgas on a cross-country flight.  Obviously, with premix, you need to know in advance how much gas you'll be buying, so you can add the oil first for better mixing.  But how can you be sure it was mixed well enough?  If you go to the airport cafe for lunch, maybe diffusion will sufficiently level any concentration gradients in the oil-fuel mix - or maybe not.  Airplane wing tanks aren't exactly the best mixing crucible shape, wide and shallow, with far away corners.  Y'all can tell me from experience if inadequate mixing has ever been a problem.  Glad to hear that altitude cruise while leaned is not.
    On leakage past the pump while stopped: I have not observed it since the OI installation a few weeks ago.  I made marks on the oil tank, and the level is holding.  I'll keep an eye out for this, though.  Looks like the next W&B will not be with empty oil tank.  Adding oil should be allow me to get an approximate arm for oil in the tank, though.  Relative to another thread, I may take a harder look at API-W3/TC ashless oils, based on Chris' favorable experience with same.
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  25. Turbo added a post in a topic New forum category! A place to introduce yourself. Please Post!!   

    Welcome, Super-D!  Like Fred says, the guys on this site are friendly, helpful, and knowledgeable.  The Avid rocks, and is inexpensive (relatively speaking) to fly.  You've definitely got a tiger by the tail!  There is so much to learn, and so many ways to build and set up the airplane the way you want.  Each of us tracks a unique path, as we come from many walks of life, ages, and even different countries.  We all share a fascination with the magic of flight, and most are more interested in the flying than actually arriving somewhere.  What is really great is that you can toss out a question to the group, and get back several different answers, or approaches to a particular problem that comes up.  You can then pick the approach you like best, or let those ideas inspire you to your own solution!
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