Turbo

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Everything posted by Turbo

  1. Turbo added a post in a topic Cross-shaft gearbox leak   

    Reading up, I have gained the impression that replacing the two seals on the crankshaft essentially mandate a new or rebuilt crank, which is expensive.  If it's the seals on the valve shaft, I may see either nothing, or brown oil goo/oil foam forming in my cooling system, depending on which seal has the issue.  So far, no goo.  I'll keep an eye on that, too.  Goo is clearly a non-starter.  Thanks for the input, Joey.  Looks like I've got some expenses on the horizon.
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  2. Turbo added a topic in Two Strokes   

    Cross-shaft gearbox leak
    Hi guys,
    My greyhead 582 has begun to leak oil, apparently out of the cross-shaft gearbox, as the level keeps going down in the little reservoir, even with the plane sitting in the garage.  This happens over the course of several days.  I am inclined to continue flying the plane locally, keeping close tabs on the oil level.  Is this a dumb idea?  That gearbox is deep within the engine, and I imagine a near-complete teardown would be required in order to renew the seals.  Ergo question #2:  Who in WA or OR works on these engines?  Not too many snowmachine shops down here, I reckon.  Thanks, Turbo
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  3. Turbo added a post in a topic 1st flt Avid - impressions   

    Randy,
    I live on the other side of the Columbia, in Mill-A, but it will be fun to meet and compare notes.  Just let me know when you're in town so-to-speak.  HR airport has grass, but also the dreaded glider ops, so I am liking CG regional in Dallesport, with its 100' wide and long runways.  Wind often dumps out of the Gorge and right down runway 31 there.  Gotta love that!
    - Turbo (Art)
     
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  4. Turbo added a post in a topic 1st flt Avid - impressions   

    But Leni, you are a poet!    I gotta admit that my fear of that embarassing groundloop has my dance steps a little choppy and nerdy-looking.  I'm zigging & zagging along the runway desperately trying to keep it on the tarmac, never mind the centerline!  I keep imagining myself the day's high amusement for the other fliers at the airport, but so far am not hearing the murmurs or seeing any smirks.  Perhaps they recall their own rights of passage.  Thank God the true terraphiliacs are blind to my plight!  Thanks for the advice and encouragement.  Gas thru the tanks!  Banzai!   
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  5. Turbo added a post in a topic 1st flt Avid - impressions   

    Thanks, Bandit.  Will give it a try.
     
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  6. Turbo added a post in a topic 1st flt Avid - impressions   

    Had 2nd flight July 26th. I found that I have the #50 idle jets, and backed the air screws out as far as I could before the o-rings started to uncork.  Adjusted idle speed down to 1800 rpm.  Idle was much better, and the bird would descend for landing just fine!  Lifting the tail helped tame the takeoffs, but green as I am, I had difficulty judging height above the runway on landings. A couple were a bit hard as I stalled too high above the runway.  I am now thinking that holding it off as long as possible is not a good plan - rather better if I just flare to a low sink rate by parking the nose relative to some reference like the end of the runway or the horizon and let the ship settle.  I am still way overcontrolling rudder on runout, and need to mix in more subtlety, and stop being such a nervous Nellie.  As Leni says - "more fuel thru the tanks" is the answer.  I'm still a little skeered of the beast,  but  JimChuk's grin is starting to appear on my face.  Can't wait to land into a headwind!  Oh yeah - I went to a different airport with no glider ops, and a longer, wider runway. Whew!  Love the smooth response of the 582, and the bird, even with all those unnecessary openings in the front of the cowl, and big bellyrad, felt slippery!  Measured 80mph at 4500 rpm.  EGTs were above 1000F everywhere except at idle, not optimal, but in the range.  CT was rock steady at 150F.
    I have just cut up a beer coaster for use as a friction disk for my cheeseball trim system, but now have to reinstall the stbd bungee.  Cork for the disk might have been better.  Thoughts?  Trim will sure be welcome!    Full flap appears to not be anything near 25 degs, more like 15 on one side with stick full over! What gives?   -Turbo
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  7. Turbo added a post in a topic PRIVATE FORUM - Think Again!   

    Funny how we build houses on the beach either in ignorance of climatic drifting, or because our timescales are related to the human life span.  Climate stasis is the myth.  I do get a kick out of "measurements" of global temps taken 50 or more years ago, when the sensor count was way below what it is now, and uncertainties much higher as a result. That doesn't stop some from extrapolating anyway. From what I've experienced, it is difficult even for educated "trained" scientists to always remain open and objective.  If I'm not mistaken, a few decades ago we were concerned about global cooling.  One of my favorite historical notes is J. Harlan Bretz' study of eastern Washington, where he saw evidence of a giant, catastrophic series of floods, stripping all topsoil out of certain areas and moving huge rocks hundreds of miles.  Presenting his findings to the geological world he was almost laughed off of the stage, as they at the time held firmly to a "gradualist" view of geological processes.  J.T. Pardee set the record straight a few decades later upon discovering evidence of a huge ice-age lake (Look at the hillsides surrounding Missoula, MT - they are like stairsteps, clearly the shores of an ice-age lake.)  The ice dam holding all that water back was roughly at the Idaho border, near lake Pend Oreille.  Evidence holds that it was undercut and failed repeatedly as the ice sheets melted and withdrew to the north.  That ice age came to a rather abrupt end about 15,000 to 12,000 years ago, no thanks to man.   So hold onto your hats boys, we're all on this rock together!  And it's not our feet on the rudder pedals, IMHO. - Turbo
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  8. Turbo added a post in a topic Left flaperion hinge failure.   

    Something looks a bit strange in the vids, in that the broken rib tails don't look to have been made from the high quality 10-layer birch plywood, but rather something a lot less strong.  I agree that this is a weak point in the design, and yet another point of vigilance.  One could argue ones self into a very long pre-flight inspection.  
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  9. Turbo added a post in a topic Need some compassion...   

    So sad to see your beautiful bird hurt.  Glad you're o.k., Fred
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  10. Turbo added a post in a topic Spar Stiffener reinforcement   

    Really, with the huge differences in strength and stiffness between plywood and aluminum, these inserts are really spar crimp preventers, not stiffeners.  Their real role is to prevent compression buckling on the top of the spar tube under high G conditions.  If the spar tubing thickness is 0.049", one could use the next tubing size down (1/8" smaller O.D.) or an internal doubler to accomplish the same thing.  But really, all you need is something to immobilize the top of the thinwall spar at this max-stress span location.  -Turbo
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  11. Turbo added a topic in Technical tasks   

    Tool for "easy" bungee install
    The pictured tool greatly facilitated the installation of new bungees on my Avid.  The tool is a wooden gantry that stands on top of the seat tube, is stabilized above by a strap to a structural tube, and supports a block and tackle with 6:1 purchase.  Additionally, a small fairlead and clamcleat are used to quickly secure the line.  For line I used green paracord.  I used parts from my collections of yahtie and windsurf stuff.  In order to grip and stretch the bungee, I used a small camcleat mounted on a bent piece of 1/8" aluminum.   In mounting the bungees I was able to pull each wrap tight with the block & tackle setup.  Vicegrip pliers were particularly useful for clamping already-tensioned bungee cord to the landing gear on the bottom.  They held well and were easy to put on and take off.  For each wrap I tried to stretch the bungee as much as I could, so that in the final wrap the end loop would start off already through the aperture in the bottom of the airplane.  I then simply fed a 12-15" piece of paracord thru the eye of the bungee, tied a simple loop knot in the other end, and attached it to the block.  After lifting with the block & tackle, and maneuvering it onto the hook with a screwdriver, I simply untied the loop and pulled the paracord piece out of the eye.  Done!  Solo! (Jimmie Durante would wag his substantial nose and say "hotcha!".)
    Some other comments are in order.  Out of curiosity I stretch-tested a plain hardware-store bungee (Installed on the plane by a previous owner) for comparison with the Mil-spec Type-1 3/8" bungee cord sold by Aircraft Spruce & Specialty.  I was gobsmacked at the difference!  The Mil Type-1 bungee is about 3X stiffer, and will go up beyond 120 lbs per strand, whereas the hardware store stuff more-or-less stopped stretching around 35 lbs.  The Mil Type-1 stuff will stretch to double its 0-tension length.  Whatever you do, DON'T USE THE HARDWARE-STORE STUFF!.  My calculations indicate that 7 wraps of the Mil Type-1 bungees can handle a 3-G landing at my TOGW of 916lbs, but the outward gear deflection is almost 19 degrees from the 0-G gear position,  and the average bungee cord stretch is more like 5 inches!  This analysis even modeled the inward roll of the contact patch relative to the wheel as the gear splays out.  I was unable to stretch either bungee to failure, but would love to know how much tension they can take!  Online one can find many purveyors of different kinds of bungee.  If you insist on wandering off of the righteous path, I heartily recommend stretch testing, followed by analysis.  Avid's recommendation for the safety cables is to allow 3".bungee deflection.  I'd go to 5", or maybe leave them off like Joey did, just adding a bungee inspection to my pre-flight inspection list.  If you, like I, bought your bird used, I would definitely take a careful look at the LG bungees.  Are they single-flecked (hardware-store) or double-flecked (type-1)?  Is there adequate deflection capability in the safety cables?  (My airplane was a double whammy on these questions, and I needed to have my seat tube repaired after a hard landing.)



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  12. Turbo added a post in a topic Wing Testing   

    Interesting in that those wood pieces are really not stiffeners, but tube crimp preventers.  The curved steel attach plates for the wing struts likely serve the same function anyway.
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  13. Turbo added a post in a topic Solo bungee wrapping   

    Great idea, Fred!  Unortunately, my nearby friends tend to be little old guys like me.  I have, however found that by far the best tool for holding the tension on wraps already made is a pair of vise grip pliers!  I have an installation tensioning tool that shows promise too, but I need to first validate that my loop terminations will not let go at maximum extension.  If successful, I'll share some pics.
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  14. Turbo added a post in a topic Solo bungee wrapping   

    Hi Fred,
    The type-1 bungee from AS&S is exactly the one you mention, 06-12400.  I am thinking of making a tool to help with the installation.  I know I am no way strong enough to install them unaided.  If the tool is successful I will share it, as you did.  
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  15. Turbo added a post in a topic L.G. bungee blues   

    I've got to admit the analysis is incomplete, though.  I just got type-1 3/8"bungees from AS&S and they feel significantly stiffer.  I wonder how much tensile preload is built in to those bungees, and at what length ratio do they stop stretching.  Also, it would be reassuring to test my end loops to failure.
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  16. Turbo added a post in a topic Solo bungee wrapping   

    Bought type-1 bungees from AS&S, made up 90-in sections with loops on ends.  Marked off the 7 increments.  Tried to stretch the first segment to the mark.  Couldn't do it!  For this old, not-too-strong guy it seems impossible!  Especially with no real way to hold the stretched segment in place.  I am about to punt, and go buy non-type-1 bungee from the hardware store.  It's not nearly as stiff.   Altrnatively, I could put on fewer wraps.  The Canadian's axe-handle trick doesn't work on the Avid.  What have others done here in terms of mechanical advantage & holding?  I think I'll stretch-test the type-1 stuff to see if I can get away with 6 wraps instead of 7. 
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  17. Turbo added a post in a topic Wing Testing   

    Interesting that the brochure for the earlier STOL models have a Vne of 97 mph, and the sandbag test gives a load factor below yield of 5.9 Gs.  If ias is close to eas, and stall is at 40 mph ias,  guess what?  The Vne is really maneuvering speed!  Yes, Virginia, you can go faster in smooth air!
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  18. Turbo added a post in a topic L.G. bungee blues   

    JimChuck, you will likely have to drill some holes along the tops of your seat truss plates for the seat lacing ( maybe you already have!)  I was thinking of putting some high-quality plywood in there, using zip-ties along the outer edges, letting the bungees contain it inboard.  On my bird, the original builder put in split rubber tubing as a buffer on the bottom seat truss bar, but used small hoseclamps to hold the rubber hose sections in place.  This abraded the bungees' outer fabric sheath, and strikes me as a no-no!  I suppose rubber cement is about all one can do, as even zip-ties would likely cause abrasion.
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  19. Turbo added a post in a topic L.G. bungee blues   

    Oops!  In my enginerdly focus I forgot that a loop or two lie on top of others,increasing the preload and likely nulling out my 0.4 inch greater maximum deflection I got over the build manual.  It is important, however, that the cables allow full stretching of the bungees first, before coming into play.  I would consider the 3" deflection allowance as a minimum, and make sure my cable-stops were a little longer.  They were too short on my bird.
    And yes, I did hard-land my bird.  It's in the weld shop getting fixed.  Uggh!
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  20. Turbo added a topic in Technical tasks   

    L.G. bungee blues
    I was in the process of replacing my bungees, and thought I'd do a stretch test with the old ones to see how bad they were, and check out the engineering behnd their use as the landing gear springs.  In my stretch test I used a fish scale and tape measure to determine the spring charactrristics, Force vs. Length.  I zip-tied one end and looped the other around the fish scale's hook, then stretched it with a boat winch.  What resulted was a sideways S-shaped curve, showing what anyone who has used a slingshot knows: that a rubber spring eventually stops stretching at some load, even as load is increased.  The Hook's law spring constant is high at the low-force end, but also becomes much higher at the high-force end, and is lower, but slowly increasing in the midrange.  Weird, but likely related to  the molecular structure of rubber.  
    Knowing that a spring's stiffness is inversely proportional to length, I then applied the stretch data to the loop geometry of the Avid's landing gear.  It's convenient that in re-wrapping the bungees, the force required is totally manageable, due to the 7 wraps used.  Of course this means we are applying a preload.  At this point we are stretching the bungees to 132% of their no-load length.  Of greatest interest to me was the realization that the bungees stretch up to 172% of their no-load length.  It is here that the bungees stop stretching, even as force is increased further.  Half of the bungee-centerline wrap distance is 8.5", and with 90" no-load length and 7 wraps (14 strands) each strand's no-ĺoad length is 6.43".  Stetching stops at 172% of no-load length, so full extension should be reached at 3.4", not the 3" prescribed in the build manual!  The safety cable is only there to prevent total collapse, but if it's shorter than full extension, you risk bending &  crimping the thinwall tube under your seat; the tube the bungees wrap around, if you land too hard.  The bungees wouldn't be able to absorb the energy before the merciless cable comes into play!  That cable applies a point load to the tube, not distributed like that of the bungee.  
    So those are the results of my analysis.  Am I nuts?  I'm sure others in the group have thought thru this as well.
    Making up my new bungees, a special thanks is due to Fred, who showed an elegant approach!
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  21. Turbo added a post in a topic 1st flt Avid - impressions   

    Checked wing incidences with inclinometer & found them to be equal to within 1/10 of a degree, the precision limit of  my tool.  Also found an area on the port aileron where the trailing edge had been bent up, likely hangar rash.  That could explain the roll moment.  Bent it back down as best I could.  We'll see if I got all of the roll moment out.  This may take several iterations.  Turns out I have the older f7 mixer arms.  No matter; Just need more airtime.  If my new, stiffer trim spring works with some flap, I'll be tickled silly!
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  22. Turbo added a post in a topic 1st flt Avid - impressions   

    The Junkers- style flaperons have the advantages of the CP peak reduction of a slotted flap if rigged correctly, and of not inheriting the wing's tired boundary layer, but at our scale tend to develop their own wimpy laminar boundary layers, which limits their max CL,  and contribution to roll authority.  It may be possible to trick them into early transition to the much more robust turbulent boundary layer with an appropriate level of surface roughness, which is likely quite fine.  Teensy VGs could also be effective in this, but it's relatively easy to overkill the problem and make things worse.  In any case, there's only so much even a slotted flap ( in our case as an aileron) can do.  Having studied the kinematics of the mixer mechanism, I was somewhat unimpressed to see greater down deflection than up deflection as flaps are lowered.  I think there is a cure, with a different mixer geometry.  Leni says they overpower the elevator at the higher deflections anyway, so maybe it's a moot point.  Maybe they are just the ticket at 15 degs as-is.  I need more experience flying the bird.
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  23. Turbo added a post in a topic 1st flt Avid - impressions   

    I had the carbs apart and they are clean, including the idle jets.  The floats had sunk, so I had to buy new ones.  Gotta look to see what size those idle jets are, though.  Joey flies out of somehere near Fairfield, which has to be less than 100 ft elevation, so maybe the #50 idle jets is a good call right out of the box.  I too will be flying out of fields at less than 1000 ft elevation.  Totally agree re static idle rpm vs on final - part of why I had a tough time getting the bird down.  Trees at approach end of runway & short strip - bad combo for green TW pilot in unfamiliar bird.  Smooth at 1400 static is my new goal!  Next time The Dalles with 5000 ft, 100 ft wide tarmac!  Just loved putting around the verdant Hood River valley & hills, though.  This is why airplanes have such magic.
     
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  24. Turbo added a post in a topic 1st flt Avid - impressions   

    From y'all's comments, I must have come across as whinging.  My bad.  It may be the curse of being an old design engineer to always think design, and it makes one perhaps a bit more critical.  The Avid is what it is, and hey, I bought it!  I like the little bird, and am looking forward to flying it, and working to improve it where I can, like everyone else on the site.  My first flight was more exciting, almost scary, than I anticipated, but that will change as my mastery of the beast improves.  I have windsurfed the Gorge in winds gusting to 50+ mph, so I know I can do this, especially with all the experience y'all bring to the site, and for which I am grateful.  Obviously what I need is lots more time-in-the-cockpit.
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  25. Turbo added a post in a topic 1st flt Avid - impressions   

    Thanks for all the tips & info, guys!  Leni's comment re running out of elevator makes me wonder why Dean Wilson didn't start with the low-moment NACA 23012 and just find an acceptable LE shape mod to keep the high CL max while using a 2.5" radius.  My experience as an aerodynamicist holds that undercambering the undersurface can help up near the L.E., but further aft does almost nothing for max CL, while adding undesirable nose-down moment, especially in the aft end, near the T.E.  Oh well!  Maybe the best place for VGs is the H-stab's undersurface.  A flat-plate stab has got to have pathetic aerodynamics.  If only there was an easy way to seal the gap beteen stab & elevator.
     Thanks, Joey for the encouragement.  I will play around with idle mixture a bit more.  It's nice to know that smooth, slow idle is possible!  The internals of the E-box include a torsional softener like the C-box has, right? 
    Looks like I'll be making up new bungees.  Merci to Fred Stork for posting a great way to fab the end loops.  Love your videos flying around France in the springtime!
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