Contributing Member
  • Content count

  • Joined

  • Last visited

Community Reputation

163 Excellent

About Turbo

  • Rank
    Advanced Member
  • Birthday 05/07/1945

Contact Methods

  • ICQ rthrpwll@gmail.com

Profile Information

  • Gender Male
  • Location Columbia Gorge, WA
  • Interests Avid model C, windsurfing, hunting

Recent Profile Visitors

2,867 profile views

Turbo's Activity

  1. Turbo added a post in a topic Sinking carb floats   

    Duuh! Just asked Google if ethanol dissolves epoxy.  Answer is Yes!  We all know it's bad for 2-strokes.  So put that first half-gallon to full gallon in your car's tank first!  
    • 0
  2. Turbo added a topic in Two Strokes   

    Sinking carb floats
    Hey y'all, Turbo here.  3 years ago sold my Avid. Now flying Corvair-powered Sonex.  Can't complain about 3.5 gph at 125 mph.  I only land on tarmac, though.
    When I had the Avid, I fed it ethanol-free premium, like I feed my chainsaws.  All went well until my first set of Bing carb floats sank!  I bought  new ones, but even they eventually sank!  And I noticed that my epoxy gas tank was softening!  I started wondering what bizarre chemistry was in that fuel.  Got a clue much more recently, which I feel compelled to share.  It could be due to ethanol!  Many times, so-called ethanol-free gas really isn't, not due to any oil company shenanigans, but simply because many gas stations dispense  ethanol-free gas from the same hose as the other grades, and the last guy who hosered up may have inadvertently left some 10-% ethanol, 87- octane gas in the hose!  My advice (really from Chicanic) is to, after selecting the ethanol-free stuff, first put a half- gallon of gas into your car, then start filling those gas cans.  This clears out the hose.
    FWIW, Guys. Take care, and fly safe,
    • 2 replies
  3. Turbo added a post in a topic Funny Accident   

    Big bear following skiiers?
    • 0
  4. Turbo added a post in a topic 1st flt Avid - impressions   

    The zero-lift angle of the airfoil itself can be estimated using a simple approximate method due to Pankhurst in the front of Abbot & Von Doenhoff Theory of Wing Sections.  I did that calculation, getting -5.64 degrees relative to the max-length line, but that may not be what you're after.  (BTW, the max length line is 1.76 deg above a line between the TE and the lowest point on the lower surface.)  I believe the term "incidence" refers to the angle of the root airfoil with respect to the fuselage reference direction.  To measure the wing's washout I simply found a straight piece of wood longer than the chord length, but thin enough to fit between the wing trailing edge and the flaperon.  I simply pressed an inclinometer up against the board, which in turn was pressed up against the wing's lower surface.  I measured this at the root and out at the tip, just inboard of the fiberglass wingtip.  For my bird, the washout was a whopping 4.5 degrees, which I think is in accordance with Dean Wilson's design.  Lots of folks, myself included, think this was a bit excessive.  Maybe Dean was trying to save us hosers from killing ourselves.  Every aerodynamicist worth his salt knows an untwisted Hershey bar wing will initiate stall at the root in rectilinear flight.  But things could be different in a tight turn, like when trying to escape a box canyon.  If you want the wing incidence relative to the fuselage reference line, that line is parallel to the door sill, so make that measurement too, and do some subtracting.
    I occurs to me that Dean was a great designer, but missed the following point:  To properly design a wing using the same airfoil shape from root to tip, it's necessary to make sure the chosen airfoil isn't coming up out of its drag bucket at 0 CL, which is what you get at the tip.  The lift always falls to 0 at the tip!  The Avid's fiberglass wingtips help, but what's going on just inboard of them?  The combination of that much washout and an airfoil with concave lower-surface camber pretty much guarantees the tips are out of their drag buckets on the low CL side, and adding a fair amount of drag.  You might want to tuft the wing there, to see if and where the flow's separated.  If it is, VGs might be called for locally!  It might reduce lift a little, but not by much, so close to the tip.  Flow separation means pressure drag! 
    Hey, Merry Christmas, my friends!   Turbo
    • 1
  5. Turbo added a post in a topic Disembodied spirit   

    Well, with more than 40 landings under my belt (not all good, BTW), the little beast and I have fought to a truce.  It's not so bad, but unforgiving of overcontrolling in pitch on landing, which is surprisingly easy to do at first.  My bird has 10, 20, & 30 degree flap positions, and I find that 10 is great for takeoffs and 30 is more forgiving than 20 for landings.  30 degs tends to slow you down and damp out any bouncing faster than 20.   The best landings are 3-point, for which it's better to touch the tailwheel first, the so-called "tailhook" landing.  How do you know the tailwheel is down?  It's noisy, like a gramophone needle on the runway!  The 10 degree position for takeoffs is good because the airplane sits with the wing at an AoA substantially below stall, so that little bit more lift helps you get off earlier.  Still, the bird first gets off in ground effect and there's often a few seconds of skimming the runway that you've got to wait out, steering with rudder, before you can really leave the runway.  Stick-back takeoffs make for a snappy un-stick departure, though, and are necessary in strong crosswinds, as the skimming along in ground effect is not something you want to do crabbed!
    Next I'm intent on trying to use VGs to tame the body side corner flow on the wing aft upper surface.  That area is separated almost all the time.  Maybe there's a weenie bit of speed potential hiding there!  First challenge - how to keep camera from departing the airframe!
    Take care all, and Merry Christmas!  --Turbo
    • 1
  6. Turbo added a post in a topic Rotax carb submarines   

    On the "new" Sonex, in answer to TJ's inquiry...:
    Thanks for asking.  Unfortunately I have not really started to fly the Sonex as yet.  It's in the middle of its annual condition inspection.  Uggh!  After an exciting delivery flight getting it home, I realized that it had more issues than expected, so have been spending time and $$ chasing them down.  In a couple of weeks, the Gorge winds will start winding down for the season, and once the inspection is done, the sky's the limit, so-to-speak.  I owe myself quite a few landings before starting to roam from the old home base.  Will need to upgrade the ELT, though.
    It occurred to me that with the new 406 mHz ELTs, since we're trying to communicate with satellites, and not other airplanes, the antenna ought to be more horizontal than vertical, so its toroidal gain pattern points up into the sky, and not just out to the sides.  Wouldn't it be great if somebody made a stick-on antenna for low-winged, canopied airplanes?  Kinda like a decal one would put on the inside top of the canopy.  No additional drag.  And at 406 mHz, a quarter-wave dipole only needs to be about 1 ft long!  Seems like a natural, especially for metal birds.  Has anybody heard of such a thing?  - Turbo  
    • 0
  7. Turbo added a topic in Rotax and other engines   

    Rotax carb submarines
    My Avid is long gone, but one thing bugged me about my 582.  It was a great little engine, but too frequently my carb floats would waterlog and start to sink.  At first I endeavored to run all the fuel out of the carbs on shutdown, but then realized that I was likely stressing the bejeebies out of the fuel pump diaphragm.  With all the petrol up in the wing, I have lately come to wonder why the damn pump is even needed.  Why not just disconnect and plug the pulse line and do without?  Fuel should go thru the one-way valves in the lifeless fuel pump just fine.  Of course, serious ground testing would be required.  This way, on shutdown, you could run the carbs dry, and the floats might not be so keen to go submarine on you so soon!  Maybe up here in the PNW we are being sold fuel with nasty additives!  Wouldn't it be great if the floats were built the old way, with soldered-together copper or brass sheet metal stampings?  
    • 5 replies
  8. Turbo added a post in a topic Avid STOL airfoil -some calculations   

    There's a European guy, Manu, I think, (Efil01 ??) who has done that.  Whether he's flying yet or not I can't say.  You would pay a small penalty in takeoff distance, but rolling in a little flaperon deflection for takeoff, 5 or so degrees, ought to get you back to equivalency with the old wing, but no flaperon, as would bigger tires (taller mains).  Its only effect is seen when you're AoA limited while the gear is still on the runway.  So if it were me, I'd go for it!  With all that wing twist, the drag ought to be reduced significantly by filling in that concave lower surface.  Less drag means more speed.
    • 1
  9. Turbo added a post in a topic Brändli Cherry BX-2   

    Very Cool!  130mph on 90hp is nothing to sniffle at!  Looks like fun!
    • 0
  10. Turbo added a post in a topic Disembodied spirit   

    Lostman, you nailed it!  The sight picture is close to that out of a go-cart.  The airplane, for being a taildragger, is quite controllable at landing speeds.  Not really directionally stable like a tri-geared bird, but controllable, with no tendency to lumber from side to side as you pump the rudder pedals.  Landing the airplane seems to have two distinct rules: 1. Let God flare the airplane, and 2. Land IN the runway, not ON it!  You must, with jet-jock steely nerves, resist flaring the airplane, as ground effect handles that very adequately.  If you chicken out at the last second, you will get into a PIO that can be hard on your landing gear and/or prop.  Please don't ask how I know this.  The bird and I will come to an "understanding" very soon.
    If you want a wheels landing, omit the "hold it off, hold it off" part.  Playing that game too long can get you a tailhook-style carrier landing, where the solid tailwheel touches first.  The tailwheel is very noisy, like it's a skid or something, as the nearly megaphone-shaped aft fuselage magnifies its interaction with the tarmac like a Grammaphone bell. 
    Still, all-in-all, it's a delight to fly, and it rocks.  I am using 200 nm for a practical range.  The fact that the wing structure sandbag tested to failure at 10.5 Gs is to me very comforting.  Pilot only it's aerobatic.  However mine, with the Corvair engine and its odd and likely heavy motor mount, would be nose heavy were it not for three little 5-lb bags of lead shot in the tail.  Don't want that stuff banging around, so I tend to keep it right-side up and pointed in the direction it's going.   Still, at times I look out at those stubby little wings and marvel at how they manage to hold me up!  It's all in the journey, and I'm diggin' it! - Turbo
    • 1
  11. Turbo added a post in a topic New Wing design.   

    For what it's worth, if a designer is going to use a constant-chord, constant section shape wing (the old Hershey bar) it's important to NOT have out at the tip an airfoil that at nearly zero lift is crawling up the inside of it's drag bucket!  This highly recommends against the undercambered airfoil section shapes.  Even some of the flat-bottomed shapes are starting to edge up the inside of their drag buckets at zero lift.  The spanwise lift distribution is, according to Otto Schrenk, about halfway between the chord distribution and an elliptical distribution.  There's also a modification to this due to wing washout, which further contributes to unloading the wingtip.  So at very minimum, I would have to chime in and say if you're going to put an all-new airfoil section shape on there, ditch the undercambered lower surface, at least out approaching the tip.  Otherwise you will suffer an unnecessary drag penalty.   - Turbo
    • 2
  12. Turbo added a post in a topic Avid STOL airfoil -some calculations   

    And a brilliant design it is!  Kudos to you!  Unfortunately, in my case, Elvis has left the building.  I am now the proud owner of a Corvair-powered Sonex!
    • 0
  13. Turbo added a post in a topic Avid STOL airfoil -some calculations   

    Fist paragraph of my last post is o.k., except for the prop's effects.  The propshaft, if at AoA, will produce a yawing moment, which would require a rudder trimtab to null out, so there's another reason for re-setting wing incidence when going to a different airfoil shape, with its different zero-lift AoA.  Cruise altitude, speed, and weight play into this, so the designer has to pick some representative cruise point for setting wing incidence.
    • 0
  14. Turbo added a post in a topic Disembodied spirit   

    Yeah, you guys are so much fun and inpiration, I may have to haunt the site from time to time!  & merci, nlappos, pour les bon mots!
    • 0
  15. Turbo added a post in a topic Disembodied spirit   

    Nice to hear, Lostman!  I am so looking forward to getting the "bird in hand" and enjoying the many adventures that await.
    • 1