Turbo

A belated "Way to go, Vance!".  The bird looks great!

Can't disagree there.  4.5 degs washout on an AR 7ish  wing is a lot!  Interesting that Denny pulled a lot of that back out in the KF.  I'm not going to change mine, as it looks like a lot of work, and I'd rather fly anyway.  Best of luck with your wing rebuild.  I'm sure you'll end up with a better performing bird.

O.k., it's in the sequence of operations.  My assumption was that the strut attachment location had been established first.  I would think that if you were building the short-wing version, the first thing you'd do is cut the spars down.

Wouldn't cutting the spars down at the root end move the strut attach points inboard?  This would add unnecessary complexity while limiting ability to extend the span later.

And yeah, that washout is a tradeoff of increased drag for increased safety.

Seems to me one of the first wind turbines in the US had only one blade.  The name "Grandpa's Knob" comes to mind...

Many aspect-ratio 6 wings have no washout at all, since the induced flowfield unloads the tips anyway, so the root stalls first.  Avids are a bit over 7, so one might think we don't need the 4.5 degs of washout spec'd for them.  That may well hold if you have VGs, and can't stall when landing anyway, since your nose would be pointed so ridiculously skyward.  Without VGs, the stall, at least with the Avid STOL airfoil with cylindrical leading edge, is abrupt, so the washout may be there to soften the stall.  Another argument for the washout is that it allows tighter-radius turns at low speed without the inboard tip letting go first.  It could save your bacon if you inadvertently got too deep into a box canyon.

If your short wings are already built, you may be stuck with the washout you get by extending them.  Otherwise, you'd be adding stress to the wing structure, unless there's a way to relieve it.

If you look at the picture of the wing sandbag load test in the original brochure, you'll see that the cantelevered part of the wing outboard of the strut attachment shows the greatest bending deflection, and clearly the highest spar-bending stress is right at the strut attachment.  If you have the wooden "spar stiffeners"  I wouldn't extend the span, since these only prevent the spar tube from crimp failure.  If you have the aluminum tube internal stiffeners with the vertical web, you have a spar stiffener and strengthener, so should be able to carry more bending load.  In this latter case, by how much you can safely extend the span should be the subject of an engineering stress analysis.  With an extended span, maximum loads will be higher in other places in the airframe as well.  To first order, the max bending moment (and bending stress) at the strut attachment point varies as the cantelevered span squared.

Sounds like you had a great time!  Nice pics.  PPC looks like the perfect sightseeing machine!

Sorting things out is difficult, especially with very little background in biological science.  There are simple and cheap solutions to non-life-threatening things like leg cramping, so I typically spend some time online going to multiple sites and look for agreement.  Sometimes I will sit through a 30-minute speil with the predictible $50 / bottle ending, just to see what the critical ingredient is.  To justify the price they usually include a set of exotic-sounding but essentially useless all-natural ingredients.  It's an interesting game.  Still, for sigificant health issues, I am wary of oversimplification, and put my trust in mainstream medical science.

I like the rudder trim idea, but I don't have any scissors that big!  Springs and maybe a turnbuckle would seem to do.  My old Tri-Pacer had a primitive aileron-rudder interconnect.  Neat idea, but difficult to do on the Avid, I reckon.  Maybe stiffer rudder springs would reduce the tendency to wallow about in turbulence, by effectively making the fin seem bigger.

Oh, on the CG issue:  I installed a luggage compartment in my C, which I intend to use.  This will certainly help move the CG aft.

Actually, I am very close to test-flying a very simple relief tube system that uses a men's external condom-style catheter, connected to some small tygon tube that runs about 1/2 way down the inside of my pantleg before emerging.  This quick-connects to another tube anchored to the seat truss, that runs about 2/3 the way down the inner landing gear strut trailing edge.  A little extra tubing makes sure the system remains intact even in a hard landing as the LG flexes.  Preliminary testing indicates that this is quite secure; when the moment comes you can just let go.  It feels like you're peeing your pants, but you stay dry!  Oh yeah - you have to designate one junky pair of pants for flying, as you have to make a small opening where the tube emerges to outside your pant leg, so you can plug it in to the airplane.  The catheters are painless, come in sizes ranging from PeeWee to Magnum, so you have to first establish the correct size.  The catheters are made of thin silicone rubber, and have a weak adhesive on the inside, which keeps it on, and assures a good seal.  The distal end of the catheter fits snugly over 1/4" tubing, making for a secure seal.  They can be worn for up to 24 hours, and cost about $2.00 each.  There is, however, the potential for ending up with a bit of a sticky dicky!  They say the adhesive comes off with warm, soapy water.  Getting out of the airplane, say for getting gas, etc must be done carefully, as you have peed uphill, so disconnecting has risk.  In my system, I keep nearby a small stopper for use on the tube running down my pantleg, which I will carefully install before getting out!  I can include some pix of the system if there's interest.

Coffee flavored salty virga! Yeah!

Say, how does one add that extra stuff at the bottom of the message?

Wow, Randy, you guys must play a lot of football on those hunting trips! But bringing a spare in case you lose the first one - well, that's planning ahead!

Hi Leni,

Typical CG ranges between 12.4 & 12.8 in.  But the real problem is not having flown in smooth air for a while.  It's really just a matter of me whinging a bit too much.  As you well know, the Avid C has no provision for pitch trim except the flaperons, so I have a simple stick-force mitigation setup with an adjustable-tension spring as a poor man's pitch trim, kinda like JimChuk's bungee setup.  That, along with power and flaperon settings are what passes for trim on my machine.  Once I get the opportunity to set up for cruise in still air, I will definitely take a look at rudder trim.  Currently I have no tab on the rudder, and hopefully none will be needed.

I'm planning an 880 nm flight out to Ft Collins, CO for mid August, and am trying to get all important issues resolved beforehand.  Biggest Q? is what to take in case of emergency.  I am thinking warm clothes and food, water, matches, and some kind of first aid kit.  I am now not planning any leg longer than about 150nm, maybe shorter coming back against the weather.  Headwinds really slow these poky birds down!  I plan on having maps with course drawn on them as backup for the GPS (my Samsung tablet).

And I think I have a viable solution to the problem you so eloquently addressed.  Could launch a new thread, if I can keep the language such that I don't inadvertently get myself kicked off the site!

Wow, Leni, that's hard to top!  I dunno about the rest of you mugs, but my bird is like a helo, in that left alone, seemingly would love to dive into the ground all on its own.  Just putting on or taking off a jacket is next to impossible.  Toss in a little turbulence, and staying rightside up and pointed roughly in the direction of travel becomes a full-time job!  Of course almost all airplanes suffer from spiral instability, as this is preferable to Dutch roll.  Nobody enjoys puking!

On the magnesium issue:  The oxide form is cheapest, and seems to stick with you longer, but may predispose one towards diarrhea.  The glycenate and citrate forms are said to have greater bioavailability, but are typically sold in smaller doses per pill than the oxide form.  My read on this "bioavailability" is that it gets into your bloodstream faster, but may not stick around as long.  The pill bottles advocate 3 pills a day.  So I, for one, am back with the oxide form.  

I now have cobbled together a relief tube system.  This allows me to stay hydrated, which will help with leg cramps.  Hell, I can even have a cup of coffee at the airport cafe!

Thanks, WyPaul!  Stuff slides out the back door in 40+ years!

My Avid C STOL has a 582 with 3:1 C-box.  I have been looking into swapping out the 3-bladed IVO for a PowerFin prop, to reduce rotational inertia for smoother idle, less forward mass for a small CG improvement, and improved prop section shapes and blade twist, hopefully resulting in  improved cruise efficiency.  I am not impressed with the IVO's sharp leading edge and weird twist distribution, and feel that it might be leaving a more-than-insignificant amount of performance on the table.  Does anybody out there have experience with PowerFin Props?  With the biggest "F" blade, can I get away with a 2-bladed prop instead of 3?  There's more to life than static thrust.

I too was at one time contemplating a revised seat design, but in the end just decided to use a small pillow for some semblance of lumbar support.  But man the Avid sure is short on legroom, no matter what you do with the seat.  Maybe it is worth a second look, though.  I agree that if the shape is right, you don't need much padding.  Good luck!

Oops Allen!  Sorry we expropriated your thread!  No harm intended!

Two very ordinary spst switches work fine for me, but I pull the string to start the engine.  Leaving the old ignition switch there might deter would-be thieves.  I have been thinking about putting in a dummy ignition switch.

Interesting approach to saving weight, and providing greater legroom.  Wouldn't the seat truss bar and the transverse bar the sling seat attaches to tend to dig into the backs of your knees and shoulder area of your back?  I would also want to validate that this new minimist sling seat can take as many G's as the wing spars.  A failure could have you sitting on the floor, with no forward visibility!  Those fuselage-bottom truss tubes would be subjected to bending loads.  Are they strong enough?

Just some musings...

Exactly what I'm contemplating, minus the bag.  I figure I'll connect to a tube running partway down the LG strut, then let the airstream break it up into malenky droplets.  Salty virga, so-to-speak!

But OMG, this means that in some states the cars would be nosing us out!  With the slightest hint of a headwind...

I'm working on a relief-tube system.  My little Avid seems to require constant attention on the controls, so it had better be simple to use, like just peeing your pants, but not messy or wet.  The big plus is now staying hydrated would be possible, lowering the likelihood of your legs cramping. 

An airport acquaintence says he had the distinct pleasure of peeing on all the crazy lefties and antifas in Portland, a thought that resonated with me.  Remember: Chavez, the socialist, was put in power via a free election, a triumph of propaganda over common sense.  Now the Venezuelan people are starving.  This same path is a very real possibility here in the States.  Despite very stiff headwinds, Trump has accomplished much on behalf of people of both parties, and will likely go down in history as the best president since Lincoln.  He is, however, an existential threat to creeping beaurocratic corruption, so must be stopped!  If the Venezuelan "cautionary tale" has a message, it is that Big Daddy will not look out for little you, but will instead abuse you. 

As I like to say: Progressivist endgame: equality in misery!

Doug,

I have a speedwing rib, which I could trace and measure, but no coordinate data for any leading-edge extension.  Once the rainy season sets in this fall, I plan to look at both the speedwing section and some trial geometries for a minimum-extension leading-edge glove to try to tame those nasty Cp spikes. 

Laminar boundary layer flow over fabric-covered wings, sad-to-say, is largely hype.  All it takes is the roughness equivalent of a fruit fly's post-impact guts to cause the boundary layer to transition to its turbulent form.  Considering the surface roughness due to the doped-over fabric weave, coupled with stringent requirements on the pressure distribution to achieve laminar flow, and my read is most likely we all have turbulent boundary layers on our wings.  This is actually a good thing, as turbulent boundary layers are much more tolerant of abuse.   I worked R&D on these issues for most of my professional career, mostly for large, swept, transonic wings, with some supersonic stuff tossed in there for fun, but ultimately culminating in the first production controlled laminar flow system, on the tailfeathers on the 787-9 and -10 airplanes.  Ironically, I am more concerned now with assuring that those 8"-chord flaperons have a turbulent boundary layer.  Don't polish the damn things!

Anyway, it wasn't until metal-skinned wings became practical in the 30's that NACA developed the laminar-flow 6-series airfoils.  I don't think the possibility was even envisioned for fabric wings.