C models had wing tank(s), no fuse tank. They also featured the offset fin, discontinued on the Mark IV. Really silly if your prop is right-turning! Kind of silly period, as P-factor varies with AoA and forward speed, and there's plenty of yaw authority.
Say, Manu, Have you had a chance to fly, and assess the adequacy of your add-on trimtab? If so, and you think deflections for landing trim are not excessive, I am keen to do something similar. My bird is a bit nose-heavy, so that's why I'm concerned. Thanks.
Without mode-C you can go under the shelf of Charlie airspace, but for Bravo airspace, won't the mode-C veil contine, but with adds-B (after July, 2020)? And oh yes, overflight of Charley airspace will require adds-B after the change; it requires mode-C now.
Man, with tri gear what's the concern? If you're current, are sure of the bird's condition, and understand issues related to flying behind a 2-stroke, you're good to go. Getting insurance with 0 hrs in type could be problematic. On mine, with tailwheel, & me with fresh TD endorsement, I just studied up, then went solo. Just know your bird, airspeeds, egt temps, etc. Just my two cents.
It's typically not the bungees you need to be worried about; their load on that inner span of the seat truss is distributed, at least go some extent. It's that damn safety cable, which, when in play, shows up as a concentrated shock load, pulling the top wall of the seat tube down, essentially crimping it! A wood insert would prevent the tube bending down, but may not protect against the upper wall of the hollow tube being crimped. My analysis recommends that if you choose to keep the safety cable (I didn't), size it to allow 5" of travel before it comes into play. That's a 3G landing. Fred Stork (see posts) offers an alternative approach to limiting gear deflection, that's worth considering. Nylon webbing might also be considered as the safety straps. But in my opinion, the original safety cables suck!
My advice is to make sure you replace bungees with the mil type-1 bungees from Aircraft Spuce & Specialty. 3/8" dia is really 0.41", and it's almost 3Xas stiff as the hardware store variety! Check travel allowed by safety cables; I advocate 5". On my Model C it was 2.5", and I bent my seat tube in a hard landing! There are posts on re-doing the bungees. It's a bitch without first making an installation tool. Filling in the critical seat-truss triangle with wood or something to make it more crush-proof is valuable. Study up on flying behind a 2-stroke - it's different! Welcome, and good luck!
My read on the toe-in / toe-out question is that parallel wheels is best. A priori I thought toe-in made sense, but it's all about the careening/lumbering oscillation you can find yourself in, which toe-in exacerbates. Long piece of iron pipe fit over axle, then attached to fuselage tail via come-along seems preferred way to undo toe-in, but be careful. Don't want to overdo it.
Get comfortable with fast taxiing. Work your way up to it. I needed to tighten up the rudder-to-tailwheel connection in order to have a controllable fast taxi. If you have uneven springs on the tailwheel connection, it's intended to help reduce shimmy, but the stiffer spring needs to be on the side of the downward-moving blade, or you may have uneven steering authority when moving forward, and P-factor is in effect. The just-post-touchdown phase is the scariest, and that's why I advocate getting comfortable with fast taxi. In the air, it's just another airplane! Good luck!
Hey Leni, Sho 'nuff, the check I snail-mailed to you on Jan 11 never got cashed. Maybe was part of your lost/stolen mail. Will re-send. Greatly appreciate what you have created for us. I have learned so much about our unique little birds from the site. Tons of know-how, and a great crew! Can't wait till spring to try out all the new mods! Since my bird lives in the garage, 25 miles from the airport, the days are too short for flying now anyway! Launching the bird takes time.
Leni's idea to run the safety cables thru the seat truss so it pulls down in a corner of the seat truss when in play is brilliant! Might just do that. My calculations say a 3-G landing will cause a 5" average bungee stretch, without exceeding forces to which a new bungee is capable, at least per my stretch testing. So I recommend allowing for 5" bungee stretch. Avid recommended 3". FWIW.
I'm a little old guy with the pull starter. It's not that hard, and I don't have the clutch, although it does tire you out. Usually, if it doesn't want to start, it's oily plugs. I passed on the clutch for safety reasons. If the engine stops, a freewheeling prop is very draggy, so your ability to glide to a better landing spot is very limited. A low-inertia prop is a better answer. But yeah, gotta chime in with those advocating letting him try it first. Funny, JimChuk, but I find it easier to start seated. My cord pays out about 8" before engaging the engine. This is critical to making it easy to do while seated. Gotta loosen the seatbelt first, though!
Hey Leni, I sent you a check via snail mail. Did it arrive? Hopefully it can help to ease your financial burden in keeping this wonderful site open. I would love to show up as "contributing member" when you have the time. And again, thanks for launching and maintaining this site. You are doing us all a great service.
Y'all are gonna think I'm ideologically mistaken perhaps, but I bound my bungee end loops with bailing wire! (OMG! Not aircraft grade!) The real key to it not slipping is to pre-stretch the area to be wrapped to something close to maximum stretch, since the bungee crossectional area gets smaller as the bungee is stretched. If that bungee ever gets stretched beyond the tension at which it was wrapped, you risk it slipping and the end loop shrinking. That effectively adds to the bungee's effective length, but only a teensy bit. The bungee end leg is, of course, the less likely to slip compared to the other leg in the binding. Oh yeah, and my final wrap was with electrical tape. Didn't like applying heat there for the shrink tube. It's holding very well.
I just finished switching to the OI system. I put a stop on the oil throttle arm where the marks line up, so that should preclude going below 70:1. The standard advice is to go 100:1 premix while you validate correct operation, but at the risk of spark-plug fouling (oh horrors!), I am going to run 50:1 until I have indications that things are set up correctly. Don't want to have an engine failure. It's so easy to remove & clean the plugs! Motorcycle racers say the compression gets better when running oil-rich, the limit being carb setup, i.e. jetting. No interest in messing with that. My chief worry regarding going premix is getting adequate oil mixing in the tank on fill-up at airports. The wing tank is a weird shape with remote corners. Can't shake it, and don't want to wait for molecular diffusion to accomplish the mixing! Maybe I'm just being a worry-wart, and over-thinking this. Dunno.
Of course, VGs will increase cruise drag, slowing you down a little, and the lower stall speed could make landing rollout less exciting. But this comes at a cost, as it reduces maneuvering speed along with stall speed. Unless your H-tail has enough authority to fly you to stall without dynamic effects, i.e. in straight-ahead slow-entry stall, you may not even be able to benefit from the stall-speed reduction the VGs provide, but your maneuvering speed will still be reduced. Many have indicated that with VGs, stall AoA is increased so far beyond ground angle that they're of little use. Plus, they make your airplane harder to wash!
It seems to me that the bottom of the sling seat is comfy; it's just the back that could become a pain (literally) on longer flights. I was thinking of taking a thin plywood sheet, and with the face grain in the vertical direction, drill and zip-tie it to the lacing grommets at the seat back top and then make standoffs for the bottom, allowing it to rest against the frame tubes there, since the aft seat-bottom is not laced, but has one long loop for each side, split in the middle. Some form of lateral stiffening there would be required. At this point I'm just kicking around ideas. Gluing some urethane foam at the anatomically correct height on the plywood seat-back could add to comfort. None of this modifies the sling seat, so if it's a bust, nothing is ruined. An alternative would be, after figuring out what shape would be comfortable, to design my own fiberglass or carbon seat pan as Willja67 suggests. With sufficient stiffening it could simply lace to the two steel fuselage tubes. A fair number of options exist. I just figured someone here might have worked this problem for the older Avids by now.
The sling seat forces you into kind-of a fetal position, with absolutely no lumbar support. Others have remarked that the fiberglass seatpan is uncomfortable. In a KF, there's space for big improvements in comfort, but in an Avid-C or earlier, we're cramped for space. I am contemplating a plywood seatback stiffener, with a lumbar support cushion. Any alternative ideas on this out there?
The original bungees included with the kit for my bird 26 years ago tested out 1/3 as stiff as the new ones from Acft Spruce! Anybody who has original bungees should swap them out for new! Yeah, they reached max stretch at about 30-35 lbs as opposed to over 100 lbs for the new ones! Hard to believe, huh! That sub-par stiffness is what you'd get with the hardware-store variety bungees. Make no mistake! OTOH, my plywood truss-savers probably should be vertical-grain plank. In my case this is not too critical as I have omitted the "safety cables" as C5 suggested long ago. Nylon webbing would seem a viable alternative to those cables, but isn't that what the bungee sheaths are in essence anyway?