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  1. #26
    Avistarpilot's Avatar
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    Thanks for all the replies guys. Here's another question, since I'm doing some other modifications to the bird what's the thoughts of making it a tail dragger? Would it be worth the hassle?

    Since the accident and the plane is "down for maintenance" I'm looking to install some tri-stock under the horizontal and on each side of the vertical to help strengthen the empennage a bit. The horizontal stab can actually "pivot" in its slot a bit. More than likely the rudder through holes are a bit worn out. Also want to re-hinge the ailerons and re glue the steel torque rod in the aileron as it feels a bit loose. Been wanting to do this for a while, figured nows as good of a time as any. It will also give me a chance to practice my covering skills again before I cover my decathlon build.

    Now to the props...there's no doubt the efficiency of the prop was decreased due to grass residue build up. I'm sure it doesn't take much. Hell, Ag planes have been known to go down with a layer of smashed bugs on the leading edge of their wings. Anything that's going to disrupt the laminar flow is a bad thing. I'm currently running a 10x6 prop but I have a brand new one I can try as well before I throw a .46 in it. I'm also willing to try a 10x4 or 10x5 if it will help.

    Off to the shop!
    Last edited by Avistarpilot; 06-05-2014 at 10:53 AM.

  2. #27
    Charlie P.'s Avatar
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    I agree on the 10x5 for a .40 LA

    Depending what you've had to pull apart already a tail-dragger conversion isn't bad. Move the main gear up (with suitable bracing inside - 45 corner strips on a 1/8" ply pad or similar) and get the axles about even with the leading edge. The tail wheel is always more work if you want steerable instead of just a skid or caster wheel. In the past I have done LT-40 and a Big Stik conversion to tail-draggers and in both cases was greatly pleased. Be warned that some folks hate tail-draggers and avoid them at all costs. I am the opposite. But then I always fly off grass and frequently with ruts and holes.

    Damned ruts! This is my only current trike and it has a beefy Fults double nosewheel strut now.
    Click image for larger version. 

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    Here's an old thread for you.

    avistar tail dragger?
    Charlie P. (NY) "Gravity is weak but persistant".

    AMA 747089/IMAA 30723

  3. #28
    Avistarpilot's Avatar
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    That's very tempting and doesn't look all that difficult...I've got the electronic tray removed right now anyway. Would be a perfect time to mount the ply doubler and screw in the new landing gear. Never been a fan of the cheap wire mains that many trainers have anyway. This has got me thinking...

  4. #29
    Avistarpilot's Avatar
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    Got the firewall reinstalled this afternoon. Concentrated on getting the expoxy to the left side doubler to regain structural support. Everything essentially fell right into place. Spread some thin CA over the stress cracks on the face of the balsa sheeting as well. There was nothing on the inside that showed a physical crack. I think the outer balsa creased from the bend. The inner ply doubler did pull loose on the aft edges in some places but overall I think it will be structurally sound. Just need to find some balsa stock and some covering. Need to decide on a tail dragger conv though before I cover it

  5. #30

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    I've flown the OS 40 FP on many planes over the years and I completely agree with Ken Erickson that an 11x4 prop will work best for you on that plane. I am an instructor in our club and I use a 5 lb Sig Kadet Mk II with that engine/prop combination flying off a rough grass field and it is fine.

    I once flew a Jemco Mustang on an OS 40 FP. After some experimentation I found that a 10x5 prop was best for that plane. But that plane was smaller, lighter and faster, so the plane benefited from a little higher speed potential and didn't need the larger diameter. Your trainer is bigger, slower and heavier, so you want more diameter and less pitch. It will accelerate faster on your short field and produce higher thrust at low speed, so your climb out will be safer.

    You don't need a new engine, you just need the right prop.

    Jim

  6. #31
    Sorry bout the damage good flyin to ya

  7. #32

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    Looking good avistarpilot, and I cannot stand tricycle gear(especially off grass), taildragger all the way for me. Even a castering tail wheel will work, but taxiing to and from the runway is sometimes challenging/impossible. The fiberglass landing gear I use when I convert to taildragger is like you say so much better than the stock wire gear. I am going to have to get the Fults double struts Charlie P, cause I can't keep normal single strut nose gear inline off of grass on the aircraft I have not/cannot converted to taildragger.Calvi
    Ultra Sport Brother # 144

  8. #33
    Charlie P.'s Avatar
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    By the way - I don't think it's possible to tip stall an Avistar. It's a flat bottomed constant chord wing with wash-out built in. It will always root stall before a tip stall. Stall - yes. But never a tip stall.
    Charlie P. (NY) "Gravity is weak but persistant".

    AMA 747089/IMAA 30723

  9. #34
    Avistarpilot's Avatar
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    Quote Originally Posted by Charlie P. View Post
    By the way - I don't think it's possible to tip stall an Avistar. It's a flat bottomed constant chord wing with wash-out built in. It will always root stall before a tip stall. Stall - yes. But never a tip stall.
    I would agree. I only said tip stall as the LH wing dipped hard right at take off so that's what it looked like but having never experienced one I really wasn't sure. But I guess on a constant cord wing a tip stall isn't really possible. I'm leaning towards the root cause of the accident was from multiple reasons that compounded to cause the stall. First was the fact the grass on the runway was probably a bit too long for the little 40 sized Avistar. Another would be the prop size, and age of the prop. It had some pretty heavy build up of grass on it that could easily make it less efficient. Lastly, as I was removing the wire landing gear to convert to a tail dragger I noticed the LH wheel was extremely hard to roll. It wasn't completely locked up but pretty dang close. I never really noticed it but lesson learned to check main wheels before I take it down the runway. That had to have added to the take off roll as well.

    That said the Avistar is a semi-sym wing is it not?

  10. #35

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    Yes, it's a semi symmetrical wing. Constant chord wings can tip stall though. The airfoil design is a factor, as is the wing loading. I tip stalled my Cub a few months ago on a bad takeoff. It's constant chord too, but was loaded a bit heavy with scale detailing.
    No kid, I said break ground and fly into the wind!

  11. #36

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    Full scale Cubs have washout but this gets neglected in a lot of Cub models.

    How can the LH wing dip hard RIGHT? I assume you meant left. In the original post you mentioned possibly catching some grass with the LG or wing tip. Sounds like it's hard to know what actually happened, except that you need better acceleration on your take-off run, which would suggest a lower pitch prop.

  12. #37
    Avistarpilot's Avatar
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    Quote Originally Posted by buzzard bait View Post
    Full scale Cubs have washout but this gets neglected in a lot of Cub models.

    How can the LH wing dip hard RIGHT? I assume you meant left. In the original post you mentioned possibly catching some grass with the LG or wing tip. Sounds like it's hard to know what actually happened, except that you need better acceleration on your take-off run, which would suggest a lower pitch prop.
    I had a bit of bad grammar when I wrote this thread. The LH wing dipped hard, right after takeoff I was a bit too far to the left side of the runway and as soon as the craft broke ground it immediately dipped left and didn't take long to get into the weeds. It looked like the wing and landing gear hit the weeds pretty much simultaneously. After that point there was no saving it and the cartwheel ensued.
    Last edited by Avistarpilot; 06-09-2014 at 10:34 AM.

  13. #38
    Avistarpilot's Avatar
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    Got everything ordered today for the repair and tail dragger conv. Plane was red and yellow so I just bought a roll of yellow monokote so my fuse is going to be all yellow, leaving the wing alone so it will still be yellow on the bottom and red on top.

    Went with a dubro plastic/fiberglass landing gear with Sullivan tail wheel kit. Going with 3 1/2" mains with a 1" tail. Installing a 1/4" ply doubler for the landing gear mount with 1/4 20 blind nuts and nylon bolts and also mounting a 1/16" ply mounting pad for the tail wheel as well. Hoping to get it all finished up this weekend.

  14. #39
    Charlie P.'s Avatar
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    Not sure your plan but make sure the tail wheel is supported by the fuselage; not the rudder. You should be gold with the Sullivan types.
    Charlie P. (NY) "Gravity is weak but persistant".

    AMA 747089/IMAA 30723

  15. #40
    Avistarpilot's Avatar
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    Yep it mounts to the bottom side of the fuselage. A spring is connected from the tail wheel to the rudder. Not entirely sure how well it will work but hopefully will be able to use it as a somewhat steerable tailwheel.

  16. #41

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    So, how did it work out? I'm curious because I'm on my second Avistar and had a remarkably good day of flying today. All problems listed in this thread, I've experienced. My first Avistar had a Thunder Tiger GP .42, worked fine once I upsized the wheels and made sure the nose gear provided a stance for the whole plane not nose high or nose down. I was always rebending them back to normal. Also, I found getting the CG spot on to the manufacturers recommendation by putting the battery back in the fuselage behind the former for the wing trailing edge and adding a little weight to the tail, really made the plane great. Not overly sensitive, but takeoffs and landings really made a difference. I flew the heck out of that plane untill too many poor judgements and crackups made it just not worth fixing it again. That was a great airplane and I learned a lot about flying from it.

    A few years passed and I missed the first Avistar and eventually found one on Ebay for a reasonable price and bought it. By that time I felt I was some kind of "Ace" flyer with a Spad Debonair that I put many many flights on. I built the Debonair as a straight wing taildragger and flew the heck out of it. It felt kind of sluggish, but with a Thunder Tiger Pro .46, you could power your way through all sorts of fun flights. The Deb eventually wore out and a bad takeoff made it just not worth to fix. But I had plenty of fun with it. With Avistar II I was convinced I was going to make it a hot airplane with a bearing .46 type engine with conventional gear. A Tower GMS .47 was purchased and I fought that engine for two years until I came to my senses and decided to get rid of the GMS .47 and put a nice Magnum XLS .46. Well I've finally gotten back to it, (I was flying other types of planes), and now that I've gotten it trimmed out nicely, it's a joy. Takeoffs are easy, don't rush it, but with sight elevator, she takes off nicely. Landiings are good as well, I've made sure I have a pretty good low idle. I was just elated with my good flights today, because I have had some problems up to today. Getting my ailerons and elevator throws/trim and expo corrected, made for effortless hands off the right stick level flight accross the field easy. Now this plane is flying great.

    So just curios what ever happened to that Avistar.
    Happy landings.
    Tom

  17. #42
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    Quote Originally Posted by Avistarpilot View Post
    I would agree. I only said tip stall as the LH wing dipped hard right at take off so that's what it looked like but having never experienced one I really wasn't sure. But I guess on a constant cord wing a tip stall isn't really possible. I'm leaning towards the root cause of the accident was from multiple reasons that compounded to cause the stall. First was the fact the grass on the runway was probably a bit too long for the little 40 sized Avistar. Another would be the prop size, and age of the prop. It had some pretty heavy build up of grass on it that could easily make it less efficient. Lastly, as I was removing the wire landing gear to convert to a tail dragger I noticed the LH wheel was extremely hard to roll. It wasn't completely locked up but pretty dang close. I never really noticed it but lesson learned to check main wheels before I take it down the runway. That had to have added to the take off roll as well.

    That said the Avistar is a semi-sym wing is it not?
    When taking off with minimal airspeed and full power you will need right rudder to avoid the left wing drop. Call it torque, P-factor, or tip stall, the results and the remedy are the same. Rudder to correct the wing drop will be most effective and least likely to make it worse. Taking off at very low speed with full power with that plane is very doable if you use that rudder to keep it straight, and let it gain speed before exiting ground effect.

    Do you fly out in Mason City?
    The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

  18. #43
    Avistarpilot's Avatar
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    Well a lot has happened in the last few months. Funny how a wedding can grind all hobbies to a halt

    Things are finally winding down and the Avistar should be up and flying in a few days if our weather permits. The taildragger conversion is pretty much complete. I just need to install my receiver and perform a new weight and balance, it feels a bit tail heavy due to the gear and the ply doubler I installed to help support the tail gear but we'll see what it's like when everything is installed. I'm running a bit low on time so I'll put up some pics and can go into details later.

    I present to to you the Avi-stik








  19. #44

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    Yeah, that looks good. Cut those excess wheel axles. Always takeoff into the wind.

  20. #45

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    I have learned that wheel diameter matters on a grass field. 3.5" or even 4" works for me.
    Glow Head #6, UltraSport #70

  21. #46

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    Looking good Avistarpilot,

    I like to use only two nylon #10-24 bolts in the front holes for the mains, that way they will break away without ripping the fuse open on hard landings.

    Calvi
    Ultra Sport Brother # 144

  22. #47
    Avistarpilot's Avatar
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    Thanks for the tip, I'll take 2 of the gear mount bolts out. Hope to get it out this week weather permitting. Fall is here and it's been very windy most of last week and this weekend.

  23. #48

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    Leave all four in, it's not a biggie. I've seen too many gears sheared off because of planned breakage. Think about it, you'd rather not have the bolt sheer.

  24. #49

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    Hi Tom,

    I use two #10 nylon bolts on my ultra sport mains(same as what AvistarPilot has now). I have many many landings on them and have only sheared one of the bolts on a very ungracefull landing, no damage to fuse though.

    Calvi
    Ultra Sport Brother # 144

  25. #50
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    Quote Originally Posted by Avistarpilot View Post
    Thanks for the tip, I'll take 2 of the gear mount bolts out. Hope to get it out this week weather permitting. Fall is here and it's been very windy most of last week and this weekend.
    Avistar Pilot, lots of info your way. Your machine looks like the old Avistar which was a bit better than the new breed. In any case I have trained a number of RC pilot wanna'bees and even some that are fair RC pilots that like to fly Trainers. I. myself, do so every now and then just for Sport.
    Regardless of airfoil, any airplane can be "tip-stalled" if conditions and situations set up, said conditions - situations which are mostly set up by the pilot. If you have a chance go to an airport and especially so take a look at air-transport airplanes from a good distance behind the machine. You will see that the wing next to the fuselage has a strong setting almost like a Clark-Y. The trailing edge can be noted that it becomes very close, if not actually, a symmetrical airfoil out by the tips. Therein you see the washout that real airplanes live by.
    A flat bottom wing is a sucker for tip stall when the pilot moves the ailerons. That aileron going down is a sure bet if the speed is still slow and the angle of attack is high (taking off, landing and slow, etc.) A few months ago I was helping a modeler. He had flown some years ago. We were working with an Avistar Elite. He kept having problems with turns, especially to the left. I asked him if I could make some adjustment. I rolled up the ailerons by about 4 degrees. No more problems. Smooth turns, landings were straight approaches and take-offs straight. In-flight maneuvers were smooth. The old times came right back. Was it the adjustments? I have saved a number of Big Scale Pilots with that simple little thing, washout of the ailerons. Strip ailerons, then cut the tips off a few inches and GLUE them back slightly up. Be sure to slip another hinge (any type) into the end of the working aileron. Good luck. I am not an aeronautical engineer. My son is. OTOH some 41 years, military and airline with 20,000+/- hours, I did learn a few things. The fun of checking man-carrying machines gave one a good chance to learn more for modeling.
    Horrace Cain AMA L-93

    Peace is the brief glorious moment in history when everyone stands around reloading.\" T. Jefferson


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