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  1. #1
    Avistarpilot's Avatar
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    Did I Experience a Tip Stall?

    So went out and buzzed around the patch again today but on the last flight...(literally thought to myself after the last landing I should probably pack up but talked myself into one more flight)...isn't that how it always goes? Pretty sure it's the same as "hey watch this", something will always goes wrong. Anyway, back on topic. I should mention I fly off a section of a grass runway airport that is mowed short for rc pilots around town. It's mowed short but is fairly rough. Lately it's been taking the Avistar almost the full length of the runway to get airborne. We're talking maybe 100-150ft if I were to guess. I gave her the coals and about the normal speed I feel is right I give a little up elevator and it usually takes off nice and easy. This time it wasn't having it, I let off on the elevator and try to gain more ground speed and give up elevator again and it pops off the grass but the LH wing immediately dips. With my extended take off roll I ventured a little too far from the center of the runway and the left gear leg, and the wing tip from the looks of it, touched the tall weeds on the outer skirt of the runway and pulled it in and cartwheels the plane faster than I could correct it. Funny thing...well not so funny, is it happened one time before but I was able to level off and continue with my climb out. Really didn't think much of it at the time but looking back it behaved the same way.

    Reflecting on the event the only thing I can think of is that I tried to take off too soon before the wing was ready to carry the load of the entire aircraft? Once in the air the plane flies great so I can't imagine anything changed in the cg that drastically to cause this? I'm going to chock this one up as a learning experience, rebuild and fly again.

    Good news is the rest of the plane and wings look undamaged. Bad news: the cartwheel slammed the engine rearward, breaking the firewall off and cracking the lh fuse side and throttle servo tray. I just bought a larger prop also to try and help with taking off in grass...but didn't install it yet

    Been wanting to swap the little 40LA out for a 55 AX for a while now, now might be the perfect time to do it. Think I'm going to stiffen up the vertical and horizontal stabilizers as well. They were getting kind of sloppy where the vertical bolts through the horizontal. Might glass the wing halves too. Oh. And put on some bigger tires for the grass strip.

    Damage pics:











  2. #2

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    In aviation speed and altitude are life.... I have never understood why some people don't take off with full power. It's a whole lot safer to have power you don't need than to need power you don't have.
    there is no way it should take you 100 ft to lift off unless the engine isn't tuned correctly and not making power. Or that grass your flying off of is way too long.
    Yes it sounds like a stall
    its also easier to reduce power...than to add power.
    Sorry bout the damage good flyin to ya
    Last edited by jetmech05; 06-03-2014 at 06:05 PM.

  3. #3
    Avistarpilot's Avatar
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    Trust me it was pinned. To my knowledge the engine is tuned and actually runs very well. As for the grass it could probably use a trim but I didn't think it was excessively long. There are a handful of dandelion type weeds scattered throughout the runway...fun to watch get shredded but drastically reduce rpm when they meet the prop.

    In the mean time I'm contemplating buying a low winged arf and fix the avistar when I get the time...sucks being "planeless"

  4. #4
    foodstick's Avatar
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    Avistarpilot, bummer about the crash, but it looks like you have it under reconstruction already..

    Jetmech I am gonna argue with you ! hahahahah
    There is nothing I like more than a LONG roll out on the mains and a slow scale climb out ! However it does boost the chances of an issue on the ground..so you are right there.

  5. #5

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    Slightly underpowered plane, too small wheels, inexperienced pilot= a bad combination. I doubt you tip stalled just because Avistars have pretty stall resistant wings that are designed to root stall first. What is far more likely is either you took off too slow which got you into a regular old stall that then let the plane be rolled by the engine torque, or your wheel caught a bump causing you to yaw a bit just as you took off which, at that slow speed, could set up a spin that you didn't have the flying skills to recognize and get out of.

    You're on the right track for fixing the problem. Bigger wheels will definitely help, as will more power. You don't need a 55 AX though. If you're planning another plane that needs that engine down the road then it won't hurt anything to use it, but you're currently using one of the most anemic .40 size engines available. Moving to any ball bearing .46 will give you a 25-30% power increase, which will let you do the gun and jerk takeoffs that you probably need to do on your rough runway.
    No kid, I said break ground and fly into the wind!

  6. #6

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    You can do a slow scale like climb out after you have lifted off and established a positive rate of climb. Throttle isn't an on/off switch
    good flyin to all

  7. #7

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    As Jester says bigger wheels will help a lot, but I think the power plant is more than capable of doing the job. I just finished putting an FP 40 in a trainer to replace a 46FX and the difference was amazing. It was way easyer to land with the slower air speed and a little less nose weight helped it slow down a bit more to boot.

    I am now flying my Ultra Sport 40 (after a 15 year hiatas)(three flights) and find it easyer in a lot of respects to fly than my friends old Hobbico trainer.

    I think you can repair your Avistar in very short order, a lot less time than putting another aircraft together anyway, but it never hurts to have another plane in the hangar so you don't have to be grounded when this type of thing happens.

    Calvi.
    Ultra Sport Brother # 144

  8. #8
    Avistarpilot's Avatar
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    Thanks for the constructive criticism guys, as said above I'm choking this one up as a lesson learned. Hind sight is always 20-20 but I shouldn't have tried to force the take off. The plane almost always picks itself off the ground with little to no elevator. The plane got a bit squirly towards the end of the runway, probably from the bumps and I tried to get it up anyway. Somewhat like a short field take off in the real world. Just get the wheels off and gain airspeed and climb out but we all know the end result.

    I think I can salvage the firewall, should be able to epoxy it back to where it was, then I'll get a new sheet of balsa and make a scarfed joint on the lh fuselage side. Some of the area around the firewall is pretty fuel soaked. Can you still get K2R anymore or is corn starch and alcohol just as effective?

  9. #9
    Avistarpilot's Avatar
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    Thanks for the constructive criticism guys, as said above I'm choking this one up as a lesson learned. Hind sight is always 20-20 but I shouldn't have tried to force the take off. The plane almost always picks itself off the ground with little to no elevator. The plane got a bit squirly towards the end of the runway, probably from the bumps and I tried to get it up anyway. Somewhat like a short field take off in the real world(flaps would help lol) Just get the wheels off and gain airspeed and climb out but we all know the end result.

    I think I can salvage the firewall, should be able to epoxy it back to where it was, then I'll get a new sheet of balsa and make a scarfed joint on the lh fuselage side. Some of the area around the firewall is pretty fuel soaked. Can you still get K2R anymore or is corn starch and alcohol just as effective?

  10. #10

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    K2R is available at Ace Hardware

  11. #11

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    You never mentioned the wind direction and I betting you took off in a cross wind. I been there and done that. Far too many so called pilots have no idea what the rudder is used for. I personally never learned too use the left stick until I ventured into helicopters.

  12. #12

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    If you go to a low wing then you don't want to go running through the weeds. Trust me on this. When they slap over the top of the wing they can pop a lot of holes in your covering. If you are stuck flying from a field with longer grass then you should probably look at a larger plane that can handle it without problems.
    Work is what I do for the love of it. A job is how I pay for it.
    Please visit AirfieldModels.com

  13. #13
    Avistarpilot's Avatar
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    Wind speed was negligable, a slight breeze if that. A stronger headwind would have probably helped. I've been trying to implement rudder slowly in each flight and have actually found myself using it more and more on landing without thinking about it. That said I know I need to use it more for normal flight maneuvers.

    My my next bird I was thinking about was at least a 60 sized. Originally I thought a 4 star would be a good second low wing but now it seems like there's quite a few intermediate low wings out now that can handle probably more aerobatics than I know how to perform but are still stable flyers. Been looking at a great planes escapade 60, hangar 9 pulse XT 60, 4 star 60 or 120. Any others to think about?

    I think I'll get the avistar up and flying again with some larger wheels and an 11x6 prop and triple check the tuning to make sure it's hitting its peak rpm for take off.
    Last edited by Avistarpilot; 06-04-2014 at 10:09 AM.

  14. #14
    Charlie P.'s Avatar
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    Like a Maxford Mentor-G with 4-1/2" balloon tires. I upgraded to carbon fiber struts with the Big Wheel tires and it is far and away my favorite "bush" plane. The wing is about 14" off the ground.

    Tail draggers do better in grass (IMHO) and you HAVE to have free-spinning wheels without spats. A few degrees toe-in better still.

    I was at the field having a head-scratching day with an S/K 50 that just wouldn't slip the surly bonds of Earth. I eventually noticed little cracks in the wheel spats. When the grass was hitting them they would push on the tires - becoming effective brakes. Took them off and never used a set on grass thereafter.

    The Pulse is a great flier. I have a similar Saratoga 40 (now discontinued) and a friend has a Pulse. Both make outstanding float planes (with the Hanger 9 Cub floats)

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    Last edited by Charlie P.; 06-04-2014 at 10:15 AM.
    Charlie P. (NY) "Gravity is weak but persistant".

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  15. #15
    Avistarpilot's Avatar
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    Thanks for the info Charlie. I'm actually in the process of building a great planes decathlon 40 as well. On the home stretch with it so I'm glad to hear tail draggers do better in grass. They recommend 2 1/2 - 2 3/4 mains if flying off grass with the wheel pants off obviously. Maybe I can convince the fiancι to get me an ARF for my birthday coming up in July!

    Started looking at engines, anybody have experience with evolution engines? They have a .46NX right at the $100 price point. But if they are unreliable I'll chuck out another $40 bucks for the O.S. .46AX.

  16. #16
    Sport_Pilot's Avatar
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    In the mean time I'm contemplating buying a low winged arf and fix the avistar when I get the time...sucks being "planeless"
    Consider this one, its fast with an OS LA and a rocket with a .46. It is simi or sport scale so you don't have to keep it looking real.

    http://airborne-models.com/html/prod...p?ProductID=46
    Glow Head Brotherhood #15

  17. #17

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    The os LA enginges do not work here, we are at over 6800 feet and I have used a 600 foot runway to get it off the ground. Lucky thats an easy fix"

  18. #18
    Avistarpilot's Avatar
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    Picked up some K2R today before work. Got it soaking overnight tonight and will scrub off the powder and reapply if necessary in the morning. Upon further inspection I'm debating leaving the LH fuse side alone and bend it back to the firewall and fill any partial cracks with thin CA. Would this be sufficient to keep the strength in the fuse or should I remove the damaged part and replace it and the doubler on the inside of it?

  19. #19
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    As per the PM, I hold full up elevator on the take off roll when flying off grass. Once it breaks free, ease off on the back pressure. We have all been there with a failed take off and hope you get the plane fixed soon.
    Tiger Flyer #49

  20. #20

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    An 11x6 is too much prop for a bushing .40 engine. It's too much prop for even a strong ball bearing .46 to make its max power. A 10x6 or 10x5 will run a lot better.

    Evolution engines are hit and miss. Some guys get them and do fine, while others can never get them to run right. Evolution does have a good reputation for service, so if you get dud you can expect them to fix it. I'm a big fan of Thunder Tiger engines personally. They are cheaper than OS engines and just as reliable.
    No kid, I said break ground and fly into the wind!

  21. #21

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    I think you could get away with just putting a doubler on the inside of the fuse Avistarpilot. We had to do the same thing to my friends after he did a pancake landing on it, now it is stronger than before. Epoxy is the way to go for this type of repair, slow set if possible and add some fillets of wood or epoxy to the firewall.

    Calvi
    Ultra Sport Brother # 144

  22. #22

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    If your take off runs are getting longer and longer, it's time to mow the grass. Judging from the photos of your prop, your prop is having to slice it's way through grass. That really drags down an engine, plus the build up on the leading edge of a prop really screws up the airfoil making it work poorly.

    But I agree with Jester on prop selection. A 10-5 will often wake up a 40 sized engine by getting it up into it's power band.
    - Supplementary insipid innocuous inane vacuous proclamation

  23. #23
    Sport_Pilot's Avatar
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    Quote Originally Posted by hairy46 View Post
    The os LA enginges do not work here, we are at over 6800 feet and I have used a 600 foot runway to get it off the ground. Lucky thats an easy fix"
    That was about the OP not you.
    Glow Head Brotherhood #15

  24. #24
    Ken Erickson's Avatar
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    I have been flying with the .40 LAs, GPs, FPs and the Tower .40 almost exclusively for more than 40 years. The best prop for a trainer or an aerobatic trainer using any of the .40 small carb, bushing engines is an 11 x 4. For the non-believes, I carry my June 1992 issue of R/C Report, to show the Brian Lee review of the "improved" .40 FP. The RPM and thrust figures show:
    11,700 and 66 for a 10x5
    10,200 and 76 for an 11x5
    10,500 and 85 for a 12x4

    We are getting 12,000 or near that in RPM with this class of engine and an 11x4 APC in our RCPRO Club 40 Sport Racing group. Folks who show up with 10x6 props take 3 times as much takeoff run as those of us with an 11x4. If they do not sustain much damage, I just hand them an 11x4 APC prop and smile.

    Your Avistar was designed to fly with a light weight bushing .40. However, on grass, that nose wheel is a problem. You will not have any better luck with the WM T-34. Look at the Sky Raider Mach II from the same manufacturer/distributer. It is better for grass as it does not have a nose wheel. It also was designed to fly with a light weight .40 bushing engine. Assembled right out of the box, as per the manual, it balances perfectly and we use them for buddy-boxing newbies.

    Prior to the SR2, my favorite trainer was the Avistar. The old one like you have, not the new one.

    Ken Erickson

  25. #25
    Ken Erickson's Avatar
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    Once again, I see that I have fallen into the old trap of giving second-level fact without stating the basic, first level fact.

    With a trainer of second airplane, one wants thrust, the power, instead of speed.

    Thrust comes from a longer, lower pitch propeller.

    Speed is generated by a shorter, higher pitch prop at higher RPM.

    Ken Erickson


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