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crashed my hog bipe

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Old 05-16-2008, 11:38 AM
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06gsx
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Default crashed my hog bipe

hi all,
i HAD a sig hog bipe i built over the winter, well i took it out for the first flight and it was great. 2nd and 3rd not so great on take off about 10 feet off the ground it rolled hard to the left ending up in a bad day. So i took it home fixed it rebalenced it checked everything and went for the 3rd flight and had no problems until i went to land as i was on my way in about 30 feet from ground it rolled again to the left. ending in a really bad day. i have been looking at some of the hog bipe forums and every body has there cg at 3 1/4 my book says cg is 25% or 3 5/8 Can any one tell me what went wrong?


thanks for the help
brian
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Old 05-16-2008, 01:26 PM
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Default RE: crashed my hog bipe

Was the airspeed slow when all this happened? almost sounds like a tip stall

Steven
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Old 05-16-2008, 01:35 PM
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Default RE: crashed my hog bipe

It does sound like a pair of tip stalls to me. I'd suspect that you may have lifted off too early or climbed out too agressively on the second flight, and that caused you to exceed the critical angle of attack, the left wing(s) stalled first, and in she went.

On the third, you evidently had the take-off speed you needed, but you didn't maintain enough airspeed for a safe landing. Bipes typically land with 1/4 throttle or so, they are very draggy compared to monoplanes. The typical idle down on final approaches we all do with most trainer and sport planes is a recipe for disaster on approach with a bipe. On approach with a bipe, keep well into flying speed until you're right down to a foot or 2 up. They're so draggy, they take little room to slow, so don't sweat that too much.

Rolling to the left is typical of a tip stall, as that's the way the engine tries to twist the airframe. The left wing carries more load than the right (due to the engine torque) and thus usually stalls first.

I'm sorry you had such a bad day, I know how disappointing it can be to damage or lose a plane when it's so new. I hope the repairs won't be too difficult, and that you'll have'er out there again soon!

Good luck,

J
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Old 05-16-2008, 02:44 PM
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06gsx
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Default RE: crashed my hog bipe

yeah i might have been a little to slow but it is my first 4 stoke engine and i thought i had enough throttle when i was landing. next time ill try more thottle. thank you for your help. on the other hand all of the the other hog bipes in the forums have a cg of 3 1/4 my book has 3 5/8 what should i do with that? and the bipe will fly again. also i had a 11/7 3 blade on a thunder tiger 75s. i do have some pics posted on my account of before the crash feel free to take a look.



once again thank you for your help
brian
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Old 05-16-2008, 03:43 PM
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Default RE: crashed my hog bipe

on your takeoff's, you should add some right rudder to compensate for the torque of the engine.
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Old 05-16-2008, 09:35 PM
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Default RE: crashed my hog bipe

Well, with your CG set 3/8" forward of what most seem to aim for, you'll have a less sensitive elevator, a plane that wants to land faster and won't flare as well, and more speed sensitive pitch trim. Probably difficult to induce a spin too. I'd suggest moving the battery or whatever else you can to get the CG closer to what others find best. Try to be within 1/8" of what they're suggesting. I've not got a Hog of my own (I find bipes very disorientating....), but it seem unlikely that they're all wrong..

That said, I doubt it had anything much to do with the crash. I guess the best I can suggest is that you learn to love the art of flying the tail, both on take-off and landing. Hey, it looks cool, and it's just what bipes and warbirds are meant to do. Think wheels landings instead of 3 points, and stretch your take off runs as long as you can, do the climb-out scale like. If the plane has any tendancy to ground loop, a degree or 2 of toe in on the main gear will help to prevent it. It'll work in that cub kit I see you've got too, that's a plane famous for ground looping, model or full scale.

Your bipe is very pretty, looks like you really took your time making her look just right. It'll look awesome once you get a handle on her.

Good luck,

J
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Old 05-16-2008, 09:42 PM
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Default RE: crashed my hog bipe

Agree on the stall theory. The paradox of bipes is that they fly slow but like to land fast. You have to keep some speed up when landing to compansate for the extra drag.
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Old 05-16-2008, 11:24 PM
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Default RE: crashed my hog bipe

that ground looping is nasty i have never had that happen before. I have 2 piper cubs one you see is unfinished the other is just a semi scale 40 from sig. that one was my 2nd plane and first tail dragger. so now i that i know what i did wrong i can fix it and hope i don't do it twice. also i never thought about adding a little bit of toe in. I will will try that.
thanks for the help
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Old 05-17-2008, 01:11 AM
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Default RE: crashed my hog bipe

thank you for your help. on the other hand all of the the other hog bipes in the forums have a cg of 3 1/4 my book has 3 5/8 what should i do with that?
Either lie and tell everyone yours is 3 5/8" as well or just adjust yours if you want yours to be like the rest of the crowd. Or stick with 3 5/8" and try to convert the others.
Sorry, I've been this way all nite. Must been something I ate. Hope you get it fixed and flying the straight and narrow. It is bad when they misbehave.
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Old 05-17-2008, 03:26 AM
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Default RE: crashed my hog bipe


ORIGINAL: 06gsx

on the other hand all of the the other hog bipes in the forums have a cg of 3 1/4 my book has 3 5/8 what should i do with that? feel free to take a look.

While I agree with the idea you may be lifting off to soon and approaching to slow (typical mistakes) but there is something else going on here.

Reading that quote, if others are finding cg works well at 31/4 and you are using 35/8 then that is a major change and it is aft not forward. The CG you are using is further aft by a substancial amont from what others are finding successful. In other words 35/8 is more tailheavy than 31/4.

An aft CG certainly can contrubute to the behavoir you are finding both on takeoff and approach to landing.

John
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