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#1 frank26all Jun 15, 2011 11:59 PM

tiger moth
 
well I was able to fly my tiger moth again today with no damage,I did however encounter some strange flying characteristics,aside from being very windy the plane had a strange bobbing manner,not sure if it was the wind or my cg,maybe the servos are a little slow to react,I sure could use some more experienced opinions from my fellow flyers. thanks for any help
tiger moth (5 min 1 sec)
tiger moth fpv (3 min 28 sec)

#2 warhead_71 Jun 16, 2011 12:54 PM

Nice Tiggie.

Your main wheels were up before the tailwheel...

I'd start by checking your CG, it looked a little tail heavy when it took off nose-first and the tail started to yaw earthward as she stereotypically rolled to the left. It's usually easy to spot tail-heaviness by making a few "bank and yank" turns... if the tail sags as you roll, you are most likely tail heavy. ("Sagging tail" could also be adverse yaw, but I doubt it on a Tiger Moth... that's more of a high-wing/high-aspect-ratio issue and most biplanes don't have that problem... but you could always mix in some rudder with the ailerons for good measure).

If your CG is to spec, next check your motor thrust angle... it might need more down-thrust and you have instead trimmed the elevator down to compensate. An easy way to tell if the thrust is off is to eliminate the motor from the equation... get some height, cut the throttle, and see how she glides in a shallow dive. If you are still porpoising with the motor off, then it's not the thrust angle.

Are your interplane struts backwards? More than once I've seen someone assemble a biplane with the struts backwards, so the top wing ends up with too much positive incidence.

Lastly, I'd just check that elevator servo... maybe it's twitchy (test it with a bit of load on it), or maybe it's too sensitive and you need some exponential. I'd try 30% and go from there.

P.S. - I see you are from Gulf Shores. My in-laws go there every other year or so for family vacation. I always make a trip to Pensacola while I'm there to check out the air museum.

#3 frank26all Jun 17, 2011 04:04 PM

cg
 
thanks for the input,the plane was in fact very tail heavy,I made a few changes in the battery compartment and I think I have it balanced out pretty good now but I will fly it again soon and report back,, thanks again

#4 semc Jun 24, 2011 04:57 PM

Quote:

Originally Posted by warhead_71 (Post 18517016)
Nice Tiggie.

Your main wheels were up before the tailwheel...

I'd start by checking your CG, it looked a little tail heavy when it took off nose-first and the tail started to yaw earthward as she stereotypically rolled to the left. It's usually easy to spot tail-heaviness by making a few "bank and yank" turns... if the tail sags as you roll, you are most likely tail heavy. ("Sagging tail" could also be adverse yaw, but I doubt it on a Tiger Moth... that's more of a high-wing/high-aspect-ratio issue and most biplanes don't have that problem... but you could always mix in some rudder with the ailerons for good measure).

If your CG is to spec, next check your motor thrust angle... it might need more down-thrust and you have instead trimmed the elevator down to compensate. An easy way to tell if the thrust is off is to eliminate the motor from the equation... get some height, cut the throttle, and see how she glides in a shallow dive. If you are still porpoising with the motor off, then it's not the thrust angle.

Are your interplane struts backwards? More than once I've seen someone assemble a biplane with the struts backwards, so the top wing ends up with too much positive incidence.

Lastly, I'd just check that elevator servo... maybe it's twitchy (test it with a bit of load on it), or maybe it's too sensitive and you need some exponential. I'd try 30% and go from there.

P.S. - I see you are from Gulf Shores. My in-laws go there every other year or so for family vacation. I always make a trip to Pensacola while I'm there to check out the air museum.

you mentioned that the interplane struts could be backward, i have just purchased an old 1/4 scale pilot tiger moth which is being refurbished and i have fitted my interplane struts but i'm not sure if they are fitted the right way, i have fitted the longest strut to the front and the shorter strut to the rear does this sound right to you, thanks in advance

#5 warhead_71 Jun 24, 2011 05:04 PM

I would think the longer strut would be to the rear, to offset for the wing being thicker at the front.

http://www.aristocraft.com/polksvbul...ead.php?t=1733


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