Mega Model Bird Dog ARF?  
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Mega Model Bird Dog ARF? - 5/22/2008 2:34:09 AM   
qwerty3


 

Posts: 50
Joined: 10/14/2005
From: Grand Rapids, MI, USA
Status: offline 		I recently acquired a never-flown "Mega Model" ARF Cessna Bird Dog, that was sold by Hobby Lobby. It is a very nicely detailed plane, for an ARF. Got several compliments on the airplane while at the field. The previous owner installed an OS 15, and a fuel tank, but never flew it.

In attempting repeatedly to take off, the landing gear bent - just in taxiing! (Our field is grass, and pretty thick in the springtime.) The only way I could get in the air was a hand launch. After trimming, it flew nicely. Only quirk noticed was that on high rates (as set per the manual) a full-up-elevator loop would cause a snap-roll at the top, with no other inputs. Never saw a plane before that would do that

I reinforced the gear with some 5/32 music wire, and tried a takeoff again. This time, one wheel must have caught on something - because the gear ripped off, twisted, and airplane ended up on its back.

Has anyone else had this problem with the gear on this plane? It appears to be made from 'dead soft' aluminum, with almost no spring.
       Post #: 1

RE: Mega Model Bird Dog ARF? - 5/27/2008 2:13:06 PM   
qwerty3


 

Posts: 50
Joined: 10/14/2005
From: Grand Rapids, MI, USA
Status: offline 		Hmmmmm . . . . . no responses?

Update: a club member (who had watched my miserable takeoff attempts) sold me a composite landing gear that was a drop-in replacement for the aluminum gear. This has been installed, and awaits flight testing. Maybe this composite gear will fix the ground-handling / takeoff problem ?

(in reply to qwerty3)
       Post #: 2

RE: Mega Model Bird Dog ARF? - 5/27/2008 2:44:22 PM   
Campy



Posts: 3396
Joined: 1/2/2002
From: Baltic, CT, USA
Status: offline
quote:

ORIGINAL: qwerty3

I recently acquired a never-flown "Mega Model" ARF Cessna Bird Dog, that was sold by Hobby Lobby. It is a very nicely detailed plane, for an ARF. Got several compliments on the airplane while at the field. The previous owner installed an OS 15, and a fuel tank, but never flew it.

In attempting repeatedly to take off, the landing gear bent - just in taxiing! (Our field is grass, and pretty thick in the springtime.) The only way I could get in the air was a hand launch. After trimming, it flew nicely. Only quirk noticed was that on high rates (as set per the manual) a full-up-elevator loop would cause a snap-roll at the top, with no other inputs. Never saw a plane before that would do that

I reinforced the gear with some 5/32 music wire, and tried a takeoff again. This time, one wheel must have caught on something - because the gear ripped off, twisted, and airplane ended up on its back.

Has anyone else had this problem with the gear on this plane? It appears to be made from 'dead soft' aluminum, with almost no spring.



As for the snap roll, you have too much elevator input (throw). Reduce the amount of elevator throw and the snap roll will stop (You will need to "play" with this to get the correct amount of throw)

For your landing gear - 1st, use (or make) a landing gear from 6061 aluminum. This is a "hard" aluminum. If you decide to make your own pm me and I will provide directions on how to do this so as not to cause any internal "fractures" in the metal.

The gear should bolt into 1/4" REGULAR plywood, not lite ply AND you should re-enforce the landing gear plate with 3/8" (or 1/2" tri stock. The tri stock gets epoxied to the plate and the fuselage side.

Flying off a grass field you want AT LEAST 2 3/4" diameter wheels (3" diameter preferred). Smaller wheels catch in the bumps, etc and tend to flip the plane, rip out gear, etc.

MAKE SURE YOU RE-BALANCE THE PLANE BEFORE FLYING.

(in reply to qwerty3)
       Post #: 3

RE: Mega Model Bird Dog ARF? - 5/28/2008 1:11:14 PM   
qwerty3


 

Posts: 50
Joined: 10/14/2005
From: Grand Rapids, MI, USA
Status: offline 		Campy:

Thanks for replying. I - guess - I *should* put larger wheels on - I was hoping to stay with something more 'scale' sized, but, yes, bigger (wheels) takeoff better from grass. This is not my first airplane, and on my 'sport' planes I usually use 3" wheels.

I'll have to take a long hard look at re-designing the gear mounting - that would not be a simple task. However, I've had that problem with another ARF - that the gear mount was pretty wimpy - just a little plywood plate, not much larger than the gear itself. That of course does NOT do a good job of spreading the landing loads out, but rather tends to just 'rip out' of the fuselage on a less-than-perfect landing.

I've had better results with a kind of triangle stock made from plywood - cut on my table saw with the plies running parallel to the longer face of the triangle; then glue that in so that those plies run at approx. a 45 deg. angle to the gear plate. This has much more strength than std. balsa triangle stock (although a bit heavier).

I guess my real question is: why would the manufacturer design and sell the product this way? How could *anyone* use it successfully? (Or, have others had good results, and the glow conversion is the source of the problem?) What were they thinking? Or, was the design initially good, but a low-bidder manufacturer made some changes for 'producibility' that screwed up the design? (Nah, couldn't be - that never happens! )

(in reply to Campy)
       Post #: 4

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