motoaire

My Feedback: (24)

I'm currently building the Goldberg ultimate and noticed on the plans that it calls for

1&1/2 degrees positive incidence on the horizontal stab with both the top and bottom

wings at 0 incidence. Does anyone who has experience with this plane know why it

calls for the positive stab incidence and the possible effect on flight performance if

built with 0 degrees incidence on the stab? This is the first biplane I've built from

a kit so any knowledeable comments would be appreciated.

Thanks in advance,
Motoaire

MinnFlyer

My Feedback: (4)

Well, I've never built one, but I have flown several - and they fly GREAT!

So I would go with the plans

donkey doctor

Hello; We recently finished one of those up for a fellow flyer. I built one about 8 years ago too, what I remember is that the top wing comes out wrong if you follow the instructions incidense-wise. We had to lower teh front of the top wing by about 5/16 to get the recommended incidences. I remembered the problem with mine when I built it, and checked Jim's ultimate (the new One) and it was exactly the same.

We checked incidence by propping up the back of teh fuselage until the horizontal stab was at 0 degrees, then measure teh lower wing incidence, write it down. Then measure the top wing incidence. It should be the same as the bottom wing. If it isn't (as I suspect) it isn't toohard to lower the front of the to wing by moving the aluminum bracket under the cabane struts and adding some material until it's perfect.

Before we did this check, the plane just about stopped when you reduced teh throttle. Too much drag to glide properly.

Then there's changeing teh landing gear to aluminum, and buying a better engine cowl, two aileron servos, and other detail changes.

tonyc

My Feedback: (4)

Motoaire: I scaled up the plans for this plane and built an Ultimate with a 62 inch wing span, giant scale. We'll as luck would have it I missed the very faint print that call for the stab o have a positive incidence. There fore mine had 0. After many trimming flights I ended up with 2% down thrust and 3% right thrust. The positive stab is the same as down thrust.
tonyc

tarvma02

My Feedback: (3)

I've built 4 Ultimates and never once checked the incidence and they all flew hands off. Here's why "checking" the incidence and comparing them to the plans doesn't help too much. Basically, unless your table is perfectly level and the airfoil perfectly symmetrical then your baseline may or may not be the actual incidence of the airfoil. Incidence meters are generally only good for changing the incidence after the fact in comparison to a baseline. But, comparing this baseline to the plans doesn't mean too much.

With all that said, if you build the plane according to the planes and balance it, I promise it will fly GREAT, adjusting the incidence or not! Then, only then, if something feels funny, should you start worrying about the incidence.

motoaire

My Feedback: (24)

Thanks for the replies guys, I guess I'll build it as per the plans and work out

any needed changes, if any, after I test fly it. donkey doctor: I've seen several

of the GB ultimates fly in the past and as you stated some of them almost

dropped out of the sky if the engine quit. I know bipes have alot more drag but

some seemed to have terrible engine out glide ratios. What you stated about

the wing incidences may have been part of the problem. I'm trying to build it

as light as possible, so that should also help. BTW I'm also using an aluminum

landing gear and making my own fiberglass cowl which should be considerably

stronger and lighter than the stock plastic. Two aileron servos are much better

than all that bellcrank linkage the plans call for.

Motoaire.

rcmiket

I'm with the others built and flown many, never checked any of that stuff just built them per the instructions. They fly great have never in 15 years not had one. Mike