Motor suggestion for Goldberg Sr. Falcon - RC Groups
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Jan 04, 2003, 12:52 AM
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rcav8r2's Avatar

Motor suggestion for Goldberg Sr. Falcon

I want to convert a Goldberg SR. Falcon to electric. What would be a good motor/gb/prop? Also number of cells. Preferably brushless.
I tried running some numbers through moto calc, but when running some of my planes that I fly now through I got feedback that some of them wouldn't fly, or fly very poorly at best, when in reality they fly just fine. I don't trust my use of MotoCalc yet, at least until I get some "real word" experience with the larger stuff.

This will be my first larger conversion and need a starting place.

Some specs:
69" wing span
810 Sq In
box says 6.25# ready to fly, so I am guessing I can get the empty airframe down in the low 5# to high 4# range. It is a shoulder wing sport plane with a semi symetrical airfoil that is rather thick.
Recomended engine is .45-.60 glow. This kit was from back in the day when the engines didn't out as much power as the present day examples. If I were to built it glow, I'm betting that a K&B .45 with a 13x6 prop would an idea power system.

The kit is built, but not covered. I got it this way from someone who is getting out of the hobby. I really can't replace any of the wood, but can take some liberties with lightenting it a bit.

I am looking for "normal" sport flying. Nothing special out of the normal loop/roll/snapping stuff. I had one of the original Falcon 56s, and flew it with a really worn out .40 FP. Certianally not a stump puller by any streach of the imagination, and it flew fine at 1/2 throttle.

I did a search and found a few references to the plane, but no mention of power system or batteries.

Any feedback would be greatly appriciated. Thanks in advance.
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Jan 04, 2003, 09:45 AM
aka neweflyer


I think the box is, well lets say optimistic about the weight. my dad flew one on a 60 two stroke and it was closer to 7 1/2 -8 pounds. That being said, if you could lighten it up some and stay at the 7-8 pound all up, it would be about the same size and weight as my astro-hog that i fly on a maxcim d-wind on 18 cells.
Jan 04, 2003, 07:25 PM
Have You Seen My SAK
3dddflyer's Avatar
get a hacker 50 xl with a 5to1 or 4.4.1 gearbax
Jan 04, 2003, 09:41 PM
Registered User
SheldonYoung's Avatar
Mega 22/30/3 geared to turn a big a prop as you can clear on 16 cells (CP2400-ish) should fly it well even if it ends up at 7.5 lbs.
Jan 04, 2003, 11:04 PM
Registered User
the Sr Falcon has awfull short legs. A 12"
prop will mow the grass w/stock lg. I know, I
flew one for 10 years on glow until the God
of the cornfields reached out and swatted it
from the sky.
Jan 05, 2003, 12:27 AM
Registered User
I had a Sr Falcon 25 years ago and it ran well on a .40. I was telling a guy in the hobby shop just yesterday about it and he said all the Goldberg models are coming back. Says he knows the original engineer that worked for them. Anybody else heard this rumor? I buy another in a heart beat!

see attached pix.
Jan 05, 2003, 08:17 AM
Don't cut the Yellow Wire
dr.E's Avatar
Make it a tail dragger and you can swing a larger prop.

A couple of motor options would be:

Mega 30--2 with a 3:1 gear on 16 cells

Mega 45-3 with a 2:1 gear on 16-18 cells

Hacker 50 10L with 5.2 gear on 16 cells

Astro 40 geared on 18 cells
Jan 05, 2003, 08:50 AM
Registered User
Ray Lowinski's Avatar
My Senior Falcon is getting a new, longer, aluminum gear. The original wire gears won't handle the weight as a tail dragger if you don't grease in every landing. You will spend time bending them down to regain the ground clearance. Don't be afraid to put longer legs on.

Keep 'em hummin'

Jan 05, 2003, 09:34 AM
Registered User
ldracer's Avatar
7.5 lbs sure sounds heavy for this model.
You also have to remember all that wing you have.
As I recall, with 70's(heavy) building techniques Getting one down out of the air was more problem than getting it up.
You are just going to cruise around this buggy , right?

I had a Mega 22-30-2 on a 6.7:1 box swinging a 20X11 APC E .
The best set up I tried produced 80oz. of thrust on the test bench, using 12 cP2400's. Current was 24.6A. This would have a wide open throttle time of 6 minutes. I ran this set up to 150oz.
but efficiency startred dying out as I added more cells.

Lengthening landing gear has become a fact of life for me on conversions. I just figure it is a necessary evil.

I too have found MotoCalc to be in left field some times.
Jan 05, 2003, 10:21 AM
Don't cut the Yellow Wire
dr.E's Avatar
Prop up to 40+ amps on the Megas and the high 40's on the Hacker. Keep the astro in the mid 30's.

All these sysytems should give you 600-700 watts of power proped around a 15x10 prop..

AUW of the Falcon should be around 8 lbs and w/lb should be around 75 watts/pound .

Mount the aileron servos on the wing (hs 85's will save you over an ounce per servo compared to a std servo) also mount the rudder and elevator servos aft of the trailing edge on a small accesory hatch.

The fuse was rather skinny on the original design and you may have to build new formers to accomodate your battery dimensions.

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