Refurbish of Carl Goldberg Sky Tiger (Build Log)

[TexMechsRobot]

I was given an airframe that is pretty much intact. It needs some work on the monokote covering which should be a good introduction to the process for me since it doesn't have many (if any) compound curves. I'm pretty new to the hobby and have only flown an RTF Hobbyzone 3ch super cub. I intend to build a swappable as my second plane to learn some building techniques and "graduate" to a 4ch low wing.

The airframe I was given is fairly large (no measurements taken yet but I'm guessing the wingspan is about 6-7 feet) and was originally a gas powered craft. it still has the fuel tubing and such in place.

My question is: how do I figure out the appropriate engine size, prop size, servo size, battery size, etc. to convert this to an electric flyer? I'm sure you'll need more information from me to help me make this assessment so ask your clarifying questions and I'll do my best to answer them

Thanks in advance for your help!

 

[BobK]

Can you post pics so we can figure out what it is? Then some specs on the model can be figured out.

 

[TexMechsRobot]

I'll do that as soon as I get home from work. I'm thinking I should attempt to weigh it as well. I'll have to use a bathroom scale so it won't be super precise but should get it in the ball-park.

 

[BobK]

If we can figure out what it is then we can find the specs and weight etc but yeah give it a quick weigh on the bathroom scale anyway. I assume you don't know what it is or the name? I get a little giddy when someone posts that they found or was given an old plane, half the fun is figuring out what it is and the cond.

 

[TexMechsRobot]

I have no idea lol. I accepted it because I knew that this would be part of the fun. Being given a brand new, perfectly working plane is fun by itself but I'm starting this hobby because I'm an avid model builder and it allows me to create something other than static displays. I was excited about the challenge of getting half a plane revamped and air worthy

 

[TexMechsRobot]

There is a "Flying Tiger" decal on the sides of the fuselage but I can't seem to find anything regarding this except it appears to be a common club name for flying clubs....

 

[BobK]

Yeah that decal could be most anything, you said it is a low wing four channel plane?

 

[TexMechsRobot]

Yep. Landing struts are fixed on the wings. It is a steerable tricycle. It has a dark canopy. And the elevator is one piece across the tail plane.

These are some things I can remember from a cursory review. I'll be home in about 2 hours and can take a few pictures and measurements.

 

[BobK]

Oh! I had a pretty good idea what you had..but the landing gear doesn't fit with my thoughts at all lol.

Anything like these?

https://www.google.com/search?hl=en&site=imghp&tbm=isch&source=hp&biw=914&bih=438&q=low+wing+radio+control+plane&oq=low+wing+radio+control+plane&gs_l=img.12...3666.10751.0.13350.28.13.0.15.0.0.139.1168.0j10.10.0....0...1ac.1.64.img..3.9.1060.Abqh_21Avn4

 

[TexMechsRobot]

This one seems to fit in some ways:

http://www.kyosho.com/eng/products/rc/detail.html?product_id=109703

I also remembered that the wing has a dihedral.

 

[BobK]

Well if that is it then you have a pretty darn nice plane there I was thinking maybe it was an old Super Sporster kit build or something like that.

 

[TexMechsRobot]

Definitely not a Super Sportster. The one I have boasts a square, flat sided fuselage. Not much in the way of aesthetics!

 

[TexMechsRobot]

The dihedral is slight though. I also found that my memory was a little off. The sticker says "Sky Tiger" and there seem to be a few more results when googling that. None of them are a perfect fit (like the tail plane configuration or canopy) but I bet they are similar in power requirements.

I took some measurements:

Airframe Weight: 67.2 oz
Wingspan: 62.5"
Wing Chord: 11.0"

From this I could calculate:

Wing Load: 14.1 oz/sq ft
Stall Speed: ~19 mph
Top Speed: ~47 mph
CoG: ~3.5" from Leading Edge
Thrust to Weight: no more than 1:1 and no less than .75:1

Linked are three images on my Flickr account.

 

[BobK]

How much do you want for it?! You have what appears to me to be a very clean and nicely built vintage Carl Goldberg Sky Tiger, and if I am correct has Robart landing gear struts. Very Nice!! Are the struts decorative or do they work?

http://www.rcuniverse.com/market/item.cfm?itemid=754749

http://www.rcgroups.com/forums/showthread.php?t=1827734

https://www.google.com/search?hl=en......1ac.1.64.img..0.18.975.Pz3Z417LSDk#imgrc=_

 

[TexMechsRobot]

Haha I think it is worth more to me as a project and learning opportunity! That definitely is the plane! Nice to know the name so that I can now search for electric conversions done by others and see how they did it.

The wind struts are hard points and the nose gear is steerable. Nothing retracts if that's what you're asking.

It appears to be a quality build. The monokote is peeling in some areas so i'm going to attempt to remove it all (big job from what I've read), refurbish anything inside while I convert it to electric, and then recover it.

 

[BobK]

I didn't mean retracts I was wondering if the struts had actual vertical suspension or if they are decorative plastic covers over the main wire.

From the pics I feel you shouldn't go through the trouble removing all the covering, you can if you want but to get a used plane in that good of cond. (especially a fuel plane) is pretty rare. If I were you I would look around the engine and fuel tank area for fuel-soaked wood, check/feel around glue joints and landing gear area for loose joints or broken wood, and if that all checks out fix the small areas of covering that need it and call it good, the covering looks good in the pics.

 

[TexMechsRobot]

Oh got it. No vertical suspension. The the torsion spring in the nose gear is all.

Concerning the covering, the pics may not pick it all up but there are many edges that are lifting including about a 13" run on the trailing edge of the wing. While I could probably get away with a patch job, I'm a bit of a perfectionist an won't be satisfied with those results. I have extensive model building experience and I know that this is something I can handle and I'm willing to put the time and effort into doing it right.

I'll turn this thread into a build log so you and anyone can track the progress! Capital is a bit low right now so I know that this project will be a slow one but you're welcome to follow along and I'd love to have your advice as I move forward!

 

[BobK]

Sounds good! I respect the fact that you are willing to take the time to do the work right and be satisfied.

I'll be watching, I love these older planes.

I am not a motor expert, but I have heard some good things about Firepower motors, and this .46 might be a fair choice in this plane. If you want to go tamer the .40 looks good also.

http://www.headsuphobby.com/Firepower-46-Sport-720kv-Outrunner-Brushless-Electric-Motor-E-285.htm

 

[TexMechsRobot]

The .46 looks like a good place to start. And this is where my inexperience shows up in a big way. Can you explain why you chose this one and how you know if will be good for the plane?

The next set of questions will revolve around the assumption that I choose this motor. How do I pick the correct prop size, ESC, battery and servos?

 

[roversgonemad]

That's a great plane! If you have any fuel soaked areas and can't get covering t stick, I have had good results using this to get the fuel out of balsa wood. Often, that's why the covering loses its grip, because the wood is fuel soaked.

Can't wait to see it shape up. RCG has a ton of good electric conversion threads.