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Old Nov 15, 2014, 12:23 PM
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The Netherlands, OV, Nieuwleusen
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Lockheed C-130H 1.75m (69 inch) first project

Hi all,

A few weeks back I started my first cargo bird scratch build. I don't have a lot of experience, so progress will probably be slow and a lot of things will be done more then twice. I'm not setting any deadline or something like that, just because I have no idea what to expect.

I've been looking through just about every thread in the Airline part of the forum, and some in the giant part of the forum and I have a reasonable idea of how I'm going to do things. If somebody things I'm being stupid doing it one way, please, educate me . I'm building it from a CAD drawing scaled to 1.75 meters.

Specs:
Wingspan: 69"
Weight: I'm looking at about 3kg, I'm wondering how to get this down by a LOT
Powerplant: 4x Rctimer BC3536/11 750KV on 2/4 blade 10x6 on 4S
ESC: 4x 35 AMP
5-7 Micro digital gear servos
Battery: 2/3x 4S 3000mAh 20C LiPo (300 grams each)
fixed gear for now
Flaps: as I'm looking at it now, no but I might need them if I can't keep weight down

The wing without engines is currently about 270 grams, but with 2 engines attached jumps to 514 grams. I'm at just over 1.1 kg with just my power setup, assuming 2 LiPo's. I clearly need some advice on light wing building My projected wing loading is 48 g/dm2, or about 21 oz/sq. ft, project stall speed is 36 km/h or 22 mph.
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Old Nov 15, 2014, 07:24 PM
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T-A looks like your C-130 is off to a superb start Sir!

Sub-me-up!
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Old Nov 15, 2014, 07:29 PM
IWC
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subbed, I love C-130s
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Old Nov 15, 2014, 11:17 PM
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United States, AL, Phenix City
Joined May 2013
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I'm not sure how to quote the photos so I will comment about them in the order they are shown in your post.

Second Photo. The spar looks rather robust and I presume it is laminated balsa. If the joints in the spar are butt joints, they will be stress risers. This is especially true of the double joint near the center of the photo. On the other hand, if these joints are angled, everything is fine. I think the angled joints are called scarf joints.

Photo 4. Broken motor mount glue joints cost me an airplane. The last joint held long enough to get into the air then broke during a full power transition to vertical flight. Adding insult to injury, as the motor exited the airplane it arced the speed controller. Your firewall glue joints don't look like they would tolerate ground strikes and gyroscopic effect of the props. I recommend adding some triangles to the fire walls.

I am looking forward to the rest of the build and the maiden flight.

Mike
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Old Nov 16, 2014, 02:36 AM
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The Netherlands, OV, Nieuwleusen
Joined Jun 2014
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Quote:
Originally Posted by PC Pilot View Post
I'm not sure how to quote the photos so I will comment about them in the order they are shown in your post.

Second Photo. The spar looks rather robust and I presume it is laminated balsa. If the joints in the spar are butt joints, they will be stress risers. This is especially true of the double joint near the center of the photo. On the other hand, if these joints are angled, everything is fine. I think the angled joints are called scarf joints.

Photo 4. Broken motor mount glue joints cost me an airplane. The last joint held long enough to get into the air then broke during a full power transition to vertical flight. Adding insult to injury, as the motor exited the airplane it arced the speed controller. Your firewall glue joints don't look like they would tolerate ground strikes and gyroscopic effect of the props. I recommend adding some triangles to the fire walls.

I am looking forward to the rest of the build and the maiden flight.

Mike
The spar is spruce, and granted, I think it is way too heavy, that small spar is 170 gram. The joints are indeed butt joints, I'm going to epoxy in some small triangle's made out of balsa. The motor mounts are held in place with screws, if I feel them, they feel very sturdy in every direction.

What do you guys think, rebuild wing with a box spar made of balsa? Other good idea's are always appreciated. What is a good weight as a goal for a wing (with/without engines)?

By the way, I'm Thom, thanks for all of your help, it is greatly appreciated
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Old Nov 16, 2014, 04:58 PM
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United States, SC, Charleston
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Quote:
Originally Posted by T_Aviator View Post
The spar is spruce, and granted, I think it is way too heavy, that small spar is 170 gram. The joints are indeed butt joints, I'm going to epoxy in some small triangle's made out of balsa. The motor mounts are held in place with screws, if I feel them, they feel very sturdy in every direction.

What do you guys think, rebuild wing with a box spar made of balsa? Other good idea's are always appreciated. What is a good weight as a goal for a wing (with/without engines)?

By the way, I'm Thom, thanks for all of your help, it is greatly appreciated
Looking great. . . Whatever choice you make Thom I would add some carbon fiber rodsto your C-130 wing's internal structure.
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Old Nov 16, 2014, 05:25 PM
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United States, NM, Rio Rancho
Joined Jul 2007
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Thom
Butt joints are never a good idea for spars or longerons. IMHO you should replace the spar to save the grief of a failure inflight There is no sense in wasting all the $ and time. Balsa doublers are also a failure waiting to happen
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Old Nov 17, 2014, 07:10 AM
HappyGoLucky
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Germany, BW, Ibach
Joined Dec 2009
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Quote:
Originally Posted by T_Aviator View Post
The spar is spruce, and granted, I think it is way too heavy, that small spar is 170 gram

What do you guys think, rebuild wing with a box spar made of balsa?
You can easily replace that wood spar with a CFK square tube spar. They are light and very strong but a bit on the expensive side when over 1000mm long. I'm using the 6mmx6mm version and I never had anything break on me.
If you don't want to rip the wooden spar out then you might think about strengthening it with two thin CFK strips, one at the bottom and one at the top of the existing spar. I'm guessing that should be enough while not adding more than a few grams. I don't think that a balsa box spar is strong enough. I have build a plane with balsa spars but it had no motors on the wings and was only about 1.7KG.

Just as an example for the tube spars, you'll have to find a supplier within your area:
http://www.sino-composites.com/pro.asp?id=89
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Old Nov 17, 2014, 11:19 AM
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The Netherlands, OV, Nieuwleusen
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Allright, I just made a mould to make a spar from fibreglass, just as a test. When I get the fibreglass I orderd I'll build it and test till failure. The only glass I got at the moment is 150 g/m2 (very heavy stuff). What is a good weight to aim for on a wing with two engines on it? The engines are 125 grams a piece.

I looked into the CF spar, looks very promising but I can't find it anywhere near me, shipping is idiotically expensive with this kind of size. If I find a local source I will definitely build a new wing with a CF spar. Fair point on the balsa stuff.

By the way, I'm sorry there is so little progress, but this is my first decent scratch build, it takes some time to get the hang of it.
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Old Nov 17, 2014, 11:29 AM
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I'm really wondering if I can use the wing I had already made, or if it's just too heavy with 270 gram without engines. I know I have to do some light modification to reinforce the engine mounts, but do you guys think I can use it and build the other wing the same way?
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Old Nov 17, 2014, 08:37 PM
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I don't know enough to advise about overall weight but wings of equal weight are important for lateral stability. This will manifest itself most in slow flight, like landing,
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Old Nov 19, 2014, 04:33 PM
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The Netherlands, OV, Nieuwleusen
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fibreglass wing spar

So, my 50 gram/m2 arrived today, I will get help fibreglassing a spar from a friend of mine. We both fly glider planes (the ones eithout remote ) and I help him every winter maintaining the fleet of our club. He has a lot of fibreglassing experience, but neither one of us has a solid idea of how many layers we need, we normally work with bigger things and heavier fibreglass. If anyone has a good idea on how many layers we need, it will be highly appreciated, otherwise we will be doing some trail and error
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