schafe3624

I am working on a 1/24 scale C-130. The plans call for 4 X .10 glow engines or electric equivalent. I will not build it with glow engines so I need help figuring out what electric motors, props, ESC's and batteries to use. So far I'm failing - badly.

The plans call for a distance between glow engine centers of 8.3" which is to scale. The plans indicate a distance of 9.3" for electric motors to use a slightly larger prop. I'd prefer to keep it scale.

I have no idea what the finished weight will be, but I'm afraid its going to be heavy. I calculate the wing area to be just under 400 sq inches.

Any ideas and suggestions are really appreciated and needed. I don't want my wife to get another "I told you so."

mattnew

My Feedback: (2)

are you going to go with a scale 4 blade prop for it?


The easy answer is to go with 1 of the "glow replacement" style numbered motors, an e-flite power 10 or O.S. OSMG9510

Both of these are designed to replace a .10 sized glow directly, and will likely have more than enough power given there are 4 of them pulling the plane. The tough part you may have is fitting the blades... You are limited to about 8" props if you go scale...

The real question is, how much is it going to weigh when done. What are your estimates.... if you are in the 6-8lb range the .10 sized glow replacements will fly it nicely, you might even be ok up to 10lbs.

My suggestion, or, if you go to the electric B-17? thread, how I decided on my motors

I decided on prop size I had to live with due to the planes size... for you thats either 8 inches or 8.5 inches.. so 8 inches... you don't really gain anything by going to 9.3" spacing as props typically aren't sold in 1/2" sizes.

I then picked a motor I thought would work.. in my case an e-flite power 15.. i measured the area I had to work with in terms of fitting batteries and made some trade offs in terms of weight vs capacity... decided on about a 2200mah 3s pack, for each motor... should give 8-10 minute flights, and at 176 grams a piece helped minimize the added weight of the batteries

I then bought 1 of each, and an ESC that was way oversized ( 80 amp ) and a wattmeter. Hooked everything up and figured out my current draw which told me how big an ESC I really need. It also gave me some confidence that the system would be sufficient for what I wanted to do.

From there I sized my final ESC's and bought the whole package...


there is no one right answer here unfortunately... and not a ton of people flying multi-engine setups... trial and error is your friend here... I would encourage trying a couple things and seeing what works and go from there....

blvdbuzzard

I have used these motors for a couple years now. They have proven to be good motors.

http://www.hobbypartz.com/96m601-big...20-1100kv.html

If you run this with a 3s 22200mah battery, 11X6 4 blade prop, it will be right at 44 amps and 77 ounces of thrust. This is 2 amps over rating, but you are not going to run it static for a long time plus it is just a calculation. Actual test will need to be done to make sure you are not over stressing the motor.

Sounds like an interesting project. Keep us posted.


Buzz.

schafe3624

Thanks so much for the support. I'm really concerned this is not going to fly and my time will be wasted. If I could only find a RTF C-130 that people say is decent I wouldn't be in this mess.

I went into this from a different angle. I looked up the RPM of an OS .10 engine. Max 18000, but it seems 12000 is more practical. From that I selected a motor that has a similar kv rating. In this case I chose a 1460kv motor that fits into the nacelles. 3 cell lipo of 11.1 volts times 1460kv equals 16206 rpm unloaded. So I guessed that the loaded RPM would be similar to the glow engine.

I bought a motor - actually I bought all 4 with 4-45amp ESCs. Testing with my watt meter I have a prop that fits in the scale configuration and draws 40 amps and creates about 400 watts of power. So that is where I am at right now.

I had someone tell me I am likely creating an interesting looking, prop driven car.

mattnew

My Feedback: (2)

@blvdbuzzard,

note that Schafe has 8.3" between engine nacelles. He won't be able to fit an 11", 4 blade prop, as each blade would extend out 5.5" from center, in other words the two blades would hit. the best he can do is 8 inches on the prop. I still think thats ok.

I like the price on that Tacon motor. I wish I had seen those before I bought my e-flite motors.. unfortunately they just arrived last week...


@schafe;
I think you have more than enough power to fly. you might even be able to simulate the JATO they used on the C-130 with that kind of power.... here is my math....
400 watts each x 4 motors = 1600 watts. If your plane weighs 10 lbs that 160Watts per lb... which should mean your C-130 will fly 3D nicely.
Typical rules of thumb for Wattage required for an electric plane

• 50–70 watts per pound: Minimum level of power for decent performance, good for lightly loaded slow fl yer and park fl yer models

• 70–90 watts per pound: Trainer and slow fl ying scale models
• 90–110 watts per pound: Sport aerobatic and fast fl ying scale models

• 110–130 watts per pound: Advanced aerobatic and high speed models

• 130–150 watts per pound; Lightly loaded 3D models and ducted fans

• 150–200+ watts per pound: Unlimited performance aerobatic and 3D models

That was taken from this article from e-flite that should give you some confidence that your plane will fly.
http://www.e-fliterc.com/Articles/Ar...ArticleID=1563

mattnew

My Feedback: (2)

BTW, I'm pretty much about a month ahead of you in this whole learning curve, which is basically why I'm chiming in. You're going through the same growing pains about learning about electric power that I am going through in order to fly a reliable multi-engine aircraft.

post some pictures! Here is what I have been working to convert to electric. My final weight is shooting to be in the 11-12lb range, powered by e-flite power 15's. The original design was powered by .19 sized glow engines.

blvdbuzzard

I just ran the numbers again, this time with a 8x6 4 blade prop with a 4s battery. It comes out to be 72 ounces of thrust at 30 amps. So 72 x 4 = 288/16= 18 pounds of thrust. I know you wanted to use 3s batteries, but with the lower KV rating of the motor, you might need to use a high voltage to use a smaller prop.

Now, if you want to push the limits, if you went with the 9.3 inch separation, you could use the 9X6 4 blade prop on 4s and get 21.5 pounds of thrust. That is an amazing amount of power out of those little motors. I think this would be over kill and would let you almost hover your C-130. It would take of at near vertical.

Here is the calc program I use. If you use the eflite motors, Tacons are close to being a copy of them.

http://www.ecalc.ch/motorcalc.htm?ecalc&lang=en

I would say use the 4s battery, 8x6 4 balded prop and you will have more then enough power.

There is a learning curve to all of this. It has been a long road for me. I have let the magic smoke out more then once. You might want to get a small plane and try the setup in. Just a stick type, easy to build test plane. That way you become familiar with all of this and can see what it is like if you change from an 8x6 prop to a 8x4 prop. It is better to crash a cheap throw away plane then a nice project.



Buzz.

schafe3624

I'm still plugging away at this problem. I have no idea what the finished weight will be, but I'm guessing it will be over 10 pounds. Turns out there are several wing calculators on the web. All have concluded it will have to fly fast if at all.

I will mention at this point that I am experimenting with a new building technique, 3D printing. I started with the exterior of a C-130 that was intended for use in a video game. I added the inside components in a CAD program using carbon fiber arrows for strength. My thought was that I would have a thinner skin than balsa and I would not have the plywood ribs and hardwood spars used in typical construction. Even though the plastic is heavier than balsa I would be using less overall material and have a 100% scale result. I am now printing the plane with 100% plastic skin and interior components.

If it doesn't fly, which it looks like it won't, I will switch to plan B. Redesign the thing eliminating most of the plastic skin. Keep the carbon fiber arrows but make plastic ribs. Cover with monokote or maybe balsa. I will stick with plastic sections where there are features that are difficult to cover like the engine nacelles, wing roots, base of the rudder, etc. I will also keep the nose plastic for the cockpit window detail. This should make it much lighter.

mattnew

My Feedback: (2)

Interesting, always cool to try new things!


One other thought... see whats out there for counter-rotating props in whatever size you choose. 3 blade and 4 blade props are a bit limited in what you can find out there. although its not scale, you may ultimately choose a 2 blade just based on availability.

schafe3624

I am officially switching to plan B. The 3D printer I have is a hobby grade plastic extruder type printer. The very thin layers I designed for the skin, .8mm at the thinnest, just wont stick to each other very well and won't be strong enough over the surface area I need. I'm going to redesign it using the standard built up style and skin it with 1/16 inch balsa.

blvdbuzzard

Have you thought about foam construction? It is very strong and very lite weight. Easy to sand to shape, can be cut with a hot wire, cross sections can be stacked to make the fuse, 1/32 sheet foam can be used for the tail feathers.

Here are a few ideas for you

http://www.gibbsguides.com/article10_C130_part01.htm

http://www.buildafoamie.com/bundle.html


Buzz.

CanDo

If you don't mind working with foam, here is a short kit for a 91" span C130 (~7lb) at Parkflyer Plastics:
http://parkflyerplastics.com/cart/in...roducts_id=503

Here are the wing cores at WOW planes:
http://www.wowplanes.com/product_info.php?cPath=59&products_id=182

I have done business with both owners and they sell quality products. Here is Keith Sparks' build log for his C130. Note, there is a lot of good information about his plane here. I hope this helps:
http://www.rcgroups.com/forums/showt...ht=c130+sparki

jofro

This is my 100" ASM, "C-130" I have built 5 years ago as IC glow set up with '52FS on inner and '32FS outer. Flew it 7 times but consistent low the idle was a pain in the neck so I switched to E-power. Probably the best thing I have done. 8.2kg AUW model has now even more power at 8.5kg thrust. Just plug it in and fly it is my motto, J.

jofro

Few more pics of the model still as an IC, J.

jofro

What ever happened to this thread? Did you finish it? or ended in the disaster?