chevronflyer

My Feedback: (9)

I am planning to convert my new 80 inch span cedarhobbies.net b-17 bomber with 4 e-flight power 25 brushless motors. I am thinking of using two thunder power 3 cell 4000mah batteries in parallel so i will have a total of 8000mah giving roughly 2000mah per motor. Here is my question though? What is the best way to wire these 4 motors together? Should i use 4 speed controls one on each motor or use two larger speed controls each wired to two motors or should i go with one large speed control wired to all four motors?

normgoyer

I believe that you have to use an individual ESC for each motor but you can use one large battery with a separate battery for receiver and servos. If the motors were brushed you can gang the motors with one esc but brushless require their own ESC. Norm

algutkin

My Feedback: (1)

Chevron Flyer,

I am very interested in knowing about the quality of the Cedar Hobbies B-17, also the scale appearance.

Norm is right in his advice about a seperate ESC for each motor, you do need to configure the plane that way.

Please post your progress in the conversion.

Al

Glacier Girl

My Feedback: (4)

Al, not to tun off the subject, but VQ Models is getting ready to introduce a B17. If it's like any of their other birds it's going to be a top shelf bird.

algutkin

My Feedback: (1)

Yep, I'll be getting a VQ B-17 the second they hit the market, I even have the power setups. However, I was eyeing the Cedar Hobbies B-17 for some time and was interested to know how they look up front and close. I'm not bashing it, but, the pictures and advertising leave much to be desired.

Al

chevronflyer

My Feedback: (9)

the quality and appearance of the cedcar hobbies b17 is much better than the website gives it credit for. It is very well built with a good covering job. for the money it is well worth what you get. And if you are ambitious you can spend a little extra time detailing it out to be scale. there are endless ways you can easily scale this bird out...

chevronflyer

My Feedback: (9)

Ok i decided on my power setup. I am going to be using 4 hacker A30-12l brushless outrunners paired with 4 X40 hacker controllers. This combo gives 400 watts peak power each. Plane will weigh just under 10 pounds or 160 ounces. this set up gives me 1600 watts total peak power so i will have 160 watts per pound peak. Does this sound like enough power for scale performance? I dont mind having extra unscale like power because i can use throttle management, i just dont want to fall short on power and have to fly at full throttle the whole time just to keep her up.

Glacier Girl

My Feedback: (4)

I'm thinking 160 w per pound would be in the acrobatic range of performance. But then again having all the "horse power" in the world won't mean much unless you have the props to make something of it. What size/pitch were you planning on going with? 3 blades?

algutkin

My Feedback: (1)

Chevronflyer,

Please post some pictures of the C17, especially the build progress.

I don't know if you are experienced in conversions, but, in my opinion, you should start the build before buying batteries or motors. You need to determine where you are going to put the batteries, the fuse, or the motor nacelles. Based upon everything that I learned, 160 watts per pound is severe overkill, the weight of the motors and batteries may affect the flying characteristics. My heavy twins, B25, A26, were built with 85 watts per pound and they fly like twin engined fighters. In addition, there is no sense haveing large motors when you are limited by the prop size. That is why I would suggest taking some measurement first.

Al

chevronflyer

My Feedback: (9)

i took all the measurements i need. there is plenty of room in the fuse for any amount of batteries i want. Also the motors i am using swing apc 9x5 up to 10x8 electric props. I determined i have space between nacelles and fuse for a max of 9 inch props so i will use around 9x8 props. Also i would like to use three bladed props for scale appearance but I cant seem to find any electric 3 blade props in the 9 inch range. Any suggestions? Yeah i am thinking the motors are a bit overkill but using throttle management, the 700 kv hacker a30 motors would be hardly working at all meaning cooler runs and longer flight times per charge.

Edd Spidell

Hi Chevronflyer,

I run Master Airscrew three blade 9x7 on my OV-10 Bronco (counter-rotating) and C-47, and three blade 10x7 on my C-160 Transall. They are very good, thin and stiff. Stay away from the APC three and four blade, use only for static display, as they have really poor in-flight performance (been there...). The Graupner three blade are good, but power hungry, as they have a very thick airfoil, made for taking the pounding of glow/gas.

Regards,

Edd Spidell

algutkin

My Feedback: (1)

Chevronflyer,

OK, it appears that you know what you are doing. Now, comes the big test. Those motors have to turn the 9X6 props 9,000 rpm. If the motor/battery combo will only turn those small props. 6,000 RPM the bird may not leave the ground. Slightly less RPM would be needed for the 10X7 props, however, motocalc will not give as good a performance factor for those props. You will get higher overall speed but use more runway.

The consideration here is length of runway, that is why I like the 9X6 props for your setup, they spool up fast and the plane will be able to take off using less runway. On grass this would be a major concern.

Welcome to the research and development department.

I am planning on getting the Hobby People C-130, will use 9X6 props. I am getting the VQWarbirds B-17 the minute it hits the market place, same configuration. Using 3520 brushless motors and 5S batteries, will yeild the magic 9,000 RPM. You ask, what is so magic about that 9,000 RPM factor. The key words are "electric conversions". A 2 cycle nitro motor will spin the same props much more than 9,000 RPM, a 4 cycle nitro is more like the electric counter part. We need to emulate the same performance of nitro or the planes will not fly right........The prop size is fixed, can't put on larger props. not enough room, so, we just have to spin those electric motors to equal the nitro or the planes will be runway huggers. How do I know, I bult a few runway huggers, it's not a pleasant sight and the end result is crash and burn.

Al

nchouker

My Feedback: (1)

hi guys,
did anyone contacted vq for their b-17, they told me there is not such a thing.
where did this vq b-17 idea came from???
[8D]

chevronflyer

My Feedback: (9)

ok algutkin, rpm is not such a critical factor when you consider the amount of thrust you get from this setup. I will be getting roughly 1600 total peak watts of power on 9x6 props. the plane weighs only 160 ounces or 10 lbs. that comes out to 160 wattsper pound of power. Most good 3D birds need 150 to 170 watts per pound. I should be able to jump off the runway and go straight vertical on this setup. So it really doesnt matter what rpm they spin as long as the watt per pound of power is there.

normgoyer

Frankly a B-17 doing 3-D should pound another nail in our coffin. Norm

algutkin

My Feedback: (1)

You're right, right now there is no such thing. Tomas alluded to the fact that something was in the works, and I took it from there.

Since the Cedar Hobbies B17 seems to be the only B17 available now, then, I suggest that you jump in and help Chevronflyer take pictures and continue with a really nice build thread. Also, you might start a build thread on rcgroups.com. I'm not advertising for them, but, there seems to be more activity over there. I want Cedar Hobbies to be sucessful with this kit.

I was considering buying the Cedar B17 many moons ago, however, the pictures and advertising is not adequate and it turned me off. It's not just me talking, I read many posts on the same subject.

Free, unsolicited business advice. If your company has the ability to pump out these kits with any kind of volume, kick up the advertising presentation.

algutkin

My Feedback: (1)

chevronflyer,

I respectfully disagree.

Your prop size is limited, you can put Merlin 12cyl motors in that plane and it will go knowhere. Your prop size is limited, so, you need to sping those props at a higher RPM to move the air. 9X6 props are considered to be propping in low gear for a C-160, but mine jumps off the ground with those props, and even though it won't break a speed record, the response is more scale and even. Watts mean nothing, when there are other restrictions, such as batteries in series, and prop size. 4S and 2820 Axi motors will get 9,000 RPM and hardly take any watts.

I could be wrong, sometimes I am, but, I did many a conversion and my thinking works better than Motocalc.

Al

curtishawk

My Feedback: (22)

Thought I'd jump in with a few words on the cedar B-17. You are correct about the promotion pictures being less than what they could be. I purchased one a few months ago and was surprised at the construction of this bird. It's subframe is well constructed, the exterior sheeting isn't too bad. As I read different posts, I have to agree on opening up the cockpit window frames. The one thing I decided to do right out of the box was strip the covering off and recover it with ultracoat silver. It only took an hour and a half to completely strip the complete plane. I did notice a few joints did need to be reglued, but other than that, the construction look good for what you pay for this model. I plan on using 4 Magnum .15 glow engines, as I have been advised not to over do the power mainly for slowing this bird down for landing. Time will tell. Hope to have it complete by the spring, (have other planes on the table at the same time).

gborn

curtishawk
I finally took my dedar hobbies B-17 out of the box to start this plroject. I plan to go electric but have not done any multi electric. What would you recommend as to motors esc's and hook up? Thanks Gene

kenny newton

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