tmojosh

Starnes Carbon Fiber Vtol

Why : I want a Rc that can hover with great amount of stability, be safe as possible and carry a payload of 3 pounds whenever need for Arial photographs.

I am making this post because Ineed help figuring out the best parts to use, some Ihave done a great deal of research based on other experience and some math too. I know which Axi motors im using for main props but Ineed to get a motor Ican attach a pinion to the shaft so that Icam mount it to mate with the input gear of the trex tail rotor shaft drive kit.

Layout: Two 3 blade 10x6 props on the front in Tilting nacelles provide lifing thrust and tail is for balance at hover and to adjust pitch in forward flight. One motor for each prop and a motor to turn the rear tail rotor which needs to turn 10000-12000 rpm. In some ways the layout loks simimar to the Avatar Heli , but the way that thing flies isnt completely possible so Im not looking to recreate the movie heli.

Requirements: 7 min flight time, carry 2 pounds or better with no more than a prop switch and up throttle, needs to hover and have pitch, yaw ,roll control , and change modes to forward flight.

Parts collected so far: I have purchased a Heli Align Trex 450 Shaft drive Tail boom and tail rotor kit. I have purchased three sets of props to expirement with,

Groupner 10x7 , 10x7 pusher ( so they will be counter rotating)

GWS 10x6x3 EP counter rotating set.

GWS 9x5x3 EP counter rotating set.

Hitec 645MG High Torque 133 oz in Servos ( for tilting nacelles)

JR Mini High speed digital .09 second for tail rotor pitch control

Align TREX 450 v3 Shaft drive tail and gear set, 1.1 input to 1 output

Align Trex 450 se Tail rotor kit ( blade holder, pitch mechanism, linkage , control arm ect)

Axi 2814 Motor mounts and Prop adapters

Motor selection: I am going with Axi Gold brushless 2814/12 , I felt the 10 turn would be too many rpms for a smaller prop, they turn over 12500rpm with a 3s 11.1 v battery. So 2814/12 is around 9800 rpm full throttle but even then I wont see full throttle , avg rpms will be 4000-7000 estimated. Here is how I came up with the motor selection. The motor calculator on this page helped me figure the actual oz in for the motor prop combo.I used the 5000mah batt selecion. brantuas.com/ezcac/dma.asp

Ichose the Axi 2814/12 1270 Kvbecause it could produce over 1.2 to1 thrust to weight ratio based on a 5 lb model weight and keep my amps lower in the 40s, and maybe high 30s per motorin a hover.

tmojosh

In the real world not everything works like it doeson paper , but the best Ican do it calculate possible setups and then purchase 2-3 prop choices and test them once Ihave the frame built and motorsi orderedfrom hobby-lobby , for these calculations i used that brantuas.com/ezcalc/dma1.asp It doesnt have the option for 3s Lithium Polymer batteries which are far more efficient so Ichose the 4500 mah Nue Energy just to get a close fugure.




Axi 2814/12 , 1270 Kv 1.06 in oz /amp

This is Full throttle estimate:

10x6x3GWS prop est 45.9 amp draw , 66.9 % Efficiency Prop speed: 55mph

RPM: 9678 Static Thrust: 70.1 oz

AXI motors 70.1 oz x 1.85 ( est for efficiency loss between two motors) = 129.6 oz thrust

129.6 oz thrust / 16 oz = 8.1 lbs thrust

8.1 lbs vertical thrust power/ 5 lb model goal wieght = 1.62 lbs

Power to weight ration = 1.62 to 1

Power needed for vertical lift 1.1 to 1 , so this motor set exceeds the requirements

9x5 GWS Alt prop comparison

APC 9x5x3 prop

est amp draw 32.79

RPM 10945

Static thrust 54.5

54.5 x 1.85 ( 2 motors minus efficency loss) = 100.82 oz

100.82 oz / 16 oz = 6.3 lbs

6.3 lbs / model weight 5lbs = 1.26 lbs

GWS Prop 9x5x2 and Axi 2814/12 produces est 1.26 to 1 Thrust to weight ratio

Finally I wanted to know possible difference of using a stronger prop like Groupner

Groupner 10x7 reg prop ( not three blade)

45 amp draw , 9684 rpm , 64.3 oz thrust. 1.85 x 64.3 = 7.43 lbs thrust ,

7.43lb thrust / 5lb model wieght = 1.48 thrust to weight ratio

And just for giggles , I dont have this prop but a 10x8x3 master airscrew ( because a counter rotating pusher is available and its a strong prop)

Full throttle amp draw 56.9 , 3/4 throttle 42.6 amps

RPM 8624

Static Thrust 74.2 oz

1.85 x 74.2 = 137.27

137.27 oz / 16 oz = 8.57 lb thrust

8.57 lb thrust / 5lb model weight = 1.71 to 1 thrust to wieght ratio

3/4 throttle: .75 x 8.57 = 6.42 lbs thrust

A 5lb model would lift well and hover just below 3/4 stick throttle

tmojosh

Itried a couple times copying the URL for my sketchs so that they show here but it didnt work either time. I will try this way.

1st pic: this shows both nacelles, with ducted rings around them. Each nacelle is mounted to a tube which slides over a slightly smaller tube that is directly afixed to the top carbon plate. Its not perfectly scale, Ihad drawn it at a angle so Itook the last picture to give a comparison of where everything will be placed, Iestimate about 10 inches inbetween the props, that would make is 32-43" wide

2nd pic: This is a close up view of the nacelle first concept. It would be a large tube with a rounded nose cone Iwould probably snitch from some model rocketry parts, However after checking cooling concerns Ieither need to leave the top open and vent the bottom or Mount in heat sinks. Istill may go this route it definalty looks better this way for a more " scale" look.

3rd pic: this is the inside of the nacelle tube, There is a x shaped mount from Axi motors and the wires are fed through the larger mounting tube that connects to the main fuselage. If Iuse the tube configuration it has to have a gap so air can be pulled through and exhuast out the bottom. Iwill revise this to actually show a 1/2" intake and exhaust for cooling purposes Ibelieve.

4th pic: This the a cut away of the top of the fuselage mount , two large brackets clamp down the stationary tube that the larger Macelle mounted tubs tilt on. The boxes under the mechanism are propose mounting positions for the Hitec 645MG servos , The servo horn mounting position will have 1-2 posistions farther to tip giving it a little leverage, It needs to tile at least 45 degreed, maybe 60 degreed for fast forward flight.

Ideas not drawn yet, Ibeleive Iwill have " short wings" that will function as stablizers coming from the sides of the fuselage close to center of gravityIimage these wouldnt be more that 6" on each side , Imay also have the landing gear in these , maybe retractable , also there will be a tail of some kind, also for forward flight stability.

dknovick

Looks like a nice design, but if this is all your looking for, have you though about a multirotor craft, like a hexa or octocopter? I'm messing with a Hexa XL now, that can lift 3.3 lbs.

tmojosh

hi , thanks for looking as i get measurements for the internal parts i will post more planning drawings , yeah i want something with fast forward flight , so the nacelles will rotate w45 degrees forward ( or whatever angle is needed) and combination of a rear elevator.

dknovick

I look forward to seeing it progress. When I get the chance, I'll look over some of your calculations.

tmojosh

Ok update for parts being collected. These parts were ordered last friday previously. I opted for axi 2814/10 because it will allow me to use lower pitch and higher rpm for smoother power delivery. 2 x 2814/10 45 amp axi $184 , 1400Kv brushless 10 amp motor ( for tail rotor) 18.99, blackhawk 450 arf fuselage (for donor to make mold) $90 , prop apc 9 x 5 e , prop apc 9 x 5e pusher , 18T motor pinion. I have descided I will recreate the avatar scorpion helicopter as closely as I can , scale. the closest relative to the avatar scorpions fuselage i found was the blackhawk helicopter. Though I will try to find nacelles to fit the movie did not have anything covering the shaft drive system. I will try to find more detailed pics.

tmojosh

Thanks im waiting on the fuselage to start making molds of stuff. With the mold I can lay 3 layers of carbon , that shoild be about 1mm - 2mm thick depending whhat part of the fuselage im laying the matt in. the hard bends and ouside curves need the extra layer to stay rigid. Im trying to keed the wieght down to similar weight as if I just used the plastic fuselage but I would need to install several ribs if I was to use plastic. Also I would like lighting suggestions , all aircraft have lighting , beacons ect , id like to make it as scale as a fictional helicopter can be with the exception of the props themselves, thanks everyone

tmojosh

Just recieved props today , the gws props "felt" to flimsy but I may still test them. The apc thin electric set I just recieved have a very aggressive design with more "bite". They are apc 9 x 6e and 9 x 6ep contra rotating set. Apc says they are good for constant use up to 16000 rpm when I asked , but ill be around 6000- 7000 rpm in hover and full throttle at 12900 according to brauntus calculator , however it doesnt take into account im using the "thin" electric version I imagine it will still perform well. Is it safe to paint a prop? By that I mean should certain types of paint be avoided. The grey props will probably need to be sprayed black with vinyle dye or auto pait. Also I need to know if its needed to balance these props? Does that mean physically removing material from one edge? Ill be honest on previous apg glow props I never bothered balancing them.

TRCX

Any updates? really interested to hear. Why not use variable pitch props? would be cool if they were counter rotating like the real avatar helis. but that would be a mission to build

tmojosh

Hello , ive been busy moving and stuff the last couple weekends. Anyways i was waiting on a set of ball bearings 5/32" id, finally recieved them and the music wire to press them onto. At this point im making the nacelle mounts and top of the fuselage. I already built in winglettes and rocket launcher mount like the movie. I have 95 percent of what i need to finish so hopefully ill have test flights in a couple weeks. Right now i just need a charger for my spektrum dx 7 tx batteryi bought. Oh and by the way they are counter rotatng , thats the only way i could manage a stable hover, the tail rotor is only for forward fight and yaw axis controlled by tilting nacelles in opposite directions just like in the movie.
I have several pics of the build , i think everyone will like it.