Achmed

I am returning to the world of rc flying after 16 yrs away and have been flying a Gentle Lady glider this year to get my hand eye coordination back. I purchased a Hobbico Avistar a couple weeks ago and want to convert it to electric. I chose the avistar because of the semi symmetrical wing. I dont want a lot of dihedral in the wing so when i make the trial assembly i might take some of the dihedral out of it to make it more of a sport flier than a trainer.

I have read many posts on various forums about electric power systems and how to choose them to suit the plane and i think i have a real good grasp of it thanks to a program i found called "Web O Calc"

http://flbeagle.rchomepage.com/softw.../webocalc.html

It's very simple and easy to use but i'm not sure how accurate it is. I see other programs to do this but most seem too complicated. I understand they are used for a good starting point anyway. If i am not thinking in the right direction please correct me.

I have seen many people saying that 80-100 watts/lb is good for a trainer and others saying 100-120 watts/lb is a trainer. Which one is it? I don't know which is correct so i chose the first, 80-100 w/lb as being correct, as i have read it takes at least 50 w/lb just to get off the ground.

Based on 80-100 w/lb as a trainer i ran lots of motor specs through web o calc, changing settings. I decided 120-130 w/lb for this Avistar because it has the semi-symmetrical wing and can do most aerobatics. I want the extra power to keep from getting bored with this too quick and wanting something faster so i opted to push the power envelope a little. Based on the nose gear the biggest prop i can run is an 11" without buying a new nose gear which i was thinking of doing anyway because it uses the metal motor mount, (that i dont need), to support it. I do have some 3.25" wheels i could mount and then possibly run a 12" prop. I want to keep a scale looking appearance so i dont want a 15 or 16 inch prop.

The Hobbico Avistar SPECIFICATIONS
Wingspan: 59 in (1500 mm)
Wing Area: 602 inē (39 dmē)
Wing loading: 19.1 oz/ftē (58 g/dmē)
Weight: 5 lb (2270 g)
Fuselage Length: 44.8 in (1140 mm)
With a little modification i can get a 6s 5000mah 20c lipo battery to fit

I calculated approximately 80oz flying weight. The plane is an arf and i weighed everything that came in the box including the glow fuel tank and came up with 45oz's. I did this so it weighed slightly heavier than it actually will be so my watts/lb would be slightly higher.



These are some of the motors i was thinking.....

NTM Series 35-42A 1250Kv 600W Hobby King $18.99
http://www.hobbyking.com/hobbyking/s...dProduct=16092
web o calc says at 14.4v. 46a and a 10x5 prop would be 662.4 watts in and 132.48 watts/lb

NTM 35-42 Series 1000KV / 700W $18.99
http://www.hobbyking.com/hobbyking/s...dProduct=16233
web o calc says at 14.4v, 40 amps and 11x7 prop would be 576 watts in and 115.2 w/lb

MonsterPower 46 (670kv) OutRunner Brushless Motor
http://www.hobbypartz.com/monsterpow...ess-motor.html
web o calc says 18.0v and 40 amps 12x8 prop 720 watts and 144 w/lb

Tacon Big Foot 32 Brushless Out Runner Motor for Airplane (770KV)
http://www.hobbypartz.com/96m604-big...520-770kv.html
web o calc says 14.4v, 40 amps 12x8 prop 576 watts, 115 w/lb


Questions....

1) What is the max watts/lb to run on the avistar without ripping wings off?

2) Is this Web O Calc program reliable with the statistics it provides(good starting point)?

3) When ordering from Hobby King and it says out of stock how long can i expect to wait to get the item?

4) Are those NTM motors any good.

5) Is the 4mm shaft in the motor too small for 600-800 watts?

6) If i get a programmable ESC can i set a limit on how many amps go to the motor?

7) I know i havent listed an ESC yet but that depends on the motor. More than likely a 60-70amp w/o BEC. I want receiver battery separate.

8) The exceed monster power 46 has an 8mm shaft and i hear if i damage the prop adapter that comes with the motor i will not be able to find a new one. Any thoughts on that?

Thanks

Turner

I can't answer all of that but...

I never order anything from HK if it is out of stock. If one item is out of stock it will hold up the whole order.

I'm doing a similar conversion, just slightly larger. I chose the Monster Power 46 in part because of the larger shaft. 4 mm seems too small to me for a plane this size. I over build everything though.

An esc cannot limit amps. Your choice of prop will.

I don't know about the prop adapter. Maybe one from another brand will fit. E-Flite has a similar one for their Power 46 that is available separately but I don't know if it will fit.

Turner

It looks like the E-Flite prop adapter has only three bolts while the Monster 46 has four. There seems to be a number of collet type prop adapters for 8mm shafts though.

1320fastback

Just throwing out some ideas since you havent glued anything yet.

1. Flat wing
2. Anhedral wing
3. Bolt on wing
4. Tail dragger

My Avistar (glow) is one of my favorite airplanes. It currently has the wings uncovered. I am installing flaps that will use the center mounted servo and have dual aileron servos in the wings. Also clipped the tips to be square edge reducing the dihedral effect further.

Having it a tail dragger is a blast and very easy to convert to.

kyleservicetech

IMHO, you can't go wrong with a Hacker motor, I've got 7 of them, and all of them perform exactly per their specs. And most of them are on their third or forth year of flying. At least two years ago, I've found that Hacker is supported in the USA.

They are expensive, but they work.
http://www.aero-model.com/Hacker-Brushless-A40-10S.aspx

As for the ESC, check out the Castle Creations ICE series, with a built in switching power supply type of uBEC (Battery Elimination Circuit)

Those uBEC's work much better in our models than the linear BEC's commonly used. If you buy the PC adaptor for the CC ICE ESC, you can also download from the ESC a LOT of information on the performance of your power system to a PC after a flight, or flights.

The www.motocalc.com computer program for electric models is pretty close when used with a quality motor, such as Hacker, and several others. Free for 30 days, then $39.

Check into the APC-E electric props specially designed for electric motors. They are more efficient than glow engine props, but more important, on a bad landing they will often shed their blades before bending up the motor.

Also check into one of those wattmeters that allows you to check your selected motor/esc/battery settup for watts, amps, volts and so on. Astroflight is one supplier that makes a good one.

Good luck, and let us know how you come out!

Achmed

Thanks for the help!

I have been seriously been thinking of making it a tail dragger because i already have a set of main landing gear that will work and also allow a much bigger prop than 11".

I would like to make it a bolt on wing but dont know how to keep the leading edge of the wing seated to the fuselage without some major modifications.

As far as dihedral, i want a little just for stability purposes as i plan to teach my grandson to fly and i want this to be an easy flyer with a little kick if i want to push it.

I can appreciate the Hacker motors but i simply cannot afford the price.

Yes, a wattmeter is a must!!!!

Achmed

One other thing i forget to mention....dual aileron servos will be installed before flying. I like the idea of putting the flaps on it, hadn't thought of that. I expect that those full length ailerons will give enormous roll rates so the flaps may be doable.

kyleservicetech

If you've got "large" ailerons on your model, and, if your transmitter supports it, check out the "Flapperons" on your transmitter.

I've done this on several of my models with my Spektrum DX7 transmitter, it works well.

Achmed

do you have any pictures you could share to give me an idea how to convert this to a bolt on wing?

1320fastback

I havent got that far yet to get pictures of that.

I plan to make a center spar which will join the two wing halves. This center spar will have forward facing piece that engages a bulkhead at the front cockpit window.

The rear of the wing will have two holes drilled it and nylon bolts will engage a new bulkhead at the rear with blind nuts. The rear of the wing is already solid formed where the bolts will pass thru.

This pic is from a SR. Telemaster conversion on Google.

Your avitar/Jeff Bonham: I kill you!!

Achmed

I was having a boring day at work so i got out a pencil and paper and came up with the same idea for the bolt on wing. My version is a bit different but i havent looked at the fuselage yet. However it did not occur to me to put the spar out the bottom of the wing. That would make the former stronger. I like that and may use it.

I plan to cut the top of the fuse off in front of the wing to allow a quick remove battery hatch. Then i remembered reading someone put a hood scoop on the battery hatch to force air into the fuselage and out an exit hole in the rear. so that modification will be done also.

I tried to find a plane similar to the avistar in a kit but those are getting hard to find. My next plane will be a kit so i can modify as i'm building.

Yea i love jeff dunham the best thing to come along in comedy in quite some time.

Achmed

I got a new Hitec 2.4ghz 6 channel sport radio and i'm hoping it will do the flaperons as i want to try that. I opened the box to inspect it on delivery (3 weeks ago) and haven't opened it since. LOL

Achmed

Just an update...i know its a bit late. I got the plane done, made the wing totally flat and it flew absolutely wonderful. This is a great flying plane!! No bad habits but with the flat wing the landing seem a little fast or maybe i am just paranoid about stalling. Anyway i enjoyed flying the avistar for several months before i did a stupid thing and nosed it in on a landing. I liked this plane so much that when i got home i ordered another one, the same day LOL.

Its been several months since crashing the avistar and am waiting on the weather to warm up so i can get out to the shed and start working on the new one. I still got the old one and plan to build exactly the same.

1320fastback

Old thread that I forgot about.

Like you I also finished mine. I ended up bolting the wing down but instead put the bolts on the side at the rear instead of the top. They are now hidden under the wing and looks very clean.

I used the Bent Spar technique to make the wing perfectly flat.

Like yours I feel that with these mods this is a wonderful flying plane.
I recommend larger that stock (width) ailerons and possibly make them outboard only.
I ended up using 1 1/4" aileron stock for the flaps also.

I will post some pics later on.... Even though its glow

1320fastback

This shows the LEDs I installed into the wing.
Also the holes for the DuBro Hinge Points.




Mounting Ribs for the Servo Trays.




Epoxying in the block for the Hinge Points to have something to grab into.



Showing servo blocks and CF plate reinforcement.
Also Used this access points for the Lateral Balance Weights after plane was all finished.



1/4" 5Ply Wing Joiner. Note Tongue at front that locks into new bulkhead.



Finished!
Flaps, Ailerons, Lights and NO Dyhedral!

soarrich

Yes, I have a http://hobbyking.com/hobbyking/store...dProduct=16231 with a 11x6 would work well for your app.

Here's my findings on this motor:

Great motor to power a .40~.46 plane. I mounted mine on a 4.5 pound Kaos 40 with a 11x7 it has unlimited vertical, too much for a 70's .40 pattern type plane, so I did some test using my Kaos with 4000 mah battery: MA 11x7, 55.3 amps, 834 watts, unlimited vertical 6.5 minutes. APC 10x7, 11200 rpm, 48 amps, 739 watts, great power 7.5 minutes. APC 9x9, 11100 rpm, 48.3 amps, 741 watts, great speed 7.5 minutes. APC 9x6, 12500 rpm, 34.3 amps, 540 watts, great speed 8.5 minutes, flies about like a 70's .40 powered plane really flew. My friend recommended this to me, he uses his on .40 size trainer for fun flies.

Achmed

I crashed my avistar last year so i bought another one and have started the conversion once again.

The wing has dihedral built in and i want a flat wing so i sanded the bottom half of the wing ribs at the wing joint until the wing joint was flush. I then cut out the wing ribs with a tongue shown in the picture so i can bolt the wing on. The tongue will slip into a slot on the former that has yet to be cut. I will wait to do that when i get the wing done and the new former glued in place Also in the picture is a former that will be epoxied next to the second one from the front for reinforcement for the wing rib tongue to slip into. Both the ribs and the former are 1/4" plywood.

Achmed

This picture shows i cut the aileron single serve actuator rods from the wing. I filled the hole with hard balsa epoxied in place.




Here i have the wing servo mounting plate and the support spars to screw the mounting plate to.

Achmed

Set the wings aside so the epoxy can set up on the servo mounting.

In this picture i cut the monocote off the front of the fuse so i can make my hatch. I then took an x-acto knife and cut between the soft balsa on top of the fuse and the plywood side rail and popped the top off being careful not to separate the joint so i can preserve the angle and reuse it for the hatch cover. If you are gentle you can slip your knife between the balsa and ply and twist and the balsa will pop off. Its not glued real secure.


and here i have the top of the fuse popped off



you can see i preserved the top as well as the angle so i can reuse it.

Achmed

Its getting late and didn't want to start anything involved so i took one of the plates that was supplied for servos (i think) and filled in the round hole as well as the small rectangular hole, not shown in picture as filled in. This is where the lipo battery will sit. I know i jumped ahead but i only had about 30 minutes to kill so i did a small project.

Achmed

My hatch cover is nearing completion. I cut the top off and put a hood scoop on it to force air through the fuselage to cool the battery and esc. I put a hood scoop on the previous avistar but i only made it 1/4 ". You can see i glassed the bottom of the hatch cover to stiffen it and glued some blocks for some pins to slip through the firewall to hold it down. As you see i had the hatch covered but i changed my hold down. I was using a wood screw but this time i glued a washer to the top of the hatch and will use a blind nut in the former i put across the top of fuse to bolt it to. After the glue is dried i will cover the washer and drill a hole and install the blind nut.

Achmed

The first picture shows the supports for the nose gear. The glow version has the nose gear supported at the top by the glow motor mount. The second picture is the new electric motor mount. This is 1/8" ply which will break before breaking the motor or bending the shaft, i know from experience this works.

Achmed

Here is the battery tray for the 4s lipo

Achmed

Trial fit of the motor which is an E-maxx GT 2826-06 710kv. Its the same motor i had on the previous avistar and had no problem going vertical but i don't know if it's going to work. It took a beating and a little stiff but not too bad. Its got a 5mm shaft and is unbent from a nose in. The break away motor mount did what it was designed to do. I do have a new motor on the shelf just in case this one pulls too many amps. This E-Maxx motor is tough for $29.00!!!

Achmed

I don't know whats going on with posting these pictures and the words jumping around, sorry about that. Maybe i will figure that out sometime.