Simple Twin Trainer

[rcspaceflight]

I could probably tell a long story of the background as to how I got here and why I designed this. But I'll try to keep it short.

I'd call my flying skill level beginner. Not to be confused with newbie. I can go through an entire battery without any crashes, but not every time. I don't stick to any sort of pattern while flying, I just fly around aimlessly and I'm not entirely sure I could hold a flawless, simple pattern.

I'd like to avoid breaking props or bending motor shafts as much as possible because I still do crash. I should say that I still make "newbie" mistakes while flying. Everybody crashes. I've broken way too many props and I have bent a motor shaft or two.

When I first started building, I used Flip Side brand foam board which is just like Elmer's brand. About twice the weight of Adam's (Dollar Tree) but is water resistant as is, has color on one side and white on the other, and is more durable. Here is an article I wrote when I first got my hands on some Dollar Tree so I could compare it to what I was using: http://www.flitetest.com/articles/comparing-foam-board

I want to go back to using Flip Side because it is better than Adam's in some ways. The downsides is the weight and that it's much harder to work with. But I think the advantages outweigh the disadvantages. Especially since I'm making my design with as little foam board as possible to keep the weight down.

In order to protect the props/motors, I'm doing what the Hobby Zone Duet did. http://www.flitetest.com/articles/beginner-indoor-planes-review


I didn't 3D model the power pods/motor mounts.


I'm going with a simple undercambered wing. I think I'm going to make a flat plate to mount power pods onto. But I'm going to glue the pods into place.




The thinking is that the wing tips and nose will hit the ground instead of the props. (I'll add landing gear so I don't break props with belly landings.)


I don't like the look of twin boom pusher planes. I was going to make a Bixler or Smash Drone type of plane, but I didn't like how tall the fuselage would have to be. I've never build/flew a twin engine before, but I love the idea of one. It's my understanding that torque roll doesn't exist with two motors (when using CCW and CW rotating props). So with two 8x4 props it will have more than enough get up and go without any torque roll. This just seems like the best route for me.

Today I bought two sheets of yellow Flip Side foam board, which is why I colored it yellow. It's the exact color scheme I'm going with. I think I'm buying all new motors and ESCs for this plane. Maybe even a new Tx. So I'm unsure when I'll actually get it done/flyable.

Considering all of the options, I think this is what's best for me. A 4 channel plane that is resistant to breaking props.

 

[ofiesens2]

In that case you might as well put a landing gear on the top!
I'm interested to see how this turns out, mostly because the plane that I have built that you designed flew great! (it was your "Noob Tube" that used a lot of FT Flyer parts). I built it for science fair testing and got a 60 foot hand launch glide out of it with the Baby Blender wing with polyhedral. And thanks for that great design (or in other words, you saved me from failing science class.)

 

[ghost civic]

im working on a simple twin engine, twin boom. 40''x10'' kfm3 wing.
my motor mounts will be really simple, since my motors are "stick mounts"....so the stick that will serve as the boom will simply extend beyond the wing 1/4'' for the motor to mount onto.
just waiting for the motors, so I can figure out how long the booms will need to be for proper CG.

 

[rcspaceflight]

im working on a simple twin engine, twin boom. 40''x10'' kfm3 wing.
my motor mounts will be really simple, since my motors are "stick mounts"....so the stick that will serve as the boom will simply extend beyond the wing 1/4'' for the motor to mount onto.
just waiting for the motors, so I can figure out how long the booms will need to be for proper CG.

I love your idea for using the stick booms to mount the motors to. What motors did you go with? Right now I'm shifting through all the choices and trying to find the right motor.

I'm going with 40" x 8" wings. Which means for a wing cube loading of 6, my plane should weigh 20 ounces or 567grams. So I'm shooting for a 20 ounce flying weight. I figure I should go with a 2S battery set up. A 2S battery and two 8x4 props swinging at 1100kv is about 23ounces of thrust. And an estimated top speed of 30mph. Which should be a really good trainer setup.

I really want this battery for the flight times (2S 5000mah) : http://www.hobbyking.com/hobbyking/...00mah_2S_35_70C_Lipo_Pack_USA_Warehouse_.html

I haven't calculated out yet whether I can get away with a 286gram battery. But I can always bump it up to 40" x 10" wings. Then I can have the total flying weight 28ounces to still have a cube wing loading of 6. ... but then I may want bigger/higher KV motors.


I know I'm putting too much thought into this. But I have high hopes for this to be a great plane that will last me a long time. All I ever wanted this hobby to be was something to do once in a while when the weather is right. I just want a plane I can grab and go.

 

[rcspaceflight]

I just placed an order with Hobby King and this is what I'm going with:

- 2 Turnigy Aerodrive 1200KV motors: https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26487

- 2 Turnigy Plush 18amp ESCs: https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=30683

- GWS 8x4 props: https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=38759

- Zippy 5800mah 2S 20C battery: https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=21115

I'm taking a risk on the motors because it doesn't come with a recommended prop size. But I found a motor with less max amps that can handle an 8x4 prop with a 2S so it should be fine. Since the max current on those motors are 16amps, that means the max amps that will be pulled from the battery is 32amps. A calculator I found on the internet says I'd only expect just shy of 10 minutes flight time if I run full throttle as 32amps. But I highly doubt it would actually be that high.

I think I'll have to go with 40" x 10" wings for the better flying characteristics because I know it's going to weigh more than 20ounces. Luckily the 1200kv motors with 8x4 props on a 2 cell battery is actually 27.5ounces of thrust total. So it should be a good slow plane. Even if 30mph top speed seems too slow.

 

[ghost civic]

http://www.nitroplanes.com/60p-csn010-bm2810-kv1200.html

http://www.nitroplanes.com/60p-dy-1006.html

1st link is to 1 motor, $8
2nd link is to the combo pack of which I bought 2 off. motor, 18a esc, 3 servos...$25.
that combo pack is the same electronics as the dynam icanfly. that was a 40'' wingspan cub running a 9x5 prop on a 3s and it would do 30-35mph. it couldn't hover or anything, but provided plenty of lift. 2 of them on a plane of similar size and weight should be pretty good.

 

[NewZee]

im working on a simple twin engine, twin boom. 40''x10'' kfm3 wing.
my motor mounts will be really simple, since my motors are "stick mounts"....so the stick that will serve as the boom will simply extend beyond the wing 1/4'' for the motor to mount onto.
just waiting for the motors, so I can figure out how long the booms will need to be for proper CG.
View attachment 20569

Ghost, do yourself a favor and look at the "Funder and Lighting" on RC groups or just google it. it is almost exactly what your looking for, and can be scaled up to 40" ws, I'm building the single tractor now, but the stick mounts you are talking about will make this a very easy twin build for you, with a plane that is tried and true!

 

[ghost civic]

thanx for the info, those are pretty cool.

I want to do a twin boom, twin motor tho. and mine is 80% done.

here is that stick mount motor on my delta wing...which will hopefully have its maiden flight this weekend!

 

[NewZee]

thanx for the info, those are pretty cool.

I want to do a twin boom, twin motor tho. and mine is 80% done.

here is that stick mount motor on my delta wing...which will hopefully have its maiden flight this weekend!
View attachment 20584

No problem, I like to do my own designs and builds as well. but if you just extend the stick lengths on the Funder and Lighting out past the leading edge of the wing you have your twin mounting points, and the CG's etc. are already figured out for you. keep us "posted" on your progress.

 

[rcspaceflight]

I finally got around to working on it. Here are some pictures of my progress.

The square tube is 30" long with 2" sides and 3/16" strips cut out between the 2inches.


I cut 3/16" notches 2" deep centered into the tail end of the tube.


A notch into the elevator too.


Those notches are for the tail assembly.


It didn't turn out completely square, but close enough.




I have the rudder come down below the fuse incase the tail ever drags.


The 11" elevator might be too small, but time will tell.

 

[rcspaceflight]

More pictures of my build.

The wings are two 20" by 10" pieces taped together. The score cut is 3" back from the leading edge.


I used a wire safety flag as a spar in the score cut, it's also to help bind the two halves together. Not that the spar is necessary in any way.


The airfoil created by the score cut.


This is a third 20" by 10" piece that will serve as the flat bottom for the center of the wings and as a mounting plate for the motor pods.


An estimation of where to mount the motors. The plate is 6" back from the nose of the fuselage, and the motor is centered off of a 5.5" mark from the side of the fuselage.


I ended up cutting a hole into the fuselage because I decided to permanently mount my "black box" alarm into the plane. http://www.flitetest.com/articles/black-box-alarm-system


I wanted the 9volt battery for the alarm to be mounted better, but hopefully it'll stay in place during a hard crash with the way I have it. Otherwise it won't serve it's purpose. Which is to power a 100db alarm when I turn off my Tx or if my plane battery is disconnected in a crash.


Because the ESCs that I'm using only have a 2amp BEC, and because I need to power 4 servos and a relay, I think I'm going to use two Rxs on my plane. Each ESC will power one Rx and two servos. Maybe not the best set up, but I think that would be better than 2amps trying to do more than it's capable of.

 

[rcspaceflight]

Okay, so I had issues with the ESCs and motors because I didn't solder them together very well. I don't know if you ever tried it, but soldering two wires together is tricky, especially when one is very thin small wires and you can't mesh the wires together very well.

Anyways, I cut off the two motors I had mounted and turned it into a single engine noob tube.


But I ran into issues with that set up too. I re-used an FT Firewall that I had used bigger screws on, and using slightly smaller screws into those same holes resulted in this:


I ended up trading my broken Corsair for a motor with a stick motor mount. I was going to use it to make a similar slo-stick plane, but I figured I would just add it to a perfectly good plane I already have.






Hopefully I can test fly it soon. But it's supposed to be stormy for the majority of this week. My only concern is power to weight ratio. The plane currently weighs 850grams (with 2.2amp 3S battery) and I think I need to add nose weight to get the right CG. (I used Flip Side foam board, which weighs twice as much as DTFB. I also have my home made plane finder alarm installed in the tube. So it certainly isn't built as light as possible.) But a static thrust calculator says I should see about 990grams of thrust, so it should be fine, unless I end up adding too much nose weight.

 

[Foam Addict]

Hmm, that motor looks familiar...
I'll pull up my model for it in drive calc and give you a more accurate answer. Silly question, what's your altitude?

 

[rcspaceflight]

Hmm, that motor looks familiar...
I'll pull up my model for it in drive calc and give you a more accurate answer. Silly question, what's your altitude?

I was going to PM you so you saw this thread / that I'm using the motor you gave me. But your inbox is full!

Uhh... the internets sayz "Elevation, 1,243 ft" for the nearest town. Which is probably correct because I live on top of a hill, but so is the nearest town and we look to be about the same height. The top of Blue Mounds State Park is over 1,700 ft, but that's the neighboring high point. Blue Mounds the town is only a few feet higher than Mount Horeb (fore-mentioned nearest town).

You're just being picky if you're calculating air density too.

 

[Foam Addict]

I am, be back soon!

 

[Foam Addict]

Looks like around 8 amps and around 700 grams of thrust at approximately 75% eff.

Not as good as I measured in real life though, I need to check my measurements again.

 

[rcspaceflight]

Looks like around 8 amps and around 700 grams of thrust at approximately 75% eff.

Not as good as I measured in real life though, I need to check my measurements again.

I don't think my noob tube needs a 1:1 power to weight ratio. 700grams should be enough to make it fly. I did fly it fine with a 1300kv motor and a 7.5 x 5 prop. So 1100kv and a 9x5 should be even more pulling power. Plus I have a 30amp ESC plugged into it and I'm using a 2.2amp 3S battery. So the flight times should be okay with no possible power issues.

 

[ghost civic]

I don't think my noob tube needs a 1:1 power to weight ratio. 700grams should be enough to make it fly. I did fly it fine with a 1300kv motor and a 7.5 x 5 prop. So 1100kv and a 9x5 should be even more pulling power. Plus I have a 30amp ESC plugged into it and I'm using a 2.2amp 3S battery. So the flight times should be okay with no possible power issues.

that's the same motor I had on my noob tube. same motor as on my p-38, gws slow stick and snowball. 1100kv (I have 2 black ones that are 1300kv, same design) and run either 8x4 or 9x5 props.
still unsure why my noob tube wouldn't fly. just seemed like it didn't have enough lift really.

just looking at the pics, yours looks lighter and your under camber wing should provide more lift than my km wing did (especially since I still had not gotten that right either)

the static thrust calc shows a 1100kv motor with 9x5 prop would in theory produce 2.5 pounds of thrust. Id imagine it would be a little less than 2 pounds. but should still be plenty for most DTFB planes. I wish I could measure the weight of my p-38, but I can tell you it is not as light as I would have liked.

these motors work awesome on the gws slow stick!

 

[rcspaceflight]

just looking at the pics, yours looks lighter and your under camber wing should provide more lift than my km wing did

I do have more lift because of the undercambered wing, but it's heavier than what your noob tube was. At least in all likely hood. Mine is all Flip Side foam board which weighs twice as much as Dollar Tree. I thought I had the weight of my "black box" somewhere but I couldn't find it. I think it weighs about 100grams or more.

But the cube wing loading is 6.5 oz/sq ft which is in the trainer/park fly category.

 

[ghost civic]

I do have more lift because of the undercambered wing, but it's heavier than what your noob tube was. At least in all likely hood. Mine is all Flip Side foam board which weighs twice as much as Dollar Tree. I thought I had the weight of my "black box" somewhere but I couldn't find it. I think it weighs about 100grams or more.

But the cube wing loading is 6.5 oz/sq ft which is in the trainer/park fly category.

the fuse on my noob tube was not adams, but elmers. probly the same weight as the flip side. I may try another noob tube later one. seems like a good, simple design that would be sturdy. just not certain why mine failed...but that's the risk of not using plans and just looking at a plane and doing something similar.