So... I haven't played with inline motor/props before but I expect power wouldn't scale linearly. The air coming over the second prop would be at a much higher speed and may require a different prop on the second motor.
300% FT Viggen for FliteFest 2015!!!
- Thread starter joker24458
- Start date
So... I haven't played with inline motor/props before but I expect power wouldn't scale linearly. The air coming over the second prop would be at a much higher speed and may require a different prop on the second motor.
joker24458
Member
Hmm, interesting....do the full scale planes with contra-rotating props use different pitches of props? I don't think most of the RC ones do but your idea does seem correct.
joker24458
Member
Interesting post here: http://www.rcgroups.com/forums/showpost.php?p=21846029&postcount=6
Very interesting. Like I said I've never tried it before. It does seem to me like you could run into a situation where the rear prop was basically stalled, but the only way to know for sure is to give it a shot! I'd love to see it done!
joker24458
Member
I'm working on the plans right now.....barely halfway and it has already taken well over 10 hours. 
This is some boring and exhausting work....quite possibly my least favorite part of building.
At this point with my schedule (still have other things to do) I'm just hoping to get the plans done by FliteFest. Wish me luck....:black_eyed:
This is some boring and exhausting work....quite possibly my least favorite part of building. At this point with my schedule (still have other things to do) I'm just hoping to get the plans done by FliteFest. Wish me luck....:black_eyed:
ScottyWarpNine
Mostly Harmless
I think you're right. One solution would be to use a higher KV motor in the back. You should be able to use the same prop as in front and motor current probably won't be much more since it will already be wanting to spin due to the thrust of the first motor. If you look at the inside of a jet engine, the blades, even in the same region (ie. compressor, fan, turbine) have varying pitches to account for varying fluid velocity and pressure. The use of different motor speeds can make up the difference I think.
joker24458
Member
Hmmmm, I will have to think about this.....Emax doesn't offer a GT2812 that has a higher KV than 1840, and I won't have time to buy any electronics before FliteFest....I wonder if we could achieve similar results by using different props, like a 8x4 in the front and a 8x6 in the back. Back motor would draw more amps (but would it be a significant increase in amp draw due to front motor already spinning it?) but it would push more air out.....so the first motor accelerates the air some and the back one accelerates it more. No idea how it would work in real life, just thinking about it in my head.
joker24458
Member
So I'm thinking the MonsterViggen might not happen this year..... For several reasons.
1. The plans are still not done, those require a lot of time and effort and it would be a pain to do them on site.
2. Even though I enjoy building and I realize that building will still allow me to socialize with others, I don't want to spend the whole time there building...
3. I am volunteering for this year's event so that already takes out a bit of time, plus building a MonsterViggen....
4. In podcast 80 Josh said that Peter will be doing a big community build, and I figure that most people will want to help him. Plus, I also would like to help him build, so I would not even be working on the MonsterViggen.
So, the MonsterViggen will most likely not happen this year. Maybe next year....
For several reasons.1. The plans are still not done, those require a lot of time and effort and it would be a pain to do them on site.
2. Even though I enjoy building and I realize that building will still allow me to socialize with others, I don't want to spend the whole time there building...
3. I am volunteering for this year's event so that already takes out a bit of time, plus building a MonsterViggen....
4. In podcast 80 Josh said that Peter will be doing a big community build, and I figure that most people will want to help him. Plus, I also would like to help him build, so I would not even be working on the MonsterViggen.
So, the MonsterViggen will most likely not happen this year. Maybe next year....
joker24458
Member
Oh no! This is what I was primarily hoping for at Flite Fest! I heard it in the podcast and was super excited. Sorry you can't do it this year
Yeah, I am kind of bummed out too.....
but it is just not going to happen this year. We'll see about next year though, that will give a whole lot more time for preparation. 
NCC1701
New member
Yeah, I am kind of bummed out too.....
Well being social and flying with others is much more important. Hope you have a good Flite Fest week!
Let me start off by saying that I always have to be building something.
This time it will be a 300% (not 150%.....not 200%.....but 300%) FT Viggen. I figured since I have a 100% Viggen and David's original MiniViggen (45%), it's time to build a MonsterViggen (just came up with that name).
The MonsterViggen will be about 9.5ft in length (that's almost two of me! yes I am short) and close to 7ft wingspan. The airframe will cost around $30 which includes 23 sheets of FliteTest/DTF foam and wood spars. It will be an EDP (electric ducted prop), which means that it will use a normal motor and propeller, but all contained inside of a duct similar to an EDF. Using an EDF at this size would be too pricey for me. I am planning to use a 3s 2200-3200mah lipo to power an NTM 35-36A 1400kv motor swinging a 8x6 or 8x8 APC prop. The 8" prop is due to the size limitation of the EDP duct; using an 8" prop will result in less than 1/2" of clearance inside the fuselage/duct.
While the name "MonsterViggen" may sound intimidating, it will actually/unfortunately not be a very fast plane at all. At first, I planned to make the airframe around 8lbs, but it was difficult (I won't say impossible, but it's pretty close) to find a motor that could produce 8lbs+ of thrust (or even half that) while only using an 8" prop. Therefore the goal became to make it as light as possible. From some rough calculations I have concluded that the (lightened version) airframe alone will weigh around 3.5lbs, so a motor that could produce 2.5lbs of thrust should at least get it in the air.
From that I can estimate the AUW including the battery to be around 4 to 4.5lbs, and with a wing area of approximately 3000 inches sq, the wing loading should be just shy of 3.5 oz/sq ft. This will make for a very slow plane, but it should still be pretty fun.
By the way, a canard on the MonsterViggen will be bigger than a wing on a normal sized Viggen.
I hope to either finish this for FliteFest 2015 or finish it at the event - let me know what you guys think about that. Any other ideas or suggestions would be welcomed as well!
I know I´m late but since it seems like you haven´t actually started yet (I only read the first and last page) I´d recommend you this 90mm EDF which actually produces 3.6kg (pretty spot on 8lbs) of thrust on 8S: http://www.turbines-rc.com/en/edf-d...r-dps-90mm-11-blade-8s-1400kv-out-runner.html
I think it is definitely worth spending that money (135€ is actually kinda cheap) on the powerplant for such a big plane
