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80% FT Viggen

nerdnic

nerdnic.com
Mentor
#1
MAIDEN FLIGHT

DETAILS
After the Viggen was released I wasted no time getting it built. I really enjoyed how stable it flew and was pleased with my first EDF. After a half dozen crashes I had to retire her and have been wanting to rebuild ever since. I have been on a roll lately building 80% FT planes so the Viggen is up next!

I had originally planned to use the 2700kv NTM motor but it was damaged in a crash so I have opted to use the 2200kv NTM instead.

PLANS
I have added the plans here.

SPECS
Motor 87g 700w 2200kv
Prop 7x6 APC
ESC 70a Dynam
Battery 2000mah 3S
AUW 595g
Speed 85mph

PICS
The plans fit on 2 sheets of DTFB, and that would include making 5+ noses as well.
photo 1 (8).JPG

The build went fast, a lot faster than the full size. I was able to get everything cut an assembled in just a few hours.
photo 4 (3).JPG

Weight with just servos is 151g - not bad at all.
photo 3 (5).JPG

80% next to my beat up full size.
photo 5 (1).JPG

Mounted powerpod
photo 5.JPG

photo 1 (1).JPG

ESC is mounted in the duct for max airflow.
photo 2 (1).JPG

Plenty of room for my 2000 3S and TX.
photo 4.JPG

Control rod is running through a straw and powerpod is mounted with two BBQ skewers.
photo 3.JPG

AUW 595g.
photo 2.JPG

REVIEW
Pros
- Very fast and stable at high speeds
- Tracks really well, no dipping or loss of altitude
- Very small

Cons
- Motor caused tremendous torque roll that is uncontrollable at low speeds
- Very unstable at low speeds due to weight
- Difficult to land due to instability at low speed
- ...basically you have to fly fast, always :)

Comments
Boy is she fast! There are 5 other videos that I have not posted of my maiden of this plane. I didn't post them because they are all 4 seconds long and include the Viggen immediately death spiraling into the ground even when giving 0 control input. The torque roll is just that bad. I was very lucky to land each of these attempts on the belly so there was no damage sustained. Each throw I would adjust the angle to try and gain altitude right off the bat, the 5th attempt was the keeper and I actually got airborne.

I can't launch this bird without doing at least 1 roll from the motor torque. This makes take off very tricky and stressful. Once I got up to speed it does handle very well, though. A lot more stable than I had originally thought it would due to its compact size. If I bring the speed below 40% throttle it becomes unmanageable and doesn't respond to control inputs, it just kinda starts doing it's own thing. This makes landing tricky as I have to set it up perfect in a downward glide and set it down fast and hot otherwise a nasty crash will be inevitable. My maiden landing was awful as I hadn't realized how finicky it would be, but I was able to set her down okay.

All in all
Would I suggest you build an 80% Viggen? Yes, but don't use this motor. Get a lower KV and bigger prop that will give you more thrust. I have a few other motors I'm going to try and will update my review with the results. I am hoping a larger prop/more thrust will help to alleviate at least some of the bad tendencies.

 
Last edited:

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#2
Holy-Moley! Here I was thinking, "ooh, smaller airframe . . . maybe I could get it to work well with the 64mm fan, or even my 50mm fan", and here you are building a Rocketship!

That motor would make the full sized hussle, on that guy it'll SCREAM the scream of a thousand a little girls at a boy-band concert!

Looking forward to blurred pics and video in the air!
 

nerdnic

nerdnic.com
Mentor
#4
Holy-Moley! Here I was thinking, "ooh, smaller airframe . . . maybe I could get it to work well with the 64mm fan, or even my 50mm fan", and here you are building a Rocketship!

That motor would make the full sized hussle, on that guy it'll SCREAM the scream of a thousand a little girls at a boy-band concert!

Looking forward to blurred pics and video in the air!
LOL! I'm hoping to break 100 :)
 

SteevyT

Senior Member
#9
I was not expecting this to work, but I found a frequency analyzer app for my phone, grabbed two clear points where I could easily see the spike in the frequency spectrum from the plane (one while the plane was coming, one while going). Solved a couple equations pulled from Wikipedia, and came up with a speed of 87 miles per hour on that full throttle pass in your video.
 

nerdnic

nerdnic.com
Mentor
#10
I was not expecting this to work, but I found a frequency analyzer app for my phone, grabbed two clear points where I could easily see the spike in the frequency spectrum from the plane (one while the plane was coming, one while going). Solved a couple equations pulled from Wikipedia, and came up with a speed of 87 miles per hour on that full throttle pass in your video.
That...that is awesome! Please, explain how this was done?
 

SteevyT

Senior Member
#11
First, find a good frequency analyser app for your phone. Spec Scope finally gave me nice clear results after going through about three or four apps.

Then, find a point where you can see a clear spike in the frequency with the plane coming, make a note of it, and another with the plane going.

I plugged those values, and the speed of sound in air into the first equation here https://en.wikipedia.org/wiki/Doppler_effect#General You will end up with an unknown origin frequency and speed in two equations. Solve the system of equations for speed (will be in meters per second) convert to miles per hour. (or you can cheat and use a graphing calculator rather than solving equations, but you still have to convert to miles per hour)

When plugging the values in, you are the receiver, the plane is the origin.
 

nerdnic

nerdnic.com
Mentor
#16
SteevyT - I ended up getting a GPS sensor for my Taranis and your calculation is dead on. I was constant at 85 during passes, and any wind variation would +/- this by a small margin.

Fun stuff!
 

jayz 84

Posted a thousand or more times
#17
You should try it with the hobbyking funfighter motor setup. Much lighter setup better glide and super fast on 3and 4s
 

jayz 84

Posted a thousand or more times
#19
Hey nerdnic how well dose this thing fly. Im in the middle of putting the plans on the board now. Its gonna be my first elevon jet setup. Gonna be putting NTM Prop Drive 28-36 1800KV / 438w. 4S and 6x4 prop for now till i get the 6x6. Should push 80+
 

nerdnic

nerdnic.com
Mentor
#20
Hey nerdnic how well dose this thing fly. Im in the middle of putting the plans on the board now. Its gonna be my first elevon jet setup. Gonna be putting NTM Prop Drive 28-36 1800KV / 438w. 4S and 6x4 prop for now till i get the 6x6. Should push 80+
To be honest? I basically never fly it. When I'm packing my stuff up to go fly it doesn't even cross my mind 'I should fly my 80% Viggen.' This is partially because it's not easy to fly at slow speeds, at all. But mostly it's because I love the other planes I have more.

The full size Viggen is 100x more stable and I'd probably recommend that over the 80%.