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Old Jul 10, 2014, 10:41 PM
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United States, CA, Sunnyvale
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85mph 480mm FT Viggen

MAIDEN FLIGHT
80% FT Viggen (4 min 6 sec)

DETAILS
After the FT 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.


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.


Weight with just servos is 151g - not bad at all.


80% next to my beat up full size.


Mounted motor




ESC is mounted in the duct for max airflow.


Plenty of room for my 2000 3S and TX.


Control rod is running through a straw and motor powerpod is mounted with two BBQ skewers.


AUW 595g.


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.

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Old Jul 16, 2014, 02:54 AM
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EasySimes's Avatar
Australia, NSW, Gladesville
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Good post. I am building a Viggen as well but I am limited in my choice of motors. I was going to put 1000 kv nom in it but am concerned about torque.

I thought that a slow large prop developed more thirsty than a small fast on, am I mistaken?

Simon
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Old Jul 18, 2014, 10:04 PM
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Hmm that's a good question. I could be totally wrong, anyone else have any thoughts?
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Old Jul 19, 2014, 03:56 AM
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Hey I just saw the motor you are using - wow, that is a beast of a motor!

I am going to put in the same brand and size motor (NTM 28-36) in the full size motor but mine is only 1000Kv. do you think that will be enough for the full size viggen?
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Old Jul 19, 2014, 04:10 AM
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Just sat an watched the video again - wow she is fast. Rather you than me mate!
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Old Jul 19, 2014, 10:04 AM
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Others have successfully used that motor on the full size Viggen so I think you'll be fine.

One of the things I found interesting was how long my flights are on this plane. I get over 4 minutes at WOT. With the same power set up on my 800mm Spitfire I get 3, and 2.5 on my 800mm Mustang. The only real difference I know of is cooling. The better cooling matches with the longer flights.

Is this normal?
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Old Jul 19, 2014, 05:39 PM
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That is good to know about my motor - it was the 1000kv version they we using and not the beast you have? I am only checking as once I put the motor in I can't easily take it out as I do not intend to use a power pod and am instead putting in a Cross Piece of foam at the back for a pusher configuration.

As to battery life, I am sure that the temperature plays a part but it is also a function of drag and effort. Of course I write this but I am not sure how much more drag if any a 800mm Spit or P51 would have. Probably the temp.

Just FYI I was in the middle of buildig the viggen and discovered a Draken that really turned my head and that is the one that I am concentrating oon right now. I think you would really like it.

Prop in a Slot Draken
http://www.rcgroups.com/forums/showthread.php?t=1113351

Simon
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Old Jul 19, 2014, 08:34 PM
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85mph 480mm FT Viggen

Cool I'll definitely check that out!

So I doubled checked and I don't know anyone with the 1000kv version but with a 4S and 9x6 it produces about 1kg thrust which is enough for Viggen but it's not going to be very fast. You'll probably have to hold 75% throttle to stay stable.
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Old Jul 20, 2014, 09:35 AM
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No problem - once I have maidened it and assuming it is still in one piece I will buy a 2200Kv version. Persosonally I still try to fly all planes on a 3s 2200 as it is much simpler that way.

I am not yet experienced enough to go really fast - you bird is way out of my league.

To quote Dirty Harry - "Man's gotta know his limitations" (now one of my motto's).
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Old Aug 07, 2014, 12:45 AM
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Quote:
Originally Posted by EasySimes View Post
No problem - once I have maidened it and assuming it is still in one piece I will buy a 2200Kv version. Persosonally I still try to fly all planes on a 3s 2200 as it is much simpler that way.

I am not yet experienced enough to go really fast - you bird is way out of my league.

To quote Dirty Harry - "Man's gotta know his limitations" (now one of my motto's).

Hey man did you get to maiden yet?
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Old Aug 07, 2014, 09:02 AM
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Australia, NSW, Gladesville
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Quote:
Originally Posted by nerdnic View Post
Hey man did you get to maiden yet?
No not yet. I got side tracked by the Draken and also an F22 Raptor I am building. We have had bad weather here on the weekends so I have not yet maidened anything except my Bloody Wonder which flew great then inexplicably spiralled in to the ground. Repaired and looking forwards to Saturday when I have the Bloody Wonder to fly again, the Dfraken to maiden and then there is a P47 I just picked up.

Anyway I was a little put off building the Viggen due to my "weedy" motor - not sure if I should go EDF or just buy an NTM 2700 or even put one of my many 2826 2200kv in it (they are supposed to be pretty powerful).

Thoughts?
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Old Aug 07, 2014, 02:23 PM
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Quote:
Originally Posted by EasySimes View Post

Anyway I was a little put off building the Viggen due to my "weedy" motor - not sure if I should go EDF or just buy an NTM 2700 or even put one of my many 2826 2200kv in it (they are supposed to be pretty powerful).

Thoughts?
stick with prop, EDF are power wasters makes lots of noise then speed
for the same power system (battery)
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Old Aug 07, 2014, 07:01 PM
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OK will do - thanks fr clearing that up as I was toying with the idea but all the 70mm EDF's need 4S batteries etc.

I think I will build the Viggen with the 2826 2200KV motor now - I can always swap it over later to another.

Time to start building. BTW I am pretty certain Torque roll is exacerbated by larger props and slower motors as there is more mass involved. If you want your baby viggen to not roll on hand launches I would thing the 2700KV and 6 x4 or 5x5 prop would do the trick.
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Old Aug 08, 2014, 05:03 PM
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have seen it some where here

to lower the risk of torque roll,
it's better to have the prop shorter then 25% wing span
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