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Pumpkin drop event

FT VIGGEN Will NOT TAKE OFF

Afnan101

Junior Member
#1
Hi , im a newbie and this is my first plane. I made this from scratch , (used Depron Sheet instead of dollar tree)
My specs :
MOTOR : Turnigy L2855-2800 EDF Outrunner (630w) ( its ratted 4s)
EDF : change sun 10 blade 70mm
Battery : Zippy 3s 2600mah 25 c
Esc: 40-50A HK (opto only)

I took it for a test but the plane wont take of , it just glides off when i throw it , PLEASE SOME ONE Help
 

jayz 84

Posted a thousand or more times
#2
Sounds like you not getting enough power to weight with your setup that motor puts out 630w on 4s that 3s is not giving you enough power to carry the weight. And just to let you know its not a good first plane so set you rates low
 

pgerts

Old age member
Mentor
#3
You might expect about 300W with 3 cells. You will not get a lot of power but more than enough for level flying.
It is normally good for a light delta. Depron is a lot lighter than DT.
What is the weight of your plane with everything?
How fast can you throw the plane to start flying?
 

edfjockey

Junior Member
#5
Most EDF's use inrunner motors that I've ever used because you want rpm not torque in an EDF. With a 70MM fan I have found that you need atleast a 3600KV motor and I have run a modified FT-22 off of 3s 2200 Zippy packs without an issue. You really need to check the position of your EDF in the viggen, I found to get optimum flight characteristics you need a ratio tapered exhaust tube diameter 2/3 the diameter of the fan at the exit and a length 1.5 times the diameter. Static bench and speed tests have found this to cruise easily at half throttle and will reach liftoff speed quickly from a hard runway. EDF's don't like grass takeoffs as they don't have the torque to pull through it. Happy flying.:cool:
 
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quorneng

Well-known member
#6
Afnan101
Any chance of a picture(s) of your EDF installation?
Have tried measuring the static thrust?
You really need a Watt meter to measure its actual power.
What I am trying to get at is whether it is simply not drawing sufficient power or your installation is simply not producing the expected thrust from the power it is drawing.
In very simple terms you will need a static thrust of about 3/4 of the planes weight for it to fly reasonably.
 

stay-fun

Helicopter addict
#7
Is your plane powered at all? I see you have the OPTO version of the ESC, which means you need a separate power supply (BEC) for your receiver and servos.
 

Afnan101

Junior Member
#8
Sorry for the late reply and thanks for all the support and replies.
As i said im a newbie and i literally didnt understand any thing you guys said , not a word :| . Sorryy . All i did was watch the video and make as accurate measurements as i can. The Viggen itself is perfect and all , the weight is 950 g (+-30g). After some local suggestions ive reprogramed my ESC to (1.2ms-1.8ms throttle acc , instead of auto and also changes the timing to 15 degrees ). And of course i have a BEC.And can you like breif me about static thrust and all ... Thanks a bunch .Here are some pictures IMG_20140904_150856.jpg IMG_20140904_192841.jpg IMG_20140908_202937.jpg
 
#10
Yes i know , and it is , the thrust produced by the plane is alot and everytghing works , but when i through it , the plane tries to fly but instead it glides after a few seconds (the nose is upand the plane is diagonal when it falls)
I think im doing something wrong at launching the plane :|
 

quorneng

Well-known member
#11
Afnan101
From what you describe I suspect its centre of gravity is too far back.
A delta, and a canard delta in particular, does not stall in the conventional sense but continues to give lift at very nose up attitudes but it creates a huge amount of drag doing it, more than the the EDF thrust.
The result is the plane simply stops flying, the elevons loose all effectiveness and it sinks (crashes?) to the ground. The motor torque is still there so it tends to make the plane roll over in the opposite direction to the fan rotation.

The first flight of my Depron EDF Fairey Delta 2 only lasted a couple of seconds and did exactly the same. I was convinced it did not have nearly enough thrust but moving the battery forward by about 30mm completely transformed it although it still 'stops flying' if you try to go too slowly in a nose high attitude. I would expect your Viggen will be the same.

You might try measuring the thrust by holding it vertically with its nose on a set of scales. Much less than 600g thrust and it will struggle to fly. A thrust close to its weight would be better. Remember your Viggen is not the most aerodynamically efficient airframe.;)
 

willsonman

Builder Extraordinare
Mentor
#13
I suspect you are also stalling the EDF. They are horribly inefficient at low speeds. Combine a careful analysis of your center of Gravity (CG) as referenced on the plans with a more aggressive launch. Given that you are on 3S do not try to climb too fast on your launch but try to maintain level and gradually climb out once you are more up to speed. If you go to 4S I suspect you will have a lot less of an issue here but that would be my $0.02.
 

ztoon

Gone with the Mistral
#14
Hi Afnan,
I made also a FT Viggen with Depron and tape (black tape which I never use again to cover a full aircraft as I found it horrible afterward and nearly impossible to see in the air). Mine is 75% scale, about 53cm wingspan. I bought a cheap 20$ hobbyking 50mm/3S Max and mounted it in, to discover online that this particular edf was more 300gr real thrust (some said <250gr) than the 450gr thrust hk said it was. But my small Viggen is about 300gr without battery, add a 1000mAh/3S (about 90gr) I was not so confident it will fly but it did.


I think you choose a plane not well suited for a first one, but don't give up at the thing.
Look again at that CG spot location.