Ok, so I am building a H.K. Yak 54, ( AKA Art tec yak 54 ) but, Hobby King does not have any instructions. I downloaded from art tec. The instructions state that the c.g. is 2 1/2 '' from leading edge. I was taught a long time ago that a rule of thumb is one third of chord length. This wing is 10.75 " so I think it is about one inch short at 2 1/2 " because it is VERY tail heavy with the battery in. I set the balancer up at 3 3/8 " and it is just about perfect. It will hold level, tap the nose a little and it will drop a little. Tap it rear and it will fall aft a little ( one bubble either way on the level ). Am I to assume that one third chord length is correct ? Or am I going to have to put a brick on the nose ?
General trying to find c.g.
- Thread starter cobieg
- Start date
RandyDSok
Well-Known Member
There are going to be several factors that could contribute to what you are seeing with the CG vs what the manual you found was stating... For instance if you are using a different motor, esc and/or battery than what the manufacturer uses, it could explain a lot.... In this case, if your setup is lighter in weight, that would explain why you need to move back that inch ( or so ) in order to get it to balance.
Until you find someone that has the exact same model... go by the manufacturer recommendations.
Once you do get ( or verify ) the CG... The following can help once you get the initial setup and have gotten it into the air to further tweak the settings... These instructions are made more for 3D and Sport fliers and not trainers that may have a flat bottom wing ( ie Clark Y or modified Clark Y etc )
After reaching a good safe height... a quick way of finding the optimal CG is to pull back to 1/2 throttle at altitude. Fly well above the minimum glide speed - cruising speed. Make several passes up and down the field at several hundred feet, playing with the elevator trim until the airplane flies level with no transmitter inputs.
Leaving the throttle alone, force a 30 to 40 degree dive. When the plane has gained a 20% to 30% increase in speed, (say 50 ft. or so), so that it's accelerating, take your thumb off the stick. If the airplane continues on straight, (hopefully not too long!), it's at the lateral perfect center of gravity. It is neutrally stable. The airplane doesn't change direction, it just keeps on going. If it starts to go up, then it is tail heavy, if it starts going down, it is nose heavy.
If you are a pretty decent pilot... Bring the plane back up to a good safe altitude again and return it to 1/2 throttle... go inverted. If the CG is correct it will either continue straight and level or ( more commonly ) will require a slight down input on the elevator to maintain a level flight path.
Really good pilots will also check the plane in knife edge flight... but I don't recommend it unless you are pretty proficient already.... so I'd suggest you skip this test until you are more experienced.
Until you find someone that has the exact same model... go by the manufacturer recommendations.
Once you do get ( or verify ) the CG... The following can help once you get the initial setup and have gotten it into the air to further tweak the settings... These instructions are made more for 3D and Sport fliers and not trainers that may have a flat bottom wing ( ie Clark Y or modified Clark Y etc )
After reaching a good safe height... a quick way of finding the optimal CG is to pull back to 1/2 throttle at altitude. Fly well above the minimum glide speed - cruising speed. Make several passes up and down the field at several hundred feet, playing with the elevator trim until the airplane flies level with no transmitter inputs.
Leaving the throttle alone, force a 30 to 40 degree dive. When the plane has gained a 20% to 30% increase in speed, (say 50 ft. or so), so that it's accelerating, take your thumb off the stick. If the airplane continues on straight, (hopefully not too long!), it's at the lateral perfect center of gravity. It is neutrally stable. The airplane doesn't change direction, it just keeps on going. If it starts to go up, then it is tail heavy, if it starts going down, it is nose heavy.
If you are a pretty decent pilot... Bring the plane back up to a good safe altitude again and return it to 1/2 throttle... go inverted. If the CG is correct it will either continue straight and level or ( more commonly ) will require a slight down input on the elevator to maintain a level flight path.
Really good pilots will also check the plane in knife edge flight... but I don't recommend it unless you are pretty proficient already.... so I'd suggest you skip this test until you are more experienced.
RandyDSok
Well-Known Member
I am not arguing for or against what they printed in their manual... I'm saying that it is important to get verification and not guess at it before you fly... The rest of what I posted is so you can verify it yourself once in the air.
PS... when editing a quote in a forum... don't cut off the beginning quote or trailing quote tags.... You removed the trailing bracket "]" in the above quote which is why it isn't displaying properly.
PS... when editing a quote in a forum... don't cut off the beginning quote or trailing quote tags.... You removed the trailing bracket "]" in the above quote which is why it isn't displaying properly.
RandyDSok
Well-Known Member
Hopefully someone will pop in, or you'll find the info so you can get it verified...
Oh, and when you are ready to get a good flying, well behaved plane... check out the 3D Hobby Shop models... They even have a 46" Yak 55 ( in blue or red ) if that is the design style you like... and there will be no need to second guess their manuals.
Oh, and when you are ready to get a good flying, well behaved plane... check out the 3D Hobby Shop models... They even have a 46" Yak 55 ( in blue or red ) if that is the design style you like... and there will be no need to second guess their manuals.
