ahff71

My Feedback: (5)

Where is the CG for a Nitroplanes Yak 50cc purchased in Nov., 2009? I've just completed building it with a DA50 and I am not confident the enclosed manual CG is correct.It balances quite tailheavyusing the manual's CG. Several photos in the manual do not match the actual plane. Model 90A183R (ignition battery on motor mount box, Rx battery in fuse under wingtube.)

Please suggest CG measurement from leading edge of wing both at fuse and end of wing.

thanks for your help,

Andy

opjose

I'm not sure what you mean by "It balances quite tailheavy using the manual's C.G.".

The C.G. occurs wherever the plane balances level. If it balances level, it balances..

If this point is in front of or behind the manufacturer recommended point, then the idea is to adjust components so that the plane balances level at the recommended point.


That's not to say the manual is not wrong.

I've often found the CMP manuals giving measurements that tend to put the C.G. too far back, making for some pucker factor first landings.

As a result of such experiences I normally employ the 20-23% rule, that is I place the C.G. around at around 20% of the MAC as measured along the wing root of a somewhat straight winged plane.

At least this way the plane will fly and land well for the first flights...

Once I've trimmed it out in the air, I start looking to see how far back I wish to move the C.G.

Normally I go with .5" increments on 50cc planes, until I get to the point that the plane drops the nose ( when inverted ) where I want it, while the plane is trimmed out for level upright flight.

A better way to do this is to trim the plane out so that the nose drops an equal amount both upright and inverted, then take the C.G. back a little at a time, to deminish the amount of drop, but not totally eliminate it.

ahff71

My Feedback: (5)

opjose, thanks for your reply.

some clarificationI tried to say at using the 164mm CG point indicated inthe manual, the plane balances very tailheavy.  I'd be afraid to fly it if indeed it's that tailheavy.   the acutal balance point is about an inch behind that at the fuse, or about 1 1/2" behind the wing tube when balanced at the wing end.

I don't believe it's a CMP plane.  The manual cover says Fly Model and logo, model xy-183. Your info is Item# 90A183R_Gas_GiantYak54-50CC-Red.  I purchased it about 60 days ago and have installed a DA50.  Everything but the Rx and Rx battery are on the engine box.   Those two are right at the wing tube. 

As many of these as nitroplanes has sold, I'd think someone could provide an accurate CG measurement.  I appreciate you adjustment suggestions, but I'm afraid to fly it the first time without further CG info.  And excuse my ignorance, but I don't understand your "MAC" suggestion. 
Everything but the Rx and Rx battery are on the engine box.   Those two are right at the wing tube. 

I'm really looking forward to flying this nice plane.  I hope you or someone else can provide a CG measurement I'll feel comfortable about.

Thanks in advance.

opjose

Do you mean that with the plane suspended at the 164mm point, the tail is lower than the nose of the plane when you place it on your balancing device?

If so your C.G. is not at 164mm, rather it "occurs" wherever the plane remains level.


That doesn't sound too far off for a YAK, but it may be a bad point to start with.

Move your battery packs all the way to the nose, and fly it with the C.G. right or just behind the wing tube, say around 110-120mm.

That's what I normally do with the YAK's I have. I'll them shift weights around to achieve my desired balance point.

Remember the C.G. is only a recommendation.

Advanced 3D flyers tend to move the C.G. back to the point that the plane is neutral both inverted and upright.

This is what the YAK is designed for, and this will seem tail heavy for someone not used to flying 3D planes.

However the margin between neutral and VERY hard to control/tail heaviness may only be about 1", so it is best to work back in small increments, say .5" at a time.

MAC = Mean Aerodynamic Chord

20-22% of the MAC ( measured from the wing leading edge ) is very safe for initial flights and many sports models never go further back than this.

3D models may move the C.G. back as far as 33%-35% of the MAC, but this needs to be done with CARE.


See: [link=http://adamone.rchomepage.com/cg_calc.htm]Click me![/link]

The above calculation link lets you figure out target C.G. ranges for any plane.


Put both packs on the engine box initially and fly the plane.

Perform some trimming tests to see how you like it, and if you feel it should be more neutral, move one pack back at a time.

Leave your Expos at around 50% so that even if the plane is too responsive, you'll have the ability to control it.

Moving the C.G. back causes the elevator to become more responsive... too far will cause the plane to behave strangely and if you keep moving it back, eventually uncontrollable.

opjose

More info on MAC

[link=http://www.airfieldmodels.com/information_source/math_and_science_of_model_aircraft/formulas/mean_aerodynamic_chord.htm]Click me - MAC Info.[/link]

ahff71

My Feedback: (5)

Thanks for your reply.

Yes, what I'm trying to say as that the current, actual balance point is about an inch behind the 164mm suggested in the manual.

I'll take your advice and move the Rx battery up to the motor box and try and move the Rx itself forward as well. Whether that will make an inch change in CG, I'll find out.

And thanks for the MAC info and links. I'll print them out and study them.

Hopefully, after moving the battery and learning about MAC, I'll be confident enough to fly the plane.

If you come up with an actual, accurate CG measurement recommendation, please share it. I'm assuming you can't verify the 164mm offered in the manual.

When I get everything worked out and have flown the plane successfully, I'll report back with the CG I'm using.

Thanks again for your help,

Andy
Colorado

opjose

"Accurate" is unfortunately relative.

I can tell you that the plane flies well for me at 130mm-140mm, but it may not be to your liking.

On the calculator, pay particular attention to the neutral point versus C.G.

Remember that 3D'ers are looking for a more neutral plane, so they can roll it upside down without ANY nose drop, etc.

Pattern flyers want a better tracking plane so opt to have the C.G. more forward, but not too far.

Sports flyers prefer it still further forward for easier landings.