Laser 200 Centre of Gravity Problem
 

I have a slightly scaled up Wayne Ulery Laser 200 89" Span and have just removed a Zenoah G62 and replaced it with an MVVS 58 (Evolution) which will give a substantial power boost with no weight penalty in an already light model (17.5Lbs). The model incorporates plug in foam cored wings instead of the original built up ones. The original plan gives absolutely no indication of where the reccommended CofG should be.

The model was originally built and flown by my son some 9 years ago and we can't remember where the centre of gravity was, but it did fly well. The MVVS is significantly lighter that the Zenoah but it's centre of mass is probably 1/2" further forward than the Zenoah's was, the Ignition unit and ignition battery bring the total weight close to the Zenoah but they are well behind the engine so in theory the CofG should have moved back when the engine was changed. Now to my problem:-

The CofG is now at 24.7% of the Mean Aerodynamic Chord therefore it figures that with the Zenoah it would have been even further forward (way too far forward in my opinion)yet it flew extremely well in ullimited IMAC flying so it must have been reasonably correct.

I have written a fairly complex program to calculate where on the MAC the CofG should fall taking into account the tail volume and tail moment and this tells me that a good starting point would be 31.33%. Now to further complicate this problem I have a Carden 30% Extra amd the recommended CofG is at 26.5%. The bottom line is that I am unsure of a good startine point and to get it back to 30% I will have to put the flight pack in the rear of the fuselage.

I would appreciate any advice as to a good starting point if anybody can make a recomendation or has any experience with models having the Laser's wing planform and tail moment. I don't want to end up with a model that is hard to flare when landing.

Thanks in anticipation

RE: Laser 200 Centre of Gravity Problem
 

That sounds very near to the size of the Lanier 1/3 scale Laser. What I would do is contact Lanier and see what the proper CG for their Laser is and go from there.




Shawn Berkheimer

R/C blimp Productions.com

RE: Laser 200 Centre of Gravity Problem
 

Shawn,
Thanks for the input, I did have a look at the Lanier web site before posting my query. I was able to have check out the ".pdf" manual and all it said was to balance the model on the wing tube.

There is no guarantee that I placed the wing tube on my Laser in the same relative position as did Lanier, I had to modofy the wing structote from built up one piece to foam core plug-it and I placed the tube at 30% as I did so.

I will try emailinf Lanier and see if they will respond to my question.

Mike

RE: Laser 200 Centre of Gravity Problem
 

Here you go. I would follow Dick Hanson's advice - he has some experience in these matters.

http://www.rcuniverse.com/forum/fb.a...681605&key=MAC

RE: Laser 200 Centre of Gravity Problem
 

I would start the CG at about 30%from the leading edge of the wing. DO a balance check. Then adjust from there with weight changes. That may be off a little but it wont be in danger of a crash. At least you can get it in the air and figure out its bad flight charcterisitics from the good and see if the CG needs to be moved back or forward.

RE: Laser 200 Centre of Gravity Problem
 

I have looked at the link to Dick Hanson's comments and found what he had to say interesting. I have followed Dick's work since way back when he wrote the pattern column in Flying Models and of course he was responsible for the Tiporare design flown by Dave Brown for quite a long time.

Thanks for that, I will leave the CofG where it is as it falls close to where Dick said he had a good stable IMAC model and this model in my son's hands with the Zenoah in it was certainly stable and extremely capable. I saw it perform a tail slide that must have gone back down for a distance close to 150 feet (had me concerned about snapping the tail off on pull out) and single roll rolling circles with snaps at each 90 degrees at a height of around 15 feet. It had to be stable to do this kind of thing but to me it may have been a bit too nose heavy as flaring when landing required a heap of elevator which had to be in high rate "or else..."

Thanks to everybody who contributed here I appreciat your input.

I may go fly it later this morning if the weather remains OK, it is forecast to be 35 Degrees C (95F) with strong winds.

RE: Laser 200 Centre of Gravity Problem
 

In more aesy way, how is the CG for 3D in the Laser 200 1/3 Lanier?[:-]

RE: Laser 200 Centre of Gravity Problem
 

Hi RomanRC,

I have flown this model quite a few times since I asked for assistance and have the CofG back at 31.4% which I have found to be about right and there is no problems with flaring when landing in low rate elevator which was my original concern due to my feeling that it was way too nose heavy. It has in the past pulled the undercarriage off twice, once due to my son landing in a patch of sand filling a hole in the field and once due to him not having high rate elevator selected when landing.

As for 3D this model is not really designed for 3D, the ailerons do not come as close to the wing root as is desirable and the surfaces are not double bevelled, even the rudder can't have it's throw increased without major surgery doe to design constraints. The originsl design was by Wayne Ulery in the late 1980's as a TOC model for Dean Koger and if I remember correctly it was powered by a geared .91ci engine.

Mike

RE: Laser 200 Centre of Gravity Problem
 

Thanks for the info. I feel the plane nose heavy, and yes is not a 3d plane but does blenders, and torque rolls nice. If I put the CG in wing tube is OK?

RE: Laser 200 Centre of Gravity Problem
 

I mentioned where I now have the CofG in my previous post but I did contact Lanier when I was trying to establish where the model should balance and here is an excerpt from their reply:-

Most aerobatic planes will need to be at least 30% to fly well. Most 3D
planes will be 35% or more. I would start at 28% so as not to have any
surprises on the first flight.

This information is relative to their 1/3 scale laser and I am guessing that the wing tube is placed somewhere in that vicinity.

Mike

RE: Laser 200 Centre of Gravity Problem
 

Thanks:D I will do tomorrow;)