Large Model Association Forum

Hi Guys,

I have just completed building the LMA Super Greenley. I have a Desert Aircraft 50cc petrol at the front with a Zimmerman can. The problem I have this morning when I put it on the axle stands to get the C & G correct is that it is very tail heavy. I need to put 3lb 12 ounces including both battery's at the very front of the aircraft.. I have the balance point correct to the drawings, 4 3/4 from leading edge.

Can anybody help on this problem I have.

Thanks
Jamie

Jamie,
there is an ongoing discussion regarding where to put CoG of my own plane under that thread. Have a look here and see if any of this helps...
http://www.largemodelassociation.com/viewtopic.php?f=9&t=1688&start=160
Regards, Andy

The one I had had a great chunk of lead up front, not sure what it weighed tho. Flew fine.

Mine was the same - I put a longer mount behind the Zenoah 38. It's due to too much paint on the tail. . . . .

Chris Lane wrote:Mine was the same - I put a longer mount behind the Zenoah 38. It's due to too much paint on the tail. . . . .

My 50cc Petrol is on a 4" long box extension on the front of the fire wall.
RX and engine Sub C battery packs are in the box. No lead needed.
I bought it like that . Flys just dandy.

Simon

Jamie

I suspect the problem is with the wood selection for the tail. A Greenley should balance without any lead and with the batteries under the wing. Heavy wood in the tail is the most likely reason for the model coming out tail heavy.
The original Greenley was designed around a Zenoah 38 / quadra 42 motor and your choice of the DA 50 (a lighter motor) will make matters worse. Depending on how much work you want to do I would suggest the following
1) Put lead in it (yuck!)
2) Put a box on the firewall to move the motor forward
3) Make the tail surfaces outer of lighter wood.

I also note from your photo that you have put a horrible metal undercarriage on the model and not a design as per the plan. you have mounted it to far forward and this will cause the model to bounce on landing. Please move the wheels back to the position shown on the plan for better ground handling.

A final point from your photo is the header from the DA 50 to the silencer looks way to long. It is difficult to see the exact length but a header something like 220 mm long will be about right. This will help your balance problem by moving the silencer forward.

Trust me, it will be worth the effort to get a nice flying model.

John Greenfield
Greenley Designer.

I have to agree with John about the undercarriage, it look like the same one as the LMA Sky-120 if so you will be forever bending it back in, even a light bounce on landing makes the undercarriage spread. Nice model though love the colour scheme. Well done.

I have tried all sorts of things to try to get the weight forward in my Super Greenley. The best solution is to extend the nose to move the engine forward. You can rig up something temporary to find how much you need to extend. This is simple and won't mess up your very smart paint job and it doesn't seem to affect the flight characteristics.
You can reduce the tendency for alloy under carraiges to bend by reinforcing with piano wire attached with saddle clamps.Bend a thin length to get the right shape and then copy it with some quarter inch dia piano wire using a sturdy bench vice.
Best of luck.

Peter

I note your comment about strengthening an ali U/C with piano wire but why not just make it out of piano wire as per the plan in the first place !!? Strong, light weight and will not rip off the bottom of the fuz in a bad landing.

John

Uhm, that U/C looks the same as the one on the Genesis as well.

I have another plane with ally U/C that I strengthened with the piano wire technique, except that there is a 'gap in the piano wire in the middle and a large bunch of rubber bands.....works a treat.

I agree John, but :
1. The builder already has an alloy undercarraige , my suggestion is the best way of making use of it.
2. I am building a sky 120 which has an alloy undercarraige and the advice may be useful to someone else.
3. You have not seen my landings !
Regards, Peter.

John Greenfield wrote:Peter

I note your comment about strengthening an ali U/C with piano wire but why not just make it out of piano wire as per the plan in the first place !!? Strong, light weight and will not rip off the bottom of the fuz in a bad landing.

John

I think the biggest challenge for me in doing the piano wire u/c is actually bending the piano wire at that size. I needed heat and that has softened the wire too much so also get sagging u/c.....

Any advice on bending would be appreciated as I am tempted to go for a glass u/c, which isn't the right way to go I know....

This is what I did on my Sky-120 Undercarriage I bit rough and ready but it seem to work.

Peter, it is nice to here you don't need the advice because you don't have a problem landing, I only wish I could say the same.

I think you misunderstood my comment Dave, my inference was that any under carraige I use has to be strong and resilient. If the builder doesn't have facilities to bend heavy gauge wire the elastic band / spring modification is probably as good if not better. Regards, Peter Clare

This is how I arranged my piano wire undercarriage. Properly the wire should be "let down" by heating it to red heat and then slowly cooling it. After bending it needs to be hardened and tempered to the stiffness required. I can't remember the figures and unless you have a proper temperature controlled electric furnace forget it. . . .

I bent the undercarriage wires cold using a good vise and a piece of substantial steel pipe over the wire to give me an extended grip and some protection. The wire was arranged so that the required bend point was about a diameter above the vise jaws and orientated to allow a straight pull towards me; then it was a matter of foot up against the bench and a good heave! This requires that you make each bend sequentially from one end of the piano wire to the other.

Hi All,
Thanks for all your helpful comments on my post. I know now looking at what I done, I used slightly thicker wood on the outer construction on the rear end. I am going to sell the DA50 and I will purchase a Zen 62 for it. This should help the weight up front. As far as the undercarriage, I will put the wire one on that I made up for it.

Kind regards
Jamie

Peter Clare wrote:I think you misunderstood my comment Dave, my inference was that any under carraige I use has to be strong and resilient. If the builder doesn't have facilities to bend heavy gauge wire the elastic band / spring modification is probably as good if not better. Regards, Peter Clare

No problem Peter, I didn't take it the wrong way, maybe I should have chosen my wording better.

Dave Parry wrote:This is what I did on my Sky-120 Undercarriage I bit rough and ready but it seem to work.

DSCF1005.JPG

Peter, it is nice to here you don't need the advice because you don't have a problem landing, I only wish I could say the same.

Dave, that is identical to how I have done 3 of my models, the bands, the end caps !!!! Who got the patent first???

Andy Boylett wrote:

Dave Parry wrote:This is what I did on my Sky-120 Undercarriage I bit rough and ready but it seem to work.

DSCF1005.JPG

Peter, it is nice to here you don't need the advice because you don't have a problem landing, I only wish I could say the same.

Dave, that is identical to how I have done 3 of my models, the bands, the end caps !!!! Who got the patent first???

Andy, that is a good question, great minds and all that