CG question
 

I've just completed repairs on my Hangar 9 Arrow post crash. I've converted from trike to taildragger and because of the robustness of my repairs I'm a bit worried about being nose heavy. I'm wondering if I can swiss cheese my Great Planes landing gear to save some weight without compromising their structure. http://www.greathobbies.com/producti...od_id=GPMQ1820 . This is the repair thread, http://www.rcuniverse.com/forum/m_8606307/tm.htm .

Thanks

Ryan

RE: CG question
 

Until a couple yrs ago GP sold a Swiss Cheese landing gear

Use common sense in making your holes

RE: CG question
 

By common sense would you be referring to leaving a significan amount of material...say no more than 50% of the width removed?

RE: CG question
 

Like this perhaps?

RE: CG question
 

I used a set of these GP gear on my Gizmo so I could have a little bit wider wheel base than the stock gear.
I also used them for my float plane conversion of my Nextar as well, the float plane needed a cross bar to strenthen the gear sisnce they were so bouncy.

there very light weight to start with so I am not sure if lightening holes are going to be all that much of a benifical.

there also made from soft aluminum and are really flexable, mine have started to splay out a bit and need to be bent back into shape by drilling holes in the gear I really dont know if your going to save all that much weight for the weakening of the LG that you will have done to them, if your going to drill holes in the gear I wouldn't make them all that big

RE: CG question
 

This is the typical pattern for lightening holes in a landing gear as shown above
http://image2-6.rcuniverse.com/e1/fo...39/Mk27456.jpg

RE: CG question
 

How's that for common sense...and on my first doodle...HA...this obviously isn't rocket science. Compared to the wire gear that this plane came with the aluminum gear is horrendously heavy.

RE: CG question
 

The amount of material you are going to remove by making those holes will NOT have a significant difference on the C.G., but may have an adverse affect on the landing gear.

Don't bother.

You'll never even notice that difference in weight.

RE: CG question
 

I have a hole saw for the biggest hole in the top so I cut that one out. I figued I'd get eveything together and check my CG and go from there. Turns out even with all the repairs and the mods and the weight of the landing gear I'm actually a bit tail heavy....just wherer I want it actually. The spec calls for 3 and an eighth inches from the leading edge and it balances perfectly level at 3 and a quarter. Should be nice enough weather for a flight report tomorrow...

RE: CG question
 

Hey all. The Arrow flys great. The CG feels just right, rolls have a little less flop with very little down elevator inverted to keep it level. I got in four flights with about 14 ground loops. First experience witha taildragger and no tail wheel control was an adventure. The field is still very damp on and off the runway which made touch and goes and landings a bit more exciting than usual. All and all another great start to another flying season.

RE: CG question
 

Great - - but you need a steerable tail wheel

RE: CG question
 

Any suggestions are certainly appreciated w8ye..... the elevator rod comes straight out the middle of the rear of the fuse, the rudder linkage comes out the top of the other side of the fuse to the rudder.....and the hinge line for the elevator is about a quarter inch behind the rearmost part of the bottom of the rudder....

RE: CG question
 

There a couple ways to skin that cat

The main solution is that there has to be a torque tube going up through the fuselage that is in line with the rudder hinge line. In other words run a brass or aluminum or hard nylon tube down through the fuselage that goes to one side or the other of your elevator control rod and out the bottom of the fuselage. It has to be on the center line of your rudder hinge. It will have to terminate on the bottom into a piece of plywood. It can be 1/8" in scrap lite ply or some thickness maple ply.

There will be a piece of 1/16" music wire that goes up through this tube and up between the rudder and fin. It turns into the center of the rudder at a right angle about a 1/2" from the bottom and is epoxied into place. The bottom of this torque rod will be bent at a 90 degree angle to the centerline of the fuselage. (It will stick out to one side.) Use a connector such as these http://www3.towerhobbies.com/cgi-bin...?&I=LXD899&P=7 to connect a pushrod to your tail wheel wire which is bent the same way

Here's my LT40 but my rudder was more straight up and down and I ran the torque rod and the tail wheel wire as one
http://image2-6.rcuniverse.com/e1/ga.../lg-123518.jpg
http://image2-6.rcuniverse.com/e1/ga.../lg-123516.jpg

RE: CG question
 

My view is it would be awaste of time emoving material from the aluminum undercarriage. It's so close to the CoG that the minimal reduction you'd achieve would be worthless.

Adding whatever weight is required to the tail would achieve a lot more. Remember that the tail is probably 20 times the distance from the CoG that the undeercarriage is, and even if you managed to remove 1 ounce from the gear, you'd only need 1/20th of an ounce added to the tail to achieve the same effect.

I've just read a little further and note that you're still tail heavy, so you'll not need to remove weight from the gear or ad weight to the tail, but weight to the nose!!

Now the tail wheel is the problem. I have a castering tail wheel, rather than steerable, on a Swoose, and it works very well. It's worth considering if the steerable option becomes too difficult.

RE: CG question
 

Well, after some trial and error I have a steerable tail wheel on the Arrow. I drilled a hole from the bottom up on the hinge line right next to the rudder hinge. I then inserted a brass tube into the hole and CA'd it in place. I first tried using a piece of sixteenth inch aircraft cable to link the rudder to the bellcrank on the bottom of the fuse but it had too much twist when the rudder turned so I replaced it with a piece of pushrod. The pushrod is bent at the top and captured behind the rudder tiller. on the bottom I fashioned a bellcrank out of a 16th inch collar and an old servo arm I had laying around. On the tail wheel I did the same thing with a smaller servo arm and on a hole closer to the tailwheel wire to give me a bit of amplification of movement. I tried using some springs in a pull-pull setup but the springs put too much tension on the tailwheel bracket and it bound up the wire so it was very dificult to turn. if I loosened the spring tension everything just got floppy and it didn't turn at all... I ended up just using a single pushrod from the front bellcrank to the back one. What do you all think about it????

RE: CG question
 

The most important part is what do you think? How well does it work?

Looks pretty good to me

RE: CG question
 

Seems to work okay on the bench, haven't had a chance to taxi around with it yet. It doesn't look like it turns enough buit that might be deceiving on the bench. I spoke to one of the fellas in the club here and he put me on the idea. I came up with the design and put it together. I'm sure if it doesn't do what I want I can try something else to get it right.

RE: CG question
 

you did what I had in mind

The proof is is the flying. You may want to change the ratio between the belcrank and the tail wheel?