Hi Eardoc,

Thanks for the compliment, I though you guys would think I was stupid buying three sets of Kitchen sales. I know the bloke in the shop did.

I too find it really difficult holding up my models on my fingertips with any accuracy.

I do like the idea of weighting the entire model and then just measuring the nose wheel weight.Should make it simpler and cheaper.

Regards

TommyW:
Didn't realize that in your original post you used 3 sets of scales!!! If you by a good digital scale (or buy your wife a nice kitchen scale for her birthday!) you only need 1 scale. Then use wooden blocks of the same height as the scale under the other two wheels to keep the model level. As in the previous post, the key measurements are the weight in the nosewheel and the total weight of the plane.
You now need to put your two "spare" sets of scales up for sale. Still a very useful thread for those who have trouble holding 15lbs on one fingertip.

File not found... [sm=confused_smile.gif]
Why?
Thanks in advance.
Best Regards

Hi,
could someone send me the spreadsheet, please?
Thanks in advance.
Best Regards

Guys

I found some very nice digital scales on Ebay that are great for this. The ones I purchased were 0-25# with a digital readout that is connected with a 2 ft extension cord. The scales were under $15 each plus a little shipping. A great and easy way to weigh your plane and check the CG accurately

Best regards

Greg Anixter

Simple is good. After an email exchange with pilott28 from a
[link=http://www.rcuniverse.com/forum/m_5267614/anchors_5267614/mpage_1/key_/anchor/tm.htm#5267614]similar thread[/link] and digging up the article, I came up with a simplified version in both US and metric flavors. A page sample appears below. I think Dreamworks will have a copy of the (newer) spreadsheet in their Tips Section.

Mike

When I built the DC-10s, it took a lot of head scratching to find the CG.

I did just what you did except with only one scale and blocks of foam.

Did all tha work and 1 hour before the first flight I put a 1 lbs of water in the nose.... Just to be sure !!!! hahah
never took it out.

Eddie Weeks

Guys,

For those of you using the 'scales' method to find the CofG, can you confirm if anything different needs to be done for trailing link u/c setups?

There are 2 data entry values of "Distance Between Nosewheel and Mains" and "Desired CG Distance from Mains". Are these distances taken from where the wheels contact the ground rather than from, for example, the centre line of the oleos etc?

Just wanting to be sure!

Thanks,
Mark

Measurements are between the centers of the axles.

and last check before I do this tonight.....

The value "Desired CG Distance from Mains" - if the CofG is infront of the main axles, this number is positive and if behind them the number entered is negative???

Thanks,
Mark

Yes. Sometimes people do taildraggers. All that is going on here is to find the point where the moment ahead equals the moment behind and that point is the current Cg location.

The first time thru this will take maybe 30 min to hour to get the airplane level and get the measurements. The more accurate the leveling and measurements, the more accuate the location of the Cg is determined. Subsequent setups could be done in as little as 15 to 20 mins. This really isn't very hard. Couple of drafting squares, yardsticks and a surface to draw lines on. Probably harder to get the airplane level more than anything else.

What airplane are you doing?

Just

This is my spreadsheet for doing Cg. Change the file extension on this file to .xls

Thud Driver,

It's a Skygate Hawk.

I have it up on my flat building board. Using a set of pretty accurate digital bathroom scales and placing the model up on boxes the same height as the scales.

Rgds,
Mark

Nice!

Just a note. With oleo's, nosegears that raise/lower the nose slightly, and such, raising the mains to the level of the scale usually doesn't make the fuselage level. Yours looks pretty good in that respect, but I try to find a place on the fuselage where I can use a level to verify it.

Hi Mark,

I would worry about the resolution of the bathroom scales. Mine only give 100 gram resolution. I guess it will depend on how heavy your model is and waht precentage 100 grams is.
My scales resolve to 1 gram.


I have since purchased a device on which i can place the heaviest model. I got it from someone on the web but can't remember where. I will try to find the site.


Here it is:-

http://www.ezbalancer.com/


Regards

http://www.rcuniverse.com/forum/m_55...tm.htm#5560662

Guys,

Model is hovering around 20kg - just a fraction under.

The scales 'show' tenths of a pound i.e 3.1lbs, 3.2lbs, 3.3lbs so 'should' be fairly accurate. I can't find any 'accurate' scales that go to the weight I am after.

My concern is that I have tried various formulae and they all give different results.

Am going to spend some time doing this very carefully at the weekend - hopefully I can get away from what appears to be a need for some weight in the tail. At the mo it looks like the ECU battery is going to end up behind the stabs!!

Rgds,
Mark

something else I have tried is:

on my suky and extra, I cut a piece of ply that goes over the spar and an anti rotation pin. I placed it on the aircraft and measured with a plumb where the desired cg was supposed to be and drilled a hole and a few holes either side.

then put it all together with the ply wedged in and picked it up by a string atached to the middle hole to check CG. it should hang fairly level. I did my 25 pounder that way recently. then when I wanted to move the cg back 1/4 inch, just hung it from the next hole back and moved the batts to get it.

pretty simple if you dont have scales or a mount.

The JPO website has a spreadsheet formula for CG.

I used the JPO spreadsheet a la Keith Sievers for my Lightning and a 140 inch wingspan ME 262 and it was a spot on way to do it. The lightning was the best CG'd effort I ever had, on the maiden, the CG felt SPOT ON.