Mar 07, 2012, 02:02 PM
Registered User
Discussion

Hi All,

How can one find the Empty Weight of an RC-aircraft? Please bear in mind this is at design stage so we ideally want to calculate the empty weight BEFORE it has been built, so how can this be done?...

This empty weight is needed to calculate the wing loading on the same design thereafter.

Eagerly waiting for replies my friends

Best regards

Charlie
 Mar 07, 2012, 02:26 PM An itch?. Scratch build. You can't 'calculate' the weight of a model before it's been built, or even designed. You can weigh all the components that will go into building the model and then add them all up, plus allow a little extra for the glue etc. Wing loading is based on the total flying weight. That would include the batteries, fuel (if IC powered), etc.
Mar 07, 2012, 02:35 PM
Registered User
Quote:
 Originally Posted by eflightray You can't 'calculate' the weight of a model before it's been built
Well, in theory you can. If you measure the density of the foam you're using you can multiply that with the calculated total surface area of all the foam parts (including internal bits like formers etc.). Then you can measure the average weight of the glue you're using per length of joint and multiply that with the calculated total length of all glue joints. Then add the weight of all the hardware.

In theory..

In practice you always seem to end up 10% to 20% heavier than you expected even if you include the 10% or 20% extra weight in your original prediction
 Mar 07, 2012, 02:49 PM Registered User Slebetman wow thanks for that very informative reply you never cease to amaze me! Do you have a personal email to keep in contact with you my friend, just pm me with it if you'd like I shall calculate this using your suggestion tomorrow and will keep you updated my friend Eflightray: thanks for the feedback it's much appreciated my friend
 Mar 08, 2012, 10:23 AM Registered User For the past few years I've been recording the weights of various components and now have a spreadsheet where I can predict weights with reasonable accuracy (+/- 20%). But there are so many variables in terms of materials and coverings that until you've actually built a few models with those techniques and have some real data it's hard to generalize. Calculating areas and multiplying by the weight of the materials is a good start. Then based on previous builds, I know that I have to add a percentage to account for glue and reinforcements etc. Another possibility that requires more searching, is to find threads of models built with similar materials, size, and coverings that give a finished weight and extrapolate from that. For example, flat foamies seem to come in around 4-8oz/sqft. Full fuse maybe 6-10, Full fuse, built up wing, maybe 8 to 12, scale types covered with glass, retracts etc, 10-18.