Another Weight Question

[Lewis95]

Hello all! 

 

So, I've tried to google these 2 questions and I still haven't found a thread that satisfies my need for knowledge so here goes .... 

 

1. When building an aircraft, how do you know if it's gonna be a tail sitter?
2. If a kit just says, add weight, how much weight should I be adding?
3. If a kit doesn't say add weight, how can I tell if it's just oversight and it will need weight anyways? 

 

I get that Q.3 is effectively like Q.1 but my reasoning for this is simple. Not all kits are created equal, and therefore, not all instructions are created equal either. To my untrained eye, a kit like a Cessna 172 wouldn't need weights but after reading a review of a kit, the builder recognized and added weight to counteract (no knowledge as to how he knew it would tail sit or how much to counter it). 

 

Thanks all! 

[Troy Smith]

1 hour ago, Lewis95 said:

Hello all! 

 

So, I've tried to google these 2 questions and I still haven't found a thread that satisfies my need for knowledge so here goes .... 

 

1. When building an aircraft, how do you know if it's gonna be a tail sitter?

other models say so...

You will probably have an idea if it's got a tricycle undercarriage and more of thw eight behind the main UC legs

1 hour ago, Lewis95 said:

1. If a kit just says, add weight, how much weight should I be adding?

see other folks,  or, dry assemble, find pivot point, add weight until it no longer tips.   Scrap lead sheet is great if you can get some,  you don't need much.  

1 hour ago, Lewis95 said:

1. If a kit doesn't say add weight, how can I tell if it's just oversight and it will need weight anyways? 

I get that Q.3 is effectively like Q.1 but my reasoning for this is simple. Not all kits are created equal, and therefore, not all instructions are created equal either. To my untrained eye, a kit like a Cessna 172 wouldn't need weights but after reading a review of a kit, the builder recognized and added weight to counteract (no knowledge as to how he knew it would tail sit or how much to counter it).  

 

have a search,  and see my answer to 2, a dry run.   Pretty much anythinh with a tricycle uc that does not have a long nose will have some weight.

A method I have part tried, (as in the magnet will hold down quite a weight)  is to use very strong small rare earth magnets, you can get them 2mm diameter,  I got some 2x3mm, drill hole into base of nosewheel,  and use metal baseplate.

This is a work in progress, but early trials look OK,  more for kits which you can't put in much weight. 

[modelmaker]

Assemble all the main pieces, tape together as best as possible. Doesn't need to be perfect, for example tail parts can all be taped in place on the rear fuselage in one piece. Next you need something to act like a jig to support it to see how it 'sits'. After lots of temporary jobs I hit upon some Wilko ertsatz Lego, one flat base piece, then just make up some little towers which you can place appropriately under the wings at the place where the u/c legs will eventually locate. Voila! It will probably tip backwards. Now tape your chosen ballast at the front end, and distribute it according to where it will eventually fit (engine nacelles in things like Bè5s, for example, when things are desperate). I use old fashioned lead (with great respect for the dangers therein) so tape works for me. 

There are lots of ways to balance the model while you 'weigh' it, but I found the Lego type system useful for helping me jig a model when trying to check dihedral and such like, at which I do NOT excel. I eventually superglued a suitable thin metal rod up the middle of the 3 support towers for supporting the roughly assembled model. Works quite well. 

 

If necessary you can heartlessly Rob a young child if you have one, real Lego is quite expensive!

[Lewis95]

Thank you both for your replies. I'll run some preliminary tests on my current build before adding the canopy as fuselage is sealed up now. 

 

If it does tip, does a PVA/liquid weight (the small ball types) have a good chance?