Working out nose weight?

[Lewis95]

Hi all, 

 

Does anyone have a method for figuring out the nose weight for an aircraft that needs it? It's all well and good looking it up online but a method for working out the weight..... 

 

Give a man a fish vs give a man a fishing rod eh? 

[ckw]

Good question which i wish I knew the answer to - I suspect that by weighing all the individual parts then laying these weights out on a diagram you could calculate the centre of gravity - but sounds like a lot of work.

 

What I do is 

 

1 - ignore the instructions. I've used the suggested weights in the past - almost never enough!

2 - assemble the aircraft as much as possible with tape and then tape weights to the nose (or elsewhere if necessary) until I get it about right

3 - add 10% more for safety

 

Of course quite often you won't have enough space in the nose to add the necessary amount (unless you have access to a supply of osmium) and of course adding weight further aft means adding even more weight! 

 

I use lead tape (stuff used by golfers to make their clubs something or other), and it's quite easy to shape this into parts to fit under floors etc. or even replace parts - radio boxes, panels etc. Of course you can overdo it, so while stuffing lead into every available crevasse, you need to think about how strong the landing gear is - it may need reinforcing or replacing with brass rod or similar. 

 

Cheers

 

Colin

[bootneck]

I don't know of any technical method to work out noseweights, and I probably wouldn't understand it if there was. 

The method I use is to dry fit as much of the model as possible but without any undercarriage or pylons, then place a pencil under the body across the wheel wells.  I then place weights into/onto the nose or cockpit until the model dips forward and that usually gives me the weight I need.   After that, I weigh the pieces and then work out what material would match that weight and would fit in the available spaces up front. 

The weights that I personally found best are tiny little metal balls, they really are tiny but heavy and very good for fitting into 1:144 scale kits.  

 

I think I got them at a model railway shop because the liquid glue that I use to set them in is a railway modelling item.  Railway modellers may be able to tell you what the weights are called.

 

Mike

[Lewis95]

1 hour ago, ckw said:

Good question which i wish I knew the answer to - I suspect that by weighing all the individual parts then laying these weights out on a diagram you could calculate the centre of gravity - but sounds like a lot of work.

 

What I do is 

 

1 - ignore the instructions. I've used the suggested weights in the past - almost never enough!

2 - assemble the aircraft as much as possible with tape and then tape weights to the nose (or elsewhere if necessary) until I get it about right

3 - add 10% more for safety

 

Of course quite often you won't have enough space in the nose to add the necessary amount (unless you have access to a supply of osmium) and of course adding weight further aft means adding even more weight! 

 

I use lead tape (stuff used by golfers to make their clubs something or other), and it's quite easy to shape this into parts to fit under floors etc. or even replace parts - radio boxes, panels etc. Of course you can overdo it, so while stuffing lead into every available crevasse, you need to think about how strong the landing gear is - it may need reinforcing or replacing with brass rod or similar. 

 

Cheers

 

Colin

Quite a good suggestion for the lead taping there. Thankfully I've got access to a fair few weight options!

 

21 minutes ago, bootneck said:

I don't know of any technical method to work out noseweights, and I probably wouldn't understand it if there was. 

The method I use is to dry fit as much of the model as possible but without any undercarriage or pylons, then place a pencil under the body across the wheel wells.  I then place weights into/onto the nose or cockpit until the model dips forward and that usually gives me the weight I need.   After that, I weigh the pieces and then work out what material would match that weight and would fit in the available spaces up front. 

The weights that I personally found best are tiny little metal balls, they really are tiny but heavy and very good for fitting into 1:144 scale kits.  

 

I think I got them at a model railway shop because the liquid glue that I use to set them in is a railway modelling item.  Railway modellers may be able to tell you what the weights are called.

 

Mike

Possibly the Deluxe Products Liquid Gravity of which I happen to have a container of. 

 

With your advice regarding pencils, do you also place one underneath the forward wheel well? Rigging up a jig sounds like the easiest way of figuring the weight out. 

[Tailspin Turtle]

The only refinements that I would add to Mike’s process is to locate the pencil (I prefer something with triangular cross-section for more precision) under the fuselage at the point where the wheels touch the ground and support the aft end of the model at its nose up angle when at rest (if any) before adding the weight until it tips forward. The nose-up consideration is because the amount of weight added when the model is level might, if just enough to keep it from tipping back in that attitude, be aft of the wheel contact point when it is sitting nose up.

 

The other consideration is concern about too much weight overstressing the nose landing gear. There will be very little load on it if a reasonable amount of weight is added - note that the model tips back because there is no load on it. An overload on the nose landing gear results from setting the model down so the nose wheel contacts the surface first, which is exacerbated if you add more weight to the model than necessary to keep it from being a tail sitter. Like the actual airplane, you should set the model down so the main landing gear touches first (when landing a real airplane: touching down nose landing gear first with too much of a sink rate will result either in a bounce because the rebound increases the angle of attack and therefore lift or the nose landing gear will fail because its strength is minimized to not much more than holding the nose up during taxi and while parked in order to minimize weight).

Edited February 11, 2021 by Tailspin Turtle

[bootneck]

No, just the CoG (ish) so that the model tips forward when the weight is greater at the front.

[Alex Gordon]

I found this website the other week when I searched for what volume is 20g of lead.Could be handy sometime.

 

https://www.aqua-calc.com/calculate/weight-to-volume/substance/lead

[Lewis95]

Thanks everyone I shall investigate the next time I build a tail sitter! 

[Corsairfoxfouruncle]

What I do is build or tape as much of the aircraft together. I then use two cut pieces of sprue in the main gear bays. Add anything to the rear that cant be glued/taped. Then add nose weight until you get a nose down attitude. Should look a bit like an airplane shaped teeter totter. 

[dnl42]

Another vote for just taping enough of the model together and then adding weight to balance plus a margin. There is a more analytical method but it's not at all worth the effort.

 

And a demonstration of @Tailspin Turtle's note about the nose gear. Freedom Models' 1/48 X-47B weighs in at 170g; the weight on the nose gear is 15g; the MLG load is 155g.

[Harry Callahan]

12 hours ago, bootneck said:

I don't know of any technical method to work out noseweights, and I probably wouldn't understand it if there was. 

The method I use is to dry fit as much of the model as possible but without any undercarriage or pylons, then place a pencil under the body across the wheel wells.  I then place weights into/onto the nose or cockpit until the model dips forward and that usually gives me the weight I need.   After that, I weigh the pieces and then work out what material would match that weight and would fit in the available spaces up front. 

The weights that I personally found best are tiny little metal balls, they really are tiny but heavy and very good for fitting into 1:144 scale kits.  

 

I think I got them at a model railway shop because the liquid glue that I use to set them in is a railway modelling item.  Railway modellers may be able to tell you what the weights are called.

 

Mike

 

 

 

I do exactly the same method and use the same lead balls as you,and this method is doubtless the best.

[John_W]

I will use the dry fit method. sticking matches/cocktail sticks in to the undercarriage holes to get an approximate. I think with experience, you can look at a kit and tell if it is going to need a serious amount of weight. Being a fan of liquid gravity I will put in as much as I think the Undercarriage will hold. I am also working my way through a large bag of lead air rifle pellets from our last range day when I emptied the pellet catchers. 

The most serious tail sitter I have had is a Catalina, which only just sits on its nose, and now sits in a cradle as the Undercarriage cant cope with the amount of weight. Glazed nose bombers such as the B25 have led me to filling cowlings and engine nacelles as well. At least with a B24, you can copy the US Groundcrew method and stick a .50 cal ammo crate under the tail bumper.

[Jamie @ Sovereign Hobbies]

It can, of course, be done technically because that's how real aeroplanes have to be designed and once designed and built, there needs to be a way to verify the centre of gravity as stuff is added, removed and coats of paint are applied etc.

 

You need first to know the distance fore and aft of the fulcrum point (i.e. the main wheels) that you're measuring from. We will measure "Moments" but a moment is a combination of a force acting through an arm. A big force through a short lever arm can be less of a problem than a small force through a very long lever arm. On this Monogram B-29 I needed lots of weight through a short moment arm to offset a relatively light but very long tail.

 

 

Essentially you tabulate it out, then start weighing the how heavily the tail sits on the scales.

 

 

As I figure out where I can add known weights up forward I add them to the table, and can verify by reweighing the tail. You can see the initial ~80g has been reduced down to 5g. Total weight on the main wheels has gone up substantially, of course.

 

[Sparkie]

11 minutes ago, Jamie @ Sovereign Hobbies said:

It can, of course, be done technically because that's how real aeroplanes have to be designed and once designed and built, there needs to be a way to verify the centre of gravity as stuff is added, removed and coats of paint are applied etc.

 

You need first to know the distance fore and aft of the fulcrum point (i.e. the main wheels) that you're measuring from. We will measure "Moments" but a moment is a combination of a force acting through an arm. A big force through a short lever arm can be less of a problem than a small force through a very long lever arm. On this Monogram B-29 I needed lots of weight through a short moment arm to offset a relatively light but very long tail.

 

 

Essentially you tabulate it out, then start weighing the how heavily the tail sits on the scales.

 

 

As I figure out where I can add known weights up forward I add them to the table, and can verify by reweighing the tail. You can see the initial ~80g has been reduced down to 5g. Total weight on the main wheels has gone up substantially, of course.

 

 

Had to read this 3 times to get it straight in my head, but really useful, Thanks Jamie

[Lewis95]

Very useful post there Jamie. Will take me a good read to properly understand it though! 

[Jamie @ Sovereign Hobbies]

To be clear, I don't usually bother with this and it's completely overkill in the vast majority of cases. In the case of Monogram's B-29, I did it because I'm fitting the fully detailed interior and everyone told me it couldn't be done without filling the cockpit with lead. I don't like taking "no" for an answer so did it by mix of calculation and re-measurement to work out how to ensure it sat on its wheels without sacrificing the cockpit moreso than to eliminate trial and error. This was more iterative assurance than bonafide one-hit-right-answer driven