By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

Adding nose weight

All Topics | Latest Posts

Search for:  in Thread Title in  
alex nicol22/06/2020 09:00:39
avatar
388 forum posts
17 photos

I need to add around 350g of nose weight to balance out my latest airframe. In order to add as little as possible I was thinking of melting some lead down and adding it to the spinner.

Can anyone advise if this is feasible and if so what should I watch out for. The model has a 75mm (3" aluminium spinner on the end of an ASP 1.80fs. I understand some balancing may be required and there could be an element of flywheel effect.

Thanks in advance

Alex

Ernie22/06/2020 09:07:53
avatar
2536 forum posts
24 photos

Well, Alex?

My opinion is that its a NONO, Just too much to go pear shaped.

BUT, An old friend of mine, a very accomplished modeler (he talked me through my first wobbly loop) regularly filled plastic spinners with lead shot and epoxy..never saw one go wrong

ernie

Edited By Ernie on 22/06/2020 09:09:15

Denis Watkins22/06/2020 09:15:31
4524 forum posts
121 photos

No never

Just my opinion

You save 10gram adding 340gram to the End of a spinning crankshaft

Just no

alex nicol22/06/2020 09:26:29
avatar
388 forum posts
17 photos

Hi Ernie,

Thanks for your response, if lead shot/epoxy in a plastic spinner worked the aluminium/lead combo is theoretically possible. Ideally there will be someone out there who has tried this and can advise. Alternately it'll need to be a 'suck it and see' approach.

Cheers

Alex

Ron Gray22/06/2020 09:28:43
2226 forum posts
978 photos

Taken from Mick Reeves' website pages:

We recently fitted a steel disc weighing 1 kg on Jims engine shaft, ahead of the prop. To achieve the same effect with ballast on the firewall, it would need 1 1/2 kg.

Brian Cooper22/06/2020 09:57:40
avatar
564 forum posts
27 photos

I saw this practice done once way back in the 1960s. . . It didn't end well.

Leaving aside the issue of finely balancing this kind of arrangement, basically any increase in "G" loads puts an excessive amount of force on the crankshaft. So any aerobatic manoeuvres will be a cause for concern. . Indeed, even a bouncy landing could impose 4 or 5 "G" on the thing. Eventually, the crank will bend, fatigue and/or break.

The one in the 1960s broke the crankshaft while being revved up in the pits. Happily nobody was in the way when it let go...... and it went a long way.

Keep in mind the adage:: "If it CAN happen, then it ruddy well WILL happen" ..and then ask yourself if you would fly in it if it was full size.

Frankly, having seen what a heavy, broken crankshaft, complete with its propeller can do, (and how far it can go) I would personally throw someone out of the Club for adopting this dangerous practice.

B.C.

alex nicol22/06/2020 10:00:09
avatar
388 forum posts
17 photos

Apologies Gents,

I should clarify, if the spinner idea is a go the actual ballast required will be in the region of 250g as opposed to 350g if bolted to the firewall.

My other alternative is to shape some lead strip and fit it inside the cowl just behind the spinner ring. (Model has a non detachable balsa cowl)

Jon - Laser Engines22/06/2020 10:12:35
5550 forum posts
270 photos

How heavy is the model? If the 350g is less than 10% of the overall weight then just ignore it.

Filling spinners with lead is a really bad idea. Bolting great big weights to engine crankshafts is also not brilliant as any imbalance will ruin the engine bearings in short order.

I have to confess, i dont understand the hysteria related to adding ballast to a model. The thing needs to balance to fly, and it needs X amount of ballast to balance...so just add the ballast and fly it. Why such a fuss?

My big Sea Fury is 23 lbs, and 2 of them are lead. The engine/spinner were about as heavy a combo as was available short of a radial, the batteries/servos etc were as far forward as possible, and i built a new elevator that was lighter than the original. That left me needing 2lbs of ballast under the engine to make it balance. I ended up with a 23lb 80 inch WWII fighter with a laser 360v for power. Would i want to be any heavier? not really, would i want it to have any less power? not really, does it go like a scalded cat? ohhh yes :D

Keith Berriman22/06/2020 10:12:51
745 forum posts
11 photos

Alex I was once in your predicament and solved it by fitting the Rx battery in the engine bay is this an option

brokenenglish22/06/2020 10:12:55
avatar
580 forum posts
30 photos

I would prefer the 350g on the firewall!

Edited By brokenenglish on 22/06/2020 10:14:12

perttime22/06/2020 10:24:07
avatar
160 forum posts
11 photos

Is there anything else in the model that can be moved forward?

I'd prefer not to add weight to a component that is spinning rapidly.

alex nicol22/06/2020 10:41:02
avatar
388 forum posts
17 photos

Gents,

Thanks for your experiences/opinions. I think I'll go for fixed non spinning ballast epoxied and glassed to the inside of the cowl as far forward as possible. (I've no desire to create anything that may be at risk of parting company with the airframe

Cheers

Alex

Peter Miller22/06/2020 11:08:22
avatar
11206 forum posts
1321 photos
10 articles

Just to show what even a slight problem can cause:

Way back I had a conntrolline model with a Kiel Kraft plastic spinner which had a screw on front cap, which was very light.

The nose cap came off in flight and removed one propellor blade.The imbalance instantly removed the complete engine,tank and bearer assembly which departed across the flying field and very luckily missed the spectators.

250 Grams!!!! The men in white coats will be coming along soon!!

Nigel R22/06/2020 11:21:24
avatar
3970 forum posts
714 photos

Any possibility of screwing some sheet lead onto the engine mount? That might gets it half way between firewall and prop.

alex nicol22/06/2020 11:31:24
avatar
388 forum posts
17 photos

Admittedly I had doubts about the spinner weight, hence the original reason for asking the question.

With regards to things departing airframes, many moons ago (early/mid 70's) I flew a lot of control line combat where mid airs and motor departures were common place (this was pre engine tethered to bell rank rule) The distance and damage a 15 sized engine could go/do never ceased to amaze.

alex nicol22/06/2020 11:39:40
avatar
388 forum posts
17 photos

Hi Nigel,

It's quite a neat fitting cowl with not a lot of clearence around the mount. It looks like I'm just going to have a look just now to see what I can do. In short the battery is as far forward as I can get it and the ballast will be as far forward as I can get it and remain firmly fixed and behind the prop.

Cheers

Alex

Geoff S22/06/2020 12:21:20
3689 forum posts
29 photos

I'm sure I've seen extra heavy prop nuts advertised specifically to get ballast as far forward as possible. I nver thought it a good idea, mostly because of the damage it could cause to bearings but the thought of an actual crankshaft's breaking hadn't occurred to me. Anything flying off the front of a running engine/motor could be very dangerous.

It's amazing hw high G forces can increase even at apparently modest rpm. About 40 years ago I was involved in the design of short range radio telemetry for aero-engine temperature and stress measuremnt (by short I mean millimetres!). The housing for the electronics (which were epoxy potted) were about 350mm diameter and rotating at around 7000rpm IIRC. We were dealing with 25k g! Amazingly the only things to fail were the inter-module and transducer wiring.

On my current build, which will certainly need lead, I'm intending to screw it to the cowl. I've made sure the cowl is very securely attached.

Geoff

Peter Miller22/06/2020 12:47:34
avatar
11206 forum posts
1321 photos
10 articles

Many years ago(You are old father Wiliam!!!!) I designed a small scale model of the Taylor Monoplane with an OS20 Four Stroke.

That had a circular intake in the cowl and I cast a lead ring to fit right at the front. That worked.

Ron Gray22/06/2020 13:13:11
2226 forum posts
978 photos

Like Peter I made a nose weight for my ESM Hurricane by adding lead shot to some slow setting resin and pouring it into the front of the cowl which had a waxed beaker pushed into the engine shaft hole. The lead / resin mix formed a nice ring around the front inside face of the cowl.

Keith Berriman22/06/2020 14:14:56
745 forum posts
11 photos

What size Rx batteries are in the model can you put some bigger cell batteries in ??

AA to say 2/3 cell or Sub C

All Topics | Latest Posts

Please login to post a reply.

Latest Forum Posts
Support Our Partners
Slec
Sussex Model Centre
electricwingman 2017
CML
Advertise With Us
Sarik
Latest "For Sale" Ads
Has home isolation prompted you to start trad' building?
Q: The effects of Coronavirus

 Yes - for the first time
 Yes - but Ive bashed balsa before
 No - Ive existing projects on the bench
 No - Im strictly an ARTF person

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E!