Centre of gravity

[David Gillieson]

Greetings! I'm fairly new to all of this, and have fitted a new 3 blade prop to my Savannah recently. Previously it had a 4 blade Brolga prop. I've noticed that the plane now tends to be a little nose heavy and less sensitive to trim adjustment. My battery is mounted inside the small rear door and I wondered about putting some additional weight there to shift the C of G back a bit. Does anyone have any advice?

 

Many thanks,

 

Dave

 

 

[fly_tornado]

try it!

 

 

[rankamateur]

If you hang a few goodies on the front end you have to hang a bit of lead in the tail. With no goodies on the front end you might be better to drain the tanks and redo your weight and balance and see if in fact you need it. Where is Mr Kyle when we need him?

 

 

[Guest Nobody]

try it!

Surely you are Joking?

 

 

[eightyknots]

Greetings! I'm fairly new to all of this, and have fitted a new 3 blade prop to my Savannah recently. Previously it had a 4 blade Brolga prop. I've noticed that the plane now tends to be a little nose heavy and less sensitive to trim adjustment. My battery is mounted inside the small rear door and I wondered about putting some additional weight there to shift the C of G back a bit. Does anyone have any advice?Many thanks,

Dave

A heavy duty battery may help. But going from a 4 blade prop to a 3 blade prop (ceterus parabusa), shouldn't the nose be a bit lighter rather than heavier?

 

Perhaps a proper W & B check is in order??

 

 

[Mriya]

It would seem timely to remind everyone that the aircraft log book has a section which should be kept up to date regarding weight and balance changes. The data from the original weighing in order to gain a CofA becomes the benchmark. Every time you make a modification the weight increase or decrease + datum should be recorded in the logbook giving you a clear understanding of the current CofG. If you do not understand this, then make it a priority to sit down with someone who does, in order to accurately record weight and balance changes as they occur.

 

I also can only assume that the 'try it!' comment was a joke, as mistakingly allowing your CofG to move outside of the approved limits is a sure way to invite disaster.

 

Accurate records and calculations plus an understanding of the terms (ie. datum, moment, etc) are the fundamental to success regarding getting weight and balance figures correct. Invest the time, sit down with your logbook, experiment with adding and subtracting theoretical weight from the aircraft at various locations and observe how it changes the CofG location.

 

 

[David Gillieson]

Thanks everyone for that advice, my latest weight and balance figures are well within limits. I will do the theoretical calculations first as suggested.

 

 

[Kyle Communications]

Hi David

 

If you read my blog I have just gone through a major CG change to my Savannah VG XL much more radical than changing a prop. I would doubt there would be a lot of CG change between the 2 props in fact the 3 blade should be lighter than the 4 blade. The easiest way is of course is to weigh both and see what the difference is between them but 1 kg would not make that much difference I should think. I shifted 8.5 kg plus extra wiring down the back of mine about 2.5 mfrs and it made a major difference but a prop wouldn't make a big noticeable difference from what I have measured and flown.

 

You need to do a new weight and balance to see that is the only true way. I did many prelim ones before I actually changed things around and when the real w&b was done it was exactly as I had calculated and the aircraft now flys so much better but is also well within the limits on the chart. You need to weigh both props to get a proper idea of what you are dealing with

 

Mark

 

 

[rankamateur]

Is it really worth unistalling the prop just to weigh it when the real point is to get the W&B right in the current configuration, when the difference is likely 100's of grams not kilos?

 

 

[Kyle Communications]

Well it would have been a good idea to do so before changing the prop but the manufacturer should have the weight when you buy it...then just weigh the old one but as I said I dont think there will be much difference to make a big noticable change to the CG

 

 

[crashley]

first off is the plane registered 24 or 19 and any difference in weight is going to make a difference to the w&b And this change must be noted in the maintenance manual and raa must also be notified of this change If you know the exact weight of the new and old props you can calculate the new w&b but if you dont know the exact weights it is back to scratch and out with the scales and calculator