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Savannah Weight & Balance


Flyinglion2000

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I was reading through Mark Kyle's build log on this site and came across the subject of weight & balance and the adjustments he put his aircraft through to adjust his aircraft's W&B to where he worked out it needed to be for optimum trim and performance.

 

So I dug out my W&B and plotted it as per the manual and got an initial surprise - my W&B was well forward of the forward most CoG line provided by ICP in the manual. For reference the graph I initially used is found in CAP12. FIRST FLIGHT pages 1-2/4 dated 12th January 2010.

 

Here is my data and graphic overlaid on the ICP W&B chart. My Sav S is the blue line. This was done using lb metres.

 

Then I tried it using the W&B chart Mark Kyle was using for his aircraft. This chart is in kg metres.

 

Lo and behold I was well within the forward and rearward limits of CoG. But this was for a Savannah XL VG?!?!?!?

 

Getting very confused now

 

So I went back to the manual and in the Pilot Operating Handbook (not the Construction Manual) I found another set of W&B charts - one in Kg metres and the other in lb feet. I immediately noticed that the kg metres W&B chart has the same CoG limits as for the Sav XL VG! Shouldn’t they be different ?!?!?!?

 

So I plotted again in lbs and ft and I got the same result smack in the middle of the forward and rearward limits of CoG just like as it was for the W&B chart in kg metres above. Not unexpected if ICP did the change from metric to imperial correctly but is this the right W&B chart for a Sav S???

 

So my questions are:

 

1. Which W&B charts are correct for a Savannah S? The one in the construction manual or the one in the pilot operating handbook (which seems to be the same as the one for Sav XL VG!)

 

2. I would have thought that the Sav S is a little different in construction to the Sav XL VG so would therefore have a different W&B charts for each aircraft. Yes/no?

 

Savannah S weight & balance lb metres.pdf

 

Savannah S weight & balance kg metres.pdf

 

Savannah S weight & balance lb metres.pdf

 

Savannah S weight & balance kg metres.pdf

 

Savannah S weight & balance lb metres.pdf

Savannah S weight & balance kg metres.pdf

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The S and XL are exactly the same aircraft except for the rounded rear corners of the fuselage the only other differences are the flap control connections and how they come out of the fuselage at the flaperons but the measurements of cabin length from the rear wing mounts to the spinner and the wings are the same and the tail lengths are the same so it would hold true that the XL and S weight and balance should be the same chart the moments and arms are the same. I looked at a S manual and checked this. Mine flew great when she first flew but the nose wheel would always touch the gound very early on landings and I could not hold it up that well. Also on final the elevator I always had to hold a fair bit of pressure on it and if I released it the aircrafts speed accelerated quite fast so this is why I decided to look into changing the balance.

 

I did all the calculations for the weights on the wheels WITHOUT weighing the aircraft and doing all the calculations and arrived at the chart I posted. I readjusted the trim as per the manual where the manual says 30mm mine originally was like 10mm now it is more like 30mm. I use a RC Allen servo and led display my takeoff trim and level flight it 2 bars down from the top so I still have some forward trim available and with first stage of flap and full up trim I can let the stick go and the aircraft stays rock solid at 50 knots. It is perfect. Elevator is what some may call sensitive in level flight but what I did notice was before I always had to just keep trimming for level flight a little….now once set the trim attitude remains solid and I put this down to the aircraft previously being too nose heavy even though it was ok in the chart but it was toward the nose heavy line but well inside it.

 

I will post the actual figures soon as I have to do a new weight and balance for the 600 kg mod and submit them with the paperwork I expect the figures to be pretty much what I calculated because it flys like them.

 

Mark

 

 

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Thanks Mark

 

I emailed Reg Brost and I think we worked out the first chart i used (in pounds metres ?!?) was flawed and tus not to be used.

 

Yes that was very interesting to see how the baggage weight has a very dramatic effect on the CoG. Do you think the chart is specified for the extended bagage area that most of us seem to installing? I hope so.

 

I enjoy (as do many others) reading your posts on your aircraft build and flying - great to see. Hope you get back in the air soon - good flying weather is coming!

 

ps

 

Its a battle to stay at 80kg! too much amber fluid in my diet me thinks

 

 

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The S and XL are exactly the same aircraft except for the rounded rear corners of the fuselage the only other differences are the flap control connections and how they come out of the fuselage at the flaperons but the measurements of cabin length from the rear wing mounts to the spinner and the wings are the same and the tail lengths are the same so it would hold true that the XL and S weight and balance should be the same chart the moments and arms are the same. I looked at a S manual and checked this. Mine flew great when she first flew but the nose wheel would always touch the gound very early on landings and I could not hold it up that well. Also on final the elevator I always had to hold a fair bit of pressure on it and if I released it the aircrafts speed accelerated quite fast so this is why I decided to look into changing the balance.I did all the calculations for the weights on the wheels WITHOUT weighing the aircraft and doing all the calculations and arrived at the chart I posted. I readjusted the trim as per the manual where the manual says 30mm mine originally was like 10mm now it is more like 30mm. I use a RC Allen servo and led display my takeoff trim and level flight it 2 bars down from the top so I still have some forward trim available and with first stage of flap and full up trim I can let the stick go and the aircraft stays rock solid at 50 knots. It is perfect. Elevator is what some may call sensitive in level flight but what I did notice was before I always had to just keep trimming for level flight a little….now once set the trim attitude remains solid and I put this down to the aircraft previously being too nose heavy even though it was ok in the chart but it was toward the nose heavy line but well inside it.

 

I will post the actual figures soon as I have to do a new weight and balance for the 600 kg mod and submit them with the paperwork I expect the figures to be pretty much what I calculated because it flys like them.

 

Mark

Interesting mark.

 

The savannah S that I rent is like yours used to be. Full back trim, and one stage of flaps, and the stick is a long way back with quite considerable weight on it. Being a 24- rego though I dont see how it could be rectified.

 

 

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Interesting mark.The savannah S that I rent is like yours used to be. Full back trim, and one stage of flaps, and the stick is a long way back with quite considerable weight on it. Being a 24- rego though I dont see how it could be rectified.

yes very nose heavy..exactly how mine was....now she is a thing of beauty to fly :)

 

 

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Your Xl file seems to work perfect although the fuel arm is only slightly out

 

attached is the original with the battery in the front and the "new one done with initial weights but need to still do it properly it is with the calculations I did

 

Savannah S weight & balance new KgMetres.pdf

 

Savannah S weight & balance KgMetres.pdf

 

Savannah S weight & balance new KgMetres.pdf

 

Savannah S weight & balance KgMetres.pdf

 

Savannah S weight & balance new KgMetres.pdf

Savannah S weight & balance KgMetres.pdf

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another thing that pretty much confirms these graphs is when first built my sav I could lift the nose right up and the tail would never sit on the ground now I can lift the nose up and the aircraft sits on its tail with a little weight on it…this is confirmed in the "new" chart when you look at it

 

 

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Yes it will be interesting to see how your actual W&B checks out when youre done rebuilding and ready to fly again. I gather having teh aircraft's W&B just right of centre of the two CoG limit lines is an optimum configuration.

 

The fuel arm I used is 0.495M - it shows up in the table as 0.50M - is that right?

 

 

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yes the exel file is truncating the 2 decimal digits.....my D1 and D2 are a bit different...I don't know why. I have fitted the new main undercarriage and have to turn my nose fork back around I will do a remeasure for this and see what it ends up....I am not sure why mine are so different originally

 

 

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Yes I have only used the distance values of the landing gear from the manual. My actual distances are aprrox 20mm smaller. I will dig them out and adjust.

 

Your main gear distance arm seems comparatively small. Mine is 654mm, the manual says 675mm.

 

My reference point is the leading edge.

 

 

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yes I don't know why mine is 617mm I measured all the distances like 10 times to be sure because mine are a bit different to the manual but from what I have seen everyones distances all seem to be different , don't know why either, ...you need to do it with your distances....I note your nosewheel weight is 75kg I thought mine was heavy at 71.5

 

Probably on Friday I will get a chance to remeasure it all but cant get the weights done yet..... also when you do the weights I hope you blocked up the main wheels so a spirit level on the top of the rear deck showed it was level because if you don't you will get false weight values on your scales

 

 

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  • 1 month later...

Ok did a new W&B on my rebuilt Sav here are all the actual weights and chart. Pretty much exactly as I had calculated when I shifted the battery

 

Kyle Savannah weight & balance-2.xls

 

Kyle Savannah actual weights.xls

 

Kyle Savannah weight & balance-2.xls

 

Kyle Savannah actual weights.xls

 

Kyle Savannah weight & balance-2.xls

Kyle Savannah actual weights.xls

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