Re: Weight and Balance - help with choosing additional nose ballast - or not


Mike Tooze
 

Hi Marcus,

You are very right to reassess your W&B after a few (15) years.

However, you are now at a stage with your Long that you ought to be refining its performance.

I recently wrote on another point "".... Add(remove) ballast as necessary to achieve your minimum trim drag at the speed you choose to fly."

It is not simply to push your CoG back as far as safely possible. I worked all my carer in aerospace, a large part of that was in 'stability and control'. This included FBW systems that allowed reduce stability margins brought about by flying with rearward CoGs to attain more efficient flight. (mil and civil). Mainly for tailed aircraft this is the case but for a canard aircraft things are slightly different. - the canard gives positive lift whereas a tailplane pushed down. So, by moving the CoG of a plane back if it is 'tailed' this reduces the down-thrust required from the tailplane , increasing efficiency (but reducing natural stability margins). But for a canard moving the CoG further back, incrementally, means less lift is needed from the canard - good to start with but if that means that the canard elevator is now required to produce 'down trim' to the extent of adding drag that is where the rearward CoG efficiency gain idea starts to fail.

But Forget All that, there is a much easier way. Following the quote above....

i.e What airspeed do you wish to fly with your required load? - Say, 160kts
Then run a test with your nominally safe ballast at a reasonable CoG. Run at your chosen airspeed (160kt) and note the amount of trim you need to maintain 'stick free' straight and level flight.
If the trim is significantly 'down' and/or you need to augment the trim for level flight with more 'nose down stick' then this indicates that you need more nose ballast. If it is 'up' then you can reduce the nose ballast. (But keep within the given CoG limits)

After an iteration or two you will be flying with slight elevator trailing edge, TE, floating above the in-line position for minimum canard drag. Thus for that flight condition you have your main-plane and canard balanced for minimum trim drag.

For the Long and VE I have found that the faster the chosen airspeed the more down trim, stick nose down force, is needed to maintain level flight, so expect to increase ballast for increased 'chosen airspeed'.

Running you spread sheet as you go will keep you inside safe limits.
I hope this is of some help. OMV.

Best with it,

Mike Tooze
O-235 VE, Last winner of EuroCAFE, in our 38th yr.

On Thursday, 18 July 2019, 19:04:22 BST, 'Marcus Borom' borommarc@... [canard-aviators] wrote:




Hi Canardians,

 

After flying for 15 years on my last weight and balance determination, I enlisted the help of George Snyder and his certified, digital scales for a re-weigh.  I am considering adding additional nose ballast, either 10 or 25 pounds..  I would like some advice on whether I should choose 0, 10, or 25 pounds of nose ballast.  The nose already has 23.4 pounds of ballast installed.

I am attaching an Excel spreadsheet with the comparisons showing the effect on the CG for various scenarios of loading.  I have indicated the position for the CG for each of the loadings, and color coded each as follows:

 

Green (in the first flight box),

Yellow (in the CG box, but aft of the first flight box)

Pink (in the CG box, but near the aft limit)

Red (dangerously aft of the CG box)

 

Question.  Do I want to favor the nose ballast that places the CG in the first flight box.?

 

The CG box is shown at the bottom of the spreadsheet. You can play with the weights by just changing them.

 

Thanks in advance for your input.

 

Marc Borom

LongEZ  N966EZ

Ryan Field

Tucson, AZ


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