Matt Throckmorton's ("DocThrock") Team Rocket F1 EVO Kit Plane Construction Pages
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Team Rocket F1-EVO   Weight and Balance   Page       Last Modified: 
  
On This Page:  Weighing      Empty Weight CG    Extreme Forward CG     Extreme Aft CG    Weight & Balance Calculator


Weighing The Airframe

JohnAndBillWeighing.JPGThe weight and balance is an extremely important calculation with any aircraft. With my EVO, it's going to undoubtedly be done more than once. When the plane is finally airworthy, the plane still won't be finished because the paint and interior are going to be done by someone else at a different airport. And since the weight will undoubtedly change, you can expect to have to re-weigh and re-calculate the W&B when there is a significant change in weight.

I bought a pair of digital bathroom scaled from Walmart. They are Healthometer scales capable of 400 pounds. I need two scales for each main wheel and another for the tail. Some guys actually buy 5 of the same scales. I bought two and elected to weigh each wheel independantly. In order to do this technique, I used a hoist to lift each main wheel and change the two scales from wheel to wheel, and swap a pair of 2x4s with a 1/4 inch piece of plywood over them to duplicate the heigth of the scales (and common board).  

Since each main wheel is going to weigh about 600 pounds or more, I had to use two scales on each wheel. In order to get an accurate reading, I simply used a sheet of 1/4 inch aluminum plate that covered the measuring surface of each scale back to back, then dropped the wheel gently but quickly in the middle between them. It took some doing and the help of two other guys to get any kind of consistancy with the measurements. Thanks to John Watler and Bill Foraker on their help getting the plane loaded with all the parts and then going through the measurement motions. I think we ended up weighing each main 6 to 8 times. Then we ended up throwing out the high and the low, then averaging the final numbers. The numbers that were averaged were generally within about a 5 pound spread. Not bad for cheapo bathroom scales. We all climbed on them to test our weight, and even threw some known balasts on the scales to test them. We figured that the scales were within about 1 pound or less of being correct.

MattLeveling.JPGWeighing the tailwheel was easy enough. Just drop the tailwheel onto the elevated scale and check the number. Since the tailwheel doesn't wobble around so much as the mains (with the wings hanging way out in the breeze), when it drops down, the numbers come up dead nuts on the same 4 or more times in a row. That was the easy one.

The plane has to be in level flying attitude to check the weights. That means getting out the digital level and checking the top rivet line on the turtle deck and across the canopy rails at the back.

It was a little scarey dropping the mains onto the scales each time to get a new measurement because the whole plane would shake and wobble. With bathroom scales you have to turn them on so that they zero, then quickly add the weight and then wait for the calculations to stablize and read the weight. Then they shut off and you have to do it again. So the bathroom scale idea is tougher than using real aircraft weighing scales. But then again, the bathroom scales are about 4 thousand dollars cheaper than real aviation scales.






Reading two scales before they shut off. A bit of ballet mixed with Three Stooges!  Have to drop the hydraulic hoist gently, make sure the tailwheel stays on the leveling aparatus (blocks and buckets), and read both scales before the thing shuts off. Did each wheel about 10 times to get a good average. After a while, we were getting values within 5 pounds. Not bad considering the wings and tail would wobble when the plane was dropped onto the big plate between the scales. 
WheelOnScales.JPG


Here's the skinny on my W&B:

Left Main:     624.8 pounds
Right Main:   627.2 pounds
TailWheel:      62.0 pounds

Total Empty Weight: 1314 pounds

Datum:  68.7 inches forward of the firewall web.
Main Axle Centerline: On my F1-EVO measured to be 77.625, but opted to use 77.75 like the manual suggests in lieu of measuring accuracy.
Tail Wheel Axle is 188 inches from the Main Axles.

Max Gross weight allowed is 2100 pounds for the F1-EVO.




Empty Weight CG Calculations:

TW Distance to Mains 188 inches x TW Weight 62 pounds  divided by the TEW 1314 =    Tail Wheel CG     8.87

TW CG 8.87 + Main Axle Centerline 77.75 =                                 Empty Weight CG    86.62   






Extreme Forward CG Sample Calculation:
(87.7 inches approved forward CG)


                                   
Weight (pounds) Arm (inches) Moment
Aircraft Empty Weight 1314 86.62 113818.68
Oil  (12 quarts) 24 49 1176
Pilot 200 104.5 20900
Fuel (52 gal) 312 89.25 27846
Passenger 0 131.5 0
Forward Baggage 0 157 0
Aft Baggage 0 182 0
Total 1850 163740.68

Total Moment / Total Weight = CG
163740.68 / 1850 =  88.51

In this situation the plane is loaded with just me and full fuel and oil.  87.7 is the acceptible forward limit and 97.4 is the acceptible aft limit. Since 88.51 falls between the limits at the two extremes, it is acceptible for me to fly solo with full fuel and nothing in the back and still be within the CG envelope.




Extreme AFT CG Sample Calculation:
(97.4 inches approved aft CG)


Weight (pounds) Arm (inches) Moment
Aircraft Empty Weight 1314 86.62 113818.68
Oil  (4 quarts) 8 49 392
Pilot 200 104.5 20900
Fuel (5 gal) 30 89.25 2677.5
Passenger 250 131.5 32812.5
Forward Baggage 80 157 12560
Aft Baggage 0 182 0
Total 1882 183160.68

Total Moment / Total Weight = CG
183160.68 / 1882 = 97.32

In the extreme aft CG calculation above, I'm flying to minimum reserve fuel with a heavy passenger in the plane. Looks like if the passenger weighs around 250 I can get by with about 80 pounds of baggage in the forward baggage compartment. No fat guys and a pair of golf club sets on long cross country flights, though. And as a general rule, staying away from an AFT CG is a really good idea. I think with a heavy load of passenger, I'll try not to run to minimums

The F1-EVO is rated for 2100 pounds gross weight. From the looks of the sample CG calculations it's going to be hard to get that much weight in the plane and stay within the loading envelope. However, by myself I'm inside the envelope and also I can carry a big passenger without worrying too much about CG.

Weight & Balance Calculator

Click here to go to my Rocket W&B Page.


REVISED WEIGHT AND BALANCE AS OF 11/2010

FORWARD CG LIMIT for EVO:  97.25
AFT CG Limit for EVO:  86.50


Left Main:     623 pounds
Right Main:   643 pounds
TailWheel:      53 pounds

Total Empty Weight: 1319 pounds

Datum:  68.7 inches forward of the firewall web.
Main Axle Centerline: On my F1-EVO measured to be 77.625, but opted to use 77.75 like the manual suggests in lieu of measuring accuracy.
Tail Wheel Axle is 188 inches from the Main Axles.

Max Gross weight allowed is 2100 pounds for the F1-EVO.




Empty Weight CG Calculations:

TW Distance to Mains 188 inches x TW Weight 53 pounds = 9964, then divided by the TEW 1319 =    Tail Wheel CG     7.55

TW CG 7.55 + Main Axle Centerline 77.75 =                                 Empty Weight CG    85.30   


Weight (pounds) Arm (inches) Moment
Aircraft Empty Weight 1319 85.30 112511
Oil  (8 quarts) 16 49 784
Pilot 200 104.5 20900
Fuel (52 gal) 312 89.25 27846
Passenger 0 131.5 0
Forward Baggage 0 157 0
Aft Baggage 0 182 0
Total 1847 162041

162041/1847=87.732     Which is inside the forward CG envelope.



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