aalexander
Registered User
Anchorage
This is one of those things that you hear frequently. I wish I had a nickel for each time I've heard someone say, “well, if you put an adult in each seat, you can't legally take off with full tanks”. But when you actually think about it, it doesn't make any sense at all. I was reminded of it just the other day at the Alaska Airman's Association Trade Show. There was an airplane on display with a big sign that said something along the lines of “full seats and full tanks”. The reality is that an airplane for which this is true is unnecessarily compromised and less versatile than it could be. In a sense, an inferior airplane, one in which poor design choices have been made. Before anyone gets hot under the collar, let's think this through:
A given airplane has a max takeoff weight and an empty weight. What you can carry is determined by this. Empty weight subtracted from max takeoff weight is useful load. Simple stuff, and I know everyone know this, but I'm repeating it so we're all on the same page. So, lets say you have an airplane, a 4 place airplane. It's the R-100 model, It's max gross take off weight is 2500 lb, and the empty weight is 1500 lb, so you can carry 1000 lb of fuel and people and other stuff. Now, lets say that you could choose the size of the fuel tanks, with no weight change for any size tank. What size tank would you put in it? If you'd like to fill the seats and fill the tanks, like a lot of folks seem to, here's what you do: There's a whole bunch of folks who weigh over 200 lb, so lets pick that for the size of our “real” adult. Average is likely lower, but, you aren't always going to have average or lighter friends. So, 4 X 200 is 800 lb, that leaves 200 lb of fuel load. Avgas is 6 lb/gallon so, you'd install tanks with 33 gallons total capacity. So you if put in 4 adults you fill the tanks, and you can legally take off. That's important, right? Where can you go? Well the R-100 cruises 150 mph and consumes 12 gal/hr, so full tanks with VFR reserves will give about 300 miles range, or roughly from Anchorage to Fairbanks. (actually, a little farther) OK, so you can take 4 adults (including yourself) to Fairbanks. But what if you're not carrying 3 of your friends? What if you're by yourself? How far can you go? Still just to Fairbanks. What if you want to fly to Bethel? Can't do it, non-stop, gotta stop in Aniak for fuel. What if you want to drop off your buddy and 150 lb of his gear on a mine strip 30 miles west of Sparrevohn, then fly back to Anchorage? can't do it. You'd have to go on to Aniak to refuel, which would add 200 miles to your day, plus avgas in Aniak is not cheap (and you'd just make it into Aniak on fumes).
But, if we dropped the silly notion that you should be able to fill the seats and the tanks in an airplane. and installed bigger tanks, we could do more things.
Same airframe, but we put in 80 gallons of tanks; now, with 4 people, the range hasn't changed, we can still go to Fairbanks, and that's about it with 4 adults, but you can drop of your buddy and gear and make it back to Anchorage nonstop, plus a little contingency fuel. Or, you can fly out to Bethel yourself, and fly back without buying fuel at Bethel prices. Obviously this is a more versatile, useful and practical airplane, merely because it has larger tanks, but you can't “fill the seats and the tanks”, so a lot of folks will lose sight of the fact that it's a more capable airplane, and complain because you can't “fill the seats and the tanks”.
I suppose that the reason folks buy into this, is because they look at the R-100 with it's 500 mile range and 4 seats and wish that they could fly 4 people 500 miles. That's the catch, if you need to fly 4 people 500 miles non-stop, you shouldn't have bought the R-100, because it can't do it. You should have bought the R-200, The R-200 has a max t/o weight of 3500 lb, and weighs 2000 lb empty, it can fly 4 people 500 miles. But, its more expensive to buy and operate, and the thing is, the R-200, has 6 seats and a 700 mile range, and you'll have the same folks complaining because you can't load up 6 adults and fill all the tanks.
If you're not satisfied that you can't “fill the seats and the tanks” in your airplane, there's a simple solution. Tear out the fuel tanks and replace them with smaller tanks. If this sounds silly, it is, but it's no sillier than wanting to “fill the seats and fill the tanks”
A given airplane has a max takeoff weight and an empty weight. What you can carry is determined by this. Empty weight subtracted from max takeoff weight is useful load. Simple stuff, and I know everyone know this, but I'm repeating it so we're all on the same page. So, lets say you have an airplane, a 4 place airplane. It's the R-100 model, It's max gross take off weight is 2500 lb, and the empty weight is 1500 lb, so you can carry 1000 lb of fuel and people and other stuff. Now, lets say that you could choose the size of the fuel tanks, with no weight change for any size tank. What size tank would you put in it? If you'd like to fill the seats and fill the tanks, like a lot of folks seem to, here's what you do: There's a whole bunch of folks who weigh over 200 lb, so lets pick that for the size of our “real” adult. Average is likely lower, but, you aren't always going to have average or lighter friends. So, 4 X 200 is 800 lb, that leaves 200 lb of fuel load. Avgas is 6 lb/gallon so, you'd install tanks with 33 gallons total capacity. So you if put in 4 adults you fill the tanks, and you can legally take off. That's important, right? Where can you go? Well the R-100 cruises 150 mph and consumes 12 gal/hr, so full tanks with VFR reserves will give about 300 miles range, or roughly from Anchorage to Fairbanks. (actually, a little farther) OK, so you can take 4 adults (including yourself) to Fairbanks. But what if you're not carrying 3 of your friends? What if you're by yourself? How far can you go? Still just to Fairbanks. What if you want to fly to Bethel? Can't do it, non-stop, gotta stop in Aniak for fuel. What if you want to drop off your buddy and 150 lb of his gear on a mine strip 30 miles west of Sparrevohn, then fly back to Anchorage? can't do it. You'd have to go on to Aniak to refuel, which would add 200 miles to your day, plus avgas in Aniak is not cheap (and you'd just make it into Aniak on fumes).
But, if we dropped the silly notion that you should be able to fill the seats and the tanks in an airplane. and installed bigger tanks, we could do more things.
Same airframe, but we put in 80 gallons of tanks; now, with 4 people, the range hasn't changed, we can still go to Fairbanks, and that's about it with 4 adults, but you can drop of your buddy and gear and make it back to Anchorage nonstop, plus a little contingency fuel. Or, you can fly out to Bethel yourself, and fly back without buying fuel at Bethel prices. Obviously this is a more versatile, useful and practical airplane, merely because it has larger tanks, but you can't “fill the seats and the tanks”, so a lot of folks will lose sight of the fact that it's a more capable airplane, and complain because you can't “fill the seats and the tanks”.
I suppose that the reason folks buy into this, is because they look at the R-100 with it's 500 mile range and 4 seats and wish that they could fly 4 people 500 miles. That's the catch, if you need to fly 4 people 500 miles non-stop, you shouldn't have bought the R-100, because it can't do it. You should have bought the R-200, The R-200 has a max t/o weight of 3500 lb, and weighs 2000 lb empty, it can fly 4 people 500 miles. But, its more expensive to buy and operate, and the thing is, the R-200, has 6 seats and a 700 mile range, and you'll have the same folks complaining because you can't load up 6 adults and fill all the tanks.
If you're not satisfied that you can't “fill the seats and the tanks” in your airplane, there's a simple solution. Tear out the fuel tanks and replace them with smaller tanks. If this sounds silly, it is, but it's no sillier than wanting to “fill the seats and fill the tanks”
