That’s another good point about fuel transducers… see this
Also, you would need a mass flow meter, not a volumetric flow meter to measure fuel flow.
Your tank has a volume of X gallons or litres, and the turbine fuel totaliser transducers measure volume flow, which is right.
To generate the right mixture, in a FADEC box, you either need to measure mass flow (complicated) or you tweak the mixture continually for peak EGT (or close). Except when you don’t want peak EGT e.g. engine not warm yet, going up a hill, VW software 
A mass airflow sensor is about USD25. I wouldn’t call the implementation “complicated” :-)
Airborne_Again wrote:
No???As Silvaire pointed out, the stresses on the tanks will be higher.
Seems I was thinking along the wrong lines, i.e. mass & balance and not structural limits. I was just referring to the M&B calculation. When it comes to structural limits, I don’t know the assumptions and I agree there might be implications.
The “stresses on the tanks”, whatever they are, will be higher but if the aircraft has wing tanks the bending moment on the wing will be lower.
There is a mod for the King Air 90 which increases MAUW by adding weights at the wingtips amongst other things.
Neil wrote:
The “stresses on the tanks”, whatever they are, will be higher but if the aircraft has wing tanks the bending moment on the wing will be lower.
There have been endless discussions about this regarding RVs and aerobatics. Some argue that since the fuel is in the wings, then that fuel can be disregarded when calculating max aerobatic weight, and thereby achieve a higher effective limit. This sounds like a nice proposition, but is of course fundamentally flawed. Even though one can argue that the fuel may even have a positive effect on the main wing spar, it is not like the weight of the fuel disappear. It is still there, and something has to carry the weight of it. Stresses on the tail, horizontal stab, vertical stab will also be higher when weight goes up. The outer wing sections will have to carry more weight and so on. The skin on the wing panels will be more stressed for instance.
LeSving wrote:
It is still there, and something has to carry the weight of it. Stresses on the tail, horizontal stab, vertical stab will also be higher when weight goes up.
But, and that was what I was trying to get at with my first comment, the MTOW will not change, so you would eventually just have to put in less fuel (or go on a diet) to remain in the limits already determined for your plane. How would heavier fuel affect the tail, horizontal or vertical stabilizer then?
Rwy20 wrote:
But, and that was what I was trying to get at with my first comment, the MTOW will not change, so you would eventually just have to put in less fuel (or go on a diet) to remain in the limits already determined for your plane
Yes, it will hardly make any difference when you put it like that. But if you mix it with 100LL/UL91, you will only have an approximate idea of how much you have unless you measure the density or mass flow. The endurance will be an unknown variable. Sometimes it could be 1000 NM, other times 1340 NM, most often some unknown quantity in between. You somehow hav to measure the exact quantity of fuel in either volume or mass. How are you going to do that when the density and composition are unknown variables? The only way I can think of is a dip stick or a sight tube or something. If you only fill this new fuel, no problems of course.
With a good fuel totalizer, this will be a planning problem, but not an operational one – once established in the cruise at the approximate mixture, you will see the fuel flow in litres or gallons, and fuel remaining, so while you might be disappointed at the range you get, you won’t run out of fuel inadvertentley.
At the planning stage, you could keep track of how much of each fuel you put in, and a simple calculation shuold work. And you need to keep track of that anyway to do weight and balance correctly.
The above assumes that these fuels mix evenly. If they separate in the tank, neithrr of the two methods above work, and you have to assume the worst case – AVGAS…
They better mix otherwise you will need to adjust the mixture from time to time, whereas presently you climb up and leave it.
No, they should not separate. Even avgas + diesel fuel won’t separate (according to Phil Croucher, 1/3 avgas + 2/3 diesel fuel = emergency replacement for Jet B – e.g. when you have to choose between flying away and being shot at).
