The $64M question will be:
What will your fuel totaliser read?
Peter wrote:
SWIFT claims improved range
So we would have to lean more aggressively? Obviously, at a given FF/RPM/MP combination the engine would actually run richer with Swift Fuel. Would the engine run richer with T/O power set, i.e. would the FF be the same? Or would it run at lower FF due to the higher density (viscosity?) of Swift Fuel? How would that affect temperatures? Questions upon questions…
@Peter, my EI flow transducer is a turbine, so measures volumetric flow. I believe turbine volumetric flow meters are sensitive to viscosity but not density.
If you do the arithmetic on the Swift fuel, they’re claiming that the fuel is 10% denser and accordingly has 10% higher volumetric energy density. That does strike a slightly odd chord, because on that basis the density is the same as ‘heavy’ jet fuel.
I’m guessing to get 10% more air for a given volumetric fuel flow, you’ll need to ‘re-jet’. You can often reset the idle mixture and you can lean appropriately in cruise but I think running 10% rich otherwise might be a problem.
I agree the totaliser meters volume flow so it should still read correctly, relative to the usable fuel if measured in litres or gallons.
The issue is that on takeoff, with all 3 fully forward, the fuel servo will have been adjusted to deliver X USG/hr for a given airflow velocity. At MSL, ISA, IO540-C4, this is about 23 USG/hr. If the fuel has 10% more molecules to burn per unit volume and has the same flow through the servo then the engine will be getting the equivalent of 25 USG/hr of the 100LL fuel, which is still completely fine. I know of TB20 owners who got their servos adjusted to 26 USG/hr (this is “illegal” as the spec is much tighter than that) in an attempt to keep their CHTs down during climb.
And after takeoff, you can (should) lean as required anyway.
The interesting Q is the " has the same flow through the servo" bit. AIUI, the RSA servo is fed with a constant pressure feed, from the engine driven pump. It measures the airflow (via the four little tubes) and uses this to open a valve. This doesn’t strike me as a constant volume mechanism. I reckon that a “heavier” fuel may well flow more slowly, and thus compensate the postulated servo error to some extent, possibly fully.
..and what about weight and balance? Denser fuel will obviously mean more mass per unit volume so full tanks will weigh more with this new fuel than with 100LL. 60 lbs or so extra weight for full tanks is certainly enough to interest the regulators I would imagine.
I presume this therefore mean that someone will need to issue new, formal, approved, certified weight and balance charts for insertion into our plane’s flight manuals as part of the STC process, referring to filling the plane with pure Swift 102.
Howard wrote:
I presume this therefore mean that someone will need to issue new, formal, approved, certified weight and balance charts for insertion into our plane’s flight manuals as part of the STC process, referring to filling the plane with pure Swift 102.
It’s interesting to consider where that might go, but on a technical level the weight and balance requirements are unchanged – its still the same plane. At a given gross weight with full wing tanks the wing bending is lower with denser fuel because the fuselage is carrying less weight and therefore lighter. The detail stresses on tank structure and mounts (as applicable) would be higher.
Howard wrote:
full tanks will weigh more with this new fuel
Planes aren’t certified to be able to fly with full tanks, and mass and balance isn’t based on litres, but lbs/kg, so nothing needs to change IMO.
Rwy20 wrote:
Planes aren’t certified to be able to fly with full tanks
No???
and mass and balance isn’t based on litres, but lbs/kg, so nothing needs to change IMO.
As Silvaire pointed out, the stresses on the tanks will be higher.
the stresses on the tanks will be higher.
That’s a very good point and I wonder how it will be addressed. I find it hard to believe that nobody has thought of this already. It is however only a small % increase, well within the stress the aircraft structure has to cope with within the G limits plus a margin on top.
Peter wrote:
It is however only a small % increase
It’s 13.4% increase. I wouldn’t call that small. God knows how this fuel works with capacitive or resistive fuel senders. Also, you would need a mass flow meter, not a volumetric flow meter to measure fuel flow.
The interesting question is what it consists of. Toulene ? Propanol? Xylene?
