Erroneous Bonanza TN Fuel Flow values
-
Hi all!
Just enjoying the Bonanza these days, I've noticed the turbonormalized version has very low FF during takeoff and climb out, and decide to "research" a little and to my disappointment they were WAY off.If you read the turbonormalized STC POH addendum, the Tkof and CLB fuel flow should be 35GPH and the FF gauge on the bonanza doesn't even have that mark on. Maximum value is 30 and you can only get somewhere around 20GPH which is WAY off. Even the Normally Aspirated Bonanza gives us higher FF. If you notice the STC recommendations, it's very "centered" on FF during most phases of flight, even in Go-around and this won't be able to be replicated. We end up with a MUCH MORE economic airplane in the end.
For reference:
Takeoff:
Then:
-
Luckily, I have been spending a great amount of time with the Baron and Bonanza this week, as I've been adding many new features from the Dukes. I will take a look at these fuel flow values later today and let you know what I find. I can't imagine why the fuel flow would be higher in the normally aspirated version, so there might be something more "interesting" going on. I suspect that this is just what I've seen in other aircraft where MSFS underestimates fuel flow at the highest power settings significantly, which is something I overcame in the Dukes with a little math.
-
As such things usually go, I spent most of my day working on this today trying to arrive at as satisfactory solution.
While the supplement centers many of its suggestions around the 35 GPH number, it indicates almost no increase in fuel flow at cruising altitude over the normally aspirated aircraft, and no mention of overall range. I found evidence supporting this online. I haven't flown turbonormalized aircraft myself, but only assume they mimic the throttle characteristics in turbocharged aircraft, whereby most of the excess fuel flow that we're observing over that of the normally aspirated version takes place at the very end of the throttle's travel.
Something else I hadn't accounted for, turbonormalized aircraft require effectively 2 inHg of power to see the same manifold pressure as a normally aspirated engine (and associated fuel flow increase) due to backpressure from the turbocharger.
At the end of the day, I have solution that allows you to follow the POH by achieving 35 GPH at maximum power, and requiring you to lean when this number is exceeded with cold ambient temperatures. Unfortunately, this has the side effect of making the mixture control even more sensitive than it was already. This is slightly mitigated by my improvements to the overly-rich power falloff curve, so at least the power output will not fluctuate so severely beyond the critical altitude while adjusting the mixture setting.
I have also included a flag in the *.flt files that users can use to disable this new behavior if they liked how the aircraft behaved before.
I also found no difference in fuel flow between the normally aspirated version of the aircraft and the turbonormalized one before I engaged in this line of investigation.
Lastly, I obviously had to add a new scale for the fuel flow indicator in the turbonormalized version, as called for by the supplement.
Thanks for writing and letting me know. I hope the solution I created will be adequate for you. It's definitely not perfect, but I will revisit this topic again at a future date to see if I can learn more about exactly what causes this behavior and how to best simulate it.
-
@Black-Square THANKS for your response and usual pro-attitude regarding researching and fixing things up Nick! That's why Black Square is so good!
