Turbine Duke Range
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Hi, great plane :)
Just wanted to ask under what circumstances you have tested the range of this one. We have done some comparisons on the MSFS forums, and it's nowhere close to the 1 200 nm (+reserve), more like 800 nm + reserve, without passengers, at 25 000 feet. The tablet range predictions also show similar results.
Did beta testers have to use some specific settings for cruise to check this one?
Not saying it's wrong, there might be a lot of additional factors, just want to check out if you know what setting to use to get maximum range. With turboprops it's often not obvious.
Tried to do some math:
According to this article:
https://flycasey.com/royal-turbine-duke/65 gallons per hour is expected in cruise. Which is also as much as I have seen cruising at 25k. No idea if it was with or without any load, mine was without.
We have 260 gallons usable tank capacity, so it's 4 hours.
The plane roughly makes 300nm an hour. So this is probably how we come to the 1200 nm.
But, it doesn't seem to take into consideration that you first have to reach 25 000 when you burn more.
Also, this is the normal range and not the maximum range. Shouldn't flying empty be the maximum range of 1,5K?
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Sorry for double post, here the tablet, which seems to be right :)
In my testing the temperature was above ISA (-20C at FL250), but I would not expect it to have that crushing influence on the results and the tablet probably doesn't take it into consideration :)
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@Tadeus72 What exact power settings are you using? If you look in the manual, for the normal power setting tables, you are getting exactly the range the tables describe. If you want to push the plane to maximum range, you need to use the maximum range table. Here's the tables:
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Yeah, I've noticed the same thing with greatly reduced range, even when adjusting for density altitude, I'm getting much higher fuel flow for a given power setting--at least at the 26,000' altitude where I've been doing several flights. During my last flight, density altitude was 27,300' and I was getting 27-28gph with a torque of 670ft-lbs to 700ft-lbs and 2050rpm. The charts above show a much shorter range than the specs, and my actual performance in the sim is worse than the "maximum range power" chart.
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Hello All,
Thank you for taking so much interest in my aircraft. I hope you didn't think I was being quiet on purpose. When it comes to more nuanced questions like this (as opposed to simple code fixes), I like to take my time to really assess the situation on my own so that I can give you the best possible answers. I spent several more hours with this tonight, and I think I'm ready to answer.
1. Tablet Range - A bug and an oversimplification. The tablet range is just a simple "normal cruise power" range. It is not looking at your current fuel flow, and will not change as you adjust power. I did this so that you could get a rough estimate while loading, otherwise you would have to tell the tablet your intended cruise parameters, which is already a function of so many trip planners and GPS units, that I did not feel the need to duplicate the functionality. The range on the tablet is currently well under the actual estimated range due to one misplaced parenthesis on my part. I accidentally created a rounding error. Thank you for helping me find it. For reference, the tablet (after the rounding error fix) will assume 80 GPH fuel burn, and 285 KTAS cruise.
2. Range Numbers - Accurate tables, inaccurate coversheet. I found that the range numbers within the first few pages of my manuals (referenced in this thread as ~1,200nm normal range) is not accurate. I apologize for losing track of these numbers. I won't try to make excuses, but you would be surprised at how easy it is to let a faulty range number into your manual when you're far more concerned with 10,000+ lines of code that may crash the whole simulator. I have revised the normal cruise range to 840nm, and a maximum range of 1,170nm. On the other hand, I found that the range estimates in the performance tables were accurate with one exception, which I will address momentarily.
3. Fuel Flow. I few several test flights end-to-end tonight (thank goodness for time acceleration) with the TDS GTNxi fuel planning functions as my guide. I found the fuel flows were as close to the tables as I could expect for MSFS. Whenever I find a limitation in MSFS, I design my aircraft to operate most accurately in the primary zone of operation, while performance might be slightly off at the extrema. I found the fuel flows to be most accurate in the normal cruising altitude range between 20,000 and 26,000 feet. The only notable exception was the example given above at the maximum altitude, maximum range power setting. I found the sweet spot that actually maximized specific fuel consumption was at a slightly reduced power setting of 760 ft-lbs, 2,050 RPM, and 28 GPH/Eng. I have also revised that line of the performance tables.
4. A note on interpreting range numbers. You might have noticed that the 1,135nm maximum range power table figure still differs from the 1,170nm maximum range that I mention above. My performance table numbers are all at maximum gross weight, but the maximum range (as opposed to normal range) number specified in aircraft advertising is usually the full-fuel range with only one occupant. This is often referred to as the "ferry range." In my tests, I was able to hit this number with single occupancy at 25,000ft, 670 ft-lbs, 2,050 RPM, 24 GPH/Eng., and 228 KTAS. Starting with 270 gal of fuel, this resulted in arriving at cruise with 246 gal after ~50nm. Burning just under 50 GPH total in the cruise takes us to TOD 4.4hrs later with 35 gallons total remaining. Reduce power to around 500 ft-lbs and 18 GPH/Eng. for a 100nm descent, and we touch down with 25 gallons of fuel remaining, having covered 1,170nm in a little over 5hrs of flying time. I would hate to be the ferry pilot that has to stretch that 20 gallons of usable fuel for the extra 30 minutes, at 550 ft-lbs and 20 GPH/Eng., but I'm sure we've all been told by our instructors not to expect that you can replicate the ideal numbers created by a team of test pilots to satisfy the corporate boardroom.
In conclusion, thank you for helping me find a small bug in the tablet, make a correction to the advertised range numbers at the front of my manuals, and make a small adjustment to the maximum range performance table. I realize that this is the literal definition of "your mileage may vary", but I hope that my testing and observations help satisfy the curious and careful minds in this thread. Thank you all so much for your input, and for enjoying my aircraft!
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Your dedication to the realism of your products and your interaction with your customers is second to none!
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@Black-Square Thank you for getting back to us on this. A 33% drop in expected range! Does the Piston manual have the same kind of error?
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Great question!
Well, well, well... at a quick glance, I think we found where the bad range numbers came from for the Turbine Duke. I think I accidentally swapped the two. The Piston Duke manual calls for nearly identical range numbers (at the front of the manual) to what I settled on for the Turbine Duke, while the previous Turbine Duke numbers look almost identical to the performance table numbers in the Piston Duke manual!
It's good to know that I wasn't just making up numbers from nowhere!
I want to take just as much time as I took with the Turbine Duke to review the Piston Duke's performance,
but from a first glance, the Piston Duke's range should be about 33% better than what's quoted at the top of the manual, and should be accurate to what's in the performance tables. I'm just going to refrain from quoting those numbers here, until I've had time to review the entire picture, which might happen later today. -
@Black-Square said in Turbine Duke Range:
"the Piston Duke's range should be about 33% better than what's quoted at the top of the manual"
Does this mean that the Turbine needed to go down by 33% and the piston will go up by 33%, making the piston more of a long range flyer?
Looking forward to the numbers!
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@mmcmah I think he means the turbine needs to be increased in range by 33% and the piston decreased. I know that would have helped me last night--after a 5 hour 20 minute flight from California headed to Hawaii, I ran out of gas on short final with the carrier I was going to refuel on. :P I was way behind the power curve trying to keep my landing as slow as possible, so that didn't help either.
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This is why I don't like to speak about these things until I've had a chance to look at them carefully. I now believe that the Piston Duke's range will stay the same as quoted at the top of the manual. Please stay tuned until I publish my full review of the Piston Duke's performance in one of the other threads on this forum shortly.
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@Black-Square Thank you for the update. Would you mind posting a link here to the thread where you end up putting your analysis?
