PROs and CONs of Engine Choices

[nyrikki]

OK I found more data in my docs and wanted to ask for more input.

The 914 at 75 % continuous performance is 5.4 gph and continuous HP is ~98.5 HP and 75 % ~74 HP. Rated at 80 HP continuous the x340 burns 5.5gph at 75%.

From the Rotax 914 user manual PDF


While the docs are harder to find now that conti owns the titan brand the earlier EFI/CDI claim was 5gph at 80hp but 5.5 seems more typical from guesses from the carbon cub users and some loose math.

Obviously not having a continuous prop and the induced drag from the extra weight will impact this significantly but the burn rate is pretty close at lower power ratios may actually slightly favor the 340 at lower airspeeds. Purely because of timing + efi.

Feedback would be appreciated as my soon to be home airport is 7142' MSL and the 914 is only normalized for takeoff to 8000' I am concerned that some work will be in the less than linear part of the power band as the ECU will be limiting boost on fairly typical days DA and obviously I will be past that value at pattern altitude.

Hopefully someone will talk some sense into me to shoot for that useful load, but it is unclear if that 8000' limit is just a limitation of the turbo and power drops in a predictable fashion or if the ECU is limited on pressure differential and power could drop by a large fraction when the waist gate is opened.

I can deal with the implications of DA but with the reported non-linearity of the boosted power band of the 914 and the fact that I will hit their normalized limit when getting to pattern altitude even under standard conditions it is a bit concerning.

I may be overthinking this as the SS7 with the 912ULS is set to a service ceiling of 16K which I assume is when climb drops below 300fpm and the 914 ceiling has been reported at 25,000' so it is really concerns about an abrupt change in behavior by the waste gate being opened.

To be honest the 912ULS may be fine but without hard climb numbers at around 10K DA I am planning on erroring on the expensive/heavy side.