Overview
The Bing Carbs along with the inlet manifold used on the Rotax 912 are a practical compromise but far from ideal, there are many aftermarket EFI systems but all share a flaw - single channel.
The Rotax 915 features dual-channel electrics/electronics or in plain language a redundant system with two means of fuel/ignition, while ideal, its complex and adds weight with the 915 tips the scales at 84 kg plus extras.
Aftermarket EFI systems have no reported history of failure, most pilots will never in their flying careers use any of the dual redundancy incorporated into a typical certified aircraft engine but this only means there is a very small statistical chance of a failure but when it is required its 100% significant to that pilot at that point in space and time.
Regardless of which EFI is used, they share one common requirement, that's for the Rotax's regulator to keep working and it's the one item incorporated into a Rotax engine that is considered a weak link. The electronics operating an EFI system use's 5 - 8 amps, leaving only 10 amps available from the Rotax alternator to maintain the battery and panel electric's so a larger alternator may be required, more weight/cost but at least there is a backup available.
The need to have an operating electrical system also means you have to have a larger [heaver] battery and the 1 kg battery that is installed will not provide the necessary flight endurance to an alternative airfield.
Note: In the event of total electrical failure there is a high drain on any battery and at 11V a battery is considered dead flat.
Dog Aviation review on the RV12 and the Standard Ducati Regulator
Photos are taken from Dog Aviation images investigating a series of
RV12 regulator failures
RV12 regulator failures
SDS EFI "Aircraft engines are essentially constant rpm load devices, spending the majority of their lives at fixed power settings for long periods of time. Once a power setting is established, the injector on-time and ignition timing remain the same until power is changed.
For this reason, we feel that 3D mapping offers no useful benefits, it merely complicates understanding and operating the system for most people"
An alternative was not available until Joe Newman from Marwen discussed with Pual from Rotec that the TBI should work with a supercharger as the new Mk2 version incorporated an internal pressure reference, at this point both agreed that they could not see a reason why it could now not operate under positive pressure, it was unproven but now worth a look, Joe had with one in his bag on his return to Rylstone.
Note: The Mk 2 Rotec TBI now an upgraded version of the proven Ellison TBI
Installation of the single Rotec TBI onto the Tucano engine was the only option as the dual TBI setup would not fit.
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| Service kit - it's that simple |
At this time the FAA approved plastic Ultem 9085 was selected to manufacture all the necessary parts using FDM printing. A lot of time was put into to optimising the design with FEA to obtain a feel for how the plastic would perform. FEA can create an unreliable results with plastics so the design parameters used were at 140 degrees C to analyse a single state, while not a 100% accurate it's better than a guess.
A Rotax 914 engine cannot be operated at greater than 88 degrees C and therefore 140 degrees C was selected as the structural design point with 100 C as a maximum operating temperature. A Rotax cam has little overlap so pressure waves from the opening of the inlet valve have been ignored as a design load.
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| Material Specification |
A 3D model estimated an assembled weight of 1.8 kg for the throttle, body/manifold/primer which is 1.2 kg lighter than the Rotax assembly it would replace.
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| Proposed Manifold/TBI/Inter-cooler 3.5 kg as shown [design weight 4 kg] |
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| Elevation |
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| Plan |
Note: A Rotax engine MUST NOT exceed 88 degrees C, so a temperature probe is to be installed at the inter-cooler outlet allowing the temperature to be monitored.
The biggest issue at this time is this may not work, why, the Mk 1 Rotec will not operate under positive pressure but the Mk2 may because of a major design change Joe from Marwen noted at Oshkosh.
To prove the design a 3D printer will be purchased early next year to manufacture a working prototype and it up to both of us to prove it works as a system. If it does work it will be 2/3 the price of an injection system and lighter - worth the look.
If it does not work back to the drawing board and on go the Bings.
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| Meshing basic manifold |
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| Stress at peak [red] about 4 Mpa with 20 Mpa on Z axis allowable at 140C Simple manifold used as this is within the limits of the package available The model has a 3 mm thick wall, a wall thickness of 2.5 would be acceptable |
Comment
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| What if, what if? |
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