Joshhartung
New Member
Hi folks,
Just joined so please forgive - this is my first post. I just bought an Avid Mk4 and it's got a new Rotax Rick 618 on it. I'm planning on running this for bombing around the Palouse area for a while but I really don't want to take it over trees or into the backcountry. I think I'd like to eventually convert to one of these Yamaha engines with the Skytrax gearbox on it. It's an attractive package considering weight, power, and of course, price.
For that reason, I'd like to start a conversation regarding safety of the non-mechanical systems. I haven't been able to find much on this. In my estimation, there are two critical areas of redundancy lacking in these conversions: ignition and fuel injection. Let's forget carburetors in this discussion - operationally a fuel injection system is superior in every way.
First, it seems like ignition is covered well enough for the 3 and 4 cylinder engines since each cylinder has an independent coil. Failure of any single cylinder ignition system should not completely disable the engine. Please correct me if this is a bad assumption.
Second (and linked with ignition) is the EFI system, which consists of pumps, sensors, injectors, and compute. Let's look at these systems individually:
Pump: in EFI systems I'm familiar with there are usually two pumps: a low pressure pickup in the fuel tank and a high pressure injection pump. It seems reasonable that one could install a redundant high pressure injection pump that could be manually (or automatically - more on that later) activated in case of the failure of the primary. I assume that most of these conversions omit the low pressure pump in favor of gravity feed.
Sensors: There are multiple algorithms for fuel injection and I'm unfamiliar with the one that Yamaha EFI uses (please enlighten me). Depending on the algorithm, certain sensors are required while others are used for optimizations such as fuel trim. I'm imagining though, that all sensors should be able to be installed in parallel such that one could make the critical ones redundant. I'm thinking it would likely be MAF, O2, and temperature. Am I missing any?
Injectors: Due to mechanical constraints (no place to mount them), I don't think you could mount redundant injectors. However, in the case of failure of a single injector we have redundant cylinders so we should be able to get home or to safety with "limp" power similar to the failure of an ignition system. Thoughts?
Compute: The EFI computers in these snowmobiles were clearly not engineered for safety critical applications so in order to have a safe system we'll need a fully redundant computer and the ability to confirm that it's actually working either at run-up or real-time during operation.
Why break the system down in this way? I'm thinking that what's needed here is a "safety controller" that would manage switchover to redundant components - either sensors, pumps, or compute. The controller would need a way to monitor the operational status of these components and to keep the backup components "hot" (especially the EFI computer) so that switchover would be instantaneous. It could also perform "wear leveling" where the active components were switched every other flight so that you don't end up with components either wearing out early or failing due to lack of use.
Just spitballing here, but are any of you aware of any work in this area OTHER than complete aftermarket EFI systems (such as SDS)? I feel like the off-the-shelf components are usually of very high quality and tuned for their respective engines very well already. We just need a way to provide some redundancy.
Just joined so please forgive - this is my first post. I just bought an Avid Mk4 and it's got a new Rotax Rick 618 on it. I'm planning on running this for bombing around the Palouse area for a while but I really don't want to take it over trees or into the backcountry. I think I'd like to eventually convert to one of these Yamaha engines with the Skytrax gearbox on it. It's an attractive package considering weight, power, and of course, price.
For that reason, I'd like to start a conversation regarding safety of the non-mechanical systems. I haven't been able to find much on this. In my estimation, there are two critical areas of redundancy lacking in these conversions: ignition and fuel injection. Let's forget carburetors in this discussion - operationally a fuel injection system is superior in every way.
First, it seems like ignition is covered well enough for the 3 and 4 cylinder engines since each cylinder has an independent coil. Failure of any single cylinder ignition system should not completely disable the engine. Please correct me if this is a bad assumption.
Second (and linked with ignition) is the EFI system, which consists of pumps, sensors, injectors, and compute. Let's look at these systems individually:
Pump: in EFI systems I'm familiar with there are usually two pumps: a low pressure pickup in the fuel tank and a high pressure injection pump. It seems reasonable that one could install a redundant high pressure injection pump that could be manually (or automatically - more on that later) activated in case of the failure of the primary. I assume that most of these conversions omit the low pressure pump in favor of gravity feed.
Sensors: There are multiple algorithms for fuel injection and I'm unfamiliar with the one that Yamaha EFI uses (please enlighten me). Depending on the algorithm, certain sensors are required while others are used for optimizations such as fuel trim. I'm imagining though, that all sensors should be able to be installed in parallel such that one could make the critical ones redundant. I'm thinking it would likely be MAF, O2, and temperature. Am I missing any?
Injectors: Due to mechanical constraints (no place to mount them), I don't think you could mount redundant injectors. However, in the case of failure of a single injector we have redundant cylinders so we should be able to get home or to safety with "limp" power similar to the failure of an ignition system. Thoughts?
Compute: The EFI computers in these snowmobiles were clearly not engineered for safety critical applications so in order to have a safe system we'll need a fully redundant computer and the ability to confirm that it's actually working either at run-up or real-time during operation.
Why break the system down in this way? I'm thinking that what's needed here is a "safety controller" that would manage switchover to redundant components - either sensors, pumps, or compute. The controller would need a way to monitor the operational status of these components and to keep the backup components "hot" (especially the EFI computer) so that switchover would be instantaneous. It could also perform "wear leveling" where the active components were switched every other flight so that you don't end up with components either wearing out early or failing due to lack of use.
Just spitballing here, but are any of you aware of any work in this area OTHER than complete aftermarket EFI systems (such as SDS)? I feel like the off-the-shelf components are usually of very high quality and tuned for their respective engines very well already. We just need a way to provide some redundancy.
