I think it’s something like the engine of a chainsaw, or similar “gardening engine”, that can use up to 4/5% of oil
back
2 comments
Sure, but the whole point of reducing the oil percentage in two stroke engines has been (since like 40 years) to reduce the formation of carbon in the combustion chamber and - particularly - to have cleaner spark plugs (which imply better ignition) besides better combustion.
Less oil in the mix (as long as lubricating is sufficient) is better.
The traditional 4-5% is for mineral oils.
Synthetic (totally or partially) oils can usually go on 2% (or 50:1) and in some cases as low as 1% (or 100:1).
Modern chainsaws and similar are already at 2%, see (examples):
https://www.stihlusa.com/information/how-to-guides/mixing-oi...
https://www.husqvarna.com/au/forest/when-working/usage/how-t...
https://www.amsoil.com/p/outboard-100-1-pre-mix-synthetic-2-...
Ignition in an engine for airplanes/drones/etc. is - obviously - much more important than in a common 2 stroke engine (chainsaw or similar), a "common" 2-stroke engine used in ultralights is the Rotax 582 (an earlier model was the 532) check its "limitations":
https://en.wikipedia.org/wiki/Rotax_582
The 582 has twin sparks (two spark plugs per cylinder) and runs on 50:1 mix:
Might be for safety reasons, an engine seize in a flying drone would be catastrophic and dangerous compared to merely inconvenient as in most small engine applications.
OTOH, piston scoring from burning oil will probably increase the chance of a lock up over time.
Except the onboard combustion engine is just to generate electricity, no? An engine sieze means you just have to land quickly.
That is true for HYBRiX, but there are other hybrid multirotors, which do not have a design well-balanced enough to being able to stay aloft on just batteries (batteries to lift a 25kg MTOW drone are heavy, so the drone needs to be very light, while still robust, to work properly.. it is tricky ;)
For reference, the Stihl chainsaw I just purchased had a 50:1 gasoline to oil mix. That is 2%, of course there are probably 25:1 or 20:1 engines out there as well.