I have done all the groundwork for this exercise with a Rutan Quickie (Q1) and have the aircraft and the electric powertrain donor in my hangar. The project is currently awaiting more of my time (unlikely for a year or two). I would like to humbly pass on some suggestions/observations:
1. Scope out the minimum power requirements (take-off, cruise) and the propeller RPM range you will accept for full power delivery. For instance, on the Quickie, 3500 rpm is what the original 18-22hp engine used due to prop sizing and tip speed constraints. Convert your brain and calculations from hp to kW (1kW = 1.34hp). The Q1 needed about 16kW for take-off at MGW and needed 8kW for cruise. I then hunted for a long time trying to find the perfect motor that would deliver these parameters. You will be severely weight-limited in this project due to energy density constraints of electric batteries so chances are you need to dismiss a propeller speed reduction unit at the outset. Look for a direct drive arrangement i.e. Prop RPM = motor rpm. 2. In parallel with this, the maximum battery+motor weight available in the airframe of choice must be considered. In simple terms, add up the weight of all the unneeded current gas engine components and the max fuel capacity weight. That will be your starting point for total weight available for the electric motor, controller, and battery (which may or may not contain the battery management system - BMS). Then add anything left over from full fuel payload with the specific pilot in mind. 3. Now calculate the maximum battery capacity available for the weight you just calculated (minus the motor weight). This is where you will have your first reality check. For instance on the Q1, The original engine plus full fuel added up to ~120 lbs. I’m a light pilot, so I managed to get another 75 lbs of payload capacity to bring it up to MGW. The electric motor was ~37lbs, motor controller another 10 lbs, leaving 148 lbs for batteries. 4. Now comes the maybe demoralizing part. Energy density in a very good battery PACK (including all the casing and essential safety connectors etc) is ~12 lbs/kWh. Don’t be seduced by data about just the individual cells. So 148 lbs = 12.3 kWh. I think 5 mins at T/O (max) power is a reasonable requirement, then the rest of the flight can be calculated at best endurance speed or range speed depending on your goal. If you can honestly get take-off power (5mins) plus cruise endurance to give you more than 1-1.5 hours you’re doing well. For example, on the Q1, takeoff power is 16kW for five minutes uses 1.3 kWh. Subtract that from the maximum battery capacity calculated in para 3 and you have ~11 kWh remaining. Cruise at 8kW will give another 1.375 hrs, or 1hr 22.5 mins. No reserve. Total flight time until the motor stops ~1.5 hours. 5. Perhaps now, the reason I chose a Quickie design is becoming clear. These numbers work for a super-efficient aircraft that only needs 8kW to maintain cruise speed. I don’t know the numbers for the KR, but is the available battery weight capacity going to make up for the higher cruise power requirement? 6. Implications. Due to the need to have the maximum possible battery capacity onboard, you will probably be at MGW THROUGHOUT THE FLIGHT AND LANDING. Think hard about this. How does your KR fly at MGW? This is how it will behave whether you have a full battery charge or nearly empty. This is not a trivial consideration. 7. Now for the good news. After diving down many Chinese electric motor website rabbit holes I stumbled on the powertrain from Zero motorcycles based right here in the USA (Santa Cruz/Monterey, CA). A year or two later, I managed to afford a 2014 Zero SR which had the particular motor I was interested in and came with an 11.4kWh battery pack as standard. It then dawned on me to use the whole powertrain from the motorcycle, not just the motor and battery. This solves the motor controller choice, the ’throttle’ controller, the battery pack and battery management system all in one go. The powertrain can wake up and not realize it isn’t a motorcycle…I think this will save years of development work from the project, you just need to find a Zero model that matches your requirements. You can always optimize it later. If the above excites your curiosity and doesn’t put you off, then please go and succeed or learn while failing. I am a hard-over disciple to this idea, even though it may seem I am trying to discourage you. Coincidentally, I have a beautiful working (I ride it now and again) 2014 Zero SR motorcycle for sale as I figure I can just buy another one in a year or two when I have the time to move my own project forward. I’m not sure the specs will be sufficient for a KR project (67 hp, at 3500 rpm) but that’s for you to decide. You may need a newer, more powerful model. Good luck, I look forward to hearing how it goes. Tristan KR-1 project (95% done) Rutan Quickie (minus FWF) electric project Cozy IV regular flyer. > On Jun 14, 2020, at 12:54 AM, Gary Sack via KRnet <krnet@list.krnet.org> > wrote: > > I will go one further and offer 81JM as a test bed to anyone who can put > together a credible plan to electrify her. She is currently flying with all > basic instruments working. > > On Thu, Jun 11, 2020, 11:36 Mike Stirewalt via KRnet <krnet@list.krnet.org> > wrote: > >> >> Someone in the initial thinking/designing phase of a KR project might >> consider using electric power instead of our tried and true engines. >> Pipestrel just got their trainer approved by EASA and the FAA can't be >> far behind. Once the gate is open there will be a flood of electric >> planes getting certified and hitting the market. None of us with engines >> would give up our known power sources but for someone thinking of >> building . . . I haven't looked into it be just from general impressions >> an electric motor, maybe one taken from a wrecked Tesla, hooked up to a >> self-sought controller and batteries and other components . . . Pat >> Panzera probably already knows someone in the LSA or Experimental field >> putting together turn-key electric propulsion solutions for homebuilders. >> Electric planes are good only for training or flying around the ranch >> but Pipestril is saying they'll have a four-seater with three hours of >> range certified a year from now. Their EASA certification arrived a year >> earlier that they had been projecting so this technology is moving fast. >> In ten years I would expect fast chargers sitting next to the fuel bibs >> at just about any airport except the smallest. >> >> Just an observation prompted by the Pipestril certification. Electric >> power is the future, and not that far away. The KR is a slick fuselage >> with a wing that carries a lot of weight without much trouble - >> relatively perfect. If someone were to buy NVAero and start thinking >> electric our KR designs will be part of the evolution. >> >> Mike >> KSEE >> >> >> >> _______________________________________________ >> Search the KRnet Archives at >> https://www.mail-archive.com/krnet@list.krnet.org/. >> Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. >> see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change >> options. >> To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org >> > _______________________________________________ > Search the KRnet Archives at > https://www.mail-archive.com/krnet@list.krnet.org/. > Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options. > To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. 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