Test ride in Pipistrel electric plane

nomadpete

Well-Known Member
#5
Fair comment Octave. I rather enjoy the banter here. And sometimes stretch my mind around some of the mind boggling strides in science. Thanks.
 

Yenn

Well-Known Member
#6
I knew that the prop made a lot of noise, but that video proves it. It sounds noisier than my Corby.
Does the prop regenerate power for the battery when it glides? If not I would have expected to see the prop stopped for the final approach.
 

pmccarthy

Well-Known Member
#7
I suspect that the prop need some to spin at some idle rate to present what is effectively a fully feathered profile to the airflow. In other words, a stopped prop would steepen the glide, whereas spinning it at an idle rate would need almost no electrical power.
 

facthunter

Well-Known Member
#9
You can't get something for nothing. from an electric motor-generator. If the plane is climbing it's providing extra power to do that. If it's in level fight cruising the thrust has to be a % of the weight dependent on the planes L/D figure. On descent the engine can spin freely or if you use regenerative power, the EXTRA drag will make the descent steeper.. In a clean plane some saving may happen doing circuits if you use engine braking instead of flaps to get you down but the % of extra time in the air will never be a game changer. In say, a 7 min circuit the time getting some electricity back, At a SMALL rate would be lucky to exceed a minute and your time to circuit height at full power is full take off run plus time to downwind turn and about 60% power on downwind. so the input likely is Small bikkies in the big scheme of things. IT probably cost little or nothing to have it, but if someone is claiming BIG advantages, work it out for your self.. Nev
 

octave

Well-Known Member
#10
You can't get something for nothing. from an electric motor-generator. If the plane is climbing it's providing extra power to do that. If it's in level fight cruising the thrust has to be a % of the weight dependent on the planes L/D figure. On descent the engine can spin freely or if you use regenerative power, the EXTRA drag will make the descent steeper.. In a clean plane some saving may happen doing circuits if you use engine braking instead of flaps to get you down but the % of extra time in the air will never be a game changer. In say, a 7 min circuit the time getting some electricity back, At a SMALL rate would be lucky to exceed a minute and your time to circuit height at full power is full take off run plus time to downwind turn and about 60% power on downwind. so the input likely is Small bikkies in the big scheme of things. IT probably cost little or nothing to have it, but if someone is claiming BIG advantages, work it out for your self.. Nev
I don't think they are making extraordinary claims about how much charging is produced just a case of squeezing out every ounce of efficiency.
 

facthunter

Well-Known Member
#11
Perhaps it would be better if they were a little more specific as to the quantum of the effect, is the way I see it. They are making a "thing" of it in the advertising, so the average person would assume it's of some real significance.. On a standard cross country flight it would have no effect at all unless some descent had to be steep for other reasons. Like a mountain ridge near your destination that keeps you up high. That sort of thing is so rare it can pretty much be ignored.. You have to configure the flaps to get the approach speed back some time before you come over the fence and once you've done that you aren't interested in using the motor as a generator . Trying to do it could upset your flying priorities also. You are there to fly a plane, not charge batteries, for a brief period.. Nev
 

octave

Well-Known Member
#12
Nev they do qote some figures. I have no idea how accurate they are. I can probably post a link to a vid with an interview with the test pilot and designer. Are you saying that regen is not useful in anyway? These aircraft are being used in flying schools in Europe and a flying school in Perth. Time will tell if they are successful or not.
 

facthunter

Well-Known Member
#13
I think I've covered it already in principle. It is some advantage but could be a distraction to JUST flying the thing. Like people who creep along the road in a hybrid and talk of how little fuel they use... . IF the school modifies the way they fly to suit the plane's capability significantly it could be anti intuitive. Just something else distracting to get in the way of FLYING the plane and judging your circuit accurately and not getting in the way of others.. I'm all for electric aircraft, but I wouldn't play the regen card too much.. It's there, but in the big scheme of things, It's small bikkies. IF you are using regen on descent you COULD have descended earlier and saved cruise power usage. Nev
 

Bruce

Well-Known Member
#14
Nev is right on regen. My new electric bike doesn't have it and it would hardly help. It would only cut in during braking, if the motor could be made to work as a generator then. With suitable electronics, energy sure could be fed back to the battery but it would be very little because the time spent braking is very little.
With the Jabiru, the descents are usually shallow and take place at reduced but positive power. Maybe just at the very last moment, the prop thrust becomes negative and some negligible power would be available for regeneration.
There was once a proposal to extract energy from road traffic by having hinged flaps with hydraulic rams. The cars pushed the flaps down and made hydraulic power as they drove along. I think the proposer thought that this would give free energy. He wrote to the paper with this idea.
Mind you, if these flaps were deployed where a red light was stopping traffic anyway, the drivers would save on brakes and everybody would be happy I guess... Maybe not those who paid for the system because I bet the energy would be very expensive.
 
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octave

Well-Known Member
#15
On the Avweb vid there does not seem to be any special procedure in fact on some of the vids the passenger asks if they are using regen I cant see anything in the Avweb vid that looks to be radically different am I missing something? I think to generate a modest amount of power does not require diving towards the ground.
For a description a circuits
Pipistrel Alpha Electro: The trainer of the future? - AOPA

Several other articles do quantify the amount of regen. I can only assume that it does provide some benefit without reducing performance or safety. Would be interesting to talk to the flying school in Perth to see what their real experience .
 

Bruce

Well-Known Member
#17
Octave, my r/c electric "free flight" models use the motor to climb and then you shut it down to glide. ( My favourite models are the Dixielander and the Playboy, converted to r/c and electric )
The motor can windmill when you shut it down at the top of the climb and then it makes more drag than a stopped prop. Yes there would be energy available for regeneration from the windmilling prop, but not that much unless you did a shallow dive to keep the airspeed up. I don't think any r/c system does regeneration.

Regarding the electric trainer, I reckon its great. Students will be able to experience the "power-out" situation better. I reckon that a hitherto unknown sound of silence can and has caused pilots to panic and crash.
 

facthunter

Well-Known Member
#18
But it won't apply to other" More normal" aircraft. I'm not knocking this plane . Just quantifying the supposed efficiency gain. If you fly other types (as you are permitted to do) you had better be prepared for a significant difference in how its performance varies. Some people do this instinctively and others transition painfully..Thinking you are IN another plane is not helpful. It's more than where the blinker switch is located, stuff. If your engine fails (regardless of how noisy it is/was you must be trained to act appropriately to the situation. With electric there should be a large improvement in reliability as the INFERNAL COMBUSTION reciprocating engine is notorious for failing. It also runs out of fuel due to no fault of it's own. An Electric power unit will also run out of fuel. Planes should be operated on an energy considered basis. Height or speed interchange to a certain extent. High and fast and you must get rid of energy. Low and slow and you are in the Poo as you need energy fast.. Controlling speed with pitch is not an option then. Nev
 

spacesailor

Well-Known Member
#19
". Planes should be operated on an energy considered basis. "
You mean "61 mpg @ 100mph" American of course.
Now they're bragging 130 mph (on a little motor).
spacesailor
 

octave

Well-Known Member
#20
But it won't apply to other" More normal" aircraft. I'm not knocking this plane . Just quantifying the supposed efficiency gain. If you fly other types (as you are permitted to do) you had better be prepared for a significant difference in how its performance varies. Some people do this instinctively and others transition painfully..Thinking you are IN another plane is not helpful. It's more than where the blinker switch is located, stuff. If your engine fails (regardless of how noisy it is/was you must be trained to act appropriately to the situation. With electric there should be a large improvement in reliability as the INFERNAL COMBUSTION reciprocating engine is notorious for failing. It also runs out of fuel due to no fault of it's own. An Electric power unit will also run out of fuel. Planes should be operated on an energy considered basis. Height or speed interchange to a certain extent. High and fast and you must get rid of energy. Low and slow and you are in the Poo as you need energy fast.. Controlling speed with pitch is not an option then. Nev
Nev, what are the claimed figures? Within the stuff I posted they do quantify the expected return, I am just wondering if you have read the claims and dispute them, and if they are incorrect what do you calculate the actual return to be? I understand that plane manufacturers tend to give optimistic specs but I would be surprised if it was totally false. I can only go the published figures and various flight test videos. The manual which I have downloaded points out that the approach is slightly stepper than without regen but not dramatic. In terms of the transition from another plane, well, of course, it would be foolish to just a jump in a different aircraft. I fly a Tecnam and sometimes a pioneer 300 if I haven't flown the 300 for a while I get a check flight. This aircraft is specifically a trainer for use in the circuit., it is designed to be cheap to run and quiet enough to not annoy the neighbours. The circuit pattern does not look radically different and I imagine it would not take long for a piston engine pilot to transition, Here is a training vid of a typical circuit. It doesn't seem to vary wildly from a piston aircraft.


Nev, it doesn't bother me that you are sceptical and I am interested in what you have to say. It makes for a better discussion when the original material and facts and figures are sited and critiqued. The quoted figures may be incorrect but I would expect the flying schools operating these aircraft would have real-world experience.
 
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