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octave

Test ride in Pipistrel electric plane

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Sorry to be pedantic Octave, but I think you probably meant to post this in the other forum.

No offence intended.

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Sorry to be pedantic Octave, but I think you probably meant to post this in the other forum.

No offence intended.

 

Actually no, I did intend to post it here as a technology post. I seldom contribute to the other place.

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Fair comment Octave. I rather enjoy the banter here. And sometimes stretch my mind around some of the mind boggling strides in science. Thanks.

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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.

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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.

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This aircraft has a new design of prop which is optimised for thrust and regen

 

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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

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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.

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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

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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.

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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

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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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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 .

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It just occurred to me that the flaps could be used on downhill grades too...

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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.

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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

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". 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

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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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Regen performance with different propellors

 

An Optimal Propeller Design for In-Flight Power Recuperation on an Electric Aircraft

Pipistrel reduces by 6% the energy consumption of an electrical aircraft by optimizing its propeller with FINE™/Turbo

 

Full paper at An Error Occurred Setting Your User Cookie

 

678696346_Pipistrel4.thumb.png.299c0608da344cae82fd83b852b71b28.png

 

 

620686779_Pipistrel5.thumb.png.5fd18d7858dd70d1ae6ebd2caab67d6c.png

I would imagine these figures were obtained under ideal conditions with a test pilot and therefore may not be realised in everyday flying.

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There's NO area of aviation where excessive performance claims are let go without challenge so questioning them is certainly warranted particularly with the experience of them In U/L's in the past In general terms it has been bordering in utter deception particularly with "CLAIMED" stall and cruise speeds and climb rates of many models.

I've fully explained exactly where the logic is of this is and the small savings that are likely to be obtained. Flying schools operating these may be seen to have a vested interest (maybe and most likely) in promoting their acquisition. They are hardly likely to want to be over critical of the brand they use... I don't care WHO makes a plane that has electric regen. The issue is the same. There's not much opportunity to get back significant amounts of energy in NORMAL operations.. If you are dropping parachutists, yes. Re entering from space Yes.Going for an altitude figure yes. Hypothetically it's possible to get SOME energy back but in a normal x country or even circuits It's a small % by any reasonable analysis, and if you delay flap extension, or descent point or deviate from any normal technique to do it it's an extra THING to occupy your attention not worth the energy you might get by doing it.

Read all that stuff carefully. They are comparing it with "other" propellers and doing a 500' circuit I get the regen% at less than 3. for the best example.. Actually if you follow their logic at the regen rate all the way down you could fly forever. It's promotional material and sounds like so much of what we constantly get. Aeroplanes obey the laws of physics ,like everything else.. Perpetual motion is imaginary. Nev

.

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I've fully explained exactly where the logic is of this is and the small savings that are likely to be obtained.

 

I agree these are likely to be small savings. I believe in their literature they quote 13% "theoretically" of course we know that manufacturers will provide the most advantageous figures they can calculate.

I am happy to accept your calculations of 3% The modern car is a lot more fuel efficient than the car of 30 years ago. These improvements happened in small increments. A car designer would be pleased with a 3% improvement in economy.

 

I think your other criticism was if I understand you correctly that because of regen the flying technique would be so different that it may endanger a pilot who has trained in this aircraft when they fly a more standard plane. I learnt to fly in a Thruster then transitioned to a Gazelle and now I fly a Tecnam or occasionally a Pioneer 300. When you pull the power on approach all of these aircraft behave differently. A pilot who learns to fly in a slippery aircraft and then transitions to a draggy machine needs to be taught to get that nose down before reducing the power.

In any aircraft, I have flown, landing is about the pitch and power - (sorry not trying to tell you how to suck eggs). I don't really see that there is a world of difference. In any of these aircraft approach speed is king. If in your electro you if you are maintaining your 60 knot approach speed and because of a steepened approach due to drag from regen you find yourself low then you bump up the throttle 10% giving you no regen so less drag and slightly more power. I don't doubt that there are probably some techniques that are different in this aircraft but the differences between a thruster and a rutan varieze are also important. I guess my point is requiring a different technique should not stand in the way of progress.

 

 

I started this thread specifically in this forum rather than the other one because I was hoping for a broader discussion on technological progress. We seemed to have gotten bogged down in one aspect. I mean for all I care they could remove the regen function or they could just call it an airbrake. I am more interested in the big picture.

 

I am not a Pipistrel fanboy but I do like that they seem keen to invest in progress, whether it be the 4 seater electro or the more ambitious 12 seater hydrogen plane. I believe that the future of most areas of aviation will NOT be battery powered but this training aircraft designed for circuit use not cross country is a good thing and a necessary step along the way to further progress.

 

nomadpete was probably right, I may have generated a broader conversation on the other forum.

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Octave, I really think you should read what I've put out a little more carefully. I did qualify everything I said and that article like so many is making excess claims. I would suggest it's even misleading. The regen rate (maximum) is the same as the thrust rate but to GET that rate your extra drag would be more than the max thrust figure considering that a propeller designed to generate would have the flat surface on the other side to normal. It would come down like a brick if you were to try to get the full re gen rate because you would have the normal sink rate for a glide which on that plane would probably be as little as 350 ft/min clean PLUS a drag figure effect of a force greater than the thrust at full power in the opposite direction potentially. Someone will try this as sure as day follows night,. just because they CAN..Nev

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It would come down like a brick if you were to try to get the full re gen rate

 

It may be more accurate to phrase this "if you come down like a brick you will get full regen (not sure what you mean by full regen)"

 

"Whilst I accept that a company selling a product may exaggerate or lie this has not been my only source of information. A search of the net does turn up academic papers and conference presentations such as "Matthew D. Olson. "A Conceptual Approach to Flight-Training Mission and Cost Analysis of an All-Electric Aircraft Equipped with Regenerative Energy Devices", Georgia Institute of Technology

I can only read the first page but I have ordered the rest (not to have an argument but because I genuinely would like to learn more).

Of course, I do need to carefully read the whole paper when I get it but it dose say

 

"Incorporating energy recapture devices improves mission performance by increasing overall at the expense of greater cost and complexity, but large uncertainty as to the device cost and performance exists. They were not considered vital for mission accomplishment in the current state of technology and accounted for 5.4% of the total mission energy requirement"

An Error Occurred Setting Your User Cookie

 

It will be interesting to read the whole thing. Now, this is neither a ringing endorsement for regen of various types but it also would suggest that it is not a ridiculous idea.

 

Here is a clip of a circuit in a electro. From the 7 minute mark, you can see base, final and touchdown. During this time mild regen cuts in and out and for much of time is at net 0. The approach does not seem extraordinary.

 

My position is this. The company probably exaggerates, possibly quoting the figures obtained a skilled pilot in ideal weather. Interestingly in the clip with Paul Bertorelli from Avweb he asks if there is any regen whilst landing and there was none because the gusty conditions called for an approach with some throttle. So I suspect that at this stage its advantages are probably minimal and a lot would depend on the cost to benefit.

I do not believe that it makes this aircraft into a death machine (slight exaggeration of what you are saying). Whilst the notion that an inexperienced pilot might be chasing regen by lowering the nose too much it is also possible that I could look at the fuel flow meter in the Tecnam and decide that if I poke the nose down I will reduce the fuel flow but of course if I reach the ground before the runway I am in trouble

Anway pending any new information I am probably done.

 

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