Great storyteller, but not exactly a reliable source for science, or much of a role model. (Didn't give credit to the writers on his radio show. For the longest time I thought he wrote all that material. He didn't.)
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Electric planes
- Thread starter doug
- Start date
-
- Tags
- Electric Vehicles
Great storyteller, but not exactly a reliable source for science, or much of a role model. (Didn't give credit to the writers on his radio show. For the longest time I thought he wrote all that material. He didn't.)
Etna
Member
Sure but the 737-800 is not a short range regional turboprop aircraft like electric airplanes can only ever pretend to be.
All short range regional airplanes have their max landing weight equal or pretty close to their max takeoff weight.
Any case you could design a 737-800 having its max landing weight equal to max takeoff at the structural cost weight of a payload equivalent to a row or two of seats. Nobody does that because it is an entirely different set of design constraints.
That's basically moving the goal posts from "best selling commercial aircraft of all time" to "crappy airplane but look at the specs....they're crappy too!"
Also, you have taken my example out of context. Several people were claiming that aircraft landing weights are normally the same as their takeoff weights. I cited the NG 737-800 as a prime example that most successful commercial aircraft have takeoff weights well above their landing weight since fuel is burned off during flight. Point proven.
The fact that the landing weight does not reduce from takeoff weight, is going to limit the payload capacity and range of EPs. There is no getting away from that. Unless it sheds battery modules like a multi stage rocket 
Etna
Member
All short range airplanes, from crappy to outstanding, have their landing weight near their takeoff weight, it is just a fact and primarily a result of different fuel mass fraction requirements at max payload (10%-ish versus 25%-ish) and typical mission fuel burn.
The 737-800 is not a short range aircraft so you simply cannot make that comparison.
Plus, it does not matter anyway. Electric airplanes face a long list of challenges, and this landing weight deal ranks very low behind more important issues like battery energy density, power distribution, thermal management, etc.
Etna
Member
No it would have zero effect.The fact that the landing weight does not reduce from takeoff weight, is going to limit the payload capacity and range of EPs. There is no getting away from that. Unless it sheds battery modules like a multi stage rocket
Let's say you want to carry 10 passengers or a payload of 2500 lb. And you have 2500 lb of batteries. Plus you consider an empty weight mass fraction of 50% (typically it is 60% but let's keep the calculations simple). Then the takeoff weight would be 2500 lb payload + 2500 lb batteries + 5000 lb empty weight = 10000 lb takeoff weight.
Now, the empty weight includes structures weight and systems weight. There will be a structures weight penalty relative to conventional airplanes resulting from this higher takeoff weight. This weight penalty will only exist in reality when comparing to long range airplanes (which typically have a lower empty weight mass fraction in part due to this). But for the sake of this analysis, let's say that we need to beef up the structure because the landing weight needs to be 10000 lb instead of 9000 lb. The resulting landing gear and airframe weight penalty would be on the order or, say a crazy high 500 lb (reality is less than 100 lb out of 5000 lb empty weight).
So your empty weight now is 5500 lb. Oh my god, we need to reduce the payload by 500 lb and we lose two seats payload capacity!!! The sky is falling!!! This is not feasible anymore!!!
Just. Relax.
Instead, you increase to the takeoff weight to 10500 lb and you get your 2500 lb payload capacity back.
Now you tell me you need more power and more batteries to get the same range and performance, and that's correct. Let's say to keep it simple you need 3000 lb of batteries and 500 lb more weight on the propulsion system, and another 1000 lb structural weight penalty to carry all that.
So now we end up with 2500 lb payload + 3000 lb batteries + 6500 lb empty weight = 12000 lb takeoff weight.
Done.
See how I got away from impacting payload capacity and range of an EP? Zero impact. Nada. Nice trick isn't it?
Aircraft has same range since it has the same battery weight fraction of 25%.
That specific process is a subset of what is called "aircraft sizing". There are a few books written on that topic but very few aerospace engineers actually practice it.
I'm not sure I followed all that, but I think you "solved" the problem by making the airplane bigger. Which means it's more expensive to build, buy, and operate. Kind of like saying a Civic could carry as many people as an Escalade if you just made the Civic bigger.
But it's all moot, because the weight loss during flying of a conventional airplane is small compared to the weight penalty of an electric plane because batteries weigh so much more than hydrocarbon fuel.
Etna
Member
Right, keeping in mind that I "solved" a problem that does not exist in the first place. Short range airplanes already account for a landing weight at or very near takeoff weight.
However, to get any meaningful range, electric airplanes must be designed like long range airplanes when it comes to fuel weight or battery weight fraction at maximum payload. It has to be increased from a short-range typical 10% to long-range-class 30%. And that leads to a massive increase in takeoff weight, on the order of 50%, using a similar process as described above. It is for this reason that a 19 passenger electric aircraft is physically not possible to design and certify under the Part 23 limit of 19000 lb.
As Tesla has shown, it is possible to design an electric car that weighs the same as a ICE car and still have decent (not the same) range. I don't think this is possible at all for an electric aircraft, barely acceptable range will come at a cost of significantly higher weight.
Compared to a conventional aircraft, the electric aircraft is likely to be more expensive because it is so much heavier, but you still get a drastic reduction in operating costs and zero emissions, which is what this is all about.
ok buddy, keep moving the goalposts and concentrating on crappy airplanes.
Nobody will ever want them and the economics will never make sense, but hey you've got that market cornered!
JRP3
Hyperactive Member
petit_bateau
Active Member
I have actually done aircraft sizing, and I agree with the thrust of your excellent responses. There are a lot of challenges, but they will be progressively overcome.
However and for accuracy, whilst the recent 737-800 may not now be a short range aircraft, the 737 series and the A320 were originally conceived as being of short range, "fifty to sixty passenger airliner flying routes of 50 to 1,000 miles".
Etna
Member
We probably have common acquaintances, or even know each other. I would say the same about @MadScientist23 as we all know this is a small world.I have actually done aircraft sizing, and I agree with the thrust of your excellent responses. There are a lot of challenges, but they will be progressively overcome.
However and for accuracy, whilst the recent 737-800 may not now be a short range aircraft, the 737 series and the A320 were originally conceived as being of short range, "fifty to sixty passenger airliner flying routes of 50 to 1,000 miles".
Yes by short range I should maybe point more specifically to regional turboprops to which future all-electric airplanes bear more resemblances. Short range jets like the CRJ burn a lot of fuel at low altitudes and all they need is taxi, takeoff and fly a long approach and they already are at 5% below max takeoff, which explains why they don't typically have fuel dump capability.
I worked for Bombardier as an engineer at the Learjet plant and the flight test center for about 14 yrs.
I recommend those that are interested in airplanes that don't go very far, don't carry much payload, and are ridiculousy expensive start a new thread.
You could call it "airplanes that don't go very far, don't carry much payload, and are ridiculousy expensive" or for brevity "airplanes that suck".
.
You could call it "airplanes that don't go very far, don't carry much payload, and are ridiculousy expensive" or for brevity "airplanes that suck".
.
swaltner
Active Member
See the Pipistrel Taurus Electro. I have one. It's got a 40 kW motor (actual peak output is something like 33 kW), which is enough to climb at a decent clip up to soaring altitude. Battery runtime is something on the order of 20-25 minutes. It's got battery power for 8,000' of climb - enough for a few launches to 2,000' or a full day of flying if you're able to find some thermals.
There's also the GP Gliders GP15 JETA - a single-place racing glider with self-launch capabilities. Jonker Sailplanes has a version of the JS3 with an electric sustainer/self-launch motor on it. Lots of gliders that have pure "sustainer" electric motors - a sustainer has power to climb while already in-flight, but not enough power to self-launch. Many gliders use the FES (Front Electric Sustainer) System as the sustainer motor.
There are a couple trainers that people would recognize as traditional aircraft on the market now, but the longest runtime I have seen is right at an hour. That's enough for you to do training up to your cross country flights in training for a pilot license, but until the runtime is longer and there are standardized fast chargers at airports, not really practical for flying. Nothing wrong with that, just the current state of the market with the current battery technology.
lolachampcar
Well-Known Member
I was keenly interested in that UK glider with the bushless hub motor in the single central wheel to get it rolling down the runway followed by a small ducted turbine for climb/sustain. It never really went anywhere. I would be kinda neat to pull the VW in my Stemme and put in an electric power plant but that would significantly degrade that plane's capabilities.
I've lived long enough to see cars come to fruition. I'm hopeful to see at least small planes as well.
I've lived long enough to see cars come to fruition. I'm hopeful to see at least small planes as well.
JRP3
Hyperactive Member
Since this thread title doesn't specify range at all I recommend you start a thread about long range electric planes only if you're so motivated. This thread is just fine as it is.
I predict that for the foreseeable future electric planes will remain hobbyist toys. I do not mean "toy" in a pejorative sense. Rather, as something that people use for fun in their spare time. Just as most people don't buy the most economical car, a hobbyist pilot might be willing to pay more for a plane that appeals to them for reasons other than economics. If I were a hobbyist pilot, I'd much prefer electric.
I once visited an RC plane club that flew gliders and electric-take-off gliders. As @swaltner mentioned upthread, that's another very real option for the hobbyist: A glider that can take off using its own electric power, and get a power assist when needed.
There's a market for electric planes. Just not the commercial passenger market where cost is critical. (Small, short-haul electric commercial planes are possible, but I don't believe they'll ever be more than a novelty.)
I once visited an RC plane club that flew gliders and electric-take-off gliders. As @swaltner mentioned upthread, that's another very real option for the hobbyist: A glider that can take off using its own electric power, and get a power assist when needed.
There's a market for electric planes. Just not the commercial passenger market where cost is critical. (Small, short-haul electric commercial planes are possible, but I don't believe they'll ever be more than a novelty.)
Similar threads
