5 ms·

I'm curious if anyone here can answer this: what part of flight consumes the most energy/fuel? Is it the take-off? Landing? Cruising? So would a hybrid model pl

I'm curious if anyone here can answer this: what part of flight consumes the most energy/fuel? Is it the take-off? Landing? Cruising? So would a hybrid model plane make sense to use jet fuel or equivalent for the most energy consuming part, then electric batteries for the least intensive parts?

knodi123 7y ago
take-off uses far more fuel per ground-miles travelled, because in addition to trying to go forward, you're also lifting hundreds of tons of steel, several miles into the air. but take-off and cruise use probably ROUGHLY the same amount per minute flown - because why waste time cruising at a significantly lower power setting? > So would a hybrid model plane make sense to use jet fuel or equivalent for the most energy consuming part, then electric batteries for the least intensive parts? Not at all, because energy is just energy, and full batteries weigh just as much as empty ones, but full fuel tanks weigh a LOT more than empty ones. And empty ones are more efficient to keep aloft. cite: https://www.usatoday.com/story/travel/columnist/cox/2014/11/02/fuel-efficiency-passenger-jets/18196493/ https://www.usatoday.com/story/travel/columnist/cox/2014/11/...
- pininja 7y ago
  > but take-off and cruise use probably ROUGHLY the same amount per minute flown - because why waste time cruising at a significantly lower power setting? Breaking it down in my head, I come to a different conclusion. Engine power during cruise can maintain higher speeds at less power compared to takeoff. The wing generates lift most efficiently at the designed cruise speed when not changing altitude. Lower power at cruise doesn’t mean poor time trade off. Since the power is lower the energy (fuel burnt per minute) should be lower during cruise.
  - p_l 7y ago
    the relationship between fuel efficiency and power isn't linear, especially in turbine engines - the most fuel-expensive per minute periods for passenger planes are taxiing, to the point that there are at least two options on market for electric taxi motors so that engines are started only just before the runway. Also, you need that power for emergencies. Including separate "maximum power possible" that rips engines apart that is needed on current twin jets.
  - knodi123 7y ago
    > Engine power during cruise can maintain higher speeds at less power compared to takeoff. Maintain _which_ higher speeds? The ones that are lower than they could be? Yes, a plane can generate lift more efficiently when not climbing. But it can generate more speed with more power - so why would it not generate more speed if it has power to spare?
pininja 7y ago
I think it’s takeoff, regardless of the power plant in the aircraft. Fueled planes are heaviest when taking off, and fighting gravity, and Electric are still fighting gravity.
_ah 7y ago
Also: regardless of acceleration or climb, air resistance is a major factor. This is why most aircraft cruise at 30k-40k feet. Flying the same route and speed at 5k feet burns significantly more fuel.
Robotbeat 7y ago
For long-haul, it's cruise. And the energy required can thus be improved directly proportional to lift to drag ratio. What I find promising is work NASA is doing and has done on truss-braced wings to enable a ~doubling of current transonic lift to drag ratios by using an extremely high aspect ratio wing.
- yboris 7y ago
  Truss-braced wings seem really cool! https://en.wikipedia.org/wiki/Boeing_Truss-Braced_Wing https://en.wikipedia.org/wiki/Boeing_Truss-Braced_Wing

knodi123 7y ago

take-off uses far more fuel per ground-miles travelled, because in addition to trying to go forward, you're also lifting hundreds of tons of steel, several miles into the air. but take-off and cruise use probably ROUGHLY the same amount per minute flown - because why waste time cruising at a significantly lower power setting? > So would a hybrid model plane make sense to use jet fuel or equivalent for the most energy consuming part, then electric batteries for the least intensive parts? Not at all, because energy is just energy, and full batteries weigh just as much as empty ones, but full fuel tanks weigh a LOT more than empty ones. And empty ones are more efficient to keep aloft. cite: https://www.usatoday.com/story/travel/columnist/cox/2014/11/02/fuel-efficiency-passenger-jets/18196493/ https://www.usatoday.com/story/travel/columnist/cox/2014/11/...

pininja 7y ago
> but take-off and cruise use probably ROUGHLY the same amount per minute flown - because why waste time cruising at a significantly lower power setting? Breaking it down in my head, I come to a different conclusion. Engine power during cruise can maintain higher speeds at less power compared to takeoff. The wing generates lift most efficiently at the designed cruise speed when not changing altitude. Lower power at cruise doesn’t mean poor time trade off. Since the power is lower the energy (fuel burnt per minute) should be lower during cruise.
- p_l 7y ago
  the relationship between fuel efficiency and power isn't linear, especially in turbine engines - the most fuel-expensive per minute periods for passenger planes are taxiing, to the point that there are at least two options on market for electric taxi motors so that engines are started only just before the runway. Also, you need that power for emergencies. Including separate "maximum power possible" that rips engines apart that is needed on current twin jets.
- knodi123 7y ago
  > Engine power during cruise can maintain higher speeds at less power compared to takeoff. Maintain _which_ higher speeds? The ones that are lower than they could be? Yes, a plane can generate lift more efficiently when not climbing. But it can generate more speed with more power - so why would it not generate more speed if it has power to spare?

pininja 7y ago

I think it’s takeoff, regardless of the power plant in the aircraft. Fueled planes are heaviest when taking off, and fighting gravity, and Electric are still fighting gravity.

_ah 7y ago

Also: regardless of acceleration or climb, air resistance is a major factor. This is why most aircraft cruise at 30k-40k feet. Flying the same route and speed at 5k feet burns significantly more fuel.

Robotbeat 7y ago

For long-haul, it's cruise. And the energy required can thus be improved directly proportional to lift to drag ratio. What I find promising is work NASA is doing and has done on truss-braced wings to enable a ~doubling of current transonic lift to drag ratios by using an extremely high aspect ratio wing.

yboris 7y ago
Truss-braced wings seem really cool! https://en.wikipedia.org/wiki/Boeing_Truss-Braced_Wing https://en.wikipedia.org/wiki/Boeing_Truss-Braced_Wing