Propeller vs Direct drive

[Cobb]

Im sure small in wheel electric motors could be used to move the car in an dout of parking places, drive ways, parking garages, then once you are on the main road you fire it up.

[jamesqf]

Of course the real question is why? Not only are propellers much less efficient than a conventional drivetrain, they have all sorts of problems that are familiar to those of us who fly small planes, particularly off rough fields.

First, the throttle response is very non-linear. Get a wheel stuck behind a bump or similar, and you have to give lots of throttle to get over it, then you immediately start accelerating. Meanwhile, you're sand-blasting everything behind you. Oh, and that sand-blasting is also eroding the tips of your expensive prop...

Nor can we forget about the interesting effects of driving in snow or freezing rain, which causes your prop to ice up & lose efficiency, and probably shed chunks of ice outwards at high speeds. (Prop tips move at a significant fraction of the speed of sound.)

[basjoos]

Then add the negatives of high noise levels and the effect of bird (and possibly larger animals,pedestrians, etc.) strikes on the prop and what happens when plastic bags and other road debris kicked up by traffic encounters the prop and, as a minimum, throws off the balance of the prop. Aircraft ground operations occur in the fairly controlled environment of an airport, very different (for example) from that experienced by a car following a semi in the rain or snow.

[cptsideways]

We built this for some power tool drag racing

It was very very noisy & very very slow

https://www.youtube.com/watch?featur...-bBFLWTKkvf5Zw

[user removed]

I always thought it would be neat to put a bicycle in an aero envelope and add a 50cc 4 stroke engine and one of the larger model airplane ducted fans. Pedal to get up to a speed then engage the ducted fan when conditions allowed.

regards
Mech

[Superfuelgero]

Originally Posted by Ryland

I think it was around 59% energy transfer

I wonder if that is under acceleration or at constant speed, and fixed or variable pitch. A conventional drive will lose between 10-25% from friction and pumping (auto), so that's not too terrible.

Originally Posted by jamesqf

Of course the real question is why?

FAR 103, and not wanting to be limited to location.

A ducted fan or shrouded prop would help the stop and go, allow or a low prop (CG), and make shielding easy. With pitch control the drag losses might be comparable to a unshrouded/ducted, fixed prop at speed. Both of those add weight though. Maybe some emergency floats could offset that.

Did some research, oddly enough there is no law against driving with a prop, so long as your wheels don't kick up rocks.

There's also the possibility of hydrostatic, but that's heavy and inefficient too.

[jamesqf]

Originally Posted by xntrx

A conventional drive will lose between 10-25% from friction and pumping (auto), so that's not too terrible.

Not so, at least per ORNL research, which puts drivetrain losses at 4-7% Where the Energy Goes: Gasoline Vehicles Meanwhile, the BEST you can get from a prop is about 80%.

FAR 103, and not wanting to be limited to location.

So you're going to drive your ultralight around on the roads? But I'm still confused about the why part - unless of course you're planning to take the traditional meaining of IFR (I Follow Roads*) to its logical extreme.

Off topic, but I once worked for a guy who claimed he was following California Hwy 99 north of Bakersfield in the fog, and wound up flying under a freeway overpass.

[cRiPpLe_rOoStEr]

Originally Posted by basjoos

Then add the negatives of high noise levels and the effect of bird (and possibly larger animals,pedestrians, etc.) strikes on the prop and what happens when plastic bags and other road debris kicked up by traffic encounters the prop and, as a minimum, throws off the balance of the prop. Aircraft ground operations occur in the fairly controlled environment of an airport, very different (for example) from that experienced by a car following a semi in the rain or snow.

That's a good point. I have already seen some propellers damaged by collision with birds, so you can guess what would happen in case of collision with a bigger animal...

[Ryland]

Originally Posted by xntrx

I wonder if that is under acceleration or at constant speed, and fixed or variable pitch. A conventional drive will lose between 10-25% from friction and pumping (auto), so that's not too terrible. .

That 59% is in ideal conditions as I understand it, the mathematical max that you can get before air just moves around the prop.

With a regular drive-line you can get 98% with a well designed gear box or chain drive, the rest of it, tires and bearings are going to be the same because you have to have those to have wheels on the ground.

[cRiPpLe_rOoStEr]

Originally Posted by Old Tele man

instant...road-kill hamburger!

Or chop-suey