galaxy flyer

The power source isn’t going to cause “all the rules “ to change, in fact, I rather doubt much will change. They’ll still have to adress the power loss case and this configuration doesn’t fit in very well.

GF

abelenky

Actually quite a lot changes when the power plant switches from combustion to electro-chemical energy.

A few things:
TOW == LW: Empty batteries weigh the same as full batteries, so you always land with the same weight you take off at.
This has consequences down to the landing gear design.
Electric planes won't trim to balance fuel that has been burned off.
Useful load no longer includes fuel weight.

You might then think that a plane should always take off with batteries at 100%, but that's not true.
Cycling lithium-ion batteries to 100% shortens their lifespan considerably.
If the planned flight does not require the last 20%, you're better off charging to only the needed energy (ideally below 80%) to increase the lifespan of the batteries.

Out of fuel emergencies end up very different with Li batteries.
With traditional fuel, when the tank is dry, the plane just glides.
With Li, gliding at Vbg can actually recharge the batteries and get you another couple minutes of power.
If the battery ends up empty at 15,000 feet, the motor can suddenly come alive again at 2,000 and help power in to a safe landing.
That is definitely not in the current POHs.


(me: Only a PPL pilot; Lithium-Ion BMS engineer)

BobZ

When you run out of gas the chance of post impact fire is almost nil.

Do batteries burn?

abelenky

They definitely do. Great point.

We burn them in tests all the time.
Once started, they are self-fueling; the oxidizer is part of the cell. You *cannot* put them out (similar to how Mg can burn underwater)

The rules for airport fire trucks will probably have to be re-written for electric planes too.

galaxy flyer

I realize those points, but the current Part 23 and 25 address them. For example, landing gear strength.

FlyJSH

Sure will recharge the batteries. It will also add a ton of drag.
Drag: Windmilling vs Dead Prop

Knock the rust off the old MEL training: for the checkride we had to do a drag demo. In the Seminole I learned in, one windmilling prop added about the same sink as leaving the gear extended. IIRC the value was about 400 ft/min.

Ignoring the basic drag of the windmilling props, I wonder how much recharging there would be at best glide. I would think it would take an airspeed significantly higher than best glide to provide sufficient revs to build a useful charge.

Excargodog

https://youtu.be/m_8QGBv4v7E

joepilot

Hi UAL

This is only in reference to the crosswind problem.

I can think of several ways that this problem has been solved. You have certainly flown the T-38 more recently than I have, but if I remember correctly that aircraft was landed in a crab, with a 45 knot crosswind limit.

The 727 used the crab kickout method, rather than the usual airline slip method.

The C-5 had a crosswind gear that allowed landing with the aircraft in a crab, but the wheels rolling straight down the runway.

I'm guessing that the crosswind gear might be easiest to design for this aircraft.

Joe

UAL T38 Phlyer

Joe:

True on the Operational standard to land in a crab in the T-38, but the rationale: “the wings are too short; it raises your stall speed!” was bunk. So was the standard to land on the upwind side of the runway (which would make you move towards the near upwind edge of the runway upon touchdown).

Been five years since I flew it, but I think the crosswind limit was 25 kts; maybe 30. I landed in some winds pushing those limits, and used a combination wing-low/slight crab.

I think the real reason for both directives was 1. Guys overcontrolled the rudder, (so the Air Force said “crab”) and 2. They wouldn’t crab enough, so if aiming upwind...they’d drift and end up on the downwind side. “Better aim upwind...”

Guys wouldn’t apply crosswind controls during T&Gs either on huge crosswind days, so the downwind tires would get trashed. (I taught my students otherwise; crewchiefs were always amused my tires were worn evenly ).

Anyway, the Alice could have crosswind gear....but that will add more weight to a weight-critical design. And even if landing in a crab is their stated solution, turbulence and gusting winds can cause undesired banks in the flare. ie, prop strikes.

There was a post about the weight of the batteries, aircraft Max Gross, and useful load. The batteries were over half the weight of the plane. I’d guess they are in the wings, which is why the motors were tip-mounted...for weight distribution and bending-moment. I’m not sure if these batteries are the type that can spontaneously combust like Lithium, but a battery fire in a thin wing does not bode well for structural integrity.

Is it sleek, futuristic, and cool-looking? Yes. Does it have socio-political appeal for the climate-change crowd? Yes. Did they make aerodynamic compromises to achieve strength, weight, and electrical objectives? I would guess yes.

rickair7777

Yes, there's so much induced drag that charging while gliding would likely be impractical. A fast charge takes a LOT of current, and a slow charge won't help. It works for helo autorotations only because they plummet straight down so ALL potential energy is available to spin up the rotor disc. For a glider most of your potential energy is going to lift generation.