Intercity-flying/driving commuting coming in reality

[aerohead]

On occasion, at 41,000-feet, I've been in a 150-mph tailwind in the Jet Stream, giving us a ground velocity in excess of MACH-1. Which is welcome on a flight from Maui or the Big Island to Dallas.
And no sonic boom!

[Isaac Zachary]

Originally Posted by aerohead

1) with a gyrocopter, pay attention to doppler radar advisories.
2) A friend's dad was a very experienced, high-time gyrocopter pilot, however, bought the farm in a micro-burst downdraft.

From what I've seen (thanks to Google, so take it for what it's worth) is that a lot of autogyro accidents have more to do with a bad aircraft design than autogyros in general. It has to do with a rear mounted propeller. With the engine and propeller behind the pilot there are certain advantages, like being able to blow right onto your rudder giving you better yaw control at slow speeds, but it also makes the line of thrust much higher than the center of gravity.

Apparently if you fix this and put the line of thrust exactly along the center line of the vehicle through the center of gravity then control issues are solved. But this ususally means the propeller has to be mounted on the front making the vehicle longer and doesn't give you that yawing advantage at slow speeds.

Juan De la Cierva invented the autogyro to make a safer aircraft. Ironically he died in an airplane crash.

[Piotrsko]

Other huge advantages: no exhaust in your face, ditto for prop blast. Having friends that designed these, correct engine placement seems to be not that difficult.

If it won't yaw without power, then it doesn't have enough rudder.

[Isaac Zachary]

Originally Posted by Piotrsko

Other huge advantages: no exhaust in your face, ditto for prop blast. Having friends that designed these, correct engine placement seems to be not that difficult.

Surely having the engine in a the right place helps balance the vehicle. But I'm talking about propeller placement which is a totally different animal.

When the aircraft takes off the rear is going to have to go down and the front go up in order to lift off. With a propeller in the front this allows for a bigger propeller that still sits in line with the center of gravity. But a propeller in the rear means you either have to install a smaller propeller, or make the air craft sit higher off the ground on it's wheels, or position the propeller up above the center of gravity. All of these have a disadvantage. A smaller propeller, for an example, wouldnt' be able to deliver as much thrust. Therefore the most popular "solution" is to just move the propeller up above the center of gravity of the aircraft.

Look at this picture and see how the center of the propeller is very high compared to the center of gravity. This setup means that under power you're pushing the nose down. So you have to use the cyclic (rotor) pitch control to push the nose back up. This makes for a situation that certain changes could cause the vehicle to suddenly nose dive or nose up and go backwards. Lose power and you could suddenly nose up. Lose air speed (try to climb a little too quickly) and you could suddenly nose dive.

This is especially problematic in a vehicle that can have as little as 0 (or even negative) forward speed. If you're going very slow or even "floating" straight down and then suddenly hit the throttle, perhaps with the intention to start climbing again, you could suddenly nose dive.



With the engine in the front it can be placed in line with the center of gravity without making the propeller super small. That way it pulls the vehicle in a straight line making it just as safe (if not safer) than a fixed wing aircraft since there'd be no need to compensate for the properller being off the center of gravity. That's because thrust won't affect pitch so you don't have to compensate. Hit the throttle, let off the throttle, speed up, slow down, it won't affect pitch. The nose stays the same.

Originally Posted by Piotrsko

If it won't yaw without power, then it doesn't have enough rudder.

Remember were talking about a vehicle that can have as little as zero forward speed. Normally under zero speed you don't have yaw because you have no air going over the rudder. Going very close to 0 speed also makes you have very little controlabilty.

But with the propeller right in front of the rudder the vehicle will yaw under power even if it was previously "floating" straight down. This is because thrust from the propeller blows right over the rudder.

But with the propeller in front then yaw is much more vehicle-speed dependent. If you're "floating" straight down in a front-propeller autogyro and then suddenly want to yaw you can't just hit the throttle and a rudder pedal and turn. You have wait for the vehicle to get back up to speed in order to get enough air moving over the rudder in order to turn.

[freebeard]

It seems it would be optimal to have a battery pack in the floor to keep the CG low. And twinned contra-rotating propellers to the sides for yaw control.

[Isaac Zachary]

Originally Posted by freebeard

It seems it would be optimal to have a battery pack in the floor to keep the CG low. And twinned contra-rotating propellers to the sides for yaw control.

Why would you want the center of gravity low? Wouldn't that make things worse? The propellers would have to be mounted even lower or you'd still have that effect from the misalignment between the center of the propellers and the center of gravity pushing the nose down.

But the twin propellers sounds cool to me. It would also allow for smaller propellers so you could center them to the center of gravity better.

In my mind batteries could be placed higher in order to raise the center of gravity in line with the propeller(s).

Another thing I forgot to mention is the effect of momentum. If the propeller(s) are above the center of gravity then acceleration would cause the nose to dive too from inertia.

[freebeard]

As you can tell, I'm no High Altitude Hybrid. The thought process prolly went something like -- it hangs from the rotor like a Christmas Tree ornament so make it like those inflated boxer toys with the weight in the bottom. So much for reasoning by analogy.

I also notice that I argued past the sale, assuming an electric autogyro.

If the mass of the batteries was a spinning gyroscope you could use that for attitude control.

[Isaac Zachary]

Originally Posted by freebeard

As you can tell, I'm no High Altitude Hybrid. The thought process prolly went something like -- it hangs from the rotor like a Christmas Tree ornament so make it like those inflated boxer toys with the weight in the bottom. So much for reasoning by analogy.

I also notice that I argued past the sale, assuming an electric autogyro.

If the mass of the batteries was a spinning gyroscope you could use that for attitude control.

Now that's a great idea!

Spining mass in the rotor (like at the tips in aerodyamic pods) could give a pretty neat advantage. If you have a way of spinning up the rotor while on the ground and have a collective rotor pitch control you could disconnect the rotor and then do a vertical take off using the momentum in the rotor to elevate the autogyro.

Actually your other idea of side-by-side propellers could also work as a type of helicopter for take offs and hovering. Have a reversible blade pitch control on one of the propellers would make it so you could counteract the torque of the rotor during liftoff and hovering.

For an electric aircraft, however, I'd still be more in favor of the airship. If the airship could be made to fly above the weather (especially clouds) and were covered in effient, yet light weight PV cells, it could fly with not much need for a heavy battery, at least during the day.

[freebeard]

1930s autogyros had a power take off to spin the rotor up. But I was thinking of a reaction wheel that would be like a stepper motor that could spin up either way. Maybe pairs that can spin with or against each other. Commutator to pass the power in and out.

edit: almost forgot. I'd watched this earlier.

https://www.youtube.com/watch?v=zNfAD-LBjEk

[Piotrsko]

Both of you don't fly.

If the thrust isn't on centerline, you offset the thrust to compensate. The pacer I owned had 3 degrees down and two degrees right. Built into the mount tubes. You could go full throttle and not need to re trim until the airspeed got much faster. Might need to do right rudder, but that was P force and airspeed sensitive.

Even with the motor off, there is still a forward component otherwise the big fan on top slows down. Might be less than walking speed, but that will include a steep descent. This is illustrated by the slowing the rotor to a stop after landing through drag (although some have brakes on the mast).