Rat

[raytoews]

My initials are occasionally spelled that way,,,,I dont know if that is an indication of who i am?

But I have a more relevant question.
I have a new airplane, EFIS and electronic fuel injection so flowing electrons are a must.
Most peopl put in a spare battery and land asap.
What if there was a (better) way.
Airliners and fighters all have one.
A RAT ram air turbine that can be shoved out in the slip stream.
A small dc motor will act as a generator if spun, a little fan on it on a hinge a voila, backup power?

[rwanttaja]

My initials are occasionally spelled that way,,,,I dont know if that is an indication of who i am?

But I have a more relevant question.
I have a new airplane, EFIS and electronic fuel injection so flowing electrons are a must.
Most peopl put in a spare battery and land asap.
What if there was a (better) way.
Airliners and fighters all have one.
A RAT ram air turbine that can be shoved out in the slip stream.
A small dc motor will act as a generator if spun, a little fan on it on a hinge a voila, backup power?

Wind generators. Lotsa folks talk about them, few actually install them.

http://www.bowersflybaby.com/tech/wind_gen.html

Ron Wanttaja

[raytoews]

Way back on the.old.days, the 70s my first airplane was an old beatup Taylorcraft that had a windgenerator to run that old vht3. Worked well. Couldnt tell if it was noisy, too much engine and wind noise.

[cub builder]

You don't say the speed of your aircraft, but if it's fast and slick, you may very well overspeed the prop on a wind generator. They are fine for Champs, Cubs and Taylorcraft. Not so much on a slick airframe.

I've been seeing more and more people using a backup alternator mounted to the vacuum pump pad. In case of alternator failure, you minimize your electrical load if necessary and toggle over to your light weight backup alternator system. No need for a backup battery as you still have the capability to maintain your battery, and you have the capability of continuing your flight to your destination, and home again for repairs. In this scenario, a primary alternator failure is only an inconvenience, and not an emergency, or for that matter, not even an urgent situation unless your are flying at night and need more power than your backup alt can provide. Those with all LED lighting and strobes can usually get away with an 8 Amp dynamo system. Others can usually get by with a 20 amp standby alternator system.

B&C makes an 8 amp dynamo type standby alternator and 20 and 30 amp vacuum pump mount alternators. Either will mount to the vacuum pump pad and are priced in the $500 range. Plane Power has a 30 amp model that mounts to the vacuum pump pad, but is a bit higher priced.

-Cub Builder

[raytoews]

My particular aircraft engine combination doesn't have an extra accessory drive so that option is off the table.
I do have a small multiblade fan attached to a small motor. I held it out the car window at 60mph and it produced 16volts so I assume it would have no problem producing an amp or 2.
I'm thinking, instead of cutting a hole in the side of the airplane for a pop out rat, why not install it under the cowling with a pin thru the blades to stop it turning. Pull the pin and, voila, electrons, enough to keep the engine running.

Ray (rat)

You don't say the speed of your aircraft, but if it's fast and slick, you may very well overspeed the prop on a wind generator. They are fine for Champs, Cubs and Taylorcraft. Not so much on a slick airframe.

I've been seeing more and more people using a backup alternator mounted to the vacuum pump pad. In case of alternator failure, you minimize your electrical load if necessary and toggle over to your light weight backup alternator system. No need for a backup battery as you still have the capability to maintain your battery, and you have the capability of continuing your flight to your destination, and home again for repairs. In this scenario, a primary alternator failure is only an inconvenience, and not an emergency, or for that matter, not even an urgent situation unless your are flying at night and need more power than your backup alt can provide. Those with all LED lighting and strobes can usually get away with an 8 Amp dynamo system. Others can usually get by with a 20 amp standby alternator system.

B&C makes an 8 amp dynamo type standby alternator and 20 and 30 amp vacuum pump mount alternators. Either will mount to the vacuum pump pad and are priced in the $500 range. Plane Power has a 30 amp model that mounts to the vacuum pump pad, but is a bit higher priced.

-Cub Builder

[blane.c]

If you do have a fast plane or even otherwise, why not have a propeller and dynamo that is sized and pitched for your cruise airspeed? Possibly not the stock propeller, even if the dynamo does not produce power at lower air speeds IE approach and landing your battery should and is supposed to be sufficient for this phase of flight. I remember from reading about these dynamo's in the 80's that sometimes the dynamo's were noticeably out of balance, this could be attributed to varying humidity in the little wooden propellers maybe? In any event making sure the unit was balanced would be one of my concerns.

[rwanttaja]

If you do have a fast plane or even otherwise, why not have a propeller and dynamo that is sized and pitched for your cruise airspeed?

Because if you do have a fast plane, the reduction in performance due to a RAT in the slipstream is more than that of an alternator being turned by gears or a belt from the engine. If that were not the case, you'd see commercial aircraft with permanently-fixed external generators.

In any case, there are operational problems with being dependent on being at cruise speed to generate power. What if there's a line to get to the runway? What happens if a student is practicing slow flight for a long time, or you're holding near an airport conserving fuel?

The modern alternator is great; it can support a significant load even when the engine is at idle. You rarely hear of "uncontained" alternator failures; a failed alternator usually doesn't look much different than a working one. But damage a prop on a RAT and you've got parts getting flung like ape doo-doo, and, usually, no way for Jane to stop that crazy thing. It spins until you slow way down or it disintegrates.

Ron Wanttaja