# Air driven generator?

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#### Dan Thomas

##### Well-Known Member
I forgot to add 'auto engine' and I guess I should have BOLD/CAPITALIZED/flashing neon colored the 'emergency' part.

While a second Lithium battery might be a better bet, we're talking emergency situations. It doesn't need to be perfect, it just needs to do what it needs to do. Say 6-10A for a fuel pump, an amp or two for the ECU, a couple for the coils, say 30-40A for an engine and radio on an emergency bus. Car motors need a lot of gadgets to run... I've accepted any/all performance hits for the simple ability to actually afford to be able to fly.

That 'minipod' was 2lbs for 4A.

Duralast Gold New Alternator 14130N 40A, 11lbs with pulley. Not a huge penalty. You could shave off some weight. Getting it to spin 2000rpm to get enough out of it... that's might be an issue.

Batteries age, and need to be maintained/charged. A second alt. would just sit there until you needed it.
ULpower's UL260 uses a 30-amp PM generator and rectifier-regulator. The engine and fuel pump alone eat up 15 amps. Seems that EFI and EI need plenty of power.
UL260i | ULPower Aero Engines

#### pfarber

##### Well-Known Member
HBA Supporter
ULpower's UL260 uses a 30-amp PM generator and rectifier-regulator. The engine and fuel pump alone eat up 15 amps. Seems that EFI and EI need plenty of power.
UL260i | ULPower Aero Engines
The fuel pump is the largest load and even then its less than 20 amps, closer to 10. ECU/spark/radio would be less than 10amps. A full load calc would need to be done.

My specific install is planning to use an electric water pump, so that's another 10-15 amps. I don't see a secondary battery as a viable solution, they just could not handle the load.

If you think about it, the weight is not a significant penality as a certified motor is dragging around an alternator AND TWO generators AND a battery.

I think with EFI, a lithium main battery, a primary AND secondary alternator, weight wise its a not a significant difference. Even if you hook up the second alt to the engine (and not try to use wind power) its not a significant hp load.

##### Well-Known Member
The Gennipod was developed by Jim Hardy if the Gen 2 GenniPod prop is flipped it can support speeds over 120 otherwise it is optimal for 60-90 I think. Can you advise what speed generated 4A?

MAtt
It was on an Airbike ultralight. Speed 55-60 mph.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
This project will be a great opportunity to collect some data points once the system is operational. It's probably the first water pump driven by electricity driven by a turbine/generator driven by thrust from a propeller driven by internal combustion. Let's see how it does.

#### pfarber

##### Well-Known Member
HBA Supporter
It was on an Airbike ultralight. Speed 55-60 mph.

#### pfarber

##### Well-Known Member
HBA Supporter
This project will be a great opportunity to collect some data points once the system is operational. It's probably the first water pump driven by electricity driven by a turbine/generator driven by thrust from a propeller driven by internal combustion. Let's see how it does.
I'm still working out how Bumblebees fly first. Then I plan to reconcile Newtons 3rd law and Bouronilli's Principal. Someone needs to figure out how an airplane wing works. Then I'll hit the water pump/propeller/turbine/alternator.

Should be done by noon tomorrow. But early results seem to indicate the answer is 7.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
Bonus points for sarcastic wit, pfarber.

I was actually being serious though. I'm interested to hear how it works out.

#### pfarber

##### Well-Known Member
HBA Supporter
Bonus points for sarcastic wit, pfarber.

I was actually being serious though. I'm interested to hear how it works out.
I've actually thought of a good viability test, simply get an alternator (amp from a econo-box from the junkyard) and mount a rough propeller (basically take some sheet metal and bend it so I can get some of that newtons 3rd law action), bolt it to a pipe, hang it out the window and drive 75mph. See what kind of RPMs I can get. If I can't spin it at least 2000rpm I don't think I will get enough out of it.

From there find a 'better' prop (another reason to play with SolidWorks, thanks EAA!) and get it 3D printed.

This would be an emergency use item, so 'working' is more important than 'efficient'.

#### TFF

##### Well-Known Member
A driven propellor is different from a driving one. You would have to get that right to see any speed. Ram Air Turbine, RAT. They are quite noisy.
Depends on load needed. The ones I had to work on ran the emergency hydraulic system. No hydraulic no flight controls. It had an adjustable pitch blade too. If it’s some radios and maybe an EFI, a battery is way better when comes to complexity. A friends plane would have to run out of gas more than twice to use up his backup battery. Checking was a pain to spin up one of the generators. Lots of drag to spin one.

##### Well-Known Member
I've actually thought of a good viability test, simply get an alternator (amp from a econo-box from the junkyard) and mount a rough propeller (basically take some sheet metal and bend it so I can get some of that newtons 3rd law action),
I used a home made sheet metal fan to turn my air generator. In a short while one blade broke off and you can imagine the vibration that resulted. Thought the plane might come apart. Made a quick landing in a field and removed the fan so I could continue the flight. The next time I used a large wood model airplane prop and that worked well.

#### Dan Thomas

##### Well-Known Member
Way back in the 1970s I was towing gliders with an Auster, the same airplane I later bought to restore. This aircraft had no engine-driven generator, and in its original configuration it had a wind-driven generator mounted in the wing leading edge. That generator was long gone. So we had to occasionally recharge the battery for the radio and starter, though I usually hand-propped-it.

One of the guys in the club took an old generator (from a VW, I think) and mounted the two-blade radiator fan from an old Austin on it. (Austins were cars made in England and plentiful in the '50s and '60s before the Japanese imports outclassed and underpriced them. Japanese cars didn't use Lucas electrics, for one thing.) Mounted it on a wing strut. That fan spun the generator OK, until one day, flying back from a glider meet, it started to howl. The fan was just twisted sheet steel, and twisting shortens the blade length. Fan RPM at flight speeds was higher than it was in the car, and centrifugal force caused the blade to untwist and go to a lower pitch, which increased the RPM, which increased the centrifugal force, which untwisted it more, which made it go faster.........

I was terrified that the fan would break and either send a chunk of steel through me or a fuel tank, or the imbalance would tear the strut off.. I slowed down to about 50 MPH (stall was mid-30s) and crawled toward the home airport, the fan howling like a siren. Made it, and bent the blade back over the strut when I got out. They replaced it with the plastic fan off a Datsun, which turned much slower.

It hadn't overrevved before that trip because all the flying was towing gliders at 70 MPH and descending at 60 and 70, landing at 40. Cruising at 110 caused it to start untwisting.

That's one reason I made the little 3" prop for my 1.5-amp generator out of welded-up steel. Stout and stiff.

#### pfarber

##### Well-Known Member
HBA Supporter
I get that thin metal props are not safe or a long term solution.

It would be used for nothing more than a viability test. At 75mph can I even hope to get the RPMs high enough to make +12v and a couple dozen amps.

But I guess 'doom and gloom' is the theme of 2020.

Instead of long missives of old cars and bent parts, you put some thought into 'how could you NOT break the thing' or something helpful along those lines.

If I get an hour to two I'll fiddle with it more.

#### Dana

##### Super Moderator
Staff member
The fan on the Gennipod looks like it came from a big computer fan.

How much current does a starter draw? Lessee... the Odyssey battery in my plane is rated at 170 CCA and 16Ah nominal capacity. Say the starter draws that full 170 for, say, 10 seconds, that's about 1/2 Ah so you might get 30 starts. The Gennipod puts out 4A so it'd take 7.5 minutes to recharge the battery from a single start, not counting any other loads. That sounds reasonable.

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#### pfarber

##### Well-Known Member
HBA Supporter
The primary engine alt. would do normal charging duties.

Since I am running a car motor with EFI I would like (but not 100% positive I need) another power source. Although if the battery dies and the alternator breaks then things have gone very wrong.