External Alternator - 2 Reasons why

Model Specific Discussions about the Sling TSi.
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msejourne
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External Alternator - 2 Reasons why

Post by msejourne »

Hey guys, here are 2 reasons why you may want to consider the optional External Alternator:

1. MINIMIZES AFT CG PROBLEM
For all those of you who have used the Excel Weight & Balance calculation file, you would see the huge benefit it provides. Again, if you want a copy of the Excel Weight & Balance file, shoot me an email (specify Imperial (inches) or Metric version) to mikesejourne@gmail.com.

2. FULL IFR ELECTRICAL LOAD REQUIREMENTS (from Steve OConnor @ Midwest Panel Builders)
"Hi Steve (Steve Wallace) and Mike (myself),

I would be happy to share my thoughts.

First of all, I would definitely opt for the external alternator and especially in your case. We have wired many of these onto Sling 4 aircraft and we are doing one for a TSi builder in Canada because of the extra equipment he plans to put into his plane.

When we do an electrical load analysis for our typical 2 screen advanced IFR system with lighting and a heated pitot, not only do we exceed the 80% that is required by the FAA in certified aircraft but we exceed the 30amps available from the Rotax generator. Having said that most people will not fly with the pitot on for real long periods and if they do, they are in a cloud and can shed some load by turning off their lights such as strobes since they won’t be seen anyway. This juggling act keeps them from drawing on the battery.

However, I would not bypass the 30 amp alternator. I would use it in conjunction and actually wire the external alternator to be optional by switching the field. You use it if needed such as the loss of your 30 amp generator or if your loads exceed 30 amps. After all you want redundancy and wiring them to work together will do just that. Also the generators in the Rotax system need to be used as the stored amperage in them can actually do harm if not being used. This is the reason we use the Rotax 30amp first and only use the alternator as needed.

As for your concern that the Engine ECU will not warn if the 30amp generator fails. Not to worry, the G3X system can alert you to this failure. First of all , by monitoring your volt meter you can see a failure, as your voltage starts to drop below 13.8v you can suspect the system is not properly charging. Also we can set a warning for the ammeter to turn on the master warning light if the battery sees an excessive draw. If the system is working properly the battery shunt should show 0 amps which means the battery is not charging or discharging, as soon as we see a discharge we know you have either exceeded the capacity of the main generator or it’s not charging. A small amp draw is typically from exceeding the capacity and a large amp draw is a sign of complete failure of the generator. Back this up with looking at the voltage reading and you can learn quickly what has happened.

Another thing that could warn you is the back up batteries we install. All of our IFR systems get 2 backup batteries that will power all of the essential avionics. The avionics wired to them are wired as a passthrough and the batteries have logic that if the main bus voltage drops below approximately 11.5V they automatically kick in to keep your avionics running uninterrupted. When this happens the batteries send an alert to the G3X and shows a CAS message on the screen that you are running on the backup batteries.

As for weight and balance. I think it will be negligeable as the external alternators are rather small but it certainly won’t hurt you.

I hope this helps

Steve"
=============================
Food for though....

Cheers!!
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PhilipRueker
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Re: External Alternator - 2 Reasons why

Post by PhilipRueker »

Thanks for the fantastic writeup.

I was considering adding some dummy weights to the front to move the CG, but if adding the external Alternator could help alleviate some of that, and also help with the far end of the electrical load, then I'll have to give that another closer look :)
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huzilulu
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Re: External Alternator - 2 Reasons why

Post by huzilulu »

Im in the same boat - I can get by without the alternator but I could use some dummy weight... the cost of the alternator plus new cowling (already have my cowling) makes adding the alternator not worth it - so looking at adding 10-15lbs upfront somehow...
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ibgarrett
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Re: External Alternator - 2 Reasons why

Post by ibgarrett »

Arg - you know... I thought about getting the extra alternator but passed on it. What's the difference on the cowling size that makes it different?

The load information on the electrical system would be helpful when placing the order so the proper sized alternator is recommended. I figured one would be enough. I figured wrong.
Brian Garrett
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msejourne
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Re: External Alternator - 2 Reasons why

Post by msejourne »

Hi Brian, below is a copy & paste from last year showing the External Alternator option (CAUTION Nov 2020 prices).
Give TAF a call, hopefully it's not too late... Good luck!

SLING TSI KIT EXTRAS
Dimpled FuselageƗ $500.00
Dimpled WingsƗ $1,550.00
Dimpled Empennage $750.00
Long Range Tank Kit (Parts Swap Out) $3,500.00
Long Range Tank Kit - Assembled for Quickbuild $7,295.00
ROTAX 915iS Turbo Injected Engine, Firewall Forward Kit, and Airmaster Constant Speed Prop $55,895.00
External Alternator, Bracket, Slip Ring and Cowling Modification $2,895.00
Parachute cables in canopy but no mount or parachute $1,200.00
Magnum 901 parachute recovery system with mount and hardware $10,995.00
Electrics, switches, circuit breakers, batteries, wires, trim actuator $3,595.00
Dual toe brake kit complete instead of standard T pedals and centre brake $1,595.00
Split Rear Seat $500.00
Leather upholstery, carpets etc. $3,500.00
Avionics - Quoted to order
Prices EXCLUDE TAXES and are subject to change without prior notice
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ibgarrett
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Re: External Alternator - 2 Reasons why

Post by ibgarrett »

I talked to Barry on Monday (well, emailed) and my kit is boarding the boat this week (hopefully)... so it might be too late for this round, but I'm a long long ways from even getting the engine much less paint. I'll drop him an email and see if there is some horse trading I can do to change that up.

Thanks for bringing this up...
Brian Garrett
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hpmicrowave
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Re: External Alternator - 2 Reasons why

Post by hpmicrowave »

I just ordered the external alternator as an add on to my complete TSi kit. This means I will have to modify the cowl with a little bulge to support the extra alternator but this is what the factory does themselves when this is ordered, not that big a deal. Anyway my 3 reasons include some of the above plus one as follows;

1). The Rotax is a great engine and it has 2 independent electronic ignition systems but they are not self powered, they require a fully functional electrical power system and that is from 2 small alternators (1 is smaller than the other). If there is a alternator failure the computer will shed electrical functions depending on which alternator fails but your likely to loose some systems. You then have a electrical issue that could (but not likely) turn into a full emergency, but any way you will land with with a definitely broken airplane. Is loosing an alternator likely to happen, yes. Is the airport you land at likely to have a spare alternator for a Rotax engine, no. Would you fly home with only 1 operational alternator? Some folks might, I wouldn't. It's almost the same as flying with only one operational magneto. Anyway my logic is having that 3rd fully functional alternator gives you 100% freedom to continue on given the above failure scenario. There are other possible failure scenarios with the Rotax, fuel pumps, engine computer, etc but this one you can do something about.

2). Supporting a full IFR electrical load, yes I will be flying my TSi IFR, and having the extra alternator will definitely provide peace of mind that an alternator failure at the worst time will not impact my safety.

3). Helping the TSi CG, yes the potential CG issue has been in my thoughts for some time, CG is not a big issue as it's very manageable but I was looking at putting a bigger (heavier) battery on the firewall for backup electrical if one of the alternators died to both help the CG out a little and provide emergency electrical support, but the external alternator supports the broken alternator issue completely and does help a little with the CG.

Anyway. My reasons for adding the external alternator.

Cecil
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gordsh
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Re: External Alternator - 2 Reasons why

Post by gordsh »

FYI, I am the Canadian Builder that Adam referred to above.

I have the External Alternaster and modified cowling on my plane/kit.

This was mainly because of the fact that I added the Garmin Traffic GTS-800 to my build for local traffic which increased my AMP draw. I was also planning to install an electric A/C unit but the W/B did not work out so I dropped that idea.
Sling TSi - Ontario, Canada
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msejourne
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Re: External Alternator - 2 Reasons why

Post by msejourne »

Thank you for sharing the information! By the way, when the kit comes in, would be mind posting a picture of the modified cowling? I don't think anyone in the Forum has one or seen one yet.

Cheers!
gordsh wrote: Thu Apr 29, 2021 5:58 pm FYI, I am the Canadian Builder that Adam referred to above.

I have the External Alternaster and modified cowling on my plane/kit.

This was mainly because of the fact that I added the Garmin Traffic GTS-800 to my build for local traffic which increased my AMP draw. I was also planning to install an electric A/C unit but the W/B did not work out so I dropped that idea.
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gordsh
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Re: External Alternator - 2 Reasons why

Post by gordsh »

Upfront weight addition.....order the Sling Pedals which will add 5 lbs upfront.
Sling TSi - Ontario, Canada
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