[Wardo]

Thinking about using plane powers 30A continuous duty alt as my primary.

Skyview-10" w/ autopilot, trutrak backup attitude gyro, Aveo LED LNG, taxi, position and strobes. Aux power in forward & rear, heated pitot. Electric trim and flaps, obviously.

Thoughts.

 

[F1R]

When I turn on the pitot heat it draws 30 AMPS for a few seconds then backs off to about 20. Without pitot heat, I think your plan might be OK for a VFR no ice ship.

 

[Wardo]

ALT

When I turn on the pitot heat it draws 30 AMPS for a few seconds then backs off to about 20. Without pitot heat, I think your plan might be OK for a VFR no ice ship.

I hear what you're saying. I guess if there was a need for more amps than the ALT was providing, the battery would supply as needed??

 

[rzbill]

Simple

Determine Mission.

Determine equipment for mission

Do electrical load analysis for all aspects of mission

Obtain output curve (by RPM) of alternator and do not rely on max rating for all calculated conditions.

Compare output curve at predicted RPM to loads at each flight condition.

I considered a 20A vac pad for primary until I saw the curve. It basically said I would be discharging the battery from start to takeoff and it would not support some of the flight conditions that included pitot heat even at top rpm. Unacceptable for IFR in my book. For VFR, I would do it in a second.

YMMV for your equipment selection.

 

[viperpilot]

I, too, have a Plane Power standby alternator; yet to be installed. However, I think it is rated only for 15-20 amps at cruise rpm; maybe the 30-amp for maximum rpm. The info is listed on the installation instruction sheet, I think.

 

[SHIPCHIEF]

I'm thinking about removing the vacuum system, installing EFIS and installing the vac pad mounted SD-8 amp alternator for back up, or a small battery.

 

[F1Boss]

Plane Power = good stuff

I am still a beta tester on this unit. Great product for my use, but behaves a bit like a generator in that it produces no usable power until 950-1000RPM on the tach. I have seen it whack out 35A after a decidedly difficult hot start - I think it is rated for 30? No matter, as it is based on the 60A Denso, so it's plenty capable. The problem is the lack of RPM available to turn it up to unit rated RPM, and there is no fix for that.
On the good side, it has no bracket to break, or belt to fly off or wear out.
This is NOT the 20A unit from B&C, which is 20A, and performs in a similar manner.
While I would not ask it to supply power for the entire equipment list on your ship, but it is a very good unit. Changing to a sensing heated pitot would solve the amperage problem.
Ask yourself: when are you gonna be flying around with EVERYTHING on anyway? You could shed load, if necessary, to be able to use the heated pitot continuously. If IFR is part of your mission, then as RZBill said, you will need a more capable unit, driven in the normal manner.

Carry on!
Mark

 

[Danny King]

Skip the pitot heat

PITOT HEAT IS NOT REQUIRED FOR IFR.

I have never seen an RV of any type that is equipped for flying in icing. As I've said before: loss of airspeed due to an iced over pitot will be the least of your problems!

Many heated pitot setups have problems with airspeed accuracy. Van's simple tube works great and draws zero amps! The low draw glass panels you plan to use should work fine with a 30 amp alternator.

I have a belt driven 40 amp B&C alternator and have never come close to over working it.

 

[Wardo]

RE: Danny

PITOT HEAT IS NOT REQUIRED FOR IFR.

I have never seen an RV of any type that is equipped for flying in icing. As I've said before: loss of airspeed due to an iced over pitot will be the least of your problems!

Many heated pitot setups have problems with airspeed accuracy. Van's simple tube works great and draws zero amps! The low draw glass panels you plan to use should work fine with a 30 amp alternator.

I have a belt driven 40 amp B&C alternator and have never come close to over working it.

Thanks Danny, good thinking. Im glad to hear that your BC 40A is more than plenty.

Love the plane by the way!!

 

[Mile High Relic]

PITOT HEAT IS NOT REQUIRED FOR IFR.
I have never seen an RV of any type that is equipped for flying in icing. As I've said before: loss of airspeed due to an iced over pitot will be the least of your problems!

But if you have a heated pitot, perhaps it won't be another, compounding, problem.

Not all icing is created equal. There are times when you may see just a trace, and your pitot will ice over before you even see a hint of rime on the wings. I flew through some weather once a very long time ago and ice accumulation was visible only on two tiny spots. One spot was the tip of the OAT gauge sticking through the windscreen, and the other spot was the pitot tube.

That was my first and last encounter with ice, and I try hard to keep it that way, but I'm still glad I have a heated pitot on my RV. If by some bad luck or poor decision someone ends up picking up some ice, it sure will be nice to know the airspeed is working as you either climb or descend to try and solve the big problem.

This is in no way suggesting that you should ever fly a non known-ice aircraft into icing conditions.

 

[Danny King]

But if you have a heated pitot, perhaps it won't be another, compounding, problem.

Not all icing is created equal. There are times when you may see just a trace, and your pitot will ice over before you even see a hint of rime on the wings. I flew through some weather once a very long time ago and ice accumulation was visible only on two tiny spots. One spot was the tip of the OAT gauge sticking through the windscreen, and the other spot was the pitot tube.

That was my first and last encounter with ice, and I try hard to keep it that way, but I'm still glad I have a heated pitot on my RV. If by some bad luck or poor decision someone ends up picking up some ice, it sure will be nice to know the airspeed is working as you either climb or descend to try and solve the big problem.

This is in no way suggesting that you should ever fly a non known-ice aircraft into icing conditions.

------------------------------------------------------------------------
If your aircraft is taking on ice, but your airspeed indicator is working because you have pitot heat...... what speed will you fly? What is your stall speed?

You have become a test pilot of an ever changing airframe, with all new numbers. Again, the airspeed indicator will be of limited use to you because you won't have a clue what to do with it! Your best bet would be to exit the icing ASAP, being keenly aware of the feel of you flying machine to avoid loss of control.

You might also have to deal with a frozen over windshield because you didn't install window deice. You might notice increased vibration, because you didn't install prop deice. There is nothing you can do about the ice building up on the wings and tail, because you didn't install boots.

Let's face it.....you are in big trouble, and the only way to avoid this is through careful flight planning, and good decision making. This is similar to continued flight VFR into IFR. You just don't do it!

If you are worried about the total amp draw (vs) alternator output then this is a no brainer!

 

[Mile High Relic]

------------------------------------------------------------------------
If your aircraft is taking on ice, but your airspeed indicator is working because you have pitot heat...... what speed will you fly? What is your stall speed?

You have become a test pilot of an ever changing airframe, with all new numbers. Again, the airspeed indicator will be of limited use to you because you won't have a clue what to do with it! Your best bet would be to exit the icing ASAP, being keenly aware of the feel of you flying machine to avoid loss of control.

If your airframe isn't taking on ice, but your pitot is, what airspeed are you flying? You ignore the scenario I mentioned, and "limited use" is not the same as no use. I completely agree that everyone should avoid ice, but I believe a heated pitot is a useful accessory, and I wouldn't fly IMC without one.

I also agree that the only thing to do is to get out of icing ASAP. Does a heated pitot hurt in that case? If the goal is to stay with a smaller alternator I can see it, but I personally wouldn't fly in the clouds for more than 5 minutes.

 

[MarkW]

My original plan for my new RV-9 is IFR cross country. I assumed I would use a heated Pitot until someone reasoned with me. I will also have speed through other sources. Ground speed through at least 2 other sources and maybe 3. Garmin 430W, Trutrak Gemini and probably EFIS. I will not be so close to stall with ice on the plane that the difference in GS and AS will make much difference. I should have a pretty good idea of wind strength and direction at all times while IFR.
I will be IFR without heated pitot.
Apologies to the OP.

 

[Danny King]

If your airframe isn't taking on ice, but your pitot is, what airspeed are you flying? You ignore the scenario I mentioned, and "limited use" is not the same as no use. I completely agree that everyone should avoid ice, but I believe a heated pitot is a useful accessory, and I wouldn't fly IMC without one.

I also agree that the only thing to do is to get out of icing ASAP. Does a heated pitot hurt in that case? If the goal is to stay with a smaller alternator I can see it, but I personally wouldn't fly in the clouds for more than 5 minutes.

I didn't address it because it is without merit. If you are taking on icing, it is silly to assume that you could get an iced over pitot without picking up airframe icing in general.

The original thread was about a vacuum pad alternator with a max of 30 amp output. The builder was worried that the amp draw of pitot heat would eliminate his alternator of choice. Like many, he might not have known that pitot heat is not required for IFR flight, and therefore should not become a limiting factor in his choice of alternator for his RV.

 

[Mile High Relic]

I guess all those PIREPS I've heard/read over the years reporting trace icing are without merit and silly. Sorry to take the thread off course, and as you say, the OP doesn't have to have a heated pitot tube.

 

[Wardo]

I didn't address it because it is without merit. If you are taking on icing, it is silly to assume that you could get an iced over pitot without picking up airframe icing in general.

The original thread was about a vacuum pad alternator with a max of 30 amp output. The builder was worried that the amp draw of pitot heat would eliminate his alternator of choice. Like many, he might not have known that pitot heat is not required for IFR flight, and therefore should not become a limiting factor in his choice of alternator for his RV.

Thanks Danny. I was trying to remember what we were originally discussing.