Jump to content

Speedbrakes on avionics or battery bus ?


Airways

Recommended Posts

My little firebreather is in the shop for an avionics update. Apparently the speedbrakes are connected to the avionics bus, and they ask whether I want to keep it on the avionics bus or connect it to the battery bus.  Any opinions on this ? Avionics bus+engine failure = no speedbrakes. Then again, how much amps do the speedbrakes drain from the battery ? My speedbrakes are pneumatically operated...

Link to comment
Share on other sites

I think anything with a motor on it (high momentary current draw) is best kept away from the power that supplies the more sensitive electronics...

it is more in the category of flaps, gear, and anything else that adds drag.... if concerned with emergency things to remember when things go pear shaped...

For back-up to your logic... find a CB panel from any long body... they all got speed brakes from the factory...

PP thoughts only not a mechanic...

Best regards,

-a-

  • Like 1
Link to comment
Share on other sites

1 hour ago, PT20J said:

What does the installation manual say?

I can only find the manual for the electrically operated speedbrakes.  Since the SB were installed at the Mooney factory I hoped I’d find something in the maintenance manual but alas...

Link to comment
Share on other sites

2 hours ago, Airways said:

I can only find the manual for the electrically operated speedbrakes.  Since the SB were installed at the Mooney factory I hoped I’d find something in the maintenance manual but alas...

On my M20J, the speed brakes are wired to the main bus, but they are electric and should have a much higher current draw. If you have the schematics from the Mooney Service and Maintenance Manual for your airplane you could check to see if the factory originally wired them to the avionics bus. You might also email Stacey Ellis at technicalsupport@mooney.com -- I usually get an answer back pretty quickly.

Skip

  • Like 1
Link to comment
Share on other sites

5 hours ago, Airways said:

My little firebreather is in the shop for an avionics update. Apparently the speedbrakes are connected to the avionics bus, and they ask whether I want to keep it on the avionics bus or connect it to the battery bus.  Any opinions on this ? Avionics bus+engine failure = no speedbrakes. Then again, how much amps do the speedbrakes drain from the battery ? My speedbrakes are pneumatically operated...

They should be wired to the main battery bus.

  • Like 2
Link to comment
Share on other sites

3 hours ago, Airways said:

Clear & concise, @StevenL757 :). I like that ! Could you elaborate ?

 

3 hours ago, Airways said:

I’d like to learn the reasoning behind it. Or find a reference document.  I have zero technical background but I like knowing what happens to my plane.

Simply put, speed brakes are not avionics.  Conversely, TKS is on the avionics bus; however, it is part of essential equipment - in that when you shed load by switching from the primary ALT FIELD to the EMERG BUS / STBY ALT (in airplanes so-equipped), TKS remains part of the essential/emergency bus...for obvious reasons.

On the G1000-equipped Ovations and Acclaims, everything is on the primary bus, so when you power up the cockpit from "cold and dark", everything comes up...displays, avionics, TKS, standby instruments, etc.

  • Like 1
Link to comment
Share on other sites

3 hours ago, Airways said:

I’d like to learn the reasoning behind it. Or find a reference document.  I have zero technical background but I like knowing what happens to my plane.

It’s possible that it was wired to the avionics buss because there were open optional circuit breakers at the time of the installation.

Here is a typical circuit breaker panel layout from the maintenance manual.  Personally I’d power it from the main buss not the avionics buss

Clarence

83826AA1-C01A-4D90-AC32-4788367AAB2A.jpeg

Link to comment
Share on other sites

OK, first point: An electrical busbar (often shortened to 'bus') only has one 's'. Buss means a kiss (https://www.dictionary.com/browse/buss). Some of the confusion probably originates from the common usage of Buss brand fuses. But 'Buss' is a shortening of the name of the German immigrant inventor Bussmann (https://dynamic.stlouis-mo.gov/history/peopledetail.cfm?Master_ID=2015).

Now to the second point. Mooney has long installed speed brakes at the factory during production using the Preciseflight STC (I once asked why and was told that the paperwork to get the speed brakes added to the type certificate was not worth the trouble), Since the OP's speed brakes were installed at the factory, there was presumably a reason for connecting them to the avionics bus. I would try to determine the factory configuration before changing anything (but that's just me -- Being an engineer myself, I assume that the factory engineers had a reason for whatever they did). 

I agree, however, that it makes more sense to connect speed brakes to the main bus as the factory-installed electric speed brakes are in my 1994 M20J. The activation button on mine is on the left yoke horn and easily bumped when reaching for the heading knob on the Aspen PFD. After accidentally extending them once while changing course to extricate myself from icing -- and having them not fully retract -- I put a red ring on the circuit breaker and pull it now if there is any chance of encountering ice.

Skip

 

  • Like 3
Link to comment
Share on other sites

7 hours ago, PT20J said:

OK, first point: An electrical busbar (often shortened to 'bus') only has one 's'. Buss means a kiss (https://www.dictionary.com/browse/buss). Some of the confusion probably originates from the common usage of Buss brand fuses. But 'Buss' is a shortening of the name of the German immigrant inventor Bussmann (https://dynamic.stlouis-mo.gov/history/peopledetail.cfm?Master_ID=2015).

Now to the second point. Mooney has long installed speed brakes at the factory during production using the Preciseflight STC (I once asked why and was told that the paperwork to get the speed brakes added to the type certificate was not worth the trouble), Since the OP's speed brakes were installed at the factory, there was presumably a reason for connecting them to the avionics bus. I would try to determine the factory configuration before changing anything (but that's just me -- Being an engineer myself, I assume that the factory engineers had a reason for whatever they did). 

I agree, however, that it makes more sense to connect speed brakes to the main bus as the factory-installed electric speed brakes are in my 1994 M20J. The activation button on mine is on the left yoke horn and easily bumped when reaching for the heading knob on the Aspen PFD. After accidentally extending them once while changing course to extricate myself from icing -- and having them not fully retract -- I put a red ring on the circuit breaker and pull it now if there is any chance of encountering ice.

Skip

 

I looked through all of the factory K model schematics and could not find one that had a speed brake circuit breaker.  Your assumption on Mooney having powered them through the “avionics bus” may not be correct, it may have been moved in the decades since leaving the factory.

Clarence

Link to comment
Share on other sites

1 hour ago, M20Doc said:

I looked through all of the factory K model schematics and could not find one that had a speed brake circuit breaker.  Your assumption on Mooney having powered them through the “avionics bus” may not be correct, it may have been moved in the decades since leaving the factory.

Clarence

All of the Mooney 252 speed brakes were vacuum operated.

In 1997-98 when Mooney revived the K model and called it an Encore they used electric speed brakes.

Link to comment
Share on other sites

3 hours ago, M20Doc said:

I looked through all of the factory K model schematics and could not find one that had a speed brake circuit breaker.  Your assumption on Mooney having powered them through the “avionics bus” may not be correct, it may have been moved in the decades since leaving the factory.

Clarence

You could well be right and probably are.

Link to comment
Share on other sites

11 hours ago, LANCECASPER said:

All of the Mooney 252 speed brakes were vacuum operated.

In 1997-98 when Mooney revived the K model and called it an Encore they used electric speed brakes.

While true, they still had an electric control circuit, hence one would think a circuit breaker?

Clarence

Link to comment
Share on other sites

Great test for the find the right CB Test....

I went through them all hoping it would stand out....

I had to go through a second time fully reading each label... before I found it... :)
 

Definitely good to have the colored switch caps on the important stuff.
 

Thanks for posting the pic!

Best regards,

-a-

672B70C4-A58F-4808-8A2C-C7C55BAAFB63.jpeg

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.