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Remove the drip pan on 912ULS

E

Ex Bonanza Bucko

Well Known Member
Has anyone really removed the drip pan on a 912 to allow dropping the carb bowl? If you have please give me the steps you used to do that in 1,2,3, order.

As far as I can tell the only way to get the drip pan away from the carb on my 912 is to remove the carb from the intake manifold by taking out two bolts that go through the flange. Then, however, the drip pan is not removed from the carb but the carb removed from the drip pan. :) The drip pan is riveted to everything it impinges upon......so far as I can tell you can't "remove" it.

If you think this is wrong please tell me why.

BTW....inspection of the floats has been done on my bird but it was not done by removing the drip pan as called for in the SB.....but without the SB explaining or showing how to do that.

EBB
 
The drip pan isn't delivered with the engine from Rotax so yes, it can be removed in the same manner it was installed. But it doesn't need to be, to remove the float bowl from the carb.
It has been previously discussed in service bulletin threads here in the forum.
The carb. can be removed from the engine by loosening one screw.
Anyone with Rotax training, and authorization to work on your RV-12 will already know how to do it (and likely was done that way by who ever did your float inspection).
 
RVbuilder:

I know about how to get the carb loose with one screw and the spring as was described in another thread; that's how we inspected my carb floats. We had to remove the carb bowls because the ferule and injector required by the SB have been "back ordered" since the SB was issued on October 6.

My purpose in asking the question was to call attention to the inadequacy of the SB because of that excessive delay and also because it simply says "remove the drip tray."

If we are to get multiple "mandatory" SBs from Rotax, as it seems will be the case given recent history, I think we should expect and demand complete instructions and descriptions of what Rotax demands. In this case it would have been appropriate for Rotax to mention that the drip tray was not installed by Rotax so removal of it would require procedures not evident to the writers of the SB. If a Rotax qualified mechanic followed the SB to the letter that mechanic would have drilled out quite a few rivets unnecessarily. If Rotax wants us to adhere to the letter and intent of a "mandatory" SB I think we should expect Rotax to completely describe exactly what the SB demands.

That raises, again, the question as to whether or not a "mandatory" SB is required to be performed to maintain airworthiness under part 91 of the FARs. A couple of contributors to this blog say that the FAA told him that such was not the case and that only ADs are "mandatory." In any case I think we should comply with Rotax's SBs because they are intended to make the engines safe.

But, bottom line, it certainly appears that the quality of this SB, and perhaps some others, should meet a higher standard. We also should remember that Rotax made a pretty good video about compliance with this SB and it made no mention of how to remove the drip tray.

Also, if an SB is not legally "mandatory" then compliance within a specific time period (60 days this time) or hours of operation (25 this time) would not be required; the SB could be performed concurrent with other maintenance for instance. If that is the case I think Rotax would want to announce that in the interest of good customer service. There are a great many FBOs, flight schools and recreational fliers who will want an engine like ours because it promises good quality, economy and durability. But they are going to be hesitant to buy an airplane with a Rotax in it if we are faced repeatedly with less than adequate service instructions and if those instructions are described as "mandatory" when they are not.


EBB
 
Ex Bonanza Bucko said:
My purpose in asking the question was to call attention to the inadequacy of the SB because of that excessive delay and also because it simply says "remove the drip tray."
Click to expand...

It is as impossible for Rotax to issue airframe specific instructions regarding their engine, as it was for Continental to do so regarding engines installed on the Bonanza's you owned.

- Rotax has an entire induction system they sell as an option.
- The RV-12 doesn't use it because it doesn't need it, and it is very expensive (controlling overall kit/airplane cost)
- The optional Rotax supplied drip trays are removable from the induction system allowing for removal of the float bowls (so the S.B. covered details of what they sell).
Rotax issued the S.B. with a couple of different methods to comply, because there are many different airframe specific installations of the engine. The expect the mechanic doing the work to be able to decide what is best for a specific situation.
As for the rest of your complaint, I suggest you take it up with you local FAA FSDO.... in the end, their interpretation is the only one that matters......
 
EBB there are some 200 aircraft manufacturers installing Rotax 91x engines in their airframes. It would be difficult for Rotax to describe how to take off all the non-Rotax drip trays in the SB.

Similarly, they don't tell you in the SB how to take the engine cowlings off to get to the drip trays either.

Where will it all end....?!
 
My first 912 was on a Searey I built. There were no drip pans since the engine sat out in the breeze. Just a caveat to point the tubes aft so the bowls weren't pressurized by the slipstream. My understanding is that the ROTAX air intake box has the overflow tubes connected to it. Which leads me to my question: why not just run tubes from the carburetor overflow nipples out the bottom of the cowling and get rid of the drip pans? Anybody see an issue with this approach?
 
The airflow in the RV12 cowl is considerable. It is going right past the drip trays to the dual carb air filters. The short drip tubes drip onto the drip tray where the airflow would almost immediately evaporate it. No need to extend them to the bottom of the cowl.
 
Bill_H said:
The airflow in the RV12 cowl is considerable. It is going right past the drip trays to the dual carb air filters. The short drip tubes drip onto the drip tray where the airflow would almost immediately evaporate it. No need to extend them to the bottom of the cowl.
Click to expand...

And for proper carb operation, it is extremely important that the float bowls be at the same air pressure that exists at the inlet to the carb. The drain tubes are the vent to the float bowl, so what ever pressure the end of the tube would be located in, that is the pressure the float bowl would be at.
If you ran the drains to some other location, it would be very difficult to assure it was at the correct prssure.
 
My neighbor has a RANS S-9 with the same engine and his overflow tubes run to the bottom of his cowl, just FYI.

And Jerry, I agree with you 100%. :cool:
 
aerofurb said:
EBB there are some 200 aircraft manufacturers installing Rotax 91x engines in their airframes. It would be difficult for Rotax to describe how to take off all the non-Rotax drip trays in the SB.

Similarly, they don't tell you in the SB how to take the engine cowlings off to get to the drip trays either.

Where will it all end....?!
Click to expand...

What Rotax COULD have done is?notify aircraft manufacturers that use their engines (not that numerous to be difficult) that they had an SB coming out and allow them to notify their customers in turn regarding aircraft specific items?like drip trays.
When I contacted Vans last week about the latest SB on coolant sensors they had no answer?said they'd only just heard about it too!!

Part of this float SB is CYA for Rotax, and the other part concerns the floats.

Say what you like, several Rotax owners I've spoken with agree with EBB's view that the SB isn't well thought out as far as compliance.
The RV-12 builder community takes it in stride I think because of their 'build/problem-solve' culture whilst the SLSA owners have their hands tied.

FWIW?my mechanic removed the bowls, replaced faulty floats (I've had 3 out of 4 on a July 2014 new SLSA delivery) without removing the drip trays.
 
I get the feeling that there is a bit of misinformation forming about the 'float chamber venting lines'. Their primary task is to vent the float chambers. If the float chamber becomes to full then fuel will drain out of the vent lines.

It is not there solely as a float chamber drain line.

The carb drip trays are there to catch fuel from the carbs in general, not just the vent lines if there is an issue with the carb float chamber.

In the 912ULS installation manual ( http://www.flyrotax.com/portaldata/5/dokus/d04967.pdf Chapter 73-00-00 Para 2.1.1) it says:

Flat Chamber Venting Lines:

The float chamber venting lines have to be routed into a ram-air and vacuum free zone or into the airbox according to the requirements and release of BRP-Powertrain. See chapter 'air intake system.

These lines must not be routed into the slipstream or down the firewall.

Pressure difference between intake pressure and pressure in the carburettor chambers may lead to engine malfunction due to incorrect fuel supply.

Para 2.1.2) Drainage Piping on Carburetor

The primary function of the carburettor float chamber venting lines, is to provide ambient air pressure to the float bowl chambers. However, it is possible for fuel to be expelled from these lines.

The Rotax airbox (not used on the RV-12) has the vent lines fed into 'stagnant' areas of the airbox. With the K&N set up as used on the RV-12, the vent lines finish in a 'pressure-free' area by being held in place by the float chamber bowl spring clips.
 
The static port on my Cherokee is at the stagnation point on the aft side of the pitot mast. It seems that if the float chamber vent lines were extended to the bottom of the cowl and restrained to point aft they would track altitude. Is the critical issue to match ambient air pressure at the air filter (probably includes a ram air contribution) or to sense barometric altitude?

I'm interested because I'd like to get rid of the trays if it doesn't cause a problem.
 
RFSchaller said:
Is the critical issue to match ambient air pressure at the air filter (probably includes a ram air contribution) or to sense barometric altitude?
Click to expand...

Quoting from previous post because I'm lazy....

rvbuilder2002 said:
And for proper carb operation, it is extremely important that the float bowls be at the same air pressure that exists at the inlet to the carb. The drain tubes are the vent to the float bowl, so what ever pressure the end of the tube would be located in, that is the pressure the float bowl would be at.
Click to expand...
 
RFSchaller said:
The static port on my Cherokee is at the stagnation point on the aft side of the pitot mast. It seems that if the float chamber vent lines were extended to the bottom of the cowl and restrained to point aft they would track altitude. Is the critical issue to match ambient air pressure at the air filter (probably includes a ram air contribution) or to sense barometric altitude?

I'm interested because I'd like to get rid of the trays if it doesn't cause a problem.
Click to expand...

Rotax say where to place the float chamber vent lines and I strongly advise you heed their advice that's in their installation manual for their engine...

I would a tube imagine facing aft out of the cowlings or anywhere on the firewall is going to be sitting in a negative, low pressure area that is going to potentially upset the float level.

Regarding the PA28 pitot head mounted static port, your comment isn't strictly true. There is a single pitot port on the leading edge but two static ports. One on the lower face of the head, the other, a very small one sited on the trailing edge that is joined internally to the lower one.

Some PA28s such as the PA28-236 Dakota use the same pitot head but the static source is on the rear fuselage.

Pics below of a Diamond DA40-180 we have in on an Annual and that uses the same type of pitot head as a PA28.



 
Jerry,

I think that bottom hole is a pitot drain hole. I once had a pitot mast freeze over and the airspeed went to zero, but did not change with altitude changes like a classic blocked pitot.

Rich
 
RFSchaller said:
Jerry,

I think that bottom hole is a pitot drain hole. I once had a pitot mast freeze over and the airspeed went to zero, but did not change with altitude changes like a classic blocked pitot.

Rich
Click to expand...

Rich, it is in fact as I described it in my photos.

The PA28 (Hershey Bar) Cherokee maintenance manual says:

'Pitot air system consists of a pitot mast located on the underside of the left wing, with its related plumbing. Impact air pressure entering the pitot is transmitted from the pitot inlet through hose and tubing in the wing to the airspeed indicator on the instrument panel......

Static air system consists of a port located on the bottom of the pitot mast....'


The PA28-151/161 Warrior maintenance manual expands on the static system:

'The static air system consists of interconnected static ports on the underside and aft side of the (pitot) static mast. The ports are connected to the airspeed indicator, altimeter and vertical speed indicator.....'

I've carried out hundreds of pitot static calibration and leak checks in my time as an aircraft engineer (mechanic) - many of them on Piper style pitot static masts and I know which hole is connected to which!

This is no attempt at point scoring, I merely want to point out that aft facing vent tubes will not be at ambient static pressure and may well adversely affect the float chamber air pressure.

Rotax say don't do it and they probably know best.... ;)
 
Interesting. All this time I thought it was a drain hole because it is so much larger than the port on the trailing edge of the mast.
 
Besides making removal of the float bowls a PITA, the drip pans serve two other useful purposes.

They prevent raw gasoline from dripping on the exhaust pipe if the float bowl should over flow.

They serve as a heat shield that helps prevent radiant heat from the exhaust boiling the gasoline out of the float bowl when you shut down which makes a hot restart much easier.

If you think it is difficult to open the float bowl on your 912, try a 914. The bowl is attached with a bolt, not a slip off bail so you need more clearance and the airbox is attached to the turbo with a large, stiff hose making removal more difficult.

Jim Butcher
Europa XS, Rotax 914, GRT EFIS
 
Pop the carb back out of its rubber flange and then lift it up. Whether you have a baled or bolted float bowl it makes it easy to remove.
 
New Rotax

I just received my 912 (12-15-14) and am in the process of installing the drip trays. Can I test the floats before I complete the install? The Rotax SB says to idle 1-2 minute before the test....
 
ben barron said:
I just received my 912 (12-15-14) and am in the process of installing the drip trays. Can I test the floats before I complete the install? The Rotax SB says to idle 1-2 minute before the test....
Click to expand...

Yes, but I don't see any benefit in doing so. If I were you, I would just install it. That will take you a while... by the time you are done, there might be a different float available.

The floats need to spend some time immersed in fuel to do the test. The point of the test is to detect whether they have internally absorbed any fuel.
The reason for the 1-2 minutes is to assure the float bowl is at its normal level before doing the syringe test. If removing and weighing the floats, it is not necessary.
 
You can put the floats in a mason jar half filled with gas for a few days/weeks while you build. Weigh before and after.
 
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