Fuel Pump Orientation

Hi Rotax - Owner,

"We don't know what kind of ill effect this would have on the fuel pump/fuel pressure as we have never tested this"

Assuming, the internal design of the pump allows for cover rotation; the orientation of the cover/spigots can have no impact on the ability of the fuel pump to deliver the same pressure/volume of fuel.

I am stunned that no one seems to have explored this possibility - being able to rotate the cover OR purchase a pump with the preferred orientation, would give the aircraft builder/maintainer more fuel hose routing options. 

"Thousands of aircraft fly around with the fuel pump orientated in the original postion and with the fuel lines routed above the engine ..."

You have confirmed my own observation on the pump orientation & fuel line routing.

"......with no issues"

This is not correct - carburetor Rotax 9's operating in hot climates must be managed to minimise/prevent the potential for fuel vaporisation. This is a well know characteristic of the engine. Analogues to carburettor icing - design and management are usually combined to minimise the potential.

My question was speculative - I have no intention, at this time, in attempting to reorientate my brand new pump housing BUT at the next 5 year rubber replacement, I will be dismantling the old fuel pump, to determine how easy it might be to rotate the pump housing, then SAFTLY reassemble. I would not be surprised if there are internal features that prevent workable rotation.

I  have successfully managed the fuel vaporization issue with the  Rotax 9, for 11 Australian summers. However IF the problem (& it is a problem in hot climates) can be mitigated by routing fuel lines under, rather than over the engine - why not explore this?

Consider that in flight, the temperatures above the engine are likely considerably less than below anywhere near the exhaust pipes and muffler. Heat shields would mitigate that, but you still have to get fuel up top to the carbs. Do you have a return line to the fuel tank installed? That, and 100LL are the main reducers of vapor lock problems.

Hi Jeffry,

"the temperatures above the engine are likely considerably less than below"

I don't know, you may be correct for in flight however most fuel vaporisation problems occur on the ground and/or takeoff due to the hot engine continuing to heat the fuel line/stagnant fuel.

"anywhere near the exhaust pipes and muffler. Heat shields would mitigate that"

For most if not all applicators that I (inexperienced) have seen, this should not be a problem and as you say where it is, heat shielding/insulation can be used.

"still have to get fuel up top to the carbs."

The carburettor spigots point down - so receiving fuel from below the engine should not be a problem.

I don't have a fuel vaporization issue - I have been flying behind a Rotax 9, in Australia, for about 11 years and employ a number of, so far successful, management strategies to minimise the problem during the summer months.

What I don't understand is why Rotax do not;

Offer a fuel pumps with spigot orientation options

AND/OR

Instructions in how to orientate (rotate the cap) to the owners preferred direction for their application.

We posed your question to the Rotax Factory, and here is the response: If you turn the fuel pump connections => the height difference to the carburetors always becomes greater, and the fuel line gets longer, resulting in an unequal supply of the left and right carburetors. Rotax has tested this very often and in different ways from the beginning. The best is to keep the lines as short as possible, have them centered for an equal supply of both carburetors, and most importantly, have a fuel return line to the tank. If customers turn the fuel pump connection direction, it voids all warranty from Rotax as there are many hours of testing on the design.

To sum up: There are better and safer ways to solve a vapor lock issue. Tens of thousands of Rotax flying around in many different types of aircraft with the fuel pump orientated /clocked in the original location.

"the height difference to the carburetors always becomes greater, "

?????????? - cant see this. The height relationship, pump to carb. float bowl remains the same

".... the fuel line gets longer"

Possibly.

"resulting in an unequal supply of the left and right carburetors."

What? - there is a single hose supply to carb.  which must be divided. How & where the installer divides the hose/supply will influence the length of the two hoses. I am sceptical that, over this short distance, there can be a significant difference in fuel supply to each float bowl.

"If customers turn the fuel pump connection direction, it voids all warranty"

To what does the "warranty" apply - pump? whole engine? I doubt that an engineer/lawyer could successfully argue that a change in fuel routing, of the type I am speculating on, could cause damage.

"There are better and safer ways to solve a vapor lock issue"

I would suggest that the fuel vaporisation issue is a characteristic of the current Rotax 9 carb. fuel supply, as such  it is unlikely to be "solved", only mitigated through having a fuel return line/ cowl design/ shielding/ insulation/ management strategies.