Fuel Flow Rates for 912is

[tracstarr]

Just wondering if anyone can provide me what fuel flow rates they are getting. My buddy wants to compare the rates we just calculated for his which he feels might be a bit low.

[efwd]

All that is required is 120% of what the 912iS motor is requiring on takeoff. That is with the fuel pump running. The manual will tell you what the fuel requirement would be. Im fixing to do that same thing probably Friday but I forget exactly what that value is. I believe you must do the check on each of the two pumps while in level, flight attitude and again with the tail slightly lower than what climb attitude would be.

[tracstarr]

Thanks. Yeah, although we've passed the 120% (i think it was 135%) he is still uncertain that this is ok and asked me to ask what others were getting.

[efwd]

I did my fuel flow on my 912iS Friday. Each of the two pumps pushed 1 gallon in 1minute and 10 seconds. That's over 51 gallons an hour. The 912iS needs 6.9gal/hr at 5800rpm. If those are the kind of numbers your friend had then I am confused over the concern. I am questioning whether I did this correctly. Did he check the flow via gravity and not with the pumps? My flow, so far exceeds the 150% that I am confused. I think I did this correctly because I don't believe the fuel injection will operate by gravity flow but it requires the pumps. However, how does a pump pushing 51gal/hr cause any concern in your friends mind?

[jrevens]

I believe that the test is generally done to check flow capability of the system without the pump(s) operating. I might be wrong as I’ve never built an airplane that required a fuel pump, and fuel injection adds another factor. If the engine won’t run at all without a pump, then there would seem to be little reason to test without. Checking with the pumps running is a good idea anyway of course, but it’s good to know what the flow rate is if a pump fails.

[tracstarr]

I will discuss with him tomorrow how it was done etc.

[efwd]

I did note that there is a flow by gravity but I didn't time that. I believe the 912iS requires fuel pumps as the injection system requires pretty high pressure. My document that was supplied with the registration paperwork (EAA) has two ways from which you must select from, one for gravity fed systems and one for fuel pump systems presumably high wing and low wing arrangements. Naturally I have selected the fuel pump version since its my understanding the engine won't run without a pump. In fact, both pumps are to be in the on position for takeoff. Quite honestly, I don't recall turning pumps on and off during my flight training with Stick and Rudder. That is why I am going back to train more before first flight. I have an email in to John to confirm the test is with pumps. I will let you know.

[rosslr]

H Eddie

You are right about the engine not running without one of the pumps. But I did the gravity flow test ( and it delivered heaps more than the engine uses) as I thought that was most important - there must be adequate fuel delivered to the pumps so they can deliver it at the pressure required by the engine. If the pumps are working then they will deliver the fuel at the pressure needed - no doubt about that. But if they are not working chances are it will be an electrical fault. That is why we have two pumps. I turn one off after take off as it makes my pressure too high with both - actually it is about 47psi with both which is at the upper limit.

cheers

r