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Fuel flow woes

L

leaker311

Active Member
I was hoping someone could help me out with this one...

RV-7
Setup: Mattituck IO-360 std pistons
Precision airmotive silverhawk EX fuel system
Airflow performance boost pump

I cant really say when these symptoms started, it was (apparently a slow process) not a sudden something is wrong kind of thing...

On take-off I am getting 15gal/hr fuel flow (sea level and 85F) and with 120 kts and after only 1500 feet climb my CHT's reach 400 degrees. This combination leads me to wonder whether or not I have a slightly low fuel flow. I somehow remember that in the past I was seeing more than 16, almost 17 gal/hr (which would also match the 1gal per HP rule of thumb).

I did the standard troubleshooting steps, cleaned all filters (boostpump and servo inlet filter), checked the fuel systems max FF (60gal/hr) and checked the flow gauge accuracy (less than 0.2 gal/hr off).

What would you say is the next step? I did not flow check the nozzles yet since the CHT's are within a couple degrees. I figured that this would mean that all nozzles would be clogged the same amount (which is a rare occurrence).
I was thinking about checking the flow divider (clogging, binding?) but have no clue how to do that. Can I just lift the cover off with the housing mounted to the engine or will I have springs and diaphragms flying in all directions if I do that?

this setup is only 150hrs young so I have no idea what is going on OR if I even have a problem and I am imagining things. The engine runs great otherwise, cruise, climb, idle all smooth.

Thanks in advance for all your help

Marco
 
aerhed said:
Don't forget to ensure the cables put the levers on the stops.
Click to expand...

... This is usually what is going on. Also if you have a C/S prop be sure to check its cable adjustment as well. A change in RPM could account for the fuel flow deviations....
 
Are your TO EGT's normal? How about RPM and MP?

And like said above, definately check that throttle and mixture are on the stops.

If all these check and indications are "normal", then I would suggest pullng the servo and distrubution manifold and have them flow checked.
 
On mine, both fuel pressure and indicated fuel flow go up when the boost pump is on. Do you normally use your boost pump on takeoff? If so, have you verified that it is working? Filter before the boost pump clean?

You say you have 150hrs, but we don't know if that was all during a cooler period...I can get 400 degrees at 120kts on climb out after a climb of 1500 to 2000ft if the OAT is in the 80's.

Also, timing can dramatically affect CHT's. Check that it hasn't drifted. Your temps sound normal to me, but it's good to chase down changes...
 
thank you for your help

Ok, here's what I checked so far.

Checked all the linkages, still tight smooth and free from stop to stop.

Checked the MP, RPM, EGT based on last flight's datalog.

MP engine not running - 29.87
MP full power takeoff roll - 29.37 (I have the standard smooth cowl with air filter in front of cilinder no.2. I guess this is a reasonable number based on filter loss etc. but I would love to hear your opinion)

RPM - 2690 until the governor kicked in in seconds then stab. at 2660

FF - 15.93 gal/hr peak then slowly decreasing to 15.15 as the aircraft gains altitude. From browsing through the silverhawk manual I get a feeling that the servo compensates but please check my reasoning on this)

Peak EGT during takeoff roll and climbout
EGT 1 - 1252
EGT 2 - 1307
EGT 3 - 1255
EGT 4 - 1318

These numbers dont seem too crazy to me, are they? Sure the FF is not matching the 1 gph for every HP rule of thumb; however, when I look at the Lycoming chart "part throttle fuel consumption" (granted not the exactly applicable here but the best I could find) for 100% power with 2700 rpm I find 87 lbs/hr for best power (which would roughly be 13.6 gal/hr).
This would mean a little over 2gal/hr extra for cooling the cilinders?
Do I need to start looking for other sources of the higher temps?

Someone had a suggestion to check the EGT trend while leaning in flight, unfortunately I haven't been able to get out so this is the best I could do.

Sorry for the long post, I really appreciate your help since I fly a lot over water I want to be able to have faith in my engine.

Thanks a bunch

Marco
 
leaker311 said:
Ok, here's what I checked so far.

Checked all the linkages, still tight smooth and free from stop to stop.

Checked the MP, RPM, EGT based on last flight's datalog.

MP engine not running - 29.87
MP full power takeoff roll - 29.37 (I have the standard smooth cowl with air filter in front of cilinder no.2. I guess this is a reasonable number based on filter loss etc. but I would love to hear your opinion)

RPM - 2690 until the governor kicked in in seconds then stab. at 2660

FF - 15.93 gal/hr peak then slowly decreasing to 15.15 as the aircraft gains altitude. From browsing through the silverhawk manual I get a feeling that the servo compensates but please check my reasoning on this)

Peak EGT during takeoff roll and climbout
EGT 1 - 1252
EGT 2 - 1307
EGT 3 - 1255
EGT 4 - 1318

These numbers dont seem too crazy to me, are they? Sure the FF is not matching the 1 gph for every HP rule of thumb; however, when I look at the Lycoming chart "part throttle fuel consumption" (granted not the exactly applicable here but the best I could find) for 100% power with 2700 rpm I find 87 lbs/hr for best power (which would roughly be 13.6 gal/hr).
This would mean a little over 2gal/hr extra for cooling the cilinders?
Do I need to start looking for other sources of the higher temps?

Someone had a suggestion to check the EGT trend while leaning in flight, unfortunately I haven't been able to get out so this is the best I could do.

Sorry for the long post, I really appreciate your help since I fly a lot over water I want to be able to have faith in my engine.

Thanks a bunch

Marco
Click to expand...
Little lean in my opinion,,, if it where mine I would fatten it up, I?d be looking for 18gph on a 180hp engine, My 200hp IO-360-A1A feeds 20 to 21gph at full power and the egt are in the high 11 hundreds to very low 12hundreds, My cylinders don?t get hot.
 
sorry for the slow response

Sorry Jeremy I noticed your reply after I submitted mine.

I just checked my logs and My fuel flow (and pressure) indeed increases a bit as soon as I turn on the boost pump. I always take off with the pump on and I checked the filter and it is clean.

The reason that I did not elaborate on the conditions in which the aircraft was flown is because I cannot say anything intelligent (story of my life ;-) ) about that. The hrs were flown over an almost 2year span in Texas summers/winters and Florida (dry and rainy season I guess). Somewhere in there I had (as many do) problems with my oil temps going through the roof so at one time I replaced the SW 9row cooler with a bigger cooler. There are so many variables at play when looking at the distant past that it makes it nearly impossible to pin anything down.

The idea that I am toying with around right now is that the bigger cooler is robbing enough air that I now replaced high oil temps with high CHT's.
I am sorry, I wish I had something smarter to say. The cooler was swapped during cooler weather a long time ago in a galaxy far far away and I was so focussed on lowering the oil temp that I did not analyze what the bigger cooler did to the CHT's. I was so happy that (again during cool season) now all the temps were in the green and did not worry any longer.
Recently I am flying in warm (85F) humid Florida weather and now I am starting to notice the high CHT's. Having said that I am really encouraged by your reply when I read that in 80+ temps you are seeing 400F around 2000' which is exactly what I am seeing.

I am thinking about blocking the oil cooler some (the oil temps are fine, a little cool actually) and see what that does to the CHT's. Whaddaya think is that an idea?

Russ
This exactly what I was afraid of, how can I fatten it up? I try to read the manual but the idea I am getting is that the only way to do this is replace the servo innards (ie no adjustment screw other than the idle one).

Anyone with a silverhawk EX-5VA1 IC3 servo that knows how to do this?

thanks guys
 
Last edited:
O.K. Marco, it looks like you are following the same path I went down. At first I was oil temperature limited in climb, changed to bigger oil cooler and then I was CHT limited. Part of this process was learning what was "normal". I don't think my CHT's went up much when I changed to the bigger cooler so much as my attention stopped being so much on Oil Temps when they went from 230 in climb to 180. I am not sure 400 degrees is too high, but CHT is now what you are using as your behaviour modification indicator:rolleyes: 400 degrees equals shallower climb!

I have just finished a modification that looks like it might yield significant improvement in CHTs but I have yet to have a really warm day to really test. So far, it looks like around 15 degree improvement. It was the fabrication of a curved firewall outlet at the exhaust/cylinder cooling air exit area. I'm off to test some more, but my data is a bit squishy...I only have a few data points and it's hard to recreate them on different days and atmospherics:( An engineer friend compared the drag of a 90 degree exit (existing firewall air outlet) to a curved/faired exit and it was an enormous difference. Add to that all of the draggy tubing in the way of the exit area on a nosedragger and I thought that cleaning up the exit airflow should really improve things. I copied some templates from a friend on the airfield and then modified them for my set-up.
 
leaker311 said:
Russ
This exactly what I was afraid of, how can I fatten it up? I try to read the manual but the idea I am getting is that the only way to do this is replace the servo innards (ie no adjustment screw other than the idle one).

Anyone with a silverhawk EX-5VA1 IC3 servo that knows how to do this?

thanks guys
Click to expand...
I don't know how,,,, take it off and send it in as per what Walt said would be my best guess.
 
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