Yesterday I went out to fly my airplane and ran into an interesting issue. I recently changed my oil and did not run it after the change so yesterday when I got to the field I checked the oil level and started the engine. I let it run long enough for the oil temp to get to 150 and shut it down to check for leaks after the oil change. The engine ran fine at 1000 rpm. After I checked for leaks I did a preflight and taxied to get fuel. I put 12 gal. of 100 LL in and then left the airplane at the pump to let it settle. I let it settle for about 10 minuets checked for contamination jumped in and started it up with no problems. The run up was fine with about 50 RPM drop between both Mags and the carb heat dropped about 100 RPM. During the take off roll I was thinking that it was taking a long time for the tail to come up but it did and as I was climbing out I knew something was not right and checked the RPM and was only getting 2100. I came back to the field and made an uneventful landing. When I got back on the ground I did another run up with the same results. Every thing appears to be normal but at full throttle I am only getting 2100 RPM. I am at sea level with about 70 degrees F so I should have a lot more.
The only thing that I can think that would cause this is bad fuel. I am the only person using the fuel out of this tank and I know that it has been in the tank a long time, I don’t know how long. I did fill the A/C tanks up with fuel from this tank less than a month ago and it was fine then.
Any ideas?
Loss of engine power
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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Bruce Fenstermacher
- Posts: 10318
- Joined: Tue Apr 23, 2002 11:24 am
Bill
First a few comments about your procedure for looking for contaminants (water) in the fuel. I see this all the time on the ramp and just shake my head. People full their tanks totally mixing any water they had in the tank with the gas they just put in. then they immediately sump for water. Their not going to find any in the tanks cause it hasn't settled out yet. You at least waited ten minutes but I'll bet it takes much longer than that. I've not tested 100LL and measured the depth of our tanks but in a UH-1H which had much deeper tanks and of course used JP-4 it would take better that 2 hours to settle out.
OK now for you problem. First I doubt if it's the fuel. I'm assuming you've gotten higher static RPM with similar conditions before.
When this has happened to me I usually find I've left one mag off or have the carb heat on. Ok you've checked the mags and with both checking out OK and still the same low RMP I'd look real close at the carb heat.
Does the carb heat actually open and fully close in the carb heat box when activated by the carb heat knob?
While you looking at the carb and cables does your throttle cable actually move the throttle plate lever on the carb from the idle stop to full open.
Anything blocking the carb air intake? How is your air filter? On a clean macadam ramp I would not be afraid to remove the air filter and do a run up to compare with and without.
Last if you don't find anything and your RPM returns next time at the airport I wouldn't discount carb ice. It's unlikely but it could happen and not being there myself to witness the atmospheric conditions and your exact procedure I wouldn't rule it out.
First a few comments about your procedure for looking for contaminants (water) in the fuel. I see this all the time on the ramp and just shake my head. People full their tanks totally mixing any water they had in the tank with the gas they just put in. then they immediately sump for water. Their not going to find any in the tanks cause it hasn't settled out yet. You at least waited ten minutes but I'll bet it takes much longer than that. I've not tested 100LL and measured the depth of our tanks but in a UH-1H which had much deeper tanks and of course used JP-4 it would take better that 2 hours to settle out.
OK now for you problem. First I doubt if it's the fuel. I'm assuming you've gotten higher static RPM with similar conditions before.
When this has happened to me I usually find I've left one mag off or have the carb heat on. Ok you've checked the mags and with both checking out OK and still the same low RMP I'd look real close at the carb heat.
Does the carb heat actually open and fully close in the carb heat box when activated by the carb heat knob?
While you looking at the carb and cables does your throttle cable actually move the throttle plate lever on the carb from the idle stop to full open.
Anything blocking the carb air intake? How is your air filter? On a clean macadam ramp I would not be afraid to remove the air filter and do a run up to compare with and without.
Last if you don't find anything and your RPM returns next time at the airport I wouldn't discount carb ice. It's unlikely but it could happen and not being there myself to witness the atmospheric conditions and your exact procedure I wouldn't rule it out.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bill, before you go to too much trouble, you might want to consider whether your memory serves you well as regards prior flights. Have you consciously looked at your tach on EVERY takeoff?
It's a habit we all should be doing. Unless we look at the RPM developed at the start of the takeoff roll, and unless that RPM is close to the rated/stated RPM,... we shouldn't continue the takeoff.
The Type Certificate Data Sheet (TC or TCDS) states that with the McCauley props which are standard with this airplane, the static RPM shoud be 2230-2330 (DM prop) or 2250-2350 (MDM prop). These are all relative to the standard props, generally in the 7653 dia/pitch range.
The Sensenich prop is almost identical, calling for 2220-2320 (M74DR prop.)
There are other considerations. 1- Is your tach accurate? Have you actually had it checked with a digital tach-accuracy meter? (If you are a TIC170A member (and I see that you are), I have one I can loan you for the cost of postage.) 2- Have you taken into consideration the "parallax" which exists from the left seat? This is generally in the 50-100 RPM range, and makes the tach appear to read higher than actual, however. (Not likely a helpful factor in your case.) 3- Did you take the reading in calm wind conditions? 4- And, as Bruce and Trake have pointed out, ... are you certain that engine controls are functioning correctly, and are correctly set for takeoff? 5- Magneto timing is a common problem regarding low static RPM. In modern times, with modern electronic/computer ignition in our vehicles, we frequently forget just how easy it is for timing settings to slip, not only because of vibration, etc., but also because of simple wear of the points-rubbing-block and gear wear. Have your mags timing and your mag-to-engine timing checked. You might be surprised how easy it is to slowly accept a deteriorating condition as "normal". I've seen engines gain 200 RPM with a simple mag timing check! No kidding. The airplane had been annualed for years by the same lazy mechanic/inspector who'd taken the owner's happy comments as to how it was running too literally. I doubt the mag timing had been checked for over 3 years. The plugs were almost completely fouled with lead deposits and the center electrodes were a thin ellipse. (Owners frequently praise their airplanes to mechanics prior to annual inspections. Wonder why?)
A physical inspection of the air filter is also warranted. The filter should be clean and/or new, and the area behind the filter should be inspected for a healthy fire-screen and carb-heat/throttle plates which are fully open.
One item not yet mentioned is the mixture setting. Normally, if the carb is set and operating correctly, the mixture should be full rich for takeoff... but for troubleshooting, I'd suggest you open the throttle wide, then lean it for max RPM to see what static you can achieve.
Be very careful if you do operate with the filter removed. Have a helper with a fire extinguisher handy, and make certain everyone is briefed to stay away from that prop and the prop blast.
Make sure you either have the tail tied down, the wheels chocked, and/or you have the brakes set, yoke full back, and preferably a safety observer in the cockpit with you. It'd be a shame to roll into something or otherwise have an accident/incident while distracted during troubleshooting.
Finally, it's never a bad idea to load the plane to gross wt, and actually measure the ground roll required for takeoff on a paved, level runway. It should be very nearly what the Owners Manual states for the atmospheric conditions.
Let us know what you find.
It's a habit we all should be doing. Unless we look at the RPM developed at the start of the takeoff roll, and unless that RPM is close to the rated/stated RPM,... we shouldn't continue the takeoff.
The Type Certificate Data Sheet (TC or TCDS) states that with the McCauley props which are standard with this airplane, the static RPM shoud be 2230-2330 (DM prop) or 2250-2350 (MDM prop). These are all relative to the standard props, generally in the 7653 dia/pitch range.
The Sensenich prop is almost identical, calling for 2220-2320 (M74DR prop.)
There are other considerations. 1- Is your tach accurate? Have you actually had it checked with a digital tach-accuracy meter? (If you are a TIC170A member (and I see that you are), I have one I can loan you for the cost of postage.) 2- Have you taken into consideration the "parallax" which exists from the left seat? This is generally in the 50-100 RPM range, and makes the tach appear to read higher than actual, however. (Not likely a helpful factor in your case.) 3- Did you take the reading in calm wind conditions? 4- And, as Bruce and Trake have pointed out, ... are you certain that engine controls are functioning correctly, and are correctly set for takeoff? 5- Magneto timing is a common problem regarding low static RPM. In modern times, with modern electronic/computer ignition in our vehicles, we frequently forget just how easy it is for timing settings to slip, not only because of vibration, etc., but also because of simple wear of the points-rubbing-block and gear wear. Have your mags timing and your mag-to-engine timing checked. You might be surprised how easy it is to slowly accept a deteriorating condition as "normal". I've seen engines gain 200 RPM with a simple mag timing check! No kidding. The airplane had been annualed for years by the same lazy mechanic/inspector who'd taken the owner's happy comments as to how it was running too literally. I doubt the mag timing had been checked for over 3 years. The plugs were almost completely fouled with lead deposits and the center electrodes were a thin ellipse. (Owners frequently praise their airplanes to mechanics prior to annual inspections. Wonder why?)
A physical inspection of the air filter is also warranted. The filter should be clean and/or new, and the area behind the filter should be inspected for a healthy fire-screen and carb-heat/throttle plates which are fully open.
One item not yet mentioned is the mixture setting. Normally, if the carb is set and operating correctly, the mixture should be full rich for takeoff... but for troubleshooting, I'd suggest you open the throttle wide, then lean it for max RPM to see what static you can achieve.
Be very careful if you do operate with the filter removed. Have a helper with a fire extinguisher handy, and make certain everyone is briefed to stay away from that prop and the prop blast.
Make sure you either have the tail tied down, the wheels chocked, and/or you have the brakes set, yoke full back, and preferably a safety observer in the cockpit with you. It'd be a shame to roll into something or otherwise have an accident/incident while distracted during troubleshooting.
Finally, it's never a bad idea to load the plane to gross wt, and actually measure the ground roll required for takeoff on a paved, level runway. It should be very nearly what the Owners Manual states for the atmospheric conditions.
Let us know what you find.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
All,
I thank you for your input.
Bruce,
I am with you on the contamination being suspended for a long time after you fill the tanks, but I check it before I take off, it might be ten minutes or 1 hour it just depends on the situation. I will be checking the linkage (throttle and carb heat) the next time I am at the field. I had thought of the carb heat but I was getting a good drop when I did the run up but I am going to be looking at every thing so I will check that out also.
George,
In my other life I am a C130 flight engineer and as such it is in my nature to monitor engine output on every take off. You are correct on the timing issue and I had not thought of that so that is something I will be checking also. I was planning on replacing the plugs this annual and I am now thinking that I will go ahead and do that now and not wait.
I do want to thank you all for a very valuable service and I think that it is well worth the $45.00. Mailings or not.
I thank you for your input.
Bruce,
I am with you on the contamination being suspended for a long time after you fill the tanks, but I check it before I take off, it might be ten minutes or 1 hour it just depends on the situation. I will be checking the linkage (throttle and carb heat) the next time I am at the field. I had thought of the carb heat but I was getting a good drop when I did the run up but I am going to be looking at every thing so I will check that out also.
George,
In my other life I am a C130 flight engineer and as such it is in my nature to monitor engine output on every take off. You are correct on the timing issue and I had not thought of that so that is something I will be checking also. I was planning on replacing the plugs this annual and I am now thinking that I will go ahead and do that now and not wait.
I do want to thank you all for a very valuable service and I think that it is well worth the $45.00. Mailings or not.
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Jr.CubBuilder
- Posts: 517
- Joined: Thu Aug 12, 2004 10:33 pm
Ok I'll up my membership bid to $43.52, but that's my highest offer................I'm kidding, that's a joke, really.
I just got an email from George, and I'm guessing from Bill's comment that my post about a $10 online membership must have started something, however it got moved to the members only section so I don't know. Hey it was just a suggestion, not a complaint.
Bill I just thought I would mention I had a sort of similiar experience last year with my new to me 170. It turned out to be a bad ignition cable on one of my mag harness's. It had gone south while I was flying, and I had a vague gut feeling that the motor wasn't running as smooth as it had but shrugged it off because that happens every time I fly over water or mountains. Turned out it wasn't my imagination when I went flying a week later. Just a thought.
Oh if you do run into that, my mechanic showed me a neat trick to check that. Just run the motor for a minute or two on one mag, shut it off, then use a squirt bottle with water to find the cold exhaust pipe (riser?). Worked like a charm.
I just got an email from George, and I'm guessing from Bill's comment that my post about a $10 online membership must have started something, however it got moved to the members only section so I don't know. Hey it was just a suggestion, not a complaint.
Bill I just thought I would mention I had a sort of similiar experience last year with my new to me 170. It turned out to be a bad ignition cable on one of my mag harness's. It had gone south while I was flying, and I had a vague gut feeling that the motor wasn't running as smooth as it had but shrugged it off because that happens every time I fly over water or mountains. Turned out it wasn't my imagination when I went flying a week later. Just a thought.
Oh if you do run into that, my mechanic showed me a neat trick to check that. Just run the motor for a minute or two on one mag, shut it off, then use a squirt bottle with water to find the cold exhaust pipe (riser?). Worked like a charm.
Most shops also have a "high tension lead tester" that can check such things also. I have one in my "fly in kit",... a set of diagnostic tools I usually bring to Fly In's (including a compression testor, digital tach testor, etc. etc.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.