Thorp Air Command - T18.net

I have been flying my new engine here recently and I have noticed something odd. When I am in level cruise flight, and I go full throttle and full rich, I think I feel the plane surging. The rpms are steady, fuel pressure is steady, every reading is dead steady. I almost thought that I was hearing a surge as opposed to feeling a surge, but I was unable to determine which one. When I throttle back and lean the mixture, I do not sense this surge. I do not sense this surging during take offs (where I am full throttle and full rich). Have any of you felt or heard your plane surging? I have a wooden, fixed pitch prop.

My (actually Wendell's N51863) 0-360 runs very rich even at sea level, try leaning it a bit. Also, have you had it dynamically balanced? You may be feeling a hamonic effect of an imballance at higher RPMs.

_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD

yes, leaning did help the issue. I have not had the prop dynamically balanced, but that is on my to do list. I think I will move that closer to the front of the list and see what happens.

The Lycoming peple will tell you "If it is not under full power, lean it" I use full lean on takeoff and lean as I reduce power. even when taxing lean it.
Do you see a change in RPM or manifold pressure?
Different engine could cause harmonics in the fuselage giving the feel of surge, exhaust hitting cowl etc.?

If you feel a surge but don't hear it, or no other visual indication, it may be the fuel sloshing fore and aft in the tank. I have felt that numerous times in the past. If the tank is low, it won't do it as not enough mass to be felt even if it is sloshing. Maybe try flying with a 1/4 tank and see if it still does it. Also, if in smooth air, fly straight and level for at least a couple minutes with no movements to give the sloshing time to die.

Bernie Fried
N18XS

Weird, I had the same suspicion on occasion over the past few months, yet could not see/detect an RPM fluctuation - I have a C/S prop....my plane is just out of conditional - the throttle armature was a little loose, so I ended up pulling the (recently rebuilt) carb and replacing the bushings and putting a new arm in - in the process, we noticed the screw that goes in the front of the carb near the top (I don't have it in front of me, so pardon the generic description) was sticking out into the carb throat and it was obvious there was an "eddy" being created when the fuel was atomizing while being jetted up the carb....We fixed that condition and I just flew it for the first time Tuesday evening and noticed my idle had improved - ticking smoothly along at 700-725, vs 800 RPM previously - I did not look for the "surging", but am suspecting that the slight disruption of the air/fuel mixture through the throat at that "eddy" may have been a cause. Think of an eddy or standing wave in a river, and how it "ebbs and flows" irregularly.

Food fer thinkin....

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

Bill
I don't see a change in RPM or manifold pressure. My exhaust does just touch the side the bottom cowl where it exits. I will address that. That's a good thought. I too lean for taxi.



Bernie
I will give this a try too. I never had this sensation while flying with my 0-290 up front, but anything is worth a try



That's interesting Frazier. I will check that while I am reducing my idle rpms. I have it set a little too high right now.

I too have experienced the "Surge" and thought I was imagining things (I do that on occasion). After reading this thread I've scheduled a dynamic balance for next week, I'll let you know the outcome.

Bernie, you going to OSH?

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Chuck Kincer
Richmond, Me
575CK
KIWI

Yes. Planning on arriving July 27 and leaving Aug 2. Hope to see you there.

Bernie Fried
N18XS

I have the AD prop and on occasion at a certain RPM I hear what sounds/feels like a surge . I am not a prop guy , but I suspect some sort of harmonic in balance at that RPM . Increasing/decreasing the power slightly makes it go away ? BOOM ! My 0-360 runs rich on the ground and I lean to the max . Full rich for TO , but once airborne it likes to be leaned out immediately . Once at cruise my fuel flow is about 8-8.5 gph at 2400 rpm . Arriving at OSH on the 28th and departing on the 3rd .

RB

Just got back from getting my prop "dynamically Balanced". Turns out it was .50 ips out (inches per second?) once finished it was down to .02 ips, they added 32 grams to the flywheel. The balancing thus far seems to have made a positive improvement, no more vibrating GPS screen for one!

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Chuck Kincer
Richmond, Me
575CK
KIWI

Got an hour on the plane since fixing that little carb fuel eddy issue during conditional - have not felt a surge since - am perdy convinced that was causing it - though for good measure and added protection, I put a surge protector in my flight bag as well.

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

Please leave your surge protector and other toys at home prior to our flight to OSH ! POW !

RB

Do a search at www.flyhusky.com. The Husky has had surging
Problems forever and fine wire spark plugs seems to be the cure.
Dave