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Deceleration after take off.

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PensacolaPilot

Member
Here's a puzzler: I replaced a master brake cylinder on the left side and bled the brakes afterwards. No issues. On the next takeoff I noticed some sudden deceleration, like a car being driven through a puddle. ( around 150 ft agl, so not immediately after lift off) Lasted maybe one second, the rest of the flight was uneventful. Next takeoff, same thing, except there were three or so decelerations, each lasting less than a second. I landed, checked mags, fuel, air, but everything checks out OK.
I mentioned the brake job only because it was the last maintenance performed, the plane flew great before, not so great afterwards. I cannot imagine the two events being related but I don't believe in coincidences either. Any ideas? My next step is to remove the wheel fairing and examine the tire and brake assembly.
 
I don't see any conceivable way that a brake job could affect the plane in the air. However, it's entirely possible that something under the hood got jostled while you were in there. If it were me, I'd start looking around to see if something knocked loose, like maybe a p-lead or something.

If nothing presents itself, you may just have to start believing in coincidences...
 
How are you measuring "deceleration?" Did the airspeed fall off precipitously? RPM drop? MAP drop? People on the ground start pointing/waving at you? :)
 
Yes, first thing I’d check would be if one ignition or mag is dropping out.
Second thing would be prop governor control cable & governor fluctuation
Third thing would be fuel pump & pressure.
 
I agree with Terry - I don’t see any way brake maintenance can effect in flight performance. You mentioned a deceleration as your indication of something not being right. To me that means either an increase in drag, or reduction in power to your prop. Did you notice in a change in engine sound? Was there an indication of reduced manifold pressure, RPM, fuel flow, or a sudden change in EGT? Is there anything structural that could have come loose causing an increase in drag? If that was the case, it doesn’t seem like it would just go away. I would start by looking at loose intake tubes, spark plug wires, fuel delivery plumbing (carb or FI), especially if the engine operation stayed smooth without a miss, or rough running. Almost sounds like carb heat suddenly came on and then went off. Possibly some sort of fuel delivery issue.
 
Do you use your auxiliary fuel pump on take off? Sounds like a fuel issue to me. Just after take off is when you will have one of the highest fuel flows for the engine. Try taking off with the auxiliary pump if you don’t normally use it and see if anything changes.
 
PensacolaPilot said:
Here's a puzzler: I replaced a master brake cylinder on the left side and bled the brakes afterwards. No issues. On the next takeoff I noticed some sudden deceleration, like a car being driven through a puddle. ( around 150 ft agl, so not immediately after lift off) Lasted maybe one second, the rest of the flight was uneventful. Next takeoff, same thing, except there were three or so decelerations, each lasting less than a second. I landed, checked mags, fuel, air, but everything checks out OK.
I mentioned the brake job only because it was the last maintenance performed, the plane flew great before, not so great afterwards. I cannot imagine the two events being related but I don't believe in coincidences either. Any ideas? My next step is to remove the wheel fairing and examine the tire and brake assembly.
Click to expand...
I could not "measure" aka quantify the deceleration, hence my analogy of driving a car through a puddle. Just enough to startle me.
I use my electric stand by fuel pump on takeoff. No RPM drop. Can't be the governor because I have a fixed pitch prop.
I'll start troubleshooting this weekend, and hopefully find something. Very unnerving. Thanks for all the inputs!!
 
Well, then I want to change my previous comments; If you're sure there's no RPM drop, then thrust isn't changing so that only leaves drag. Have you possibly got a loose wheel pant or faring? Those are obviously something you mess with during a brake job and I can imagine if you have a wheel pant flopping around it might cause a bit of drag...
 
Almost sounds like gusts/shear. WX at the time? Any more repeats? I agree this would really erode my confidence in the aircraft until I had some kind of explanation and a fix.
 
Would depend if your rpm's went down or didn't. First thing I thought when I read your post is engine sucking air. An air leak in the fuel line system can cause intermittent or full on power loss in any engine. Had that happen on a boat once, and took forever to figure out a fuel filter I replaced was not fully seated and sucking air at higher throttle levels. Failing fuel pump would be another. If it's carbureted the high angle of attack along with a carb float problem/needle valve issue developing could also be the culprit. Unfortunately could be a lot of things and not easy to trouble shoot.

A static full power run up, and watching your fuel pressure on the electric pump and on the engine pump would be a start. Check your weep line on your mechanical fuel pump for gas leaking. Then, if you're brave, take the plane up nice an high and over an airport, and replicate take off power and pitch attitude, and see if you can reproduce the symptoms. Of course only if your piloting skills are up to all the possibilities.
 
Fuel pressure on the electric fuel pump and the engine driven pump. Did you have good pressure after the miss/deceleration?
 
I think everyone is wasting their time. OP joined in 2011, 8 posts since then, looks like random questions to start the thread then pulls a disappearing act.

Sad.
 
PensacolaPilot said:
Not disappearing, just really busy. And reading threads is still activity. Sorry I don't have more issues with my plane....
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If you're going to ask questions, then it's usually considered good courtesy to respond back to questions that are asked of you. Do you have data from the engine monitor that we can look at? What have you done based on the suggestions given in this and other posts? Did you solve the issue? Etc.

This is an interactive forum, so people expect some interaction, not just the internet equivalent of "hey, here's my problem, fix it for me" and then disappearing. Let us know what you have tried, if you identified the cause and fixed it, etc.

Otherwise, don't be surprised if people stop responding.
 
RV7A Flyer said:
If you're going to ask questions, then it's usually considered good courtesy to respond back to questions that are asked of you. Do you have data from the engine monitor that we can look at? What have you done based on the suggestions given in this and other posts? Did you solve the issue? Etc.

This is an interactive forum, so people expect some interaction, not just the internet equivalent of "hey, here's my problem, fix it for me" and then disappearing. Let us know what you have tried, if you identified the cause and fixed it, etc.

Otherwise, don't be surprised if people stop responding.
Click to expand...
I see. Unaware as far as etiquette goes, I am sorry.
Anyway, I believe I have found the root cause to be a sticky carburetor float valve. It works great on the ground, but on climb out, with the change in pitch, it sticks. Talked to an owner of a flight school, and he told me that several of his airplanes had this problem. Next step will be to remove the carburetor and see if it needs rebuilding. This will take some time but I will post once this issue resolves itself. (or not)
 
Desert Rat said:
I don't see any conceivable way that a brake job could affect the plane in the air. However, it's entirely possible that something under the hood got jostled while you were in there. If it were me, I'd start looking around to see if something knocked loose, like maybe a p-lead or something.

If nothing presents itself, you may just have to start believing in coincidences...
Click to expand...
Please see my post at the bottom of this. ( sticky float valve) Would be one heck of a coincidence!
 
PensacolaPilot said:
I see. Unaware as far as etiquette goes, I am sorry.
Anyway, I believe I have found the root cause to be a sticky carburetor float valve. It works great on the ground, but on climb out, with the change in pitch, it sticks. Talked to an owner of a flight school, and he told me that several of his airplanes had this problem. Next step will be to remove the carburetor and see if it needs rebuilding. This will take some time but I will post once this issue resolves itself. (or not)
Click to expand...
😑Oooooommmmmmmmm.................

Respond when you are able. Good thing you aren't in junior high and not responding to your girlfriend's texts!!:ROFLMAO:😂

OK: it could be the float valve. I would do what was advised in post # 11 and reproduce your takeoff AOA and power at altitude and see if the problem occurs. It seems odd that a sticking float valve would be that momentary and not during cruise. No RPM loss, right? How many hours are on your engine? Sometimes these problems are tough to chase down.

Case in point: I was having rare momentary pauses in the Cub that were almost an afterthought. Kind of like "auto-rough". Did I feel something.....? Hmmm. I wasn't sure I was really even feeling anything. Then one fine morning after flying to a back-country strip an hour away, was halfway back home (one hour out and 30-40 minutes of flight time coming back) and had a sudden but significant power loss for about 5-10 seconds......or was it 2 days....it seemed like forever! I did all my engine out procedures (which I regularly practice, by the way, including 'where are we going to land'....) and was setting up to put her down in a stubble field and the power came back. Landed at a friend's strip 5 minutes away and did a ground runup: nothing. Flew the 30 minutes home without incident and nothing felt. Do I have engine instruments? Yes: tach, oil pressure and temperature! 😆 My altimeter has one needle!:oops: She was born in 1946!

Drained the float bowl (PITA), took the carb screen out, the gascolator apart: nothing. Finger screens in the tanks and quick drains out and cleaned: nothing. Mag check including wires: nothing. Compression check: nothing amiss. Spark plugs: all checked out. Huh. Flew for 3-4 more hours before she did it again. Time to get serious. Changed all soft fuel lines and blew out all the hard lines. Inspected tank interiors. Installed a new, more modern gascolator. Installed rebuilt mags (~400 hours since new on the old ones) and carburetor. Took the selector valve apart and cleaned it. New spark plugs. What else was I missing? She has an "Armstrong" starter (hand propped) and, after all that, when I was starting her, felt a slightly soft cylinder.....with the compression test being normal. ⁉️ She started normally so I warmed her up (normal running) and took her to the runup area. She ran up fine but didn't feel quite right at full throttle. Sometimes that feeling is all it takes. Took her back to the hangar and shut her down. Pulling the prop through and, after ALL THAT, found a stuck exhaust valve on one cylinder!! Short end of a long story: replaced the cylinder and she has been fine since. And look at all the new things she has!

So: could you have a momentarily sticking valve? Done the wobble test lately? If you are sending the carb off you'll have plenty of time to do that! Just an idea. IMHO; YMMV....
 
Just started reading this thread and the first thing that came to mind was the carburetor. I had a Luscombe that was great at start and mag check but on takeoff power went to idle at about 100' agl. Pretty big pucker factor. Turned out to be a tiny piece of cotton (?) in the float bowl that partially plugged the main jet. You're smart to investigate now before you fly again.
Be sure to let us know what you find.
danny
 
I’m very confused by this scenario. If its a carb with a sticking float or valve being implicated you would have gone over rich if stuck open or lean out if the needle vavle stuck closed. And then I can’t understand how you would translate this to several individual seconds during a climb out. That said it was also mentioned RPM didn’t change through All this. If the carb stuck, one way or another how does this not translate to a reduction in RPM (if it’s feeling like a deceleration). it simply doesn’t sound like a sticking float, but of course I could be wrong.
That said, if it is a sticking float or something related to fuel delivery then take a more conservative approach. Do the climb test without the engine running. Meaning, set your attitude of the fuselage to climb attitude and see if you are actually delivering fuel as expected. Maybe you have an intermittent blockage. In flight is no place to discover this.
Just my own thoughts of course.
 
Roadjunkie1 said:
😑Oooooommmmmmmmm.................

Respond when you are able. Good thing you aren't in junior high and not responding to your girlfriend's texts!!:ROFLMAO:😂

OK: it could be the float valve. I would do what was advised in post # 11 and reproduce your takeoff AOA and power at altitude and see if the problem occurs. It seems odd that a sticking float valve would be that momentary and not during cruise. No RPM loss, right? How many hours are on your engine? Sometimes these problems are tough to chase down.

Case in point: I was having rare momentary pauses in the Cub that were almost an afterthought. Kind of like "auto-rough". Did I feel something.....? Hmmm. I wasn't sure I was really even feeling anything. Then one fine morning after flying to a back-country strip an hour away, was halfway back home (one hour out and 30-40 minutes of flight time coming back) and had a sudden but significant power loss for about 5-10 seconds......or was it 2 days....it seemed like forever! I did all my engine out procedures (which I regularly practice, by the way, including 'where are we going to land'....) and was setting up to put her down in a stubble field and the power came back. Landed at a friend's strip 5 minutes away and did a ground runup: nothing. Flew the 30 minutes home without incident and nothing felt. Do I have engine instruments? Yes: tach, oil pressure and temperature! 😆 My altimeter has one needle!:oops: She was born in 1946!
o hold only 80 knots
Drained the float bowl (PITA), took the carb screen out, the gascolator apart: nothing. Finger screens in the tanks and quick drains out and cleaned: nothing. Mag check including wires: nothing. Compression check: nothing amiss. Spark plugs: all checked out. Huh. Flew for 3-4 more hours before she did it again. Time to get serious. Changed all soft fuel lines and blew out all the hard lines. Inspected tank interiors. Installed a new, more modern gascolator. Installed rebuilt mags (~400 hours since new on the old ones) and carburetor. Took the selector valve apart and cleaned it. New spark plugs. What else was I missing? She has an "Armstrong" starter (hand propped) and, after all that, when I was starting her, felt a slightly soft cylinder.....with the compression test being normal. ⁉️ She started normally so I warmed her up (normal running) and took her to the runup area. She ran up fine but didn't feel quite right at full throttle. Sometimes that feeling is all it takes. Took her back to the hangar and shut her down. Pulling the prop through and, after ALL THAT, found a stuck exhaust valve on one cylinder!! Short end of a long story: replaced the cylinder and she has been fine since. And look at all the new things she has!

So: could you have a momentarily sticking valve? Done the wobble test lately? If you are sending the carb off you'll have plenty of time to do that! Just an idea. IMHO; YMMV....
Click to expand...

I was flying a friends RV7A, 100 feet up on climb out lost what seemed 75% power (was able to hold only 80 knots level). About to crash land in a field when fill power came back, was able to land at airport.

Thinking ignition plugs they where cleaned etc then successfull 30 minute flight, turned out to be sticking exhaust valve. Lycoming had sold a batch of cylinders with a too tight exhaust valve guide clearance. At approx 100 hours valve would stick. Afte reaming the guide all has been well for 150 hours
 
Roadjunkie1 said:
😑Oooooommmmmmmmm.................

Respond when you are able. Good thing you aren't in junior high and not responding to your girlfriend's texts!!:ROFLMAO:😂

OK: it could be the float valve. I would do what was advised in post # 11 and reproduce your takeoff AOA and power at altitude and see if the problem occurs. It seems odd that a sticking float valve would be that momentary and not during cruise. No RPM loss, right? How many hours are on your engine? Sometimes these problems are tough to chase down.

Case in point: I was having rare momentary pauses in the Cub that were almost an afterthought. Kind of like "auto-rough". Did I feel something.....? Hmmm. I wasn't sure I was really even feeling anything. Then one fine morning after flying to a back-country strip an hour away, was halfway back home (one hour out and 30-40 minutes of flight time coming back) and had a sudden but significant power loss for about 5-10 seconds......or was it 2 days....it seemed like forever! I did all my engine out procedures (which I regularly practice, by the way, including 'where are we going to land'....) and was setting up to put her down in a stubble field and the power came back. Landed at a friend's strip 5 minutes away and did a ground runup: nothing. Flew the 30 minutes home without incident and nothing felt. Do I have engine instruments? Yes: tach, oil pressure and temperature! 😆 My altimeter has one needle!:oops: She was born in 1946!

Drained the float bowl (PITA), took the carb screen out, the gascolator apart: nothing. Finger screens in the tanks and quick drains out and cleaned: nothing. Mag check including wires: nothing. Compression check: nothing amiss. Spark plugs: all checked out. Huh. Flew for 3-4 more hours before she did it again. Time to get serious. Changed all soft fuel lines and blew out all the hard lines. Inspected tank interiors. Installed a new, more modern gascolator. Installed rebuilt mags (~400 hours since new on the old ones) and carburetor. Took the selector valve apart and cleaned it. New spark plugs. What else was I missing? She has an "Armstrong" starter (hand propped) and, after all that, when I was starting her, felt a slightly soft cylinder.....with the compression test being normal. ⁉️ She started normally so I warmed her up (normal running) and took her to the runup area. She ran up fine but didn't feel quite right at full throttle. Sometimes that feeling is all it takes. Took her back to the hangar and shut her down. Pulling the prop through and, after ALL THAT, found a stuck exhaust valve on one cylinder!! Short end of a long story: replaced the cylinder and she has been fine since. And look at all the new things she has!

So: could you have a momentarily sticking valve? Done the wobble test lately? If you are sending the carb off you'll have plenty of time to do that! Just an idea. IMHO; YMMV....
Click to expand...
the plot thickens...
I tore the fuel system apart, everything looked good. I erred on the side of caution and had the carburetor rebuilt. The mechanic told me it looked "perfect" when he took it apart. The only hint of a smoking gun was him finding "some soot in throttle body Venturi area which could be indicative of an ignition backfire/misfire. "
My next move is to re-check the ignition system. I have one regular magneto which was overhauled 200 hrs ago, and one eMag with 200 hours on it. It's last run up was perfect but at this point I am going to re-visit the ignition system.
I hope that I find something there, otherwise I am looking at boroscoping the engine to see if I have a sticking valve. It's a high compression engine so the "Armstrong" test won't work on her.
I'll keep you guys posted....
BTW, what's the "wobble test?" and what is IMHO and YMMV? yes, I am new at this.
 
PensacolaPilot said:
I hope that I find something there, otherwise I am looking at boroscoping the engine to see if I have a sticking valve. It's a high compression engine so the "Armstrong" test won't work on her.
I'll keep you guys posted....
BTW, what's the "wobble test?" and what is IMHO and YMMV? yes, I am new at this.
Click to expand...

Borescoping won’t necessarily indicate a valve that isn’t sealing properly. You can do a version of the Armstrong test by making sure both ignitions are off then pulling the prop through four compression strokes. If one of the strokes feels softer than the others you *might* be seeing a cylinder that has an exhaust valve that isn’t sealing properly.

If you aren’t comfortable doing this get help from someone who is familiar with this procedure. This is a useful test but safety is paramount. The wobble test can be performed by your mechanic if he thinks a faulty valve is likely.
 
I think what RV7A Flyer was driving at was getting some quantifiable data from your engine monitor, assuming you have them. I'm not familiar with the "Vision system" you referenced or what it can do, but many monitors capture and log myriad engine parameters that can be saved to an SD card or a memory stick. If you can review the data from an engine monitor, were EGTs or CHTs dropping off? If so, were there individual cylinders that were affected or did it affect all of them in unison? Were there any other anomalies like dips in fuel pressure? Your engine may be providing clues, but you gotta be able to see what it's trying to tell you. Also, have you ruled out the possibility of a loose fairing that may not have been attached properly after your brake job? Lastly, did the engine actually run roughly or miss, or did you just feel the "rain puddle" effect of slowing down?
 
PensacolaPilot said:
the plot thickens...
I tore the fuel system apart, everything looked good. I erred on the side of caution and had the carburetor rebuilt. The mechanic told me it looked "perfect" when he took it apart. The only hint of a smoking gun was him finding "some soot in throttle body Venturi area which could be indicative of an ignition backfire/misfire. "
My next move is to re-check the ignition system. I have one regular magneto which was overhauled 200 hrs ago, and one eMag with 200 hours on it. It's last run up was perfect but at this point I am going to re-visit the ignition system.
I hope that I find something there, otherwise I am looking at boroscoping the engine to see if I have a sticking valve. It's a high compression engine so the "Armstrong" test won't work on her.
I'll keep you guys posted....
BTW, what's the "wobble test?" and what is IMHO and YMMV? yes, I am new at this.
Click to expand...
The Pmags are known to lose timing and other anomolies. The soot in the carb is definately indicative of backfires and that is almost always ignition. Very possible that the pmag losses its TDC for a moment and recovers, creating the decel that you feel. They are known for bearing failures and these cause large gaps at the senor and therefore lose the rotational indication. Once they do, they start sparking at the wrong angle and this will make a noticable change in power output. sticking valves do not really appear for 2 second intervals several times early in flight. Also, when they stick, that cyl stops firing (no power) and you cannot confuse running on three cyl's with a slight deceleration: it is rough. They tend to stick when cold and do not start moving again until the head heats up. My next step would be to send te Pmag back for repair.
 
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I don't know about time to send the PMag in for repair just yet, but it is definitely high on my suspect list. I would suggest you look into a product by the name of EI Commander, developed by Bill Repucci - it will help you keep track of the Pmags and what they are doing.
 
Test
airguy said:
I don't know about time to send the PMag in for repair just yet, but it is definitely high on my suspect list. I would suggest you look into a product by the name of EI Commander, developed by Bill Repucci - it will help you keep track of the Pmags and what they are doing.
Click to expand...
-I test-flew the plane today with a rebuilt carburetor, checked-out fuel system. Run up was uneventful, takeoff normal, but some backfiring at 500 AGL. I isolated the problem, it is the left (electronic) mag. Switched to the right mag and landed. Next step is working through the trouble-shooting guide from eMag to see which LED lights up when. I ll keep you posted, but at least now I have a "smoking gun".
Fly safe!
I'll also research the product you mentioned.
 
Have you examined your plugs since all this started? Especially if one set of plugs not working well, may just have lead build up in some bottom plugs after the fueling issues you had. You won't see anything tearing down a carb that has a sticking valve or float. It is just something that happens in situ. Sound like the carb could have been the issue.
 
Mdragon said:
Have you examined your plugs since all this started? Especially if one set of plugs not working well, may just have lead build up in some bottom plugs after the fueling issues you had. You won't see anything tearing down a carb that has a sticking valve or float. It is just something that happens in situ. Sound like the carb could have been the issue.
Click to expand...
I examined the plugs and they look fine. What's frustrating me is that the problem only occurs in the air; run up's at 1800 rpm and at full power do not reproduce this. I suspect vibration level in flight that don't occur on the ground?
Talked to the factory rep at eMag and he wants me to send it in. Not quite there yet.
 
airguy said:
I don't know about time to send the PMag in for repair just yet, but it is definitely high on my suspect list. I would suggest you look into a product by the name of EI Commander, developed by Bill Repucci - it will help you keep track of the Pmags and what they are doing.
Click to expand...
I talked to the factory rep and he wants me to send it in but I'd like to do some analysis first. I found the "El Commander" but it is a bit pricey. thanks for the info!!
 
PensacolaPilot said:
I could not "measure" aka quantify the deceleration, hence my analogy of driving a car through a puddle. Just enough to startle me.
I use my electric stand by fuel pump on takeoff. No RPM drop. Can't be the governor because I have a fixed pitch prop.
I'll start troubleshooting this weekend, and hopefully find something. Very unnerving. Thanks for all the inputs!!
Click to expand...
Minor shear/change in wind speed/direction?
 
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