JRam Posted January 1, 2019 Report Share Posted January 1, 2019 I was having a nice leisurely flight over the mountains from Asheville to DC today when I noticed my airspeed starting to drop fairly rapidly. It went from 160 TAS to 100 TAS in about 60 second and then it would go back up. It did that 4-5 times. Then while watching it closely, the engine started to sputter. I flipped it from the right tank to the left and it came back to life and back up to speed. Thankfully I was close to my destination and landed without coming up on anyone's news feed. I've had some issues I've been trying to get some folks to look at with my Fuel Flow Reader for a while now. It would fluctuate quite a bit and even go down to 0 for a number of seconds. It didn't show up in the performance of the airplane though so everyone figured it was either the FF or the probe. Now, I'm not so sure. I sumped the tank quite a bit before takeoff and didn't have any issues other than just a couple small "floaters". Any thoughts? Quote Link to comment Share on other sites More sharing options...
gsxrpilot Posted January 1, 2019 Report Share Posted January 1, 2019 Your first paragraph sounds like you just ran the right tank dry, which is no issue and actually a good thing to do occasionally. Although it's better when you're expecting it. Did you fill the right tank on landing, how much fuel did it take? Is there a chance that it was just empty? Your second paragraph seems completely unrelated to the first, unless this only ever happens on one tank. I would not be comfortable flying very far from the pattern without knowing the issue. I'd especially be hesitant to fly into the Smokeys without knowing for sure what the issue is. 1 Quote Link to comment Share on other sites More sharing options...
KLRDMD Posted January 1, 2019 Report Share Posted January 1, 2019 15 minutes ago, JRam said: I was having a nice leisurely flight over the mountains from Asheville to DC today when I noticed my airspeed starting to drop fairly rapidly. It went from 160 TAS to 100 TAS in about 60 second and then it would go back up. It did that 4-5 times. Then while watching it closely, the engine started to sputter. I flipped it from the right tank to the left and it came back to life and back up to speed. Thankfully I was close to my destination and landed without coming up on anyone's news feed. I've had some issues I've been trying to get some folks to look at with my Fuel Flow Reader for a while now. It would fluctuate quite a bit and even go down to 0 for a number of seconds. It didn't show up in the performance of the airplane though so everyone figured it was either the FF or the probe. Now, I'm not so sure. I sumped the tank quite a bit before takeoff and didn't have any issues other than just a couple small "floaters". Any thoughts? Do you really mean your true airspeed (TAS) dropped 60 knots or was it your indicated airspeed (IAS) ? Was the autopilot on ? If not, did you have to make significant control inputs to maintain altitude or did altitude change too ? 1 Quote Link to comment Share on other sites More sharing options...
gsxrpilot Posted January 1, 2019 Report Share Posted January 1, 2019 Yep, wondering the same thing. I'm a proponent of running a tank dry periodically. But I've always noticed the stumble in the engine long before any major reduction in speed. And the M20K's can sometimes take 10 seconds to re-light when in the high flight levels. I've still never noticed that kind of reduction in speed. Curious. Quote Link to comment Share on other sites More sharing options...
Guest Posted January 1, 2019 Report Share Posted January 1, 2019 Lots of great minds hang out here willing to help sort this out. Tank out of fuel as suggested or venting issue with the tank causing flow issue? When you say someone to look at you fuel flow indicator, what model do you have and what’s it doing? Clarence Quote Link to comment Share on other sites More sharing options...
DanM20C Posted January 1, 2019 Report Share Posted January 1, 2019 I think your hoskins FF is messed up and you should replace it with a JPI 900 asap. But I don't think it has anything to do with the slowing down/engine stumbling. I like Clarence's idea of a plugged tank vent. That is a easy one to check. Cheers, Dan Quote Link to comment Share on other sites More sharing options...
FoxMike Posted January 1, 2019 Report Share Posted January 1, 2019 A couple of comments, maybe ideas. Airspeed changes of that magnitude could only be caused by fuel starvation if the engine lost significant power, like going from 70% to 20%. You certainly would have noticed a trim change. It could be you were experiencing up and down drafts that could cause a the fuel in a low tank to unport (flow away from the pickup). If this is the problem more fuel is the fix. If you have had this problem on other occasions when the tank was fuller you might have a mechanic drain all the fuel and remove the quick drain and see if a large piece of junk in in the tank that could cover the fuel pickup. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 The tank definitely did not run dry, it was full when I departed (topped off) on both sides and I took off on the left and switched to the right about 1/3 in to the flight. I do mean IAS, but I had it configured to show my TAS as well. Autopilot was on and keeping me at the right altitude. I was well above the mountains but my first thought was maybe downdrafts just causing it, but I discounted that as I would think only my ground speed would drop. I had a strong tailwind the entire flight. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 27 minutes ago, M20Doc said: When you say someone to look at you fuel flow indicator, what model do you have and what’s it doing? It's a Hoskins FT-101. It shows the proper flow and then at times it just starts losing it and will go from 10 GPH to lower and finally show 0 for an amount of time that scares me but ultimately doesnt affect the engine. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 4 minutes ago, DanM20C said: I think your hoskins FF is messed up and you should replace it with a JPI 900 asap I've decided to go to the 900. I just have to figure out the timing. I found out recently that I'm probably moving back to San Antonio Texas in the next couple months so I am hoping to hold out until I'm there, but this may have forced my hand. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 Both tanks are still over 3/4 full after the flight. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 So this is my instrument. Showed 160 in the TAS white area...so it really went from 150ish IAS to 100 IAS. Quote Link to comment Share on other sites More sharing options...
DanM20C Posted January 1, 2019 Report Share Posted January 1, 2019 Did you notice a drop in manifold pressure? Congratulations on getting back to TX Cheers, Dan Quote Link to comment Share on other sites More sharing options...
carusoam Posted January 1, 2019 Report Share Posted January 1, 2019 How close to the mountains were you? (Altitude above) What were the winds like? Down drafts can certainly cause airspeed challenges when the AP tries to hold altitude. When your FF indication does funny things, did you try the electric fuel pump? FF meter errors... Air entering the fuel system usually shows up as higher numbers instead of lower numbers... the engine continues to deliver fuel properly, but gets extra volume of air...look for blue stains around the engine area...and back to the tanks... including in the cockpit at the fuel selector... FF numbers going lower sounds like the paddle wheel is getting stuck... this is a remove and clean sort of thing... the Ft101 has a magnet in the spinning paddle wheel. The sensor is a counter detecting the number magnetic passes over time... combined with the K-factor it is converted to GPH data... the paddle wheels are known to get dirty. Power check... MP and RPM, stable means power is being delivered in a stable fashion... If MP is dropping, or rpm drops, these are indications of power not being delivered as expected... FF is what I use during acceleration on T/O to verify the other two are telling me the truth... Winter in the NE, with wind, near small mountains, can generate down drafts that are stronger than a Cessna’s climb rate... (my IR training experience in a C172) not very fun. There is a procedure for escaping this situation... something like... Set attitude for Vy, and cross the direction of the down draft..... the down draft may be longer than it is wide? Or maintain attitude to keep speed up to escape...? Were you on the leeward side of the mountains? A couple of thousand feet above them? See if any of that matches your experience... Having the AP select going that much slower, trying to maintain altitude... is more in line with the AP making decisions in place of the PIC... You have come to the right place to discuss what is happening... PP thoughts, not a CFI.... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted January 1, 2019 Report Share Posted January 1, 2019 Like above. Did you run into a mountain wave? It can cause airspeed changes like you said. If it was your engine you would hear and feel it. 1 1 Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 30 minutes ago, DanM20C said: Did you notice a drop in manifold pressure? No drop in MP or RPM. 8 minutes ago, carusoam said: Were you on the leeward side of the mountains? A couple of thousand feet above them? I was on the Leeward side of the mountains flying at 9000 feet and the highest peaks were no higher than 5000. I flew direct from KAVL to KHEF. Quote Link to comment Share on other sites More sharing options...
JRam Posted January 1, 2019 Author Report Share Posted January 1, 2019 3 minutes ago, N201MKTurbo said: Did you run into a mountain wave? It can cause airspeed changes like you said. If it was your engine you would hear and feel it. Maybe? I was no less than 4,000 feet above the mountains but it could have been a mountain wave. I definitely felt and heard no issues with the engine until it started to stutter. Although, that could be a separate issue all together from the sounds of it. Quote Link to comment Share on other sites More sharing options...
FoxMike Posted January 2, 2019 Report Share Posted January 2, 2019 Any chance you got a load of water when you bought gas? A lot of Mooney tanks have been repaired over the years and sometimes the holes in the rib that are to let the water move to the low point get blocked during the repair. Water does not get to the quick drain until some of the fuel is burned as it trapped behind the rib. Quote Link to comment Share on other sites More sharing options...
carusoam Posted January 2, 2019 Report Share Posted January 2, 2019 Looking at it as if it were a mountain Wave... 1) plane enters strong down draft... 2) AP commands elevator to increase AOA, so the plane is climbing evenly with the descent rate of the air around the plane.... 3) Pilot doesn’t add any power... engine maintains MP and RPM... which may be a bit funky with a turbo and pressure controller... 4) plane is climbing a few hundred feet per minute against a descending column of air of a few hundred feet per minute... 5) The net climb rate is zero... but the plane is acting as if it were climbing. 6) The airspeed changes significantly to accommodate the pilot not adding any power. 7) being a constant speed prop, you may hear a few things as the blade angle changes to a flatter pitch during the pseudo climb. 8) repeated experience is probably related to the number of peaks you are passing. Going in and out of ‘columns’ of air. 9) 5k’ Mtns are tall enough to create down drafts. 10) when suspecting mountain waves... add power and climb, at least know that you have enough power left to maintain speed and altitude. When you run out of additional power... you start running out of speed and altitude... you start looking into exit strategies... to avoid the tree tops... a real issue when short on power and close to the ground.... 11) updrafts on the other side of the mountains are more fun... maintaining altitude, the plane behaves as if it is descending and there is a noticeable increase in speed... avoiding Vne becomes key... adjusting the power out is a normal pilot response... That kind of covers flying into and out of mountain waves... Now, onto engine sputters... that is an odd behavior worth digging into... 1) Got an engine monitor? 2) can you get the data out of it? 3) need help taking a screen shot? 4) need help learning how to upload it to Savvy.com? PP thoughts only, not a mechanic or CFI... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
JRam Posted January 2, 2019 Author Report Share Posted January 2, 2019 58 minutes ago, FoxMike said: Any chance you got a load of water when you bought gas? A lot of Mooney tanks have been repaired over the years and sometimes the holes in the rib that are to let the water move to the low point get blocked during the repair. Water does not get to the quick drain until some of the fuel is burned as it trapped behind the rib. Sounds like it's possible from what you describe. I didn't see any in what I drained (about half a cup from each side before takeoff) but maybe it hadn't made it down there. It rained overnight before the flight. 44 minutes ago, carusoam said: That kind of covers flying into and out of mountain waves... Now, onto engine sputters... that is an odd behavior worth digging into... Do you think the mountain waves could affect me being over 4,000 feet above the peaks? I was at 9,000 the entire flight. I have included my Saavy Analysis from the flight. Unfortunately the fuel flow isn't connected to the EDM700, part of why I want to just get the 900 upgrade done. Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted January 2, 2019 Report Share Posted January 2, 2019 The only time I have had an significant unexpected drop in airspeed was due to wind shear. No indicated loss of power, or change in engine sounds. Admittedly, mine only happened once, presumably as I moved from one air mass to another. Quote Link to comment Share on other sites More sharing options...
carusoam Posted January 2, 2019 Report Share Posted January 2, 2019 When it comes to air flowing over objects... Strong winds run into the mountains and get lifted, which runs into the next parcel of air, so it gets lifted too, and so on, and so on... Read up on glider pilots, ridge soaring, going to very high altitudes, under the right conditions... Cold, dense, air moving at a 4k’ wall... can probably cause some significant shifts 4k’ in height, above the 4k’ tall wall... Then on the backside of the mountain, the descending occcurs... the air at 5k’ is descending to 1k’ or so....all the parcels above will descend too.... This is quite the simplification, and depends on the air being as stable as possible... cold dry air is pretty stable... The faster the wind is moving, the faster the up and down drafts will be acting... See if you can find some basic info regarding mountain flying... this is covered briefly in flying 101 kind of books, but mountain flying covers the details in much greater detail... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
carusoam Posted January 2, 2019 Report Share Posted January 2, 2019 When it comes to looking at Savvy data... When it is really clean... flight segments are easy to identify... for a PP... start up taxi run-up T/O climb cruise mixture changes descent traffic pattern and landing When it gets many adjustments in the flight, it isn’t as clean... and it helps to annotate the time line... If you put some times associated with the list I proposed here... that will help identify the time where you had the engine ‘sputter’... Your description of the event indicates you felt something that was worthy enough to motivate the changing of the selector... Another thing to add to the to do list... check the hours on the mags since they have been OH’d. If it has been a while, you might be getting skips in the ignition at higher altitudes...? A significant drop-out in the ignition can usually be seen in the EGTs... one plug dying usually causes a rise in EGT... a mag dying... causes all the EGTs to rise... a sputter sounds more than these issues... Do a nice slow run-up allowing 10-15 seconds to collect some good data, in each switch position... Often @kortopates Paul has some excellent insight to Savvy graphs... More Pp thoughts only... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
JRam Posted January 2, 2019 Author Report Share Posted January 2, 2019 16 minutes ago, carusoam said: If you put some times associated with the list I proposed here... that will help identify the time where you had the engine ‘sputter’... I'll try to put some notes, but based on my flight tracker (https://flightaware.com/live/flight/N57241/history/20190101/1730Z/KAVL/KHEF/tracklog), I believe it was at that drop in temps at 1:30. You'll see my speed dropped pretty hard at that point. Quote Link to comment Share on other sites More sharing options...
larryb Posted January 2, 2019 Report Share Posted January 2, 2019 I have experienced a significant mountain wave at 17,000 feet and not near any mountains. I think it was in New Mexico with terrain below at around 7,000 feet. I watched as my IAS dropped to 90 kt. At that point I added full power to get some speed back and maintain altitude. I was confident the engine was not causing this since my MP, RPM, FF, and all temps did not change during the event. After a few minutes the effect went away and I returned to cruise power. That said, it does seem that you may have an engine issue as well. The big drop in temps across the board indicates your power went down. I am thinking that you may have an air leak in the fuel system between the tank and the engine. It could be an o-ring in the selector or a loose fitting somewhere. Does this always happen on one tank, or have you seen it on both tanks? That could help isolate it. An air leak would cause erratic readings in you FF gauge. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.