An extraordinarily bizarre airspeed mystery that no A&P can solve

Totally left field but how bout the Engine mounts? Would having a slightly askew prop slow a plane?
 
Just some troubleshooting advice, free of charge and probably worth exactly that. Quite often, when working on something that doesn’t make sense, start with the obvious other issues. 9 time out of 10 that will lead you to the solution
 
So far I’m more entertained by this because I haven’t thought of much to contribute, and haven’t even looked up your airplane type. But, I’ll throw a question or two out. You said ever since the GPS antenna change.

Is this GPS antenna a simple GPS antenna or does it have any remote sensing capability like an Aspen RSM would that is used as part of instrument indication? Is the GPS antenna same dimensions as the old one and it’s installation is solid and not in question (not creating any new drag)?

Regarding the out of rig issue that has always been there, has the engine mounting been verified to be exactly as it should be? (If it’s even possible to be out of design spec)
 
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Lindberg said:
Being lighter in front can make you slower.

Something changed.

You've batted off a thousand explanations of what it could have been based on your fastidious (I didn't say obsessive) record keeping and analysis. But it's either one of them or something else. And you've changed a lot of stuff, so it could very likely be a combination of things. Maybe rig the airplane correctly, add a couple of pounds to the nose, put the old prop back on, and see what happens. Or move on..... ;)
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Something definitely changed. That's the mystery I'm seeking help with. But the prop and rigging of the plane aren't the problem because I was flying perfectly fine at 120+ KTAS with the prop and rigging the way that it is.
 
MauleSkinner said:
Should make you faster, actually.
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And that's what's funny. The airplane should be slightly faster than before given the OAT is colder now, and there's slightly less weight up front. POH says I should be flying 1-2% faster TAS with the colder temps.
 
Notrub said:
Totally left field but how bout the Engine mounts? Would having a slightly askew prop slow a plane?
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Engine mounts were inspected back in February and even had new rubber isolators installed then.
Ed Haywood said:
Assuming you were actually flying 120+ KTAS before.
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I was. Nav logs calculated with 120 KTAS cruise had me arriving exactly when I was expected to. Now I always arrive late.
 
AlphaMike said:
Just some troubleshooting advice, free of charge and probably worth exactly that. Quite often, when working on something that doesn’t make sense, start with the obvious other issues. 9 time out of 10 that will lead you to the solution
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I agree. And the most obvious explanation is usually the correct one.
 
When you test your time to climb, I suggest using density altitude from the old flight data as the parameters for the test rather than simply climbing to 10,500 with a stopwatch running. Do the climb to 10,500 but run the clock from, say, 3,000 DA to 9,000 DA, whatever those end up being, and compare the time to how long that part of your past climb took.

Same with testing speeds. Try to get to the same density altitude rather than just working from a particular indicated altitude. It's just that much less of a variable you're fighting against.

And, while you're at it, try to get the same gross weight and CG as you had before. That might be harder to recalculate for an old flight, but if you're in doubt you could at least try to get the CG close to where it would have been with the old prop on. Not that moving the CG forward will speed you up in normal conditions, but honestly with how weird your mystery is maybe it will. And that will tell us something ... although we've no idea what!
 
TrueCourse said:
Is this GPS antenna a simple GPS antenna or does it have any remote sensing capability like an Aspen RSM would that is used as part of instrument indication? Is the GPS antenna same dimensions as the old one and it’s installation is solid and not in question (not creating any new drag)?

Regarding the out of rig issue that has always been there, has the engine mounting been verified to be exactly as it should be? (If it’s even possible to be out of design spec)
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It's a Dynon SV-GPS-2020 antenna mounted below the windshield just aft of the cowling. It's exactly the same antenna in exactly the same spot. It just was weak so Dynon replaced it under warranty.

I actually wondered a few months ago if the need for so much rudder trim was because the engine was mounted slightly off, so I had a conversation then with my A&P about that and he said there's no possible way to mount the engine off alignment.
 
Just one more thing I wanted to mention. I’m sure you already know it but I just wanted to point out that there are some pretty “serious issues “ flying around uncoordinated. Honestly to me I would be more concerned about that than losing 10 knots. Those pictures show a half ball deflection left rudder and right wing low. that will definitely affect your stall speed, not to mention if you did stall the spin that could come next. On a lesser note you won’t have full rudder available in a right x wind Landing. Just something to consider
 
iamtheari said:
When you test your time to climb, I suggest using density altitude from the old flight data as the parameters for the test rather than simply climbing to 10,500 with a stopwatch running. Do the climb to 10,500 but run the clock from, say, 3,000 DA to 9,000 DA, whatever those end up being, and compare the time to how long that part of your past climb took.
Same with testing speeds. Try to get to the same density altitude rather than just working from a particular indicated altitude. It's just that much less of a variable you're fighting against.

And, while you're at it, try to get the same gross weight and CG as you had before. That might be harder to recalculate for an old flight, but if you're in doubt you could at least try to get the CG close to where it would have been with the old prop on. Not that moving the CG forward will speed you up in normal conditions, but honestly with how weird your mystery is maybe it will. And that will tell us something ... although we've no idea what!
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Good suggestion, thank you. I will time it to the same DA as before, as I recorded after the new prop was dialed in (attached).
 

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I may have missed this question, but have you manually calculated your TAS before and after the issue started or have your TAS readings always been automatically calculated by your avionics?
 
AlphaMike said:
Just one more thing I wanted to mention. I’m sure you already know it but I just wanted to point out that there are some pretty “serious issues “ flying around uncoordinated. Honestly to me I would be more concerned about that than losing 10 knots. Those pictures show a half ball deflection left rudder and right wing low. that will definitely affect your stall speed, not to mention if you did stall the spin that could come next. On a lesser note you won’t have full rudder available in a right x wind Landing. Just something to consider
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Mike, I get it and I appreciate it. I assure you that the flying in a skid issue will be addressed and thank you for repeating it. I'm just trying to focus on solving the airspeed issue for now.
 
TrueCourse said:
I may have missed this question, but have you manually calculated your TAS before and after the issue started or have your TAS readings always been automatically calculated by your avionics?
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Yes, have manually calculated. I was matter-of-factly flying faster before than I am now and it's not an indication error.
 
When reviewing ALL your pictures of the attitude indicator before and after have you noticed if the pitch of the airplane is any different? That is to say, related to the speed anomaly issue.
 
TrueCourse said:
When reviewing ALL your pictures of the attitude indicator before and after have you noticed if the pitch of the airplane is any different? That is to say, related to the speed anomaly issue.
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Looks about the same across the board. Attached is a comparison. There are some from before when I was flying faster where my nose is pitched up a couple degrees more in cruise.
 

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I sympathize with what you are going through. It's been over ten years since last I've been around a Tecnam. I know that the P2002 Sierra is not the same but, this aircraft was very light weight and troublesome. In order to meet the LSA weight requirements many things where under built and broke over the +2000 hours the flight school operated it. With no wheel pants at all the plane easily cruised at 125 kts. The instructors liked the plane and it was a good money maker.

With all that said, people who flew it lost trust in it. The landing gear was very much under built to save weight. The control system had several service bulletins and it seemed like every S.B. applied to this aircraft. The Stabilator electric trim actuator only worked half the time. Both seat frames broke and had to be highly modified. The canopy slide had to be modified with safety cables. Several times the instructors reported the aircraft not flying hands free and it would ground the aircraft. Because of some previous items that failed the pilots didn't want to take any chances if it didn't taxi & fly totally true. Some of the things that were discovered could have caused a serious accident. Just from my personal experience, be very careful with a light weight plane that's not flying straight.
TecnamS100122.jpg
Good Luck finding the problem.
 
Klaus M said:
I sympathize with what you are going through. It's been over ten years since last I've been around a Tecnam. I know that the P2002 Sierra is not the same but, this aircraft was very light weight and troublesome. In order to meet the LSA weight requirements many things where under built and broke over the +2000 hours the flight school operated it. With no wheel pants at all the plane easily cruised at 125 kts. The instructors liked the plane and it was a good money maker.

With all that said, people who flew it lost trust in it. The landing gear was very much under built to save weight. The control system had several service bulletins and it seemed like every S.B. applied to this aircraft. The Stabilator electric trim actuator only worked half the time. Both seat frames broke and had to be highly modified. The canopy slide had to be modified with safety cables. Several times the instructors reported the aircraft not flying hands free and it would ground the aircraft. Because of some previous items that failed the pilots didn't want to take any chances if it didn't taxi & fly totally true. Some of the things that were discovered could have caused a serious accident. Just from my personal experience, be very careful with a light weight plane that's not flying straight.

Good Luck finding the problem.
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@Klaus M , I'm with you 100%. I do not like Tecnam. I think they are an awful company and make a great many mistakes on the products they build (and after sales support is nonexistent). It's a top down problem with their awful leadership and the family who owns and operates it. But it is the plane that I have and I am invested a great deal into it at this point.
 
even with a level ai it takes longer than you think for the speed to stabilize after even a tiny pitch change.
 
I commend you for trying to figure out your loss of airspeed. I would probably chase it too, that’s a lot of knots. But, if I’ve exhausted everything obvious I’d probably attack the other issue (rigging/drag) to see if I can gain it back. If not, then I’d go back to the mystery again.

I’ve been convinced about a timeline induced change only to discover later the time of change was not accurate. Not saying this is what is occurring for you, but I recalled this as I scratched my head thinking of your issue.
 
So....If I fly my Bonanza with the skid ball off to the side....will I fly faster or slower?
 
I would have someone knowledgeable in your A/C type check the rigging with a fine toothed comb before going any further. While the factory may not think anything should be amiss if service work hadn't been done on it, I'd want everything verified and adjusted to ensure it's not part of the speed loss. Of course your other checks (GOPro, time to climb, etc) are also great, but I think the rigging is just as important at this point and not worth delaying until you've sorted this out. I'd also really look at the factory specd dimensions for wing/empanage as well as the engine mount/thrust alignment. I wouldn't be surprised if something has shifted slightly (like an engine mount brace even though your mechanic says it's impossible).
 
kicktireslightfires said:
Yes, have manually calculated. I was matter-of-factly flying faster before than I am now and it's not an indication error.
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Your certainty may not be justified. Indication error is more plausible than your airplane suddenly becoming 10 knots slower.

kicktireslightfires said:
I assure you that the flying in a skid issue will be addressed and thank you for repeating it. I'm just trying to focus on solving the airspeed issue for now.
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Several people have tried to tell you that the slip (not skid) issue and the airspeed issue may be one and the same.
 
Ed Haywood said:
Your certainty may not be justified. Indication error is more plausible than your airplane suddenly becoming 10 knots slower.


Several people have tried to tell you that the slip (not skid) issue and the airspeed issue may be one and the same.
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Ed, if they are one and the same how do I have pictures showing my panel flying in the same slip at the previous 120+ KTAS?
 
I have not read all the posts in this longish thread, but if you have demonstrated the TAS based on an accurate method excluding any indications contributed by your instruments, that would be important. As has been said, a verification of the same before you noted the disparities would have certainly helped to verify if any change in TAS occurred by change in power or drag.

Having said that, SINCE YOU HAVE ELECTRIC TRIM, I will present to you an issue that happened to me related to a sudden unsuspected loss of indicated airspeed after my aircraft came out of annual. Both my AS indicators were showing readings at what I thought were proper, but the aircraft seemed to be climbing not as well, and the AS was lower in cruise, and TAS calculated from my Aspen were slower than usual despite normal engine monitor and tach indicators. So was it decreased engine performance or increased drag? It was neither.

After fiddling around, and noticing my gps ground speed on final approach to landing coupled with the known winds on the ATIS, I came to the conclusion that my AS was indicating 10-20kts slower than actual.

My Static/ Pitot mast was untouched during annual, but my electric elevator trim was coincidentally inop while it had been working just before annual. This led my A&P to discover that an electrical fault existed on a relay on the electric trim assembly, which is a small panel located under the dash somewhere. When I asked about the the pitot problem, he indicated he thought he had bumped the assembly earlier with his elbow when under the dash, and the pitot connection was jarred off: There is a sensor on this module that accepts the pitot pressure connector and works to shut off electric trim power in the event of an uncontrolled or runaway airspeed above a certain value.
 
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MajorTurbulence said:
I have not read all the posts in this longish thread, but if you have demonstrated the TAS based on an accurate method excluding any indications contributed by your instruments, that would be important. As has been said, a verification of the same before you noted the disparities would have certainly helped to verify if any change in TAS occurred by change in power or drag.

Having said that, SINCE YOU HAVE ELECTRIC TRIM, I will present to you an issue that happened to me related to a sudden unsuspected loss of indicated airspeed after my aircraft came out of annual. Both my AS indicators were showing readings at what I thought were proper, but the aircraft seemed to be climbing not as well, and the AS was lower in cruise, and TAS calculated from my Aspen were slower than usual despite normal engine monitor and tach indicators. So was it decreased engine performance or increased drag? It was neither.

After fiddling around, and noticing my gps ground speed on final approach to landing coupled with the known winds on the ATIS, I came to the conclusion that my AS was indicating 10-20kts slower than actual.

My Static/ Pitot mast was untouched during annual, but my electric elevator trim was coincidentally inop while it had been working just before annual. This led my A&P to discover that an electrical fault existed on a relay on the electric trim assembly, which is a small panel located under the dash somewhere. When I asked about the the pitot problem, he indicated he thought he had bumped the assembly earlier with his elbow when under the dash, and the pitot connection was jarred off: There is a sensor on this module that accepts the pitot pressure connector and works to shut off electric trim power in the event of an uncontrolled or runaway airspeed above a certain value.
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I don’t quite follow what you’re saying. How did an inop electric elevator trim result in you having decreased climb performance AND your airspeed indicating 10-20 knots slower than actual? Maybe it’s just late but would you mind clarifying? Thank you.
 
kicktireslightfires said:
Ed, if they are one and the same how do I have pictures showing my panel flying in the same slip at the previous 120+ KTAS?
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You could be just a little further off than you were in the old pictures and not see it. The ball isn’t exactly a precision instrument.
 
kicktireslightfires said:
This is what the maintinanece manual says:

The nose gear is a free-castoring type with a self-locking nut to provide the correct steering friction.The steerable assembly is entirely made in light alloy while the steering axle, nose gear welded assembly and shock absorber fitting are made in 4130 steel. An oleo-pneumatic shock absorber provides the adequate damping and reaction against ground loads. Nose gear steering angle is limited to 40° while the torque setting must be sufficient to guarantee that rotation with loads of less than 5kg/11lb applied on the wheel axle is not possible. This will avoid any shimmy hazard even if the NLG architecture and characteristic angles offer a shimmy proof design.

If I read that correctly, it should take 11 pounds of pressure to move the nose wheel in either direction when weight is lifted off it. I would say mine seems to be exactly that much and within spec, but I'd have to get a gauge to be sure it's exactly 11 lbs. Sounds like fixing it is easy though and if the nose wheel is flying askew, all I'd need to do is tighten one bolt slightly more.
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11lbs is a lot of force. As components wear preload is often lost. I am still betting the nosewheel is cocking over in flight. This results in the rudder trim issue and loss of speed.
 
kicktireslightfires said:
I don’t quite follow what you’re saying. How did an inop electric elevator trim result in you having decreased climb performance AND your airspeed indicating 10-20 knots slower than actual? Maybe it’s just late but would you mind clarifying? Thank you.
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The important point from this incident for every pilot flying a plane for the first time after annual is: do a very careful preflight, and consider yourself a test pilot expecting almost anything to happen.

For you specifically and others with an electric trim, this is an example of not knowing what you don’t know about this system, and how it can manifest itself even in ways that can be confusing.

So the fact that my electric trim was discovered to be inoperative on run-up was interesting but not a no go item for me on departure, and not the actual reason for the airspeed disparity, since the electric trim could have been functioning and still result in the same airspeed problem. But what it did do is point to the real problem. I will speculate here that that ELBOW BUMP during annual was not only sufficient to cause the electrical fault in the relay of the electric trim assembly, but also sufficient TO KNOCK OFF THE PITOT CONNECTOR TO THE SENSOR, and which was actually found to be disconnected by my A&P in that assembly under the dash. My airplane is a PA28-181. I would not be surprised to find that as part of the electric trim system of your airplane, there is a module to prevent electric power to the trim in an uncontrolled airspeed condition. So if you have that module, look to see if the pitot connector is properly connected, or is leaking in some way.

On climb out, not only is the attitude of the plane on instruments and outside view with the vertical speed indication informative of the sufficiency of the climb, but I’m primarily watching my airspeed indicator. Since it was unknowingly falsely low, I had to keep my climb much shallower to get the airspeed to my normal climb speed on the gauge. In hindsight, this was a false airspeed and was actually 10-20 knots faster. But by compensating for that, it would create a climb much slower simulating increased drag or faulty engine performance.
 
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Jeff767 said:
11lbs is a lot of force. As components wear preload is often lost. I am still betting the nosewheel is cocking over in flight. This results in the rudder trim issue and loss of speed.
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Ball/trim was out exactly the same when I was flying faster, so if the nosewheel is responsible for that and was cocking over in flight before, that wouldn't explain it.
 
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