MauleSkinner
Touchdown! Greaser!
Yes.
that picture looks like you’re in a slight bank…am I interpreting correctly that it’s slightly left wing down?
An extraordinarily bizarre airspeed mystery that no A&P can solve
- Thread starter kicktireslightfires
- Start date
- Joined
- Mar 15, 2016
- Messages
- 4,576
- Display Name
Display name:
Ari
The digital "ball" in my GI 275 was out of whack when the plane came out of its upgrade and they had to recalibrate it. Can you get the plane level on the ground (left-to-right and front-to-back) and see if your skid-slip indicators are all centered?
Could the engine gauges be inaccurate? It's hard to imagine a digital tachometer being off by any amount other than 50% or 100% (either of which would make it pretty much stuck to the ground) but maybe your engine is just not going as fast as the gauge shows.
Could the engine gauges be inaccurate? It's hard to imagine a digital tachometer being off by any amount other than 50% or 100% (either of which would make it pretty much stuck to the ground) but maybe your engine is just not going as fast as the gauge shows.
110 knots is 7.95 inches of water pitot pressure; 120 knots is 9.48", a difference of 1.53". 1.53 inches of water corresponds to an altitude difference of about 100'. What this means is if the static system pressure is 1.53" higher than ambient (either due to a misaligned static source or a leak in a higher pressure area), the ASI will read 110 when it should be 120 and the altimeter will read 100' low.
Any pitot or static errors will affect all connected devices equally, of course.
Have you verified that your tachometer is accurate, and the engine is running at the rpm you think it is?
Or... the Rotax has an overload slipper clutch, no? If it's slipping, the engine could be at the indicated rpm but the prop might be turning slower.
Any pitot or static errors will affect all connected devices equally, of course.
Have you verified that your tachometer is accurate, and the engine is running at the rpm you think it is?
Or... the Rotax has an overload slipper clutch, no? If it's slipping, the engine could be at the indicated rpm but the prop might be turning slower.
455 Bravo Uniform
Final Approach
Yes, in various increments to see if the ball is indicating wrong.
Ed Haywood
En-Route
One other consideration. The Dynon requires a unique testing method during pitot static tests or damage/calibration issues can result. Did this start immediately after your system test? Many A/P’s used to working on certified aircraft don’t know this!
When a pitot or static test is performed, the ADAHRS/EFIS is being exposed to dynamics that are impossible to achieve in a real aircraft flight environment – namely, there are large airspeed changes without the accompanying accelerations and rotations. This false condition will cause a well-calibrated unit to incorrectly adjust its calibration. Furthermore, when a unit is in a test situation a change in applied pitot or static pressure will cause the attitude to pitch up or down. This is expected.
Basic Principles
Ensure unit is warmed up during each test reading.
Unit should be powered off when changing pressures.
Keep aircraft still (do not move) when pressure is applied.
Steps
1. The aircraft itself should be temperature stable. For example, if the aircraft is moved from outside in the sun to a hangar for testing, tests should not be started until the airplane has stabilized at the hangar temperature.
2. Turn EFIS on and let it warm up until the altitude reading is stabilized. This period should be at least 5 minutes, but may take longer depending on environmental conditions.
3. Turn EFIS off.
4. While the EFIS is off, apply the pressure required by your test to pitot and/or static port via your
test equipment.
5. Turn on EFIS (external or internal battery power is acceptable). Keep aircraft still while EFIS is
powered on. Do not adjust the pitot or static pressures being applied to the EFIS/ADAHRS while
it is powered on.
6. Verify airspeed and/or altitude reading.
7. Turn EFIS off (using button 1 is a good option for this operation ) .
8. Repeat steps 4-7 for each required pressure point in the test.
When a pitot or static test is performed, the ADAHRS/EFIS is being exposed to dynamics that are impossible to achieve in a real aircraft flight environment – namely, there are large airspeed changes without the accompanying accelerations and rotations. This false condition will cause a well-calibrated unit to incorrectly adjust its calibration. Furthermore, when a unit is in a test situation a change in applied pitot or static pressure will cause the attitude to pitch up or down. This is expected.
Basic Principles
Ensure unit is warmed up during each test reading.
Unit should be powered off when changing pressures.
Keep aircraft still (do not move) when pressure is applied.
Steps
1. The aircraft itself should be temperature stable. For example, if the aircraft is moved from outside in the sun to a hangar for testing, tests should not be started until the airplane has stabilized at the hangar temperature.
2. Turn EFIS on and let it warm up until the altitude reading is stabilized. This period should be at least 5 minutes, but may take longer depending on environmental conditions.
3. Turn EFIS off.
4. While the EFIS is off, apply the pressure required by your test to pitot and/or static port via your
test equipment.
5. Turn on EFIS (external or internal battery power is acceptable). Keep aircraft still while EFIS is
powered on. Do not adjust the pitot or static pressures being applied to the EFIS/ADAHRS while
it is powered on.
6. Verify airspeed and/or altitude reading.
7. Turn EFIS off (using button 1 is a good option for this operation ) .
8. Repeat steps 4-7 for each required pressure point in the test.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Thanks, Jeff. But no, this started several weeks before the pitot-static leak test was performed. That was performed a couple of days ago by Sarasota Avionics, and by one of the best technicians they have.
MauleSkinner
Touchdown! Greaser!
And I’d start by holding rudder to put the ball back where it was before the tab was adjusted.
Well back to the nose gear again!
Stewartb
Final Approach
A few drops of water in the carb bowl. Drain the bowl or add some isopropyl fuel dryer.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
No carbs. Fuel injected.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Just went up and tested this. Could not get any higher airspeed regardless of where I held the rudder. I tried increments in both directions. All it did was either no change or slower, not faster.
Ed Haywood
En-Route
If you are out of trim, you are flying in a slip. Slips add drag.
How much drag depends on how cross-controlled you are. My aircraft does not have flaps. I can add enough drag with a slip to bleed 20 knots of speed while in a steep descent to the runway.
Do I think that is your issue? Dunno. But don't dismiss it by thinking you are just accounting for the drag of the trim tab. You are accounting for the drag of the aircraft being half a ball out of coordination and flying in a slip to maintain heading.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
You are correct! You did notice something that I had not before. Well, actually it was right wing down, not left. But in cruise it flies with the right wing ever so slightly down. I do not believe this is the cause of the airspeed problem as even when I manually correct it, the airspeed does not increase. But I will bend the aileron trim tab up a little for the next flight (up so that it pushes the right aileron down more in cruise) and hopefully that should fix the slightly dropped wing in cruise.
Attachments
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Worth mentioning that this issue of the right wing being slightly down in cruise is *NOT* a new thing and the plane was flying at 120+ KTAS like that before. So I don't anticipate correcting that will solve the airspeed problem. See these panel shots showing the right wing down condition while flying at the faster speeds.
Attachments
Ed Haywood
En-Route
That is to counteract your left yaw. You are flying in a slip.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Why would I have left yaw causing me to flip in a slip? And how do I fix it?
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
But... I was in the half a ball out, right wing down condition with the faster 120+ KTAS speeds, as seen in the screenshots posted above.
MauleSkinner
Touchdown! Greaser!
roll Input will most likely be a result of yaw…don't correct the aileron tab until you’ve got the rudder trim locked in. As @Ed Haywood said, you're flying in a slip.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Okay, so:
1) How do I correct the flying in a slip condition?
2) The airspeed question still persists given the slip condition existed when I was flying at the higher airspeeds so that can't be causing the airspeed loss problem I posted about.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
My A&P checked the exhaust a few days again and even noticed a minor exhaust leak where the muffler connects and corrected that.
455 Bravo Uniform
Final Approach
Sounds to me like you’re fixing a wing low condition with rudder and thats what’s slowing you down. Fix that and get your rudder back closer to neutral.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
It's potentially what's causing the half a ball out, but can't be what's slowing me down 10 knots because the wing low and half a ball out condition existed when I was showing 120+ KTAS on the panel.
MauleSkinner
Touchdown! Greaser!
apply rudder towards the low wing (and whatever aileron input is required) until it holds heading with zero bank.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
I meant without manual input, lol. More rudder trim to push the rudder right more, right?
MauleSkinner
Touchdown! Greaser!
use manual inputs until you figure out what you really need to correct the airplane, then make trim adjustments.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
I'm confident the digital ball isn't out of whack because I know what the horizon looks like when the plane is coordinated and how it feels and when the ball is centered, all my senses check.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
With the TAS VIA GPS Calculator, I think we've not established that it's not an indication error and I actually am flying slower.
I haven't verified my tachometer, but I am very attuned to what it always sounds like and I can tell if it's just 200 rpm off by sound. My CFI used to play a game with me where he would tell me to close my eyes, adjust the throttle and ask me what the RPM was at. He got frustrated when I would say what it was to within 100 rpm every single time. So I don't think the RPM is wrong.
Could the prop RPM be wrong due to clutch slipping? Possible. But I know my gearbox was just serviced less than 100 hours ago. I would have to get a laser tachometer to measure that. I'm not even sure what the prop RPM is supposed to be.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Not sure I follow. My airplane only has electronic elevator trim. Rudder trim and aileron trim is a manual trim tab. How will using manual inputs tell me exactly how much I need to bend the trim tabs once on the ground?
There is an app (both android and istuff) called "engineRPM" that measures rpm from the sound, it works quite well.
The prop rpm is the engine rpm divided by the 2.43:1 redrive ratio.
- Joined
- Dec 5, 2010
- Messages
- 5,170
- Display Name
Display name:
GeorgeC
Easy enough to blow it out and rule it out.
What kind of fuel? E0? E10? 100LL?
See @EdFred's thread:
Next step to trouble shoot airspeed discrepancy ? (SOLVED)
Last August I got my static system checked and the airspeed was out of spec. Option was to OH or buy new. Comparing the two prices, I went with new. Airspeed read slow. Came in like I normally did and floated foooorever. My initial thought was that the old airspeed indicator was the issue...
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
Thanks! I will buy a laser tachometer and verify the prop RPM is correct and no gearbox slipping.
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
I always run 100LL.Easy enough to blow it out and rule it out.
What kind of fuel? E0? E10? 100LL?
See @EdFred's thread:
Next step to trouble shoot airspeed discrepancy ? (SOLVED)
Last August I got my static system checked and the airspeed was out of spec. Option was to OH or buy new. Comparing the two prices, I went with new. Airspeed read slow. Came in like I normally did and floated foooorever. My initial thought was that the old airspeed indicator was the issue...www.pilotsofamerica.com
Thanks for the link. Just read the whole thing. Based on the resolution at post #96 in that thread, it seems after two years @EdFred merely disconnected the fitting and got static pressure from *inside* the tailcone and that fixed his airspeed indication problem? Interesting. And perhaps I should try disconnecting the static tube going into the back of my standby altimeter on the panel and see what that does. But then again, based on TAS VIA GPS calculator, I'm *actually going* 10-15 knots slower, it's not just my instruments telling me that I am. The speeds represented on the panel appear to be accurate and down significantly from what they were.
Last edited:
Flocker
Line Up and Wait
- Joined
- May 24, 2013
- Messages
- 693
- Location
- Peachtree City GA (KFFC)
- Display Name
Display name:
Flocker
What make and model aircraft?
Klaus M
Pre-takeoff checklist
If you have a steerable nose wheel then the rudder and the nose wheel connection need to be adjusted according to the maintenance manual. The rudder trim tab should be straightened back out to zero. Then after each flight adjust the rudder cables, steering linkage or springs until there is no need for rudder inputs at all in level cruise flight. You may notice there's adjustable rod ends on most of the aircraft's control linkage and that there's also turnbuckles on the control cables. Some aircraft have springs holding the rudder pedals forward. Those springs are usually adjustable also.
What make/model aircraft are we talking about?
The leading cause of flying slow is rigging. Well rigged aircraft will fly faster then the manufacturers numbers.
wanttaja
En-Route
Does YOURS have only a six-inch tube coming off the back of the altimeter and taking cockpit static pressure?
In any case, it would be really stupid system. In flight, the cockpit is a low-pressure area. The faster you go, the more the pressure differential in the cockpit.
I have had carbon monoxide issues in my cockpit.. and I fly an open-cockpit airplane.
Look at the airflow atop the fuselage...note that it's actually shaped like an airfoil. Just as bad with a closed-cabin design.
Get under your panel, find the static connection to the airspeed indicator, and trace where it goes. My guess is that it got pinched/disconnected/plugged somewhere.
My cheap-a** homebuilt takes its static reading from a boom half-way out on the left wing, and routes it back to the cockpit through a combination of plastic and aluminum tubing. I once tested a consumer device that combined compass and altimeter. Just sitting on the ground, and doing a runup, the altimeter would rise since the device had an integral static port.
Ron Wanttaja
kicktireslightfires
Pre-takeoff checklist
- Joined
- Jun 11, 2020
- Messages
- 344
- Display Name
Display name:
kicktireslightfires
It's a castering nosewheel, so no steering linkage, nor are there any centering springs on the rudder pedals. It's a Tecnam Astore.
I noticed yesterday that to taxi straight on the ground, a good amount of right rudder is needed. Along with differential braking, of course. But shouldn't my pedals be neutral while taxi'ing? I could taxi straight with rudder pedals neutral, but it requires a lot more right brake pedal.
I won't be attempting to realign my rudder cables by myself -- my A&P will -- but does anyone know if this can be done from the point in the attached photo at the back of the rudder? Or must it be done at the point of the central pulleys (which happens to be in the most difficult to reach part of the plane)?
Again, still, this cannot be the source of the airspeed problem as this was a pre-existing condition when I was still flying faster.
