Bob_Belville

Laminar Flow Wing and disturbed flow

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As some here will know, I had my plane painted this year. It turned out well, looks great.

But the plane is noticeably slower and I am trying to figure out why.

One possible issue is the paint trim stripes. The ends of the wings and (horizontal stabilizer) has 4 stripes angled and tapered, top and bottom. There's a paint ridge, perhaps as much as 1/16" high between all the stripes. Since the airflow over and under the wing passes over these ridges I suppose there is disruption.

So... does anyone here have experience/knowledge as to whether this might be causing drag?

And... what would be the best way to remove the ridge without screwing up the paint job? 

Thanks! 

 

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Don’t mean to question it but 1/16” sounds excessive to the point of damn near impossible for trim coats. That said, don’t overthink this. While the flow is technically laminar in this section of the wing, there is still a boundary layer (where the flow goes from freestream velocity to zero) that should be thicker than the paint surface discontinuity.  It would take some calculation to determine the thickness of the boundary layer for various conditions but really isn’t necessary.  You ever notice the rivets go from countersunk to universal as you move down the wing chord?  It’s because the heads are within the referenced boundary layer this far back. The presence of the protruding heads have no real effect at that point; just an example of how thick the BL is at that point. IMO, anything you tried to do to “improve” the flow here wouldn’t be measurable in performance.  Likewise, these attempts could quite possibly have the opposite effect. Seriously, don’t let anyone talk you into clear coat. Spend your time/efforts/money elsewhere. Enjoy your nice looking plane. The paint scheme makes it look 20 knots faster anyway. 

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Small ridges, unlikely. Control surfaces not put back exactly how they were removed,  very likely. 

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Weight difference Before new paint vs after? 
as @jackn said, the way the control surfaces were reinstalled would create a lot more drag than paint. 
I know I've drooled over this paint job in the past few months, but never saw the original paint job before. Questioning how a "smooth" paint vs. a previously "rough" job would cause more drag. 

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Nothing slows a Mooney down quite like poor rigging. And no one seems to be able to coax as much speed out of a good rigging job as Don Maxwell.

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17 minutes ago, gsxrpilot said:

Nothing slows a Mooney down quite like poor rigging. And no one seems to be able to coax as much speed out of a good rigging job as Don Maxwell.

My fuel servo has slowed mine down considerably over the past 3 weeks.... Top speed has been 10-15 ktas, behind a tug, back and forth from the mechanics hangar and mine. 

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2 minutes ago, CDNflyby said:

My fuel servo has slowed mine down considerably over the past 3 weeks.... Top speed has been 10-15 ktas, behind a tug, back and forth from the mechanics hangar and mine. 

that's moving a bit fast, I would recommend 5 kts max

Brian

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1 minute ago, orionflt said:

that's moving a bit fast, I would recommend 5 kts max

Brian

Pure estimates.... But, yeah your right. Strong tailwind? :P

 

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I have seen people hauling ass towing planes, while that in it self isn't a major issue the problem is more the force on the nose gear when you turn, or  need to slow or stop. a sudden stop could cause the gear to collapse and turns at high speeds will increase side loads on the nose gear. when you are taxing at higher speeds you are breaking with the mains so there is no load pushing back on the nose gear, turning at high speeds can put increased side load on the gear but that load is exaggerated by a tow bar attached to a vehicle. 

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42 minutes ago, orionflt said:

that's moving a bit fast, I would recommend 5 kts max

Mine was last towed behind a small, dark red riding mower with the deck removed, with the mower running backwards to pull the plane from the ramp to the A&P's shop . . . Not quite my own [slow] walking speed . . . .

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37 minutes ago, orionflt said:

I have seen people hauling ass towing planes, while that in it self isn't a major issue the problem is more the force on the nose gear when you turn, or  need to slow or stop. a sudden stop could cause the gear to collapse and turns at high speeds will increase side loads on the nose gear. when you are taxing at higher speeds you are breaking with the mains so there is no load pushing back on the nose gear, turning at high speeds can put increased side load on the gear but that load is exaggerated by a tow bar attached to a vehicle. 

I'm happy to have a AME that's cautious, and works on a lot of Mooney's.... He's slow as F&&K when it comes to getting things done (Fuel Servo has been back from OH for 11 days now... just finishing putting it on today), but he's careful and meticulous. 
My comment was that it wasn't going 145 kts like it should... 

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When your airplane was disassembled for paint and re-assembled could the rigging have been effected?  How is the rigging currently?  Does the ball sit centered when you are in level flight?

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4 minutes ago, aviatoreb said:

When your airplane was disassembled for paint and re-assembled could the rigging have been effected?  How is the rigging currently?  Does the ball sit centered when you are in level flight?

Eric, presumably the ailerons were put back on exactly as they were taken off, at the hinges, without changing the rigging. There is a definite possibility that the trailing edges of the control surface were changed. Lynn and I are in the process of re-tweaking them. Ball is centered in cruise.   

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Not only the rigging but I know you also had that new cowl.  Is it noticeable after the cowl to after paint or before the cowl to after paint.   How many kts is "noticeable"? The good news is it LOOKS FAST!!!!!!!

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1 hour ago, wcb said:

Not only the rigging but I know you also had that new cowl.  Is it noticeable after the cowl to after paint or before the cowl to after paint.   How many kts is "noticeable"? The good news is it LOOKS FAST!!!!!!!

You know - dawling - its now how you feel, its how you wrook.

And you wrook MAAAVELOUS!

Edited by aviatoreb
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1 hour ago, Bob_Belville said:

Eric, presumably the ailerons were put back on exactly as they were taken off, at the hinges, without changing the rigging. There is a definite possibility that the trailing edges of the control surface were changed. Lynn and I are in the process of re-tweaking them. Ball is centered in cruise.   

No way that any of the control surfaces could be incorrectly installed, about the only thing that could be done improperly beyond balancing them would be too not use the proper hardware which can be verified visually.  Neither effects rigging. 

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Bob, with the amount of stuff done to that airplane the last thing I would think about slowing it down would be paint stripes.

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Not only the rigging but I know you also had that new cowl.  Is it noticeable after the cowl to after paint or before the cowl to after paint.   How many kts is "noticeable"? The good news is it LOOKS FAST!!!!!!!
We finished the cowl just in time to fly to the painter so no data to distinguish. But the other planes with the SabreCowl all report speed gains.

Sent from my XT1710-02 using Tapatalk

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Check

Alternate air button position

Pitot tube paint residue 

Static ports paint  residue 

Static and pitot tube paint residue.

 

José

 

 

 

 

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1 hour ago, Bob_Belville said:

We finished the cowl just in time to fly to the painter so no data to distinguish. But the other planes with the SabreCowl all report speed gains.

The fact that other aircraft reported gains doesn't automatically mean yours will.  Too small a sample size to really make solid predictions.

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55 minutes ago, Piloto said:

Check

Alternate air button position

Pitot tube paint residue 

Static ports paint  residue 

Static and pitot tube paint residue.

 

José

 

 

 

 

I think Jose is onto something.  When I had my G5's installed and they re-certified my pitot static system I was having some false readings and they had to track down some leaks.  Therefore, you might actually be going as fast as it looks but just reading slower.

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1 hour ago, Bob_Belville said:

We finished the cowl just in time to fly to the painter so no data to distinguish. But the other planes with the SabreCowl all report speed gains.

Sent from my XT1710-02 using Tapatalk
 

Bob,

But you had the ARI cowl before, the others I believe just had the LASAR lower enclosure and some still had the air and oil filter out front.  It would make sense that those planes would see genuine gains where yours may not.

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Just now, kpaul said:

Bob,

But you had the ARI cowl before, the others I believe just had the LASAR lower enclosure and some still had the air and oil filter out front.  It would make sense that those planes would see genuine gains where yours may not.

I Agree. The ARI was fine. But it is not that I've not gained speed, which I did not expect to gain much if anything, I have lost at least 5 kts, maybe more.

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1 hour ago, Piloto said:

Check

Alternate air button position

Pitot tube paint residue 

Static ports paint  residue 

Static and pitot tube paint residue.

 

José

 

 

 

 

Thanks José. 

The plane had a static system certification after the paint job.

IAS seems to be accurate. I made a round trip to Smithfield (about 150 nm due east) last week and the GPS  ground speed was 160 kts with a strong tail wind and 115 on the return. 7000' and 6000', 8.1 GPH LOP. Not to assume too much precision, that's an average of 135-140 kts. I would have expected about 145 TAS under those conditions. 

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