Laminar Flow Wing and disturbed flow

[takair]

13 minutes ago, Bob_Belville said:

yes

 

13 minutes ago, Bob_Belville said:

yes

I have a couple of ridges in my paint as well.  No speed reduction, but I too would like to knock them down, would love to hear from a painter on that subject.

Regarding rigging, that’s my guess, but maybe not the primary surfaces.  Others mentioned gear doors, that one is hard to get right, and they were likely removed during paint....so worth jacking and checking.  When mine got painted, I found the hinge bolts were finger tight. Also, check flap droop, the stops may now have paint on both surfaces and may cause some fractional amount of droop, which could be worth a little speed.

[Bob_Belville]

2 minutes ago, takair said:

 

I have a couple of ridges in my paint as well.  No speed reduction, but I too would like to knock them down, would love to hear from a painter on that subject.

Regarding rigging, that’s my guess, but maybe not the primary surfaces.  Others mentioned gear doors, that one is hard to get right, and they were likely removed during paint....so worth jacking and checking.  When mine got painted, I found the hinge bolts were finger tight. Also, check flap droop, the stops may now have paint on both surfaces and may cause some fractional amount of droop, which could be worth a little speed.

Joe, the painter, did not have any great ideas on an easy way to smooth the ridges. He was polite as usual but I think he is skeptical that that is the problem,

I did mask and wet sand with 1500 grit paper. We've got a good aircraft detailer here who is going to see what he can do with his buffer techniques. 

I sure wouldn't be messing with the paint if I had not already investigated everything else I can think of!  Thanks for all the input. 

[jaylw314]

8 hours ago, Bob_Belville said:

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!

Looks great!

As others have mentioned, it seems doubtful the paint seams could be a major contributing factor, but have you asked the painter about using a bead of clear polyurethane along the seams?  that might soften the transition without any scraping or polishing.

[Bob_Belville]

1 minute ago, jaylw314 said:

Looks great!

As others have mentioned, it seems doubtful the paint seams could be a major contributing factor, but have you asked the painter about using a bead of clear polyurethane along the seams?  that might soften the transition without any scraping or polishing.

Clear coating is a possibility. The paint is all Imron, a very hard paint, so I suppose the clear would be less so and would alter the color somewhat. And prepping the paint for the clear coat might be as much work as polishing. 

I am no expert on the subtleties of the various choices so I am listening... 

[jaylw314]

Just now, Bob_Belville said:

Clear coating is a possibility. The paint is all Imron, a very hard paint, so I suppose the clear would be less so and would alter the color somewhat. And prepping the paint for the clear coat might be as much work as polishing. 

I am no expert on the subtleties of the various choices so I am listening... 

I was thinking just a bead of it along the paint seams with a paint brush, so any color change should not be an issue.

[Bob_Belville]

13 minutes ago, bluehighwayflyer said:

I wouldn't clear coat it, Bob. It will yellow and/or peel. I have no idea why, but clear coat just doesn't work as well on airplanes as it does on cars. 

I'm sorry and surprised to hear about your troubles. 

Jim

Thanks Jim. It is not under consideration. (Lynn has my hangar neighbor's nice Cherokee 6 in the shop today for annual. It does have a clear top coat.)

[KSMooniac]

I'd follow Jose's list, and also fly a 3 TRACK airspeed calibration test flight for a couple different power settings in smooth air, noting your indicated airspeed, altitude, barometric pressure, and temperature.

On the ground, follow your POH corrections to get calibrated airspeed, then calculate true airspeed given the test conditions. Then use the 3 stabilized ground speeds from the three different tracks and an online TAS calculator to get your real TAS. Then you'll know if you have an indication problem or a real problem.

Flying tracks is crucial here...not headings. Set OBS mode on your GPS and dial up the desired tracks 90 degrees or 120 degrees apart, and let the autopilot fly them. Hand trim to zero-out pitch input from the autopilot as well.

If there really is a problem, I'd look at gear doors and flaps first.

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[Bob_Belville]

53 minutes ago, KSMooniac said:

I'd follow Jose's list, and also fly a 3 TRACK airspeed calibration test flight for a couple different power settings in smooth air, noting your indicated airspeed, altitude, barometric pressure, and temperature.

On the ground, follow your POH corrections to get calibrated airspeed, then calculate true airspeed given the test conditions. Then use the 3 stabilized ground speeds from the three different tracks and an online TAS calculator to get your real TAS. Then you'll know if you have an indication problem or a real problem.

Flying tracks is crucial here...not headings. Set OBS mode on your GPS and dial up the desired tracks 90 degrees or 120 degrees apart, and let the autopilot fly them. Hand trim to zero-out pitch input from the autopilot as well.

If there really is a problem, I'd look at gear doors and flaps first.

Sent from my LG-US996 using Tapatalk
 

Thanks Scott. I have done 3 heading speed checks and know the plane is slow.

I am also well aware of the gear and control surfaces as well as the retracting step.

We are in the process of going through all the elements of rigging for the umpteenth time. The plane tracks straight with the ball centered hands off. 

My question is about how to smooth the paint. Bob Kromer has taught us that a few bugs on the leading edge costs speed and that a fresh wax job is the best speed mod. The ridges on the edges of paint stripes have to be more disruptive as bugs or dull paint. OSISTM 

[aviatoreb]

8 hours 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.   

That was my thought.

After my paint job the ball was ...not quite centered anymore.  A slight tweek to the tail trailing edge fixed that.

[KSMooniac]

I'm not trying to be snarky but if you flew headings you can't use that data for an accurate TAS calc. As experienced as you are with your current and past E models I believe that if you think it is slow, then it likely is. I do not believe the paint stripes on the wing would give you a measurable speed loss like you're describing, though.

If you're convinced your rigging, especially flaps and gear doors, is perfect, then your next step should be to smear some oil with colored powder on to your leading edge and go fly. If you have an early transition to turbulent flow you'll see it in the pattern on the wing. You might put a gopro looking out the window to record it as it flows in case the pattern dissipates before landing too.

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[carusoam]

Lots of ideas regarding friction being covered...

The other half of the speed equation is power generation...

Anything standing out related to changes in MP, rpm, FF, engine airflow/filter...

Any changes in raw EGT numbers since the new cowl / air intake was installed?

PP guesses only, hoping to ignite an idea in somebody else’s mind maybe...

Best regards,

-a-

[Bob_Belville]

5 minutes ago, KSMooniac said:

I'm not trying to be snarky but if you flew headings you can't use that data for an accurate TAS calc. As experienced as you are with your current and past E models I believe that if you think it is slow, then it likely is. I do not believe the paint stripes on the wing would give you a measurable speed loss like you're describing, though.

If you're convinced your rigging, especially flaps and gear doors, is perfect, then your next step should be to smear some oil with colored powder on to your leading edge and go fly. If you have an early transition to turbulent flow you'll see it in the pattern on the wing. You might put a gopro looking out the window to record it as it flows in case the pattern dissipates before landing too.

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I've used this site several times, it calls for flying 3 headings. Is there something wrong with it?  http://www.eaa62.org/technotes/speed.htm

[Bob_Belville]

39 minutes ago, carusoam said:

Lots of ideas regarding friction being covered...

The other half of the speed equation is power generation...

Anything standing out related to changes in MP, rpm, FF, engine airflow/filter...

Any changes in raw EGT numbers since the new cowl / air intake was installed?

PP guesses only, hoping to ignite an idea in somebody else’s mind maybe...

Best regards,

-a-

Good thoughts Anthony. I have been meaning to verify that the HP factor in the EDM 930 is still correct. It has been several years and changes.

MAP seems to be fine. Departing ECP (sea level) after Summit it hit 30.1, FF hit 17.8. 

When @Sabremechput his cowl on Matt's F model he initially left the RAM air. Their test flights indicated that the MAP gain was only 0.1 - 0.2" so I opted to eliminate the RAM air when we did mine. With David's cowl the air filter moves inside the cowl, very much like the J model. It is obviously more efficient than the old cowl. 

RPM: we replaced the governor a couple of years ago and verified the RPM. It hits about 2700 on TO roll.

EGTs: I have not noticed any change thought I could go compare data... Peak EGTs for the most recent flight:1510/1448/1476/1486. Without pulling up some old flights I think that is about what I'm accustomed to. 

[carusoam]

Bob,

An overall power measurement I have used in the past...

Waas source / portable gps and CloudAhoy app... measure T/O distance in feet...

Compare to the graphs in the POH...

Similar to measuring 0 to 60 times... the wind resistance doesn’t have much time to cause an effect here...

Also compare climb rates to the POH...

Both make good comparisons for HP production...

If you are off in hp production check with Lynn about measuring your ignition timing... is it 20 or 25 BTDC, or has it moved a few degrees closer to TDC...

Its more amazing that Al didn’t have these fancy tools and charts when developing the M20... he really could have used MS...

If you have time and desire to experiment. Reflexing the flaps upwards might be interesting... this is in search of the proper position in case they have been accidentally moved downwards...

But this has now gone in the direction of rigging control surfaces.... which I have never done...

Best regards,

-a-

[Bob_Belville]

3 minutes ago, carusoam said:

Bob,

An overall power measurement I have used in the past...

Waas source / portable gps and CloudAhoy app... measure T/O distance in feet...

Compare to the graphs in the POH...

Similar to measuring 0 to 60 times... the wind resistance doesn’t have much time to cause an effect here...

Also compare climb rates to the POH...

Both make good comparisons for HP production...

If you are off in hp production check with Lynn about measuring your ignition timing... is it 20 or 25 BTDC, or has it moved a few degrees closer to TDC...

Its more amazing that Al didn’t have these fancy tools and charts when developing the M20... he really could have used MS...

Best regards,

-a-

Thanks. Timing for my engine is 20 BTDC. We check it at annual.

I'll check out CloudAhoy. As you know, the Mooney owners manuals in '66 require a fair amount of interpolation. And I'd need to adjust for weight and altitude. 

[carusoam]

See if you can get an E’s POH from 1977...

Lots more data between its covers...

I bought two manuals for my C... one for 65, to be legal... one from 77 to have the data... 

Worst case... you can always compare against the J’s POH... if you can’t beat that we have some searching to do...

I got the POH recommendation direct from Bill Wheat by telephone... in Y2K... I had no idea who Bill was at the time.  I do now.

Best regards,

-a-

[M016576]

A few other ideas:

check flight aware to see if it is indeed slower than you remember.

highly unlikely the paint alone would cause a 5kt reduction in speed- unless it’s a *total* hatchet job- which it does not appear to be- even with the ridges you describe.

incipient / induced drag (more the low speed factors- certainly a likely issue for a mooney- relatively low horsepower motor for the speed it can develop) vs parasitic drag (a factor as well for top end speed)... did you add anything.. antennas for ADS-B... wingtip fairings.. anything while the plane was in for paint? Did you remove anything?  What was the weight in the aircraft during your last flight? Configuration? Air temp/density?

Pitot static system contamination can be verified using a GPS- sounds like you’ve already checked that?

Motor/prop running OK? Sounds like you’ve checked that too already.

before you take sandpaper to your new paint- I’d take a long/hard look at aerodynamics in relation to the speeds we’re flying at- and what “laminar flow” actually means in terms of maneuverability vs top end speed and where the boundary layer exists along a wing moving at ~150 knots.  I’m not saying it’s “impossible” for a paint job alone to crush 5 knots... I’m just saying that it’s highly unlikely in your case- where it appears to be a professional job.

Of course- I’m not an A&P, and I still call your power plant a motor.  So take all this for what it’s worth.

 

Edited November 8, 2018 by M016576

[wcb]

9 hours ago, Bob_Belville said:

Good thoughts Anthony. I have been meaning to verify that the HP factor in the EDM 930 is still correct. It has been several years and changes.

MAP seems to be fine. Departing ECP (sea level) after Summit it hit 30.1, FF hit 17.8. 

When @Sabremechput his cowl on Matt's F model he initially left the RAM air. Their test flights indicated that the MAP gain was only 0.1 - 0.2" so I opted to eliminate the RAM air when we did mine. With David's cowl the air filter moves inside the cowl, very much like the J model. It is obviously more efficient than the old cowl. 

RPM: we replaced the governor a couple of years ago and verified the RPM. It hits about 2700 on TO roll.

EGTs: I have not noticed any change thought I could go compare data... Peak EGTs for the most recent flight:1510/1448/1476/1486. Without pulling up some old flights I think that is about what I'm accustomed to. 

Lets say the MP decrease by removing your ram air was on the top end maybe even .3" can that equate for a knot or two?  Then add the difference in the ARI mod vs your new mod could that be a knot or so?  Then add small weight balance change, small airflow changes with paint, small rigging differences from before and after paint another knot or two?

What I am suggesting (based on everything you have looked at already and how well you know your plane) is that it is not one change that has potentially impacted your speed.

[Marauder]

Bob - I thought you dialed in the TAS difference before painting?

I often wonder how much weight gain a plane sees with a new paint job, especially if they add a lot of Bondo to fix cosmetic issues.


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[David_H]

It seems hard to believe that paint would make a noticeable speed difference. 

I'm in the camp that thinks something else is going on.

[wcb]

35 minutes ago, Marauder said:

Bob - I thought you dialed in the TAS difference before painting?

I often wonder how much weight gain a plane sees with a new paint job, especially if they add a lot of Bondo to fix cosmetic issues.


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I am surprised none of our polished aluminum "naked" brethren have said "that is why flying naked is better".  In an earlier post in this thread Bob said he went strait from David's to paint.

[Piloto]

I have found that an application of Rain-X for plastics on my old paint job increases TAS by 5kts and reduces ice adhesion. Try it on the leading edge and top bottom surfaces of the wing.

José 

[Bob_Belville]

13 minutes ago, Piloto said:

I have found that an application of Rain-X for plastics on my old paint job increases TAS by 5kts and reduces ice adhesion. Try it on the leading edge and top bottom surfaces of the wing.

José 

ISTM that confirms the importance of the wing surface and might suggest that the ridges could well make a noticeable difference. 

[Browncbr1]

@Bob_Belville , I was talking to Lynn there at AGL about doing my rigging a while back..  He said, one of his past customer's planes was especially difficult to rig, so he weighed the plane to figure out the lateral weight balance and found that the right wing had something like 10 lbs more paint, so he had to add some lead to the left wing tip.

[Bob_Belville]

48 minutes ago, wcb said:

I am surprised none of our polished aluminum "naked" brethren have said "that is why flying naked is better".  In an earlier post in this thread Bob said he went strait from David's to paint.

At the same time that we added the new cowl we added bladder extensions. I am still in the habit of topping the tanks so I'm probably flying at a 75# higher weight. That assumes the new paint did not add more weight. (The plane was completely stripped including old filler so I assume the new paint did not change the aircraft weight significantly.)