Laminar Flow Wing and disturbed flow

[Bob_Belville]

39 minutes ago, Ragsf15e said:

While I generally agree that drag is more important than power, I’ve done a lot of speed testing in my F and I know th ~.75” of manifold pressure I get from opening the ram air is worth a good 3 or 4 knots.  Are you sure your engine is running strong and all the compressions are good?  I had a barely noticeable exhaust valve wobble and I first noticed the speed loss.

 I have done speed tests at different weights and it definitely makes a noticeable difference, but really takes several hundred pounds of weight to make more than a knot or two.

Honestly though, probably a rigging issue since all the surfacs were just off, stripped, painted, balanced, put back on.  That’s the most likely.

Compressions:

Mar. 18: 79/80; 79/80; 78/80; 78/80.

Feb. 17: 78/80; 78/80; 78/80; 78/80.

Dec. 15: 79/80; 78/80; 77/80; 78/80. 

Oct. 14: 78/80; 76/80; 77/80; 77/80                (fresh engine reinstalled after Triad overhaul - prop strike.) 

[Guest]

7 hours ago, Bob_Belville said:

Thanks Lance, we are working on the aileron. With a straight edge across the yokes the right aileron is level and the left is down about 1/4". Lynn is going to check behind me and check with the rigging boards. He may need to tweak the adjustment even though we do not believe the painter could/would have messed with the adjustment. 

The rigging, particularly the subtle bending of the trailing edges of ailerons and rudder, is on going. As several here have noted this is no doubt a factor.

But I started this thread to get ideas from this august mob about the paint issue and possible fixes and I've received several useful ideas.  

Be sure to check that all of the shim washers are installed between the aileron pushrod aft rode end bearing and the aluminum fitting on the aileron.  Without them the rod end can move laterally on the bolt shank allowing the aileron trailing edge to move up and down.

While on the subject of shim washers, make shire that all of the elevator and rudder fittings have the required shim washers installed.  It is quite common to lose the washers when flight controls are removed.  If they are missed the fittings on the stabilator trailing edge get bent when the hinge bolt is tightened.

Lyn will know where to look.

Clarence

[Ragsf15e]

Good in March, I guess my thought is, how are they now?  

[Bob_Belville]

2 hours ago, M20Doc said:

Be sure to check that all of the shim washers are installed between the aileron pushrod aft rod end bearing and the aluminum fitting on the aileron.  Without them the rod end can move laterally on the bolt shank allowing the aileron trailing edge to move up and down.

While on the subject of shim washers, make sure that all of the elevator and rudder fittings have the required shim washers installed.  It is quite common to lose the washers when flight controls are removed.  If they are missed the fittings on the stabilator trailing edge get bent when the hinge bolt is tightened.

Lynn will know where to look.

Clarence

Thanks Clarence! I'll ask Lynn to double check all. @AGL Aviation

The aileron fit to the wing seems tighter than previous, I've assumed thinker paint... wonder if your shims affect that fit...

[Bob_Belville]

4 minutes ago, Ragsf15e said:

Good in March, I guess my thought is, how are they now?  

March was annual inspection after which the plane went to the painter. I've only flown 35 hours since and I have not had any reason to check compressions. Lance Keve and I took our airport manager to JNX to pick up a friend's Cherokee 6, we were at gross and climbed to 7000' just fine. 

[Ragsf15e]

Probably good hp if climb is normal.  I agree.

[rpcc]

I'm guessing you could achieve the same ridges with a vinyl wrap - why not try a wrap in similar configuration on a friends plane. Do some pre and post speed tests.  Should be an easy theory to prove/disprove.  

I wouldn't  touch the paint until I proved it was causing the issue - my 2 cents - best of luck. 

[EchoMax]

On 11/7/2018 at 10:41 AM, 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.

I recently purchased the late @Bob_Belville's beloved and bewitching bird, "The Gypsy Rose" (N943RW).

Does anyone know how his quest turned out?  Did Bob ever find the elusive five knots that he lost after the paint job?

[PT20J]

4 hours ago, EchoMax said:

I recently purchased the late @Bob_Belville's beloved and bewitching bird, "The Gypsy Rose" (N943RW).

Does anyone know how his quest turned out?  Did Bob ever find the elusive five knots that he lost after the paint job?

That's a lot of speed change. I would doubt it is the paint. However, a lot of parts get removed to do a paint job -- control surfaces, gear doors, etc. The first thing I would do is to check all the rigging. I would also check both the pitot and static system for leaks to make sure that the airspeed indicator is correct and I would do a GPS TAS check https://www.ntps.edu/information/downloads.html

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