How fast can an M20F really go?

[MikeOH]

3 hours ago, EricJ said:

My understanding is that it moves, just slower than the further layers.    It slows down even further as it travels along a surface.    This is why Mooneys have flush rivets along the first parts of the wings and fuselage and non-flush toward the tail and trailing edges.    I've noticed this on older airliners as well, the first half or so of the fuselage is flush riveted, the back part not.    I got to see a 787 up close last year and it is flush everywhere, so maybe the construction economics have changed or it is considered more useful than it used to be.

Perhaps.  I had thought that flush rivets maintain laminar flow farther back on the wing.  So, I suppose a rough surface could destroy laminar flow prematurely causing increased drag. Wax away!

[GDGR]

5 hours ago, hmasing said:

My paint is chalky and won't hold a shine.  :-(  

Paint is my next upgrade, once I re-skin my flaps and ailerons from some visible hail damage.

Mine needs a refresh as well. The airport I’m at is having the runway resurfaced in June, so I’m scheduled for annual and plan on stripping and paint at the same time. 

[1964-M20E]

I have all the mods except presti cowl and lower gear doors.  I plan on 145 but fly it LOP.  Usually right on for my flights.

If you put all mods on an F or E you will go trans-sonic.

[A64Pilot]

10 hours ago, MikeOH said:

Perhaps.  I had thought that flush rivets maintain laminar flow farther back on the wing.  So, I suppose a rough surface could destroy laminar flow prematurely causing increased drag. Wax away!

That theory has sort of evolved over time, a newer theory is to trap a layer of air a few molecules thick at the surface and let the air molecules shear against themselves gives less drag than shearing against a smooth surface.

I’m not sure where it came from, I believe maybe when Military aircraft began to be painted in rough and not smooth paint and didn’t slow down? Go feel CARC paint, it’s so rough it feels almost like sand has been added to the paint, the roughness is for IR suppression, no glare. An IR missile can lock on canopy glare for instance so shiny paints out.

About 1980 jet ski racers roughened the bottoms of their skis and went faster. I think that was an independent discovery, discovered because you beach skis and that roughens the bottom of course. But all this is supposition. I’ve learned seen any papers on the subject

Edited April 17, 2021 by A64Pilot

[Shadrach]

https://flightaware.com/live/flight/N6339Q/history/20210416/1413Z/KHGR/KILG

https://flightaware.com/live/flight/N6339Q/history/20210416/1551Z/KILG/KHGR

round trip from KHGR-KILG-KHGR.

Block speed round trip for my box stock F model from touchdown to touchdown was 137kts. This included climb, descent and pattern work. I’ll also note that the winds were a touch stronger on the return trip home (headwinds) and that I was a bit higher.

Cruise setting was WOTRAO 2500rpm 20LOP.

Edited April 17, 2021 by Shadrach

[MikeOH]

1 hour ago, Shadrach said:

https://flightaware.com/live/flight/N6339Q/history/20210416/1413Z/KHGR/KILG

https://flightaware.com/live/flight/N6339Q/history/20210416/1551Z/KILG/KHGR

round trip from KHGR-KILG-KHGR.

Block speed round trip for my box stock F model from touchdown to touchdown was 137kts. This included climb, descent and pattern work. I’ll also note that the winds were a touch stronger on the return trip home (headwinds) and that I was a bit higher.

Cruise setting was WOTRAO 2500rpm 20LOP.

Thanks for the honest post!

[Shadrach]

16 hours ago, MikeOH said:

Thanks for the honest post!

Sure. Although, I hope your take away isn’t that my M20F’s cruise speed is 137kts. Block speed is significantly less than cruise. I would bet that the delta in block speed between my airplane and a typical 201 to be less than 8kts, probably ~5kts. Also note that this was a short trip of about 100kts. Block speed would’ve been higher with more time spent in cruise. If you look at my cruise speed only, you’ll see that it clusters right around 150kts when corrected for wind. I know that my bird will cruise above the magic 150kt number because in addition to all of the air testing I’ve done, I frequently see 150kt GS flying into forecast (light) winds when westbound.

Edited April 18, 2021 by Shadrach

[jaylw314]

17 hours ago, MikeOH said:

Perhaps.  I had thought that flush rivets maintain laminar flow farther back on the wing.  So, I suppose a rough surface could destroy laminar flow prematurely causing increased drag. Wax away!

In theory, airflow at the surface in laminar flow is zero.  The theory of smooth surfaces is so you don't have bumps that project upwards into the layers that ARE moving.

My understanding is that rough surfaces and bigger bumps cause increased drag as well as potentially triggering turbulent flow

[Ragsf15e]

When you’re talking about stationary boundary layers one molecule thick, paint chips and no wax is probably like big draggy bumps to the moving molecules above the stationary ones.

[A64Pilot]

Laminar flow is notoriously difficult to actually occur, even dead bugs will trip flow into non laminar, it’s exceedingly difficult to get a manufactured metal wing in laminar flow for more than a small amount of its chord.

This is where a composite material wing, if and only if it’s molds are nearly perfect have us beat, but maintaining molds to that level takes an artist

‘My airplane has a lot of leading edge paint damage from rain, so I assume it’s almost all non laminar, yet I get what’s most often quoted as realistic cruise speeds for a J model, roughly 155 kts true at 65% power.

‘Decades ago, I believe it was NASA that built an aircraft with thousands of slots in the wing, the idea was to pull a vacuum and suck boundary layer air into the wing to maintain laminar flow, it worked and reduced drag drastically, sort of proving how difficult it is to achieve laminar flow

 

On edit, apparently the suction method has a whole lot more history than I was aware of, even back before WWII

https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf

Edited April 18, 2021 by A64Pilot

[MBDiagMan]

On 4/15/2021 at 1:01 PM, Marauder said:

I've owned my F since 1991. With a 201 windshield, gap seals, step removed, lower cowl enclosure and PROPERLY rigged, I see consistently 152 KTAS with 65% power. Cold winter days, it will creep up to the 155 range, hot summer days closer to 149. These numbers are cross checked using both mechanical means (Aspen reported TAS and TAS calculated using the airspeed from the ESI-500 applying the old factory CAS adjustments and the TAS calculator on the Garmin) and the ground course calculation using ground speeds.

I think the predominate factors that play a role are the rigging, quality of the paint and the health of the engine. When I added the lower cowl enclosure, I don't think I saw much change in airspeed (less than 1 knot) but did see better uniform CHTs.

A "YAHOO!" day below.

 

 

My ‘67 F is easily comparable to the above speed results..  It has J Cowling, J windshield, gap seals, tail mods.  Except for the wings, aerodynamically it’s virtually a J.  When posting on this forum what I had seen, however, I had many doubters.

[Browncbr1]

At gross & 8-9k DA, mined does 140-145ktas (CAS).. 65% 0-20 LOP    

2500lbs, add a few more kts or add 5kts for 2300lbs. (Typically 147-149ktas)

Add an additional 2-3kts for fresh wax.

The only mod I have is 201 windshield and brake rotation.   My rudder is a little bit out of rigging.  

 

[ArtVandelay]

Best speed mod is to fly in cold,dry air...those of us in Florida are at a disadvantage when it comes to bragging rights.

[KB4]

On 4/15/2021 at 7:26 PM, GLJA said:

The plane had spent a considerable amount of time outside prior to my purchase, and the paint was rough to the touch. So I polished and waxed the plane.... gained 6 kts.

 

Yes. Best speed mod is clean plane. I have tried almost every product, best I found is gallon jug of micro polish for 30$ at spruce.  Wipe the off dust, dirt, and bugs.  Then spray a mist of micro polish then just wipe.  

[GDGR]

3 hours ago, KB4 said:

Yes. Best speed mod is clean plane. I have tried almost every product, best I found is gallon jug of micro polish for 30$ at spruce.  Wipe the off dust, dirt, and bugs.  Then spray a mist of micro polish then just wipe.  

I bought 4 different grits of NuShine and did the entire plane. Took a few days, but the difference was noticeable 

[DCarlton]

My '67 has every possible mod (belly, windshield, gap seals, fairings, cowl, etc) and a three blade prop.  A few years back, I made 85 flights between KCRQ and KFFZ with plenty of time to compare flights.   My conclusion...  153 kts.   Since then my engine has been overhauled.  Really haven't watched speed that closely since then. 

 

Edited April 20, 2021 by DCarlton