11 knots slower

[skyking1]

After annual I have found my screaming eagle to be ten to eleven knots slower at same altitude and power settings. Any ideas? Only change was an elevator bell crank

[kmyfm20s]

Was there a Pitot Static cert done? Maybe they either fixed a leak or created one.

[carusoam]

It may help to post the data you used for before and after...?

MP, rpm, altitude, OAT are good for hints...

Best regards,

-a-

[kmyfm20s]

The reason I asked is because there is a static line that runs to the tail of the plane a T's off to the left and right. Many shops when they do the test will pull apart the T and block the line instead of the left and right ports for the test. Mine became separated and gave some funny readings.

I would also have them recheck the timing if they adjusted it.

[Marauder]

The reason I asked is because there is a static line that runs to the tail of the plane a T's off to the left and right. Many shops when they do the test will pull apart the T and block the line instead of the left and right ports for the test. Mine became separated and gave some funny readings.

I would also have them recheck the timing if they adjusted it.

Or in my case they found a leak in the pitot line.

[takair]

If you look back at the tail, is the elevator flying the same as previously? Do you recall previous trim setting for similar weight and balance? Did they check rigging?

[M20S Driver]

After annual I have found my screaming eagle to be ten to eleven knots slower at same altitude and power settings. Any ideas? Only change was an elevator bell crank

 

TAS or with GPS flying NWSE headings?

[skyking1]

Taking it back fri will post more then ! Thanks for the help

[skyking1]

Everything checked out normal. Could some of you let me know what performance you get with your screaming eagle? Thanks

[M20S Driver]

Everything checked out normal. Could some of you let me know what performance you get with your screaming eagle? Thanks

 

Full throttle and top of the blue arc on EGT,  3100 lb at take off, cruising at 6500 feet gives me 186 knots at 19 gal/hour versus 180 knots at 17 gal/per hour (75 deg rich of peak).  I gain 6 knots but burn 2  gallons more fuel per hour.  My conclusion is that at 180 knots, the engine, the airframe, and my pocket book are happier. 

[rbp]

Full throttle and top of the blue arc on EGT,  3100 lb at take off, cruising at 6500 feet gives me 186 knots at 19 gal/hour versus 180 knots at 17 gal/per hour (75 deg rich of peak).  I gain 6 knots but burn 2  gallons more fuel per hour.  My conclusion is that at 180 knots, the engine, the airframe, and my pocket book are happier. 

 

yes, induced drag goes up by the square of the airspeed. 6 knots is 3% more airspeed for 10% more fuel burn.

[aviatoreb]

yes, induced drag goes up by the square of the airspeed. 6 knots is 3% more airspeed for 10% more fuel burn.

 

Its worse than that - you are working your engine harder and only going a little faster, so it is producing more heat that is not being carried away by air cooling as easily - so you need to use even more fuel than what you said to keep the engine cool.

[RobertoTohme]

After annual I have found my screaming eagle to be ten to eleven knots slower at same altitude and power settings. Any ideas? Only change was an elevator bell crank

You're not alone on that boat...  I took mine to the factory back in 2009 for new paint and interior, and ever since it's been a solid 12 knots slower.  Final weight after the work done was +6 lbs from incoming weight, so that's not it; balance shifted 0.15" to the front due the removal of the whole vacuum system, both primary and aux, so that's not the culprit either.  I've had Brian Kendrick himself mess with the plane several times with no improvement.  For those who don't know who Brian is, he was the manager of the factory service center before the shutdown and now works by his own.   We have explored rigging, seals, baffling, you name it, and couldn't get the speed back up to what it used to be.  He mentioned the fact that most planes had leaks in the pitostatic system that gave higher numbers, but I've got enough groundspeed data over the same courses with similar wind conditions over the years that proves that this was not the case either, and my plane has 2 independent air data computers that match, so the wind conditions are verified.   The only thing I notice is that the tail doesn't fly where it used to, but I've been swore to death that it's rigged properly so the only thing that comes to mind is that I somehow had a misrigged tail for years that escaped the annual checkups before painting it....

 

If you find your lost knots please let me know how!  I'm most interested in getting mine back too.

[FlyDave]

Have you tried loading the plane with a lot more weight in the baggage compartment/aft CG?

If the CG moved forward and all else is equal I'd try that and see if it makes a difference. I know that an aft CG in my Bravo is faster than the forward CG I initially flew the plane at.

[RobertoTohme]

Have you tried loading the plane with a lot more weight in the baggage compartment/aft CG?

If the CG moved forward and all else is equal I'd try that and see if it makes a difference. I know that an aft CG in my Bravo is faster than the forward CG I initially flew the plane at.

 

I've loaded it almost to the edge of aft limit and it does 2 kts better; balance is not it since it just moved about 1/8" forward from what it was before (empty), and tried to compensate with more cargo in the back...  Believe me, it's been 6 years of tinkering with it and nothing had worked.

[rbp]

Rear CG improves cruise speed because it reduces the AOA necessary to generate the same amount of lift, but at the expense of longitudinal stability.  Stay within the envelope, otherwise you may not have enough forward elevator authority to recover from a stall

[RobertoTohme]

Off from original thread subject, but out of all the hot-rods I've flown, the M20S is the one I never liked to get towards tail heavy; the other 2 fly nicer the closer I load them to the aft limit.

[Super Dave]

Moving the CG aft for a given weight will reduce drag and improve performance. But adding weight just to move the CG aft will not improve performance.

In other words, moving a 50lb bag of tools from the front seat to the baggage compartment will make some small speed improvement, but the airplane will be even faster if you leave the tools in the hanger.

[jetdriven]

I experimented with adding weight to the baggage area and never could quantify any speed increase by adding 100lb or even 150lb to the baggage area. The CG does move aft which reduces trim drag, but the extra weight cancelled that out with induced drag.

Moving my seat full aft and reclining it fully was worth a couple knots however.

[Guest]

On my E model having the ball off center by a very small amount scrubbed off several MPH, easily enough to see the needle moving.

Clarence

[aviatoreb]

I'm voting for a change of your instrementation of some kind, a change of the pitot system?  Leading to a measured difference but no real difference.

[aaronk25]

Did his adjustments to timing end up retarding it back to spec or did the timing get rechecked to ensure it correct.

5 degrees in timing could cost 10kts on a big 6 cylinder.

[Piloto]

This kind of obvious but check that both elevators line up with the stabilator. Check the speed with the autopilot off. The A/P trim output may not be working properly causing a divergence that causes drag.

 

José

[skyking1]

Thanks to all of you for the help! Taking it back again as the mech adjusted the fuel flow and pressure during the annual. We are checking that and the timing. Will let you know

[kmyfm20s]

Thanks to all of you for the help! Taking it back again as the mech adjusted the fuel flow and pressure during the annual. We are checking that and the timing. Will let you know

You should be able to notice a change in FF at take off. Is it the same? What is your takeoff FF?