Impacts on Airspeed

[mooneyflyer]

A friend owns a 1998 Ovation.

He feels it's slower. Does anyone have data on the impact to airspeed at cruise with:

1. Vortex Generators

2. Air Conditioning

Thanks

[kmyfm20s]

The airconditioning unit adds 1 large scoop on the bottom and 2 medium scoops on the side of the tail. I think it cost you 4 to 5 kts.

[Hank]

If by "vortex generators" you mean the little thingies on the wing that lower stall speed, they also lower cruise speed. In my opinion, the laminar flow wing on the  Mooney does not benefit much at all from these. The faster you fly, the more additional drag they create, which slows you down.

[carusoam]

Some good news maybe...

Swapping out the vortex generators for an AOA meter could help...

It's one thing to lower the stall speed and a similar benefit of knowing better where it is???

Fly with precision and avoid the need for lower stall speed.

How much is the stall speed reduced by the VGs?

Who want's to tell him the radiator is still a drag?

The AC's capacity is related to airflow through the radiator. At altitude or in cooler climes like NJ, when the AC is not needed, the drag is still there. He would benefit by a system that closes over the vents when the system is turned off. Does that system exist?

Best regards,

-a-

[PMcClure]

My Ovation gets book speed even with A/C.

[Jeff_S]

The POH says that with A/C turned on, airspeed should suffer by about 1.8%. So not the 5 knots noted above, but some slight degradation of airspeed could be expected.

[orionflt]

The POH says that with A/C turned on, airspeed should suffer by about 1.8%. So not the 5 knots noted above, but some slight degradation of airspeed could be expected.

that 1.8 % loss of airspeed is based on the power from the engine needed to drive the AC compressor, that number doesn't take into account the airframe drag created by the additional scoops and condenser coil installed. because the scoops are not closed off when the AC is not in use the aircraft with AC installed will be slower then those without AC whether the system is being used or not,

 

Brian 

[DAVIDWH]

 Perhaps your friend is flying the ovation too high. It is a burner at low altitudes. For the higher air he would need to spend some extra $$$ and purchase the Acclaim.

 

Anyway, he is already faster than a lot of twins.

[WardHolbrook]

 Perhaps your friend is flying the ovation too high. It is a burner at low altitudes. For the higher air he would need to spend some extra $$$ and purchase the Acclaim.

 

Anyway, he is already faster than a lot of twins.

Anymore, proper altitude selection is simply a matter of using one of the flight planning programs that incorporate winds aloft into the calculations and provide multiple, altitude based, calculations showing total times and fuel burns. One of the best and most popular free programs is fltplan.com. All that being said, 3 or 4 knots is simply inconsequential.

[jlunseth]

Foreflight has an excellent in-app function for selecting altitude.  In the Nav screen, just touch the altitude and a long list of other possible altitudes, head/tailwind velocities, and ETE's will come up.  It is not as good as fltplan for actually computing ETE.  Foreflight only assumes a single TAS, it is not possible to make a custom profile for your aircraft with different TAS's for different altitudes, and therefore Foreflight's ETE for a turbo flight in the flight levels, for example, will always be wrong.  fltplan allows a complex custom profile, so you can have a climb TAS and TAS's for various altitudes.  Its ETE will be much more accurate, probably +/- 5 minutes even for a long flight.  But its display does not give you the choices that Foreflights does.  Foreflight will list all the altitudes from ground on up to the flight levels.  fltplan gives you only five, if you want a different five you have to back out of the navlog screen that shows the computed ETE's and change altitude in the basic flight plan, then go back into the Navlog and see a different five altitudes and their ETE's.

 

I use Foreflight to decide what altitude to cruise at, then put that altitude into fltplan to get an accurate ETE.

[Robert C.]

If by "vortex generators" you mean the little thingies on the wing that lower stall speed, they also lower cruise speed. In my opinion, the laminar flow wing on the  Mooney does not benefit much at all from these. The faster you fly, the more additional drag they create, which slows you down.

Do we have hard data on that?

The folks that make and sell the vortex generators claim they have no impact on cruise speed on Mooney Ovations. I seem to recall they indicated a 2-3 knot reduction on some models of the brand B and others so have the impression they aren't automatically exegarating.

[aviatoreb]

Do we have hard data on that?

The folks that make and sell the vortex generators claim they have no impact on cruise speed on Mooney Ovations. I seem to recall they indicated a 2-3 knot reduction on some models of the brand B and others so have the impression they aren't automatically exegarating.

 

Apparently he just knows.

[DAVIDWH]

E=MC Squared.

 

Just a simple patent office employee.

 

He just knew.

[Will W]

Why are there vortex generators? There is your problem! Why would you ever put that on a Mooney? Whoever sold that idea should never work on a Mooney again. Just an absolutely terrible idea to have done.

[philiplane]

Unless they are in the wrong place on the wing, VG's have negligible effect on cruise speed on any wing.

 

More likely there is a CG problem that is slowing the plane. Forward CG will easily cost 4-7 knots.

[Will W]

I still can't get over someone putting VG's on a Mooney Ovation.

[FoxMike]

I put a set of VGs on a T210 that I owned.  I was genuinely impressed with the low speed handling qualities.  At the time my home base had no tower and was under Denver Class B.  I had little room to maneuver while following 172s that were in front of me in the pattern.  The VGs really helped particularly when i was heavy.  I raced the airplane once a year and found the speed difference was about 5kts.  During normal cross countries I hardly noticed the difference.  If your engine ever quits and you have to land off airport you might be very happy you have VGs.