Honest cruise airspeed to expect on a Savannah S?

[Jim Bair]

Hi, I'm new to this forum and possibly about to purchase a Savannah S tailwheel version.  Valter tells me I will have the first one in the US if I get one.  I am curious as to what people are actually seeing on their speed meter when cruising along at, say, 5000 RPM with a 912ULS.  Almost every manufacturer I've ever seen quotes numbers that seem to vary from a bit optimistic to wildly so and generated by the head of the sales department instead of the chief test pilot.  I built a Just Super STOL some years back and don't want to end up repeating that experience.  I can now say I have flown across the Great Plains in it's entirety, into the wind, at 72KIAS.  I think manufacturers tend to get numbers by taking the airplane to its optimum altitude, carefully calculate the TAS, have the throttle full in, then given they are at 8,000' calculate that the engine is at 75%, and bingo, publish a cruise speed at 75% power.  Then the pilot levels off at a couple thousand feet, pulls the power back to a nice setting of say 5000RPM and discovers he's doing considerably less than expected.  So my question is to you folks who have practical experience with this, what do you actually see on the airspeed indicator in this scenario of a couple thousand feet and 5000 RPM?  And does tricycle vs TW make any difference?  

[dan tonner]

Hi Jim;

I have a 2010 VG XL tricycle and I see 85 MPH on the airspeed indicator at 5000 RPM.  

Dan

[Thruster88]

Most airspeed indicators are a little to a lot optimistic due to errors in the pito static system. Certified aircraft have charts to correct this. A four way speed run using gps at 8000 feet were the engine can only produce 75% power is a good way to know true airspeed.  

[IBob]

Hi Jim, I can't speak for the tailwheel version, but my tricycle S gets about 86kts (99mph) at 5000RPM. This is with a Bolly 70" prop pitched to give a good compromise between STOL performance and cruise.

The Savannah will certainly go faster, but like most STOL designs it has a fair bit of drag, so power requirement and fuel consumption rises exponentially above this speed: at 86kts it feels to be cruising easily.

This is with a 912 ULS.
I believe Dan Tonner's VG XL (above) is a 912UL?

You may like to visit John Gilpin's Stolspeed website: he has done a great deal of work with VGs different props etc on his Savannah VG: https://www.stolspeed.com/

Edited July 4, 2022 by IBob

[Neil_S]

Hi Jim,

 

I've owned a factory-built nosewheel Savannah S with a 912ULS for the last 6 or 7 years with a 3-blade DUC prop. My experience with revs around 4800-5000 in cruise, usually flying at around 4500ft, is somewhere in the region of 80-83 knots.  

 

HTH,

Neil

 

Edited July 5, 2022 by Neil_S
added "nosewheel"

[Old Koreelah]

Jim a couple of our club members have Savannas with nose wheels and are happy with them. Given their draggy appearance I have been surprised that they can cruise near 100kt, if enough petrol is poured into them.

[Kyle Communications]

My savannah did 85kts at 5000 rpm....most do the same especially with a bolly prop 69 or 70 inch prop. Fit a Eprop to it and set it up as per Eprop instructions and you will get around 90kts at 5000 rpm.

The problem with savannahs they are a drag bucket and the airframe starts to tell you that maybe your pushing it a little. At 90kts the sound on the airframe changes and changes even more the faster you get. The XL that I had at 5600 rpm WOT the way it was pitched I got 97 kts. The VNE of the XL is 108 kts. The S ...VNE is I believe 124kts????...I think

Every single savannah I have supplied a Eprop to and thats around 25 now I think all have had at least a 4 to 5 kt cruise speed increase. A taildragger savannah may go a little faster but I doubt it as the nosewheel doesnt add that much drag to the airframe when you take into account the amount of drag on that design

 

 

 

 

[facthunter]

The DH82 did 78 Knots TAS with a 130 Hp Gypsy 1c and good fabric. Nev

[Jim Bair]

Big thank you to everyone who responded.  It really helps me get a feel for the performance of the airplane.  As I try to read the tea leaves and combine everyone's info, I suspect that it will fly very sweetly at 80 kts, turn into a brick at 95, and possibly cruise at 85 reasonably and even 90 if I'm in a bit of a hurry and should have just left home 10 minutes earlier.  🙂

[IBob]

7 hours ago, Jim Bair said:

Big thank you to everyone who responded.  It really helps me get a feel for the performance of the airplane.  As I try to read the tea leaves and combine everyone's info, I suspect that it will fly very sweetly at 80 kts, turn into a brick at 95, and possibly cruise at 85 reasonably and even 90 if I'm in a bit of a hurry and should have just left home 10 minutes earlier.  🙂

I think you've picked it about right, Jim.

Regarding the minimum cruise speed, there is a general sense that the Rotax is best run at 5000RPM and above, so a combination of that and prop pitch (which is a compromise between takeoff and cruise performance) will tend to define your minimum cruise speed. Or that has been my experience.

[MartyG]

My 2010 XL 912ULS indicates around 82-85kts at 5000rpm, 66inch Bolly 3 blade