|
Propeller Selection
As a general rule, a
longer, slower blade will be more efficient, however, it is important that
the prop tips not exceed the speed of sound and that the prop not be too
heavy for the engine. The values listed below ensure a safe rotation rate.
- On all installations, prop diameter should be
measured to ensure adequate ground clearance in all attitudes of ground
maneuvers
- On all applications, clearance to any part of
the airframe or wing must be considered
- Pay particular attention to the prop tip
clearance. When an engine first starts, the prop blades tend to bend,
sometimes as much as 4-5 inches. This is particularly critical for flexwing applications where the wing is able to move
in pitch, roll and to a lesser extent, yaw.
Verner Factory Recommendation:
2-Blade Standard Carbon Fiber Prop (HPL Hub Rotax
Pattern) Diameter …… 68” - 72”
3-Blade Standard Carbon Fiber Prop (HPL Hub Rotax
Pattern) Diameter …… 68” - 72”
NOTE: Verner 133MK and 133S are internal reduction geared
and require left rotating propeller as viewed facing the propeller end.
Verner VM25T is cog belt reduction and requires right hand rotating
propeller as viewed facing the propeller end.
Propeller Test
Information:
Verner Factory Tests:
WARP DRIVE - 3 blades - 68"
maximum static thrust - 180 kg
PESZKE PROP - 3 blades - 68"
maximum static thrust - 172 kg
KIEV PROP - 3 blades - 71"
maximum static thrust - 158 kg
DUC FC - 2 blades - 68"
maximum static thrust - 90 kg
FlyDiver, llc has done comparison testing with several
props including 2&3 blade Warp, 3 blade Powerfin
and 3 blade GCS. A 64” Sport Prop is in use on one Verner 133M and its owner
is quite pleased with its performance, however, the Verner factory does not
recommend props less than 68”. Ivo told us that
their props are too light for the higher horsepower of the Verner. The Verner
factory has added a reduction ratio of 2.29:1 to eliminate possible
sympathetic vibration using 2 blade props on the 2.0:1 reduction.
Test Parameters: In all
tests, pitch was set for a maximum of 5000rpm with the aircraft tied to a
fence post (static). Pitch was measured at the blade tips using the protractor
supplied with Warp props.
- Warp
2 & 3 blade 72 & 70”: Very well balanced propeller with excellent
thrust. Tested in 72” 2 blade on 2.0:1 reduction and 70” 3 blade
on both 2.0:1 and 2.29:1 reduction. The 2 blade had more vibration on the
2.0:1 reduction but delivered similar thrust characteristics to the 3 blade.
Pitch was set between 8-10 degrees to achieve 5000rpm maximum.
- GSC
70 and 72” 3 blade: This is a wooden propeller made in Canada. It
delivers thrust that matches the Warp props and is considerably less
expensive than comparable carbon fiber props. This prop was tested in 70” on
both reductions and 72” on a 2.0:1 reduction. The
GSC delivered thrust comparable to the Warp props. During initial testing we were unable to
achieve more than 4800rpm due to the minimum pitch setting that comes from
the factory. After consulting with the GSC factory, a small amount of
material was removed from the hub to allow less pitch and a 5000rpm maximum
static rpm. Pitch was set to 5 degrees.
- Powerfin 72” 3 blade: The test engine had a vibration problem between 1500
and 2000 rpm caused by poorly balanced carburetors. The Powerfin
reduced the total amount of vibration but spread the vibration over a larger
rpm range. Thrust was noticeably less than both Warp and GSC props. Pitch was
set at 12 degrees to achieve the static 5000rpm maximum.
- Brolga 70” 3 blade: This Australian made prop was tested on a 2.0:1
reduction that had Bing 54 carburetors installed. Unfortunately, the Bing carburetors
will not produce the maximum power that the engine would normally develop so
thrust was not tested. The prop did
exhibit very good balance on an engine with minimal vibration. FlyDivers judged this prop to be entirely
acceptable as tested.
|