I
understood from conversations with some prop designers a few years ago (can’t
recall who) that the fewest number of blades to get the job done is most
efficient. One blade would be best except for obvious balance
issues. So the remaining factors include how much HP one blade can
absorb. I seem to remember that three was the minimum for an engine that
goes much over 300 HP at least for the hubs and props we were looking at for
the IVP. This info may have come from MT because I was looking at the
five blade MT vs four. My understanding at that time was that more
blades result in quieter smoother ops but give up small amounts of
efficiency.
Don’t
believe anything I say here. The memories are about 10 years old.
John
Barrett
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of Stevens
Family
Sent: Monday, June 30, 2014 7:39 AM
To: Lancair
Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for
I-550
I am interested in this subject, because I purchased a partly built
kit some years ago, (which I am still building!) which came with an MT 3
bladed constant speed prop. In my conversation with a builder in South
Australia recently, he mentioned that he had swapped out his 3 Blade MT prop
for a 2 blade prop, and increase his cruise speed by 7 knots. (Can’t recall if
that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the
graphs which indicate the 3 blades are more efficient! It was my understanding
that because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.
Rob Stevens
Perth, Western Australia.
From: Lancair Mailing
List [mailto:lml@lancaironline.net]
On Behalf Of Charles Brown
Sent: Monday, 30 June 2014 7:38
PM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade
or three-blade prop for I-550
I've enclosed the spreadsheet provided to
me by Les Doud of Hartzell. In 2009 his phone number
was Phone:
937-778-4262 . He believes that the 3-blade
is more effiicient than the two blade even in cruise. I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
Of course, my airplane is probably not as clean as the
prototype.
But the 3-blade prop sure looks
cool.