Rotorblade/hubset

waynep

Newbie
Joined
Apr 2, 2019
Messages
51
Location
Boone, NC
Airworthy balanced set wanted for 650 lb MTOW machine that will work on a Bensen type head. Looking at buying new Sportster 7" 25' for a basic capability if I can't find a deal.
 

gyrojake

Gyro Rehab Candidate
Joined
Jan 1, 2007
Messages
2,172
Location
E-City, Florida
Aircraft
Gyroplanes
Total Flight Time
A few hours
Airworthy balanced set wanted for 650 lb MTOW machine that will work on a Bensen type head. Looking at buying new Sportster 7" 25' for a basic capability if I can't find a deal.
If you have an MTOW of 650lbs, Why do you want a 25' rotor system?
How does your engineering math work this out?
 

waynep

Newbie
Joined
Apr 2, 2019
Messages
51
Location
Boone, NC
If you have an MTOW of 650lbs, Why do you want a 25' rotor system?
How does your engineering math work this out?
Using Jukka Tervamaki calcs. Also Sir Hollmann's. I'm at 3600 ASL. Running their calcs seem to work. I have not developed my own math or codes on this. I am an engineer with tons of math and physics. However, I need to rely on people that have been there and done that. Please, please give me your insights.
 

j4flyer

Member
Joined
Apr 7, 2004
Messages
201
Location
Woodland, Ca
Wayne think twice about a Sportster. They look cool but weren’t the most stable of designs. If you want a Gyro from that era look at a Barnett. They are much more pilot friendly. Yes, I’ve flown in both.
 

gyrojake

Gyro Rehab Candidate
Joined
Jan 1, 2007
Messages
2,172
Location
E-City, Florida
Aircraft
Gyroplanes
Total Flight Time
A few hours
Using Jukka Tervamaki calcs. Also Sir Hollmann's. I'm at 3600 ASL. Running their calcs seem to work. I have not developed my own math or codes on this. I am an engineer with tons of math and physics. However, I need to rely on people that have been there and done that. Please, please give me your insights.
I would really like to see the math used that come up with 25' disk at 650 MTOW.
Ya know, equation = answer
 

waynep

Newbie
Joined
Apr 2, 2019
Messages
51
Location
Boone, NC
I would really like to see the math used that come up with 25' disk at 650 MTOW.
Ya know, equation = answer
There's a bunch of math, but I like the rule of thumb Hollmann asserted: around 1.9 lb/sq ft disk loading (DL). That's similar to specs ultralight fixed wing planes are designed. For a 650 lb MTWO at 25' rotor diameter (2r) : DL = MTOW/pi*r^2 = 650 /(3.14*12.5^2) = 1.32 lb/sq ft. ... Low. Could go to 20 ft diameter ... gets about 2 lbs/sq foot. Another factor, solidarity is percentage of blade area to disk square footage. Hollmann had another target number for that. I plugged into Tervamaki's calculator get to a rotor size that would optimize rate of climb at about 1000 ft/min given my projected MTOW, 50 hp max engine and optimized propeller. I would prefer a larger rotor since I start out at 3600 ASL.
 

waynep

Newbie
Joined
Apr 2, 2019
Messages
51
Location
Boone, NC
Wayne think twice about a Sportster. They look cool but weren’t the most stable of designs. If you want a Gyro from that era look at a Barnett. They are much more pilot friendly. Yes, I’ve flown in both.
Thanks. I have Hollmann's design book. His main work was back in the 70's ... but he updated over time. A lot of good stuff. But there's been a lot done since. I use his work as a thoughtful reference. The sportster was a mechanically busy machine and seems to have had a high thrust line. Don't know. Don't have those numbers.
 

Gyro28866

David McCutchen
Joined
May 8, 2009
Messages
1,873
Location
Dickson, Tn. USA
Aircraft
Benson B7m & B8m, Dominator II; Kolb Mark III Classic
Total Flight Time
750 combined FW & Gyro
Radius squared time pie; divide total weigh by the disk area.
25' disk equals ???
12.5 x 12.5 = 156.25 x 3.14 = 490.62
650 # / 490.62 = 1.32 wing/rotor load - and reducing as you burn fuel
This should give you approx. 367 RRPM
and 481 ft/sec tip speeds.
Also, bear in mind; as the density increases from altitude and/or temperature the rotor will compensate and increase rpm.
.
My Dominator
27' - 13.5 x 13.5 = 182.25 x 3.14 = 572.265
720 # / 572.265 = 1.25 rotor loading
.
You cannot have your cake and eat it too!
With a light load there are other challenges which will present themselves when you are flying and especially landings. You will have to develop a skill set to effectively fly this machine. It would be like putting Glider wings on an RV-8.
 
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