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.
 
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?
 
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.
 
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.
 
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
 
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.
 
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.
 
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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