Blade Attachment Example

[Deleted User]

I was working on this example and thought it was interesting. I figured you might find it interesting too. The aluminum blade attachment shown can safely support the equivalent of four african bush elephants (13,000 lbs each). That's roughly 28 US tons. This yields a factor of safety of ~2. So the max steady load is about eight elephants. The largest consumer trucks in the US are 3.5 ton capacity. So four elephants is about the full load of eight Ford F350 trucks. The more common truck in the US is the Ford F150. Four elephants equates to the full load of nineteen Ford F150 trucks. This is from a blade with a cross-section area of about 5.7 inches^2. The airfoil is approx. 9.4 inches long by 0.9 inches at it's thickest point.

Due to limited computer resources, I broke the model up into different parts and analyzed them separately. Attached is some pictures of the blade root. This is where the highest blade stresses are located. I meshed the model in Netgen v6.1 experimental and imported the *.vol file into Mecway v5.

The blade attachment is similar to what you might see on a propeller, fan, compressor, or turbine. I used PROP_DESIGN to determine the geometry. This particular geometry is for an optimized propeller for the Airbus A400M. It has 11 straight blades, spins at 840 rpm, is ~90% efficient at the cruise condition of Mach .72 37,000 feet. At cruise the propeller makes ~599 pounds of thrust using 850 shaft horsepower. To do this, the propeller moves 566,063 CFM of air.

I did the analysis of the blade retention in ANSYS Workbench student, since I can easily utilize cyclic symmetry in this program. Depending on the design of the retention system it can handle the same load as the blade or half that. For a blisk, or fixed pitch propeller type attachment, the same load as the blade can be used. For a dovetail design, half of the blade load can be attained. Full load was 10,000 psi of pressure on the airfoil surface near the root. This is where the green arrows are located on one of pictures below.

Sergio

Great job prop_design! Would be nice to be able to compute some metrics on the mesh quaility on Mecway itself. On your picture of the mesh quality, what is in the horizontal axis?

Regards!

[Deleted User]

Thanks Sergio and I agree with you. I have asked Victor about that in the past. But not sure it is a high priority for him. The x-axis is the element quality metric and the y-axis is the number of elements. That is one reason why I use Netgen. The other is I can mesh things that cause Mecway to crash. Changing the min mesh-size option from the default of 0 to 1 seems to prevent Netgen from crashing.

prop_design

just wanted to say I joined the forum again after a long time away. my old posts say deleted user. but anything related to prop_design would have been from me. I've been testing mecway for awhile now and am very happy with it. it even seems capable of composite propeller/fan blade design. a great value for sure. I also have some screencasts showing mecway off some. they are on my new youtube channel 'prop_design screencasts'. they're mostly for prop_design users, but they do highlight mecway too.