Fuselage Drag

[mayork]

We need to figure out how to get fuselage drag Cds for different sized fuselages. Thoughts?

I'm personally leaning towards MTflow data fit.

[1ozturkbe]

MTflow sounds like the right idea. I have no experience running it in the past, but I remember you mentioning that @mjburton11 had some idea perhaps? Mike, if you could get us started, that would be great!

[mjburton11]

Sure. I've got it installed on my computer. I'll send you the tat file when I have a chance. May be hard to install on a non unix machine.

[1ozturkbe]

Thanks Mike!

[1ozturkbe]

@mayork we have not followed up on this for a while. Do you think we need to pursue this aggressively? This is going to be more important when we perform the 'optimal-size aircraft' study, but I think it is peripheral for the first paper where we validate models and demonstrate the capabilities of SPs. What do you think?

[mayork]

we need to pursue aggressively for the final report out to Aurora where we evaluate the different D8 configs

[1ozturkbe]

What's the timeline on that?

[mayork]

final report out is 14 june but i'd like to be done my 25 may...we're very close

[1ozturkbe]

Going back to this after our discussion with Woody about adding a Mach drag rise. The fuselage drag fudge factor I think is the wrong way to handle this. After mroe research, I realized that 9% is an underestimate; 9% it turns out is the actual flow power savings to propel a fuselage with BLI, not the drag reduction. I am starting to think that a basic momentum defect calculation may be more appropriate. I will work on this, assuming that 40% of fuselage BL defect is absorbed (as all of the literature assumes).

[mayork]

going to note that as of https://github.com/hoburg/d8/commit/5f1b370f2743efff07aa2c32292e9ac3f662e178 we have a fuselage drag model that at least captures all pertinent trends and i think is ample for now....although this is certainly an are for continued improvements

[mayork]

@1ozturkbe we need to figure out the right 'f_{BLI}' ASAP. Can you look in the paper Brian mentioned and try and sort this out? I think it's top priority

[mayork]

looks like the paper says a 6% power savings which I think is a 6% drag savings since velocity is constant, yes?

[mayork]

I want to document a discussion I had with Neil today. So an aircraft's drag is roughly 1/3 wing 1/3 fuselage 1/3 wake dissipation. When an aircraft is switched to a BLI configuration there is an approximately 7.5-8% power savings. Of that 3% is due to engine efficiency improvements. Another 3% is due to surface dissipation improvements (almost 100% from nacelle drag savings). Finally, 1.5-2% is from a decrease in wake dissipation. This means our total drag should be deceased by a factor of f_BLI 0.33 .02.

[1ozturkbe]

K sounds good to me! Glad we figured this out.

[mayork]

I think it will just require a refactor on the way we handle the fuselage drag coefficient...also, I discovered a small error in how I was handling the engine inlet stagnation pressure drop. Will fix this tomorrow. Assuming that everything works after these changes all that i think is left is making sure the nacelle drag is being handled properly. I have already added sensitivity factors to all weight constraints.

[1ozturkbe]

So are we done here? @mayork let me know. I'm still not 100% sure we are handling the fuselage drag rise with Mach number properly, but it may be just me.

[mayork]

I don't think honk we necessarily are either. The ultimate goal here I think is still MTflow