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02-15-2011, 09:09 AM
Replies: 160
Views: 27,725
Posted By z-8

With the stand-in motor driving an 8x7.5 on 4...

With the stand-in motor driving an 8x7.5 on 4 cells, I'm convinced I'm well above 100 mph by the bat-out-of-hell visuals, but verifying it with the low RCS is proving difficult. I might need to...
02-13-2011, 06:46 PM
Replies: 160
Views: 27,725
Posted By z-8

With copious new expo settings, reduced elevator...

With copious new expo settings, reduced elevator throw, straightened thrust angle, and an firewall covered in aluminum foil to pump RCS - new F8F radar trials (hopefully) in calm-light winds tomorrow.
02-13-2011, 06:43 PM
Replies: 160
Views: 27,725
Posted By z-8

I haven't posted anything that isn't patient and...

I haven't posted anything that isn't patient and kind--thanks for your contributions to this thread, see ya.
02-13-2011, 06:04 PM
Replies: 160
Views: 27,725
Posted By z-8

Thanks but no thanks. We are already way off F8F...

Thanks but no thanks. We are already way off F8F topic and that adds nothing. I haven't used my propulsion degree for ages as was an F-16 pilot by trade and now in retirement I'm very lucky to be...
02-13-2011, 02:25 PM
Replies: 160
Views: 27,725
Posted By z-8

Yes the pizza analogy is good, as I discussed in...

Yes the pizza analogy is good, as I discussed in detail in post #125 (http://www.wattflyer.com/forums/showpost.php?p=784695&postcount=125).
02-13-2011, 01:04 PM
Replies: 160
Views: 27,725
Posted By z-8

Actually, it is the same. All that matters is an...

Actually, it is the same. All that matters is an instant in time.

You left out the most important part - that is only for constant chord blades with twist. Constant chord blades can be used very...
02-13-2011, 04:49 AM
Replies: 160
Views: 27,725
Posted By z-8

Np. It isn't often that 22 years after I got my...

Np. It isn't often that 22 years after I got my Aero Engineering degree in propulsion I learn something new - I hadn't considered that re-circulatory down wash from a hovering prop above ground...
02-13-2011, 12:06 AM
Replies: 160
Views: 27,725
Posted By z-8

Read the whole book, he talks about theoretical...

Read the whole book, he talks about theoretical hub block out, specifically, as negligible. But you still seem hung up on V being the only term in the Lift equation. V^2 is of identical degree in...
02-12-2011, 11:49 PM
Replies: 160
Views: 27,725
Posted By z-8

You read too fast. Read the last sentence on the...

You read too fast. Read the last sentence on the previous page, "for blades with constant chord..."

Taper and twist combine, both with hyperbolic variation (see my first book quote), to create...
02-12-2011, 10:55 PM
Replies: 160
Views: 27,725
Posted By z-8

The "ideal" linear distribution he derives has a...

The "ideal" linear distribution he derives has a higher thrust loading at the hub, offloading thrust towards the tip (see attached). If you read this whole concept in context (too many pages to...
02-12-2011, 09:39 PM
Replies: 160
Views: 27,725
Posted By z-8

Source: Principles of Helicopter Aerodynamics...

Source: Principles of Helicopter Aerodynamics (Cambridge Aerospace Series) J. Gordon Leishman D.Sc.(Eng.) Ph.D. F.R.Ae.S....
02-12-2011, 08:44 PM
Replies: 160
Views: 27,725
Posted By z-8

V^2 has a whole lot to do with area in the lift...

V^2 has a whole lot to do with area in the lift equation, it is multiplied by it. Same goes for Cl.

The velocity hits what?

I suggest you read this post...
02-12-2011, 06:27 PM
Replies: 160
Views: 27,725
Posted By z-8

I'm sure you are right about most people...

I'm sure you are right about most people believing there is more lift toward the tip of a prop blade based on simple circular area (due to V^2), as it is such a common misconception. :) BTW, Lift is...
02-12-2011, 05:44 PM
Replies: 160
Views: 27,725
Posted By z-8

Ok, I admit, it did happen once. That just proves...

Ok, I admit, it did happen once. That just proves that huge companies can produce total crap designs. (Not that it was ever in doubt.)
...
02-12-2011, 04:34 PM
Replies: 160
Views: 27,725
Posted By z-8

I think we are in agreement that lift is zero at...

I think we are in agreement that lift is zero at the tip of any efficient wing design.

Where we disagree is in the lift distribution over the span. I contended that (properly designed) wings or...
02-12-2011, 04:20 PM
Replies: 160
Views: 27,725
Posted By z-8

Flat camera resting on flat sill, timer set. ...

Flat camera resting on flat sill, timer set.

http://ecx.images-amazon.com/images/I/51REzpQERkL._AA300_.jpg

On a flat bottom airfoil, the chord line is the bottom. Good point about cambered...
02-12-2011, 12:52 PM
Replies: 160
Views: 27,725
Posted By z-8

Yep, as I point out in my blog article on motor...

Yep, as I point out in my blog article on motor selection, it is maximizing efficiency of the overall solution in achieving set objectives, not max efficiency of each sub-element in a vacuum, that...
02-12-2011, 12:41 PM
Replies: 160
Views: 27,725
Posted By z-8

There are no (properly designed) fixed pitch...

There are no (properly designed) fixed pitch props that generate more lift at the tip by design. Same for wings. The example I showed above, with 0 AoA at 72.88% airspeed efficiency is a non...
02-12-2011, 12:37 PM
Replies: 160
Views: 27,725
Posted By z-8

The whole point of (a .3 to .5) taper is to...

The whole point of (a .3 to .5) taper is to reduce lift to 0 near the tip (or approximate an elliptical plan form), so whenever you see an elliptical wing/blade, or a .3 to .5 tapered wing/blade,...
02-12-2011, 03:25 AM
Replies: 160
Views: 27,725
Posted By z-8

Here is the final analysis. This is a simple...

Here is the final analysis. This is a simple Alpha 40's custom matched 10x4x3-blade. The prop/airframe designer's assumption was ~75% forward airspeed efficiency.
02-12-2011, 12:49 AM
Replies: 160
Views: 27,725
Posted By z-8

Only a guess, but I would bet these are usually...

Only a guess, but I would bet these are usually constant speed props that minimize tip losses by varying the angle of the entire blade. That gives them a max power option (with poor efficiency) when...
02-12-2011, 12:20 AM
Replies: 160
Views: 27,725
Posted By z-8

A very interesting way to control the tip vortex...

A very interesting way to control the tip vortex is to break a high aspect ratio wing into a lot of low aspect ratio wings. Then use the spinning vortex off of each sub-wing to increase the distance...
02-12-2011, 12:09 AM
Replies: 160
Views: 27,725
Posted By z-8

It is not just stress, stress is the mech...

It is not just stress, stress is the mech engineering part, the aero engineering part is controlling lift as a function of span, and ideally, to zero it out at the tip. This is because an infinite...
02-11-2011, 11:48 PM
Replies: 160
Views: 27,725
Posted By z-8

If you graph lift from an elliptical wing form...

If you graph lift from an elliptical wing form with a higher velocity over the tip and no twist to compensate, than obviously an asymptotic term will not override a parabolic term. No graph...
02-11-2011, 09:34 PM
Replies: 160
Views: 27,725
Posted By z-8

Rectangular wings, or elliptical wings, or...

Rectangular wings, or elliptical wings, or tapered approximations, are all valid options for any application. Plan form (as it relates to chord/surface area) is only one variable in the lift...
02-11-2011, 06:28 PM
Replies: 160
Views: 27,725
Posted By z-8

The outer part of the circle having more area...

The outer part of the circle having more area than the inner part has already been accounted for with the increase in radial velocity. More V sweeps more area. So to consider it again, is double...
02-11-2011, 04:44 PM
Replies: 160
Views: 27,725
Posted By z-8

Most efficient props - APC, elliptical/slow...

Most efficient props - APC, elliptical/slow flight, scimitar - modulate the increase in AoA (twist) and chord (taper) towards the root to precisely equalize lift after accounting for the radial V...
02-10-2011, 01:08 PM
Replies: 160
Views: 27,725
Posted By z-8

I disagree that scimitar is atypical. It is...

I disagree that scimitar is atypical. It is relevant to this discussion because its primary purpose is to optimize aerodynamic efficiency by blending lift to zero as the span progresses root to tip....
02-10-2011, 06:33 AM
Replies: 160
Views: 27,725
Posted By z-8

I thought the math was a little too simple to...

I thought the math was a little too simple to show, and intuitively not necessary given that a thought experiment more than suffices, but sure -

If you take that 11x5" scimitar I pictured earlier...
02-09-2011, 09:45 PM
Replies: 160
Views: 27,725
Posted By z-8

Sure - imagine a prop that twists to flat (zero...

Sure - imagine a prop that twists to flat (zero AoA at the tip). So at the tip, the AoA will be negative with any forward airspeed vector. The faster the airspeed, the more negative it goes. Most...
Showing results 1 to 30 of 53
 


 
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