Replace towel bar antenna with blades

[Blue on Top]

PS 2.  Yes, with Covid, engineering consulting and public speaking has, well ... , come to a halt. I've been working on aviation-related, STEM-style posters, T-shirts and maybe mouse pads.  The themes are: 4 forces of flight, 6 degrees of freedom, weight & G-load, Bernoulli principle, how a wing creates lift, AOA and how a propeller creates thrust.  The first two (2) can be customized with YOUR airplane ... you have to send me a photo that is nearly in the correct orientation.    

[tmo]

5 hours ago, Blue on Top said:

PS.  Why do TKS owners put up with the loss of 8-10 knots?

A fellow in the UK added full TKS to his N-reg TB20 and reported that he lost about 1kt; he believes the high reported speed losses are due to incorrect fitting of panels, especially on elevators. If one reads through that whole thread, it is obvious how much work and re-engineering went into his project.

His summary post is available on EuroGA.

[ArtVandelay]

A fellow in the UK added full TKS to his N-reg TB20 and reported that he lost about 1kt; he believes the high reported speed losses are due to incorrect fitting of panels, especially on elevators. If one reads through that whole thread, it is obvious how much work and re-engineering went into his project.
His summary post is available on EuroGA.

It’s crucial to reduce potential drag from the leading edge of the wing. I removed the retainer (Mooney stopped using it also) that covers landing light lenses (#2) and gained 3 knots.

[Bob - S50]

12 hours ago, M20Doc said:

Go to YouTube and search “Fluid Dynamics of Drag, part 4” It makes a compelling argument for streamlined versus any other shape.

Clarence

The problem is that the blades are only minimum drag a one specific AOA.  Any other AOA and they are no longer streamlined.  Now if you could mount them on a pivot so they always streamlined like an AOA vane maybe it would be better.  And if you could use smaller blades.  And while you're at it, since they are rotating to stay streamlined, why not use them for AOA?

12 hours ago, PT20J said:

I would think the cat whiskers would have the lowest drag because they have such a small area. I would think that the towel bars would have the highest because circular cross sections are draggy. Both are ugly, though. The more aesthetic blades should have drag somewhere in between, I'd think, because they have a fair amount of wetted area. Also, I'd expect them more sensitive to mounting -- you'd want to get them at the zero-lift AoA at cruise. Perhaps @blueontop might have some better insights. 

At any rate, I am always impressed with Byron's workmanship. 

Skip

That was what the article said.  Cat whisker antenna was the lowest drag.

[aviatoreb]

It looks like a lot of work to replace a towel bar with a blade antenna.

So then this makes me wonder how much more work beyond that would it be to hide the antenna in the wing tips which surely is even better?

[jetdriven]

2 hours ago, Bob - S50 said:

The problem is that the blades are only minimum drag a one specific AOA.  Any other AOA and they are no longer streamlined.  Now if you could mount them on a pivot so they always streamlined like an AOA vane maybe it would be better.  And if you could use smaller blades.  And while you're at it, since they are rotating to stay streamlined, why not use them for AOA?

That was what the article said.  Cat whisker antenna was the lowest drag.

The local airflow there is actually angled downwards about 2 degrees.  But the blades looked dumb like that with the leading edge up.  They theoretically provide downforce when placed level, which is adding force in the direction the tail needs it anyway, so theoretically it unloads the stab a little.  So, not sure how much total drag they actually add.  I still think its slightly less than a 28" wingspan steel rod cat whisker.

[Bob - S50]

23 minutes ago, jetdriven said:

The local airflow there is actually angled downwards about 2 degrees.  But the blades looked dumb like that with the leading edge up.  They theoretically provide downforce when placed level, which is adding force in the direction the tail needs it anyway, so theoretically it unloads the stab a little.  So, not sure how much total drag they actually add.  I still think its slightly less than a 28" wingspan steel rod cat whisker.

I took the time to look up the reference.  It is actually a response to my letter to the Editor in the June edition:

Antenna Drag - See letters to the editor

[aviatoreb]

2 hours ago, jetdriven said:

The local airflow there is actually angled downwards about 2 degrees.  But the blades looked dumb like that with the leading edge up.  They theoretically provide downforce when placed level, which is adding force in the direction the tail needs it anyway, so theoretically it unloads the stab a little.  So, not sure how much total drag they actually add.  I still think its slightly less than a 28" wingspan steel rod cat whisker.

That makes me thinking of a fun idea.  Are there rules where you must install the VOR antenna?  A very big-oversized blade "antenna" What if you installed it on the nose so as to act a bit like forward canard like on the Cessna Katmai to reduce stall speed?

[Blue on Top]

7 hours ago, Bob - S50 said:

I took the time to look up the reference.  It is actually a response to my letter to the Editor in the June edition:

Antenna Drag - See letters to the editor

@Bob - S50  Thanks, Bob!  It's great to know that someone is actually reading my monthly blurbs.  I didn't get there with the Mooney tail shape for December, yet (my fault), so I think that I'll do something on wing tips, winglets and sharklets.  Hint: There are no winglets or sharklets on Mooney aircraft ... that I know about.

[Blue on Top]

BTW, even blade Nav/Comm antennae are draggy, too.  Interestingly, it's the base that causes drag.

Very generally, what we call excrement drag (non-aircraft shape) is 30-35% of the total drag of small GA airplanes.  Of course that percentage goes down as the airplane gets bigger as the same antennae are utilized on most all airplanes.

[carusoam]

It’s a blast reading the Mooney Flyer...

Just about every name in there is recognizable...

It’s a real memory test because most of the MSer user names aren’t there...

Ron’s is pretty easy to recognize... Blue on top and his logo are both there...

His depth of aviation knowledge shows up everywhere he goes... 

Best regards,

-a-

[Bob - S50]

14 hours ago, Blue on Top said:

BTW, even blade Nav/Comm antennae are draggy, too.  Interestingly, it's the base that causes drag.

Very generally, what we call excrement drag (non-aircraft shape) is 30-35% of the total drag of small GA airplanes.  Of course that percentage goes down as the airplane gets bigger as the same antennae are utilized on most all airplanes.

So removing antennas like those for the NDB or Marker Beacon, and burying as many others as possible can make a big difference?

[N201MKTurbo]

It seems to me that the blade antennas would be optimal at only one trim setting. At any other trim setting the blades would be pitched up or down.

[aviatoreb]

On 11/18/2020 at 7:47 PM, jetdriven said:

I replaced the cat whiskers ...

 

That's a lot bigger job than I would have guessed Byron.  How much bigger a job would it have been to hide the antenna entirely within the wing tips?  Certainly some work stringing wires through the wings but no body work.  Surely the drag would be even a tad bit better improved by hiding the antenna entirely.

So I see the job as you did it wouldn't even be plausible for tks airplanes.

 

 

 

[Blue on Top]

23 minutes ago, Bob - S50 said:

So removing antennas like those for the NDB or Marker Beacon, and burying as many others as possible can make a big difference?

@Bob - S50  Yes, burying as many antennae as possible will reduce drag.  Replacing the red rotating beacon with conformal wing tip strobes, doors that don't seat properly, excessive cooling drag (pilots note when they leave their cowling door open too long ... even in my Cessna P172D.  Aft facing steps are poor ... even worse than forward facing ones (in most cases).

[Blue on Top]

PS.  The VOR/LOC blade antennae are draggy by themselves.  I worked with COMMANT a little while in CA, but we didn't get anything finalized.  There were 2 great older gentlemen there that were awesome.   

[jetdriven]

21 hours ago, aviatoreb said:

 

A far bigger job for me.  to replace the flat rib wingtips with the modern style would require new ailerons (7K, and I had already bought new flat aileron), and reskin the outboard section of the wing, plus the wingtips.  So, 12 grand plus labor.  I know folks use the Lasar kit which retains the flat ailerons in a slot. Ive seen this and it looks cheap. Plus, often the aileron end is sticking into the breeze,

.

those black parallel lines are the local airflow at 160KT IAS

[aviatoreb]

5 minutes ago, jetdriven said:

A far bigger job for me.  to replace the flat rib wingtips with the modern style would require new ailerons (7K, and I had already bought new flat aileron), and reskin the outboard section of the wing, plus the wingtips.  So, 12 grand plus labor.  I know folks use the Lasar kit which retains the flat ailerons in a slot. Ive seen this and it looks cheap. Plus, often the aileron end is sticking into the breeze,

.

those black parallel lines are the local airflow at 160KT IAS

Oh well that makes sense.  Just playing through - is it that expensive for the more modern wing tips?

How did you capture those black lines?  I am guessing you did something with oil streaks in flight?

Did you measure any before and after flights to see if there was a measurable difference in speed by switching antenna?

E

[jetdriven]

5 minutes ago, aviatoreb said:

Oh well that makes sense.  Just playing through - is it that expensive for the more modern wing tips?

How did you capture those black lines?  I am guessing you did something with oil streaks in flight?

Did you measure any before and after flights to see if there was a measurable difference in speed by switching antenna?

E

For a flat wingtip early model, yes, its expensive.

oil streaks.  photographed.  then drew with sharpie.

no measurable difference.  The KX170B was only receiving the glideslope 8nm out, after, 20nm out. So we needed to do something.

[aviatoreb]

14 minutes ago, jetdriven said:

For a flat wingtip early model, yes, its expensive.

oil streaks.  photographed.  then drew with sharpie.

no measurable difference.  The KX170B was only receiving the glideslope 8nm out, after, 20nm out. So we needed to do something.

Well that makes sense - you made the change for radio instrumentation reasons besides speed mod reasons.  Well it looks great.

I still love your wing work as the benchmark of speed obsession elbow grease.

[jetdriven]

17 minutes ago, aviatoreb said:

Well that makes sense - you made the change for radio instrumentation reasons besides speed mod reasons.  Well it looks great.

I still love your wing work as the benchmark of speed obsession elbow grease.

this

 

[Blue on Top]

"Flat" wingtips (the wing ends at a rib) is not as bad as people believe.  Shedding a clean vortex on the wing tip is actually good.

As for the aileron going all the way to the tip ... not so good.  The aileron is less effective.  Any tip past the end of the aileron will make the aileron more effective.

[aviatoreb]

2 hours ago, jetdriven said:

this

 

A thing of beauty!