Author Topic: Slots?  (Read 165 times)

Offline jrbirdman47

Slots?
« on: July 09, 2020, 10:38:56 AM »
For the scienterrificlly minded folks here:

I thought about this during wing building and I keep thinking that one could "slot" the leading edges fairly easily: Just cut the slots top and bottom in the plywood between the wood nose ribs, in the proper positions, then hot wire cut foam plugs to glue inside to smooth and direct the airflow, and voila! Slots!

Might add a few ounces, or maybe break even, considering plywood removed/ foam added, but to what end?

*Do you think it would have aerodynamic advantages to offset any added weight?

*Would the difference be so little that one could use VGs to accomplish the same thing more easily?

*Shut up Rick, quit thinking, and just build it like the plans say?

Just wondering out loud here

Thanks for humoring me,

Rick

Offline okdonn

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Re: Slots?
« Reply #1 on: July 09, 2020, 12:43:24 PM »
This is experimental aviation, go for it! To be fair, you should build two sets of wings, one with slots, one without, so you can get apples to apples comparison results. You could then add VGs to both for more data points. Be sure to share the results with us!
Don in Okla.  DE Plans B-40 (small), CE plans CE-02 (all weather),  Tailwind project #746 (medium),  C182A (large)
One size does NOT fit all!

Offline jrbirdman47

Re: Slots?
« Reply #2 on: July 09, 2020, 03:20:53 PM »
Rather than building multiple sets of wings I was thinking about gathering data with the standard wing, then doing VG's and noting the difference. (Easiest to do) Then If I got brave and bored over a winter, maybe try the slot idea. My thinking is that with a flight envelope that is so small, (About 40 knots), any changes would be in very small amounts, for instance, lowering the stall speed: a 15% decrease is quite substantial but is still only 3 to 4 knots. The landing distance might be about 40 feet shorter. Not sure it would be worth it for so little difference. Still fun to think about.

Offline okdonn

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Re: Slots?
« Reply #3 on: July 09, 2020, 05:28:09 PM »
Optimizing performance is always fun, even if the gains are small. Maybe the next step would be to add Fowler flaps?
With two sets of wings, you can just swap them if you don't like the slots. I guess ou could fabric over them if they don't work out, but that adds weight and the airfoil is still changed.
Don in Okla.  DE Plans B-40 (small), CE plans CE-02 (all weather),  Tailwind project #746 (medium),  C182A (large)
One size does NOT fit all!

Offline Kamcoman77

Re: Slots?
« Reply #4 on: July 09, 2020, 05:38:14 PM »
Most people that have installed VG's report improved aileron feel/control, but no change in stall speed.

Offline Dan_

Re: Slots?
« Reply #5 on: July 09, 2020, 06:01:28 PM »
Attached is a scholarly read about it.  I haven't read it yet but I noticed it has a section on Clary Y...

I did read the Wikipedia on it and concluded that full span is out of the question due to drag and pitching moment unless you are willing to redesign the entire airplane...  Stinson 108 style may be more appropriate.

Buttercup wing is said not to have any pitch trim change when deployed because the flaps actuate the movable leading edge.  I'm thinking more lift at the front of the wing counter acts the nose down pitch from the flaps.  Both of which are lower drag when not deployed. 

My personal take on the Buttercup is yea it flys slower and lands shorter, but you do not get what Steve Wittman got out of it unless you are willing to go behind the power curve...


“A superior pilot uses his superior judgment to avoid situations which require the use of his superior skills.”

– Frank Borman, Apollo 8 Commander

Offline jrbirdman47

Re: Slots?
« Reply #6 on: July 09, 2020, 06:43:31 PM »
I was thinking about the Stinson wing as an example, not anything close to full span. I was thinking maybe just the outboard 3 or 4 "bays" or so, (4 to 5 feet of slot per side) I figure it would augment aileron effectiveness more than anything else, although there might be a bit of decrease in stall speed.
I like the idea of VGs, just because it is a simple install and easily removed if it doesn't work out. Thanks for all the comments, it's definitely fun to kick around ideas.

Offline Chuck in Indiana

Re: Slots?
« Reply #7 on: July 10, 2020, 08:53:52 AM »
Quote
My personal take on the Buttercup is yea it flys slower and lands shorter, but you do not get what Steve Wittman got out of it unless you are willing to go behind the power curve...
I don't understand..

Offline Chuck in Indiana

Re: Slots?
« Reply #8 on: July 10, 2020, 09:06:21 AM »
I vote for
Quote
*Shut up Rick, quit thinking, and just build it like the plans say?
:grin:
I've had airplanes with slots..Stinsons and restored a Commonwealth Skyranger.. and they give some aileron control authority at the stall.. a good thing. They also slow the airplane down..a bad thing. I'm not sure the Legal Eagle can afford to be slowed down much more.  :)

Offline Dan_

Re: Slots?
« Reply #9 on: July 10, 2020, 04:56:10 PM »
I don't understand..
Instead of flying on the backside of the power curve you land the plane on the backside of it...

Wittman had a standing $100 bet when he was the FBO at the Oshkosh airport.  You bring whatever you have and take off here.  We will mark that distance, and I will take Butter Cup and land AND take off inside that distance.  Word is, he never lost a bet.

Another standing bet of his was "landing in the hangar".  He would take Butter Cup up to 1000 feet and cut the engine, in the days of no starter.  He would then land on or near the apron and roll it into the hangar.

At the time Butter Cup had a C-85 with high compression Chevrolet pistons.


Another definition of the back side of the power curve is flying at an AOA at which you cannot ascend unless you lower the nose.

Below was snatched from here:  https://www.boldmethod.com/learn-to-fly/aerodynamics/the-aerodynamics-of-slow-flight/




Flying On The "Back Side" Of The Power Curve
When you demonstrate slow flight on a check ride, you are required to "establish and maintain an airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in a stall warning" (e.g., aircraft buffet, stall warning, etc.). according to the new Airman Certification Standards.
This is a little different than the old FAA PTS standards for slow flight. Regardless, there's a lot to understand about the aerodynamics affecting your airplane, which we'll cover below.
slow flight old vs new
Flying at this speed means that you are on the back side of the power curve, also known as the "region of reversed command." In normal cruise flight, you pitch the aircraft to maintain altitude, and power the aircraft to maintain airspeed. However, on the back side of the power curve, the inputs are the opposite. You pitch the aircraft to maintain airspeed and use power to maintain altitude. Why is this? The answer lies in induced drag, which dramatically increases as the aircraft's angle-of-attack (AOA) increases to maintain sufficient lift at low airspeeds.
Here's what the FAA has to say in Chapter 4 of the Airplane Flying Handbook:
"Since slow flight will be performed well below L/D MAX, the pilot must be aware that large power inputs or a reduction in AOA will be required to prevent the aircraft from decelerating. It is important to note that when flying on the backside of the power curve, as the AOA increases toward the critical AOA and the airplane's speed continues to decrease, small changes in the pitch control result in disproportionally large changes in induced drag and therefore changes in airspeed. As a result, pitch becomes a more effective control of airspeed when flying below L/D MAX and power is an effective control of the altitude profile (i.e., climbs, descents, or level flight)."


“A superior pilot uses his superior judgment to avoid situations which require the use of his superior skills.”

– Frank Borman, Apollo 8 Commander

Offline jrbirdman47

Re: Slots?
« Reply #10 on: July 10, 2020, 06:24:13 PM »
So, after reading the scholarly paper on slots, it looks like they cannot be readily made from the existing leading edge because the bottom of the leading edge of the slot would not be located low enough. Slats would be an alternative, but would be weight prohibitive.

Chuck, it looks like I'll just shut up and build it according to plans! That Leonard dude keeps getting smarter all the time.  :grin:

Offline Chuck in Indiana

Re: Slots?
« Reply #11 on: Today at 09:13:44 AM »
 :grin:

 


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