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Author Topic: Laminar Airfoil  (Read 2552 times)

Online Ken Culbertson

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Laminar Airfoil
« on: August 07, 2018, 05:03:23 PM »
Does anybody have any experience using a near laminar airfoil?  I have a 18% thickness with a 40% high point center line to 45% at the tips with a blunt parabolic LE.  It flew well when I used it in the 60's with a 10oz wing loading.  It is going on a Classic so I hesitate to change it but I also want to use it for PA.  I am in Texas so wind penetration is a must.

It is not sheeted yet so I can still move the high point if I have to but that would likely jeopardize it being Classic.  Thanks.

Ken
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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #1 on: August 07, 2018, 05:14:26 PM »
I think it would suck, and not literally.  If you're stuck with it for Classic authenticity, I'd consider building a different Classic plane.  "Laminar flow" airfoils are designed for problems we don't have: maximizing laminar flow for drag reduction at low lift coefficients and lots higher Reynolds numbers than our airplanes, and keeping the maximum flow speed less than sonic.  They suffer from low maximum lift coefficients for our use. Some stunt planes-- Igor's, for example-- have trip strips to force transition from laminar to turbulent flow. 
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Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #2 on: August 07, 2018, 06:43:38 PM »
I think it would suck, and not literally.  If you're stuck with it for Classic authenticity, I'd consider building a different Classic plane.  "Laminar flow" airfoils are designed for problems we don't have: maximizing laminar flow for drag reduction at low lift coefficients and lots higher Reynolds numbers than our airplanes, and keeping the maximum flow speed less than sonic.  They suffer from low maximum lift coefficients for our use. Some stunt planes-- Igor's, for example-- have trip strips to force transition from laminar to turbulent flow.
Thanks Howard, I was afraid of that.  I can probably move he highpoint up to about 35% with some false ribs and flatten the part aft of the highpoint some which would make it just about a "slightly thick Nobler airfoil" - Humm.  I knew Bob, he wouldn't mind and since I designed the plane I guess I would be the authority on the airfoil.  I would build another classic but I have always wanted to use the plane I designed and flew as a teenager.

Ken
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Re: Laminar Airfoil
« Reply #3 on: August 07, 2018, 09:55:18 PM »
Ken, it would be interesting to see the airfoil you are talking about here.

On our stunt models, we have a symmetrical airfoil that looks perfectly normal (except sometimes it might look kind of fat), then we stick what is essentially a flat plate called a flap which is sometimes somewhat tapered from the LE to TE of that flat plate.  This gives a somewhat looking polywog shape to the airfoil that in a way resembles what a "laminar airfoil" that is sometimes seen on full scale aircraft except that "polywog flap extension thing" is much broader than that section of a laminar airfoil that shows a reflex portion on the top of the airfoil near the wing TE.

As Howard explained, the laminar airfoil sometimes used on full size aircraft is for an entirely different ses of requirements than we have for our CLPA models.  For example, part of the success of the P-51 Mustang, not disregarding its marriage to the Merlin engine, was its wing with the laminar flow airfoil that provided less drag (improved speed and longer range) over conventional designs.  The British put a laminar airfoil on a straight wing with a double taper on a late model Spitfire, called it the Spiteful and had one of the fastest prop driven fighters, if not the fastest, at the end of WW II.

Keith

Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #4 on: August 07, 2018, 11:32:48 PM »
Ken, it would be interesting to see the airfoil you are talking about here.

On our stunt models, we have a symmetrical airfoil that looks perfectly normal (except sometimes it might look kind of fat), then we stick what is essentially a flat plate called a flap which is sometimes somewhat tapered from the LE to TE of that flat plate.  This gives a somewhat looking polywog shape to the airfoil that in a way resembles what a "laminar airfoil" that is sometimes seen on full scale aircraft except that "polywog flap extension thing" is much broader than that section of a laminar airfoil that shows a reflex portion on the top of the airfoil near the wing TE.

As Howard explained, the laminar airfoil sometimes used on full size aircraft is for an entirely different ses of requirements than we have for our CLPA models.  For example, part of the success of the P-51 Mustang, not disregarding its marriage to the Merlin engine, was its wing with the https://stunthanger.com/smf/stunt-design/laminar-airfoil/?action=post;msg=528642laminar flow airfoil that provided less drag (improved speed and longer range) over conventional designs.  The British put a laminar airfoil on a straight wing with a double taper on a late model Spitfire, called it the Spiteful and had one of the fastest prop driven fighters, if not the fastest, at the end of WW II.

Keith
Laminar may have been a poor choice of words.  It is the far aft high point that I am most concerned about and the forward shape.  I knew nothing about airfoils when I was 16 and I sort of stretched a Nobler.  The original flew extremely well and cornered like nothing we fly today but it was very light and very big.  38oz 630sq.  The rebulid is probably going to tip the scales at 50oz.  I am not into single layers of Jap Tissue anymore!

The attached is the "Artists Rendition" but it is pretty close.  I have already flattened the aft 25% a bit in this drawing which should make it less laminar and more like a thin traditional stunt airfoil.
« Last Edit: August 08, 2018, 07:13:28 AM by Ken Culbertson »
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Offline Mike Alimov

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Re: Laminar Airfoil
« Reply #5 on: August 09, 2018, 09:08:51 PM »
Itís not the airfoil I would be worried about as much as the weight increase. What saved you in the past was the ultra low wing loading. If youíve never seen indoor 3d aerobatics, open YouTube and search for ďF3P world championships ď. They fly amazing maneuvers on flat plate wings, very slow too. Their wings are thin carbon frames covered with ultra thin mylar(?).
My stunt kites are the same thing: carbon frame with a sheet of nylon fabric in between. They donít stall despite pretty high angles of attack.
If you build your old design 30% heavier, then you need to worry about all the tricks that were invented for porky airplanes: optimized airfoil, more power, etc etc.
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Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #6 on: August 17, 2018, 11:33:03 AM »
I was able to thin the back and round the front better but I still have that 40% highpoint.  Here is my delema, the wing has turned out very straight and relatively light (12oz with controls less flaps + 1oz built in tip weight) which is not too bad for 660sq + I am going to grind out another oz before covering.)   I want to build it out as a PA instead of Classic and drop in a larger engine.

So my question is:

How does the high point of the airfoil affect what we do?  It is no longer laminar, just an aft high point.  I opted to leave the forward part, which is more "Nobler" like to deal with the always present Texas wind.
I was able to get a 3/4" diameter on the LE.

I just need to know what to expect, not how stupid I was to use this airfoil in the first place, I already know that!

Ken
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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #7 on: August 17, 2018, 01:52:28 PM »
It won't get as much lift as one with the max thickness farther forward.  It won't turn as tight a corner.  You can get Javafoil free and fiddle with different shapes.  Use 400,000 for a Reynolds number. 

Do you have flaps?  If there are flaps added to the back, the max thickness will be less than 40% of the whole thing, which ain't as bad.
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Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #8 on: August 17, 2018, 02:14:03 PM »
It won't get as much lift as one with the max thickness farther forward.  It won't turn as tight a corner.  You can get Javafoil free and fiddle with different shapes.  Use 400,000 for a Reynolds number. 

Do you have flaps?  If there are flaps added to the back, the max thickness will be less than 40% of the whole thing, which ain't as bad.
Thank you.  I will trade the corner for the penetration.  The original cornered like a piece of angle iron but it was really light.  This one won't be that light.  Bottom line - it may not fly as well as an SV-11 but it will work.

Thanks again - Ken
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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #9 on: August 17, 2018, 05:10:28 PM »
Iím not sure what ďpenetrationĒ is (in this sense), but I donít see how that airfoil would be any better at it than one with more lift capability.
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Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #10 on: August 17, 2018, 05:48:26 PM »
Iím not sure what ďpenetrationĒ is (in this sense), but I donít see how that airfoil would be any better at it than one with more lift capability.
Wind penetration.  IMHO the less blunt airfoils handle wind better.  As I said before, I am not trying to defend this airfoil, only determine if it will work.  It is not thin, just an aft high point.

Ken
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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #11 on: August 17, 2018, 08:28:06 PM »
Can you elaborate on what wind penetration is?  Two things you might be thinking of are drag and susceptibility to turbulence, but I'm only guessing.

Drag is the component of aerodynamic force on the airplane in the direction that the air is blowing on it.  People intuit that a sharp-nosed airfoil has less of it than a blunt-nosed airfoil-- you can slice a peach easier with a knife than you can with a chopstick.  The only LE-radius drag comparison I've done is an Xfoil-program run comparing a standard NACA 0018 with one having LE radius reduced by NACA's airfoil-drawing formula.  The first picture is the drag polars for that pair.  The sharp-LE has less drag only for a little range.  The difference is maximum at about .8 Cl, where it's about 5% of induced drag.  You wouldn't notice the drag difference until you turned a wee bit tighter, where the sharp-LE wing would stall and drag would go way up.

I'd think that susceptibility to turbulence (for a given wing planform) would be inversely proportional to wing loading.  For a given corner radius, the wing loading you could get away with would be proportional to maximum Cl.  For this pair of airfoils, the blunt one looks like it has about 10% higher maximum Cl (second picture).  A more extreme example is one Frank Williams posted in reply 95 of http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=371054&sub_topic_id=371056&mesg_id=&page=#371283 .  That blunt airfoil has 30% more max Cl than the sharp one he compares it to.  You could build an airplane 30% heavier with that blunt one, take advantage of the reduced turbulence effect, and still get around the same corner as with the sharp one. 
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Offline Igor Burger

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Re: Laminar Airfoil
« Reply #12 on: August 17, 2018, 10:58:56 PM »
That blunt airfoil has 30% more max Cl than the sharp one he compares it to.  You could build an airplane 30% heavier with that blunt one, take advantage of the reduced turbulence effect, and still get around the same corner as with the sharp one.

OR ... you can make 30% smaller wing with that blunt airfoil, it will give 30% less drag (the drag is linear to wing area) and you have wing with probably smaller drag (because drag coefficiets are very close) and thus better "penetration".  VD~

Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #13 on: August 18, 2018, 12:54:12 PM »
Can you elaborate on what wind penetration is?  Two things you might be thinking of are drag and susceptibility to turbulence, but I'm only guessing.

Drag is the component of aerodynamic force on the airplane in the direction that the air is blowing on it.  People intuit that a sharp-nosed airfoil has less of it than a blunt-nosed airfoil-- you can slice a peach easier with a knife than you can with a chopstick.  The only LE-radius drag comparison I've done is an Xfoil-program run comparing a standard NACA 0018 with one having LE radius reduced by NACA's airfoil-drawing formula.  The first picture is the drag polars for that pair.  The sharp-LE has less drag only for a little range.  The difference is maximum at about .8 Cl, where it's about 5% of induced drag.  You wouldn't notice the drag difference until you turned a wee bit tighter, where the sharp-LE wing would stall and drag would go way up.

I'd think that susceptibility to turbulence (for a given wing planform) would be inversely proportional to wing loading.  For a given corner radius, the wing loading you could get away with would be proportional to maximum Cl.  For this pair of airfoils, the blunt one looks like it has about 10% higher maximum Cl (second picture).  A more extreme example is one Frank Williams posted in reply 95 of http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=371054&sub_topic_id=371056&mesg_id=&page=#371283 .  That blunt airfoil has 30% more max Cl than the sharp one he compares it to.  You could build an airplane 30% heavier with that blunt one, take advantage of the reduced turbulence effect, and still get around the same corner as with the sharp one.
Thanks -  This helps.  In looking at your chart, my airfoil is close to the green one. 

Ken
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Offline Dennis Toth

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Re: Laminar Airfoil
« Reply #14 on: September 07, 2018, 08:19:02 AM »
Ken,
For OTS look at the original Palmer Smoothie or for Classic the Veco kit version (inverted cowled engine). The story goes that Palmer was looking for a design that would handle turbulence and higher winds he had a friend at Lockheed. His friend was working on the C130 and gave him the airfoil they were using for the stab/elevator indicating that it would fit the bill. Smoothie's have won their share and although not Bob's favorite in tough conditions it did the job.


For some full scale Laminar flow airfoils look at this site:  http://airpigz.com/blog/2010/9/9/airfoil-shapes-in-the-fast-lane-world-of-the-reno-air-races.html

Best,   DennisT

Offline Serge_Krauss

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Re: Laminar Airfoil
« Reply #15 on: September 09, 2018, 10:52:48 AM »
I always thought the Palmer "Smoothie" airfoil, as published in Air Trails, was questionable. Later Bob was quoted in one of these forums (probably SSW) as saying that he had used a different section on his actual plane. People who should know, having been involved with current kit offerings, have posted that current kits have authentic wing sections, but at this point, I'm not sure what's authentic. Wing plan-view shape is what made the "Smoothie" a "windy-weather" flier, as quoted in ads.

Offline Howard Rush

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Re: Laminar Airfoil
« Reply #16 on: September 10, 2018, 12:21:36 PM »
His friend was working on the C130...

Bucking rivets, perhaps
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Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #17 on: September 10, 2018, 01:08:57 PM »
. His friend was working on the C130 and gave him the airfoil they were using for the stab/elevator...

Best,   DennisT
The C-130 was still under development under a military contract in 1951 when the Smoothie appeared.  I hope Bob had a security clearance! LL~

Ken
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Offline Dennis Toth

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Re: Laminar Airfoil
« Reply #18 on: September 11, 2018, 04:18:21 PM »
There have been lots of stories about the Smoothie. Bob is suppose to have told John Brodak that he built a second version with a conventional airfoil and only flew the "real" Smoothie in rough conditions. I have not seen any photo's of Bob with the alternate version. Seems if it was that much better they would have made the change for the Veco kit version. The airfoil of the publish Smoothie has a high point back near 40 - 45%. It was flown fairly fast. I guess the combination of the airfoil coupled with the elliptical plan form and higher speed worked to get you through the tough stuff.  As I remember Bob had some discussion in the article about the design, maybe someone can post the article. I tried to post the plans but it must be to big a file.

Best,   DennisT

Offline John A Miller

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Re: Laminar Airfoil
« Reply #19 on: September 13, 2018, 12:48:04 PM »
This is an interesting discussion, but,as it relates to Bob Palmer, and his Smoothie design, some often heard "facts"are being reported..

I have some insight to the questions, as I drew the CAD plans for Brodak's Smoothie kit. Bob sent me his originals, plans drawn in pencil on  "Butcher Paper".  In those days, creating drawings on Butcher Paper, was in style with scratch builders. As the CAD Drawings progressed, the question regarding the airfoil difference came up.

Here's Bob's answer, as correctly as I recall it.

He told me that the fellow doing  the kit, and who also had major impact on the published article, ( I wish I could remember his name.Hi comes to mind, but I don't believe that's correct, (must be early Alzheimer's). Anyway, this fellow was anxious to get the design published,  and get the kit out on the Hobby Shop shelves. The problem was Bob was out of the country. He told me where, but my memory tells me, he was either in England, or Africa, on tour.  Bob had  built the first Smoothie previous to leaving, so the only plans at the time were for the thinner, aft high point, airfoil we all are familiar with, in the published and kitted version.


Bob was still showing signs of agitation after all these years, as he explained his Smoothie being published and kitted without his final blessing. He wanted the airfoil changed closer to the normal 4 digit version. He was upset that they had released the design before he returned and  before he had made his final changes. Thus the skinny wing being in the original published and kitted design. In a moment of clarity, Bob reported That the money made a difference0in paying some orf his bills, that's why He didn't push things too hard  back then.

He told me that after his return from his tour, he revised his design to reflect his final desires  for the Smoothie. He wasn't happy with  some aspects of performance with the skinny wing. In decent stunt winds, the normal symmetrical airfoil flew better shapes. This was what he  wanted the design to be. 

He said that he would go to contests at venues such as Santa Anita parking lot on a Sunday Morning. He would have both versions, in identical paint schemes. in the trunk of his car. He would check out the wind conditions, below a certain limit, he would use the 4 digit Smoothie. Windy,over the limit, he would use the skinny winged version. He was tickled, very few folks ever caught onto his selection process.

You may question the use of such sneaky methods in stunt practises in those days.

Remember, in the 50's through some of the 70's, it was common to have your special little Stunt Secrets. secrets such as handles, lines, wing styles, (such as the Detroit style, or I Beam wing.) engines, Push rod Geometry, on and on.

In the early 70's, as PAMPA formed and grew, we started sharing and teaching what were formerly secrets.
 
I believe, after spending many hours talking with Mr. Palmer as we collaborated on the Creation of the Cad Drawings,  used with the Brodak Smoothie version. That what was being drawn in CAD, was the Smoothie as Bob wanted it, and as he peferred to fly on most occasions.

Bob was happy, as he said the new Smoothie drawings  represented what he wanted the Smoothie to be, and was what he flew, (except those very windy days).
« Last Edit: September 13, 2018, 01:07:40 PM by John A Miller »

Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #20 on: September 13, 2018, 01:46:30 PM »
In those days, creating drawings on Butcher Paper, was in style with scratch builders
Real men still use Butcher Paper to sketch the design. y1  $13.99 for 500' at SAMS.  Papermate Sharpwriter mechanical pencils have the best erasers to help you revise the "plans" for how you actually built it then you can roll it up and save it to build something completely different next time! :!

What is this CAD thing anyway? LL~

Ken
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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #21 on: September 13, 2018, 02:37:17 PM »
This is an interesting discussion, but,as it relates to Bob Palmer, and his Smoothie design, some often heard "facts"are being reported..

I have some insight to the questions, as I drew the CAD plans for Brodak's Smoothie kit. Bob sent me his originals, plans drawn in pencil on  "Butcher Paper".  In those days, creating drawings on Butcher Paper, was in style with scratch builders. As the CAD Drawings progressed, the question regarding the airfoil difference came up.

Here's Bob's answer, as correctly as I recall it.

He told me that the fellow doing  the kit, and who also had major impact on the published article, ( I wish I could remember his name.Hi comes to mind, but I don't believe that's correct, (must be early Alzheimer's). Anyway, this fellow was anxious to get the design published,  and get the kit out on the Hobby Shop shelves. The problem was Bob was out of the country. He told me where, but my memory tells me, he was either in England, or Africa, on tour.  Bob had  built the first Smoothie previous to leaving, so the only plans at the time were for the thinner, aft high point, airfoil we all are familiar with, in the published and kitted version.


Bob was still showing signs of agitation after all these years, as he explained his Smoothie being published and kitted without his final blessing. He wanted the airfoil changed closer to the normal 4 digit version. He was upset that they had released the design before he returned and  before he had made his final changes. Thus the skinny wing being in the original published and kitted design. In a moment of clarity, Bob reported That the money made a difference0in paying some orf his bills, that's why He didn't push things too hard  back then.

He told me that after his return from his tour, he revised his design to reflect his final desires  for the Smoothie. He wasn't happy with  some aspects of performance with the skinny wing. In decent stunt winds, the normal symmetrical airfoil flew better shapes. This was what he  wanted the design to be. 

He said that he would go to contests at venues such as Santa Anita parking lot on a Sunday Morning. He would have both versions, in identical paint schemes. in the trunk of his car. He would check out the wind conditions, below a certain limit, he would use the 4 digit Smoothie. Windy,over the limit, he would use the skinny winged version. He was tickled, very few folks ever caught onto his selection process.

You may question the use of such sneaky methods in stunt practises in those days.

Remember, in the 50's through some of the 70's, it was common to have your special little Stunt Secrets. secrets such as handles, lines, wing styles, (such as the Detroit style, or I Beam wing.) engines, Push rod Geometry, on and on.

In the early 70's, as PAMPA formed and grew, we started sharing and teaching what were formerly secrets.
 
I believe, after spending many hours talking with Mr. Palmer as we collaborated on the Creation of the Cad Drawings,  used with the Brodak Smoothie version. That what was being drawn in CAD, was the Smoothie as Bob wanted it, and as he peferred to fly on most occasions.

Bob was happy, as he said the new Smoothie drawings  represented what he wanted the Smoothie to be, and was what he flew, (except those very windy days).


I suspect he flew the one with the bad airfoil in blustery weather so's not to chance hurting the good one.
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Offline Tim Wescott

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Re: Laminar Airfoil
« Reply #22 on: September 13, 2018, 02:53:10 PM »
Real men still use Butcher Paper to sketch the design.

So the masking tape on the building board with sharpie tick-marks for the rib locations isn't a Real Man way to go about it?  Darn.

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Offline Howard Rush

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Re: Laminar Airfoil
« Reply #23 on: September 13, 2018, 02:56:25 PM »
There's a similar story about a combat plane.  I met Bill Carpenter, who won combat at the 1960 Nats, at the 1964 Nats.  He told me that the Swoop, the airplane he flew in 1960, had a "laminar-flow" airfoil recommended to him by an aeronautical engineer.  He made a later version with a better airfoil.  When Sterling kitted his Super Swoop, he advised them to use the better airfoil.  Somehow Sterling decided to use the substandard Swoop airfoil-- maybe because it was recommended by an aeronautical engineer.  Thus the Super Swoop wasn't a very good airplane.  Carpenter was flying a plane at the '64 Nats that had a decent airfoil.  I think its name was Super Too.
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Offline Dennis Toth

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Re: Laminar Airfoil
« Reply #24 on: September 13, 2018, 06:48:50 PM »
I always liked the Smoothie, it is to bad that there's no records of how the publish version did in competition in the tough conditions. In most of our contest down here in FL the wind come up for second round. Having a ship that works well in tough conditions could do really well.

Best,    DennisT

Online Ken Culbertson

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Re: Laminar Airfoil
« Reply #25 on: September 13, 2018, 07:33:07 PM »
So the masking tape on the building board with sharpie tick-marks for the rib locations isn't a Real Man way to go about it?  Darn.

That qualifies but you have to make at least one modification on the fly. n1

Ken
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Offline Chuck_Smith

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Re: Laminar Airfoil
« Reply #26 on: November 10, 2018, 07:14:22 AM »
I always thought that the crazy low Re's we operate in that Al Rabe's approach was elegant: Shape the airfoil for a smooth curve on the lift side with with full flap deflection and let the bottom side be what it is.

That, or just start with a Flite Streak airfoil, since it worked so danged good.  #^

One of aerodynamics' dirty little secrets is that all symmetrical airfoils have the same lift slope until you get to the hairy edge, and that lift slope gets affected by the aspect ratio regardless of the airfoil. But as noted, the shape has a lot to do with the drag. I'm so old now I've come to realize drag is my friend on a ship. When I'm going uphill it's about power and in today's world, if you have the resources, excess power is a given. So now when I'm going downhill I know the drag increases with the square of the velocity and that means a draggy ship takes a few extra milliseconds to get to the bottom of the square eights and will turn tighter there since V^2/R is lower.


Why the rambling above? Because a laminar flow airfoil is designed to lower drag, and in my world view of high thrust/high drag being desirable it doesn't fit. That, and in the scale in which we fly I doubt the classic laminar flow shape has any meaningful effect. I suspect in it's heyday, the laminar flow was airfoil was as much about reducing drag divergence at high subsonic speeds as anything else, anyway.

I've embraced drag as the speed-control of the ship. If she slows, the drag goes down and she recovers, If she speeds up, drag holds her back. Throw in low mass and you have a really nice flying ship that you can fly through the bottoms with ease.

All of the above is IMHO and alternate viewpoints are worthy.

Chuck
« Last Edit: November 10, 2018, 08:39:35 AM by Chuck_Smith »
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Offline Perry Rose

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Re: Laminar Airfoil
« Reply #27 on: December 12, 2018, 02:34:48 PM »
Bill Netzeband says the Smoothie's recommended speed is 70 mph around 450 sq. in wing, 50 sq. in. of flaps. Airfoil 15% thick at 45% of chord. Stab and elevator about 100 sq. in. with 45% moveable. The elevators moved 45 degrees both ways and the flaps 30 degrees. Quite nose heavy at 36 ounces is the reason for the elevator movement.
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