A comparison of Blejyzk airfoils

[u2builder]

I "built" a Serafin a while ago and decided I'd like to build another Blejyzk that would be a capable aerobatic ship with some thermal ability. I wanted to know a bit more about airfoils for "speed" and "thermal."

I asked a few questions about HN1033, S6063, and S7012 airfoils on the Modeling Science forum over on RC Groups and got some answers from someone who knows a lot about airfoils. Included are the plots of each airfoil.

HN1033, S6063 and S7012 airfoils - RC Groups

Discussion HN1033, S6063 and S7012 airfoils Modeling Science

www.rcgroups.com

 

[Konrad]

Love Selig's question (post #9)

This is a classic case of needing to know your audience.

 

[Konrad]

Trying to understand why the airfoil designer did what he did also helps a lot. You have Selig's attention. He was one of the first to work the real low Reynolds number airfoils in the wind tunnel.
(Please note that he showed that even the slightest surface irregularities destroyed any benefit from these modern computer airfoils. So, much of this is just academic and doesn't apply to most models as we really can't manufacture wings that adequately reproduce the airfoil. Heck, many of the lower cost high dollar molded models can't make a true profile. As you can see the substructure distortion on the the skin.)

Another guy you might run into is Martin Hepperle. He was into pylon racing and found that his fast airfoils actually worked rather well in thermal ships. Remember that no matter how great your thermal ship is it can't soar if the air is sinking. Key to a sailplanes performance is how fast can it get out of sink. Not how slowly it can core a thermal.

As Selig said the S7012 is basically a modern RG15. While these both are a bit dated they are great. What I noticed about these is that they can carry the weight so well. The heavier the ship the better the airfoil seemed to perform!

 

[Wayne]

S7012, RG15, MH32 - I tend to lump these into being about the same. You can argue for one over the other, but they are widely accepted in our models as they offer a nice range of performance without any real drawbacks. They are a safe bet.

I have heard the argument that we can't "adequately reproduce" our airfoils. Perhaps this is true, but I do think we get close enough to the correct shape to make it worth the effort. Even a flawed airfoil is better than no attempt at a real airfoil.

 

[Konrad]

Looking at 10 inch chord airfoils and plotting their corodinance we find that many are the same within a tollerance band of 0.015". Yet the performanc plots would indicate them to have quite different performances. 0.015 is a swipe or two with the sanding block!

What is the difference between a flawed airfoil and a real airfoil? Isn't the flawed airfoil just one that we haven't defined? Heck, it might actually be that lost magic airfoil that does everything well with no downside. Now let's not talk about cat backed airfoils!

 

[Doc J]

There is no magic aerofoil and there is only one real test, and that's actual flying within the model's design envelope by at least two skilled pilots on the same day, same model, same conditions. Anything else is simply a waste of time - and a lot of hot air.

Model performance equation (Assuming that the model/aerofoil have been well designed with specific performance goals) :

Pilot skill = 60%
Wing planform/lift distribution = 25%
*Others, including the aerofoil = 15%

* Aerofoil = 10%
* Fuselage, tailplane, joints = 5%

As long as the aerofoil has been suitably selected and is a good choice for the job it has to do, then computer simulations are highly dubious unless you want to fly your digital aerofoil in steady, coherant, speed-controlled flight in simulated digital air. Otherwise, for your local slope its probably more accurate to toss a coin.

Doc.

 

[Raymond Gaskins]

There is no magic aerofoil and there is only one real test, and that's actual flying within the model's design envelope by at least two skilled pilots on the same day, same model, same conditions. Anything else is simply a waste of time - and a lot of hot air.

Model performance equation (Assuming that the model/aerofoil have been well designed with specific performance goals) :

Pilot skill = 60%
Wing planform/lift distribution = 25%
*Others, including the aerofoil = 15%

* Aerofoil = 10%
* Fuselage, tailplane, joints = 5%

As long as the aerofoil has been suitably selected and is a good choice for the job it has to do, then computer simulations are highly dubious unless you want to fly your digital aerofoil in steady, coherant, speed-controlled flight simulated digital air. Otherwise, for your local slope its probably more accurate to toss a coin.

Doc.

Doc,
I continue to be amazed at how top drivers and pilots can make almost anything look like “it” gave them the edge. I have seen my aerobatics instructor, Dave Scott, fly rolling circles and slow roles with a basic RC trainer that looked like an Extra on rails. Pilot skills continue to be highly undervalued as the most important variable in competition.
As you inferred, a true test of design vs skill can be sorted out in one design competition such as one design pylon racing.
Raymond

 

[u2builder]

There is no doubt that skill is important and that a glider top pilot with a Gentle Landy would likely outperform a mediocre pilot with an expensive molded glider.

But it worth noting that most modern gliders are flying with airfoils designed by aerodynamicists (using computer simulations and wind tunnel testing) . When the skill levels are comparable, the equipment matters, as does the pilots choice of which equipment to choose for specific conditions. The aerodynamicists designed airfoils for various conditons.

In this case a glider with the HN1033 would in fact be best for thermal flying, the S6063 for slopes, and the S7012 for all around, just as Professor Selig indicated , no matter the skill level of the pilot. That's why the Bletzyk designers matched the airfoils to their respective planes. There is no doubt that even a halfway decent pilot could out perform me in a thermal contest if he/she was flying an S6063 and I the HN1033, but my guess is if I flew both I'd do better with the HN1033 under "normal" conditions. I think I will really like the Tom because when I get frustrated "gliding" I can use that motor and unwind!

 

[Doc J]

There is no doubt that skill is important and that a glider top pilot with a Gentle Landy would likely outperform a mediocre pilot with an expensive molded glider.

But it worth noting that most modern gliders are flying with airfoils designed by aerodynamicists (using computer simulations and wind tunnel testing) . When the skill levels are comparable, the equipment matters, as does the pilots choice of which equipment to choose for specific conditions. The aerodynamicists designed airfoils for various conditons.

In this case a glider with the HN1033 would in fact be best for thermal flying, the S6063 for slopes, and the S7012 for all around, just as Professor Selig indicated , no matter the skill level of the pilot. That's why the Bletzyk designers matched the airfoils to their respective planes. There is no doubt that even a halfway decent pilot could out perform me in a thermal contest if he/she was flying an S6063 and I the HN1033, but my guess is if I flew both I'd do better with the HN1033 under "normal" conditions. I think I will really like the Tom because when I get frustrated "gliding" I can use that motor and unwind!

So there, you have answered your own question.

Good to go.

Doc

 

[u2builder]

Well, actually Professor Selig answered my questions. I merely added the link here because I thought that the airfoil plots and comments he posted might be of interest to someone interested in the Bletyzk gliders. The descriptions of the planes certainly indicate the best application, but I wanted a little more info and I think the plots helped me visualize the difference not that I have any real understanding of airfoils or aerodynamics.

Edit: Just found the Aerodynamics Channel. I should posted my question there. Very informative Q&A's

 

[Konrad]

Selig is absolutely correct! I thought that the Blejyzk/Aloft gave much the same recommendation in the sales page as to what wing to select.
Eppler, Hepperle, Selig and other with their code (computer) were responsible for the huge jump in glider performance in the 80's.

In the early 60's most RC gliders had a airfoil a kin to a banana. This only worked if you were already in a thermal or better yet, a dust devil! But heck we've all seen trash bags, literally going up in thermals. Then in the 70's Graupner came out with the flat bottom Cirrus that we learned that we need legs to avoid the down drafts. The key to the flat bottom airfoils was the lowering of the camber. If one can't see thermals and launch into them you don't want a banana for your airfoil. Yes, there were a few throw backs in the 70's like the Hobbie Hawk that while they look cool really where dogs in their day, heck even today. This can be directly traced to the under-cambered banana airfoil.

Selig/Donovan put the power of the computer to the realm of our toys and low Reynolds numbers. Now Selig developed a very low Reynolds number wind tunnel at the university of Illinois to validate his code generated airfoils. As these would benefit the model community he asked for modelers that could build airfoil coupons in 10 inch cords and be accurate to (0.005" [IIRC]). His code is well proven empirically both in the wind tunnel and in free air! Anybody that tells you computer generated airfoils are of little or no value in the real world it just a Luddite!

Based on our talks I think you are getting a bit frustrated as a thermal hunter and are looking for that extra edge/boost to keep the model up in the air. This is normal, we all hit learning plateaus. I think you can drive the gliders just fine and even read the gliders. But if you can't find the thermal the gliders just won't go up. I'd like to point you to the writings by Joe Wurtz on how to read the air.

Now the ship you choose is important. I'm of the opinion that the 2 meter can only take the novice so far. I like to see guys like yourself move up to the 2.5 or better yet a 3 meter ship. This is because they signal, find thermals a lot better than the smaller gliders. Or put another way they are more efficient. An experienced flier can make the 2 meter fly just fine. But the novice will more likely than not just be practicing landings with the 2 meter on less than idea days.

For most sport glider drivers an airfoil call out of under-camber, flat bottom, semi symmetrical and symmetrical would suffice. I think you have moved on to understanding the meaning of the camber line. And that is what Dr. Selig was focusing on.

The airfoil is important but get those wing tips further a part.

I've been flying thermal glider since the mid 80's and I can't tell an RG15 from an s7012, nor can I tell the difference in philosophy between the Dr. Eppler and Dr. Quabeck airfoils.

 

[u2builder]

Yes Konrad, you read the lines or between the lines well. I have seen a few Joe Wurtz videos. I think in one he ranked terrain from 1 to 5 in terms of thermal qualities. Our field would be ranked at the bottom. It is an floodplain deep in a valley, pretty wet, green foliage, bordered on both sides by steep, densely forested hills that are a little too far away and out of bounds anyway. We live in a cool climate, and by the time the ground starts to warm up around 11 in the summer the winds come up. The turkey vultures do come out to play on some sunny afternoons but the rising air they find is just at the edge of our vision and over very hostile terrain as well as out of bounds in terms of our lease from the Corp. Once in a while my flying buddy or I do find thermals over our flying area and we can often at least manage to stay up until our old necks get sore.

I am not really that frustrated. Mostly I like an excuse to try build another plane. The Blejyzk Serafin was a new experience and just had to get another to make it through the long winter. I have a lot of e-gliders already so I thought I should try the the Tom, such a unique and pretty plane, an all-in-one as Prof Selig noted. It will not be the most aerobatic plane I own, I am too old to be into "fast", and in our field thermal lift may be rare, but it will look great, glide well, and do the simple aerobatics I enjoy.

Back to airfoils, I am very impressed with the Blejyzk sheeted airfoils. They seem very clean, with very tight gaps on the ailerons/flaps, and resistant to twisting. And the symmetrical wood grain is lovely. The fuselages are pretty nice too.

I know a longer wing would be good, and that remains on "my list."

 

[Konrad]

I too love the tech we see in the veneer foam wings from Blejyzk. While you are experimenting with what you might like in a thermal glider I actually think the Blejyzk line is just about perfect and a great value. And I actually love his fuselages.

 

[Doc J]

Hi U2 - actually I should apologise for being a bit flippant here. Having been designing model gliders since the early '70's I sometimes forget that and at times automatically assume others have the same experience. But, unfortunately exprience cannot be taught.

Anyway, I have made and flown two "Blej" Gliders - Dayum all those x's and y's confuse my two-finger typing - and I think they are not only well designed, and great value for money - to an old skooler woodie like me they look great too. I made a trainer out of one - though I can't for the life of me remember its name - and although I added flaps it was pretty much orginal and flew very well in trainer guise - heck it even survived the training!

As I mentioned in my first post though, if you buy a commercial design, then you hope that the designer has chosen an aerofoil that is suitable for the job - though I have seen some that are not. But as Konrad rightly points out these are very small wing sections compared to full-sized sailplanes and therefore its extremely hard to reproduce them exactly - even with CNC machining of the positive moulds. I use my own sections simply because I designed them, I have tested them against others by difefrent designers, and I simply know more about them and what they do than the Epplers, Quabecks and SD's. Having said that, I have used Prof Selig's SD8020 for many years for variety of symmetrical aerobatic models, and the reason for that was that it was the lowest drag section available, and for years I couldn't make any better.

Happy flying!

Doc

Me happily holding a Blej trainer after its maiden, and below that, my ugly mug again this time with my latest design. Both taken in Taiwan.

Though years have passed - you can still see that my tailor has a sense of humour.

 

[u2builder]

Hey Doc,

Not having really been in this glider forum until fairly recent, I thought perhaps you didn't have not see much value in computer modeling. Then I found the Aero Channel and discovered I was badly mistaken. Whoops. I've been reading the posts in the Aero Channel. It's great, It answers a lot of things I wondered about. I may even have a few questions of my own eventually. Thanks for creating that.

BTW, nice gliders.

 

[Doc J]

Hey Doc,

Not having really been in this glider forum until fairly recent, I thought perhaps you didn't have not see much value in computer modeling. Then I found the Aero Channel and discovered I was badly mistaken. Whoops. I've been reading the posts in the Aero Channel. It's great, It answers a lot of things I wondered about. I may even have a few questions of my own eventually. Thanks for creating that.

BTW, nice gliders.

Actually, U, I do see the value of computer modelling but I take the results with a very large pinch of salt as they often do not carry forward to real, actual, in-the-air flying. In looking at model glider designs, too many people make two big mistakes:

1. Some think that computer simulations actually apply, verbatim, as is in real flight. OK, If so why do our aviation companies and educational facilities still need expensive, noisy wind tunnels?

2. Many people think that the Aerofoil section is the BIG DEAL, the B-All and End-All for deciding the performance of a model aircraft. Well it aint, in fact is a relatively small part of a big collection of stuff.

This is why any designer worth his salt should be able to stand by his design and answer any, and all questions as to the design points and why they were used - including the aerofoils.

I guess all this aerofoil aerofoil, aerofoil, discussion by the armchair aerodynamicists is because aerofoil plotters are readly available, and a little knowledge can turn out to be a bad thing. At our toy aeroplane sizes, I can tell you from hours and hours of actual testing - in wind tunnels - that very little full-sized knowledge is useful, or even applicable.
This 'scale effect' should also be common sense because as general rule if you want to test even the most basic aerodynamic performance of a full sized aircraft then (Unless you work at NASA Ames) your model has to be at least 33% of the actual size. In fact we modelllers are talking about tiny aerofoils performing a very low Reynolds numbers and where the boundary layer departure begins at only 40 to 45% of the chord.
This fact in itself makes a travesty of all this wise "hot air" aerofoil analysis.

Its a fact that a NIKE Size 12 (mod) or Converse size 13-mod aerofoil would work just as well as any vaunted 'super' section as long as the curves were in the right places and the front end was rounded and the back sharpened up.

So for our models, if the aerofoil is modern (Though a lot of the oldies are REALLY good too), and the model is well designed to do its job, then there will be a large variety of sections available, and in actual flight the difference between them will be very little.

I can also tell you that despite disparagement, the old adage "If it looks right, it flies right" really is true.

Glad you like the models!

Cheers,

Doc.

 

[u2builder]

"I can also tell you that despite disparagement, the old adage "If it looks right, it flies right" really is true."

Interesting.

"Some people take their airfoils seriously, and some don't. For some years I drew my master ribs with a French curve: lay out the chord line, draw a cross section of the leading edge stock on one end and a cross section of the trailing edge on the other. Lay a French curve between both cross sections and zip-zip I had an airfoil. " Dave Thornberg, Old Buzzard's Soaring Book, 1990, Chapter 11, Some Notes on Designing Your Own, Part I, Wings., in which he presents his take on the "evolution" of airfoils up to the time the book was published. It is an interesting and entertaining chapter. Sometime I am going to ask a few questions on the Aero Channel, but I've got a lot of reading to do first.

 

[Konrad]

Ah, the Ol' Buzzard's concept of the river of air is a great way to visualize how thermals move. To this day I still think there's a thermal breathing monster that generates the pulsing thermal.

Dave Thornberg's Do You Speak Model Airplanes is another entertaining and informative book.

 

[Doc J]

"I can also tell you that despite disparagement, the old adage "If it looks right, it flies right" really is true."

Interesting.

"Some people take their airfoils seriously, and some don't. For some years I drew my master ribs with a French curve: lay out the chord line, draw a cross section of the leading edge stock on one end and a cross section of the trailing edge on the other. Lay a French curve between both cross sections and zip-zip I had an airfoil. " Dave Thornberg, Old Buzzard's Soaring Book, 1990, Chapter 11, Some Notes on Designing Your Own, Part I, Wings., in which he presents his take on the "evolution" of airfoils up to the time the book was published. It is an interesting and entertaining chapter. Sometime I am going to ask a few questions on the Aero Channel, but I've got a lot of reading to do first.

If you have an eye for a curve Raymond it would probably work just as well.

But...the only way to tell is FLYING it.

Doc.