Why no flaps?

[Razncain]

As good as it is at a landing speed of 30mph listed, surely others have wondered too, why not put flaps on it, just to see how much lower it could have went. I know it’s simpler, but as homebuilders, we just can’t leave well enough alone, so are others considering building this plane with flaps? I imagine Bob has explained his reasoning behind this somewhere, but I haven’t found him discussing this just yet.

[dedgemon]

its weight!

[Razncain]

Thanks, David. Just a swag, but from flap handle to the necessary components getting it to the flap itself would be perhaps 10-15lbs. If that’s what it would be for another 5-7 mph lower landing speed, or whatever it may be, I wouldn’t mind this weight penalty. I also believe the wing flap area itself, by taking place of a part of the main wing would almost be a wash in that area.

[jaredyates]

I think it was a matter of cost-benefit analysis. He saved weight and build complexity, and ended up with a landing speed that was still slower than any of his other airplanes by a significant margin. He could tell you exactly how many pounds he saved, and don't quote me for sure, but 30 pounds comes to mind for some reason.

[Razncain]

I appreciate the feedback. Okay, Jared, I won’t quote you, but if it’s 30lbs, I better get at least 7mph off of the stall speed. I guess I’m going to have to talk to Bob, and see what he says.

I’m ready to go with a Bearhawk, just having trouble figuring out which one right now. Leaning towards LSA, but probably will put it in the EAB category. I’ll be glad when I decide, so I can get on with it.

[jaredyates]

I think it's time well-spent to make sure you choose the right project. I spoke with Bob a week or so ago and he was just about to take his LSA to Idaho for a few weeks. If you have trouble reaching him, that might be why.

[Papa Foxtrot]

I’m ready to go with a Bearhawk, just having trouble figuring out which one right now. Leaning towards LSA, but probably will put it in the EAB category. I’ll be glad when I decide, so I can get on with it.

If you're thinking of building the LSA and certifying to 1,500 lbs and want flaps, then I can't think of any reason not to build the Patrol.

Just my $.02.

Patrick

[Razncain]

Mainly because of the smaller traditional engine choices I could use on the LSA, but wouldn’t work for the Patrol since the minimum it says one could use on it is the 115HP. I suppose one engine that might be flexible for both planes would be the IO-233. I’ve already got me a fast plane which I’ll keep, but at 8gph, kind of want a gas sipper this time around. Mainly wanting it for just STOL though, and getting to locations besides airports. I’ll figure it all out eventually.

[Battson]

Didn't someone do a calculation which estimated the flaps added 60lbs total??

[Razncain]

I think, or at least hope it is about half that figure. For comparison the wingspan of the RV-9 is 28’ (BH LSA 34’) and the builder of a 9 weighed his wings and it came in at 55lbs each w/o fuel tanks, flaps and ailerons. With those attached, he estimated 80+ without fiberglass wing tips installed, and I’m sure this would be without paint also.

http://www.n2prise.org/rv9a014.htm

[wpackard]

Here's a video interview with Bob about the LSA. He starts talking about the flaps around 5:47. He mentions that flaps would add "about 20 lbs" of weight and discusses some other reasons the LSA doesn't have flaps.

Wayne Packard
Kit Building 4-Place
Plans # 850
Fallbrook, CA

[Razncain]

Wayne, thanks, that's what I've been looking for. Here Bob answers the right questions, unlike the video on youtube that was done at Oshkosh. He covered everything that I had on my mind and more, so sold me. For others that want to go directly to the video that Wayne recommended this will take you right to it:

http://www.eaavideo.org/video.aspx?v=3418272292001

For those that that don’t want have time for it, here is the reasons he went with this airfoil and why no flaps, but anyone with any interest in this plane at all, should make time to watch all of it. A little more info on the airfoil:

The airfoil is a Ribblet 30-6135.

The 30 is for the series of airfoil

The 6 is 6% camber

The 135 is 13.5% thickness

For flaps, Bob addresses a lot of ground here of why there are not used. Points primarily are:

Flaps would cause interference drag whet the flap meets the wing. Add another 20lbs. More complex and time consuming.

He said this plane was designed to be a slipper. He gave it plenty of rudder, and with the 6% camber on the wing, when you get it down, you’ll get the drag you need down low, and with tip losses and induced drag, you’ll be down plenty quick. The guy he took a ride in obviously was impressed with how quick and short of an area Bob needed, and must have sold him on the idea because he was ready to trade in his other popular plane and start on this one, but he was already further along with it. He said he wished he had known about this plane earlier.

That video covers a lot more of area in detail that was just for those two things I was most curious about. He said Harry Ribblet has often consulted him, advising him what he thought would be best, and he obviously took a lot of his suggestions.

This plane suits me just fine because I do just want something more simple, and a gas sipper that can chug along at 4gph sipping auto gas by choosing the right engine.

Wayne, thanks again,

John

[wpackard]

You're welcome, John. Glad it helped you make your decision!

[kestrel]

Updated link for Bob's EAA video:

https://www.eaa.org/videos/3418272292001

[Jflyer]

The '30' of the 30-613.5 translates to the thickest part if the airfoil will be be 30% of the cord in from the leading edge. The thickest point of the airfoil will be 13.5% of the cord length.

[Razncain]

Thanks, I thought the 30 number probably could use more clarification, I was writing down bits and pieces of what Bob was saying, without fully understanding all he was referencing at the time, and don't recall him saying much about the first two numbers. Definitely want to look and understand numbers more of what they represent on wings.

[Jflyer]

I posted the following on another thread in reference to why the Patrol outperforms the CUB by a wide margin:

I've been doing a lot of research on the airfoil for the Patrol lately. Basically I'm trying to lay out the Patrol airfoil in AutoCAD in order to make the rib forms on the CNC as well as cut out the ribs themselves. Interesting information can be found about the Harry Riblett Airfoils, which Bob Barrows used a modified version of for the Patrol (Ribblet GA 30-413.5).
I'm not an airfoil designer/expert nor an aeronautical engineer, but I play those parts in my dreams. That being said, I think the one major item you can point to as why the Patrol is better performing than the Cub is the Ribbett Airfoil design on the Patrol over the Clark Y on the CUB.

I've recently purchased and have read Harry Riblett's Book "GA Airfoils - A catalogue of airfoils for general aviation use." It's actually a very educational read and has a tremendous amount of information pertaining to the various airfoils that have been used over the years based on NACA and NASA research, and their short comings. I recommend this book to anyone building homebuilt airplanes. Harry Riblett redesigned the better airfoils from those series into what is now known as Riblett GA Airfoils. Many coffee breaks and naps in between chapters. Zzz…would love it. There is a small reference to the 4212 airfoil that is used on the Bearhawk 4-Place as well as the Clark Y. There is also in the book a numerical catalogue of the 98 various GA airfoils listed in station, camber, and ordinates to plot out the airfoils. Harry Riblett left to anyone who wants to read it, everything needed to create the GA airfoils for any wing cord size by simple mathematical equations. Amazing stuff!.

In addition to airfoil design, Mark Goldberg stated "the aluminum skinned wing will outperform the fabric wing."

This is also mentioned in Harry Riblett's book where the aluminum skinned wing holds the correct and true airfoil better than the fabric. Attached is the page from Harry Riblett's book with the stations, and ordinates for the 30-612, 30-615, and the 30-618 airfoils. In order to plot out the 30-613.5 for the Bearhawk LSA, you need to scale down from the 30-615 and use Ord and GA-6 columns to create the new 30-613.5 airfoil.


30-615.pdf

[Battson]

The aluminium wing gives you a better "achieved" aerofoil, as compared to the "designed" aerofoil.

That does not consider is the whole picture though. The weight difference is almost certainly a more significant factor in the opposite sense?

Is there empirical evidence that the Patrol is superior to a Super Cub??

Also I read the Super Cub has a Super Cub USA 35B airfoil, is that different to the Clark Y?