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Thread: Riblett GA 30-613.5 Compared to GA 35 A 412

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    Riblett GA 30-613.5 Compared to GA 35 A 412

    In my ultimate quest for a STOL airplane, I built a Just Aircraft Highlander and replaced the standard wing with a Riblett GA 30-613.5 and added a moveable leading edge slat and full span 30% cord flaperons. This aircraft has a 912S 100 hp engine. I currently have about 65 hours on my airplane and I am happy with the STOL capabilities as well as the 105 mile an hour cruise speed (with the 29" Bush Wheels). However, I am now thinking about building another set of wings to (occationally) replace the set that I currently have on the plane. I am thinking about going with the Riblett GA 35 A 412, an entry level laminar flow wing. My question is, if I kept everything the same (54" cord, 150 square feet, Bush Wheels, etc.) what could I expect for an increase in cruise speed? I would not do a leading edge slat and would do a 10' slotted flap with 4' deep cord ailerons instead of the full span flaperon. I would eventually take the Bush Wheels off for higher cruise with this wing, but I am curious about the apples to apples comparison between the two sets of wings. I have been told that my stall speed and my cruise speed would increase by about 10 miles per hour. Does anybody have any thoughts about this build?

    Thanks, Jim Pekola

    Riblett GA 30-613.5 Compared to GA 35 A 412-slats-1-012.jpg

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    Registered User GESchwarz's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    About all you have to go on is what data Harry has provided in his book. Just based on the airfoil description I'd say you should expect to have better cruise speed at the expense of STOL performance. I think you already know the answer.

    I have a question...How is your roll control at stall with those full span flaperons? Conventional wisdom says that you are asking for trouble. You can only get so much out of a flap before it quits. I would imagine that the only safe way to use full span flaperons is if they are of the Junker arrangement...under the wing.
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    The roll control varies depending on the degree of flap setting...I have nine notches of flap from 0 to 40 degrees. With a cross wind landing you may only want to use 15 degrees. With no wind you can use 40 degrees but you have to steer with your rudder. Because of the leading edge slat, the wing doesn't want to stall. You can fly this plane at 25 degrees angle of attack.

    Back to the data in Harry's book, I realize that I am going to lose STOL capabilities, but I want to know if the increase in cruise (10 to 20 miles per hour???) will be worth the sacrifice. Ten miles an hour in cruise is not worth the effort, but 20 mph? Maybe.

    Jim Pekola

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    Super Moderator orion's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    The trouble is that the two wings aren't the same so are difficult to compare. For instance, we know that on the Helio, the retractable slat is the main source of drag on the wing and is principal in keeping that plane's high end performance much lower than it could be. In your case, you're changing the wing configuration, the camber line, the pitching moment (trim drag), and so on. So yes, the new wing will be faster but by how much is difficult to answer without significant analysis. If I were to gut guess, I'd say yes on the 10 mph but would be doubtful of the 20 mph.
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    Registered User GESchwarz's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    If you want to get to that extra 20 mph, how about trimming the span? Design the outer portion of the wing to be detachable and see what you get. You might be able to do that with the wing you already have and save a lot of work of having to build a second set of wings. That is a huge camber you got there though.
    Last edited by GESchwarz; December 31st, 2010 at 09:43 AM.
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    Registered User wsimpso1's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    Keeping the same wing area, but trimming your wing drag will make but a small improvement in cruise. You will still have that draggy landing gear and struts and the large draggy tail with the fences, and so on. When you are trying to go someplace upwind, that 10 mph in true airspeed will make a bigger difference in trip time, but otherwise it becomes a "why bother?" for me.

    Now if you were going to decrease wing area and clean up the drag elsewhere, and make sure that the prop works well for the higher airspeeds, you might have something. Things like getting rid of the struts and fences and external springing on the gear and smaller tires with fairings and smaller openings for cooling with a better sealed cooling system... But to do that is to basically make it into another airplane. Or just build a traveling ship... Hmmm.

    Billski

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    Registered User Lucrum's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    Quote Originally Posted by Jim Pekola View Post
    In my ultimate quest for a STOL airplane, I built a Just Aircraft Highlander and replaced the standard wing with a Riblett GA 30-613.5 and added a moveable leading edge slat and full span 30% cord flaperons. This aircraft has a 912S 100 hp engine. I currently have about 65 hours on my airplane and I am happy with the STOL capabilities as well as the 105 mile an hour cruise speed (with the 29" Bush Wheels). However, I am now thinking about building another set of wings to (occationally) replace the set that I currently have on the plane. I am thinking about going with the Riblett GA 35 A 412, an entry level laminar flow wing. My question is, if I kept everything the same (54" cord, 150 square feet, Bush Wheels, etc.) what could I expect for an increase in cruise speed? I would not do a leading edge slat and would do a 10' slotted flap with 4' deep cord ailerons instead of the full span flaperon. I would eventually take the Bush Wheels off for higher cruise with this wing, but I am curious about the apples to apples comparison between the two sets of wings. I have been told that my stall speed and my cruise speed would increase by about 10 miles per hour. Does anybody have any thoughts about this build?

    Thanks, Jim Pekola

    Attachment 9905
    I plugged in the numbers into Airfoil Optimizer. It doesn't have the exact airfoils your using or considering so I used the closest ones.
    According to it, changing nothing but the airfoil, your stall speed would increase 1.2 KTS and cruise speed would increase 0.67 KTS.

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    Super Moderator orion's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    But did the airfoil optimizer account for the fixed slot on the first wing - he's not changing just the airfoil. I don't think that any of the foil programs have the capability to properly account for the forms of drag created by these devices. Assuming airfoil change only, yes your numbers are right but changing the entire geometric baseline, the benefit might be a bit better than that. But Billski is right, all the other stuff creates drag too so to take full benefit of a "faster" wing, the rest of he plane should be cleaned up too.
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    Registered User Tom Nalevanko's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    There is data on removing a fixed slat from a number of wings here: StolSpeed Aerodynamics - Performance Enhancement for Light Aircraft Perhaps it may give some insight? Blue skies, Tom

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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    Quote Originally Posted by orion View Post
    But did the airfoil optimizer account for the fixed slot on the first wing - he's not changing just the airfoil...
    No it does not, although I thought he had a movable leading edge slat and not a fixed slot on his current wing.

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    Super Moderator orion's Avatar
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    My mistake. So then the question is how accurate was that slat in its installation. However, since it is retractable and assuming a tight fit when stowed, my original estimate of performance improvement is quite a ways off. If I were to guess I'd say that the new wing will do a bit better than predicted above, mainly because of the lower trim forces on the tail and maybe a better incidence angle on the fuselage. However, in order to get even the ten mph improvement, you will have to go to smaller faired in wheels and address some of the other items posted in Billski's post above. It really is difficult to get that level of improvement when you're dealing with a pretty much fixed configuration.
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    Re: Riblett GA 30-613.5 Compared to GA 35 A 412

    Sorry for not replying sooner...no computer at my job! Thanks for all of the insight into my wing considerations. You have confirmed what I thought, but not what I was hoping to hear. Maybe some day I will build another set of smaller, faster wings and clean up some of the drag as well. I have a set of plans for a Wittman Tailwind W-10. Maybe I'll build those wings and put them on and see what it does? If it doesn't work I can always build the rest of the Tailwind! Until then I will probably just enjoy the awesome STOL performance.
    Thanks, Jim Pekola

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