Patrol Riblett airfoil on 4-place Bearhawk?

[max_burke]

Has anyone tried building a 4-place Bearhawk with the Patrol's Riblett airfoil?

Does anyone have a project in-progress with the Riblett?

Just curious. For science, and all.

[Chris In Milwaukee]

I know Bob is a big fan of that airfoil. He and I had a talk about it last year at OSH, and I get the impression if he had to do it again, he'd use it over the NACA4412. I don't think he'd build one himself, but who knows what an adventurous builder here may turn out one day!

[mswain]

It would be interesting if Bob would do a Bearhawk 2.0 wing. Incorporate everything he's learned into an updated design, assuming there are benefits to be had.

There was a discussion on here a while back where a 4 place builder was using (I think the Riblett) airfoil. They had remarked about the cascading effects of making such a change.....making the build that much more complex. I have searched but I cannot find the thread.

[Peter Bishton]

Guys

The 'knock on effect' of changing design is discussed in the Bearhawkin website.

http://www.bearhawkin.com/FAQ-Modifications.html#Modifications_and_Design_Propogation_Nightmare

My father in Australia liaised with Harry Riblett circa 1988 and used a Riblett airfoil on a wittman W8 (second set of wings). It defienatley performed differently being more efficient and let the aircfat fly more slowly. Problem then became the elevator ran out of control on flare (it hit the stop). But it could fly more slowly and gained a knot or two in cruise. riblett refiened the NACA series of airfoils using the Eppler Program. eppler is based on Fortran which is a very old type of mathematical code but is very accurate generally. the riblett airfoils work well. proof of the pudding etc.

I was keen to use a Riblett GA30-313.5 (I am quoting these ubers from memory from last nigth when i sat at home with all the data in front of me - I tried to do a post and it failed to send). Yet to build the wings. Fuse well advanced.

The LSA and Patrol is diffeent (stating the obvious) and the 4 seat would benefit from a different airfoil with different Cl at cruise - to the two Bob uses.

We often wonder why Bob went to the riblett airfoils for the Patrol and then the LSA.

Peter
4 place
# 1134

[Battson]

Has anyone tried building a 4-place Bearhawk with the Patrol's Riblett airfoil?

Does anyone have a project in-progress with the Riblett?

Just curious. For science, and all.

Yes - someone is working on this upgrade... and no, it's not me. :P Watch this space.

I had never realised the BH and Patrol used the same wings, but I now understand they are exactly the same - just the 4-place wing has a thicker cap strip. I understand there is basically zero "design knock-on effect" of fitting Patrol wings to the Bearhawk, provided you know how to beef up the cap-strip during the wing build. Of course the flight testing would need to be completed, to know whether such a huge mod is actually worth doing.

[Chris In Milwaukee]

They aren't exactly the same, actually. BH 4-place is a NACA-4412 variant. Whereas the Patrol is a Riblett-type. They do have the same spar spacing and roughly the same chord, however. (If that's what you meant by same wing, then my apologies). When I did an analysis on the two airfoils, they do react a bit differently depending on the angle of incidence. The lift curve of the Riblett is definitely smoother (in 2D analysis). It would be a good choice, methinks.

[Battson]

Yes, I realise the aerofoil is different - thus this discussion - I should have said more clearly, I meant I never realised the overall dimensions, fuselage connections, flap drive, and cable runs are identical, so they could theoretically be swapped out without any design changes if you ignored the strength and weight differences.

Apart from the obvious aerofoil differences you mention, they also have different flaps (Patrol flaps are larger on the inboard side). But that doesn't mean one wing can't fit the other fuselage.

[Chris In Milwaukee]

Gotcha ;-). I thought about it after I said it. Too feisty today, I guess. The other problem with the Patrol flaps is they go all the way inboard. The Patrol is slab-sided, whereas the 4-place bows out there. Flaps would probably hit if the wings were used in their current config. Bob and I actually had a discussion about this over the summer.

[LukeS]

When you look at the difference in performance between the two planes in terms of cruise speed and stall, the difference is relatively small when you consider the increased weight and drag of the 4-place. There is an interesting write up comparing the performance difference of two Pietenpols. One was built with the original airfoil and the other with the Riblett 612 which you can read here:

http://www.pietenpols.org/id18.html

The differences in performance wouldn't be something I would consider to be significant, and I don't think that anyone would debate that the Riblett wasn't a superior airfoil. Obviously the Bearhawk is no Pietenpol, but the airfoil is just part of the equation. This is not to say that performance gains couldn't be achieved using a Riblett airfoil, but that the airfoil is only responsible for a fraction of the performance difference seen between the 4-place and Patrol. At the end of the day, no similar airfoil will have much of a chance compensating for the increased fuselage weight and frontal surface area of the 4-place.

[Chris In Milwaukee]

Yes - someone is working on this upgrade... and no, it's not me. :P Watch this space.

I had never realised the BH and Patrol used the same wings, but I now understand they are exactly the same - just the 4-place wing has a thicker cap strip. I understand there is basically zero "design knock-on effect" of fitting Patrol wings to the Bearhawk, provided you know how to beef up the cap-strip during the wing build. Of course the flight testing would need to be completed, to know whether such a huge mod is actually worth doing.

I must confess, although I may not be the person of which you speak, I am indeed working on a project that uses the Patrol airfoil on the 4-place. It's a long story that I'll outline in another post, but it's going to be a cool project!

[Battson]

When you look at the difference in performance between the two planes in terms of cruise speed and stall, the difference is relatively small when you consider the increased weight and drag of the 4-place. There is an interesting write up comparing the performance difference of two Pietenpols. One was built with the original airfoil and the other with the Riblett 612 which you can read here:

http://www.pietenpols.org/id18.html

The differences in performance wouldn't be something I would consider to be significant, and I don't think that anyone would debate that the Riblett wasn't a superior airfoil. Obviously the Bearhawk is no Pietenpol, but the airfoil is just part of the equation. This is not to say that performance gains couldn't be achieved using a Riblett airfoil, but that the airfoil is only responsible for a fraction of the performance difference seen between the 4-place and Patrol. At the end of the day, no similar airfoil will have much of a chance compensating for the increased fuselage weight and frontal surface area of the 4-place.

Yes - I tend to wonder too - but there will be a test flight conducted before too long, and then we'll know for certain.

[whee]

I'm looking forward to reading the flight test report but I'm thinking along the sale lines as Luke, there isn't going to be much difference.

Chris, What differences did Bob think would be seen by using the Riblett?

[Chris In Milwaukee]

Smoother airflow and nicer stall were among those I remember (not that the normal wing's stall is any kind of event). Also, the taller wing allowed for the same amount of fuel storage in less space, chord wise, because the tank can be skinnier.

[whee]

Thanks Chris.

[max_burke]

I'm looking forward to reading the flight test report but I'm thinking along the sale lines as Luke, there isn't going to be much difference.

True, there may not be any at all. I'm interested to hear what Battson's source finds out though!