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Catalina 90MPH or bust

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Posted (edited)

N157AB is home for a bit while I finish up the 670 install.  The point of this kind of plane is absolutely not about covering ground, but her cruise performance was always a little bad even by Catalina standards: about 65MPH with the 582 running 5700RPM and 5.8-5.9GPH.     So I'm going to take some extra time to do all the little things that I thought might make her a tiny, tiny bit faster.   I'll document all the mods here, and let everyone know the results.   Fun?  Fun!

Here's what's cooking so far:

  • Right prop, wrong engine: the 70" 3-blade warp drive was too much for the worn out 582, and was pitched pretty flat for water takeoff performance.   It's the perfect prop for the new 670, though.  Hopefully halfway to 90MPH already!
  • Internal radiator: the flat radiator right before the prop seems like it would be a double penalty- direct drag, plus decreased prop efficiency.   I've sketched in a Kawasaki EX500 rad down by the turtle deck, with a scoop behind the rear window, and an outlet with a huge adjustable cowl flap on the other side of of the plane.  Hopefully, the cowl flap can be opened enough to suck adequate air through while flying, and the electric fan that came with the radiator will handle ground operation.  (See pic)
  • Better canopy- my canopy was reworked and is even worse than the stock one- very abrupt vertical face and rough transitions.   I'm scheming a vac formed canopy with better curves.   Again, hopefully this provides double benefit- cleaner air to the prop, plus a slight direct drag improvement. 
  • Fair the stabilizer struts, gap tape for the elevator, as all this is right in the prop blast and practically incurring double penalty. 
  • Experiment with gear doors-  Again, double benefit?  Get on step easier, maybe not need a 3-blade prop for so much static thrust?
  • Exhaust cowl?  Went to all that work to remove the radiator, the exhaust is still right there in the prop's air. 

Anyway, that's all that's planned.   What's the over/under that I'll make 90MPH on the 65HP available at 5500RPM? 

Screenshot from 2017-10-30 19-55-55.png

IMG_20171030_173458.jpg

Edited by cowlove
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Posted

PS- plywood is for prototyping and static/taxi tests.  (And for the CONSIDERABLE trial and error in getting all this stuff to clear the wing-folding geometry.  I've thought I was done like 5 times and then hit yet another interference point)

The plenum will be all fiberglass once it's done.

 

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Posted

Hey Cowlove/Jim, 

I am cruising 75% at 85-90Mph.....when I feed everything I have (100% / 95Hp) I am hitting a wall just below 100Mph and I believe this is due to the high camber wing profile. It doesn't matter what else you do aerodynamically, the wing is the culprit. This I am convinced of after trying hard myself to clean up all the details.

So if you get rid of the big offensif stuff like the radiator and the canopy I think you'll get between 80-90Mph. But then after doing these mods, I believe you will waste a lot of time and increase weight doing the small improvements (gear doors/tail feather strut fairing etc...)...= no more speed.

My 2 cents

P.s really looking forward flying in formation....

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Posted

Hey Jim, here I found an interesting article about drag reduction on an avid flyer. I find crazy that the fuel cap could rob 7% lift.....

http://avidflyer.wikia.com/wiki/Drag_Reduction

 

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Posted

I bookmarked that ^^ one!

Great article, thanks flywise!

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Posted

Thanks, Laurent.  I'd seen that writeup a while ago, it's good I can now bookmark it.  

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