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Oct 24, 2004, 11:04 PM
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Carbon Falcon MODS


I have been busy modifying my carbon falcon and I thought I would share some of the ideas that I came up with. When I first received my carbon falcon I had a fair amount of trouble getting it to fly very well. I had the common problem that I have seen posted here on Ezone. That is my carbon falcon would be cruising along and all of a sudden it would go into a step dive for no apparent reason. I tried moving the cg placement and the tip height to no avail. I installed the speed mod and it help but by no means was it the solution! I finally decided to check the ribs against the rib chart that is on the ACESim website. Bingo that was the problem!!!! The bamboo ribs had lost just about all their reflex. After reshaping the ribs I gave it a test flight. The difference was night and day! The airplane flew better than it had before. The next problem I ran into was the ribs would loose their shape (Flatten out) if the airplane were to pick up too much speed. I got talking to a good friend that happens to fly hang gliders about this problem and we came up with the idea to replace the bamboo with 1/8 inch aluminum tube. This has proved to be the best mod to date!!!! There is NO need for the speed rods if you replace the bamboo ribs with aluminum. The Aluminum ribs will not flatten out at speed or loose their shape. This allows me to fly my carbon falcon quite a bit faster than before with no bad tendency. I have a nippy o8o8 on my carbon falcon and flying it at full throttle is no problem with out the speed rods installed. I took the speed rods off my falcon and there was no difference in flight characteristics. As an added benefit by removing the speed rods it reduces the load on the warperon servos.

The next mod I did was to change the way the control rod torque tube was attached. The original system used a black lacing cord that was wrapped around the rubber fitting on the outboard part of the wing. I had problems with the control torque rod sliding up on the rubber fitting. This would cause the trim setting on the radio to change. So I have a few pictures to show my solution.
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Oct 25, 2004, 01:11 AM
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hardlock's Avatar
Excellent work! We found that we had a "soft" batch of skewers used for ribs that some planes shipped with. You might have gotten one with those as most seem to hold up well for shape. The flattening at speed I haven't explored yet but the softer ribs would definitely be more prone to this.

What do you use for the torque bearings and attachments? Looks real sweet!
Feb 21, 2005, 04:55 PM
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maximal's Avatar

Aluminum ribs, great mod!


I thought the Al tube mod sounded good when I first saw it, and I finally got around to trying it. Just did some test flying... great mod! My CF has never had this much control authority (I've owned one since late July '04). There is no more "death dive" at speed syndrome (I've been using the speed mod from day 1). After testing with the speed mod rods still installed, I took them out and, like A&P Mech, noticed no difference! I never really liked those extra rods very much, so this is a big win in my book. My only concern with the Al ribs is that they won't spring back to original shape if bent in a crash or whatever.

Don't get me wrong, I loved my CF before this mod... it flew great and I've enjoyed every minute of it (although it took some futzing to get it to fly right the first few times). But now I can do outside loops (w/out it acting like a pelican going for a fish ), nicer rolls, better inverted flight-- basically everything that requires more speed. BTW I run it with a LensRC 24T with a 9x5DD on 3S LiPos-- great motor.

I'm not sure how much of my perceived improvement is due to the new ribs being more true to the right shape (according to the template). When I took out my original ribs I discovered that only one of them matched the template exactly, and none of the pairs matched each other (see attached pic). What do you think, Ken?

Thanks,
-Max
Feb 21, 2005, 05:41 PM
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hardlock's Avatar
I think I wish I could add AL ribs to all the planes without having to raise the price! Those tubes are spendy, even in quantity. I will be using them on the high-end models for sure.

What diameter AL did you use and did you do anything for the front ends to prevent them punching through the sail?

Those ribs shown are pretty wanged alright but I've seen worse. The trouble with wood is.....

The root rib losing its camber probably has the most effect on flight. A little tweeking by hand would fix them right up.

Ideally, the ribs should be made from CF tow laid up in molds to insure accurate shape but that would be even more expensive than AL tubes.
Feb 21, 2005, 07:59 PM
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Is there a pointer to making the al ribs?
Feb 21, 2005, 08:11 PM
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maximal's Avatar
Ken, I hear ya on the cost issue. On the other hand I paid less for the tubes than for the speed mod I got the K&S 1/8" from Tower for $7 with enough tubes to do 2 Falcons (so I have lots of spares). I originally tried 3/32" tube, but that is way too thin and flexible. I also kicked around using the 1/8" with the 3/32" inside it (perfect fit) which made for a very stiff rib, but was about 2x as heavy. With just the 1/8" tubes, the Al ribs are about 1.8x as heavy as the wood, which works out about even when you remove the carbon speed mod rods.

I crimped the ends flat and de-burred them with a fine file so they would sit on top of the LE spar better and wouldn't chew up the fabric as much. I might reinforce the pocket tips with some repair tape.

Quote:
Ideally, the ribs should be made from CF tow laid up in molds to insure accurate shape but that would be even more expensive than AL tubes.
Now you're talking! I'd pay extra for that

Cheers,
-Max
Feb 21, 2005, 08:20 PM
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maximal's Avatar
Ron, I just printed out the CF rib template from the owner's hangar on Ken's site and then bent the tubes to match by hand. A tubing bender tool might help to get the curves smoother, but mine came out pretty smooth anyway. I bent first and then cut to length with a fine saw.

Hope that helps,
-Max
Feb 21, 2005, 08:48 PM
Registered User
OK, then just regular old 1/8 inch Al tubes bent by hand. I may need to try that. Has anyone else done this before? If so I guess I must have missed it.
Feb 22, 2005, 06:48 AM
Registered User

Carbon Falcon MODS


MAX,
I am glad you found the same success with this mod! It was absolutely the best thing I have done to my falcon! I have been flying my falcon with mod since October of last year and I have not had any problem with the ribs losing there shape or damaging the sail. I did flatten the front of the ribs and file them smooth.

Ray
Feb 26, 2005, 01:24 AM
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maximal's Avatar
I got a chance to fly my Falcon some more today. First calm day since I first tried the mod. Had a blast, sucked down two batteries even though could barely feel my fingers after the first (cold up here). Then again, I'm flying it way more at WOT now, because it's so much more stable! Zooming all over the place I like how it sounds at full throttle, like a big hummingbird. I really can't say enough good things about the aluminum ribs. I'd urge anyone who flies with the carbon rod "speed mod" (or feels they need it) to try this out. Thanks again, Ray!

Ken, I know you must be busy with the Kestrel, but I'm wondering if you've tried this yet? I'd like to know what you think of the Al ribs vs. the CF rod speed mod. No rush

Ray, I like the looks of that battery mount and motor skid protector (is that what they are?). Could you post some more pics/details on those? I'm curious about the torque bearings too

I'm posting a pic of my current setup, and also a bit of reinforcement I did to stiffen up the motor mount. The idea was to reduce some of the twisting that resulted when the motor is putting out a lot of torque. The problem was more pronounced when I had a geared Astro 010 on there before I got the little outrunner. It worked well, but I'm not sure how necessary it is now. If I take it off I won't be able to balance with my 3S 860 LiPos!

-Max
Feb 28, 2005, 07:27 AM
Registered User
Max,

I spent a lot of time in the Ithaca NY area when I was growing up. So I understand the frozen fingers!

Take a look at this thread. It has a few more pictures of the battery tray and the motor mount.

https://www.rcgroups.com/forums/showthread.php?t=256305

I designed the torque rod brackets and cut them out of G10. The bearings were turned out of acrylic. There are a lot of better bearing materials but I had the acrylic. It seems to work very well.


Ray
Feb 28, 2005, 10:28 AM
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LittleJon's Avatar
Looks like I'll be making a trip to my LHS to pick up some Al tuning very soon!
Feb 28, 2005, 09:43 PM
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hardlock's Avatar
Max - "Ken, I know you must be busy with the Kestrel, but I'm wondering if you've tried this yet? I'd like to know what you think of the Al ribs vs. the CF rod speed mod."

I'm planning on it ASAP. If it wasn't for the additional labor and cost having to raise the price, I'd love to make it stock and drop the speed rod option. I feel the speed rods may still be needed due to span-wise negative droop but maybe much less since the AL ribs won't lose camber under load. Can't wait to test all this and see!

Need to design a cloths wringer type contraction to just feed the tubing in and roll out the airfoil. Any toolmakers out there?
Feb 28, 2005, 10:31 PM
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maximal's Avatar
Warning! Too much "zooming around" with this great mod can lead to un-intended consequences!

(I got it down (bow/arrow/fishing line) but after it spent the night out there. Seems to have only cost me a burned-out servo, but jury is still out on the battery.)

-Max
Mar 01, 2005, 08:46 PM
Registered User
LittleJon's Avatar
I've just installed my aluminum ribs. I'll have to fly tomorrow and see how it fares. Certainly they're much closer to the rib templates than my original bamboo ones are.


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