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Postby uscgairdale » Thu Dec 28, 2006 7:56 am

Here you can see how some of the glue is still stuck to the foam, but long ago the rest lifted off of the aluminium.....
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Postby ozzie » Thu Dec 28, 2006 6:39 pm

G'day all, just a futher tip on removing rivets. when drilling them out, use a 1/8 drill bit and drill into the head then use a small narrow chisel to knock the head off and then use a pin punch to knock the body thru the hole. this will prevent the hole from elongating. the bit of mandrell remaining in the rivit will usually cause the drill bit to run off to one side and butcher the hole. takes a bit longer but result in a much better repair.
As for the foam ribs. I have one totally rebuilt spar in storage. This is what i did to get over the problem of loose nose ribs.
I reskinned the leading edge as well. before i dismantled the spar i cut my new 12 ft section of skin and wrapped it around the existing skin to give it the bend around the nose. i found it to hard and ruined the skin on a previous attempt by just trying to fold around the foam ribs. i then dismantelled the spar and did the nessesary repairs to the spar. one section was replaced. i gave up on the foam and glue. and replaced them with ali ones similar to the ones you fit to the root end. i removed the channels that the foam ribs sat in and picked up these holes to rivet the new ribs in. On the inside of the skin i treated the suface with scotchbrite and dealodine and masked off where each rib went with masking tape and painted the skin with zinc chromate. fit the lower edge of the skin to the spar and then used epoxy glue onto the ribs and then complete the fitting of the skin to the top of the spar. i did the tip the same way only you have to make all the ribs for this individually as each is different. i used 2 inch thick hardwood as a mold to make the ribs. just trace the foam rib onto the timber cut the timber out cutting 1/8th inside the line for the thickness of the ali. drill two matching holes in the timber and your unfolded ribs bolt the rib to the timber and form the edges. radius the edges of the timber first. this is not as hard as it sounds. No more loose ribs. i figured that if you are going to open up the d cell for whatever reason it seemed to make sence to fix the problem once and for all. this spar is sitting up in the loft all wrapped up. i will do the other one when i have the time. i then intend to use these spars to built my new wings which will possibly use duracore foam to replace the blue foam fit the tapered trailing edge that some are now doing and fit spoilers to help get me into some tight outlanding areas and away from those hard suck thermals we have here in Oz. if you are going to replace any of the 4 ft spars and have to remove the u channels in the cap. i found that the channels are held in with double sided tape and do not want to come out. best to soften the tape with heat( i use steam for this) that way you don't destroy them.. the end result is one tuff spar.

happy new year all Ozzie
BLUE SKIES AND FULL TANKS
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Postby aroguetrader » Fri Dec 29, 2006 6:08 pm

Glad you mentioned the intimidation factor Dave...that has been a big reason for the stall tactics on my part, but hearing from you, Tyler, Ozzie and others, I'm much more confident that I'm not going to reduce my plane to a heap of scrap aluminum. Actually, if I remember my engineering mechanics correctly, a strong bond between those nose ribs and the stressed skin will help increase the torsional and bending strength of the wing...kind of like bulkheads do for a long tublar fuselage. All in all, it sounds like all of you feel much better knowing that there are no questions remaing about the structural integrity of your wings...and that's a big deal.

Thanks for posting the pictures Dave...I thought it was interesting that the ribs, in the the one shot where you've got them all lined up, are not all the same size...I think Ozzie mentioned that too...kind of weird. Also, you mentioned that you're using the PL Premium construction adhesive. I'm familar with the stuff, it's tough as nails, and will likely use the same, but wanted to throw this question to anyone who cares to comment.

Q...As the wing flexes under load, over time would it not tend to comprimise the glue bond since the glue is rigid? Would a flexible adhesive do any better over the long haul? Do you think a flexible adhesive would result in wing that's less sturdy?

Like I mentioned, I will likely use the construction adhesive, since it's so strong and plays nice with the foam, but plan to check into the adhesives other aircraft use...Moni and I think some of the LoPresti Grumman aircraft use bonded skins.

Thanks again for the inputs everyone...enjoy the New Year.

- John
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Postby uscgairdale » Wed Jan 03, 2007 6:53 am

Aileron bellcrank before....
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Postby uscgairdale » Wed Jan 03, 2007 6:54 am

And afer.
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Postby uscgairdale » Wed Jan 03, 2007 6:59 am

Ran one of my KFMs today and it still will only make 4500 rpms or so. The carb is adjusted properly and everything else appears to be good to go. My guess is that it must be overproped and can't get up to 6000.
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Postby lazairiii » Wed Jan 03, 2007 12:45 pm

This very thing happened to me with my 185's when I received the wrong pitched props. I was only getting 3500rpm's on brand new 185's. I did everything possible to correct this including changing carbs, but only when I put on new props did the problem go away and my RPM's go up over 5000. I'd look at the props first thing!
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Postby JPXman » Wed Jan 03, 2007 4:33 pm

no way to measure thrust in pounds eh? can you put your stand on a cart and have it on wheels, and use a spring scale to get a rough measurement?

if it is a 34/20" prop then 4500rpm isn't enough for a big KFM with tuned pipes.... my JPX with standard exhaust will spin up to 4350 at 2300' field elevation, and im pretty sure you're at sea level or close so your density altitude is much higher (more air, more HP)....

if you're really stymied, i can pull off one of my props and mail it to you for a comparison 34/20 prop...

T.

PS: i get about 90 pounds thrust at 4400rpm, 85 pounds at a lower rpm richened up a bit.

PPS: if youre rings are shot, then your engine will choke under load. have you checked the compression in the motor?
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Postby uscgairdale » Thu Jan 04, 2007 6:01 pm

Good points guys. I have checked the compression and it is very good. That's probably the only good news that I've had with these engines.

4500 rpms is a long long way from 6300 for max smoke. I'd like to get at least 5800+ for a static rpm. It must be the props.....

Dave
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Postby JPXman » Thu Jan 04, 2007 9:46 pm

what kind of adjustments do you have on the carb? can you "peak it out"? take it through the peak and then have the rpm come down the more lean it gets? is that where you get 4500rpm, at that peak?

any blockage in the exhaust? leaky exhaust gaskets? is the choke stuck on?

just brainstorming

T.
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