I am updating the fleet after some years off and I have an old xp4 kit around that im going to build with a few changes... Adding some bagged tails and going to stiffen the boom perhaps... I was hoping to try top drive horns on this ship but it has servo bays already routed so i will save that for the seba wing/GT fuse/freak tails that i will build next.

anyway i noticed on the other xp4 i built a few weeks ago that wrinkles are beginning to form just outside the glass tape reinforcing the wing joint....i made that tape a bit wider than i think i used to but was wondering if maybe too wide distributes too much stress onto a weaker part if the wing...

By having a abrupt edge on the doubler you create a stress riser. The doubler in your picture is not idea. Its meant to join the panels. A ideal doubler would taper off along the thickest section of the wing

rand24:

You can still do top drive. I did, with my old Taboo.

It was easy: just cut off the control horns, route a hole through the wing, then install new control horns on top. I gained nearly ten percent in time, under near-clam conditions.

Yours, Greg

Top Drive = Highly Recommended

Originally Posted by rand24

I am updating the fleet after some years off and I have an old xp4 kit around that im going to build with a few changes... Adding some bagged tails and going to stiffen the boom perhaps... I was hoping to try top drive horns on this ship but it has servo bays already routed so i will save that for the seba wing/GT fuse/freak tails that i will build next.

anyway i noticed on the other xp4 i built a few weeks ago that wrinkles are beginning to form just outside the glass tape reinforcing the wing joint....i made that tape a bit wider than i think i used to but was wondering if maybe too wide distributes too much stress onto a weaker part if the wing...

In your defense, i've seen this same failure of the skins in almost every xp i've ever seen.

Brandon

ok on this wing i didnt use a doubler - just a regular tape piece...will see if it helps - i seem to recall having this happen a lot....

i am going to do top drive - will try and use 285's i have a mess of brand new ones...though yes they look a bit thick - i think i used to sand them down a bit ...looks like from the center of the screw head to where i am going to put a hole for the servo wire its 4mm...that doesnt seem like much...

i read about the ailerons needing to be faced but for now i just inserted the vertical grain balsa you see below - any idea if that wire is stout enough for the connections? it looks to be 1mm almost exactly.

haven't seen any good feedback on trying to stiffen the boom ...prob not worth the trouble?

Sporter [Sean] Has a nice option for stiffening booms. There are also threads decribing the use of 12k tow or carbon rods down one side of the boom , either way is quite effective

http://www.rcgroups.com/forums/showthread.php?t=1659784

For top drive:

When I converted my Taboo, I used 1/16 brass tube as bushings in the control horns (easier than it sounds: 1/16 hole, just barely seat a length of brass tube with medium CA, then Dremel it off short). The point is, the push rod I used was what ever wire fits easily in the brass tube, without slop. Whatever I used, it was certainly not 1mm in diameter, and pretty much fit without slop in the servo horns as well. (Yes, I admit it, I used D-47s! And, no, I never had any problems)

Yours, Greg

just in case anybody else ever decides to try this i thought i would complete this ...for tonight i thinned the 285's as much as possible and that means can only use a servo hole that is just outside the bearing ...this limits travel to about 8 or 9mm or perhaps a bit more but with all the torgue these servos have and the short flap horns hopefully just above the hinge line should be good - ...kind of became a bit of a battle to see if I could fit these servos in the wings with a flush "sticky vinyl" servo cover...we'll see

rand24:

You're doing it just exactly like everyone else has done it. Press on, with confidence!

Yours, Greg

rand24,

I've typically removed about 2/3 to 3/4 of the excess horn material shown on the outside of the hole in your picture. You can go a great deal thinner than you have done.

Gerald

Thanks thats very useful info...also ur fuse no. 6 next on the table...am trying to remember how to build b4 i get going on that