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Wingtip Screws

tacaruth

Well Known Member
The wingtips on my 7A are attached with stainless steel #4 screws. I just removed one of the wingtips to add an EFIS magnetometer. About 25% of the screw heads were stripped during removal (some may have been damaged during installation). Are there any better fasteners for this use?

Thanks in advance.

Tom, RV-7A N175TJ Flying
 
screw head stripping

use a new phillips head every time and avoid the tendency to strip. also I start and finish with manual driver.
 
Go with 6-32's

I have no idea who came up with idea of using 4-40's on the wing tips. There are no other 4-40's on the entire airframe, (7's anyway). They are way too small.

I originally used them on my plane during the initial build. When removing the tips for painting I stripped several, phillips head. I had the hardware and replaced them with 1000-6 nut plates. With the help of a friend we did the entire task in 2 hours. Now much easier to remove the tips.

If you are considering using the 4-40's do yourself a favor and go with the larger hardware. You won't be disappointed.
 
If you're using a phillips head screw, it will definitely strip. The only solution to avoid it is to go to a screw with a proper head that won't strip. The Torx screws from Microfasteners are an excellent alternative. I plan to upgrade to non-phillips fasteners every time I remove one on my -6, but I haven't decided between torx and robertson (square). I have to look around a bit and see what's available.
 
I agree that the 4-40 phillips screws are not very good. I would use #6 screws if I had it to do over again. I'm going to look into the torx or square drive ones since I don't want to change out the nutplates on the painted wings.

greg
 
I have many sets of wingtips that I switch

I have many sets of wingtips that I switch. I went with #8 hardware from the beginning and there have been no problems.

Bob Axsom
 
I have many sets of wingtips that I switch. I went with #8 hardware from the beginning and there have been no problems.

Bob Axsom

I don't have as many sets of tips as Bob (workin' on it ;)), but I too have #8 screws and nutplates and they've been easy to work with. Feels like too doggone many of them sometimes! :D And they are the same as the ones on my cowl and wing root fairings, so it makes for a little commonality of parts benefit (FWIW).

Cheers,
Bob
 
How often do people need to pull their wingtip?

I'm planning on pulled rivets, but I'm just wondering...
 
How often do people need to pull their wingtip?

I'm planning on pulled rivets, but I'm just wondering...

If I may offer an opinion ...

It would depend upon what is done in the wingtip and/or what is done in the leading edge.

If one is placing lights, strobes, antennas, and so on in the wingtips (or near the wingtip section of the leading edge), then it would be a good idea to have removable wingtips.

On the other hand, if one is building a day, VFR plane with little, to nothing, in the wingtips, then the pulled rivet method of attachment will probably work just fine.

I hope this helps!
 
Tap the Nutplates

Using SS with an all-metal locking device is an invitation to galling and stripping. Tap the nutplates. Run the tap in and out at least twice. I have never had a screw loosen in my wingtips since day one. On the other hand, I tried tapping out the nutplates on my wheel pants for the same reason, and landed at OSH a few days later with only four fasteners intact in one of the pants. I now use blue locktite, but only on the wheel pants.
Terry, CFI
RV-9A N323TP
 
I, too, am planning #8 hardware for the wingtips. I simply purchased an extra bag of tank attach screws and platenuts...just need to get back to work on 'em! :D
 
Another thought

I should have noted that I tested the SS torx before I abandon the 4-40's. Same issue. It is the same amount of work to put in 1000-6 (or -8's) from the get go without the later aggravation.

If you have lights, antennas etc in the tips, you'll need to check things out each year at inspection time.

I don't think you should run a tap into nut plates, it will cut material. I run a screw through each nut plate before install to "season" it. Makes things much easier. JDair is coming out with a jig for seasoning nut plates.
 
#8's on tips will make you unhappy. Too close to the edge. Will leave a wavy edge & puckers. Ask me how I know about these mother puckers.
 
#8's on tips will make you unhappy. Too close to the edge. Will leave a wavy edge & puckers. Ask me how I know about these mother puckers.

I've got #6 screws and mine are a little wavy. I really hate it! Do you know of a way to fix it so it's straight? I think some refer to this problem as "pillowing".
 
I've got #6 screws and mine are a little wavy. I really hate it! Do you know of a way to fix it so it's straight? I think some refer to this problem as "pillowing".
__________________
Nope, haven't thought of an easy way yet.
 
tapping nutplates

While I've heard of people tapping nutplates, it does seem to defeat the purpose. On all my nutplates, I use anti sieze compound when I first installed a screw, whether normal steel or stainless. That one-time application of anti sieze has made sometimes repeated installation and removal very good, while preserving the locking feature.

Just one more data point...

Jeremy Constant
RV7A Phase 1
 
I tap nutplates all the time. If too loose they can be resqueezed, no big deal. Few things **** me off more than ruining brand new fasteners the first time you remove something. I've had to drill out a thousand bucks worth of new tri-wings before and it's bad for everything around it. You'll damage these light structures more leaning on your tool than anything. I just finished a gear rebuild on a 51 yr old comanche and was reminded again that airplanes don't wear out. We wear them out taking them apart. Anyway, a new nutplate only contacts the screw on 2 sides. The tap does more rounding than cutting and may actually increase the thread contact area.
 
One small drop of oil....

...actually, less than a small drop. Just dip your #4's or #6's tip of the screw into some light machine oil. That is all it takes to keep them from stripping out.
 
Another choice I've used for some nutplates is to stick the end of the screw in Boelube .
 
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waves and puckers

I used a half inch wide strip of .070 aluminum on the back side of the wing tip, wetted it with epoxy, as I riveted the nutplates on. This does a really nice job of sealing the rivets into the fiberglass as well so hopefully preventing them from coming loose in the future and haveing "bleeding rivets".

I then used #6 screws per Van's spacing. Turned out very smooth. No waves, No puckers.

Hope this helps.
 
If you have 4-40 screws.....

I have them for my wing tips on my 6.

I had to take them off several times while fitting and filling the fiberglas imperfections.

I used the NAS514P440-6P countersunk screws

http://www.gen-aircraft-hardware.com/store.asp?alternate=NAS514P440-6P

They are made of high alloy (140ksi minimum) other steel or stainless is about 1/2 of that.

The real trick is to have a clean new quality #1 bit that is made for aircraft.
SORRY Ace Aero and Home Depot aero division.

Cleveland make a dimple die for 4-40 screws and the look pretty nice!

They also make a kit for the 4-40 set up. They do use the stainless but that works fine.

If you have trouble get a longer alloy steel 4-40 socket head cap screw, put a little lube on it and then put it in a reversible drill and (SLOWLY) exercise the installed nutplate, DO NOT TAP nutplates it ruins them.

Best wishes, I like the way the look:cool:
 
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I change wing tips and tip tanks several times each year for long range travel, long rang racing, short range racing and experimental development to get more speed. I have 48 or 49 platenuts depending on the interface. On some of my wing tips I installed a 1/2" wide 0.016" thick 2024T3 backing strip with rivets between the platenuts tying the aluminum and fiberglass together, on some I have the only the platenut mounting rivets tying the fiberglass tip and the backing strip together and on one set I riveted the platenuts to the fiberglass with no backing strip. None of them has given any problem whatsoever. I have never and will never tap a platenut. I do not usually lube the screws though I did some on the vertical stabilized cap yesterday after removing it to check the Nav antenna coax connection.

Once when I was investigating a recurring galling problem with the large titanium bolts used to attach the vertical stabilizers to the fuselage booms on the F-15 I found that the individual parts all met their requirements but the installation method, using a power wrench, was causing the problem due the heat buildup from friction during the relatively fast turning installation. The process was changed to manually install the bolts. I always install and remove the #8 screws with a good #2 Phillips screw driver. If your screw driver is worn out or is a cheap tool throw it away and buy a good one. I got some very good rubber handled magnetic #2 Phillips screw drivers from the local Tractor Supply Company. I would never use a power screwdriver on my airplane - you get no direct feed back from the work to help avoid damage (burred heads or bird heads if you prefer).

The wavy skin problem may be a hole preparation problem, a hole placement problem or an alignment problem. I do not have this problem with any of my 8 wing tips or my two tip tanks. The hole in the wing tip must not strike the dimple in the wing skin before the skin conforms to the surface of the tip. I satisfy this requirement by countersinking the wing tip sufficiently to allow the intimate flat surface contact between the inner surface of the wing skin and outer surface of the fiberglass tip or I open the wing tip hole enough to completely receive the wing skin dimple. I place my holes where they are needed to hold the skin and tips together - in the forward part of the wing I place them closer together and back where the airfoil curve becomes more gentle (nearer to being a straight line) the spacing is greater. I try very hard to get precise hole alignment between the wing skin mounting holes and the holes in the mating tip tanks and tips but since the holes in the skin are already in place and dimpled I will sometimes get a platenut installed in the pattern that is not quite perfect. I drill out the plate nut mounting rivets and install a floating platenut in place of the solid dimpled platenut I normally use. It is so pleasant to reinstall the tip with a floating platenut after the struggle to get all the screws in with some misalignment using only solid dimpled platenuts.

Bob Axsom
 
Good screwdriver is the key

Tom and Bob are right on about needing to have a good screwdriver. I have the 4-40 screws on my wingtips, and haven't had any problems. I've tried a lot of screwdrivers, including Snap-On, MAC, and etc., but the best I've found so far is the German Wiha brand. I've got both full screwdrivers and insert bits of their's, and their hex key bits fit better and hold better than anything else I've tried. They have an online store with fast turn-around. Give them a shot, regardless of what size screw you're using. ;)
 
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Excellent products

Tom and Bob are right on about needing to have a good screwdriver. I have the 4-40 screws on my wingtips, and haven't had any problems. I've tried a lot of screwdrivers, including Snap-On, MAC, and etc., but the best I've found so far is the german Wiha brand. I've got both full screwdrivers and insert bits of their's, and their hex key bits fit better and hold better than anything else I've tried. They have an online store with fast turn-around. Give them a shot, regardless of what size screw you're using. ;)

I've got a bunch of Wiha tools I use for my RC stuff. Top of the line stuff and reasonably priced.

Still don't like 4-40's on the wing tips.
 
I would replace the #4 nut plates with #6 for certain and use the Torx 100* SS screws. DO NOT tap the nut plates! Like someone else mentioned in this thread,,you will not get galling if you drive them by hand as you MAY get driving with a power driver. A tapped nut plate weakens it considerably, defeats it purpose, and is a sign of poor/sloppy workmanship. I cringe whenever I read someone suggest doing that as a "fix" for a nut plate doing what it was designed to do. If any of the nut plates are a bit tight, use a little Boe-Lube on the threads of the screw. And I agree,,,,,Anti-seize compounds ARE a mess!
 
I've used both -4 and -6 screws on my various builds. As long as you use the bit that comes with the -4 screws, they work just fine. I think -6 screws look good as well but you do need to be careful about edge distance. The best things to do is to peruse all the RVs at Oshkosh and see all the different ways that tips are attached and use the one that looks best to you. In either case I always try to the put the screw hole in the aluminum and the nutplate in the fiberglass attached to a strip of aluminum. Also, I don't like to fill in the gap between the two parts with filler either since it will eventaully crack and then chip due to different expansion characteristics.

Again, just my opinion of what works for me. Do what works for you and be happy.
 
I just replace them. Any time I remove screws I examine the drive portion. If marginal I throw them away. It happens a lot, especially on those 4-40 wingtip screws.
 
The fix, as others have mentioned, is lubricant. Use a proper screwdriver tip such the ribbed ones from Snap-On or the carbide Craftsman.

I use candle wax because it's not flakey like Boelube. A quick rub of the screw on the candle and it's ready to go. If the head gets damaged, toss the screw.

A local builder, who won an outstanding workmanship award at Oshkosh with his RV-7 uses hinge pins to hold on the wing tips. This seems to be a common trend: If Van recommends screws, someone uses hinges. If Van recommends hinges, someone uses screws. Must be the innate desire to change things.

Vern
 
This seems to be a common trend: If Van recommends screws, someone uses hinges. If Van recommends hinges, someone uses screws. Must be the innate desire to change things.
Van's did write up the hinges as an "approved" option for wingtips in a old RVator. It looks pretty slick, but whether I do it or not probably depends on how antsy I get to just fly the plane!
 
How often do people need to pull their wingtip?

I'm planning on pulled rivets, but I'm just wondering...

I installed my tips in 1993 with pulled rivets. I removed them recently only to change the tips to a different design and to install the Hotel/Whiskey ER tanks. Other than that I've never needed to remove them.
 
Van's did write up the hinges as an "approved" option for wingtips in a old RVator. It looks pretty slick, but whether I do it or not probably depends on how antsy I get to just fly the plane!

I went with the Vans approved hinge method. I knew I didn't want the 4-40screws and also had seen a few puckered tips I didn't care for.

RV-7build1056.jpg
 
run a tap through nut plates first, screws go right in, if you're marring the heads, you're doing it wrong

(i.e, wrong size bit, dirty threads, etc)
 
Wing tip screws.

Hi gang:

Another tool that might help is one of the new impact screw guns. They look like a battery powered drill, but are a impact screw gun. I used one to remove all the screws on my fuel tanks and was impressed with how well they work. The prices are starting to come down on them as well.

cheers, terry.
 
run a tap through nut plates first

I would recommend caution here because doing so will remove the "locking" feature of the nutplate. There's a reason screws & bolts take a little effort to screw into the nutplate. Although it will make it easy for the screws to go in, it might also make it easy for them to come out too--and on their own. Just saying.....
 
A tapped nut plate weakens it considerably, defeats it purpose, and is a sign of poor/sloppy workmanship. I cringe whenever I read someone suggest doing that as a "fix" for a nut plate doing what it was designed to do.
I just noticed this. Cringe away buddy, I've been doing this for a living for 30 years. Never had a nutplate "fail" and the screws don't fall out either. When you say that it "weakens them considerably" you're being subjective. In other words, you're pulling that comment out of a dark spot. Tight nutplates in thin sheets or composites often cause damage to the part itself, not just the fastener. Each situation is different. Others out there with buckets of experience will concur.
 
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