Question about wingspars

[ClipWing_T]

Hey Tcraft experts,

I have a question about my spars in my clipwing ,I am getting ready
to cover them and I was wondering about my spars .We used the original
spars when we clipped them(they look perfect)........but i was wondering
about the moisture level in 60 year old wood .Can a spar be too dry ? Would
it loose some of it's bending and springy characteristics ?........And be more
prone to cracking doing acro ?........You know that tree was probably 100
years old back in 1946 when they cut that spruce tree down , making our
spars a 150 years + old ? :-) .....I know they say wood doesn't have a
memory and fatigue like metal does ........but grab a green twig and bend
it and then grab a dried out one and bend it ????........I know good inspections are a must on these older planes and especially when doing acro
too. Any thoughts ........Hmmmm ??........I am betting I get some opinions lol !

Mike in Texas

[astjp2]

Re: Question about wingspars

You can get a wood hydrometer to check the moisture content, there is a Mil handbook on wood, it will give the specs, I dont remeber the number but I have seen it before. Check on the EAA website. Tim

[N96337]

Re: Question about wingspars

Mike, the more I think about this, the less I'd be worried about the moisture content of the wood. What would worry me, would be the glue joints in old original spars when doing acro. My spars were multiple piece (MANY scarf splices from the factory!!), and my airplane had spent most of its' life in very dry conditions (Arizona, etc.) and the old glue joints dried out and were failing when I took the wings apart. I'm not sure if mine was an isolated case, but that's what we found. Aside from that, I'd think the spars would be plenty strong regardless of the moisture content.
I'd head for a copy of ANC-19, Mil-S-6073, and ANC-18 to find out if they say anything about it.... interesting question, and as soon as I have some time, I plan on doing a little research myself.
JH

[Acroeric]

Re: Question about wingspars

Mike- not sure how you shortened the wings using original spars but your strut attach angles and locations will not be correct. I have seen this many times when folks just cut the inboard 3-4 feet of wing off. One in particular I ran across had both rear spars broken and the owner did not know it. I found it on a pre flight right before I was to go wring it out.

The Cole plans had you add a mickey mouse vertical brace to handle torsional loading caused by incorrect strut attach angles- similar to many clip wing Cubs. The Swick plans simply had you install the strut attach brackets at the corrrect angle keeping everything linear.

Call me sometime and we can talk. You may be ok but clipping the wings is much more complex than just cutting off a bit here and there. I have some photos I can share that will help show what I am talking about.

[ClipWing_T]

Re: Question about wingspars

My wings are ready to cover , They were modified the Mickey Mouse
way per the Cole plans. I do understand about the correct angles ,I
talked to Duane Cole several times and his Mickey Mouse wings never
came off ! .............. I will take my chances with my mouse wings.
I have a set of Swick plans too and have used some of Swick's mods.
My wings are 29 1/2 ' and have 1 degree of dihedral to avoid the droopy
look of the flat wing. 0-200 powered . I used to hang around Aero Country
(where the Swicks are based ) and I know Mike and have already heard many times of the superior design engineering of the "Swick T" . My airplane
is a hybrid and of course experimental .

[Acroeric]

Re: Question about wingspars

Mike-
Definately did not mean your wings were built poorly etc. . .I have seen photos of your ship and it looks awesome- I just meant that there was a better way to design the interface. I'm sure that the wings as Duane flew them are fine- I have 200 hours on a set of Cole wings with a 180 HP Lycoming doing all kind of crazy stuff. All I ever managed to do was partially collapse a leading edge but that was my fault with poor airspeed management.

My point is that there are dangers in re-using old spars and not addressing teh srtut angle. If you look at a wing loading diagram (reference some of the old NACA reports online) the area of highest stress is right outside the strut attach points. If they are linear then the stress is distributed evenly. If they are at a lesser angle (ala Cole) then the more G the more the struts try to bend the wing in a concentrated location at that high stress point. If you think about it like a rope holding up a given weight. Pull the rope to the side in the middle and there is not that much resistance. Pull the rope near an attach point and the force required is exponential.

[Guest]

Re: Question about wingspars

Mike-
Definately did not mean your wings were built poorly etc. . .I have seen photos of your ship and it looks awesome- I just meant that there was a better way to design the interface. I'm sure that the wings as Duane flew them are fine- I have 200 hours on a set of Cole wings with a 180 HP Lycoming doing all kind of crazy stuff. All I ever managed to do was partially collapse a leading edge but that was my fault with poor airspeed management.

My point is that there are dangers in re-using old spars and not addressing teh srtut angle. If you look at a wing loading diagram (reference some of the old NACA reports online) the area of highest stress is right outside the strut attach points. If they are linear then the stress is distributed evenly. If they are at a lesser angle (ala Cole) then the more G the more the struts try to bend the wing in a concentrated location at that high stress point. If you think about it like a rope holding up a given weight. Pull the rope to the side in the middle and there is not that much resistance. Pull the rope near an attach point and the force required is exponential.

Hi Eric,

I am completely unfamiliar with this?

Would you be willing to direct me to some of these sites?

Thanks, Dave.

[Acroeric]

Re: Question about wingspars

Dave- Recently it appears the server moved but this is the new location- I tried teh search feature and it stinks- sed to be pretty good though.

http://ntrs.nasa.gov/search.jsp?No=110&N=47+279

I used several of these reports in the design of my new wings/ wood ribs, and spars. Check out the dates on these- lots from teh 1930's

[Acroeric]

Re: Question about wingspars

Here are some reports I used: I could send you some more links but this should take about a year to get through!

http://ntrs.nasa.gov/search.jsp?R=794698&id=1&qs=No%3D10%26Ntt%3Dwing%252Bstrut%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

http://ntrs.nasa.gov/search.jsp?R=949150&id=3&qs=Ntt%3Dribs%257Cwing%252Bribs%26Ntk%3Dall%7Call%26Ntx%3Dmode%2520matchall%7Cmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

http://ntrs.nasa.gov/search.jsp?R=728291&id=8&qs=Ntt%3Dribs%257Cwing%252Bribs%26Ntk%3Dall%7Call%26Ntx%3Dmode%2520matchall%7Cmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

http://ntrs.nasa.gov/search.jsp?R=571582&id=9&qs=Ntt%3Dribs%257Cwing%252Bribs%26Ntk%3Dall%7Call%26Ntx%3Dmode%2520matchall%7Cmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

http://ntrs.nasa.gov/search.jsp?R=542530&id=1&qs=No%3D10%26Ntt%3Dribs%257Cwing%252Bribs%26Ntk%3Dall%7Call%26Ntx%3Dmode%2520matchall%7Cmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

[Acroeric]

Re: Question about wingspars

Last one- Here is the report I used in determining correct rib spacing for the clipwing. . . . .

http://ntrs.nasa.gov/search.jsp?R=282886&id=3&qs=No%3D20%26Ntt%3Dribs%257Cwing%252Bribs%26Ntk%3Dall%7Call%26Ntx%3Dmode%2520matchall%7Cmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c1

[N96337]

Re: Question about wingspars

Eric,
Just wondering if you remember anything that relates to his original question about the wood being too dry??? I haven't had time to sit down and dig through reference material yet, eventhough it's right here on my desk..haha
Thanks,
John

[Guest]

Re: Question about wingspars

Thanks Eric!

[Acroeric]

Re: Question about wingspars

John- I remember mention of a hydrometer as part of the certification process but nothing in any of the reports I painfully read.

How are the Clydesdales? Hope everything is good in Montana. I sure enjoyed my visit.

[pete]

Re: Question about wingspars

Drier is better for wood. The moisture tests for certification are to insure the wood is dried enough(or seasoned). Higher moisture content causes wood to lose strength and be more prone to rot. If there are no cracks or rot the wood is good. I too would check the glue joints and around holes and doublers where moisture might get into the wood and start decay.
Pete

[Len Petterson]

Re: Question about wingspars

Desing questions by Cris Heintz and many other have been answerd by reading : Analysis and design of aircraft stuctures by E.F.BRUHN.
I asked Cris heintz one time he visited our club if there a textbook on aircraft design and he recomeded it. I found a copy on the internet $75.00 1949 printing. apprently there is a 1952 53 printing as well. The book is in good shape. A previuse owner was E.F. Doyle of Ellis Ave. Chicago, Has anyone heard if him?
I am not a enginer but like reading and using book like this for reaserch material. Hope it helps.
Len