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Building a Javron Cub

I weighed the PA 14 Wing yesterday.

A new stock, uncovered Univair PA 14 wing weighs 75.5 pounds. That is without flap, aileron, fuel tank, tank cover, or landing light, but includes the flap and aileron tie rods.

I didn't get the flap, aileron, tank, or tank cover weighed yet, but I will next time.
 
P1010932.jpg

The problem.......need to mount the wing tip light. The standard SC standoff mounts don't really work so well on the square tip wing, and they are 65 bucks a piece and they are heavy...........


P10109331.jpg

The solution. Lets make our own mounts......


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Start with some .025 2024. Drill a couple of holes so the light will fit on it.


P10109371.jpg

Mark the shape......


P1010938.jpg

Cut out some tabs and bend them down.....


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Sand the edges so it has the shape you traced out.....


P10109401.jpg

Wrap it with .016. Note the use of the small C clamp. This pulls it tight to the inner piece.....


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Drill, cleco, dimple, etc.


P1010944.jpg

So simple, even I can do it. Final weight with 4 attach screws .81oz

I will finish the CF leading edge install tomorrow or Saturday.

Hope this helps

Bill
 
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Wiring Info


Hey folks. Here is a tip. I used this wire ............

FatWireblurb.jpg

in my last Cub and was so impressed I am using it again. I will also be putting it in Greg Campbells Cub this next week. Great wire, very light. Highly recommended. I used #4.
Here is the info on it taken from his website....



Super-CCA FatWireTM—The Ultimate Copper-Clad-Aluminum Cable
Copper is the best bulk conductor after silver, but if you want the best conductor per weight, aluminum is more than twice as good as anything else! It’s almost magic!
However, using aluminum wire in aircraft became unpopular years ago mostly due to half-vast ideas, misapplications and some regrettable misunderstandings about how and where it should be used. How unfortunate...!
But your electric company has no whacky “Aluminum Superstition”. Both aluminum and copper are great materials if you know how to use them.
However, we get the best of both metals if we bury each aluminum strand in a copper cladding (called CCA). This copper cladding is not “plated-on” but cold-fused to the aluminum rod before the first draw in the wire-making process.
Advantages? You can save a heck of a lot of weight, especially if your battery and starter are a horseshoe’s pitch apart.
Application? It works just like copper, has the low corrosivity of copper. In fact, it crimps the same and solders even easier than copper.
It’s covered with a special low-weight, high- strength, cut resistant, 140 °C, fuel proof, flame retardant insulation suitable for aircraft, just as you would expect.
It’s just like we’re in the future! Isn’t it?
The Super-4-CCA is made with hard-drawn Copper-Clad Aluminum to match the conductivity of AWG 4 copper cable. The Super-4-CCA is slightly larger but weighs 40%-50% less than copper.
$3.79/foot with a 15’ minimum. We can furnish 1⁄4” hole ring-tongue lugs too--$5.75 each. Samples are available, discounts too, please inquire.
Shipping is by UPS, USPS, and FedEx at cost. Payment by Paypal, Visa, MasterCard, cash or cheque. 05DEC2012


Here is a link to the website http://periheliondesign.com/ He has lots of other great stuff like wigwag modules, Over voltage stuff, etc.

So, even though you may not have a super long battery run ( I still recommend the battery on the firewall), I think this stuff is worth it.



Also.....I used this tool to make my crimps for the lugs



tt5000_with_no2_dieset_small_yff4.jpg

......http://theterminaltool.com/ worth every penny.

Hope this helps

Bill
 
More Wiring Info



You can use grommets to protect the wire where it passes through the ribs or you can use snap bushings. The snap bushings are about 1/2 the weight of the rubber grommets. 6 grommets weighed 4.6 grams and 6 snap bushings weighed 2.1 grams. Just thought you would like to know. ;)
I used 1/4IDx 3/8OD snap bushings.
The three 18 gauge wires out to the wingtip LED light weighed 7.7 oz per wing. You might be able to use a smaller wire for the LED lights but to keep everything simple I use #4 for the battery to starter, #8 for alternator, and battery to Buss, and 18 gauge for everything else.


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Snap Bushings.



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Snap bushing in the rib. It is 2 3/8 inches down from the top of the rib and 5/8 back from the front of the rib. This clears most everything, but you do have to adjust it slightly where it goes through the rib next to the aileron cable pulley.




P1010947.jpg

I doubt it is necessary but I like to put a piece of shrink wrap on the wire where it passes through the snap ring.


Hope this helps

Bill
 
Bill,

this has been said before, but your willingness to post these tips and techniques, in words and photos is incredibly generous of you. And your attention to detail should be an inspiration to all in how to perform even the simplest task the right way. Your attention to detail with regard to weights, and posting weights should save others a lot of research.

MTV
 
Bill thank you for your time in putting these helpful post together, they surely take time away form your build, so unselfish of you!!!
 
Eric - no, but I might look into doing a little of that. Good idea.
Mike, Mike and Jose - thank you for the kind words.
Had an input regarding my recommendation to put the battery on the firewall.......
Please don't encourage moving the CG forward without further explanation. Moving a battery to the firewall, to save the weight of a section of wire is not wise.
With everything else being equal, it may require more ballast at the tail post, because of moving the battery forward, than the weight savings of the length of wire. Of course you know and understand the disadvantages of forward CG, but there are some on the forum who do not.

These are wise words and I was remiss in not offering an explanation. With the added weight of larger engines, props, cowling to accommodate said larger engines, etc., it is quite possible, in fact quite likely, that your CG may end up being too far forward and out of the approved range, which would then require ballast in the tail to get the airplane within acceptable limits. In that case moving the battery aft would be a wise choice and the weight of a couple of wires a necessary compromise for safety. If you are diligent about firewall forward weight, using light weight starters, alternators, engines (no angle valves), composite props, etc. I feel it is a good option. But, if you plan to use a heavy engine with a constant speed prop or a heavy Pawnee prop you would probably be better to place the battery further aft.

STRESS RISERS - Many moons ago I took a class by Charles Dole at the University of Southern California (USC) on Aircraft Material Factors. One of the topics we looked at was the issue of stress risers and their impact on material failure, especially as related to aircraft. The textbook is available here for those engineering types that might be interested........... http://www.lancaironline.net/bookstore/lancair/aircraft_material_factors.htm

A stress riser is a point of localized stress. Imagine the evenly spaced isobars on a weather chart. Now when those isobars get crammed together we get high winds. Metal has grain that is evenly spaced, like isobars, but when we jam all those grain lines together we introduce a point of localized stress (high winds). You have a nice wing spar but you put a pretty good nick in it where your grinder got away from you a little. That nick is a stress riser and a crack could start right there. So...... tool marks, gouges from grinders, slipped drill bits, and things like that are bad. Square corners are bad. One of the most interesting aircraft mishap investigations centered around the concept of stress risers was the DeHavilland Comet. Here is a short summary of that for your aviation history education...

http://aerospaceengineeringblog.com/dehavilland-comet-crash/


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So.....while drilling into the spar cap to attach sheet metal I placed a piece of aluminum behind the cap to prevent the drill bit from hitting the main spar web when the drill bit broke through. A piece of masking tape holds it in place. So when drilling into the spar cap or working around the spar, try not to mess up the main web. The spar cap (that u channel on the top and bottom) is less critical than the main web itself. Now, I don't mean to scare anyone into thinking they can't build a Cub, it is not THAT critical but I wanted to introduce a new concept and term to those of you who might not be familiar with stress risers. And if you are going to drill into the cap be sure to protect the main spar web.

Hope this helps

Bill
 
Hi Bill. I am once again questioning a "master" on here and it makes me very nervous. BUT while protecting any part of the build is important, are you positive the spar web is more critical of an area than the caps? My understanding was that the load is all carried on the top and bottom spar caps and the web is just to keep them separated and stable in relation to each other I-beam style. I know the very top and bottom of the spar cap is a "no-drill, no-scratch" area but the web gets all kind of holes in it everywhere. The sides of the cap get holes but I think they are only close to or less than the thickness of the cap edge wall which I believe is considered all right in engineering practice.
Again I'm not questioning the need to protect everything during the build or stress risers which are both valid and important points but I am questioning whether the cap is less important than the web. Are you sure about this quote: "The spar cap (that u channel on the top and bottom) is less critical than the main web itself." If that quote is true I need to go back and review some of what I thought I knew or else I didn't understand the quote correctly.
 
Qsmx, all parts of the spar are stressed. Tension/compression are maximum at the top and bottom, but not zero in the web except at the center. Transverse shear is maximum at the very center of the web. The portion of the web Bill is referring to is stressed in tension/compression approximately as much as the extreme top or bottom part of the spar cap. Within the part of the web that is not surrounded by the cap shape, the tensile/compressive stress is linear with position, being zero at the center (where shear stress is maximum), and maximum at the outer edge. Hope this helps to clarify - -
 
Great points Bill, as always you continue with great explanations of the what- as well as the why. My only comment here is concerning battery placement. I am with you on the firewall install. Move as much of the empty weight forward as you can( keeping in mind forward C of G limits of course). Reason being is that you will never hear of a cub being loaded to gross AND having the CG too far forward. Every damn thing that you put in that airpkane (except the pilot) is located aft. Now if your mission is lots of solo flying with light fuel then a forward CG may be a concern. However anytime you want to take a friend/ go camping/ do any flying other than a turn around the home patch, you will more than likely have way more weight than you want/need to get the airplane comfortably into the middle of the CG envelope. Even a 20lb dinosaur of a battery mounted 2 feet forward of CG will be offset by that tool kit, survival kit, or big lunch stowed in the aft baggage.Once again, final decision must made made by the builder and be a mission-based choice.
 
Qsmx, all parts of the spar are stressed. Tension/compression are maximum at the top and bottom, but not zero in the web except at the center. Transverse shear is maximum at the very center of the web. The portion of the web Bill is referring to is stressed in tension/compression approximately as much as the extreme top or bottom part of the spar cap. Within the part of the web that is not surrounded by the cap shape, the tensile/compressive stress is linear with position, being zero at the center (where shear stress is maximum), and maximum at the outer edge. Hope this helps to clarify - -

It does help. I was "told" somewhere that the top and bottom of an I beam carried all of the tension/compression and I always kind of thought it must be a logarithmic function building to a lot of pressure near the edges (top/bottom). It is interesting to find out it's linear through out the spar starting at the center. I don't know for sure what transverse shear is.
 
Bill, also the guy that worked with me on my wings, stressed to center the screw hole top to bottom. If not anything, less likely to twist a screw off in the thinnest part in the center. And if to close to the bottom the possibility of a crack forming.
 
Bill

Good advice, as usual. The backing plate is a nice safeguard.

Always using a drill stop set so the tip barely penetrates the metal being drilled is also a good idea.

The CC build manual makes repeated reference in bold red text to the critical importance of not drilling the spar bulb and areas you mentioned

Chuck
 
Folks

It is tough to try to write a thread with soundbites. :oops: Sometimes when I try to simplify things (and not put everyone totally to sleep) I over simplify and don't cover things very well. QSMX440 - you are correct that the spar cap carries most of the load. I did not do an adequate job of defining the cap.

P1010950.jpg

The blue tape is the spar cap. The masking tape area is the part of the cap we can safely drill into.

Most cracks propagate from the web, thus the attention was given to that area. The outer edges of the web and the top/bottom cap are the areas we need to be especially careful of stress risers.

Wronghand - You are correct that in a perfect world the airplane would be "near" the forward limit when empty, as everything we load into it pretty much moves the CG aft, (Advantage of pods) but with 180 hp engines, heavy props and all that it is quite easy to build a cub now with the CG too far forward.
A forward CG is bad but generally not unsafe, an aft CG is unsafe. But the airplane flies like crap with a forward CG.

Remember, the SC was designed with the C-90 engine. Everyone talks about how great the early C-90 powered Cubs fly. I don't have the CG of these cubs as they came out of the factory but I think it is safe to say the CG was in the middle or even a little toward the aft part of the range. That is why they fly so nice. As Piper increased the engine size the CG kept moving forward, in limits, and the handling deteriorated, but that was offset by the guys loading it to the gills and it flew well as the CG had not gone out of the aft limit, (maybe) so everyone loved the 150hp SC. Then we added the bigger prop and 180hp engines and the airplane really is a dog when you get right down to it, from a pure flight control harmony standpoint. So we have guys like Jason G with his no electric 0-290 powered Cub, the Breeden Cub, the C-90 Cubs, that have a light firewall forward package and those cubs fly outstanding. Thus we have a dilemma. If you want a Cub you can load up and go camping you will need the empty CG near the forward limit to keep from going out the aft limit when you load up all your gear. But when light and just flying around the local area the handling will suffer. If your empty CG is near the aft limit the airplane will be wonderful to fly when just bombing around (90% of your flying for most of us) but you can have real serious safety issues when you load all your gear as the CG will likely be too far aft and out the aft limit. Thus I put in a place to bolt in removable lead in the tail area. When bumming and playing around I can have the great handling that comes with an aft CG, but when going X/C that lead can be removed, and the camping gear will not take me out of the aft limit. This is experimental folks, you certified guys can't do this. Here is a link to my post that shows the picture of the structure Jay welded in for me to accomplish this.
http://www.supercub.org/forum/showt...g-a-Javron-Cub&p=525508&viewfull=1#post525508

The bottom line here is that CG is REALLY important, from both a safety and handling point of view.

Hope all this helps

Bill
 
We fliers in the LSA camp have seen the same thing happening: very light plane designs that started out with 2 strokes 30 years ago and weighed less then 500 lbs, now have morphed into 130 and even 180 horsepower planes with the same wing area in most cases. Empty weights are now over 800 lbs! Many times the reasons stated for this power increase is "to make it a better back country plane", if so it sure isn't in the landing/short field phase! Making a plane heavier and more powerful is so seductive, people can't seem to help themselves, not to mention the space shuttle type panels I see guys putting in a plane meant for local flying mostly. You summed up the SC progression in power and weight, and it's effects, perfectly, and this more is better thing continues today in other designs. Sometimes less is more.
 
Curtis Pitts used to call these builders who always needed more, morons. They keep building and redesigning and putting more stuff on. Building to suit one's own tastes will always be a series of compromises. Look how Van's aircraft have morphed into "mini 767's" Van started his own design with an O-290 with no electric in a single seat airplane which he flew from oregon to oshkosh many times. My 2 cents worth and I should probably mind my own business.
 
Bill,

I can't disagree with your assessment of CG. You're correct.

The solution you propose, however, (adding a removable lead weight) seems pointless to me. I agree with wronghand on this: We almost always carry (or SHOULD CARRY) survival gear and perhaps a small tool kit wherever we fly. So, rather than add a removable lead weight (read useless weight), why not devise a "compartment" for a small tool kit (useful) or survival kit, which safely stores that (those) "tools" far aft while you're gee king around empty, but that allows you to move them forward as necessary when you're loaded up.

I suspect you'll find that it's probably not really necessary to actually move these things, once you get the plane finished and weighed. Your pod and or float lockers will help to keep heavy stuff forward when loaded.

And for for the naysayers on forward batteries, bear in mind that empty CG isn't what's relevant....loaded CG, including minimal loading of course, IS what is important. The aerodynamic characteristics of a plane sitting on the ground aren't of much concern, operationally.

MTV
 
I always think about my airplane with my average load. To round out it's usefulness I need to maintain a balance of landing distance and take-off distance with anticipated loads. It's not unusual for an average pilot in an average airplane (I'm average in my view) to get down and stopped in distances he can't get back out of. Add more load and that spread increases. Add obstacles and it increases more. The solution is thrust/power. It closes the gap between landing and take-off distances for loaded airplanes. Or float planes. If you never load the plane or fly floats it probably doesn't matter. If you rarely fly empty the idea that a light basic plane is superior doesn't matter. Configure your plane to suit your needs.

Center of gravity can be described as balancing a teeder-todder. Don't discount the importance of center of mass.
 
Thank you Bill and Gordon. I was checking my own info as well as yours. You are right about the sound bites. You have good writing skills so you are not as likely to mistakenly ruffle feathers as some of us with lessor skill. Thank you so much for your posts. I'll try to go back to learning now and stop with the "nit picky" questions for a minute or so :)
 
Folks

I sincerely enjoy and appreciate the inputs from everyone. A big reason for this thread is for everyone to learn, INCLUDING ME, so having other opinions, inputs, data, etc is all good.

Since we are there lets run with the whole CG thing a little.

numbers are rounded off for simplicity, from my last Cub

I used the prop face as my datum so that all numbers are positive, CG range 71 to 81

Prop face = 0
Firewall = 35
Panel = 53
Wing LE = 60
Main Axles = 62
Tanks = 82
F. Seat = 70
R. Seat = 99
Fwd Baggage = 118 (area in front of dogleg)
Aft Baggage = 153
Tail Post = 250
Tailwheel axle = 264

L wheel 537 x 62 = 33294
R wheel 530 x 62 = 32860
Tailwheel 74 x 264 =19536
____________________________
Empty 1141 = 85690 = 75.1 CG (range is 71 to 81)

Lets add oil
Oil 6 qts/12 pds at 24" = 288 85,978/1153 = 74.5 CG w/ oil

Pilot 200 at 70 = 14000
99798/1353 = 73.7 This is the most forward CG (it is with me and empty tanks)

Fuel 48 gal x 6 = 288 x 82 = 23,616
123,414/1641 = 75.2 So this is my most forward CG with full fuel

Lets see what happens when we add a 50 pound survival/tool kit at the back of the baggage compartment. The very aft edge of the compartment is at 167 inches but the center of the kit will be a few inches in front of that so lets use 160 inches.
50pds x 160 = 8000 (+123,414 previous moment) = 131,414/1691 (previous weight + 50 pds) = 77.7 not bad but the end of the range is 81 so it would take over 100 pounds in the very back of the baggage compartment to get over 80".

I like Mikes idea of a small rear compartment to hold the tool bag. Neat idea. Too late for me but a great idea.

Now lets put 30 pounds of lead in the back. 235" is where it will be.
30 x 235 = 7050 (+123,414)/ 30 (+1641) works out to be 130,464/1671 = 78 So even adding 30 pounds to the tail still leaves us well short of the 81 goal and in fact it would take about 60 pounds of lead in the tail to get the CG to 81"

I am not going to put 60 pounds of lead in the tail but it still gives you an idea of the dynamics of the envelope. You will also note from that my most forward CG is still well aft of the forward limit. This is from my last build but I doubt my numbers will be significantly different, though lighter, I hope. Now if I add a passenger that moves the CG aft, so lets see what a passenger + 30 pounds of lead looks like.....

Pax = 200 x 99 = 19,800 moment + 150264/ (200 + 1671 = 1871) = 80.3
So if I use 30 pds of lead in the tail I can haul a 200 pound passenger around the local area and be in limits.

So .....does that mean I should put my battery further back? Lets run the camping numbers......

airplane with pilot and full fuel as above = 1641pds at 123,414 moment = 75.2
passenger (future wife = 110 pds in full makeup, heels, skirt (ahh come on we have to have a little humor here, LOL))
OK, OK I've got a big friend 250 x 99 = 24,750
Camping gear 75 x 123 = 9225 fwd baggage area
Camping gear 50 x 153 = 7650 aft baggage area

165,039/2016 = 81.8 I am out of the aft limit. I need smaller friends, less camping gear, or I need to start with my CG closer to the forward limit.

All this is somewhat hypothetical but it gives you an idea of the numbers I am playing with. YOUR AIRPLANE WILL BE DIFFERENT. DO NOT USE THESE NUMBERS FOR YOUR AIRPLANE.

Hope this gives you something to think about.

Bill
 
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I don't know about weight and balance and it not done yet. But I tought it was a good and simple idea to put a rear ''cargo'' and maintenance door front of the tail surfaces. If neccessary, I could put my tool and survival bag there. And it will be handy to tie one piece fishing rods, or a couple 12 feet wood 2x4... I do have a velcro attach separator to insulate normal extended baggage to fuselage extended bagage.


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So even adding 30 pounds to the tail still leaves us well short of the 81 goal and in fact it would take about 60 pounds of lead in the tail to get the CG to 81"

Bill, like everyone else I'm enjoying your posts and appreciate the details and tips and time you're putting into this 'build manual'.

From the above quote and comments you made in earlier posts are you saying that operating at the extreme aft limit of the CG envelope is or should be the goal? Or perhaps I'm reading this wrong (most likely). I like a more reward loaded CG too and have some weightier items as far back in my extended baggage as it will ride including a tool kit and jug of water. I like the CG farther back but not at the limit. It seems to come in on final and touchdown nicely there and I can get on the brakes hard. I find though that with a backseat passenger I can almost run out of nose-down trim until the airspeed gets low. I like my CG back there too but not all the way back.
 
Dan

Honestly, I don't know yet what I will like. I suspect, as you mention, full aft may not offer the best flight control harmony and feel. I will just have to try different CG positions to find the sweet spot. I was really just using that for illustration.

Bill
 
Qsmx wrote: "I don't know for sure what transverse shear is." Sorry, that's not real intuitive until you think about it in this way - - Shear (adjacent elements of a substance trying to slide past each other) occurs in a spar subjected to bending because the outside of the bend is stretching while the inside of the bend is compressing. The farther from the center, the more stretch and compression, and the maximum difference in stretch and compression occurs at the center (the neutral axis). As adjacent elements lengthen and shorten next to each other they try to slide past each other, resulting in the shear stress called transverse shear.
But really, that's just a side-note on what Bill was pointing out. Nicks in the surface cause a local increase in tensile stress which can be critical, especially in fatigue situations. So as Bill is pointing out, the fewer geometric discontinuities (nicks) at the outer part of the spar (the cap area), the better.
 
Bill, like everyone else I'm enjoying your posts and appreciate the details and tips and time you're putting into this 'build manual'.

From the above quote and comments you made in earlier posts are you saying that operating at the extreme aft limit of the CG envelope is or should be the goal? Or perhaps I'm reading this wrong (most likely). I like a more reward loaded CG too and have some weightier items as far back in my extended baggage as it will ride including a tool kit and jug of water. I like the CG farther back but not at the limit. It seems to come in on final and touchdown nicely there and I can get on the brakes hard. I find though that with a backseat passenger I can almost run out of nose-down trim until the airspeed gets low. I like my CG back there too but not all the way back.

Dan,

Aerodynamically, operation at or near the aft limit provides the fastest cruise speed for a given power (I know...it's a cub), and provides the lowest stall speed. Move the CG forward and the stall speed increases and cruise speed decreases. May only be incremental amounts, but....

This is why Bonanzas are easy to load aft...Beechcraft designed that airplane to go fast. Aft CG means less tail down force required, thus less induced drag from the tail surfaces.

But, as Bill says, the "Feel" of the airplane may be another story altogether.

Bill, good illustration of the envelope on a representative Cub.

MTV
 
Very well said Gordon - Thank you.


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Pitot line. From Home Depot. I think it was about 2 bucks. Perfect.


P1010953.jpg

I will put an adell clamp where it curves down to exit at the jury strut attach fitting.


P1010952.jpg

Those neat little snap bushings we used for the wire will work perfect for this line as well.


Hope this helps

Bill
 
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