Building a Javron Cub

Bill,
I had a thought, if you have not yet covered your stabilizers. Since it is a possibility that you might wish to add some extra tail area when you go on floats, now would be a good time to either add some plate nuts to the tip ribs or to weld in some bushings in the tubing. Generally the instructions for stabilizer fins just tell you to drill holes and bolt on the fins. If you have welded in bushings there will be less possibility of water/rust getting inside the tubing.

Bill, what animal hat is that? Small fox?

Wag@+2 - thats a Red Fox hat. Pete - great idea, unfortunately Stabs are covered.


Folks

Fuel Pod

Today I did a quick trial fit of the Airglass Fuel Pod. Seems to fit fine even with the extended stick and box built to handle that. (noted earlier in this thread).
I think I have offered my thoughts on this but if you will indulge me I will again. I think the fuel pod offers a lot of advantages.

The Bill Rusk "Build for 90% of your flying" rule.
Most of our flying is around the local area, putzing around the local grass strips, maybe to a nearby sand bar or gravel bar. Going over to a friends house/strip. etc. Then once or twice a year we go to Johnson Creek, OK18, New Holstein or someplace like that. The bottom line is for most of us 90% of our flying is local. For that mission we don't need a HEAVY, cross country, auto pilot, reclining seat, dual door, Cub with 72 gallons of gas. What we really need, for local fun flying 90% of the time, is a light, fun to fly, C-90 powered Cub. But some of us can only afford one airplane so we make some compromises. The idea is not to compromise such that we build a Cub for only 10% of our flying and don't really enjoy the other 90%. So.......do you need lots of fuel just to putz in the local area? Probably not! (unless your "local area" includes the Brooks Range). The problem with having lots of tank capacity is most folks keeps their tanks full to avoid the moisture condensation issue. Thus not only do you have the extra weight of the tanks themselves, you are carrying extra fuel, which effectively adds weight. So with the 24 gallon tanks you add about 15 pounds (I don't have an exact #yet but I will) then you add 12 gallons at 6 pds a gal = 72 pounds, and now... just fooling around the local area you are carrying an extra 87 pounds. With the fuel pod you can be light in the local area but strap on the pod, weighs about 25pds, so it will be heavier than the added tank weight between 18's and 24's but you have an additional 32 gals Vs 12 added gallons with the larger tanks. Light when you want to be light and fuel for the long cross country trip.

Physics
The more weight you have up high in the wing the easier it is to stand the airplane on its nose upon landing. When you brake all that fuel sloshes forward and then wants to rotate about the pivot point which in this case is the wheel axle. There have been more than a few of the cubs with 72 gallons of fuel (2 X 24 tanks plus 2 X 12 tanks, a common configuration on a lot of the Smithcub/Backcountry Cub kits) that have been stood on their noses. Its just physics. It is an issue on all aircraft with the fuel located up in the wings. Pretty common on a lot of the old biplanes. So the more fuel you have up in the wings the more careful you must be while braking on landing, thus longer landing rolls. Not only must you fly faster on final, to generate the lift required to support the weight, you touchdown faster and then can't brake as hard. A triple whammy. So a 20% increase in weight increases the landing distance by 40% or more. Rough rules - don't get too technical on me folks - I'm just trying to make a point. With the fuel pod the weight is low so braking hard has MUCH less adverse effect.
The pod does not seem to add any drag, and in fact, some have reported a slight 1 or 2 knot airspeed increase in cruise. It seems the pod smooths out some of the turbulent airflow from the gear struts. There may also be some adverse effect from extra fuel in the wings on the roll rate. A pod puts the fuel a little closer to the longitudinal axis of the fuselage. Thus the wings don't have to fight the longer moment arm to move that weight. In some circumstances it is much easier to add fuel to the pod (tough to stand on a ladder on floats to get up to the wing tanks) as the port is down low, then pump the fuel up into the wing tank.

Design
As long as I am on the subject of fuel I will offer another opinion. I do NOT like the fuel tank design whereby the tank hangs from the lid. Or where the top of the tank overhangs and is attached to the spars. This is UNSAFE. This is a feature of some, or perhaps all of the 30 gallon tanks. In a mishap, even a hard groundloop, that tank top will be ripped open spilling fuel everywhere. Big time fire hazard, and if you are covered in fuel, even if you manage to get out you will be badly burned. I have personally seen this (mishap at E.Tenn fly-in) but thankfully in that case there was no fire. This feature is also part of the Hatz Classic and I still don't like it. Put the tank in a cradle as per the original Piper Supercub design.
My last Smithcub had two 24 gallon tanks and they are nice but on this build I am going back to two 18's for all the reasons above.








You might remember from a previous post I welded in some saddles with a nut so I could use an Eyebolt to attach the pod strap. It will make for a cleaner installation and also less mess when the pod is not on. (disregard the safety wire, my eyebolts were/are not long enough so I will have to order the proper ones, this was just a test fit)


Top of the saddle. You do not have to worry about the eyebolt backing out. It can not rotate once the strap is attached.

I was able to find the pod used in Portland and I owe a HUGE THANKS to DW for storing it, and then for packing and shipping it to me. THANK YOU DW.

You can also do a combo pod with cargo space and fuel, or a cargo only pod and use some type of fuel bladders in the pod. The downside to that is it can sometimes be a real pain to find a place to land, lift a 30 plus pound bladder up on to the wing to transfer the fuel. Lots of options. Choose what works for you and your mission.

Hope this helps

Bill

I am a fuel pod fan...but...

...........one disadvantage of the fuel pod, that was not mentioned, is that if you knock the gear off your Cub and you have a fuel pod........you will be sitting in a bathtub of avgas.

A local rescueman pilot has seen this situation.....luckily, without a fire.

PS, Bill, does that nut open to the inside of the longeron?....

Dave

Hmmm.... yes it does. I can see where you are going. Yes, it should have been (Added... and was) bushed. I did not think of that. I will have to be careful to seal it at all times to prevent water getting into the longeron. Excellent point Dave.

Also - I had not heard of the "ripping gear off and damaging the pod" but that is a consideration.

Thanks for the inputs (lots of smart folks on this site - and Dave is one of them)

Bill

Bill,
I'm with Dave on this. By the looks of your project, it is not too late to weld in the bushings and seal up the longerons. You could even put some linseed oil in there before you close it up. Lower the tail while welding to keep it away from the heat.

Haha - in an odd twist of fate I actually did something right. After Dave made the comment about the pod attach bolt hole being open into the longeron, something in the back of my head remembered that I was grinding while my friend was welding the saddles. Why would I be grinding on that while he was welding? So, I went out to the hangar (no easy feat, it is about 20 below 0 right now with the chill factor) and checked. I did in fact bush all the holes for the pod attach fittings.
I just did not remember it. YaaHooo.

I feel better now.

Bill

I think your more likely to be on your back with 36 gallons under you then the oddes of tearing the gear off when you have your pod on.... Statistically speaking...yea I know Dave big word for me...lol


Good on yea Bill I was going to make a comment on that till I read further ...I remember us talking about you sealing the longerons.

DW

Does the thread go all the way thru or just in the nut? What size eye bolts are these.
I just bought a belly tank for my project and need to do these.
I am also interested in a cargo pod . Could the same eyebolt attach brackets be used for a belly tank and a cargo pod ?
Would they both use the same spacing ?

Bill,

I don't disagree with your logic on the location of fuel in a cub, particularly the part about large tanks seeming to always be carrying around a lot of fuel.

that said, the thing I never liked about belly tanks is that they put that weight further aft than wing tanks, and it's easier to get an aft CG.

i still like belly tanks, though, for the reasons you noted.

MTV

Good input Mike.

Knuckles - the threads are just at the nut welded on top. Here is a link to the post on how I did it.

http://www.supercub.org/forum/showt...g-a-Javron-Cub&p=575496&viewfull=1#post575496

It is an AN-3 eyebolt. I'm sure an AN-3 eyebolt would work for any pod but I'm not sure of the spacing.
I do not know if the strap spacing is the same for all pods but a quick call to Airglass would probably answer your question.

Bill

Fuel only and pod only strap location are different.

I used to have the 32 Gallon Landis tank. Didnt use it enough to justify having it, so I sold it.

I put one of the Firmin cargo pods on and use it when I needed to haul a load. Easy to install and remove, but I had to add a couple of additional rear tabs. Make a small slice in the belly fabric and slide a couple of strap clamps over the lower tubes. Easy to do - no metal work needed and a 2" slit in the fabric you're good to go. The forward straps utilize the existing gear bolts.

If you have float fittings, you may need to modify the rear float cable attach points or cut holes in the pod for clearance. Depends on your float setup - you may get lucky and not have to do any modifications.

Thanks for the info guys....

Bill , how are your wings coming? I think i am getting the same with squared tips....

Knuckles

I honestly don't know. I have not visited with Jay in probably close to 3 weeks. I told him I was swamped and would not be able to come up there until close to the end of Feb. He is probably trying to catch up on other customers. My wings were/are going to be the first set of square tipped wings so it was taking longer as he had to put everything he did into CAD, build new jigs, do some design work as the flaps and ailerons are longer, etc. Once he has it all figured out he should be able to crank out wings at a pretty good clip. I know that once he gets all his present orders filled, he plans to build a few sets up just for inventory so at some point in the future you should be able to order a set of wings, or a kit, and have them shipped within a week or two. That is his goal. I believe he will get there. I will probably visit with him tomorrow.
Bill

Bill,

I've searched this whole thread and haven't found an answer...so I'll just ask.

You are using B&C's 8 amp alternator, and as you know it doesn't produce full power until at or near cruise RPM. How are you going to operate a radio, transponder, EFIS (or other), lights, etc., with a maximum of 8 amps (or a design load of 6+ amps) with that alternator? I would think that taxi RPMs would put you completely on the battery.

I'd like to use that same unit on my Javron O-320 but I believe it will not be sufficient. Please help me understand what you're doing.

Thanks
Jasperfield

Jasperfield

Fair question. This is what I think I know and what the "plan" is.

GRT display = 1.0 Amp draw
Sandia Transponder = .82 Amp
ICOM radio = .5 amp at rest (max 5 amp while transmitting)
Garmin 796 = .6 amps
Total avionics = 3.0 amps (except when transmitting)

LED Nav lights Aveoflash ultra = approx 1 amp (avionics plus Nav lights = a normal load = about 4 amps)
LED Landing lights 1 amp each (current plan(pardon the pun) is to have two)

Bottom line is that in cruise parameters I should be fine, but in the pattern, while transmitting on the radio and all lights on I may be pulling, momentarily, off the battery. I know that there will be times when I am using more amps than my generating capacity will supply. It is my belief that this will work. Several other Cubs are using this and doing fine. It is possible that it may not work out and I may have to add a full alternator in the future. This also impacted my auto pilot decision as that would have definitely required a full alternator and thus added considerable weight. Depending on the load, taxi may be a negative draw as well. It is something I will have to be aware of. I will have a load meter that will show if the current is flowing INTO the battery or FROM the battery. Generally I think as long as I am charging more than drawing it should work out.

I spoke to Jay. Wings are coming along nicely, we discussed some fuel tank capacitance probe installation issues (more to follow on this) and a couple of other points. Jay is going to Alaska to meet with a couple of his customers there for about a week. I hope to pick up my wings sometime after he gets back. Probably around the end of Feb.

Hope this helps

Bill

Bill,
That sounds like a good plan to me. And to help ease Jasper's mind, my Cub has several electric powered instruments, a Garmin 695 and two landing lights running on a wig-wag. The total maximum draw is about 3.5 amps. There is no electrical generating system of any kind installed. I have flown it for several hours in one day, which included at least six engine starts, with no indication of running low on electricity. At the end of the day I put a battery charger on it.

I have entertained the idea of installing a wind driven generator. So far my use hasn't pushed me to do the deed.

The think I'm beginning to notice with this system (B&C 8amp) is that if I do a lot of short flights over say a few months all that engine starting and no real long term recharging the battery will begin to drain...so I've started to us a float charger to compensate .......this is most noticeable in the winter.

DW is totally correct with the battery drain, seen it happen.

Wow, can't wait to see what those wings will weight at, but 58.9lbs is really cool! What was it that a cub wing weight at 76lbs? What does a wing with CC ribs weigh at?
I was doing some carbon work to see if I can get wings at 43lbs, but it is still a WIP for me.

Bill,

Your load calculations left out the biggest single draw on your system....the starter. As DW says, if you make a number of short hops, the battery may not fully recover between starts. As he says, putting it on a maintainer when parked may be an easy solution. I found this to be true on my old SC which had the original generator, which put out 8 amps or something close (on a good day). After several flights, the battery would have to be topped off. Alternators charge at a lower rpm, but....

If you're out in the boonies, keep the right arm toned up. If you come out west this summer, you can practice that move on my PA 11....

MTV

Thank You, Bill, and skywagon8a,

I've been thinking about the 8 amp unit, but figured I'd have to go with the longer & heavier B&C model SD-20 (which will clear the tach cable and the oil filter bracket), which is 6"+ long. I'd about decided to use a front-mounted unit until I read your post.

Aside from visibility and resale I'd not light the airplane at all. Looks like I'm going to have to do some shopping for electrics in consideration of current draw. I appreciate the effort you gave to look-up and list your electrical equipment load. And, skywagon8a; Thank you for the practical information.

Jay DeRosier, at Javron, told me today that several persons have used the 8A alternator with good results.

Your Friend,
Jasperfield

Got up on skis with MMR in his PA12 today. Then Mark took our friends Cal and Pam up for their first ski rides.


Mark flying his PA-12 on Aeroski 2000's


Landing on 30R at Poplar Grove.


Mark, Pam, and Cal

Thanks Mark.

Bill

Looks like great ski conditions! Did Cal sit in "The Chair" for the ski ride? ...and WHO stayed back to mind Hind Sight??!

Bill, what's with Mark, did he lose his computer ? He could at least check in once in a while, him and Wilber WTF

I went thru the 8amp alt program , used them for 8 years finally enough !! B&C 20 amp on my plane since 2008 never a issue of any kind
I'll suffer the two lbs weight increase for reliability!! mikeo


Sent from my iPhone using Tapatalk

Good input Mikeo

Jay Derosier of Javron will be in Soldotna, AK talking Cubs and his kits. There will be an open house and Javron weldments to look at Johns place from 1400 to 1700 (2 to 5) this Sunday Feb 16th. If you are interested in seeing what his kits look like and want a chance to talk to him in person this might be a good opportunity.

Address is ....41477 Dolly Varden Way, Soldotna, AK

Bill

Sorry for any thread creep Bill, this needs to be asked.

mikeo said:

I went thru the 8amp alt program , used them for 8 years finally enough !! B&C 20 amp on my plane since 2008 never a issue of any kind
I'll suffer the two lbs weight increase for reliability!! mikeo

Click to expand...

mikeo,
Will you please explain what you mean about "reliability". Is it mechanical or electrical? My Kubota tractor has a small dynamo which looks just like the B&C 8 amp, only being belt driven. I have not had any trouble, of any kind, with it in over 25 years. I have been considering using one just like it, to make a wind driven generator for my Cub. They are relatively short money. That's not the main reason. There isn't anything small available for wind driven electricity generation.