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Building a Javron Cub

Nope, it wasn’t an “S”. The frame was thoroughly covered with zinc chromate, and tubes treated. I don’t think that aluminized treatment started till much later in production.....like late 70s?

When they pulled the cotton off, that frame looked nearly new.....I wasn’t the only one amazed. As far as I know that plane was never hosed down after being in salt water. I always tried to land in fresh water and splash around some before going home, but never hosed down.

MTV

I worked on a Clipper from 1949 that had it.
 
I worked on a Clipper from 1949 that had it.

Interesting. Of the ~ 25 or so Super Cubs I’ve flown, I’ve only seen one with the aluminized frame, a late 70s airplane, and that one was a disaster.....lots of corrosion under the coating. I’ve never flown a Cub with the “official” S designation.
 
Remove the small aft metal clean out. Place a hose through one of the stick openings in the floor. Turn water on. I'd like to fo the same under my Cessna floor. 40 years worth of hydraulic fluid and sand need to be melted out with a good supply of hot water.
 
I bought an -18/150 in 1981 ( it was a 1960) that had the original cover on it, and it had the aluminized tubing in it.
 
This '52 A model I'm building has the aluminized frame. That along with some brown gooey oil all over the lower tubes and tail area kept the frame real clean.
 
Oversized Elevators

At times I have felt like I was not able to drive my wing to its full AOA potential. Also I felt like I was running out of elevator in the flare. So I decided to try a new set of larger elevators. I'm sure many of you will know what I am referring to, but for others, it is possible to get (in the experimental world) a set of elevators that are about 15% larger than stock. They have essentially the same shape, but the trailing edge is extended to give more surface area.
Prior to putting the new elevators on I flew the Cub too try to get a baseline set of data points so I could make a more scientific evaluation of the performance gains, if any, rather than just "feelings", and to hopefully create a experiment with some validity.
The only variable changed was the elevators. The aircraft was refueled after the first flight to try to keep the GW the same. All Stalls, and slow flight was done at 3K MSL, in the same direction (to mitigate wind affects), etc. The landings were done at the same runway. The temp did go up as the day progressed so the actual DA changed a little as well. The increased density altitude would show a higher stall speed based on TAS but since I used "indicated" speed for my measurements DA has no significant affect. All events were done three times to get an average number and to increase reliability. Accuracy was based strictly on my instruments. I did not outfit my cub with additional measuring equipment.


IMG_21543.jpg

I covered the larger elevator in the back with a sheet to give contrast. White on white was hard to see.


IMG_2155.jpg

It is about 3" larger for most of the trailing edge


IMG_21561.jpg

They don't nest very well so this is an approximation.

Stock Left Elevator = 91.02oz
Stock Right Elevator = 90.0oz
Oversize Left Elevator = 99.96oz
Oversize Right Elevator = 100.26oz
Total weight gain 19.2oz

The test was done with my cub in the following configuration......

Stock cub, square wing, VG's, fuel Pod, 180hp, 3" ext gear, 31" Bushwheels, Cato 84/43, CC gap seals,

Aircraft Gross weight during test 1450. GC @ 76.8 (CG based on prop face datum, range 70.5 to 79 ((subtract 60 for wing LE datum)) The aircraft was trimmed for 60 mph, and the trim was not changed throughout the test in order to reduce the variables.

The
baseline flight was done with the following ATIS....Winds 200/3, 9C, and 2995 on the altimeter
The new elevator test was done with this ATIS............winds 250/7, 19C, and 2984 on the altimeter

Baseline Flight Test
No Flaps, Power Off, stall at 45mph indicated, 14 degrees pitch
No flaps, 1500 RPM, stall at 41
mph indicated, 18 degrees pitch
Full flaps, power off, stall at 39
mph indicated, 18 degrees pitch
Full flap, 1500 RPM, stall at 36
mph indicated, 21 degrees pitch

Slow flight can be maintained at 38
mph indicated with full flaps 1600 (approx) RPM and will break at about 22 degrees pitch

4 sets (of three) landings were done. Final flown at 50 mph indicated, 1200 RPM, and 350 sink rate to the flare, with two notches of flaps (three notches available)
1) Idle RPM in the flare - TD at 39 mph, could not get the tail down before the mains. Definitely feel like running out of elevator
2) 1200 RPM in the flare - TD at 39mph, resulted in a 3 point at best
3) 1400 RPM in the flare - TD at 39mph, resulted in tail first.... barely
4) Full flap, 40MPH on final, Behind the power curve, 1500 plus RPM on final and in the flare gave a clear tail first landing, TD at 36mph

Oversize Elevator Flight Test

No flap, power off, stall at 43mph indicated, 16 to 17 degrees pitch
No flap, 1500 RPM, stall at 40mph indicated, 20 degrees pitch
Full flap, power off, stall at 39mph indicated, 21 degrees pitch
Full Flap, 1500 RPM, stall at 35mph indicated, 24 degrees pitch

Slow flight with full flaps could be maintained at about 36 mph indicated and close to 24 degrees pitch but took 1800rpm plus (way deep behind the power curve)

Same landing criteria as the baseline test

1) Idle RPM in the flare, TD at 37mph, three point (tail first on one of the three)
2) 1200 RPM in the flare, TD at 37mph, tail first
3) 1400 RPM in the flare, TD 37mph, easy tail first
4)
Full flap, 40MPH on final, Behind the power curve, 1500 plus RPM on final and in the flare gave a VERY clear tail first landing, TD below 35mph


Summary


​The oversize elevators add about 1pd 3oz to your weight but they do improve elevator authority a noticeable amount. I could not detect a increase in stick force required, the elevators felt the same but they do allow you to drive the wing to a higher AOA. This is very noticeable in the stall. With the stock elevators the stall was mostly a mush and it felt like the tail was stalled not the wing. With the oversize elevators you can clearly drive the wing to a higher AOA and the wing now stalls and gives a clear break. No more mushing stalls. The elevators drop the stall speed approximately 2 mph indicated in all flap configurations, and allow more elevator in the flare. It is not huge but it is noticeable and significant.


Hope this helps

Bill
 
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Bill as always...fine job and very informative! Makes me feel better knowing it help since I did a 3" stretch on my elevators too.
 
Bill,
How much did the additional 1 lb 3.2 oz move the CG aft? Did you consider that the CG shift could have been the reason for the reduced stall speed? Try placing some temporary ballast in the engine compartment in order to repeat the test at exactly the same CG.

The larger elevator should help when you are on the nose heavy amphibs.
 
Kirby - Yes. I have Cub Crafters gap seals, and they were used on both tests. My above post has been changed to reflect that. Thank you

Pete - Your point is taken ( and I know you understand the critical nature of CG on flight performance ) so let me reply to help others. As tested for the Baseline the CG was at 76.78. The new elevators would make the CG 76.92. Given a range of 70.5 - 79, moving it .14 inches would be pretty hard to account for. In order to get the test CG at 76.78 I was running 30 pounds of lead in the tail. Without the lead my CG would have been 73.48. It takes 10 pounds of lead in the tail to move the CG 1 inch. It takes a couple of inches of movement to really "feel" the difference. But there is a significantly different feel from 73 inches to 76 inches in how the airplane feels and performs. It flies much better at the aft CG range, as just about all aircraft do. However; that said, there is a sweet spot for each aircraft and it may not be the aft limit. On my aircraft, beyond 77 inches the controls feel a little too light for my preference, and I do not like the spin characteristics. The advantage of the lead is it can be , and is, removed for camping trips which allows me to load a significant amount of gear in the plane without exceeding the aft CG limit. Perhaps someday I will get the Cub back to New Holstein and give everyone two rides. Both forward CG then aft CG. Then, like you Pete, others might see, feel, and understand the difference.

Hope this helps

Bill
 
Good info Bill. I have a friend who just pulled the trigger on a Javron Cub and had lots of questions on all the options and this was one of them.
 
Many have noted the increased authority of the oversized elevators over the years. One sourdough I recovered for wouldnt let me buy mew stock ones to replace his oversize elevs, had me do repairs instead.

Interesting......Steve Kracke at Atlees told me the 2.5" extended were the largest they could go before flutter showed in testing!!! ...2.5" is big enuff for me!!

Bill, where is the datum for your w&b calcs? would be nice to relate this to a Piper Cub
 
Interesting......Steve Kracke at Atlees told me the 2.5" extended were the largest they could go before flutter showed in testing!!! ...2.5" is big enuff for me!!
With this in mind it would be appropriate to add a little bit of lead ballast in the forward corner of the balance horn of the elevator. Enough for a small amount of over balance.
 
Dave - I use the prop face as the datum. It makes it a little easier as there are no negative values. Since it is pretty much a stock Cub you can use the moment arms right off the TCDS. I added a few new moments for extended baggage, tail ballast, etc. by leveling the fuselage, and using a plumb to markings on the floor. It was also good to double check the TCDS numbers, which were surprisingly accurate (or at least matched mine).


Prop Face - 0
Oil sump - 24
Firewall - 35
Inst panel - 51
Wing LE - 60
Gear axle - 62
Front Seat - 71
Fuel - 84
Fuel Pod Fuel - 90
Rear Seat - 97
Fwd wall lower baggage - 105.5
Middle lower baggage - 136
Aft wall lower baggage - 166
Fwd wall upper baggage - 136.25
Middle of upper baggage - 162.25
Aft wall upper baggage - 189.25
Tail ballast - 233.6
Tail Post - 249
Tailwheel axle - 263.6


The Cub Crafters Top Cub TCDS is A00057SE......this link will get you close

https://rgl.faa.gov/Regulatory_and_...BB6D6B8AE9416B92862583C9006553AB?OpenDocument

Click on the little PDF symbol in the upper left and that will download the TCDS on to your computer. It is only 4 pages so don't worry it is not a huge download. The TCDS uses a point 60" in front of the wing leading edge which is exactly the prop face.
Then you can use the datums above to figure various W&B scenarios. Using their numbers the CG envelope is......
1300 -1680pds = 70.5 - 79.0
1700pds = 71.7 - 79.0
1800 = 72.9 - 79.0
1900 = 74.1 - 79.0
2000 = 75.3 - 79.0
2100 = 76.5 - 79.0
2200 = 77.7 - 79.0
2300 = 79.0

Hope this helps

Bill
 
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So I have a question, at what flight regime do you need the bigger tail on a wheeled Super Cub? I normally wheel land and don't generally come in behind the power curve in my Super Cub. Where do you find the bigger tail feathers the most useful?
 
Steve

Point well taken. On floats and when doing wheel landings you probably won't see a real need for the extra authority. I do use three point landings in some circumstances, and at times the back side of the power curve, and in that regime the extra tail authority is helpful.

Bill
 
Ok, that makes sense. When helping a friend order his Javron kit he asked me about the larger tail feathers and I told him the only reason I could see for them would be if you were installing slats or slots. I realize everybody has different missions for their airplanes and was curious where these bigger surfaces might come into play.
 
So I have a question, at what flight regime do you need the bigger tail on a wheeled Super Cub? I normally wheel land and don't generally come in behind the power curve in my Super Cub. Where do you find the bigger tail feathers the most useful?

Steve

Point well taken. On floats and when doing wheel landings you probably won't see a real need for the extra authority. I do use three point landings in some circumstances, and at times the back side of the power curve, and in that regime the extra tail authority is helpful.

Bill
Bill, Do you not trim out the elevator forces when on approach with your electric trim?
 
Pete - yes I do. But for the test I left the trim in the same place throughout just to make sure there was one less variable.

Airplane is back on floats. I will post more about the annual to hopefully help others

Bill
 
DJ - It was about mid range.


A couple of more thoughts.....

I added a Princeton Capacitance Fuel Probe to the fuel pod. This sends a quantity indication to my GRT (I'm pretty sure it would work with other Electronic flight displays like Garmin or Dynon). I tried this system in the wing tanks but it did not work well in that application. The tanks are too flat, the probe was only about 4". The fuel pod is deeper, the probe is about 9 " and seems to be working great so far. It is nice to have that input, rather than just relying on timing the pump.

I rebuilt the oil cooler baffling, but did not have time to move the cooler off the rear baffling and to the front as I had originally planned. I tightened everything up, and used more 427 high temp sealant hoping for an incremental improvement. So far that seems to be the case. CHT's seem to be about 10 to 15 degrees cooler and should be adequate for another season.

I had trouble with one of my mags during the test flying this last couple of weeks. Excessive RPM drop but not related to just one cyl. I did a lot of trouble shooting, but finally decided it was one of my Pmags. Turns out it was one that was under water so I'm sure it is not the fault of Emag Ignition. In fact I must say that Brad and company have been truly outstanding in their support and customer service. I highly recommend the product (Pmags) and the company. I am having both Pmags overhauled and also getting a new harness just to be on the safe side.

IMG_2162.jpg

This is the race from the main wheel on the floats. Two years ago it was new. Last year it had some very minor pitting but was still perfectly serviceable. This year the bearings and races from all four wheels are totally shot. If you have amphibs, you need to be doing a LOT of maintenance. I do not do salt water either, I can't imagine the wear and tear from that.

I purchased a set of the Acme Aero Gen4 Black Ops shocks. I have not had a chance to try them yet. But here are a couple of weights for you.

Bungee gear leg - 3.61 pds
Die spring gear leg - 4.47 pds
Acme Aero Blk Ops - 7.34

So, from bungee gear to Black Ops will add 7.2 pounds. Can't brake if you are bouncing down the gravel bar so it will be worth it, but just wanted you to know.


Hope this helps

Bill
 
Just saw MCS (Mikes) post above. He has it right. Don't let it sit.

Glenn - Timken

I doubt your boat trailer was in the water anywhere near as long as my floats were. Lets see....lets say you launch and recover 12 times a year. (summers are pretty short where you live). 5 minutes in the water for each event. That is 120 minutes per year in the water, so 2 hours a year x 10 years equal 20 hours. Round it up to get 24 hours, adds up to 1 day your trailer bearings were under water over a 10 year period.

When the airplane is beached the main wheel bearings are under water, the nose bearings are in and out of the water. I would conservatively say my main wheel bearings were under water 120 days in the last two years. I have to agree with MTV on this one my friend. I think the key would be to repack the bearings as SOON as the "float season" is over, rather than letting them sit all winter. I have no doubt that contributed to this problem. Lesson learned for me.

Hope this helps

Bill
 
Why I run CP bearings & races in mine and keep the axle cavity full of grease (via drilled axle and zerk) to keep the water out as best I can... and when I block her in the fall I pump fresh grease through to get all the wet goo stuff out. On year 13 with mine..
 
IMG_2162.jpg

This is the race from the main wheel on the floats. Two years ago it was new. Last year it had some very minor pitting but was still perfectly serviceable. This year the bearings and races from all four wheels are totally shot. If you have amphibs, you need to be doing a LOT of maintenance. I do not do salt water either, I can't imagine the wear and tear from that.




Bill
In my experience a pit is reason for replacement because next time it is going to be trash. Have not seen one quite as bad as yours before but have seen some pretty nasty tail wheel bearings and races.
 
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