Building a Javron Cub

[elpcub]

Folks,

FYI on CHTs. This is a follow up to Bill's comment about running close to 400 degrees. Post #2092

I just completed a build with Cont Motor (Titan OX 370) and they sent me the following #s for engine operations. Note the Normal (GREEN) area of operation for CHTs for the OX370.

Some may say it's high. But it's the data point the factory is putting out.

Again, FYI.

Shep

 

[Bill Rusk]

Tempdoug - this post here has a few pictures http://www.supercub.org/forum/showt...g-a-Javron-Cub&p=686232&viewfull=1#post686232

Two bolts on the rudder arm.

camTom12

I have data taken about 50 times all summer. I have not had a chance to sit down and study it or try to find correlations. But the temps are quite linear. I.E. the CHT goes directly with the OAT. Thus if my high CHT is 370 at 50 OAT it will be 390 at 70 OAT.
I could write a book on this, but not from a helpful standpoint. It is black magic. What fixes it for one person on this site has no affect for the next guy. There are sooo many variables, and they are probably inter-related. I do not know of a "fix" otherwise no one would have an issue with this. I do definitely appreciate that some folks are far more knowledgeable about this stuff than I am.
I have not measured my differential yet. I will do so. I do believe that is critical. But I know folks that have small differentials and no issues and others that have measured large differentials and they run hot. No easy answer.
One data set
RPM Alt MPH OAT FF CHT's EGT's
2400 4000 100 42 7.7 353,368,364,365 1407,1428,1481,1389
2400 2000 105 60 7.9 362,383,388,377 1472,1450,1494,1456

I am running lean of peak. Typically EGT is about 30* lower than peak and CHT about 10* below peak. I have this same data taken from random flights, altitudes, OAT's etc from all summer. Again, I have not analyzed it. These are not bad numbers, but as I mentioned, these are cool OAT's. I would be over 400 and not leaned in the summer. The hot cyl varies a little but it is typically 2 and 3 or 4. #2 is often the hot one and it is out front. I used the Vans baffling at first, and then just cut the top off and screwed a couple of pieces on to make a crude plenum. It worked OK, nothing to brag about, for the 200 hours I put on this last summer. I do believe the Vans baffling is often used by us experimental guys but I'm not at all convinced it is the best way to go. I think the front Cyls may be ramped too much. A typical SC has pretty much no ramps. I have the oil cooler behind #4 as is common. I can tell you with total confidence that when the oil cooler is blocked off the CHT's for BOTH #3 and #4 go down significantly which tells me that the oil cooler is the path of least resistance and clearly affecting the cooling. The interesting thing is that the ridge that I made that separates 1&3 and 2&4 (picture in link above) although not totally airtight seems like it would affect temps between 3 & 4 but it does not. Ie if I unblock the oil cooler #3 and #4 will both rise just about the same amount. Up to 40* warmer than when 1/2 the oil cooler is blocked off. Again I could write all night on this......
I can tell you that oil temp has no correlation to my CHT's. I can directly control my oil temp (see thread above) and as I raise and/or lower the oil temp it has no discernible affect on CHT's. I know some folks will disagree with that, and I understand, I am just telling you what I have seen with "my" engine. Your's may be different based on your prop, baffling, ignition, oil cooler set up, where and how you are measuring your temps, etc etc. Just too many variables to make a good apples to apples comparison.


Don - Thank you. I appreciate your inputs.

I will be posting all my baffling changes and results. Hopefully I will be able to help others as you have all helped me. More to follow but it may be a few weeks. Testing in the middle of winter does not help......but.....ya gotta work with what you have......

Web - I had a friend from the old school help with my wiring and he liked to solder connections. Not all, but way too many. I have had three solder joints fail. Fortunately I have managed to find them with minimal pain, but it still took time and effort, and thus I need to go through my wiring and make proper crimped connections. That I will do this winter. I will post pictures, findings, etc to help others.
I will also try to go through what has worked and what has not, again to help others.

Hope all this helps

Bill

PS sorry the data columns don't line up very well. I'm not set up to do spreadsheets etc

 

[stewartb]

I remember bitching to my mechanic when my -12 CHTs were at 400*. He asked what the problem was and said 400 was perfect. I've never seen any good data to disprove him. Mike Busch wrote an article years ago and said CHTs under 400 would improve engine life. I've never seen anything that supports that, yet guys struggle to achieve the lowest CHTs possible. When is good enough good enough?

 

[Steve Pierce]

I remember bitching to my mechanic when my -12 CHTs were at 400*. He asked what the problem was and said 400 was perfect. I've never seen any good data to disprove him. Mike Busch wrote an article years ago and said CHTs under 400 would improve engine life. I've never seen anything that supports that, yet guys struggle to achieve the lowest CHTs possible. When is good enough good enough?

Mike Busch got that data from his years of experience maintaining aircraft engines. 8)

 

[stewartb]

I doubt that. The basis of knowledge is science, and that requires theory to be validated by controlled experiments. What does he offer? Nada. That’s often referred to as science fiction.

 

[CamTom12]

camTom12

I have data taken about 50 times all summer. I have not had a chance to sit down and study it or try to find correlations. But the temps are quite linear. I.E. the CHT goes directly with the OAT. Thus if my high CHT is 370 at 50 OAT it will be 390 at 70 OAT.
I could write a book on this, but not from a helpful standpoint. It is black magic. What fixes it for one person on this site has no affect for the next guy. There are sooo many variables, and they are probably inter-related. I do not know of a "fix" otherwise no one would have an issue with this. I do definitely appreciate that some folks are far more knowledgeable about this stuff than I am.
I have not measured my differential yet. I will do so. I do believe that is critical. But I know folks that have small differentials and no issues and others that have measured large differentials and they run hot. No easy answer.
One data set
RPM Alt MPH OAT FF CHT's EGT's
2400 4000 100 42 7.7 353,368,364,365 1407,1428,1481,1389
2400 2000 105 60 7.9 362,383,388,377 1472,1450,1494,1456

I am running lean of peak. Typically EGT is about 30* lower than peak and CHT about 10* below peak. I have this same data taken from random flights, altitudes, OAT's etc from all summer. Again, I have not analyzed it. These are not bad numbers, but as I mentioned, these are cool OAT's. I would be over 400 and not leaned in the summer. The hot cyl varies a little but it is typically 2 and 3 or 4. #2 is often the hot one and it is out front. I used the Vans baffling at first, and then just cut the top off and screwed a couple of pieces on to make a crude plenum. It worked OK, nothing to brag about, for the 200 hours I put on this last summer. I do believe the Vans baffling is often used by us experimental guys but I'm not at all convinced it is the best way to go. I think the front Cyls may be ramped too much. A typical SC has pretty much no ramps. I have the oil cooler behind #4 as is common. I can tell you with total confidence that when the oil cooler is blocked off the CHT's for BOTH #3 and #4 go down significantly which tells me that the oil cooler is the path of least resistance and clearly affecting the cooling. The interesting thing is that the ridge that I made that separates 1&3 and 2&4 (picture in link above) although not totally airtight seems like it would affect temps between 3 & 4 but it does not. Ie if I unblock the oil cooler #3 and #4 will both rise just about the same amount. Up to 40* warmer than when 1/2 the oil cooler is blocked off. Again I could write all night on this......
I can tell you that oil temp has no correlation to my CHT's. I can directly control my oil temp (see thread above) and as I raise and/or lower the oil temp it has no discernible affect on CHT's. I know some folks will disagree with that, and I understand, I am just telling you what I have seen with "my" engine. Your's may be different based on your prop, baffling, ignition, oil cooler set up, where and how you are measuring your temps, etc etc. Just too many variables to make a good apples to apples comparison.

Bill,

Just some short thoughts from the phone:

1) I disagree on your Van’s baffle ramp assessment. I think if you were to bring the ramps down you’d see lower temps on 1 & 2 than 3 & 4. Right now your CHTs look pretty close. Also, you’re probably already familiar with this but the front of #2 and the back of #3 have real shallow fin depth. If either of them is consistently warm then some baffle stand-off is needed to allow enough air past that shallow fin depth to the lower part of the cylinder. There’s a couple of good threads on VAF about this. Search “#3 cooling problem solved” or something to that effect.

2) I’m making a guess here, but I think that area in front of your divider is where the pressure is equalizing from left to right side when you open/close your oil cooler, which might be why you’re seeing equal temp changes to the back two cylinders. Pressure is the engine in that system.

 

[pittsdriver]

Bill, I have always enjoyed following your posts so keep them coming. On the TCOW Cub I started with the Vans baffling and modified just a little bit. I built and flew a RV-7 before I did the Cub and did a lot of small mods on the baffling as I flew it. I had the CHTs running in the 380 range ROP and 340 LOP. I got it down to running less than 10 degrees from the hottest cylinder to the leanest. When I ran LOP the EGTs were also within 10 degrees high to low. On the certified Cub I started with the stock baffling that to me is really inefficient the flat ramps being the main culprit. When I started the rear cylinders ran over 100 degrees hotter than the front. I now have them running within 50 degrees and 385 on a warm day. They will get over 400 in a hard climb but come right down in cruise. The big deal is to seal the front between the two front cylinders and the case so you don't lose any high pressure air behind the prop. On #4 I build a baffle on the back of the cylinder the directs air over the cylinder but allowing enough over the top to go through the oil cooler. Sometimes slowing down the air gives better cooling as it has more time to draw the heat away from the cylinder Remember we are dealing with high and low air pressure not airflow. Don

 

[JimParker256]

Most of Mike Busch’s recommendations come from the guys who put together the Advanced Pilot Seminar (APS) This group includes the author of the “Pelican’s Perch” articles (John Deakin), along with George Braly (Chief Engineer for Tornado Alley Turbos and GAMI), and Walter Atkinson (a high-time pilot and gifted instructor. They have access to data collected in one of the most sophisticated engine test labs in the world. So it is completely incorrect to imply that there is no science behind their recommendations. In fact, Continental sends a lot of their engineers and customer service people through the APS to improve their understanding of engine operation. They have also made recent changes to their engine manuals to reflect the same things that APS teaches.

Mike sometimes over-simplifies the APS research findings and recommendations, in the interest of communicating them more succinctly to his audience. There is tons of data validating that keeping CHTs below 400 for Continental big-bores (which is what Mike’s recommendations apply to) leads to longer engine life, and dramatically reduced cylinder overhauls / replacements. They have less data on Lycoming engines, but what they do have generally correlates with the statement that lower CHTs lead to longer engine life - specifically reducing cylinder head and exhaust valve (and exhaust valve seat) issues.

 

[stewartb]

I couldn’t care less about Mike Busch. The point was about CHTs and what’s healthy vs what isn’t.

 

[mam90]

I’m just glad I don’t have a CHT gauge......

 

[flylowslow]

Bill, great to see your great numbers over the past year! In regards to your rear headliner, is it easily removable? Are you changing anything about it in your new build? Wish we could all get together at Jays new build center. Blue Skies, Denny

 

[DENNY]

PA-20/20-160
The exhaust valve/guide is the weak point in the lycoming jugs. Do a search on wobble test, SB388B. I talked to the lycoming reps at the trade show about the 500 degree CHT limit. The rep admitted that they do not run at that temp for 2,000 hours. They push to that point then back off. They made a wet head (oil cooled exhaust valve guide) to solve a early valve failure problem with the Mooney TLS. Increase in CHT will increase the valve guide wear, that is what will bite you down the road.

Bill
Have you tried running rich of peak? You will burn more fuel but may be cooler. Prop may also be part of the problem.

DENNY

 

[Bill Rusk]

flylowslow - no, headliner is not removable., but has worked great so far. Not a lot of changes planned for the new build, except will add autopilot. And avionics will be whatever is available at that time. Boy, they are changing fast, and all for the better. If you are driving to Jays, you drive right by Poplar Grove (near Rockford IL), feel free to stop and visit, if I'm there and not in Spokane.

Denny - Yes, if necessary I can run ROP and it does lower the temps a little. Throttling back has the greatest affect. I had to do that last year coming back from AK. The midwest was in a heat wave with temps over 100 all across from MT to Illinois. Made it back OK but that is what is driving me to see if I can improve on things. I want to be able to fly in the heat of the summer and not worry about my CHT's.

Thanks for all the inputs gents. It will be a couple of weeks until I can tackle this but, as always, I'll keep you posted.

Bill

 

[DENNY]

I put Aluminized tape over the cowl door hinge to help close up cowl, lots of daylight showing through that hinge.
DENNY

 

[bcone1381]

Some say that Pmag's timing curve contribute to high CHT's
Post #13 is pretty good in this thread.
http://www.vansairforce.com/community/showthread.php?t=107804&page=2

 

[Bill Rusk]

Some say that Pmag's timing curve contribute to high CHT's
Post #13 is pretty good in this thread.
http://www.vansairforce.com/community/showthread.php?t=107804&page=2

My post on the same subject

http://www.supercub.org/forum/showt...g-a-Javron-Cub&p=632017&viewfull=1#post632017

Bill

 

[stewartb]

Here's what my Superior Air Parts manual recommends for CHTs. CHT redline is 500*, just like Lycoming.

For maximum service life, cylinder head temperatures should be maintained below 430ºF (221ºC) during high performance cruise operation and below 400ºF (204ºC) for economy cruise operation, with 300-400ºF (149-204ºC) optimal.

I can't recall flying an airplane in "economy cruise" mode. Especially a Cub with a fixed pitch. elpcub posted elsewhere that his Titan engine normal temps go to 450*. It appears the manufacturers are acknowledging that these juiced-up engines run warm. I target 400* as my comfort zone limit but according to the manufacturer I shouldn't worry about 425.

 

[flylowslow]

Bill, got jays boot cowl jigged up, but now the choice of engine and exhaust, defintlty thrustline, but wanted to stay with 160hp. will stay with your idea on headliner. I liked your wing-wag taxi lights, have to look into that. Any body have an old tailwheel to let go of?

 

[Rice farmer]

Flylowslow. Still need an old tailwheel? Had an old Scott laying around.

 

[Bill Rusk]

Folks

Some random thoughts as I do the annual condition inspection.

If you operate on floats, I strongly encourage you to take the tail off every year and clean and grease the through tubes that hold the horizontal stabs on. This area is pretty much under water on every takeoff and landing and it gets a lot of abuse. It does not take that long to do.

This will be hard to visualize and understand, but for those building a Javron Cub hang with me for a bit. The rear panel for the extended, lower baggage compartment has a slope and attaches at the top crossbar via a couple of tabs, and then 2 more tabs at the bottom. Because of the angle and location of these attach tabs you can't get a screwdriver in there unless you have no upper baggage floor. I had to drill a couple of holes (one through my ELT mount, shown here) to get a screw driver in there. It is not a bad design just a point to consider for future maintenance. If I had to do it over I would use those top two tabs to attach a "U" shaped clip onto so that that back panel slides up into those clips, then has a couple of screws at the bottom to secure it in place. Thus instead of 4 screws holding that panel in, it would have two (slip into) slots at the top and two screws at the bottom.

This is a real pain. When on floats you will track a lot of sand, gravel, crud, mud, etc into the cockpit. It gets under and in everything. Removing the rear floorboards is a BIG job and involves taking all the flight controls out and apart. The seat base has to come out, seatbelt, brakes, torque tube, flap handle, etc etc. Rudder pedals with those stupid saddles and springs have to come out. Then it all has to go back together, with no binding. It introduces a lot of places for you to screw up and forget a cotter pin, nut etc. These are critical parts to the safety of flight. Next time I will do a metal belly pan in the cockpit area.


So.......folks often ask what would you do different next time.....

Metal belly to the rear gear fitting.
Larger access panels. If you use the standard Cub fabric reinforcements it will lead you into small access openings. Don't be afraid to make the opening larger and make your own reinforcements. Especially helpful in the tail access area.
Make the front seat base attach tabs about 1/2" taller so you don't have to fight the floorboard to get the attach bolts in and out
Reinforce the area where the window latch attaches to the bottom of the wing. This is in the prop blast area and it gets worked a lot.
Back cargo panel attach system as mentioned above
Increase the size of the flap access opening in the wing. Don't use the std reinforcement, use the full width of the bay between the ribs.
Paint the V brace flat black before you cover. Use a good epoxy paint so it will not wear off. You will have your hands up there a lot.
Float fitting tabs in front of the cabane V as mentioned in my float mount section of this thread.
If you use electric trim, mount the limit switches on the fuselage not the yoke. It works fine as I did it but that would be better.

Just some random thoughts that might help someone.

Hope this helps

Bill

 

[Farmboy]

If you’ve forgotten to paint the V brace flat black as Bill mentioned and you find the reflection in the windshield a nuisance along with hand wear.... True “Gaffers” tape comes in flat black non-reflective, and one strip will roll onto each tube perfectly to eliminate the nuisance. [emoji4]




Sent from my iPhone using SuperCub.Org

 

[Steve Pierce]

This will be hard to visualize and understand, but for those building a Javron Cub hang with me for a bit. The rear panel for the extended, lower baggage compartment has a slope and attaches at the top crossbar via a couple of tabs, and then 2 more tabs at the bottom. Because of the angle and location of these attach tabs you can't get a screwdriver in there unless you have no upper baggage floor. I had to drill a couple of holes (one through my ELT mount, shown here) to get a screw driver in there. It is not a bad design just a point to consider for future maintenance. If I had to do it over I would use those top two tabs to attach a "U" shaped clip onto so that that back panel slides up into those clips, then has a couple of screws at the bottom to secure it in place. Thus instead of 4 screws holding that panel in, it would have two (slip into) slots at the top and two screws at the bottom.

These work great. https://www.amazon.com/dp/B0062FSAV...nv&pd_rd_r=CPYESDTJVZAZ7DTFKP91&pd_rd_w=YfV8J

 

[mvivion]

Bill,

Good thoughts all. The first SC I flew a lot was on floats most of the year, and in salt water a lot. It had a metal belly, which was, as you noted, nice for cleaning the “basement”. Getting all those pencils observers dropped, etc. What would be REALLY nice though would be a carbon fiber belly panel instead.

That Cub worked in Kodiak from 1969 (year it was born) till 1984, when it was recovered (original cover was cotton), never hangared, and I’m pretty sure the tail feathers never came off. After it was stripped, the frame and tail was clean as can be. The rebuilder wouldn’t believe me that it had been in salt for years.

i do think taking the tail apart every once in a while is a good idea. And, if you haven’t already, remove all the float parts, clean, lube and re assemble before the plane goes back on floats.

MTV

 

[skywagon8a]

The rebuilder wouldn’t believe me that it had been in salt for years.

It depends on where the salt water is located. Alaska salt water is far less corrosive and active than Key West Florida.

 

[mvivion]

It depends on where the salt water is located. Alaska salt water is far less corrosive and active than Key West Florida.

Yes, temperatures make a big difference. That said, that cub was eventually replaced by a “brand S” and they had to replace the tail feathers after two seasons.

MTV

 

[Steve Pierce]

Bill,

Good thoughts all. The first SC I flew a lot was on floats most of the year, and in salt water a lot. It had a metal belly, which was, as you noted, nice for cleaning the “basement”. Getting all those pencils observers dropped, etc. What would be REALLY nice though would be a carbon fiber belly panel instead.

That Cub worked in Kodiak from 1969 (year it was born) till 1984, when it was recovered (original cover was cotton), never hangared, and I’m pretty sure the tail feathers never came off. After it was stripped, the frame and tail was clean as can be. The rebuilder wouldn’t believe me that it had been in salt for years.

i do think taking the tail apart every once in a while is a good idea. And, if you haven’t already, remove all the float parts, clean, lube and re assemble before the plane goes back on floats.

MTV

Was it built as a sea plane by Piper? Those airplanes along with the last Lockhaven Super Cubs had the aluminized finish sprayed on them and are really good and not having rust.

 

[OLDCROWE]

Folks

Some random thoughts as I do the annual condition inspection.

If you operate on floats, I strongly encourage you to take the tail off every year and clean and grease the through tubes that hold the horizontal stabs on. This area is pretty much under water on every takeoff and landing and it gets a lot of abuse. It does not take that long to do.

This will be hard to visualize and understand, but for those building a Javron Cub hang with me for a bit. The rear panel for the extended, lower baggage compartment has a slope and attaches at the top crossbar via a couple of tabs, and then 2 more tabs at the bottom. Because of the angle and location of these attach tabs you can't get a screwdriver in there unless you have no upper baggage floor. I had to drill a couple of holes (one through my ELT mount, shown here) to get a screw driver in there. It is not a bad design just a point to consider for future maintenance. If I had to do it over I would use those top two tabs to attach a "U" shaped clip onto so that that back panel slides up into those clips, then has a couple of screws at the bottom to secure it in place. Thus instead of 4 screws holding that panel in, it would have two (slip into) slots at the top and two screws at the bottom.

Bill,

After you get it cleaned up, and going back together get a roll of insulation/foam tape at a metal building supply and stick it in front of the floor board openings plus all the way across just in front of your front seat posts and across the back. It makes a great crud dam and you just vacuum it out ocassionally.

Kirby

 

[pittsdriver]

I put a metal belly on the last Cub I built. From now on I'll talk the customer into it.

 

[mvivion]

Was it built as a sea plane by Piper? Those airplanes along with the last Lockhaven Super Cubs had the aluminized finish sprayed on them and are really good and not having rust.

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

 

[mvivion]

Another thing that helps keep crud out of belly: Install an aluminum angle at aft end of floor, to create a dam of sorts to prevent “stuff” from sliding off the aft end of floor and falling into belly. Easy, light, and keeps a bunch of junk out of the belly.

MTV