Seaplane Lip?

How to keep the Cessna 170 flying and airworthy.

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epeltier
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Seaplane Lip?

Post by epeltier »

I have a '53 170B with the O-360A1A. Trying to lower CHT temps. #3 at 400 degrees and #4 380 and thats running 175 degrees ROP. Baffling is good and sealed up every little hole I could find. Does anyone sell the longer seaplane lip or does it have to be made? Thank You.
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ghostflyer
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Re: Seaplane Lip?

Post by ghostflyer »

I have been in the same boat as you. If you go to the VANS web site on this problem ,there are answers . With my issue on a steep climb out my no3 CHT would drop in temp and that was done time after time . I tried different climb speeds but with the same result . But in level flight up go the temperatures . I obtained my baffling from Harry Delicker and found the r/h baffle that sits in front of the r/h cylinder wasn’t long enough and was allowing incoming air to escape to the bottom of the cowl and out the front to the back of the spinner. Due to the spinners and intake design nearly 40% of incoming air was escaping around the interior of the intake opening and rushing around to the lower cowl. So using expanding foam and coating it in fibreglass this was sealed up. BUT during testing I hit [NO he hit me] a pelican that smashed my intake cowl and lower cowl. He will not be doing that again.
I managed to repair the fibre glass intake cowl [at that time temporarily] but nearly ended up permanently . The bottom cowl had to be manufactured totally by me [repaired for legality reasons]. TIP, When I was repairing the intake cowl around the lip of the cowl where the spinner sits ,I soaked some polyester rope [about 3/8 dia] in resin and fiberglassed it in . My intakes have volutes glassed in on top to stop reversal flow of air .
This really helped in controlling CHTs but some times I had these temperatures jumped up back to the original temperatures . I fitted a small camera in the top area of the engine and went for a fly. I found the top sealing baffling was blowing down and creating a huge gap allowing air to escape . So width of baffling was cut down and spring steel strips that hold the baffling against the top cowl.
Please note. Only epoxy resin was used with fire rating included.
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ghostflyer
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Re: Seaplane Lip?

Post by ghostflyer »

The exhaust baffle air opening on the bottom of the cowl on mine is about 2.5 ins wide with a spoiler of about 2.5ins wide at a angle of 30 deg s . Initially I used the original cowl with out the lip[spoiler] on the cowl and it sounded like a 747 on take off and CHT temperatures were in the red. I was using different angles of the spoiler when the pelican came to blows with my aircraft. There was a formula on the vans web site to work out the size of outlet needed and using the fixed inlet size. Unfortunately the STC for the fitment of the lycoming 180hp. doesn’t cover mods to the airframe . Thermodynamics and the thermokinetics is a very dark science and while I might have studied it at college about 47 years ago it’s been washed out of my brain by alcohol over the years .
Please do not do the Bradly mod to the baffling as this does end up in trouble . It’s ok for a Cessna cardinal but these are different aircraft .
[please note... all mods done or explained here has been done legally to my aircraft in my country ] I would seek professional [der] expertise if problems continue to cause . issues. I “think” the diff pressure between top of engine and bottom of engine is about 2.5 psi diff and airflow has to slowed to 45 to 60 mph under the cowl . As I said “think” possibly wrong . This can be checked using old ASI indicators fitted to upper and lower cowls .
My email is available in the members section if you want photos .
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DaveF
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Re: Seaplane Lip?

Post by DaveF »

I've also had high number 3 CHTs. After the major I was seeing number 3 at 420-430F. The engine has poor front-back mixture distribution, with 1 and 2 running rich, and 3 and 4 lean. It's made worse by the 10-3878 carburetor, which runs too lean. I don't know why they still use that carburetor -- back in the 1960s, Mooney had the same problem and came up with an improved main jet for the 3878. You can buy it as Marvel-Schebler kit 666-660, or built into the 10-4164 carburetor. If I ever need to replace or overhaul my carburetor, I'm going with the 4164.

I richened my carburetor by adjusting the economizer to run richer, and in all phases of flight I adjust throttle and carb heat to balance mixtures. I take off with the throttle cracked 1/4" which definitely evens out the mixtures.

I did the "cylinder 3 mod", which increases air flow around the back of number 3, but it didn't have the dramatic improvement I'd hoped.

I think the cowlings on the conversions just don't have enough delta-P to work with, which explains why you're looking at the seaplane lip, and why David (ghostflyer) did all the cowling work he did. On my Avcon, the cabin air comes from a 3-inch hole in the aft baffle, and I saw no CHT improvement when I blocked it off. That's 7 square inches of hole, so I'd say the cooling air isn't doing all it could.

Not unexpectedly, the CHT problem was worst immediately after major overhaul, so some of my CHT improvement is from normal break-in, but it took much longer than the normal break-in time to decrease. Mine isn't the only Lycoming where I've seen this.

Lots to this puzzle!
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ghostflyer
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Re: Seaplane Lip?

Post by ghostflyer »

That no 3 cylinder mod is not for slow flow cooling air as which is our Cessna 170 has. It doesn’t pass enough air and creates a local temperature extreme diff which effects cylinder/barrel cooling. It causes cracking . Talk to the guys at lycoming on this matter. They are the ones who clued me up on this . It’s a shame all the STC owners do not come up with a solution on this . You also loose a heap of cooling air through the hinges on the cowls . I opened my cowls and cleaned the area and used heat proof tape over the hinge areas. I studied the Cessna 172 cowling very closely and tried to set up mine the same way. My baffles seal pretty well these days . It’s all about the outlet size and the turbulance that’s created when leaving the aircraft . I have seen a rounded edge fitted to the sharp edge of the firewall and underside of fuselage.
The 3 in hole in the upper baffle has been calculated into the airflow cooling. It’s my belief it stops choking and maintains a flow into the upper chamber.
Superior aircraft engines have a far superior[excuse the pun] intake manifold and balances airflow a lot better. It bolts straight on and has a PMA for legality reasons .
epeltier
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Re: Seaplane Lip?

Post by epeltier »

What is the #3 cylinder mod? DaveF, do you have a fuel flow meter? I know I'm running plenty of fuel through the carb. 10.5 an hour and still seeing these temps.
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ghostflyer
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Re: Seaplane Lip?

Post by ghostflyer »

Using a EI fuel computer at 2500rpm and at altitude of sea level to 2500ft my fuel consumption is “normally “ 8.8 Us gals to 9.5 us gals a hour. However the OAT does have a governing factor . Take off rpm and at WOT the fuel consumption is eye watering .its 16gals a hour . But at 10,000ft the fuel is down to 8.4 us gals a hour.
However these figures are with 2 persons and the usual junk /fuel [1/2 tanks] on board. However I have had the odd situations where I have no explanation for it but some times I have to run very rich for smooth engine operation or very lean for the same reason.
Just checked the part number of my carb and it’s a p/n 10-4164-1 [MA-4_5]. Haven’t any idea of what economiser fitted.
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DaveF
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Re: Seaplane Lip?

Post by DaveF »

epeltier wrote:What is the #3 cylinder mod? DaveF, do you have a fuel flow meter? I know I'm running plenty of fuel through the carb. 10.5 an hour and still seeing these temps.
Is this a newly overhauled engine? 400F at 10.5 gph is not right. What are the other cylinders? How's the EGT distribution? Are you sure the FF meter is calibrated?

Yes, I have a fuel flow meter. My fuel flow is about 14.5 gph on takeoff at 5000 msl and 16 at low elevation. Cruise is 7-8 gph, depending on MP and RPM.

The cylinder 3 mod adds 0.050" to 1/8" of space between cylinder 3 and the aft baffle. The purpose is to improve air flow around the back, where the fins are shallow. It's a standard thing on RVs. The simplest form is just a washer pushed between the cylinder and baffle to space it off. Google it and you'll get lots of hits. This picture shows the thin fin area the mod addresses.
cylinderpic.jpg
cylinderpic.jpg (51.21 KiB) Viewed 2911 times
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ghostflyer
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Re: Seaplane Lip?

Post by ghostflyer »

Dave, is your engine painted bright orange?
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DaveF
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Re: Seaplane Lip?

Post by DaveF »

No, that's a picture I found on the internet. My engine isn't even painted. The crankcase is gold Alodine and the cylinders are factory Lycoming gray. It's not very attractive, but I didn't see any need to paint it.
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