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Lower cowl scoop shape

bodumatau

Registered User
Maun, Botswana
Greetings All

BCSC Rev 2 flying in VERY high ambient temps - our average day is around 80ºF-100ºF OAT while flying. On the ground we regularly see 105ºF and a couple of days a year we see 120ºF

we bought the plane with a very poorly designed lower cowl scoop (builder had done his own thing, NOT followed BCSC), which we fixed temporarily by adding an aluminum lip which we riveted on to create more "suction", this seemed to work well. now we want to re-mould the lower scoop and I have some conflicting advice from tech's around me.

side view cross section, prop would be on the left of the picture, back of plane on the right.
belly scoop.jpeg
- Option 2 - some say "extend past the firewall, "cause thats how cessna does it" - I see this option constricting the outflow of air because it narrows the cross section. might work for a Cessna that usually see 70-90kts IAS but not for a BCSC that is slow.
- Option 1 - this seems to be the most common cowl design out there from what I have observed.
- Option 3 - my gut feel tells me this one will create the most "suction", it increases the cross sectional area the most.

I know and understand that the more cooling drag I create the more it affects my speed, but since I operate most of the time at 40-60kts IAS, and when I am slow then down to 20-40Kts IAS, I dont care much for top end speed, I need cooling, cooling, cooling.

advantage of Option 1 is that if we end up not needing the lip then we can cut it back and we have the cowl ending neatly at firewall edge.

please let me know your thoughts/opinions.
 

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yeah our WINTER day temps are around 80 :lol: and thats at 3100ft AMSL, in summer the combination of DA and hot air makes it a challenge to keep engines that were designed for temperate climates cool. I have found the "difficult point" on our engine to be around 90ºF OAT, below this I can hang it on the prop and temps stay sweet, above this need to run full rich and be careful that I keep airflow moving.... it will be interesting to see how the cowl changes this.

remember I am not talking about OAT on the ground, but rather OAT when flying..
 
Not #2. That sharp lower edge of the firewall creates turbulence (read that somewhere) and outlet flow should stay away as much as possible. The lip also adds stiffness to the lower cowl which if flexible can compress and close the gap under air loads. It does that on my Taylorcraft without the removable lip installed - but that's ok in winter and acts like an auto closing cowl flap.

Gary
 
I would do #3 you could also try a small rounded edge cover on the upper sharp edge to reduce turbulence.
DENNY
 
Why would anyone want to live in a place with those kind of temps? There are probably snakes there !!!

Don't forget the other places in your cowling where air goes in or out. There are a lot of threads on this forum discussing those.

Jim
 
thanks guys, @DENNY & Gary

is this the sharp edge you are talking about?
belly ramp sharp edge.jpeg

how would you round it? put a half round on the front of it?

cheers
Heiko
 

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Why would anyone want to live in a place with those kind of temps? There are probably snakes there !!!

Don't forget the other places in your cowling where air goes in or out. There are a lot of threads on this forum discussing those.

Jim

:lol: not ONLY snakes, we also have Elephants, Lions, Buffalo, Zebras, Giraffe, crocodiles, hippopotamus and a bunch of different antelope

yep we are working on keeping our cowl/baffles/inlets/outlets all as good as possible.
 
thanks guys, @DENNY & Gary

is this the sharp edge you are talking about?
View attachment 46005

how would you round it? put a half round on the front of it?

cheers
Heiko

That might help. Experiment with a half round in front or 3/4 around the edge (metal or ? tubing cut to fit and fastened. Cessna on some models (like the 180/185) does what you did and formed a concave under belly for flow then added cowl flaps to vary the outlet area. Bellanca did similar but with a single cowl flap on their Scout that was able to be moved up and down but fixed when set. I made one for my Citabria that could be adjusted from the cockpit - piano hinge, flap, locking cable to panel. But we have winter and I needed the flap closed then. Is there room to remove material from the lower engine cowl to add opening area? That alone may help some. How about a pic of that area now?

Edit: Notice the two metal "side curtains" Bellanca added to the boot cowl channel. I assume that helps smoothly direct exit air flow by reducing the chance of turbulent air entering that area from the sides

Gary
 

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not ONLY snakes, we also have Elephants, Lions, Buffalo, Zebras, Giraffe, crocodiles, hippopotamus and a bunch of different antelope....

And I always thought hitting a deer would be bad!

FOD in Africa.jpg
 

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If this is the typical BCSC-Rev 2 cowl adding a lip as pictured or an adjustable cowl flap extended forward like the Bellance Scout pic above might help.

Gary
 

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Heiko,
If this is your cowl, cut that reverse scoop along the sides. Replace that leading edge bend with a piano hinge. Extend the height of the sides and connect it to a cockpit control so that you can vary the opening in flight.

attachment.php
 
Heiko,
If this is your cowl, cut that reverse scoop along the sides. Replace that leading edge bend with a piano hinge. Extend the height of the sides and connect it to a cockpit control so that you can vary the opening in flight.

attachment.php

yep, that is basically exactly what we are doing, except the hinge story as we never fly much below 70ºF, so never struggle with Low temps, and for the 5 flights a year we do have low temps then we can live with it. for some bizarre reason our plane builder made that scoop half the length and really deep.

so... looking at the design above, would you make that lip flush with the firewall or would you extend it 3 to 4 inches aft of the firewall..... I think we should end it flush with the firewall, even maybe one inch forward of the firewall so the lip can be flush........my technician on the other hand wants to extend it 4 inches aft of the firewall "to stop air coming in when at high AoA", I disagree with him that the relative airflow will ever allow that unless you are stalled maybe with engine off.
 
Keep the tech happy and let him design and own it. Put a camera on the gear to observe air create yarn flow in that outlet area at differing angles and airspeeds. If it works as expected everybody happy. If not then it's his to own and make right for both of you. Nothing wrong with learning and after all it is an experimental.

Others will reply but that's the way I think at my age.

Edit: It's -22F here in Fairbanks so cooling is assured.

Gary
 
Keep the tech happy and let him design and own it. Put a camera on the gear to observe air create yarn flow in that outlet area at differing angles and airspeeds. If it works as expected everybody happy. If not then it's his to own and make right for both of you. Nothing wrong with learning and after all it is an experimental.

Others will reply but that's the way I think at my age.

Edit: It's -22F here in Fairbanks so cooling is assured.

Gary

bloody marvellous idea Gary, I think I will do EXACTLY that.

yeah we get -22ºF in Maun...... but only at FL280 :lol:
 
this was our lower cowl when we got it, the "scoop" was only half the length of the cowl.

cowl scoop old.jpeg
ended about 5 inches forward of the firewall

then we put this aluminium lip on as a quick fix.
cowl scoop old side.jpeg
that worked reasonably well

we were struggling with exhaust fumes in the cockpit
cowl scoop old 2.jpeg
so we took the light bar off, that made a big difference, no more exhaust fumes in cockpit

so now my techie has made a temporary aluminium extension for the lower cowl that looks like this.
temp scoop bottom.jpegtemp scoop side.jpegtemp scoop rear side.jpegtemp scoop front.jpeg
we will test this and if it works then rebuild the whole bottom section without the sharp front end of the scoop, similar to the green BCSC posted a few post above just with a deeper sided scoop.
 

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Smoother overall would be my choice to encourage surface flow. If desired add some metal side curtains like Bellanca did above for assumably a good reason to the under cowl adjacent to the exhaust pipes. It probably (?) encourages the air nearby to flow smoothly aft and creates a larger low pressure area relative to the outlet (?). It's always easier to delete material than add.

For CO intrusion also seal leaks in the fuselage near the gear and any open areas near the tail.

Gary
 
...we were struggling with exhaust fumes in the cockpit
so we took the light bar off, that made a big difference, no more exhaust fumes in cockpit
attachment.php

For CO intrusion also seal leaks in the fuselage near the gear and any open areas near the tail.

Gary
Due to the aerodynamic shape of a fuselage it is natural for the ambient pressure in the cockpit to be lower than the pressure outside. This tends to draw air in from any openings at the tail. Thus exhaust fumes can travel along the bottom of the fuselage, enter an opening in the tail then move forward to the cockpit. Generally, sealing off the inside of the fuselage aft of the baggage area will minimize or eliminate this issue.

This picture of your nose bowl indicates that someone has reduced the size of the cooling air openings. The prop is covering the openings in the picture. That was not a good idea for a slow airplane. It appears that the reason for doing this was to mount a oil cooler to the nose bowl? In addition to opening the outlet on the lower cowl you should consider opening these intakes.
 
Yeah, I thought the same when I first saw that photo, but it is the reflection of the hangar and the upper cowl,

I have however cut the right side intake back by about an inch at the bottom

in this picture my finger indicates about what I cut off.
upper cowl intake.jpeg

here two more pics, I dont have another cowl to compare directly to but from other pics it looks about the same as the other BCSC cowls.
cowl front.jpeg
cowl front left.jpeg
here you can see i have also closed that oil cooler hole off, it now sits behind #3 on the baffle
 

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...here two more pics, I don't have another cowl to compare directly to but from other pics it looks about the same as the other BCSC cowls.
View attachment 46028
You could alter that baffle shelf in front of the cylinder to a ramp. Slope it up from the lower cowl opening to the center of the cylinder. This will smooth the airflow up and back over the top. As it is now, it is possible that the air swirls around creating an aerodynamic dam, thus reducing the amount of air which actually is able to flow back over the engine. Similar to the slope on the opposite side. On the opposite side remove that vertical section which is creating a dam. Let that air flow through the fins. If you want that piece to minimize chafing on the fins, bend it down instead of up.
 
Lots of Back Country owners have fought high engine temps. I never used my kit’s cowl and went with a home made Cub style cowl instead. No temperature issues. If anything my oil cooling potential is excessive, but not enough to change right now. Easy engine access. The first two pics are my cowl lip. That’s mostly to move air past the mufflers. Space is tight in that area. Lots of heat in very close quarters. I also have typical Cub cowl cheeks. Look at pics of Ted Waltman’s or Kevin Quinn’s Back Countrys. They added big outlet ducts on the side cowls. CC uses louvers.

IMG_0048.JPG

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IMG_4651.jpeg


Sent from my iPad using SuperCub.Org mobile app
 

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Measure the suction side pressure with respect to static. If it’s zero, getting any further gains in cooling are problematic.
Ill bet it won’t be zero....
 
Your exhaust pipes need more down turn and added length, and shrouding them from airflow will make your fumes problem worse.
 
If this is the typical BCSC-Rev 2 cowl adding a lip as pictured or an adjustable cowl flap extended forward like the Bellance Scout pic above might help.

Gary

The picture shows the factory demonstrator Rev 3. There's no "typical" Rev 2 cowl. Some of us got our cowls well after the kits and the fit was.... let's just call it challenging. I don't mean to criticize BCSC in the least but their cowls are constantly changing. While SQ2s usually used hot rodded 360s most Revs used IO400s and now IO390s. Part of that evolution was because the planes got bigger and heavier and needed more power and prop and the hot rod motors were too hot to manage. The bigger displacement and angle valve heads addressed power needs and heat management.

What guys overlook in that photo? That's an IO-390 powered airplane with a ground adjustable 3 blade. Performance reports are surprisingly good. My interest in that plane centers on the flaps but the prop evokes a bit of curiosity as well.
 
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There's something like this locally (overall black with bright green cockpit). I know the owner and will have a closer look.

Gary
 
Enter into Google.. site: supercub.org CHT

thanks Fobjob, we have, subsequent to the photos above, put a vertical fence up the front of #1
cowl front.jpeg
roughly the size of the red rectangle, this brought #1 temp in line with #4

then we cut off the stiffener in front of #2 and replaced it with another underneath
cowl front left.jpeg
roughly where the red line is and this brought #2 in line with #1 & #4

we still have about 20ºF higher temps on #3 throughout the operating range, but I must add that we have our 13 row oil cooler behind #3 stealing air from that back corner.

we will try the ramp in front of #1 and let you know how it goes.
 

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That is an interesting prop hub spacer. What are you using for a propeller? If all else fails to get your temperatures in line with your wishes you could try another propeller with more chord near the root of the blades. This will grab and push larger volumes of air into the engine. In the past there have been propellers with airfoil shaped rubber cuffs placed over the roots of the blades for cooling like on this Stinson L-1.
800px-Vultee_L-1A_Vigilant_USAF.jpg

With that propeller spacer moving the prop forward away from the cowl you have room to extend the top of the openings forward creating an air scoop which would be able to grab more air when flying at low speeds/higher angles of attack. Though difficult to see, this Bellanca has scoops extending forward from the top of the cowl openings.

Bellanca_14-13-2_C-FGGX_02.JPG
 

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That is an interesting prop hub spacer. What are you using for a propeller? If all else fails to get your temperatures in line with your wishes you could try another propeller with more chord near the root of the blades. This will grab and push larger volumes of air into the engine.


With that propeller spacer moving the prop forward away from the cowl you have room to extend the top of the openings forward creating an air scoop which would be able to grab more air when flying at low speeds/higher angles of attack. Though difficult to see, this Bellanca has scoops extending forward from the top of the cowl openings.

View attachment 46045

we have 2 props, a CATTO 84x43 and a Whirl Wind 82" ground adjustable, both props have given us very similar cooling results. WW needs balancing for which we currently dont have a tool so we have switched back to the CATTO for now. spacer is a 2,25" from SABER, different spacer for the CATTO and the WW (both made by SABER) as the WW needs 2 flush lugs for the Ground Adjustable body.

interesting idea on the scoop for the upper side of the opening, trying to think about how to make a temporary install without drilling any holes..... will let you know if I come up with something....
 
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