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Cowl flap thoughts

crabandy

Well Known Member
I think I?ve seen/googled most of the ideas out there when it comes to cooling the lycoming in the summertime. I?m sure there are many more out there that I haven?t seen. I?ve done a decent amount of work with inlets/plenum/sealing and lastly ignition timing for temp control. Most people seem to be concerned with climb out CHT?s. I currently have no issues climbing out on a hot day, I have issues taxiing after a quick turn on a hot day and I?m carbureted. CHT?s and oil temps are fine but fuel seems to be boiling, erratic chugging during taxi. Idle mixture is correct and an excessively lean mixture and RPM?s above 1000 help.

With my stock cowling I used to see heat radiating out of the upper inlets while fueling. I don?t see it with my sealed inlet boots. During ground operations the pressure diff between the upper cowl and lower cowl is very small. How many people pop the oil door open after they land in hot temps?

Most cowl flaps are installed in conjunction with the lower outlet, I?ve stared at this space on my cowling for months trying to come up with ideas. I?ve shrunk and contoured my exit to approximately 35 sq inches, not a lot of room for a cowl flap with a vertical induction carb and 2 exhaust pipes.

I?ve also been staring at the rear of my upper cowling, what about an upper cowl flap, similar to the old 30?s cars/trucks had in front of the windshield? With the low pressure diffs on the ground it would take advantage of convection in addition to a larger exit area during climb out. I kept hoping for an easy test without months of work and downtime.

I?m currently finishing an oil change and making room behind the upper engine mount to possibly add an upper cowl flap when it dawned on me, why don?t I spend 2 minutes and remove the oil door and go fly several quick turns? On 4 cylinder lycomings the oil door is behind the upper plenum and part of the lower cowling volume/pressure. Roughly 5x5 (25 sq in) in the upper cowling that is convection friendly on the ground, also pretty easy for anyone else to test fly and and see what kind of cooling the extra exit area gives them.
 
Just removing the door may not work. I'm pretty sure that part of what makes a cowl flap work is the flap only allowing exit air, which you won't have with just a hole. But by all means try it and let us know what happens!

-Marc
 
I used to fly a friends glasair 2rg that had two slots on the upper cowl with a spring loaded door. It souls open and vent off the heat when on the ground but would close itself when ramair in the upper cowl would build up.
 
When I started flying my 7, I always thought something was wrong with my engine. After landing on taxi it would pop and chug! I kept thinking my plugs were fouling! I even bought a set of fine wire plugs to solve the problem (well worth the money by the way but didn't help my problem). I was at 52F one day where Walt was inspecting my Transponder having lunch outside the diner and lo and behold, every RV that came taxiing by was popping and chugging just like mine! Boost pump helps but she's gonna pop when that fuel boils in those injector lines!
 
An idea...

Many years ago, in one of the experimental aircraft magazine (can't remember which one), there was an article on automatic shutters for the top side of a cowl.

The basis of the design was quite elegant. A set of shutters with moveable doors was installed in the top of the cowl. The activation of the shutter doors was accomplished using the charge cylinder from an automotive thermostat. The plug inside of the charge cylinder expands as it is heated past it's critical temperature and moved the shutter doors to the open position. As the charge cylinder cools, it contracts and closes the shutter doors...

Of course, with modern tech, you could accomplish the same thing using a linear actuator and a temp sensor connected to a small arduino unit...and it would be programmable for any given temperature or time...

These shutters are remade and would do the trick:

https://antisplataero.com/products/oil-cooler-air-shutter
 
I think I?ve seen/googled most of the ideas out there when it comes to cooling the lycoming in the summertime. I?m sure there are many more out there that I haven?t seen. I?ve done a decent amount of work with inlets/plenum/sealing and lastly ignition timing for temp control. Most people seem to be concerned with climb out CHT?s. I currently have no issues climbing out on a hot day, I have issues taxiing after a quick turn on a hot day and I?m carbureted. CHT?s and oil temps are fine but fuel seems to be boiling, erratic chugging during taxi. Idle mixture is correct and an excessively lean mixture and RPM?s above 1000 help.

With my stock cowling I used to see heat radiating out of the upper inlets while fueling. I don?t see it with my sealed inlet boots. During ground operations the pressure diff between the upper cowl and lower cowl is very small. How many people pop the oil door open after they land in hot temps?

Most cowl flaps are installed in conjunction with the lower outlet, I?ve stared at this space on my cowling for months trying to come up with ideas. I?ve shrunk and contoured my exit to approximately 35 sq inches, not a lot of room for a cowl flap with a vertical induction carb and 2 exhaust pipes.

I?ve also been staring at the rear of my upper cowling, what about an upper cowl flap, similar to the old 30?s cars/trucks had in front of the windshield? With the low pressure diffs on the ground it would take advantage of convection in addition to a larger exit area during climb out. I kept hoping for an easy test without months of work and downtime.

I?m currently finishing an oil change and making room behind the upper engine mount to possibly add an upper cowl flap when it dawned on me, why don?t I spend 2 minutes and remove the oil door and go fly several quick turns? On 4 cylinder lycomings the oil door is behind the upper plenum and part of the lower cowling volume/pressure. Roughly 5x5 (25 sq in) in the upper cowling that is convection friendly on the ground, also pretty easy for anyone else to test fly and and see what kind of cooling the extra exit area gives them.

?.We have had many customers mount our cowl flaps on the sides of the lower cowl as well as on the top. They report back many advantages, Lower ground operations temperature being one. Another is even lower climb out temperatures, due to the fact that the pressure in this configuration is much lower on top than on the bottom. We have seen most everything possible with flaps on top, sides, bottom and all of the above in one installation. The top mounted location is very popular in Brazil on the RV-10s. Its all good!
Thanks, Allan..:D
 
Many years ago, in one of the experimental aircraft magazine (can't remember which one), there was an article on automatic shutters for the top side of a cowl.

The basis of the design was quite elegant. A set of shutters with moveable doors was installed in the top of the cowl. The activation of the shutter doors was accomplished using the charge cylinder from an automotive thermostat. The plug inside of the charge cylinder expands as it is heated past it's critical temperature and moved the shutter doors to the open position. As the charge cylinder cools, it contracts and closes the shutter doors...

Yep, remember that one.

A simpler setup is to use a magnet to hold the door in the up/closed position, and you just give the door a push down to open it when you land. Air pressure will close it when you take off.
 
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Andy, are you using 100LL? Its vapor pressure is lower than most (all?) mogas blends, especially if you happen to get some winter blend mogas at the pump and use it on a hot day.

Disregard if you're already using 100% 100LL.
 
Andy, are you using 100LL? Its vapor pressure is lower than most (all?) mogas blends, especially if you happen to get some winter blend mogas at the pump and use it on a hot day.

Disregard if you're already using 100% 100LL.

Not 100% 100LL, but I keep 1 tank strictly 100LL for takeoff and landing. I use 91 ethanol free mogas in the other tank at lower/cooler power settings mostly in cruise. I switch to my 100LL tank with my BCGumps landing checklist, I might not have burned all the mogas out of the system as I?m taxiing in. I?m not convinced it?s a mogas Problem, but easy to eliminate the possibility with 100% 100LL usage.
 
When I started flying my 7, I always thought something was wrong with my engine. After landing on taxi it would pop and chug! I kept thinking my plugs were fouling! I even bought a set of fine wire plugs to solve the problem (well worth the money by the way but didn't help my problem). I was at 52F one day where Walt was inspecting my Transponder having lunch outside the diner and lo and behold, every RV that came taxiing by was popping and chugging just like mine! Boost pump helps but she's gonna pop when that fuel boils in those injector lines!

Mikey,
I?m carbureted with dual electronic ignition and auto plugs, I think the fuel is boiling in my carb bowl....
 
Thanks for all the other upper cowl flap suggestions, if I make an upper cowl flap I would like it to be controlled from the cockpit. Still thinking and waiting.

Pretty sure a couple flights without the oil door will tell me what the extra exit area on the upper cowl will or won?t do.
 
?.We have had many customers mount our cowl flaps on the sides of the lower cowl as well as on the top. They report back many advantages, Lower ground operations temperature being one. Another is even lower climb out temperatures, due to the fact that the pressure in this configuration is much lower on top than on the bottom. We have seen most everything possible with flaps on top, sides, bottom and all of the above in one installation. The top mounted location is very popular in Brazil on the RV-10s. Its all good!
Thanks, Allan..:D

Allan,
Not sure what is meant by ?pressure in this configuration is much lower on top than the bottom?? Can you please explain?
 
Allan,
Not sure what is meant by ?pressure in this configuration is much lower on top than the bottom?? Can you please explain?

When you're climbing, you're at a fairly high angle of attack. The pressure gradient around the airplane in that attitude creates a high(er) pressure area on the bottom of the cowling than in a normal flight attitude. This reduces cooling flow.

In that climb attitude, the top of the cowling sees a lower than normal dynamic pressure, and the sides are largely unchanged, at least in theory.

So, you may see more cooling airflow from equivalent sized vents on the sides or top of the cowling in a climb attitude compared to the same vents on the bottom cowl.

You'd need to test on your particular aircraft to definitively prove this.
 
Fuel perking?

I'm in the habit of opening the oil access door after lending. Amazing amount of hot air exits and I suspect goes a long way to keeping fuel lines and the carb cooler for departure. 5psi pressure from the aux pump on the fuel lines also helps delay any perking.
 
Not exactly a hot day today with an OAT OF 82* F, but I had the time finishing an oil change and did a couple quick flights. I did a cold start and Flight to stabilize oil at 190ish and cylinders at 350ish followed by a taxi back and sit for 5 minutes. I then remove the oil door and did a similar flight, no consideration to CHT?s in the climb as I am mostly interested in ground/taxi cooling.

Oil door installed .3 Flight time.
Preflight initial lower cowling Temp: 84* (I suspect the temp probe reads 2 degrees hotter)
Pre-takeoff after taxi and runup: 150*
Stabilized temp in cruise: 170*
After landing/taxi/shutdown: 178*
5 minutes after shutdown: 162*

Oil door removed and heat soaked quick turn .3 flight time.
At engine start: 150*
Pre-takeoff after taxi and runup: 165*
Stabilized temp in cruise: 177*
After landing/taxi/shutdown: 174*
5 minutes after shutdown: 168*

I?m a little befuddled by the ?5 minutes after shutdown? temps higher with the oil door off, but I did pull it into the hangar at the end of the flight whereas the oil door on sat outside in 15 knt winds.
The ?after landing/taxi/shutdown? temps are promising; without the oil door temps went down instead of up after landing. More flights needed especially in 95*+ quick turn and long taxi senarios.
 
Andy, the optimum top outlet location is not back by the oil door. Think of airfoil pressure plots at high AOA.

Peter Garrison's Melmoth 2 used updraft cooling and top exits. Here, read the first section: http://www.melmoth2.com/texts/CoolingFlow.htm

Great read Dan! My large round inlets and plenum take up all the room on the front top of the cowling though! And he is cooling at high AOA in Flight, I?m aiming to cool better on the ground.

I have a really neat upper cowl flap idea (in theory) but not sure I shouldn?t just keep it simple by modifying the oil door that is already there.
 
-7 side cowl flap

I have seen a recent -7 build done by a local friend that is on the forums. He had some heating issues on his, which sounds to be a similar set-up. He installed one of the electric cowl flap doors on the left side of the lower cowling, and did a beautiful job of making it look "as designed". I believe his temp drops from that system where significant. Perhaps he may chime in, or I can contact him directly for more intel.
 
Great read Dan! My large round inlets and plenum take up all the room on the front top of the cowling though! And he is cooling at high AOA in Flight, I?m aiming to cool better on the ground.

I have a really neat upper cowl flap idea (in theory) but not sure I shouldn?t just keep it simple by modifying the oil door that is already there.

Or just forget about it. The oil temps are great, with the oil door closed. CHTs apparently not an issue. The best cure for poor idle due to temperature is generally twofold; higher energy ignition, and reduce heating of the carb and fuel lines. I suspect most of that heating is radiant, so just blowing more air through the cowl is not gonna to get 'er done.
 
Or just forget about it. The oil temps are great, with the oil door closed. CHTs apparently not an issue. The best cure for poor idle due to temperature is generally twofold; higher energy ignition, and reduce heating of the carb and fuel lines. I suspect most of that heating is radiant, so just blowing more air through the cowl is not gonna to get 'er done.

My issue isn’t poor idle, it’s lack of idle and running in general. On 95* day quick turns I’ve had it quit on me (more than once) (leaned mixture, idling 1200 rpm etc) and had to radio the tower while I let it cool down and wave as the airline passengers taxi by watching me pull my airplane to the edge of the taxi way, talk about embarrassing. Also on the long taxi into OSH, and the last solar eclipse I barely made it off the runway....

CHT’s and Oil Temps are always easily within limits, I think it is radiant heating of the carb. It generally starts surging while on the idle circuit around 600 rpm, if I ride the brakes and taxi at 1000-1100 rpm it does ok for a period. If it does surge and die I’ve found the flooded start procedure works as long as I run it on the main jet at higher RPMS. Not sure I can protect the carb from radiant heating.

The fuel systems is Van’s plan with the gascolator and red cube, I have a heat shield on the exhaust from the red cube to the carb.

I’ve thought about a cooling shroud for the fuel pump, but with no pressure diff on the ground it does no good.

Remove the Gascolator? Probably help but maybe not solve.

With the stock Van’s cowling I used to see heat rising/leaking out the inlets and around the spinner after a hot shutdown. After my rubber boot inlets-plenum-crankshaft-spinner seal I no longer see this. I see it when I open my oil door though.
 
Andy, your under-cowl air temperatures are not likely to be warmer than those found under any other cowl, roughly 125F to about 240F localized in the baffle opening right under hot cylinder. We can measure it if you want.

Got photos? Let's look at the radiant heating situation.
 
I just re-cowled after the oil change and away from the airplane, lemme dig through some photos.

Lower cowl temps aft of the accessory case away from any cylinder hit 215-220 *F on a 95* quick turn, seems to be when I have trouble. I haven?t measured next to the carb yet.
 
….We have had many customers mount our cowl flaps on the sides of the lower cowl as well as on the top. They report back many advantages, Lower ground operations temperature being one. Another is even lower climb out temperatures, due to the fact that the pressure in this configuration is much lower on top than on the bottom. We have seen most everything possible with flaps on top, sides, bottom and all of the above in one installation. The top mounted location is very popular in Brazil on the RV-10s. Its all good!
Thanks, Allan..:D


Allan
Please post pictures of those side and top mounted doors.
 
Mikey,
I?m carbureted with dual electronic ignition and auto plugs, I think the fuel is boiling in my carb bowl....

I think the fuel is getting hot before it gets to the carb, where it gets hotter. You might try putting a phenolic block or similar insulator between the carb and sump to insulate it from the block heat.

You haven't mentioned if turning on the boost pump helps. If not, your "boiling in the bowl" theory sounds more feasible. Also, that gascolator is likely part of the problem, heating the fuel before it gets to the carb.
 
Honestly I did not read all three pages of posts but I LOVE MY COWL FLAP! Just built a -4 with a 200hp 360 and with my cowl flap open I can takeoff from DVT at 1,500ft and 108deg out and climb at 1,500fpm to 17,500ft and never break 400 CHT.
 
Allan
Please post pictures of those side and top mounted doors.

...Here are some photos of one guys RV-10 installation and I will try to find others
when I get on my other computer. His are a bit further forward than most we have
seen, but will work very well in this local as well. Thanks, Allan.:D











 
Finally took some recent pics, basic Van's system with Vetterman crossover exhaust. Inline screen fuel filter after the fuel selector to the facet fuel pump.

Gascolator to engine fuel pump

IMG_9741-L.jpg


IMG_9735-L.jpg


IMG_9736-L.jpg


Engine fuel pump to red cube

IMG_9738-L.jpg


IMG_9737-L.jpg


Mostly likely source for Radiant heating of the carb and fuel line.....it has the stock Van's heat shield.

IMG_9739-L.jpg


IMG_9742-L.jpg


IMG_9743-L.jpg
 
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I think the fuel is getting hot before it gets to the carb, where it gets hotter. You might try putting a phenolic block or similar insulator between the carb and sump to insulate it from the block heat.

You haven't mentioned if turning on the boost pump helps. If not, your "boiling in the bowl" theory sounds more feasible. Also, that gascolator is likely part of the problem, heating the fuel before it gets to the carb.

Boost pump generally doesn't help when very heat soaked, It clicks loudly like there is no fuel. Sometimes it helps if it is only marginally heat soaked.
 
Boost pump generally doesn't help when very heat soaked, It clicks loudly like there is no fuel. Sometimes it helps if it is only marginally heat soaked.

My buddy had basically the same problem with fuel getting hot and vapor locking. He ended up installing a small 1/8" return line to his left tank. He "T'd" in to the fuel line just prior to the red cube so that even when he has the "sweep" line/valve open, it doesn't interfere with the calculation of the fuel count. With it being such a small "metered" 1/8" line, even if he forgets it open it really doesn't affect his fuel pressure....(or very little). Even though it only sweeps out about 1 cup of fuel per minute, it completely 100% cured his vapor lock issues. He actually even installed a second red cube on that little return line and he gets an annunciation on the G3x that reminds him that the sweep line is open. You can hear the electric pump change sounds as it starts to pick up the cold fresh fuel and get rid of those hot vapors. It really did make it a whole new airplane and he has never once had to deal with vapor lock issues again. The only thing that he has to even slightly be aware of is that if both tanks are completely full he just makes sure that he has the left tank selected...because that's the tank that the little return line is going to. Even in that situation with full tanks, if he were to forget to select the left tank, the worst case scenario is that he'd loose one or two cups of fuel through the overflow. Once again, for him, it was the absolute cure to all of his hot fuel issues.

Mark
 
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Andy, got it. You do have a lot of fuel line routed around the compartment, plus the gascolator and red cube are uninsulated, so fuel is certainly picking up heat from the air. Still, I'd try a cheap and easy experiment.

The clamp-on heat shields are easy to make. Whip up two, each about 12 inches long, or whatever length fits the long straight section of tailpipe which parallels the carb and fuel line. However, don't leave 'em plain. The typical sheet aluminum "heat shield" re-radiates a lot of energy from the side opposite the hot pipe. So, add an insulator and a cover sheet to the side facing the carb, All it takes is a layer of fiberfrax or similar, covered with metallic aluminum duct tape.

If it doesn't work, well, I can't knock a cowl flap for adding mass flow, and Mark's report on the use of a recirculating line is interesting.
 
My apology to the OP don?t want to hijack his thread bout felt my info may in so,e way be connected to his issue as well.

This is interesting to ,e because I get no ( or very little) pull pressure on my gauge sometimes,
It is unchanged by turning on the boost pump. However when I turn on my boost pump the fuel flow goes up. Which left me scratching my head a bit. If the fuel was dead heading the fuel flow shouldn?t go up from 7.5 to 10.5/just from turning on the boost pump, and if it?s dead heading the pressure should show up.

No there are times when turning on the boost pump will raise the pressure and there are times when it?ll show mechanical pressure and boost pressure on the gauge, usually in first start up.
I also hear my boost pump ticking much louder at times.

I have to de cowl the airplane and look at how the lines are plumbed it?s one of the few things I haven?t been familiarized with on my airplane yet,







My buddy had basically the same problem with fuel getting hot and vapor locking. He ended up installing a small 1/8" return line to his left tank. He "T'd" in to the fuel line just prior to the red cube so that even when he has the "sweep" line/valve open, it doesn't interfere with the calculation of the fuel count. With it being such a small "metered" 1/8" line, even if he forgets it open it really doesn't affect his fuel pressure....(or very little). Even though it only sweeps out about 1 cup of fuel per minute, it completely 100% cured his vapor lock issues. He actually even installed a second red cube on that little return line and he gets an annunciation on the G3x that reminds him that the sweep line is open. You can hear the electric pump change sounds as it starts to pick up the cold fresh fuel and get rid of those hot vapors. It really did make it a whole new airplane and he has never once had to deal with vapor lock issues again. The only thing that he has to even slightly be aware of is that if both tanks are completely full he just makes sure that he has the left tank selected...because that's the tank that the little return line is going to. Even in that situation with full tanks, if he were to forget to select the left tank, the worst case scenario is that he'd loose one or two cups of fuel through the overflow. Once again, for him, it was the absolute cure to all of his hot fuel issues.

Mark
 
My buddy had basically the same problem with fuel getting hot and vapor locking. He ended up installing a small 1/8" return line to his left tank. He "T'd" in to the fuel line just prior to the red cube so that even when he has the "sweep" line/valve open, it doesn't interfere with the calculation of the fuel count. With it being such a small "metered" 1/8" line, even if he forgets it open it really doesn't affect his fuel pressure....(or very little). Even though it only sweeps out about 1 cup of fuel per minute, it completely 100% cured his vapor lock issues. He actually even installed a second red cube on that little return line and he gets an annunciation on the G3x that reminds him that the sweep line is open. You can hear the electric pump change sounds as it starts to pick up the cold fresh fuel and get rid of those hot vapors. It really did make it a whole new airplane and he has never once had to deal with vapor lock issues again. The only thing that he has to even slightly be aware of is that if both tanks are completely full he just makes sure that he has the left tank selected...because that's the tank that the little return line is going to. Even in that situation with full tanks, if he were to forget to select the left tank, the worst case scenario is that he'd loose one or two cups of fuel through the overflow. Once again, for him, it was the absolute cure to all of his hot fuel issues.

Mark

I think my problem is very similar, if I get the fuel moving with more throttle RPM the surging richness goes away. I think at idle the fuel is sitting and cooking.
 
Dan,
I was thinking of a similar heat shield on the exhaust next to the carb and fuel line.

My fuel lines are on the long side, as a first time builder I was thinking ?flexibility.?

I?m also thinking about removing the gascolator, doesn?t seem to do anything for the taildragger. Is it possible to remove the gascolator bowl and cap it off or just easier to remove it and use a bulkhead type fitting?

I think I will continue the oil door cowl flap as well, the door/hinge/hole is already there.
 
Hi Andy, you've had a lot of good advise in this thread but I thought I would add one more voice. I have similar heat soak issues and I was able to greatly limit the severity by wrapping all of my FWF fuel lines (already fire sleeved by Tom) with a reflective/insulated tape. https://www.amazon.com/gp/product/B000QFN3DU/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

It did not eliminate the problem completely but it did help noticeably. Now my engine doesn't sound like its on its last leg when I'm on the ground hot.
 
Boost pump generally doesn't help when very heat soaked, It clicks loudly like there is no fuel.

This is an interesting statement. My per-plans Facet cube pump also clicks loudly when there is no fuel present at the INLET, but when operating at full pressure and zero flow (deadhead) it gets quiet. I assume others are the same.

Totally just guessing here, but might there be an outside chance the problem is not forward of the firewall?
 
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I think my problem is very similar, if I get the fuel moving with more throttle RPM the surging richness goes away. I think at idle the fuel is sitting and cooking.

If we landed for some reason we'd usually have to wait an hour or more to let everything cool down enough so that it wouldn't vapor lock, but with the mod in place, it's never an issue. Two summers ago we were trying to take off in the middle of the summer in Lubbock Texas. If any of you are familiar with summers in Lubbock, than you know what I'm talking about. Lubbock has a runway that appears to be at least 10 miles long...well maybe not quite that long....but it's long. We started out takeoff run at the very end of the runway and we almost had to abort because we were running out of runway. I'll bet the engine wasn't making 50hp. Well long story short, we did make it out of there and as cool fuel started flowing into the system the engine continued to run better and better...but it was a close call. After that event he installed that little sweep system and has never once experience vapor lock again. To this very day though, and just to confirm that it's the modification that did the trick, he can purposely not turn the bypass valve on just to see if he can make it vapor lock...and he can. He'll then open the little valve, listing for the change in sound to the electric pump, apply full power, and away he goes.

Mark
 
This is an interesting statement. My per-plans Facet cube pump also clicks loudly when there is no fuel present at the INLET, but when operating at full pressure and zero flow (deadhead) it gets quiet. I assume others are the same.

Totally just guessing here, but might there be an outside chance the problem is not forward of the firewall?

“There’s always a chance,” but the issue is defenitely heat related FWF. I generally have fuel pressure and the loud clicks of the fuel pump go away shortly after turning it on when hot and on the ground. I have also had erratic and 0 fuel pressure and continuous loud clicking from the fuel pump, very hard to keep running at that point. I’ve also done flow checks and can fly 9 months out of the year without an issue.

As others have said I think with the airplane wings shining in 95+ temps the fuel starts out over 100*. Metal parts specifically gascolator/red cube/carb/fuel pump are bathed in 180-220 degree cooling air not to mention the temp of the accessory case and sump and radiant heat from the exhaust adds to this temp. I’m guessing when the cooling air stops the temp goes up and boils the fuel in the carb first, if really heat soaked also possibly boiling in sections of the FWF fuel lines.
 
I wonder if anyone has ever tried a fuel sump on the carb bowl itself. The idea would be when you suspect high temps on a quick turn, flip on the electric pump and sump off a couple cups of fuel until the pump sounds happy and the fuel you're sumping feels like cool gas out of the tank. Then dump what you've sumped off right back into the tank, climb in, and go.

An admittedly odd idea, but it would be cheap and potentially simple to implement.
 
A thought from the scrounger gallery. If you're going to do heat shields as Dan mentions, you can use stainless instead of aluminum. Really thin stainless doesn't weigh much (if any) more than aluminum that's thick enough to be stable. Added advantage is less re-transmission of heat.

Now for the scrounger reference. Check the local Wally World or other discount chain for a cheap stainless 'stock pot'. It cuts & deburs easily with an abrasive cutoff wheel, and you can shape the pieces with your seaming pliers, vice, etc.
 
A thought from the scrounger gallery. If you're going to do heat shields as Dan mentions, you can use stainless instead of aluminum. Really thin stainless doesn't weigh much (if any) more than aluminum that's thick enough to be stable. Added advantage is less re-transmission of heat.

Now for the scrounger reference. Check the local Wally World or other discount chain for a cheap stainless 'stock pot'. It cuts & deburs easily with an abrasive cutoff wheel, and you can shape the pieces with your seaming pliers, vice, etc.

I like the tip, I've scrounged cutting boards and various layup shapes from Wally World numerous times.
 
I had some scrap stainless, FiberFrax and foil tape so I went to work making a heat shield.

I used my roller a second time (only had it 3 years) to roll my over-sized piece of stainless and fit it over the exhaust.

IMG_9951-XL.jpg


IMG_9952-XL.jpg


I made some trim marks with a marker and scrap cardboard and went to work cutting out my piece with the die grinder. I like to use scrap angle as a cutting guide for straight lines, works well for filing too.

IMG_9953-XL.jpg


IMG_9954-XL.jpg


Heat Shield with the edges cleaned up.

IMG_9959-XL.jpg


I made and riveted some attachment brackets to the heat shield and covered the side opposite the exhaust pipe in Fiberfrax and aluminum tape.

IMG_9963-XL.jpg


IMG_9966-XL.jpg
 
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Heat shield in place.

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I don't have any "before" temp measurements, but will try to get a guesstimate based off the distance from the exhaust pipe. The opposite side has the standard vetterman crossover heat muff I suppose acts as a radiant heat shield as well.
 
I placed my temp probe just in front of the fuel elbow on the carb.

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I don't have any "before heat shield" temps, but this location by the carb/fuel line is 35-40*F hotter than the rest of the lower cowling. In cruise I was seeing 205*F with OAT's of 65*F. After a 30 min shutdown and taxi back to the runway with 86 *F OAT's the temp was 245. Only 2-3 seconds of engine stumbles right after the heat soaked engine start, aggressively leaning the mixture stopped the stumbling.
At the completion of the flight I left the airplane idling for an extra couple minutes at full rich with no stumbles. I need to fly in hotter temps and longer taxi times for further evaluation.
 
After flying 20 hours with the larger heat shield, I'ld have to say it has helped with the fuel boiling in the carb. I haven't had an issue on my hot quick turns, but its been a little cooler than normal with lower 90's.

It's condition inspection time and I would like to further improve my fuel cooling by :
1. Removing the Gascolator
2. Installing a Phenolic spacer between the carb and the sump

Is there any reason I should not remove the gascolator? As a taildragger it is not the lowest point in the fuel system and I do have a filter between the fuel selector and the electric boost pump.

I believe I could replace the gascolator with an AN6 90* bulkhead fitting like this one.

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Either I have Tom S make me a new hose with a 45 end, or a hard AN6 45* like this may work with the existing hose.

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I think the AN6 90* bulkhead fitting would fit perfectly with the existing hard line from the fuel pump inside the cockpit.

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For the phenolic spacer (Thx SnoperCod!) between the carb and the sump I think I would need to pull the studs and replace with longer ones. Perhaps use a low profile metal lock nut instead like a MS21042.

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Thoughts?
 
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Is there any reason I should not remove the gascolator? As a taildragger it is not the lowest point in the fuel system and I do have a filter between the fuel selector and the electric boost pump.

Conventional wisdom says carbs do need a gascolator.

That said, have you ever seen any water in yours?
 
I know of gascolators being found 1/2 full of water on RV's, so it probably depends on many factors (sumping diligence of pilot, etc.)

It is a misconception that gascolators are supposed to be installed at the low point of a fuel system.
That would probably be the optimal (but not always practical) location, but the primary purpose is to act as a filter by artificially positioning a low point within the flow path of the fuel. This low point, along with the fine screen filter that the fuel must flow through leaving the gascolator, separates water and other debris from the fuel before it gets to the carb.
 
I know of at least one carb'd -4 that started life with a gascolator and is now flying without; it's in my hangar. It lost the gascolator after near engine stoppage at ~1k' agl after takeoff on a 100 degree day. Since the plane has a real fuel filter, and any water in the tanks will be gone if the pilot does their job, it was decided that the gascolator's primary function on this plane was heat collector.

No more rough running in several years since.

Not telling anyone else to do it; just passing on one person's experiences.

Charlie
 
For some reason we still have gascolators. Why? Because reasons! That's the way its always been!

Would you ever drink a coke by skimming the top of the cup with a straw? That's how a gascolator works.
 
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