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Oil filler door/Cowl Flap

crabandy

Well Known Member
I've been contemplating using the existing oil filler door in my upper cowling as a cowl flap. The hole is already there and my main goal is cooling on the ground with very little pressure differential between the upper and lower cowling. Extra cooling on climb out is another benefit.

Previous issues described in this post:
http://www.vansairforce.com/community/showthread.php?t=161338&page=6

I've spent a little time mocking up templates with cardboard but have narrowed things down a bit and time to "start making scrap." I rolled some scrap .063 since it's faster to make than glass.

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It fits the cowling contour pretty good with a little extra manipulation.

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I'm down to 2 possible door styles. #1 is a one piece slider door that works like a sliding glass door sliding down using a track and linear actuator. It has to slide down because not enough room forward or aft. The bottom of the door must also slide in toward the centerline of the cowling because of the increased curve of the cowling.

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#2 idea is a 2 piece door design hinged on the upper and lower portions, excuse my errrr uh I mean my 3 year old boys drawings.

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#1 issues making a curved track inside of the existing upper cowling radius and required linkage that can also make the door flush with the upper cowling.

#2 is much easier to make flush with the upper cowling, but what kind of linkage to use to make it work. Or do I use 2 linear actuators.

I'ld appreciate any thoughts to move me along!
 
The simple chore of checking the oil could prove to be a bit of a problem?

Walt,
Cowl flap/oil door open on pre-landing checklist as I’m going for ground cooling so it would be normally open on the ground. I would have to have external screw/screws on the door to gain access in case of electrical/linkage or servo failure.
It is making the simple door more complicated, but it’s been a while since I’ve tinkered on the airplane. I need more cooling on the ground, 90* and a quick turn starts cooking my EarthX battery as noted by the over temp alarm. I was surprised how the lower cowling temps started increasing below 120 knots even though CHT’s and oil temp drop significantly. Preliminary testing without the oil door shows temps drop slightly throughout landing phase.
 
Cooling

Andy, wouldn't an opening in the top cowl just let cooling air out without passing over the cooling fins of the engine? It would seem that this might make things worse from a cooling perspective. What am i missing here?
 
low pressure zone

Andy, wouldn't an opening in the top cowl just let cooling air out without passing over the cooling fins of the engine? It would seem that this might make things worse from a cooling perspective. What am i missing here?
Depending on the engine, the oil door is on the low pressure side of the engine cooling, so all the air that would exit should have already been pushed through the engine cooling fins.
 
Umm...

The air on the upper side of the cylinders is typically high pressure, moving down through the fins to the low pressure side and out of the cowling exit...

Typically, the dipstick/fill tube is on the top side of the engine, in an area of high pressure...
 
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The air on the upper side of the cylinders is typically high pressure, moving down through the fins to the low pressure side and out of the cowling exit...

Typically, the dipstick/fill tube is on the top side of the engine, in an area of high pressure...

On a four cylinder engine, the dipstick is behind the baffle. The six has the dipstick tube in the upper plenum area ahead of the baffle. Rocketman has a 10 and is used to seeing it in that position.

Ed Holyoke
 
Andy, wouldn't an opening in the top cowl just let cooling air out without passing over the cooling fins of the engine? It would seem that this might make things worse from a cooling perspective. What am i missing here?

Paddy, on your 6 cylinder you are correct. On the 4 cylinders the oil dipstick is behind the baffles and part of the lower cowling volume.
Oops sorry it was already covered previously
 
I think this idea has some merit for increasing the battery cooling, via convection, when on the ground. I'm not so sure about in-flight. If the area above the new opening has a higher pressure than the exit area from the cowl (between the exhausts), then you will get some cool air over the battery - but at the expense of higher pressure at the exit, which may mean reduced cylinder cooling/higher CHTs. OTOH if the new opening area has a lower pressure than the normal exit area, then you will get additional flow up and out, helping cylinder cooling - but at the cost of running warm air over the battery. I don't know how to find out without actually testing in flight.
 
I remember reading about a pair of doors in the upper plenum that were hinged. On the ground they would open, but in flight the dynamic pressure would find them closed.

Never saw a picture, but by this reference maybe someone else has photos?
 
I think this idea has some merit for increasing the battery cooling, via convection, when on the ground. I'm not so sure about in-flight. If the area above the new opening has a higher pressure than the exit area from the cowl (between the exhausts), then you will get some cool air over the battery - but at the expense of higher pressure at the exit, which may mean reduced cylinder cooling/higher CHTs. OTOH if the new opening area has a lower pressure than the normal exit area, then you will get additional flow up and out, helping cylinder cooling - but at the cost of running warm air over the battery. I don't know how to find out without actually testing in flight.

Bob, Thx for the thoughts.
Convection cooling on the ground agreed!

As far as in flight I?m still assuming a lot, I?m not planning on drawing air in from the oil door. Im assuming that the area around the oil door is close to atmospheric pressure (same as he lower exit) and will be additional exit area. Lower cowling pressures of 1.5-2.0 inches of H2O at climb speeds should push air out both exits I?m thinking. Either way once I have air moving through the cowling at climb speeds the lower cowling temps drop 50+ degrees from the stagnant ground ops.
 
ideas

Many years ago, I recall seeing a guy that made automatic doors using the thermostat from an auto engine. It was a pretty neat idea...
 
I want the oil door/cowl flap to open inward, I must still be able to access the oil filler tube and cowling pins. The stock placement of the oil door isn't quite optimum for opening inward, clearance with the oil filler tube and engine mount aren't enough. If I can figure out the geometry of hinging the door at an angle I may be able to create a larger oil door/cowl flap than a horizontal hinge line, we'll see. Either way I need a smooth clean slate on the inside of the cowl.

I ground the rivets off the existing oil door hinge and strike plate and chiseled them off the cowling.

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Roughened things by sanding both sides, the drill motor sand paper flap attatchment is my sledgehammer approach to sanding. I used it to initially smooth out the epoxy ridges from the hinge and strike plate.

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I couldn't quite find that "just right" material I was looking for to act as a backer-board for the outer cowling. The plastic cutting board sheets from Wal-mart have gotten thinner and a little too floppy, I ended up using 1/8" Acrylic Sheet from the hardware store that was a little too stiff.

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A hairdryer to warm it up helped it conform a little, clecos to hold it in place.

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I made several templates with 2 mil plastic and a sharpie.

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I'm not in love with my replacement scale (up to 50lbs is too big), my first el-cheapo light weight scale worked better on the lighter weights. For most of my layups I mix the epoxy in 20-50 gram batches in tiny cups, saves on waste and exotherming. I do like putting the scale in a gallon plastic baggie and once I can no longer read the display I replace the baggie.

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I mixed a soupy batch of epoxy/flox/micro and spread it into the existing exterior flange of the oil door opening, set in a 2 ply sheet of 9 oz cloth and clecoed on the acrylic sheet. Fiberglass was wet-out between 2 mil plastic and cut out reference the previous templates with the fabric pizza cutter.

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4 more plys of 9 oz cloth filling the opening on the oil door and another fillet of epoxy/flox/micro around the edges. It was topped with scraps overlaping the oil door gaps and finally peel-ply.

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The acrylic sheet cleco'd to the cowl did a pretty nice job of fairing the new glass to the existing glass, as exepected I have a dozen or so "worm holes" to fill between the flange and new glass/epoxy filler slurry.

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I verified the oil dipstick clearance.

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I made a cardboard template and taped it on the hinge line to check for clearances for opening the door to the inside.

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The oil filler cap and engine mount limit the door size/shape when hinging horizontally on the lower side.

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I made a plastic template of the oil door for the cowling cutout and making fiberglass pieces for the oil door, it's approximately 31 sq inches compared to the stock 27 sq inch oil door. I estimated my stock cowling exit in the low 50 sq inches which I've since shrunk to about 35 sq inches. The oil door/cowl flap should increase my total exit area to 60+ square inches. Again the in-flight benefits would be a bonus, I'm mostly counting on convection cooling on the ground.

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The inside of the cowling still had protruding ridges from the stock cowling opening, I added fiberglass strips around my proposed opening, I'll have to sand most of it back off but it should leave me with a smooth surface requiring a smidge of filler to mate the oil door/cowl flap too.

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I faired in the new glass with a little micro than cut the new hole. I beveled the inside edges for a radiused lip for the oil door to seal against from the inside.

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I didn't preplan well enough and had to shim a piece of plastic cutting board in where the acrylic was too small. I wanted a tight fit without tape lines so I waxed the cowling and shot 3 coats of PVA.

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I started with 2 plys of 8.9 oz glass cut to fit the opening, I then used a slightly undersized piece of Lantor Soric core material. I've found the soric doesn't make a nice finished edge so I used a filet of epoxy/flox around the edges of the soric.

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A couple more plys of 8.9 oz glass to join it all together and make a flange to seal against the cowling.

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Stinks I didn't use a large enough piece of acrylic, I'm sure it'll take a couple extra hours to fair in the little overlap of the plastic cutting board. From the top side You can see the filet of epoxy flox around the edges of the undersized Soric.

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The new oil door/cowl flap was TIGHT in the cowling, a smidge of epoxy/flox had flowed from the door between the cowling and the acrylic. Even after sanding the new door flush with the cowling it was staying in place, I really started to have doubts that the wax and PVA didn't keep the epoxy from bonding to the cowl on the thin edge and thought I might have to cut it out. In the end I was able to slowly pry it out, I had rounded the edges of the cowling too much and it created a concave joint on the new door that kept it in place.

The new door cleaned up and in place on the airplane.

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View from the inside, I really should've made it 1/8" smaller all the way around as I only have 3/32" clearance from the dipstick and engine mount. I can still sand the flange down a tad for more clearance.

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On the positive side of things the new door offers a lot more room for:
-installing the firewall hinge pins
-oil filler/dipstick
-battery charging port
-engine sump heater port

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I've got the model of my linear servo picked out, just have to scratch my head over the geometry and stroke length.
 
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I decided on the 100MM stroke, 64:1 gear ratio P16-S linear actuator from Actuonix. The P series actuators are more robust than the L series, I would like 125mm stroke but 100 should work.

https://www.actuonix.com/P16-S-Linear-Actuator-p/p16-s.htm

I roughly calculated 31 sq in of oil door area, I currently have 1-2 inches of H2O of lower cowling pressure for most flight speeds. Calculating for 3 inches of H2O (.11psi) is 3.41 lbs of force holding the oil door closed.

I chose the 64:1 gearing not for the 90N (20ish lbs) lifting but the speed is slower, I?m also going to be operating it at an angle (still unknown) that will require more force. I?m hoping for the advertised longer life especially operating in 170-200+ *F. Most every micro servo I looked at was rated at 5 lbs and 50*C (122*F), the P series is still only rated for 50*C.
 
I decided on the 100MM stroke, 64:1 gear ratio P16-S linear actuator from Actuonix. The P series actuators are more robust than the L series, I would like 125mm stroke but 100 should work.

https://www.actuonix.com/P16-S-Linear-Actuator-p/p16-s.htm

I roughly calculated 31 sq in of oil door area, I currently have 1-2 inches of H2O of lower cowling pressure for most flight speeds. Calculating for 3 inches of H2O (.11psi) is 3.41 lbs of force holding the oil door closed.

I chose the 64:1 gearing not for the 90N (20ish lbs) lifting but the speed is slower, I?m also going to be operating it at an angle (still unknown) that will require more force. I?m hoping for the advertised longer life especially operating in 170-200+ *F. Most every micro servo I looked at was rated at 5 lbs and 50*C (122*F), the P series is still only rated for 50*C.

I have toured the factory and asked the question. At higher temperatures, the internal glue that holds these actuator assemblies together will soften. Forewarned is forearmed.

V
 
Thanks for the reply Vern, I do appreciate it.

I spoke to an associate who seemed quite knowledgeable, he stated the plastic on the internals of the motor will get soft and begin to melt around 65-70 *C (149-158F) and at some point shoutout. They experimented with higher temp rated motors but their lifespan was 25% of the lower temp rated motors and have not produced a higher temp version. I haven?t found any micro servos rated for hotter.

I may very well be throwing away my time and money just to replace the servo with a push/pull cable. But there seems to be some success out there with the 50*C rated servos out there. Just guessing the antisplat cowl flap servo is rated at 50*C, I wonder what the servo lifespan is on the current fleet? Pretty sure the lower exit where most are mounted are bathed in hotter air than the top of the cowl by the oil door.
 
Pretty sure the lower exit where most are mounted are bathed in hotter air than the top of the cowl by the oil door.

Easily as hot after shutdown. I have an air temp probe up near the oil filter right now.

If the goal is more mass flow at approach speed and slower, and given the new door closes from the inside, can you actuate pneumatically? A spring holds it open, and increased dynamic pressure closes it?

Spitballing outside the box, how about pneumatically using manifold pressure? A spring holds the door shut. Low MP pulls it open.
 
Easily as hot after shutdown. I have an air temp probe up near the oil filter right now.

If the goal is more mass flow at approach speed and slower, and given the new door closes from the inside, can you actuate pneumatically? A spring holds it open, and increased dynamic pressure closes it?

Spitballing outside the box, how about pneumatically using manifold pressure? A spring holds the door shut. Low MP pulls it open.

Hmmm, I mostly dismissed the spring hold open and pressure closing idea because:
-about .5? H2O difference for opening and closing based on speed/cowling pressures, with the 31 sq inch door about .6 lb so may be doable
-I don?t have any higher altitude (13,000-19,000) cowling pressure data, thinking the lower cowling pressure would drop enough to open the door in cruise?

I would also like the door open on initial climb out from hot quick turns, so open with high manifold pressure too.

And Thanks for the spitballing Dan!
 
Keep
I don’t have any higher altitude (13,000-19,000) cowling pressure data, thinking the lower cowling pressure would drop enough to open the door in cruise?

For 20K, q = 0.00339 x .5328 x KTAS^2

The second term, density ratio, is higher as altitude is decreased. Your cowl should be good for q*0.75 as an upper plenum pressure.

I would also like the door open on initial climb out from hot quick turns, so open with high manifold pressure too.

Doing so would only require a control valve. Close valve before takeoff for an open door at high MP. The MP tap would have a restrictor for safety, just like your MP sensor line, with the valve as a backup. The advantage to such a system is the large available force; typical MP acting on a small pneumatic actuator is much higher than available dynamic pressure.

Just more spit ;)

EDIT...ignore the 75% dnamic pressure. Lower cowl pressure is what we're dealing with here
 
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I finally got back after it today, I had a smidge bit of time since I can't do KOSH this year. Bent some .063 for the attach brackets. I had already ordered the servo before the other ideas started stirring, we'll see how long it lasts.

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I spent most of my time visualizing different ways to connect both ends, this is what I ended up with. I used nutplates to attatch the servo bracket to the oil door so I can remove the screws and open the oil door if the servo fails. I glued/sanded a chunk of foam on the cowl to match the angle of the rear attach bracket of the servo then glassed over it. I then melted the foam with acetone, roughed up the surface and drilled a hole for a 3/16th bolt. I waxed the bolt and used a metal locknut on the inside of the fiberglass then filled the cavity with a liquidy epoxy flox mixture. I also used epoxy/flox/filler to build up the rear edge of the oil door to fit the hinge. I used tape covered Popsicle sticks as temporary dams.

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Everything is installed and wrapped the servo with Fiberfrax and foil tape. Thankful I ran a couple extra twisted pairs of 22 awg through the firewall, it made wiring it up a breeze.

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Closed and opened.

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I had previously installed the cowl flap switch (Ray Allen RS-2) to cover up a poorly placed toggle switch for the auto pilot servos.

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Attempting a video of it in action, Should have some flight test numbers tomorrow.

https://andycrabtree.smugmug.com/Oil-Door-Cowl-Flap/Oil-Door-Cowl-Flap/i-JbZSPhb/A
 
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I did some flying today and got some intial numbers. I used stabilized cruise with realitively smooth air and utilizing the autopilot, I recorded 5 minute averages for speed, temps and pressures twice open and twice closed. Lower cowling pressures were obtained with a single picollo tube place vertically at the bottom of the lower cowling attached to the lower engine mount with the manometer plumber to the static system and CHT?s and TAS from the EFIS.

Opening the oil door drops the lower cowling pressure approximately 60%, .65 in H2O @110 KIAS and .85 in H2O at 146 KIAS.
LOP cruise was 161 KTAS with the door open and 164 KTAS with it closed.
Very little change in CHT?s, avgerage was 3-5 degrees cooler with the door open. Oil temp was about 1-2 degrees cooler.

I?ll need a lot more flights to try and filter any cooler climb out data. I need to check the pressure directly underneath the cylinders to see if it changes as much as the rest of the lower cowling does.
I did do 2 hot quick turns giving rides today without a single hiccup during ground ops, it was only 88* though.
 
I?ve put 20+!hours on the oil door/cowl flap, the small CHT/Oil Temp differences remain but I?ve stopped measuring them. I do like the slightly lower temps on climb but Love the RPM/Speed increase when I close the flap.
Since the addition of the cowl flap I?ve only had 1 battery over-temp alert, I was heading home after my third hot quick turn at 90+* (giving rides) after I leveled off and closed the cowl flap. Low level and hot the alert didn?t turn off on my short 15 min return flight after I re-opened the cowl flap. Needs more time and or cooler air.
Fuel boiling in the carb has been reduced significantly. With the cowl flap open on the landing checklist, lean mixture and using a higher idle of 1000 RPM I?ve been able to quick turn/hot start and taxi with minimal ?chugging.?
I?m making progress!
 
Excellent thread progression, Andy. The CHT/oil temps might have a larger delta on a max angle of climb at full throttle. At cruise and steady speeds I have similar results to you (for changes), a shallow slope effect on CHT.

You can cut out the core and back fill with flox for your pivot anchor. That will restore the glass stiffness around the bracket connection. Maybe I missed it and you did that already.
 
2 1/2 years and 250hours+ on the oil door/cowl flap with no issues just cooler temps, my carb fuel boiling issue has been 95% resolved and battery temp alarms are drastically reduced. One of my favorite mods so far!

I have found I do need to brief formation lead/wingman and other observant ground crew as an open oil door seems to draw some occasional attention!
 
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