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Oil Cooler Air Door

Neal@F14

Neal@F14

Well Known Member
To help get the oil temps up for cold weather flying, I've conjured up an oil cooler air door, electrically operated with a Ray Allen trim servo. First test flight shows it works quite well. With the door completely closed, we got it up to 195-200 on a pretty cold day, then slowly opened the door a little with the push of a button and oil temps came down to a nice 185 and stayed there, where we couldn't get 135 without the airflow restriction. The door is covered with thick felt glued on the cooler side for cushion/anti-chafe purposes. We'll keep a close eye on it to be sure there is no wear of the oil cooler face, but the felt is pretty soft and should not pose a problem. I connected the potentiometer wires of the servo to a Dynon D120 general purpose input and use the aileron trim indication on the screen to show when the door is open (left) and closed (right) as a display and it seems to work pretty slick.

Will the servo last under the cowl? Who knows...
Will it open up wide enough in the summertime? We'll find out... It can always come off quite easily with a quick pull of a piano hinge pin and the servo linkage.

It was a neat project and that's what's so cool about an experimental, you get to experiment! And if it doesn't work out, and has to be removed, it was a learning experience.

Door closed:
img4695nf.jpg


Door opened:
img4699oz.jpg


More construction pics here: http://img691.imageshack.us/g/img4686k.jpg/
 
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An obvious question would be: What will the oil temp do if the door gets stuck in the closed position?
 
PCHunt said:
An obvious question would be: What will the oil temp do if the door gets stuck in the closed position?
Click to expand...

Pretty much the same results you'd expect to get from any kind of other oil cooler door/shutter mechanism that gets stuck closed.

As long as the OAT is around 40 deg F or lower, I would guestimate the oil temps to max out at about 210-215 based on what we've seen in the air thus far with the door in place, and also with aluminum foil tape covering various amounts of the back of the cooler on previous flights. The amount of air leakage past the cutouts in the door to clear the motor mount tubes will still allow about the amount of air equivalent to always having one row uncovered.

Obviously, if the servo fails in the shut position with warmer OATs, then the door will have to come off until the servo is repaired. The door comes off easily with the snip of one safety wire loop and pulling the hinge pin, and removal of one small cotter pin and clevis pin.
 
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Oil Coller Door

Here's another great way to implement a cockpit controllable oil cooler door. This one is for a firewall mounted cooler. The parts on the #3 cyclider baffle are from a wood working shop vac system available just about anywhere wood working products are sold.
OilCoolerAirValve2.jpg
 
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***Grain-o-salt warning: I'm not an engineer***

I'd be a little bit concerned with this arrangement because it applies a non-trivial bending moment to the plunger that comes out of the servo.

The figure below shows the arrangement as I understand it at the top. Below that, we see that the force of the air pressure behind the door applies a force F to the plunger. Resolving F into x and y components, we see that the y component trying to bend the plunger is almost as large as the x component that the plunger resists by moving in and out of the servo. At the bottom is a possible revision that almost completely eliminates the bending moment applied to the servo plunger.

oil_cooler_door.GIF


An interesting question is, how great is the force applied to the door? According to this article, we might reasonably expect around 2" H2O, or 0.072 lbs/in^2 of pressure drop across the oil cooler. Further guessing that the oil cooler area is 4"x6" or 24 square inches, that gives a total force of 24*0.072=~1.7 lbs. So if you can pull about 2 lbs on the center of the door and not have the servo plunger bend or bind, you're probably OK.

If anybody sees any substantial errors in my understanding, please post up!

Thanks, Bob K.
 
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I considered the same things you did (very nice drawings, BTW!) but was limited by what space I had to work with and what parts and materials I had on hand. I would've much rather had a more straight shot with the plunger, but unfortunately the cowl on the -8 has only about 3/4" of clearance between the servo mounting plate and the fiberglass of the cowl in that area. The RAC servo specs claim to withstand a static holding force capability of about 40 lbs, and a moving thrust capacity of 20 lbs. The specs don't talk about the sheer strength of the plunger, but it seems to be made quite strong, and doesn't flex even when fully extended and I pressed on it pretty hard. I think it will be strong enough, especially considering how much the airflow slows down as it passes thru the SW oil cooler fins. If the plunger breaks, at least the door will be able to flop mostly open in that failure mode. We just wanted to whip up something quick that would help us out with the cold oil temps of winter flying. If I had more time to work on a better design, I'd probably made a fiberglass flange for the rear of the cooler that has a fitting for 4" SCAT tube, and put one of these round butterfly type air controllers inline: http://www.nonstopaviation.com/rv10-controller-cooler-p-14566.html

EDIT: After looking at my own pics a little more, I might just make a nylon wedge spacer to put between the servo and the plate. That would help get the thrust more inline with the plunger, and would be an easy, cheap and simple improvement.
 
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Due to others experience, it seems that a restriction on the front side of the cooler has been working much better than the back. Seems that the oil still get's somewhat cooled anyway, when the door is on the back. Anyway, that seems to be the experience of others. If yours is cooling satisifactory........then good.

L.Adamson --- RV6A
 
Another oil cooler option to help warm the oil is one that Larry Vetterman uses. He installed a ball shut-off valve in the oil line leading to the oil cooler, control by a vernier cable in the cockpit. In the 'closed' position it's not fully closed, but any intermediate position restricts oil flow through the cooler in varying amounts, or full open makes it like it's not there. He can control his oil temp to within a couple degrees. Larry says for his engine, the perfect oil temp is 195-197, and at this temp his engine is the smoothest. He's able to maintain this temp summer or winter with his setup.

On my RV-8, I have installed the Van's oil cooler shutter, mounted between the oil cooler and the baffle. I had to modify it because when I bolted it in the first time, tightening the mounting bolts squeezed the shutter so tight you couldn't move the lever. I cut notches in the moving shutter parts and installed a spacer in the center, top and bottom, and it works now, but still a little stiff. To make matters worse, I had to cut the length of the lever down to clear my cowl and now the force required to open/close it is pretty high. Plus the total movement length from open to closed is only about 1/2". I couldn't put it in upside down because of interference with other parts. I'm going to test fly it today, but I'm not real hopeful it will be very good. I had a blocking plate in front at first and it worked, but only worked well at a given OAT.

Sorry abut hijacking your thread. Accurate oil temperature control is frustrating.......
 
Scott Hersha said:
On my RV-8, I have installed the Van's oil cooler shutter, mounted between the oil cooler and the baffle. I had to modify it because when I bolted it in the first time, tightening the mounting bolts squeezed the shutter so tight you couldn't move the lever. I cut notches in the moving shutter parts and installed a spacer in the center, top and bottom, and it works now, but still a little stiff. To make matters worse, I had to cut the length of the lever down to clear my cowl and now the force required to open/close it is pretty high. Plus the total movement length from open to closed is only about 1/2". I couldn't put it in upside down because of interference with other parts. I'm going to test fly it today, but I'm not real hopeful it will be very good. I had a blocking plate in front at first and it worked, but only worked well at a given OAT.
Click to expand...

The oil shutter from Van's ....needs washers for spacing. Otherwise, the shutter is pressed against the fins of the cooler. Once you've got that spacing, the shutter door operates very freely. On my initial installation, I ran into the same problem. BTW -- we're having good success around here, with the shutter setup.

L.Adamson --- RV6A
 
This is how I did it with Van's firewall kit... Just made a butterfly valve contolling the amount of air to the cooler controlled via push/pull cable...Works well.... Sheldon

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LIke Sheldon's except...

I installed my butterfly valve at the rear baffle flange rather than at the cooler. I have a 3.5" scat to a firewall mounted 13-row cooler with a wedge plenum similar to Van's RV-10 firewall cooler mount, but at a steeper angle to fit near the RV-8 engine mount tubes.
 
Good results so far...

I flew for a half hour yesterday late afternoon, and for also an hour and a quarter this morning, and was able to get the oil up to 200 with OAT in the low 40's today. I left the door completely shut for startup, takeoff and climb, and then by the time I was up to 5500 MSL the oil was up to 200. Opening the door just a wee bit, brought the oil back down to 185 where it stayed for the rest of my flight even after the OAT warmed up to the low 50's. I'm pretty pleased with the performance of my oil cooler door... it's going to be a really useful feature for cold weather flying.

Next we need to stuff a stainless steel potscrubber into cabin heat exhaust muff to get the cabin heat working a little better... and do something about the cold air leaking in under the rear canopy skirt so the rear seat pax doesn't freeze his neck off :eek:
 
Very Similar

I made a door that looks almost identical. Lined it with orange baffle material for a better seal. I ran another vernier cable through the firewall however for control instead of a servo. As you noticed, a small bit of opening is almost like no door at all.
 
scsmith said:
I installed my butterfly valve at the rear baffle flange rather than at the cooler. I have a 3.5" scat to a firewall mounted 13-row cooler with a wedge plenum similar to Van's RV-10 firewall cooler mount, but at a steeper angle to fit near the RV-8 engine mount tubes.
Click to expand...

Here is a picture of Steve's oil cooler installation. Note the generous size of the plenum, an important factor in good airflow through the cooler. The butterfly is at the flange where the cooler's SCAT tubing meets the engine baffle. The arm that controls the butterfly is on the left end of its shaft; you can see the bowden cable that controls it coming up from below.

100_1802a.JPG


Thanks, Bob K.
 
The oil shutter from Van's ....needs washers for spacing. Otherwise, the shutter is pressed against the fins of the cooler. Once you've got that spacing, the shutter door operates very freely. On my initial installation, I ran into the same problem. BTW -- we're having good success around here, with the shutter setup.

L.Adamson --- RV6A
Click to expand...

The fins on a Stewart Warner are inset a little from the mounting flanges and wouldn't touch the oil shutter. However, on mine I made a 1/2" spacer between the cooler and baffle to help with cooling by holding the cooler away from the #4 cylinder a little - which did help - and that spacer was pressing against the shutter all the way around. I test flew my installation two days ago and took it on a shake down cruise to Michigan yesterday, and surprisingly, it works quite well. I can control my OT pretty precisely and have no trouble warming it up on a cold day (6 F). I didn't think I would be able to control it so well with such a short lever arm.
 
7-4-08025.jpg
7-4-08024-1.jpg


This set up works real well for us. The oil temps are always consistent. I don't have any pics of the finished product but the duct touches the oil cooler separated by Van's oil cooler install kit and felt. If you needed to put on a door on it I would think Van's sliding door would work. The front of the duct needs to be far enough forward to catch the air. The only disappointment is the cowling is beginning to crack at the vertical area where it is attached in the back. You notice that the oil cooler is angled down and back so the air flows naturally out the cowl with out any ducting. Sorry the pic is on it's side. Im still a little green at this picture thing.
 
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A question. Does the vernatherm not inhibit oil from getting to the cooler until it reaches whatever temp that causes it to open?
 
Scott, the reason I asked the question was due to a recent experience I had flying around at -20 Celsius. My oil temp was about 135 so I asked a fellow (very experienced) rv?r who has the same engine if I should block off most of my cooler and give it another try. He told me no oil was going through my cooler until the oil reaches about 180 and that is when the vernatherm forces it to do so. He also said the excess cold air coming through the cowl was the problem and told me to duck tape off some of the inlet air instead. So he was indicating there would be little to no flow going through the cooler until the oil heats up?
 
Shark said:
This is the route I took, Happy
Click to expand...

I have one of the earlier ones from Van's, same design, and it works *fantastically*. I just used a (very nice locking) push-pull McFarlane cable for it, and I can very precisely control the oil temps.
 
RV7A Flyer said:
I have one of the earlier ones from Van's, same design, and it works *fantastically*. I just used a (very nice locking) push-pull McFarlane cable for it, and I can very precisely control the oil temps.
Click to expand...

Did the same with the same result.
 
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