Thorp Air Command - T18.net

I am leaning towards routing my crankcase breather tube down to an exhaust pipe and skip the air/oil separator. Even if I install an air/oil separator, I will not return the oil to the engine. Anyone have any thoughts or suggestions and/or pros or cons on this matter?

Im curious to see if anyone has determined a best oil exit location on the Thorp airframe.

Hi Ryan,

I'm actually a Thorp wannabe, but I have stayed in a Holiday Inn Express once...
My experience comes from being a three-peat RV guy and have experimented with several crankcase vent iterations on two 0-320's and one IO-540. Early on I tried a simple line routed from the crankcase breather down to a small SS tube 1" from an exhaust pipe. This didn't work well. After some discussion an AE informed me the lower cowl area was high pressure and actually created back pressure in the line. That's when I bought an M-20 air-oil separator. I routed the exit line alongside one of my exhaust pipes and had it exit into the slipstream with a 45 degree cut aluminum tube. The drain line went back into the engine via a fitting on one of my valve covers. This setup works very well and it has a side benefit of keeping the belly clean doing sport aerobatics.
The second setup I used on my Harmon Rocket was a Slime Fighter http://www.aircraftspruce.com/catalog/e ... imeftr.php air-oil separator purchased from Aircraft Spruce. It requires very little plumbing and works very, very well. I used the identical exit tube alongside the exhaust in the slipstream. The side benefit of having your exhaust and breather in the slipstream with 45 degree angle cuts is scavenging. It's an old Steve Wittman racing technique that works.
http://www.vafarchive.com/msg/rv4/t2006007000
Give it a try, you won't regret it.

V/R
Smokey

I have the Slime Fighter on my 0-360 . Very small unit . I attached a piece of 3003 aluminum tubing to the exit outlet on the Slime fighter and ran it down to the left exhaust tube near the bottom of the cowl . I have seen NO oil on the bottom of the AC . You can see the unit in the pic . It is the small silver cylinder with the two small rubber hoses attached to it .

RB

Smokey, which way is the 45 degree cut pipe facing that was placed just along the side of the exhaust pipe?

Now that I think about it , some folks have a " Jed Clampett can" to collect the drippins . No hose or pipe to the exhaust pipe , just a hose to the "can." When the Jed Clampett "can" gets full they just mix the dippins with possum fat to cook up a mess of vittles ! Powerful good eatin ! There may be some sort of separator involved, but I know there is a collection can ? I saw 1 or 2 at KVIS .

RB

MLMP (My Little Money Pit) had a fancy stainless coffee travel mug clamped to the mount. Seemed to work well and there wasn't a whole lot of oil in it when it arrived on its last flight in 2010.

My vote is to simplicate as much as possible.

Bing. Boom. Bam.

On 7077J I have no separator. I had my tube run down the L/S gear leg into the wheel pant and then had a 45 degree angled exit tube at the end of the wheel pant. Very minimal oil on the end of the pant. Nothing on the bottom of the plane. Been thinking of addressing this on the rebuild now. Will be lurking in the back ground here to make decision.
Skeet

55RC also does not have a Air/Oil separator but has a tube that runs down the L/S gear leg. It stops at the bottom of the gear leg and exits there. I do get oil on the wheel pant but none on the belly of the plane.

Skeet,

I may have to see about extending it to the tail end of the wheel pant. Seems like a good addition. What is the connection between the gear leg and the wheel pant (to facilitate removal of the wheel pant)?

_________________
Matt Smith
Des Moines, IA
55RC

Just a piece of clear flexible tube. Aluminum tube glassed into the wheel pant has held up well. If I would have had a graphite tube I would use that as it would be more compatible with fiberglass resin.
Skeet

I have been told by those that know (tech man for ECi) that you want a small amount (.03 PSI) pressure in the crank case during operation. This keeps the misted oil in the engine, but does not have so much pressure as to blow the front seal. My tube runs down the left gear leg and exits just below the brake disc (so as to not lube the brakes). It is cut a slight angle to the front as viewed in the flight attitude. Do not forget the 1/4" hole in the tube up in the engine compartment put in the act as suction breaker and alternate breather should your vent become clogged with ice; not hard to do when you consider the amount of condensation that is present. The 1/4" hole needs to be drilled in the aft/top side of the tube so oil doesn't flow out of it as the tube drains.

_________________
Bob Highley
N711SH
SN 835
KLAL

Rich, that's rich!
I have a Jed Clampett baby bottle!
The crankcase vent tube ends in a small baby bottle with holes around the top. It's 'mounted' by the nipple glued to the vent tube, just behind the oil cooler. it does collect a little oil, but I do get a bit of oil speckling on the fire wall and down the left side of the plane.
It is the lightest weight separator I've ever seen, and to inspect or empty it, all you have to do is thread the bottle off from the top like so many of us dads have done thousands of times!
POP!! WAaa!! "Just a sec honey, Daddy will fix you right up!"

_________________
Scott Emery
EAA Chapter 326
T-18 N18TE

If I remember right...John Evens had a sweet set up ? I think he machined the parts ? Could be wrong about it ( I am NEVER wrong only slightly confused ) , but I know I saw someone that had a "closed system" similar to the Andair air/oil separator and collector can . I still put my money on the Slime Fighter for its compact size and simplicity .

RB

My installation sounds to be the same as Bob's except mine is down the RH leg (no reason why!). Never had a problem in 25yrs. A few drips of condensation after a flight so I have a small plastic bowl I place under the outlet once back in the hangar. Apart from 1" reinforced plastic tubing coming off the breather outlet the rest of the tubing is lightweight aluminium. Travels down the fwd side of gear and lightly taped to the gear. Fits nicely within the gear fairing. Have one P clip at the bottom picking up a wheel pant attach screw. Nice and simple and no expensive bits! Don't care for recovering grubby oil back into engine plus my engine uses little so don't care a small amount may go out the breather.
Tony Schischka
ZK-VMS T18C

I've made & tested about a half dozen oil separators on my T-18 (guess I had nothing better to do at the time), and finally got something that works well for me. It is my belief that the guy who makes the M-20 air-oil separators somehow "duplicated" my design (except mine comes apart & has a few additional details), as I was freely sharing it with anyone who cared, & I believe he looked at it quite closely at OSH one year. This was at least a couple of years before the M-20 came on the market. Regardless of that, I think that sometimes the simplest &/or old ways of doing things are the best, and I've tried to follow that advice on my Thorp to a great extent. With that in mind, I also think there is merit to Bob's statement about slightly pressurizing the crankcase and the way he has done it. As I recall however, some have advocated DE-pressurizing to optimize efficiency and power - I think it was the Rutan guys who were doing that, and I copied it at one time, welding a 1/2" S.S. tube with an angled cut on the end into one of my tailpipes, with the angled cut facing downstream (creating suction). I mated this with an automotive emissions system check valve, then up to the breather port on the engine with a rubber hose. The check valve was supposedly to prevent back-flow up into the engine in case of a backfire. I found that the small amount of oil that was going into the exhaust pipe was carbonizing and building up in the tube - I thought it might eventually restrict or plug it up & I didn't feel like having to clean it or worry about it, so that was the end of that experiment. Like I said, simpler is better, IMHO. I've used up a lot of time playing around, just to eliminate a couple of drops of oil on the belly of my airplane - oh well, it was fun and I have a clean airplane.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

John: I wish I had your machine skills ! To turn a blank piece of round or square stock into a part is amazing ! I took two semisters of Junior H. S. wood shop and I came up with a spice rack ! It was one hell of a spice rack and to this day I have no idea where it is ! BOOM !

RB