M20K Rocket Breather Tube-Picture Wanted

[milotron]

2 hours ago, peevee said:

Psh, I have a fix for that just take it off and send it to me. I'll put it all on ours

 

I find that even with support the action of sliding the cowl under while tilting the back but clearing the prop hub is difficult and easier with two.

It's always a lot easier if you remember to DC the cowl flaps also

I usually leave the landing/taxi lights connected and try to rip the wiring out.

 

 

Drifting even further off topic...how does the air flow over the intercoolers work? It looks like they are no in any direct path of airflow and are completely in the lower pressure area of the cowl design. I suppose that is the only place the could go, aside from something over the cylinders like in the Cirrus.

[peevee]

Worse is when you get the top cowl on and all fits just right and locked down and you realize you didn't plug them back in 

[milotron]

It's good practice, right? 

[carusoam]

Check the airflow from one side of the intercooler to the other.  There are no fans, so a pressure differential has to do the work... no airflow=no cooling, so there must be airflow...

Best regards,

-a-

[floridaflyer]

8 hours ago, milotron said:

I usually leave the landing/taxi lights connected and try to rip the wiring out.

 

 

Drifting even further off topic...how does the air flow over the intercoolers work? It looks like they are no in any direct path of airflow and are completely in the lower pressure area of the cowl design. I suppose that is the only place the could go, aside from something over the cylinders like in the Cirrus.

On my Rocket the top cowling has two scoops that pick up RAM air from the engine side of the baffle and redirect it over the top of each intercooler. Once the air passes through the intercoolers, it exits via the open area on the bottom cowling. Proper cooling requires minimal obstruction below the intercoolers.

[Jim F]

22 hours ago, milotron said:

I usually leave the landing/taxi lights connected and try to rip the wiring out.

 

 

Drifting even further off topic...how does the air flow over the intercoolers work? It looks like they are no in any direct path of airflow and are completely in the lower pressure area of the cowl design. I suppose that is the only place the could go, aside from something over the cylinders like in the Cirrus.

I also needed to know how the rocket cowl worked. I found this on the web. It must be a rocket upper cowling. 

[peevee]

of the two rockets I've flown, neither had those scoops. Our CDT temps are very low so it hasn't bothered me.

[Jim F]

Hi Peevee

look close. The scoops are all inside the cowl with no opening/scoops to the outside air flow. 

That mean all cooling air and intercooler air comes through the same 231 openings. 

Jim 

[peevee]

7 minutes ago, Jim F said:

Hi Peevee

look close. The scoops are all inside the cowl with no opening/scoops to the outside air flow. 

That mean all cooling air and intercooler air comes through the same 231 openings. 

Jim 

I see them, we don't have them.

[carusoam]

+1 for pressure differential for the driving force for air flow.

The scoops do look functional for organizing the airflow, as would something on the bottom side of the exchanger...

Keeping the pressure differential probably requires maintaining nice seals everywhere between the top and bottom of the cowling.

Best regards,

-a-

[floridaflyer]

UPDATE: the air oil separator is in and no oil loss in ground runs but still spewing out one quart an hour in flight, now it's coming out of the air oil separator breather. AirWolf says its excessive crankcase pressure which prevents the oil from returning to crankcase, and there is no separator that can keep that much oil in. So we took the plane out for a flight test with the A/S indicator hooked up per TCM SB M89-9, here's what the crankcase pressure reads at different settings. Looks like ram air leaks into the engine since pressure rises as airspeed rises. The maximum specified by TCM is 90MPH... Oil filler cap is tight so next we're going to replace the crankshaft seal and see what happens. 

Edited July 13, 2017 by floridaflyer
Added pressure readings

[floridaflyer]

OK so replacing the crankshaft seal made no difference, same readings in flight as previously reported and same oil loss BUT... closing the cowl flap in flight increases crankcase pressure by 50%. So for example cruising at 32" MP, 2400 RPM and 160 KIAS (1000 MSL) the crankcase pressure reads 80 MPH with the cowl flap open and jumps to 120 MPH when I close it. The Airwolf airsep breather scat hose ends/vents inside the engine bottom cowling about 4" above the bottom of the cowling as specified by Airwolf, I'm thinking it's where the excess pressure is picked up and works its way back to the crankcase via the airsep and the breather connecting it to the oil filler where our airspeed indicator reads pressure. According to Airwolf, excess crankcase pressure prevents the airsep from returning the oil to the engine so it has nowhere to go but out the breather which of course defeats the purpose of having the airsep in the first place. We're going to go fly for an hour with the flap open and see if there is any oil loss at the 80 MPH reading. If not it's likely a matter of moving the airsep breather hose. If anybody who reads this has the Airwolf setup on a Rocket please post the location where the breather hose vents, that would be very helpful.

[carusoam]

Hmmmmm....

That is the start of an interesting technical discussion.

How often do we measure case pressure..?

How would we know what normal is..?

We know it is positive pressure normally...

As in that is how many of us blow excess oil overboard.  Pressurize the case and blow everything 'excess' out the vent...

Now we know case pressure increases with flap closure...

It may be interesting to learn another detail about the case vent. Where it is connected and where it's other end is located..?  Most engine vents lead to a low pressure location at the bottom of the cowl near the exit of the cowling flaps(?)...

Also check the health of that tube. There is often an anti-ice hole that allows pressure to escape when ice forms at the bottom of the vent tube.  See if a hole is pushing air into that tube instead...

PP thoughts only...not a mechanic.

Best regards,

-a-

 

[floridaflyer]

Carusoam thanks for your thoughts, I don't know what normal is but maximum case pressure for big bore TCM is airspeed < 90 mph per TCM SB 89. Based on my research the higher the case pressure the more oil goes out the breather. On the ground at full power (36" MP and ~2550 RPM) my Rocket shows 60 mph. A brand new engine would probably read lower but its got 1400 hours SMOH. As I mentioned in my last post my breather hose (1-3/4" scat) is connected at the Airwolf air separator and runs about 2 feet to vent 4" up from the bottom of the engine cowling so inside the cowling as specified by Airwolf. There is no tube like with the stock 252/Rocket breather tube. Airwolf says it usually takes several trials to properly locate the vent side of the hose and they warn against placing in slipstream (negative pressure) to avoid a Venturi effect which doesn't let the airsep do its job. They do not mention the opposite problem which is positive pressure but told me the higher the case pressure the harder it is for the airsep to push the oil back into the engine. Here's probably the most thorough discussion of the airsep functionality from a respected Lancair owner: http://lancair.net/lists/lml/Message/63034-02-B/Engine. Weather is looking better this morning so going to fly to Ft Myers and back at altitude with engine cowl open all the way to see how much oil comes out, hoping none!

[carusoam]

FF,

I recall reading the Fred Moreno piece when somebody posted it to MS somewhere along the way...

It may be interesting to see if we can find who posted it, what their challenge was, and if any solution or ideas can be gained from their writing...

Another thing to consider is why the breather hose is so large... when it comes to separation of droplets and air, the speed of the air is selected for Best separations.  The increased size of the tube, the slower the air traveling through it is...

Fred's drawings kind of show how the oil droplets splatter on the wall, and run down into the collection area. Too much airspeed in the separator, may not allow the oil to stick to the wall and and run down....

consider each stage of the flight.  Attitude can push the oil level towards the vent.  Power level can cause the case pressure to increase.  Oil level can be so high, it is ready to leave the vent (typical lycoming IO360 challenge). And of course, closing the cowl flaps alters the pressure drops around the engine

It may be helpful to try to determine when the oil leaves the engine.  It might simplify the solution...

Building on your data chart of case pressure under the various conditions... add taxi, T/O, Climb, Cruise, descent... might shed some more light on the situation...

My O360 was Good at blowing oil overboard. High power climbs were bad for keeping oil in the case. Level flight at ordinary power settings oil level never changed...

Then the engine/ring wear became too high... exhaust gasses were escaping into the case.  Foaming  and other challenges start to happen.  Oil turns black and smell like exhaust. Not too hard to determine what happens when oil rings aren't doing their job....

Keep in mind these are only PP thoughts, not a mechanic... thinking out loud... without stellar memory skills....

Best regards,

-a-

Some additional MS insight to the Fred Moreno paper.... 

[floridaflyer]

1.1 hr test flight today with cowl flap open resulted in losing about 3 quarts oil and oil pressure in the yellow (30PSI) on landing... Was cruising along fine reading steady 80MPH case pressure for first 1/2 hour, then pressure inexplicably started climbing to 110MPH over the course of 30 seconds and stayed there for the rest of the flight with +/-5 MPH oscillations. Next is to extend the breather hose to vent outside the cowling and see if case pressure is reduced enough to end oil loss.

[peevee]

9 hours ago, floridaflyer said:

from a respected Lancair owne

No such thing. Look at @Yooper Rocketman for example!

[floridaflyer]

I had a Lancair IV a while back. Bought it from the guy who bought it from couple of German engineers who built it and they did a great job. I can't say as much about the other specimens I've seen. Let's just say some people can build planes and most others can't. I'm in the most other category. After 1,000+ hours all over the Carribean I can also say it beats the pants off any other experimental or certificated piston 4-seater, but that's for another forum. Mooney Rocket was half the acquisition cost and half the insurance. If only it could keep from puking oil...

[peevee]

34 minutes ago, floridaflyer said:

I had a Lancair IV a while back. Bought it from the guy who bought it from couple of German engineers who built it and they did a great job. I can't say as much about the other specimens I've seen. Let's just say some people can build planes and most others can't. I'm in the most other category. After 1,000+ hours all over the Carribean I can also say it beats the pants off any other experimental or certificated piston 4-seater, but that's for another forum. Mooney Rocket was half the acquisition cost and half the insurance. If only it could keep from puking oil...

I'd swap the rocket for a 4 if I could. There are a few down under 200k but it's probably not something to bargain shop for. Actually I've always thought a legacy with a tsio360 would be almost ideal.

[floridaflyer]

I think its all about the mission profile. Not all Lancair models are created equal. I owned a Lancair II 2-seater with Lycoming 360 and Mark I rudder with notorious loss of authority at low speed. Flying coffin. Didn't find out until I tried to land on a 20-foot wide runway. At least I didn't have to sell it after that, finding a qualified buyer can be a problem with all Lancairs. 

[carusoam]

FF,

Looks like you have a good method of measuring the challenge.  You can see it occurring.

Did you mention the RPMs you are using during your observation?

I am wondering if the increased pressure may be related to some blow by.  Changing the rpm to high will have the piston rings traversing a longer distance than low rpm...  if there is a step worn in the cylinder wall, it may be giving you a bit of a challenge...?

Still only PP advice, not a mechanic...

Best regards,

-a-

[Yooper Rocketman]

13 hours ago, peevee said:

No such thing. Look at @Yooper Rocketman for example!

Hey!!!!  Be careful.........your chances of a ride are dwindling fast!

Tom