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Darren S

Well Known Member
Ok that's a bit of an exaggeration but my plane is a mess. I knew it was coming but not this bad.

I want to compete in Sportsman this year which is a move up from Primary last year. The two new manoueuvres for me are the 1/2 reverse Cuban and the hammerhead turn.

I have inverted fuel but only a dumb, cheap air/oil separator from Aircraft Spruce. For weeks I've been reading threads on different air/oil separators, 1/2 Raven systems, accusumps, Christen inverted systems and now I'm all disoriented, no pun intended.

To do the 1/2 Cuban I pull to 45, do a quick 2 count, roll inverted, push and count 3 before pulling to finish the maneuver. Oil pressure is normally in the 55 psi. range and drops to mid 30's during the inverted segment. It recovers as soon as positive G is applied. I don't think this is harming the engine one bit.

I typically keep my oil level at 5 quarts, I guess I lost a good 3/4 quart today in a 20 min. practice session.

I want your opinions on what I should do. Sportsman is as high as I'm going with this plane and I have no interest in sustained inverted acro.

1. Get a better air/oil separator ?
2. Run the breather tube all the way to the tail ?
3. Bite the bullet and install a: 1/2 Raven, full Raven, Christen system ? I'm not sure how they differ.
4. Leave as is and just buy oil and paper towels ?

I personally would like to find an air/oil separator or something that would minimize the oil loss and then also run the breather tube to the tail. The oil pressure drop doesn't concern me as it's so short in duration.

Thanks for any advice and suggestions,

Darren
 
Darren S said:
To do the 1/2 Cuban I pull to 45, do a quick 2 count, roll inverted, push and count 3 before pulling to finish the maneuver.
Click to expand...

The solution is really pretty simple....
If you do not have inverted oil you must always maintain some level of positive G's (like 1/2 G)

To maintain positive G's you can not Push when inverted.

Sounds like you need an inverted oil system.

Also sounds like you have learned what still confuses so many people even after all of these years... A inverted fuel system on an RV (or any other airplane) is just about worthless unless you also have inverted oil. The second most misunderstood issue is related to installing inverted fuel on an airplane equipped with a carburetor (totally pointless).
 
People have suggested the half Raven system to me and from I've read they like it. At least you KNEW it was coming. My oil bath was unexpected and I almost had a cow!! :D

Happy cleaning!! Sounds like a fun job in the brisk air of Canada.
 
Go Raven

I can tell you've already got the acro bug, and you're really not going to be happy until you have a full inverted system. I have the Raven and at least half my flying is upside down, using about 1/2 quart in 10 hours with the Raven. For Sportsman known and a free style, my G meter shows 1.5 to 2 negative Gs. I really hope you do well, and holding the inverted positions will score higher. RVs can compete with those Pitts with the right equipment.
Cheers,
Bill McLean
RV-4 slider
 
Or minus 2.8G in the inverted spin...I'm quite pleased with that one...:)

Oh yes the raven system is great, just don't use a swivel hose end in addition to the Raven swivel fitting...The swivel hose end will fret and eventually suck air into the oil on start up.

Frank
 
oil

If you go with inverted oil system you will still need the breather out the tail so why not try just the breather first. I would crank that oil pressure up to at least the high 70's, the more pressure you have upright the more you will maintain for brief negative G.
 
Good advice so far, thanks.

Fitting the inverted system during the build is one thing but the retro fit is a little worrisome; because of the firewall space and the need to move things around.

I still don't fully understand the Half Raven System. Is it just a large canister that holds all the expelled oil and then dumps it back into the sump?

Good suggestion to crank up the oil pressure a bit. That's an easy one.

The tube to the back is an easy one too. The only portion of the sequence, I think, that's an oily issue is the 1/2 reverse cuban. The hammerhead, Cuban and shark tooth aren't too oily (amount of oil loss) as the zero G/ negative G segments are even shorter.

I spoke to my instructor tonight. He also said that it's not the end of the world if you take a downgrade on the Reverse Cuban because you shortened up the inverted segment. The carbureted sect. has to for the most part. Just make up for it during the rest of the round:)

I've been checking ACS and I'd like to try either the Andair or Airwolf air/oil separators. Searching the forum for either of these brings a wide range of opinions so I may have to make a gut decision.

Tomorrows forecast is for a low of -18 degrees C!! I think that oil is going to have to stay for at least another day :)

Thanks for the replies so far.

Darren
 
Christen system

Hi,

I just installed a full Christen system on my -6. I found a new second hand complete system on the classifieds here for $1250. The installation took about 3 days and everything fit fine. The air-oil separator is attached to the engine mount with adel clamps on the pax side with the oil valve on the firewall below it. Either a half Raven or the air-oil separator from the Christen system will take care of short duration inverted flight. They both have a ball check valve that will keep a breather line full of oil from escaping on to the belly when you roll upright.

I currently have fuel injection, but no inverted flop tube on the fuel so my inverted time is limited to about 15-20 seconds, and so far not a trace of oil on the belly. Which is better than I expected. No other air-oil separators that I know of will do the job since they don't have the check valve that Raven and Christen use.

HTH,
Bruce
 
See that's what I didn't know. The Raven has a check valve to keep at least some oil from coming out of the breather. Makes sense. It may not be perfect but better than just a regular air/oil seperator.

I'm calling Raven tomorrow. Paul Dye said their service was excellent. I'll report back.

Darren
 
frankh said:
Or minus 2.8G in the inverted spin...I'm quite pleased with that one...:)
Click to expand...

-2.8? Sounds like a hammerspin entry! Or a negative snap entry. :)

Darren S said:
I spoke to my instructor tonight. He also said that it's not the end of the world if you take a downgrade on the Reverse Cuban because you shortened up the inverted segment.
Click to expand...

Darren, if you're going to shorten the inverted line, shorten the positive line too, but still draw both long enough to be perceptible as lines. I would not recommend shortening only the inverted line. I say this because if you apply the judging criteria as defined, it could be easy for the line before the half roll to appear more than twice as long as the line after. This would be a 3 point deduction. And any additional imperfection in the looping portion or attitude before or after the roll could score you a 5 for the whole figure real quick. If you drew NO line before OR after, it would be only a 2 point deduction. Any visible line length variation is 1 point, and that doesn't take much. 2 points is more likely (for a 2:1 line length variation). Draw a short line before AND after, and you can get a 10. :) The shorter lines will just create a larger looping segment, which is fine.
 
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I still don't fully understand the Half Raven System. Is it just a large canister that holds all the expelled oil and then dumps it back into the sump?
Click to expand...
Yes... except the word "all" ;)

It is the 4" Raven Tank that takes the breather Air/Oil in, has a Breather out, and crucially a return to sump Oil Line / standpipe.

It will save a lot of "dumped oil", but can be beaten i.e. if you fill the tank up, do not give it time to empty.

Finally, of course if you do need a full inverted, the hald Raven can be added to make a full, whereas an Air/Oil separator will mean starting again.

Took me say 2-3 hours to fit to an already flying RV-8.

Get a better air/oil separator ?
Click to expand...
2 issues:
  1. Volume needs to be large as per inverted duration - most are too small
  2. Must have a system of returning to sump, else time gets shorter / you have to empty after each flight

He also said that it's not the end of the world if you take a downgrade on the Reverse Cuban because you shortened up the inverted segment
Click to expand...
Unacceptable - the blind/deaf brigade find enough excuses to downgrade you without handing them more on a plate :eek:

I do a "count to 3" inverted section in our display, and hardly lose any oil - search RV8tors if interested.

PS You missed:
5. Paint Aircraft bottom, errr, dirty oil colour ;)
Click to expand...
 
2. Run the breather tube all the way to the tail ?

Try your #2 first.

2. Run the breather tube all the way to the tail ?
 
Oily underbelly...

Darren,

All of the above recommendations are valid. I can't argue with the inverted oil system logic however comma, I would like to add that I have been performing the Sportsman routine in three different RV-types for over 20 years without an inverted oil system. What I do have is a modified Air-Oil Separator and line routing that is mounted fairly high on the firewall. The return line goes directly back to a rocker box cover fitting, creating a semi-recirculating system.

I have experimented with it over the years and found the best angles, and copied my good friend Jim Swick's Swick-T inverted oil routing for crankcase vent line. I utilize the classic "C" configuration Jim used so well on Buckers with Frank Price and Curtis Pitts first system which Jim designed and installed. (Frank Christensen copied many of Jim's ideas for his system) If you have any questions, email me.

Smokey

PS: The beauty of a Lycoming is negative G's actually force the sump oil onto the crankshaft and main bearings. The only downside is the lack of ventilation for a long extended period can pop the forward crankshaft seal if it's not installed correctly. Bob Herendeen knew this and his Glasair 3 had no inverted system performing his amazing shows either.
[email protected]
 
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mv031161 said:
Definetelly not a spin!
Click to expand...

Well, it probably developed into one, but negative G onset like that usually means power is on, or that the entry is accelerated (negative snap). I remember the first time I forced the Pitts into an inverted "spin" by deliberately exaggerating the inputs during a hammerhead pivot (full forward stick). I had always heard that folks would botch hammers and produce inverted spins, but had not actually experienced this. What ensued was more like a full-power buried outside snap roll, pointed straight at the ground, and accelerating. Before I pulled the power and recovered, I ended up with just over -3G on the meter. If I hadn't pulled the power, the negative G would have increased even further as the plane accelerated toward the ground.
 
smokyray said:
Darren,

All of the above recommendations are valid. I can't argue with the inverted oil system logic however comma, I would like to add that I have been performing the Sportsman routine in three different RV-types for over 20 years without an inverted oil system. What I do have is a modified Air-Oil Separator and line routing that is mounted fairly high on the firewall. The return line goes directly back to a rocker box cover fitting, creating a semi-recirculating system.

I have experimented with it over the years and found the best angles, and copied my good friend Jim Swick's Swick-T inverted oil routing for crankcase vent line. I utilize the classic "C" configuration Jim used so well on Buckers with Frank Price and Curtis Pitts first system which Jim designed and installed. (Frank Christensen copied many of Jim's ideas for his system) If you have any questions, email me.

Smokey

PS: The beauty of a Lycoming is negative G's actually force the sump oil onto the crankshaft and main bearings. The only downside is the lack of ventilation for a long extended period can pop the forward crankshaft seal if it's not installed correctly. Bob Herendeen knew this and his Glasair 3 had no inverted system performing his amazing shows either.
[email protected]
Click to expand...

I would be very interested in your modified air oil separator and plumbing diagram if you would care to share more P.S. I love the Ellison
 
sandifer said:
Well, it probably developed into one, but negative G onset like that usually means power is on, or that the entry is accelerated (negative snap). I remember the first time I forced the Pitts into an inverted "spin" by deliberately exaggerating the inputs during a hammerhead pivot (full forward stick). I had always heard that folks would botch hammers and produce inverted spins, but had not actually experienced this. What ensued was more like a full-power buried outside snap roll, pointed straight at the ground, and accelerating. Before I pulled the power and recovered, I ended up with just over -3G on the meter. If I hadn't pulled the power, the negative G would have increased even further as the plane accelerated toward the ground.
Click to expand...

Yup...sounds right as usual coming from you...

here is a video showing the ASI and Gmeter in the lower LH corner....you see the ASI when turning towards the pitot wing in showing 0 knots and close to 15 when turning towards the right....throughout the entire video you can see that the G meter (smaller gauge) does not move at all at entry, during or at spin exit...only during returning to Flight Level you see the Gmeter move...... http://www.youtube.com/watch?v=eTKea4xmlRI
 
sandifer said:
Well, it probably developed into one, but negative G onset like that usually means power is on, or that the entry is accelerated (negative snap). I remember the first time I forced the Pitts into an inverted "spin" by deliberately exaggerating the inputs during a hammerhead pivot (full forward stick). I had always heard that folks would botch hammers and produce inverted spins, but had not actually experienced this. What ensued was more like a full-power buried outside snap roll, pointed straight at the ground, and accelerating. Before I pulled the power and recovered, I ended up with just over -3G on the meter. If I hadn't pulled the power, the negative G would have increased even further as the plane accelerated toward the ground.
Click to expand...

Yes it was a botched HH..and your right the entry was pretty unconventional, I guess you could call it an outside snap now I come to think of it... But it settled into an inverted spin after about about 1.5 rotations..And spun very well it did.
 
Thanks to all for the input. And the lively video!

I've decided to go with a half Raven system. I think it's a good compromise for my needs.

Darren
 
Here's the latest. I spoke to Rob at Raven and the half Raven may not work. I have a goofy oil sump.

There are two in accessible drains on the bottom. They are blocked by the manifold. The pilot side of the sump has the oil drain and the other side has the oil screen.

The only way we figured it to work is to put a "T" fitting in the existing oil drain. One part of the T goes to the bottom of the canister and the other end will be capped and used to drain the oil.

My issue : how to safety wire the cap on? Will the T be subjected to vibration that could crack it? The airport bums say don't do it.

Here's what I want to know. Is there a big check valve fitting out there that I could put in the 3/4" breather hose? I can't seem to find one.

I'm looking for something to close down and prevent huge oil loss for the brief zero to negative one G during a reverse Cuban 8. As my first post said I lost about 2 quarts in 30 minutes.

Any suggestions welcome

Thanks,

Darren
 
hey Darren---how about post some pics------we have alot of experienced people here we'll help you figure it out.
Tom
 
oil "T" fitting

Hi,

My Christen full system came with a "T" fitting which is used to supply oil to the ball valve when upright and for draining the sump at oil change time. The bottom of the "T" has an AN cap. I drilled the edge of the cap so I could safety wire it. Seems to work fine.

I don't know why this type of fitting wouldn't work for your Raven seperator oil return. The Christen oil return fitting does have a short stand pipe on it. I assume this is to keep some oil in the sump if the line were to fail. You would not have this feature.

HTH,
Bruce
 
Hey Bruce, thanks for the reply. I'm encouraged that you use a "T" fitting and found a way to safety wire the cap. Teach me to listen to the airport bums:)

I'm going to give it a go. It's on order. I'll solicit some help with drilling the cap.

BTW. You are right, I can't use a standpipe as the oil drain is horizontal out the side of the sump and not vertical.

Darren
 
Darren, if you put the "T" out the side of the sump, with the top bar of the T horizontal, and connect the other end of the top bar to the 1/2 Raven, that should leave you a "drain" sticking straight down. On that T, put a quick-drain valve. Then you won't need to remove/replace a drain plug all the time for oil changes. The "T" can be safetied to the sump, and the quick-drain valve safetied to one arm of the T. That's my plan for when I do this to my -6.
 
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