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What is a safe oil pressure range for aeros?

R

RV7DES

Member
Being new to Aerobatics there is a lot to learn about looking after the aircraft. One area I have been working on is the oil system in my RV7, and have recently fitted the half raven system with an Auccusump, as described in a very informative thread here on vansairforce. Very happy with the system so far. I was dumping around 2 quarts of oil an hour of aeors, after fitting the raven oil seperator that went to zero and no oil on the belly. (Still burn a little oil though) Yesterday I fitted the Auccusump, and tested it. I could go inverted for about 5sec before the oil pressure dropped to 25psi which I was told is the minimum safe oil pressure.
What I read in the manual for my IO360 M1B Lycoming engine is that at idle 25psi is minimum, and at cruise 55 to 95psi is the safe to operate oil pressure range.
I am doing aeros at 2500rpm and 24.5inchs. My engine is a tuned Lycon with high compression pistons. I find the oil pressure sits around 65psi for most of my flying, getting up to around 70 at my aerobatic power settings. This hasn't changed with the accusump though the pressure changes less as expected. Before I fitted the Auccusmp the pressure would drop very quickly when I went negative to 25psi in about 1.5sec, now I still get a quick drop to 45psi when I pull negative, then it slowly decrease to 25psi. Is this good for the engine?

Any advice would be appreciated. RV's are truly amazing aircraft and I am taking part with my RV in the Sportsman section of the National aerobatic competitions here in New Zealand next week.

RV7DES
 
There's a little more to this that a straight number - do you have a c/s prop, if so what type and is it counterweighted or not? The pressure you describe is unlikely to cause any damage - what does the prop do?

Doing sportsman you probably wont see (m)any periods of negative g that would give your engine cause for concern, especially with the set up you describe. The figure most likely to cause oil pressure problems is a hammerhead (stall turn). Once you hit the vertical the oil pressure will probably start decaying (with a slight delay due to the accusump). At this point it will require a fair amount of practice before you have the bandwidth to figure what is happen to the oil pressure as well as flying the hammer.

Assuming you have a regular c/s prop it will start to go fine as the airspeed drops, and as the oil pressure drops. There is a possibility it could go very fine at the top, when you have full throttle, and that could result in a large overspeed (costly). I'm guessing you will lose control of the prop before the oil pressure gets low enough to cause any engine damage, but things might happen quickly (within a couple of seconds). If you have an aerobatic prop, with counterweights, it will coarsen with loss of oil pressure, you will lose rpm at the top of the hammer, so the hammer will be poor (no airflow over the rudder). If you have a fixed pitch then oil pressure may indeed be a factor.

Before you try anything think about what you will do if your oil pressure drops below your personal minimum (say 10psi momentary). If you yank the throttle closed you may tailslide (very dis-orientating), humptying out is probably best - it loads up the oil system and should get oil flowing again - but don't pull too hard initially or you may depart. It may be worth flying a couple of trials - first of all practice humpties. Then, from Vne (with plenty of altitude), pull (say 4g) to the vertical. Start counting out loud and watch the oil pressure. At either your minimum humpty speed, or your minimum oil pressure, or when the rpm starts to increase (prop starts to go fine) humpty out. If you got to minimum humpty speed first (I'm guessing around 40 or 50kt), then you will not have an problem with oil pressure during a hammer from a normal entry speed, go practice. If either of the other two you may have some thinking to do.

I would get some aerobatic instruction in a Pitts or Extra first so that at least you have an idea of how to fly the figures without having to learn the basics and trying to work out how to look after your aeroplane at the same time. If you intend to fly at lot of aeros (especially competitions) it may be worth considering a full aerobatic oil system.

Pete
 
oil pressure

With the Christen system there will be maneuvers where there will be a very momentary drop in oil pressure to a value below the bottom of green arc. (55#) Based on 1000 hours on one Pitts with 0 360 parallel valve, this does not hurt the engine. Never had an oil filter, never any significant metal in screen. However any sustained operation with oil pressure below 55 WILL DESTROY the engine.
One "band aid" for this is to set the oil pressure to near the top of the green. IE, if your oil pressure is 70# in upright level flight at cruise power it MIGHT drop to 60# inverted. If you increase the normal oil pressure to 80# upright it should only drop to 70 inverted. This is a gross simplification of the issue. The Christen system was actually designed by Curtis Pitts. Christen redesigned it and gave it a fancy paint job but the operating principle is still the same. Transitioning thru zero G flight the Christen system will loose oil pressure. As soon as there is any significant G load the oil pressure will recover.
There are some relative exotic systems where this is not true, but the vast majority of systems are Pitts derived.
The only other issue is sustaned knife edge flight. I don't believe you will be doing that in an RV.
With a full Pitts derived inverted oil system you should be well above 55# in level inverted flight.
I am not clear wherther you have a full inverted oil system or partial.
The new max red line oil pressure for Lycoming is 115#. Running the oil pressure near the top of the green arc in cruise is believed by some engine experts to be BENEFICIAL to engine longevity, even for non aerobatic flight.
 
Thank you for your response. I like the idea of increasing the cruise oil pressure, and thank you for your advice. I have been doing aero's for about 4 months now, and spent a lot of time at the beginning with very competent aero pilots. To be honest took a long time to feel comfortable stalling and spinning. I now have probably done on my own about 50 hammerheads, and 20 with other pilots. We never noticed an issue with the prop speeding up, even before fitting the Accusump. It is a Harzell non aerobatic prop. Yesterday to test the system I went inverted off the top of a loop and held it until the oil pressure dropped to 25psi at negative 1g. I don't have flop tubes and expected to have the engine stop before the oil dropped but it didn't.
New Zealand is using the 2012 Sportsman routine for next weeks comps, and that has a hammerhead. Once I feel very comfortable with what I can do in my plane I might move up to a higher category. Just completed a few hammer heads at around 40knts. Oil pressure didn't dip below 62psi.
 
Sounds like you're good to go - enjoy yourself!

Intermediate in an RV-7 will be tough (for you and the aeroplane) - you will almost certainly need a full inverted oil system, even with the accusump. Flick (snap) rolls are hard on the inboard sections of the wing - you would like to fly them at a relatively slow speed, but sometimes that's not possible. Rollers are going to be hard work, as are inverted turns and half loops. Not impossible, but will take practice to fly well. Might be worth flying a season at Sportsman before making the leap. Intermediate is much more a mental exercise and really benefits from being confident in the box. A Pitts S1S will be make Int much easier!

Pete
 
Thanks Pete
I have lightening holes in my flange so prohibited from snap rolls. Had enough for me to feel comfortable doing soft negative let alone intermediate. Have been offer shares in a Giles which would be a good option if I wanted to progress. Just looking forward to what I can learn over the weekend, and flying in the box. To be honest the hardest part for me in the whole routine is getting the slow roll correct. Going out this morning with an advanced Pitts pilot to practice. Thanks again for your input.

RV7DES http://1.bp.blogspot.com/-lKGCXeo7iiI/USnXnRPhQZI/AAAAAAAADwo/Z8MAmyPixoI/s1600/IMG_9787.JPG
 
Just curious - in New Zealand does your organization design its own Knowns up to Intermediate, or do you use IAC Knowns?
 
Good question. Our national competitions this week will use the 2012 ICA Knowns. We use the knowns from the previous year. Very excited as this will be my first time to take part in a box, and one of only 2 RV's there I expect.
Having a lot of trouble maintaining straight lines for slow rolls, as I drop the nose with the last 90 degrees.
 
RV7DES said:
Having a lot of trouble maintaining straight lines for slow rolls, as I drop the nose with the last 90 degrees.
Click to expand...

In my experience most of the errors made by folks learning the "slow" roll occur during the second half. Typically, the forward stick is removed too early, causing the nose to drop. The telltale sign is if you are trying to use a very large amount of left rudder (if rolling left) to keep the nose up during the last 90 degrees of roll. With proper elevator input, the left rudder input in the last quarter should not be huge. Also, a secondary result of removing forward stick too early is the nose moving off heading slightly (dishing) and ending the roll off heading to the right. Again, all this assumes left roll.

Keep in mind that if you are not trimmed for zero G, it will still feel like you are holding some forward stick at the last knife edge position. You should be holding the stick in the zero AoA position here. But it will still take a little forward pressure. So try holding foward pressure a little longer after you have passed through inverted during the roll. Start easing off the forward stick as you approach 45 degrees past the inverted attitude. And you will also need to start transitioning from right rudder to left rudder before you actually reach the last knife edge position. Somewhere around 45 degrees past the inverted portion is a key point for transitioning both elevator and rudder. Perfect "slow" rolls are quite a challenge. And remember, in competition, you want to do the "slow" roll as fast as possible. :)
 
Read about having lightening holes in the flange and prohibited from doing snap rolls
Are you talking about the lightening holes in the vertical stab spar?.. If so I had not seen anything about prohibiting snaps.. I had always heard that Van did not recommend them...
What is the story.... Am I going to be rebuilding the Vertical stab in the future.

Smilin' Jack
 
Smilin' Jack said:
Read about having lightening holes in the flange and prohibited from doing snap rolls
Are you talking about the lightening holes in the vertical stab spar?.. If so I had not seen anything about prohibiting snaps.. I had always heard that Van did not recommend them...
What is the story.... Am I going to be rebuilding the Vertical stab in the future.

Smilin' Jack
Click to expand...

He's talking about the crank flange. Snaps are not "prohibited" with the non-aerobatic lightened crank flange, but it is not a bad idea to avoid them if you are running a metal prop. I have a light crank flange in the AEIO-360 on my Pitts, which has a 25 hr AD to check for cracks. It has seen many snaps since 1976 and it is still fine. But I did recently replace the metal Sensenich with a Catto for the sole purpose of reducing stress on my crank flange when doing acro.
 
Thanks Eric,
I am ordering my engine from Carlus Gann a shop highly recommended in north Ga for engines,next week and Ihave a list of items some he has suggested and some others have mentioned.
So far we are getting an XIO-360 ECI with a superior cold air sump doing horizontal induction so now I will add a non hole acrobatic flange on the crank, I wonder what price change this will make. I'll find out more the rest of this week.. Thanks again
Smilin' Jack
 
Smilin' Jack said:
Thanks Eric,
I am ordering my engine from Carlus Gann a shop highly recommended in north Ga for engines,next week and Ihave a list of items some he has suggested and some others have mentioned.
So far we are getting an XIO-360 ECI with a superior cold air sump doing horizontal induction so now I will add a non hole acrobatic flange on the crank, I wonder what price change this will make. I'll find out more the rest of this week.. Thanks again
Smilin' Jack
Click to expand...

You can't go wrong with the heavy aerobatic flange, but for lazy loop and roll RV-style acro, I wouldn't be concerned about the light flange. The few folks who have broken light flange cranks in the past were typically hardcore airshow or competition pilots running metal props and doing lots of snaps and gyroscopics - tumbles, flat spins, etc. And I consider the light crank flange to be a non-issue with a composite or wood prop.
 
Thank you so much for your comment Eric. Yes that is exactly what is happening. In the slow roll I can stay on track and loose a little height if I use almost no rudder, however once I try to keep that nose on the horizon using top rudder and back pressure It all looks really good for the first 180, up to 225 degrees, then the last 145 to 90 degrees, the nose has dropped and I scope out at the end changing direction to the right on a left slow roll. Not maintaining forward pressure enough makes total sense to me. I will go out a try it next time I am up.
Was very pleased with a 3rd behind a Pitts and a Zlin for sportsman in the nationals, and am looking forward to the next comps.
 
Eric the lightening hole flange is on the engine crank. They developed cranks in Pitts after snap rolls, and I believe lead to a few accidents many years ago. If your engine doesn't have lightening holes in the flange you are probably alright.
 
I was looking at what others were doing in Intermediate and felt that my RV could handle that kind of aero's. However for snap rolls I have the wrong combination, which is a Hartzell metal CS prop with the lightening hole flange. It handled Sportsman very well, and if I want to step up I need to look at a different aircraft.
 
RV7DES said:
It handled Sportsman very well, and if I want to step up I need to look at a different aircraft.
Click to expand...

Don't give up the RV for snaps/crank flange issues only, since you can replace the metal Hartzell with a lightweight composite. Of course, Vans recommends against snapping the RV, although there are those who do low-speed Avalanche-type snaps with no seemingly ill-effects. I think low-speed snaps can be managed in the RV without hurting the airplane. But it's one of those maneuvers that are not well-understood by casual (and likely self-taught) recreational acro flyers who have not studied the subject. They have the potential to excessively and unnecessarily stress the airplane if done with bad technique at too high an airspeed. So I think the general recommendation against snaps is a good one.
 
Not sure if this question is in line with this post. For anyone who does more than "gentleman" aerobatics do you plan on running your engine to TBO? I don't know what interval airshow performers disassemble and inspect their eninges, but I don't believe the interval is that great. Just curious if aerobatics effects how you maintain your engine.
 
TBO

As far as I know TBO for the AE series Lyc is still 1400 hours. I flew one Pitts S2B that was used exclusively for acro training and competetion that went to 1500 hours and the engine was in near perfect condition when torn down. No oil filter, rode hard and put away wet, not even a cracked cylinder.
 
Really good points from Curtis and jrs. I couldn't find many helpful links on RV aerobatics, so had to ask questions in this link as a Pilot who bought the RV7 because it is aerobatic capable and wanting to do aerobatics safely. (Also wanted a practical cross country machine)The info I got from Jack and other users was invaluable. However there is not enough practical information I have found about using this aircraft for aerobatics that is suitable for pilots that are transitioning into aeros with RV's.
Understanding that most transitioning to aeros will be very unsure how far they can safely push their RV. I have come a long way with the help of many very experienced pilots. But they being good pilots admit they don't know the limitations of my RV7, so it comes back to how well I know my aircraft.
I am hoping with this comment someone more experienced than myself which I know there are many, starts a specific aerobatic RV forum. Jack perhaps?
There also maybe links I don't know about to learn more.
 
I should have said Eric in the last comment. Eric I guess I stay on the side of caution with pushing the limits of my aircraft. When I see that G meter getting so close to 6 after a routine, I want to be assured I look after my RV in a way it will look after me for many years to come. Not baby handling it, using it to an RV potential and not beyond.
The big point I have to state at this time is starting to learn with experienced pilots, which I did. An RV can easily go past it's limits, such as VNE on the down line.
I will be vary cautious of snap rolls because of the crank flange, and until I am confident the plane will handle it, I will not.
Other aircraft can snap roll at quite high speeds, and I would be comfortable with snap rolling them. Getting you and others supporting a forum on this site where others like myself can gain valuable confidence in flying aeros with their RV's would be awesome
 
RV7DES said:
Getting you and others supporting a forum on this site where others like myself can gain valuable confidence in flying aeros with their RV's would be awesome
Click to expand...

I'd love to see a signficant amount of RV acro chat, but unfortunately you'll find very little experience here regarding flying RVs at Intermediate aerobatic levels (snaps, significant negative G, precision flying, etc.), since most RVers don't do more than lazy positive G loops and rolls. **Please don't anyone think that I feel there's anything wrong with that.** The most experienced RV aerobatic pilots here seem to be Bill McLean (WillyEyeball), Andy Hill, and some of the Team Aerodynamix guys. Ron "Smokey" Schreck especially comes to mind. There are also a few other posters here N355DW (Damon Wack), jrs14855 (Jim Stanton), and Bill Dicus who are long-time and highly experienced Advanced precision acro guys, but who may have yet to get into serious RV acro. But acro is acro, and all will have useful input. I have much more acro experience in non-RV aicraft than RVs. I flew acro in an RV-3 for 5 years, doing all the positive G stuff you can do, but I've gained a lot more acro knowledge, ability, and experience in the last 5 years flying competitions in the Pitts than I did in the 5 years with the RV...not that I couldn't have taken the RV further.

With his RV-4, Bill M. seems to be using the most RV aerobatic "potential" that I know of....integrating Intermediate-level stuff into his routines - vertical rolls, inverted spins, and negative pushouts, all flown with precision. Seems the most common airframe issue to watch for when pushing RVs hard is possible loosening of the horizontal tail attach bolts. They are robust airplanes that ARE designed for +6/-3G aerobatics. But I'm not sure you'll find much of a track record for RVs doing snap rolls, or the the problems that may actually develop over time after repeated snaps. This, I think, is fairly uncharted territory considering how 99.9% of RVs are flown. There seems to be more "dedicated" RV aerobatic experience internationally than in the U.S. Would be great to see more acro activity and discussion here, but if you keep posting acro topics, there are a few here who would be glad to comment. :)
 
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Hi guys
I have been watching this as it goes along. Just a few comments I bought a 7 so I could also do aerobatics. But after a while decided to get a dedicated plane as well. As a old national autocross guy I knew competition and daily use don't mix. Really love the RV but can beat the Pitts and not worry it.
Dave
 
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Kansas7 said:
Hi guys
I have been watching this as it goes along. Just a few comments I bought a 7 so I could also do aerobatics. But after a while decided to get a dedicated plane as well. As a old national autocross guy I knew competition and daily use don't mix. Really love the RV but can beat the Pitts and not worry it.Dave
Click to expand...

Dave, I disagree a bit with your last statement. I don't think there's any evidence showing that the RV is any less robust over time than a Pitts when flown within limits. And despite what seems to be a common perception, the Pitts is not unbreakable, or without issues that crop up. And some can occur even when a Pitts is flown within its stated limits. This Pitts has aluminum leading edges nailed into the spar. Over time, especially when repeatedly snapped, these nails can start working out, causing bumps on the wing. There's no good fix for this. Drag wire blocks/nuts can be damaged if pushed too hard. Having fabric alone means paint cracks around the inboard ribs in the propwash will develop fairly quickly when doing lots of aerobatics. This is cosmetic, though. Some people have problems with tapes pulling loose, depending on how well the fabric was applied. Many of the experimental "S-1S's" were built with plywood Sparcraft ribs (non Pitts design), which were prone to cracking. My factory S-1S has an AD to check for cracks on the aft wing fuselage attach fitting. S-2's have a recurring AD to check for upper longeron cracks which can result from flying the airplane beyond its stated limitations. The S-2A has an AD to check for cracks in the horizontal stab support tubes.

But the Pitts is generally a very solid airplane when flown within limits, giving little trouble over its life. But I would say the same thing about an RV. I'm not sure if you have competition acro experience, but THE biggest misconception that's continually espoused by those who have never been involved is the idea that in order to do well, the airplane must be stressed harder, flown faster, or generally "abused" more in competition than when flown recreationally. It's just not true. Yeah, you might eventually break an RV trying to be competitive in IAC Advanced these days. But you could also break my stock Pitts S-1S trying to do the same in Unlimited. Every airplane has an appropriate level of performance that can be extracted from it. And most airplanes, when flown within limits, cause little trouble. Now a Sukhoi, from what I hear, is an airplane that you can "beat" with fewer issues compared to other planes. Or maybe it just raises the bar, and the airplane can now simply take more punishment than the pilot. :)
 
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Eric
Sorry if I didn't express myself well. I agree with you in all aspects the rv is plenty of airplane for intermediate competition I don't even mind the mess my non inverted engine makes on the bottom.
I just need it to go every day when I fly it (125 hrs./yr.) The Pitts on the other hand will break and need some work but I'll just fix it and not get my aero fix. I'll do my first competition next month. Wish me Luck.
Dave
 
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Great information thanks Eric. "Seems the most common airframe issue to watch for when pushing RVs hard is possible loosening of the horizontal tail attach bolts." This kind of information is really appreciated.
I am applying to do my own maintenance on my plane, and has required me to do 3 100h inspections under supervision and sit appropriate exams to get authority from our version of FAA to maintain my own RV. There are not many Lames that know RV's well. Now I am pushing it harder then I would in normal flight, I want to be aware of any issues that may arise before they become a problem, and monitor those areas well. So your comments and experience has been of great help.
Most RV owners I know of do some form of aero's (mostly light), and a discussion often pops up about managing limits not just self but aircraft. I expect I will look for another aircraft for more serious aeros in a few years, for now though every time I get into my RV I get to know it more and more, and that is what I am enjoying. What can I do in this aircraft, and how well can I do it. Next will probably be inverted spinning with the appropriate instructor on board.
 
"Seems the most common airframe issue to watch for when pushing RVs hard is possible loosening of the horizontal tail attach bolts"
Just a question on this Eric. In your opinion, will I notice the loosening of the bolts in my preflight inspection by checking for play in the horizontal stabilizer? Or will I need to remove the tail fairing more regularly than the 100h inspection? At the moment for my pre-flight I check for any play. Have there been documented incidents? If so can you point me in the direction.
Many overseas pilots use these threads, and I have started a thread more specific to aerobatics to see where that goings. Love your input thanks DES "RV's and Aerobatics."
 
RV7DES said:
"Seems the most common airframe issue to watch for when pushing RVs hard is possible loosening of the horizontal tail attach bolts"
Just a question on this Eric. In your opinion, will I notice the loosening of the bolts in my preflight inspection by checking for play in the horizontal stabilizer? Or will I need to remove the tail fairing more regularly than the 100h inspection? At the moment for my pre-flight I check for any play. Have there been documented incidents? If so can you point me in the direction.
Many overseas pilots use these threads, and I have started a thread more specific to aerobatics to see where that goings. Love your input thanks DES "RV's and Aerobatics."
Click to expand...

This issue is actually something a couple of the Team Aerodynamix guys mentioned, since they do regular acro in their routines. Would need to defer to them for more specifics.
 
Thanks Eric. I did, and they were so helpful. It happens.
"Its easily detectable by grabbing your horizontal tip on your walk around.
You can see and feel it move when its loose."
 
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