High Altitude Operations

[aaronk25]

Attached are pictures from my last flight at FL210.   The TAS was 168KTS, and fuel flow was 10.7 gph (well ROP, around 60% power).  I had close to a 45 kt tail wind, giving a ground speed of 210 kts, which is the reason I went that high.

 

CHT, CDT, and TIT were all middle green. There was certainly more speed to be had.

 

LB engine with a Merlyn waste gate controller.

 Do you have the stock 231 engine?  or the LB?  Curious because I see the red line on your MP gauge shows 40" i thought the LB was 36" also I see you were operating at about 27" or so and I think the LB engine would hold 30" at FL210 right?  Also looks like you had the RPMs back to 2250, so I bet at 2500 you'd be clipping along a bit faster.  Just curious as I am thinking about selling (although I have no idea why I just got everything spot on) and getting either a 231 LB, 252 or rocket conversion....not sure...thinking right now....

 

Thead drift....but on a trip back from Dayton Beach to MN I had to go clear to Mississippi then north because I couldn't get to FL160 that would have been needed to top the weather at Max Gross....or if I did the climb performance would have been so nill that any Ice at all would have been a bad deal.....

[fluffysheap]

The GB and LB engines both have the 40" redline.  The intercooler, not the engine revision, reduces the MP redline, although apparently the reduction in the redline varies based on the type of intercooler you have.  The LB is mostly better in cooling, although I've heard the intake is also more efficient on the LB.  All GB engines get converted to LB at overhaul, there's no STC.

 

Increasing the RPM will increase speed, but fuel efficiency is best in the 2250-2300 range.  This varies based on prop and, to some degree, altitude (most efficient prop speed is higher at higher altitude).

[chrisk]

 Do you have the stock 231 engine?  or the LB?  Curious because I see the red line on your MP gauge shows 40" i thought the LB was 36" also I see you were operating at about 27" or so and I think the LB engine would hold 30" at FL210 right?  Also looks like you had the RPMs back to 2250, so I bet at 2500 you'd be clipping along a bit faster.  Just curious as I am thinking about selling (although I have no idea why I just got everything spot on) and getting either a 231 LB, 252 or rocket conversion....not sure...thinking right now....

 

Thead drift....but on a trip back from Dayton Beach to MN I had to go clear to Mississippi then north because I couldn't get to FL160 that would have been needed to top the weather at Max Gross....or if I did the climb performance would have been so nill that any Ice at all would have been a bad deal.....

 

You asked for a data point.  I would consider this to be on the low side of performance, and it would be reasonable to expect more.  It was a beautiful day and with a 210 kt ground speed, and extra 10 (or 15)  knots wasn't going to get me there much faster.  --Now, if I had a headwind, I would be more inclined to bump up the speed.  My view is: a turbo is nice because it allows you to pick a convenient altitude for beneficial winds aloft.  If I didn't have a turbo, I would have been stuck around 15,000 with a largely quartering wind of 30 kts.  Going up allowed for more of a tail wind, and a few knots faster too.

 

I don't recall what the RPM/MP was on the climb, but I was still climbing well (500+ ft/min).   The way I fly is:  I get to altitude, level off, accelerate, several trim adjustments, then power back to something reasonable.

[aaronk25]

You asked for a data point.  I would consider this to be on the low side of performance, and it would be reasonable to expect more.  It was a beautiful day and with a 210 kt ground speed, and extra 10 (or 15)  knots wasn't going to get me there much faster.  --Now, if I had a headwind, I would be more inclined to bump up the speed.  My view is: a turbo is nice because it allows you to pick a convenient altitude for beneficial winds aloft.  If I didn't have a turbo, I would have been stuck around 15,000 with a largely quartering wind of 30 kts.  Going up allowed for more of a tail wind, and a few knots faster too.

 

I don't recall what the RPM/MP was on the climb, but I was still climbing well (500+ ft/min).   The way I fly is:  I get to altitude, level off, accelerate, several trim adjustments, then power back to something reasonable.

You know what you said is very true because 168Kts is still really good because my J will cruise at 162kts at 11k at 2700rpm, but without the turbo I had to fly and extra 4 hours because I wouldn't;t make enough horsepower at altitude to carry the load up and above the weather.  Good Points Chris....and as you said in some cases it would be nice to get higher to better align the tail wind....Thanks!  

[kmyfm20s]

The GB and LB engines both have the 40" redline.  The intercooler, not the engine revision, reduces the MP redline, although apparently the reduction in the redline varies based on the type of intercooler you have.  The LB is mostly better in cooling, although I've heard the intake is also more efficient on the LB.  All GB engines get converted to LB at overhaul, there's no STC.

 

Increasing the RPM will increase speed, but fuel efficiency is best in the 2250-2300 range.  This varies based on prop and, to some degree, altitude (most efficient prop speed is higher at higher altitude).

I read on another thread about GB vs LB engines that the throttle body is smaller on the GB. The 252 has the largest of the 3 IIRC.

[jlunseth]

Technically, all the redlines for the LB with or without wastegate or intercooler, are the same as for the factory GB.  The redlines are how the aircraft was certified, and without doing all the testing and changing all the factory instruments on the panel the redlines could not be changed.  So a redline is a limit for a function, the aircraft being certified to that limit, and the gauges and instrumentation all displaying that limit.  The MP redline, for example, is 40" for all 231's whether they have a GB, LB, or a Merlyn and intercooler.  However, when the intercooler is installed it comes with a set of tables for adjusting the POH MP's to the MP that should be used in recognition of the fact that the induction air is cooled.  So we all know (hopefully) that takeoff MP is 36-37".  We also all know that the CDT redline of 280 dF, was really meant to be an Induction Air Temp, but the factory aircraft only had a CDT, no IAT gauge.  The original intercoolers came with a differential temp. gauge, I.e. a gauge that showed by how much the CDT was being cooled, and that number is used to adjust the MP from the factory POH MP, to the MP that the aircraft equipped with the intercooler should be using.  This was the first Mooney turbo and the intercooler was an add on, so this is how it was done.  Later aircraft such as the 252 that came from the factory with installed intercoolers have different redlines, taking account for the CDT to IAT cooling.

 

We sometimes talk about the adjusted numbers as though they were a redline.  They are not the redline, those are the same as when the aircraft came from the factory.  

[RJBrown]

In the Oxygen accident I referenced above and here, http://aviation-safe...ki.php?id=38638, The bottles the FBO used were properly marked for Oxygen. The company that supplied the Oxygen to the FBO screwed up and sent compressed air in a Oxygen bottle.

 I for one would not know how to check for this issue. Any one out there with an answer?

[fluffysheap]

You could light a match and let the gas from the oxygen line blow on it.  Compressed air will blow the match out, and oxygen... won't.  Given the risk of a fire I am not sure the net effect on safety would be positive.  If you monitor your oxygen levels you will catch this (very rare - probably only happened once) problem.

[RJBrown]

There is a nitrox version o f spare air, which can be up to 40% O2.  It's in the $300 range + a fill at a dive shop + maintance + ....   If your really worried about this, maybe the more cost effective solution would be "Boost Oxygen" for $12.50, which is 95% O2. --Good for ~120 inhalations.

 

On the other hand, I recall some one here was selling low cost O2 systems.  And that might be better as a backup.

 

As for me, I do not have a backup O2 system.  I'd consider one, but weight, cost and hassle factor  seem high for the potential benefit.  Seriously, how long is it going to take with screwing around with a second O2 system vs loosing a few 1000 feet.  Speed breaks, landing gear, spiral down at 2000 fpm.

There are times that decending would be unsafe. Mountains? Ice? come to mind. I came accross Corona pass eastbound in a 182RG at 19500 once. Mountain wave got me that high. Center had given me a block altitude. I was just over a cloud deck that was full of ice. Decending would not have been an option. I always carried back up oxygen in a turbo. When it comes to breathing I guess i am kind of a belt AND suspenders kind of guy. When alone at altitude I always had a backup sitting in the passenger seat already set up. Don the hose and twist the knob and you are breathing. With others on board it was between the seats at my right elbow, set up ready to go. Often I would use the bottled Oxygen as primary and consider the onboard as the backup. Much easier to fill/swap medical E bottles than to deal with refilling the onboard. I was once unable to refill the onboard at any FBO on Dallas Love field because it was a Sunday.

[jlunseth]

Good point.  That is why I have the Nitrox Spare Air, for unusual circumstances where there is no "out" down below, or down below involves being really down below.  Yes, it can be difficult to obtain O2.  I always call ahead and check hours of availability.  As mentioned, the average line guy is not going to be able to fill your tanks.  So typical is 8 - 5 when the A&P is on duty, and probably not Sundays.  At my home base they generally have someone there all the time who is qualified, but many places do not.  In Gadsden I have had to go across the airport to a group that rebuilds foreign fighter jets, and they had to rig up a special valve because our fitting is not the same as the foreign jet fitting.  It was fun meeting them and looking at the MiGs, but not fast getting the O2. There is always a way, best to call ahead and have it in place.

[RJBrown]

Air is 21% oxygen, so 40% nitrox would be better than nothing but for $500 you can have a real backup. A 40% spare air is better than nothing. They are quite small and easy to keep handy. I can understand the logic of "Hey its better than nothing". I bought the protable O2 setup before I owned a plane and used it in rentals. It has been in the pile of airplane stuff for over 22 years so bringing it along is habit. I would feel unprepared for flight if it were not there. Even if the trip were down to Florida in a NA airplane I would still want O2.

[jlunseth]

A 40% nitrox mix will give you 20% O2 (nearly normal) at 18000, and what is considered a normoxic mix (over 16%) up to just short of 24,000.  A normoxic mix is about the equivalent of 7,000 feet.  Duration is an issue,  I estimate the Spare Air at 3.0 c.f. would be good for about ten minutes.  Time would actually be better in the higher altitudes (because the regulator allows you to breath at ambient atmosheric pressure, which is less when high up) and reduce as you go down.  Most of my flights are in the midwest where I can go as low as I like, my greater concern are the flights to the Bahamas where there is a passenger between me and the one door on the plane. 

 

About blowing O2 on a match.  In high school science class (middle of the last century) we had a kid drop quite alot of dry ice into a container of water.  Same kid later lost a finger to a snowblower.  It would be about that interesting but quite alot hotter.

[carusoam]

There are devices that can measure O2 percentages. I have used them for packaging studies. Safer than lighting a fire, but more expensive.

Check list item???

Best regards,

-a-

[chrisk]

There are devices that can measure O2 percentages. I have used them for packaging studies. Safer than lighting a fire, but more expensive.

Check list item???

Best regards,

-a-

Scuba diving devices for measuring O2 start at about $250.   Or if you use a $50 oximeter. You can see if you have enough oxygen.  And if you don't have enough, and the O2 is on, then you can go down.

[aviatoreb]

Thank you fluffy sheep.  Very thoughtful post.  Sometimes I clip the "best of" posts to keep in a file on my computer to use as reference later, and yours I clipped!

 

Just a bit of extra info - product review - for back up I use the following device since it is quick-grab - emergency -

 

http://www.mhoxygen.com/index.php/portable-constant-flow/emergency-systems/165-ntg-co-pilo2t-portable-o2

(with 2 extra bottles - so that should be enough to get me down I hope).  I keep it in a special bag at my side and just a grab and twist away.

 

For up to the upper teens, I love the oxyarm cannula system since it keeps all the pluming tubes at a minimum and it is just more comfortable since it barely touches your nose, and turns with your head more easily as it is attached to your headset.  Plus it is easier to put it on and off as you fly up and then down through the O2-needed altitudes.

 

http://www.mhoxygen.com/index.php/face-masks/cannulas/82-ez-breathe-ii

[aviatoreb]

 

You can do your own tests.  Go do some hard aerobic exercise.  Then immediately check your oxygen level with your oximeter.  It's going to be in the 80s.  Maybe the low 80s.  Anyone who exercises for half an hour is going to have oxygen levels similar to high-altitude hypoxia, and over a longer period of time.

 

Have you done that test to wear your pulse-ox during exercise?  It didn't sound right but I was not confident enough to contract you, so I just emailed to my ex-physio professor friend and he just wrote this back (which I post anonymously since I did not ask him permission to put his name, but he is a really good and well versed researcher with connections as a consultant for some of our olympic teams).

 

"wrong.  O2 sats are stable in the mid to high 90s unless at atltitude.  If they do drop to 90, the clock is ticking and you won't last much longer.  Once you start dropping down the descending slope of the O2-Hb saturation curve, it's a rapid spiral into desaturation and if exercising, you quit.  

In fact, at sea level, it is very rare to see desat even at high intensities like L5 except in elites, so, the statement "anyone who exercises.." is clearly wrong and easily refutable with a simple google.  

Hope that helps."

 

Nonetheless I am really curious to try the experiment since it sounds like fun.

[fluffysheap]

I have.... but I live at 6000'.  It's possible that even though I'm acclimated I took a little more O2 hit than someone at sea level would.

 

For the record, I would usually check right at the end of a fairly serious session (warmup jog, then weights or similar - that's anaerobic so probably doesn't matter much - then interval training on the exercise bike), when I was pretty well beat, and the value I got was usually about 87-88.  It would come back up quickly, but not immediately, after stopping.  I'm not elite, not by any stretch of the imagination, but at the time I was in decent but not amazing shape, in my late 20s, and I did go until I needed to stop.  So I'm not sure my experience, given the altitude, is that far off of what your guy is saying.  If I just did the warmup and the weights I would stay in the 90s.

 

So I guess I made three errors: First, assuming that my experience acclimated at altitude translates to sea level, second presuming that someone who was in worse shape might experience even lower O2 levels - as opposed to just stopping sooner at the same O2 level, and third not properly explaining that my experience was "train to exhaustion" rather than simply "do some exercise."

 

Even the second assumption, while it might have been wrong for someone healthy, wasn't pulled completely out of the air.  Both of my parents suffered from respiratory failure as a result of cancer, and their O2 levels after activity were routinely 85 or below (with supplemental oxygen).  In that case, the doctors were just happy if the resting level was above 90, and didn't really worry about what happened during activity.

 

There's also the possibility that my oximeter - which is the same one my parents used - reads a point or two low.  It's an older prescription one from the late 90s, but still works.

 

Although I'm certainly not in the physical condition I was in ten (wow!) years ago, I'll repeat the test, and I'll also try at sea level and the next time I'm in Leadville, just to get some extra data points.

 

Also, I did the quick Google search and the first two articles I found with actual measured data were here:

http://jap.physiology.org/content/19/2/284.abstract

http://answers.yahoo.com/question/index?qid=20070811103657AATcZ5F

 

Both of which showed 85% as possible during exercise, but only for athletes.  So it looks like my real incorrect assumption was that someone in worse shape would have a lower blood O2 saturation, rather than a higher one.  I was in shape but a short of a real athlete, so ending up around 87-88 doesn't seem out of line.  I was in good shape and dropped to the high 80s, my parents were in poor health and dropped to the low 80s.  I extrapolated and figured someone in average health would also drop into the mid-80s.  But apparently that's wrong.

 

For purposes of hypoxia-induced health problems, I'm not sure what this indicates.  I still don't think short-duration exposure to the high 80s is going to kill brain cells.

[Dave Marten]

Sheap,

 

Cannulas are only certified to 18,000ft period. Not governed by part 91, but by the certification requirements of the aircraft's oxygen system. Part 23.1447

 

Sec. 23.1447 — Equipment standards for oxygen dispensing units.

If oxygen dispensing units are installed, the following apply:

 

(a) There must be an individual dispensing unit for each occupant for whom supplemental oxygen is to be supplied. Each dispensing unit must:

(1) Provide for effective utilization of the oxygen being delivered to the unit.

(2) Be capable of being readily placed into position on the face of the user.

(3) Be equipped with a suitable means to retain the unit in position on the face.

(4) If radio equipment is installed, the flightcrew oxygen dispensing units must be designed to allow the use of that equipment and to allow communication with any other required crew member while at their assigned duty station.

( If certification for operation up to and including 18,000 feet (MSL) is requested, each oxygen dispensing unit must:

(1) Cover the nose and mouth of the user; or

(2) Be a nasal cannula, in which case one oxygen dispensing unit covering both the nose and mouth of the user must be available. In addition, each nasal cannula or its connecting tubing must have permanently affixed—

(i) A visible warning against smoking while in use;

(ii) An illustration of the correct method of donning; and

(iii) A visible warning against use with nasal obstructions or head colds with resultant nasal congestion.

© If certification for operation above 18,000 feet (MSL) is requested, each oxygen dispensing unit must cover the nose and mouth of the user.

 

 

http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/Oxygen_Equipment.pdf

 

and

 

http://preciseflight.com/general-aviation/shop/oxygen-equipment-general-aviation/products/masks-cannula/

 

http://www.aeromedix.com/blog/2008/11/oxygen-for-general-aviation/

 

http://www.c-f-c.com/supportdocs/abo4.htm

 

You wanna fly above FL180 put on the mask and that means your passengers also!

 

I'll happily provide any CFI who's advocating cannulas above FL180 a swift kick in the junk.

 

Don't screw around with O2!

 

 

 

Dave Marten

Former 231 owner- N231RX

[WardHolbrook]

All you guys who are flying around in the upper teens and lower Flight Levels without ever having sat in an altitude chamber are making a dumb mistake. It's the classic example of "Just because it's legal doesn't make it smart!"

 

If you're up above 14,000' or so you really need this training. I've had two chamber "flights". Each one was a real eye-opener. I was just sitting there fat, dumb, and happy with the pencil and paper making strange, illegible scribblings until they put the mask on me. I told them that I was OK and was still good to go. It was actually pretty frightening once I came around enough to realize what my personal response was. I understand that different people have different responses. Some people function like a ni-cad battery - they seem to doing well and then they simply go off the cliff. Others, like me just sit there fat dumb and happy with warm fuzzy feelings - totally oblivious to what's going on around them. Others I've seen crash pretty fast. You really need to have the chamber experience to see what your personal response is. It's just my opinion, but I don't think just reading about it is enough. As far as accessories go, you will want a pulse oximeter. Cannulas are only legal to FL180, above that you'd need (and want) a good quality mask. Above FL200 you'll also want a small back up bottle like this one that you can keep at your side and use to get down to a breathable altitude in the event of a failure in your main system. www.skyox.com/product/SK12-6

 

Chamber training is readily available. I've received mine at UND at a reasonable cost and the FAA and military offers civilian chamber training at little or no cost as well. Here's a link to the FAA's course: www.faa.gov/pilots/training/airman_education/aerospace_physiology/

 

You can do an internet search for other courses and training providers, but bottom line, hypoxia is nothing to screw around with. It's one of the major pilot killers. 

[AndyFromCB]

All you guys who are flying around in the upper teens and lower Flight Levels without ever having sat in an altitude chamber are making a dumb mistake. It's the classic example of "Just because it's legal doesn't make it smart!"

 

If you're up above 14,000' or so you really need this training. I've had two chamber "flights". Each one was a real eye-opener. I was just sitting there fat, dumb, and happy with the pencil and paper making strange, illegible scribblings until they put the mask on me. I told them that I was OK and was still good to go. It was actually pretty frightening once I came around enough to realize what my personal response was. I understand that different people have different responses. Some people function like a ni-cad battery - they seem to doing well and then they simply go off the cliff. Others, like me just sit there fat dumb and happy with warm fuzzy feelings - totally oblivious to what's going on around them. Others I've seen crash pretty fast. You really need to have the chamber experience to see what your personal response is. It's just my opinion, but I don't think just reading about it is enough. As far as accessories go, you will want a pulse oximeter. Cannulas are only legal to FL180, above that you'd need (and want) a good quality mask. Above FL200 you'll also want a small back up bottle like this one that you can keep at your side and use to get down to a breathable altitude in the event of a failure in your main system. www.skyox.com/product/SK12-6

 

Chamber training is readily available. I've received mine at UND at a reasonable cost and the FAA and military offers civilian chamber training at little or no cost as well. Here's a link to the FAA's course: www.faa.gov/pilots/training/airman_education/aerospace_physiology/

 

You can do an internet search for other courses and training providers, but bottom line, hypoxia is nothing to screw around with. It's one of the major pilot killers. 

 

One, some of us, especially who do not smoke and spend sufficient time CO or WY, do not even feel winded at 14,000. For me, since I quit smoking a few years back, I can do sprints on top of flattop mountain. I've spend days (5) at 14,000 with no ill effects. Others flip out and loose their shit. 

 

As to canullas, I've worn one to 24,000 while another pilot was flying with mask. Just fine for an hour. Took it off, went TU in about 10 minutes. 

 

Altitiude chamber at Offutt had no effect on me until 21,000 feet and then the drop off was severe. I quit making all sense and started seeing watermelons everywhere. I don't know why watermelons, but that was it. I was awake and talking trash until 24,000 and then I just turned off.

[AndyFromCB]

Have you done that test to wear your pulse-ox during exercise?  It didn't sound right but I was not confident enough to contract you, so I just emailed to my ex-physio professor friend and he just wrote this back (which I post anonymously since I did not ask him permission to put his name, but he is a really good and well versed researcher with connections as a consultant for some of our olympic teams).

 

"wrong.  O2 sats are stable in the mid to high 90s unless at atltitude.  If they do drop to 90, the clock is ticking and you won't last much longer.  Once you start dropping down the descending slope of the O2-Hb saturation curve, it's a rapid spiral into desaturation and if exercising, you quit.  

In fact, at sea level, it is very rare to see desat even at high intensities like L5 except in elites, so, the statement "anyone who exercises.." is clearly wrong and easily refutable with a simple google.  

Hope that helps."

 

Nonetheless I am really curious to try the experiment since it sounds like fun.

 

Yes, but the definition of elite is kind of lame around here. I can go on a 100 mile bike ride and be done under 5 hours. To most sport folks, that's considered elite. The only thing that hurts is my ass. So yes, anyone who exercises past about 30 minutes recommended is not going to respond to oxygen depravation like some here. I did Denali 11 years back at 260lb so about 30lb of pure fat and while hard, 20,000 didn't feel like much and back then I smoked a pack of Camels a day. I quit because in my 30's, a pack of smokes killed me more than a liter of gin next morning.

[aviatoreb]

Yes, but the definition of elite is kind of lame around here. I can go on a 100 mile bike ride and be done under 5 hours. To most sport folks, that's considered elite. The only thing that hurts is my ass. So yes, anyone who exercises past about 30 minutes recommended is not going to respond to oxygen depravation like some here. I did Denali 11 years back at 260lb so about 30lb of pure fat and while hard, 20,000 didn't feel like much and back then I smoked a pack of Camels a day. I quit because in my 30's, a pack of smokes killed me more than a liter of gin next morning.

 

You are definitely a healthy fit person to be able to ride 100 in under 5, as can I easily, but I am not an elite.  My friend is an ex phys prof who as I said does consulting coaching for the US National cycling team and also gets interesting runner data - which I can say come back and talk to me about elite when you can do 100 miles in well under 4 hours.  Or run a mile in about 4 minutes.  Both of those are not world class sort of times but ear marks of athletes who make training their main occupation.  Anyway he was just responding to a discussion of intervals.