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RV-7 Service Ceiling - FL 220 Today

gciampa

Active Member
All,

while flying back home today, D38 to KTTA decided to test the service ceiling on N269MC;

FL 220 was easily attained, 300 FPM from FL 200 to FL220. Decided the service ceiling for the pilot was FL 220. I was solo, 25 gallons of fuel and some luggage in the back, estimate 1450 pounds at the time.

I snapped a picture at FL200 for posterity.

nc29mc_fl200.JPG.html


Gary
 
I look forward to the day I get to do the same experiment 8^). These are great planes!
 
Dont want to be a stick in the mud

Hey guys,

Just be careful of decompression sickness above FL180 unpressurized for longer than 15 min in an unpressurized cabin. In the Air Force we require 100% O2 on aviators mask above these altitudes. I know plenty of Turbo Mooney oporators routinely fly at these altitudes with nasal canula but I wouldnt for an extended time or if I did I would take precaution.

1. drink extra fluid, best way to dissolve buubles is to add water. Thats why the fizz goes away in your coke when the ice cubes melt. Same thing happens to evolved nitrogen in your body.
2. Above FL180 is no time to practice tactical dehydration. Avoiding water to avoid the pit stop
3. Limit in flight and post flight exercise. What happens when you shake the coke can, more bubbles. Dont end your high alt flight with G maneuvers and dont exercise 12 hours post flight.

Above FL180 you will bubble, normally these bubbles dont stick anywhere and or recompress on decent. Take some easy precautions to avoid aggrevating the problem and enjoy the smooth air.
 
Nice report

All,

while flying back home today, D38 to KTTA decided to test the service ceiling on N269MC;

FL 220 was easily attained, 300 FPM from FL 200 to FL220. Decided the service ceiling for the pilot was FL 220. I was solo, 25 gallons of fuel and some luggage in the back, estimate 1450 pounds at the time.

I snapped a picture at FL200 for posterity.

nc29mc_fl200.JPG.html


Gary

Amazing report. What was your true air speed?? Hope you had o2.
 
Hey folks,

Yes, I was on O2 as per the regulations. I ended up stair stepping from 12,000, to FL180, then FL200, then FL220 while on O2 to minimize the effects of decompression and evolved nitrogen. A buddy of mine suffered from decompression sickness with severe shoulder joint pain on a high altitude run some years ago.

Refer to the AF3500 image for airspeeds and engine performance.

nc29mc_fl200.JPG.html


This was an excellent adventure! Turns out the plane is not as sensitive to altitude as the pilot... :D
 
dont exercise 12 hours post flight.

Any idea why this is true? It seems that by being at high altitude your body would start to reduce the amount of nitrogen in the tissues (by outgassing or absorption in the blood and transfer through the lung during breathing) moving toward an equilibrium state for the given altitude. By going down, your body would just start absorbing nitrogen faster which should prevent the bubbles that cause the problems.

I'm certainly no expert in this field so I'm looking to learn something. Just curious.

My 22,000ft story -

I went to 22k on the way back from KDVK - 5W5 back in May. The Blue Ridge mountains are quite intimidating and I wanted to make sure I gave them plenty of room. ;) I had the standard canulas and an SpO2 meter that I was making sure stayed above 97%.

I can't remember all the temperature details, but I could still climb at 400ft/min up to 22k. I was lightly loaded. I took the same step approach that Gary mentioned up to 22k. Stayed at 22k for ~45min.

Issues
- I started getting vapor lock around 14,000ft during the climb while using my mechanical fuel pump. Once the boost pump was turned on the fuel pressure immediately went back up and all was right with the world. I was running 100% MOGAS (93 octane, non ethanol). Once I leveled off and everything cooled down I could turn off the boost pump and had no issues with vapor lock even at 22k
- No physical issues that I noticed
 
AF 3500 performance data

Hey folks,

Yes, I was on O2 as per the regulations. I ended up stair stepping from 12,000, to FL180, then FL200, then FL220 while on O2 to minimize the effects of decompression and evolved nitrogen. A buddy of mine suffered from decompression sickness with severe shoulder joint pain on a high altitude run some years ago.

Refer to the AF3500 image for airspeeds and engine performance.

nc29mc_fl200.JPG.html


This was an excellent adventure! Turns out the plane is not as sensitive to altitude as the pilot... :D

Very cool to see your performance data at FL200. Not many of us likely have been there in an RV. Thanks for sharing
 
Fuel flow

Is your fuel flow correct? Are you really burning 8.1 gals/hr at 13.9 inches of MP? Seems really high, I was expecting in the 5-6 range. Good job, thanks for the data!
 
re: Fuel Flow: In general, my FF reads a tick higher than actual, perhaps a few tenths per hour. I am running an O-360, normal cruise I set EGT around 1400 on the leanest cylinder, around 10GPH on the meter, WOT, 21 MP, 2450 RPM.

However, as I climbed into FL, the engine was not running as smoothly with the leaner mixture setting, lower fuel flow, I ended up setting the mixture a bit richer than I expected.

Also, a critical eye will see one EGT is reading low, this is an erratic EGT probe issue. Sometimes it is spot on, other times it is erratic.
 
TAS ?

I see 41% and TAS of 151. Even at 41% I would have expected a bit higher true airspeed? What was your fuel economy if you average out the headwind?

Now I see the low IAS, That is a 40 or so difference in IAS and TAS.

Thanks for the post.

Jim
 
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I can't imagine the bends being a problem in aviation.

The reason it's an issue in SCUBA diving is that it's easy to go from high pressure to low pressure quickly, causing nitrogen to bubble out of solution in your tissues.

In an RV, even with its respectable climb rate, you don't really get to low pressure very quickly. A military jet, even pressurized, can expose the body to 10,000 feet of altitude change in a matter of a minute or two and I've never heard of bends related issues. Also, pilots aren't always on 100% oxygen. Not sure if it's different now, but in my day, as soon as you were comfortably airborne, the mask was 1/2 unclipped and swinging to the side... until it was time for some hard maneuvering.

Just trying to add some useful info here:
The reason fizz goes away in warm Coke is less that it's diluted by water from the ice, but more that warm water can hold far less CO2 when warm.

Also, exercise isn't synonymous with shaking a can of Coke. It may be that they recommend SCUBA divers not exercise after a long deep dive... possibly because of damage from bubbles going to the wrong places: http://deepstop.wordpress.com/2008/09/29/exercise-after-scuba-diving/. Should not be a factor after high altitude flying.

Lastly, be aware of the huge differences in pressure changes between flying and SCUBA diving. With SCUBA, you can get to a pressure 4X Sea Level and go back to 1X in just a minute or two. With Flying, the pressure ratio from Sea Level to FL180 is only .5.

Another way to look at it is:
Sea Level to 120' deep: 15psi --> 75psi or 60psi difference
Sea Level to FL180: 15psi --> 7.5psi or 7.5psi difference
 
Bends and flying

Just like Gray forge said,
It will be hard to get the bends while flying. From ground to space, (or back) the maximum pressure change is 1 atmosphere. But when diving, ever 30' of depth is 1 atmosphere. So the problem only comes in if one has been diving and then ascends the extra atmosphere in an airplane. For regular flying, ask any diver how many times he can go from the surface to 30 feet and back; he would probably tell you a lot. In addition, at 18,000 feet, that is 1/2 atmosphere (500 millibars) so it is even more a non issue. JMO, YMMV
 
The bends in flying might not be as rare as you think. In my 4 years of AF flying I personally know two guys that have had it. One was during my chamber ride at pilot training, don't remember what "altitude" we were at to show the signs of hypoxia but it was only 20-30 something at best. The other was a U-2 pilot I flew with (I know... this one shouldn't really count), but crazy part about his story is he temporarily went blind from it, luckily he regained partial vision before landing.
 
The instance I was eluding to was a flight of 8 F4-D's flying across the North Atlantic, one of the crew ended up with injuries that required hospitilization.

We were using O2 w/our masks fully engaged, 100% O2 did not alleviate the symptoms.
 
Altitude decompression sickness

Altitude induced decompression sickness is rare, but not non existent. I have treated about 60 cases of altitude induced DCS in my AF career. Most has to do not with how rapid an ascent but rather duration at altitude. What differs alt DCS from diving DCS is the fact that in alt DCS the bubble remained despite the recompression when you decended. The mechanism isnt entirely understood but most believe that at alt there was a local inflamatory response to the bubble and a clot forms or some other effect that hinders the bubble from continueing to pass to the lungs. Doppler of the heart during a decompression from 8,000 to FL250 shows a flood of bubbles passing thru the right side of the heart on the way to the lungs without any symptoms of DCS. symptoms occur when the bubble gets stuck. previous injury, fat, age and dehydration all seem to increase the risk of DCS.

For U2 high flights we use exercide enhanced O2 prebreathing prior to flight. You prebreath 100% oxygen while exerciseing on an eliptical machine to liberate as much of the nitrogen from those stubborn areas as possible. For high altitude airdrops we prebreath 100% oxygen as well.

Why do we recommend no exercise 12 hours post flight of a high altitude exposure. Mechanism not completely understood but believe falls back to that inflamatory response and or an aggregation of a bunch of small bubbles into one larger bubble when you exercise. within 12 hours any bubbles have worked their way thru the system.

Dont mean to hijack a glorious discussion of max performing the RV, but this is probably the right forum to discuss this so anyone contemplatnig pushing the envelope has a fun and safe experience.
 
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