ROP and LOP as related to "the feel"

[aviatoreb]

I wonder what is the highest a piston engine airplane ever flew?  The P51 had a service ceiling of ~42,000.  Did people actually go that high?  

[N201MKTurbo]

19 minutes ago, aviatoreb said:

I wonder what is the highest a piston engine airplane ever flew?  The P51 had a service ceiling of ~42,000.  Did people actually go that high?  

I think it was in the early 30s. A plane made it to 54000 feet. That record hasn’t been beaten.

well I was close.

https://en.wikipedia.org/wiki/Caproni_Ca.161

https://en.wikipedia.org/wiki/Flight_altitude_record

 

[Pinecone]

Interestingly, the current official record for a glider is 50,671 feet.  But they are waiting confirmation of a flight to 74,298 feet.

[A64Pilot]

In 1934 Wiley post wearing what looked like a deep sea diving suit reportedly took Winnie May to 50,000 ft. 

‘He was the one who discovered the Jet Stream

[A64Pilot]

6 hours ago, N201MKTurbo said:

I think it was in the early 30s. A plane made it to 54000 feet. That record hasn’t been beaten.

well I was close.

https://en.wikipedia.org/wiki/Caproni_Ca.161

https://en.wikipedia.org/wiki/Flight_altitude_record

 

Amazing maximum speed for that aircraft is quoted as 60 MPH, and look at the pitch on that prop

[N201MKTurbo]

20 minutes ago, A64Pilot said:

Amazing maximum speed for that aircraft is quoted as 60 MPH, and look at the pitch on that prop

If you blow up that image you can see the Buck Rodgers space helmet he is wearing. The American that went to 54000, did it without a pressure suit and just an oxygen hose in his mouth.

[A64Pilot]

1 hour ago, N201MKTurbo said:

If you blow up that image you can see the Buck Rodgers space helmet he is wearing. The American that went to 54000, did it without a pressure suit and just an oxygen hose in his mouth.

I don’t know who that was Wiley Post was I believe the first pressure suit. Took three iterations, first busted, second was so tight it had to be cut off, third I guess they got it right.

I don’t think you can do 50,000 without pressurization even if you pre breathe pure O2.

 

[N201MKTurbo]

31 minutes ago, A64Pilot said:

I don’t know who that was Wiley Post was I believe the first pressure suit. Took three iterations, first busted, second was so tight it had to be cut off, third I guess they got it right.

I don’t think you can do 50,000 without pressurization even if you pre breathe pure O2.

 

 

I remember reading about aviation history and someone went crazy high without a pressure suit. I can't find it now.

There are new fighter jets that can go over 60000 feet and the pilots don't ware a pressure suit. They say the G-suit can keep them alive until they can descend.

 

That pressure suit is still around.

[Pinecone]

14 hours ago, N201MKTurbo said:

There are new fighter jets that can go over 60000 feet and the pilots don't ware a pressure suit. They say the G-suit can keep them alive until they can descend.

In the 50s and 60s, there was a "semi pressure" suit.  It had inflatable rolls that caused the flight suit to compress on the body.   

Modern fighters are pressurized.  So that helps.  A G--suit only compresses the lower body and legs, not the upper body and arms.

"If the human body is exposed to a low enough absolute pressure, then surface fluids (tear film, saliva, and the air-exposed surface of alveoli) will begin to boil at normal body temperature. This occurs at around an altitude of 60,000 feet (approximately 11.4 miles or 18.3 kilometers) depending on exact atmospheric conditions."

"Under 34,000 ft 100% oxygen in a tight-fitting mask will deliver near ground level oxygen to the tissues. Pressure suits or pressurized cockpits must be used beyond this level to maintain near sea level oxygenation to the tissues."

 

[N201MKTurbo]

1 hour ago, Pinecone said:

In the 50s and 60s, there was a "semi pressure" suit.  It had inflatable rolls that caused the flight suit to compress on the body.   

Modern fighters are pressurized.  So that helps.  A G--suit only compresses the lower body and legs, not the upper body and arms.

"If the human body is exposed to a low enough absolute pressure, then surface fluids (tear film, saliva, and the air-exposed surface of alveoli) will begin to boil at normal body temperature. This occurs at around an altitude of 60,000 feet (approximately 11.4 miles or 18.3 kilometers) depending on exact atmospheric conditions."

"Under 34,000 ft 100% oxygen in a tight-fitting mask will deliver near ground level oxygen to the tissues. Pressure suits or pressurized cockpits must be used beyond this level to maintain near sea level oxygenation to the tissues."

 

I was referring to dealing with a pressurization failure above 50000 feet. The modern jets don't have their pilots wear a full pressure suit. The modern G-suit has chest pressure along with leg and abdominal pressure. It was determined that this along with pressurized oxygen was sufficient for the pilot to descend to safer altitudes below 40000 feet. The jets have a valve that inflates the G-suit in case of a pressurization failure. I understand it is very hard to breathe in that situation.

Here is an excerpt from the hearings on the F22 hypoxia problems:

General Martin. Mr. Congressman, I will let General Lyon 
discuss perhaps some of the warfighting characteristics of the 
operational environment, but from a system design and human 
systems integration perspective, the F-22, unlike all other 
aircraft, can operate routinely and in a sustained manner above 
50,000 feet. Typically, the Air Force has required its air 
crews to use a full pressure suit when operating above 50,000 
feet, even though the cabin pressurization is adequate and 
safe. Should there be a rapid decompression at those altitudes, 
the effect on the blood and the effect on your ability to 
properly inspirate or breathe is very, very challenging without 
supplemental pressure to keep your lungs from exploding and to 
ensure that you are able to process the oxygen that is 
delivered.
    The F-22 does not have a full pressure suit, and it was 
designed to operate with a partial pressure suit, the upper 
pressure garment, a different anti-G suit and those sort of 
things. So that airplane operates in an environment different 
than what we had operated. For instance U-2s, SR-71s, those 
airplanes, all of those air crew members fly in a full pressure 
suit. The F-22 pilots do not, and therefore, it is important 
they not only understand where they are vulnerable and the 
limitations of the equipment but also the performance of the 
equipment as they operate in those areas. So our concern was 
making sure that not only did we have the right equipment and 
that it would perform well and provide the protection that it 
was intended to, but that the air crews would also know what 
the differences were and how to operate in that environment.

 

[A64Pilot]

I’m thinking an F22 can descend from 50,000+ to well less than 40,000 in a matter of seconds.

It’s only 2 miles or so, and they aren’t nearly as constrained in speed as most aircraft.

It’s all about partial pressure, as you ascend the pressure drops of course so you breathe ever increasing Oxygen to maintain hopefully the partial pressure of 21% O2 at sea level pressure, at some altitude even pure O2 can’t maintain that and you have to wear a pressure mask, which is a very obnoxious thing, has to be very tight to not leak and you have to force an exhale and talking is difficult.

But even supplying O2 at pressure has its limits of course, one of those is the bends, the N2 in your blood will come out of saturation at low pressures, so to try to prevent that you pre-breathe pure O2 for a long time to flush any N2 from your blood stream.

Even back 100 yrs ago the risks and problems were known, but Wiley post for instance still breathed pure O2 from a liquid O2 dewer I think, it may not even had a regulator, I think it just boiled off and the suit was pressurized with a simple pop off valve. I think. I’m thinking that’s the simplest way and how I would do it, not sure how he did.

Spacecraft used to be pure O2 and if not already surely will be again, that ended with Apollo 1, but if you breathe pure O2 I think you only have to be at 1/3 sea level pressure to maintain sea level partial pressure, so a space craft can be much lighter as it only has to hold 5 PSI or so instead of nearly 15 PSI.

[Pinecone]

Since air is 21% O2, you need to go to where the pressure is about 1/5 sea level for pure O2 to be the same partial pressure as at sea level.

Pressure at Sea Level + 14.7 PSI.  O2 partial pressure 3.087 PSI.  So where the air pressure is 3.087 PSI, breathing pure O2 is the same as at sea level, and that is 37,400 feet at 15C.

But you don't need 3 PSI O2 to live.  OSHA allows down to 19.5% O2, but that is for pretty much any working altitude

[A64Pilot]

I had to look because I know 3 PSI will work, but NASA suits are 4.3 PSI and Russian 5.8 PSI, both I’m pretty sure are pure O2 rebreathers. I don’t know that but only a rebreather makes sense and a pure O2 one is simple.

The reason for the higher pressure is the bends, coming out of a high N2 atmosphere with 21% O2, dropping from 14.7 PSI to 3 PSI could give you the bends, unlikely if you could pre breathe O2 long enough to flush the N2 from your system, but I think most suits are made to be used in a hurry if needed.

Interesting that the Russians are more conservative than the Americans, because I’m sure the higher pressure makes their suits much harder to work with.

Wiley post flew at .5 atm or about 7 PSI, I guess he was real conservative.

[211º]

Building on this thread…
While flying westbound with a good 15 kt or so headwind, I was flying LOP. So far so good.
Then (because I was a little bored) I increased to ROP.
I probably need to do the spreadsheet, but it seemed like the relative difference (or extrapolated) increase in IAS was not linear with the increase in GS. My GS increased about 15% greater than IAS.
That made me wonder… could the Airspeed indicator be less precise at lower IAS.
Sent from my iPad using Tapatalk Pro

[Pinecone]

Wind could have changed speed or direction.

[carusoam]

59 minutes ago, 211º said:

could the Airspeed indicator be less precise at lower IAS.
Sent from my iPad using Tapatalk Pro

 

Interesting concern…

We do have a place to look that up too…
 

Did you mean less accurate?

because it’s precision seems to be identical throughout the range as the same needle, rotates in front of the same hash marks, that are equally spread, from one end of the gauge to the other…

PIC is part of the precision, as is parallax….

 

Unlikely less accurate as well…

Since the stall speed is probably the most important piece of information delivered by that instrument…

 

Errors in airspeed are pretty well known… because we have a couple that get documented in our POHs…

Some of the older Mooney instrument errors are a small bit different than newer Mooney instruments…

I May have to look them up later for a nice review…. 
 

Best regards,

-a-

 

[0TreeLemur]

6 hours ago, 211º said:

Building on this thread…
While flying westbound with a good 15 kt or so headwind, I was flying LOP. So far so good.
Then (because I was a little bored) I increased to ROP.
I probably need to do the spreadsheet, but it seemed like the relative difference (or extrapolated) increase in IAS was not linear with the increase in GS. My GS increased about 15% greater than IAS.
That made me wonder… could the Airspeed indicator be less precise at lower IAS.
Sent from my iPad using Tapatalk Pro

From the theory:

The airspeed indicator is just a pressure gauge with a particular set of marks on it to correspond to the solution of the equation V=sqrt(2*delta_P/rho) where delta_P is given by (P_pitot - P_static), and rho is sea-level STP air density.

What's causing delta_P in terms of mixture, etc., cannot affect it.

My guess is that while you were doing your test, you flew into a different air mass having a different wind component.  That's a more likely explanation.

[Rick Junkin]

7 hours ago, 211º said:

Building on this thread…
While flying westbound with a good 15 kt or so headwind, I was flying LOP. So far so good.
Then (because I was a little bored) I increased to ROP.
I probably need to do the spreadsheet, but it seemed like the relative difference (or extrapolated) increase in IAS was not linear with the increase in GS. My GS increased about 15% greater than IAS.
That made me wonder… could the Airspeed indicator be less precise at lower IAS.
Sent from my iPad using Tapatalk Pro

Depending on what altitude you were flying a majority of that 15% can be accounted for by the incremental increase in true airspeed as compared to the incremental increase in indicated airspeed. Run the true airspeed calculation for the conditions you were flying in and see what you get.

Cheers,
Rick