12,500 feet MSL over Oceano

I had not identified the practical ceiling for the Predator with the IO-320B1A and my three blade 68inch 47” pitch Catto propeller.

The prop is a little over pitched but we are hoping it will be just right for Mariah Gale. We climbed out at 2,400 rpm.

The winds were relative calm and the altimeter setting was 30.9.

It was 59 degrees F (15 C) when we took off from San Luis Obispo with full tanks and a full stomach. I firewalled her and left it there. I leaned her every 2,000 feet of additional altitude.

I called Santa Barbara Approach and told them I wanted to find my practical ceiling over the Oceano airport and asked for flight following. They gave me a transponder code and radar contact was established 1.7 miles from SBP at 2,200 feet.

50 minutes later I had climbed to 12,500 feet. I actually climbed to 12,700 feet but that picture didn’t come out.

My 30 foot, 8.5 inch chord Sport Copter blades were turning 369 RPM.

At 12,000 feet MSL Santa Barbara Approach asked me if I had oxygen on board. I did not.

I don’t know if it was the thin air or my fear of heights but I felt light headed.

I found on the way down that at 50kts we descend at 960 feet per minute and 800 feet per minute at 40 kts indicated air speed with the engine at idle. I coasted for 12 statute miles, all the way to SMX and did a practice engine idle landing. That is a 5 to one glide ratio.

This means I can fly to Big Bear and on a cool day take off from Leadville, Colorado.

She burned 6.5 gallons.

It was more fun than I expected and I am still a little wound up.

Thank you, Vance

Wow it must have been a thrill being up 12.5! Getting light headed can be very much from lack of Oxygen up there. But again a whole lot of other things can make one light headed at even lower altitudes. I love your adventures thanks for sharing

When working with high altitude, is there any risk to the effectiveness of the rotor? IE: not enough density to maintain proper rotor rpm to stay airborne? Other than biophysical symptoms, what should a pilot be aware of when getting to high and how will I know I'm in a danger zone for the aircraft?

Additionally, I understand that the aircraft performs less efficient at high altitude but is it "dangerous" like the rotors lose effectiveness and just slow, flap, stop, etc?

willisbr said:

When working with high altitude, is there any risk to the effectiveness of the rotor? IE: not enough density to maintain proper rotor rpm to stay airborne? Other than biophysical symptoms, what should a pilot be aware of when getting to high and how will I know I'm in a danger zone for the aircraft?

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Brian, the rotors turn at higher RPM the higher you fly. Piston engines without turbo or superchargers lose about 3% of their horsepower every 1,000 feet. So eventually, the machine just can't go any higher.

The biggest problem with flying at those altitudes is that we don't have a practical way to practice for the effects. The onset of hypoxia brings a euphoric feeling, and you lose the ability to notice how much ability you've lost, if you follow me. A very easy thing to do under mild hypoxia is lean the engine too much, and damage it. Your ability to deal with additional workload is also compromised.

The requirement to spend no more than 30 minutes above 12,500' without going on supplemental oxygen is one of those regs that qualifies as a very loose fence. It's a worst-case they can bust you for, not a recommended procedure.

Vance said:

I had not identified the practical ceiling for the Predator with the IO-320B1A and my three blade 68inch 47” pitch Catto propeller...

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Vance, while you were up there, did you think to note the altitude at which your climb rate dropped below 100 FPM? That would be your service ceiling, although the technical definition requires being at max gross weight.*

* I've always wondered how any aircraft which took off at max gross could get thousands of feet in the air and still be at max gross. Mid-air refueling?

Wow 3%/1k? That's pretty significant! I thought that maybe the air would be so thin that the rotors would eventually not have anymore to work with. I am needing to study more on density and altitude conditions. I suppose maybe at 20 or 30k the rotors would be spinning near a max recommended rate since you say they increase in RPM as it goes higher. Makes sense. But the faster they go, dyssimetry of lift decreases and chance of retreating blad stall is more a risk? Trying to FLex my knowledge that I have learned. Am I headed in the right direction?

Vance,

I think you have inspired us all! Great job and sounds like an awesome adventure!

Keep safe,

Mike

Vance...

Vance...

I gotta ask, just what the heck were you wearing?
by my meager calculations it had to be somewhere around 0 to minus 5 degrees at altitude...do you have heat coming up through a vent?
I flew my single place up to 5280 once and tried to take a picture and well you can just see how cold it was.....
hats off to you, I couldn't take the cold.
Ben S

Vance- Nice adventure. Do you think ATC was timing you since they knew you didn't have oxygen? Something tells me someone punched a timer when you hit 12500 feet. Stan

I found it exhilarating and edifying.

I found it exhilarating and edifying.

I found it very exciting Gabor, beyond my expectations. Part of the thrill may have been exceeding my expectations. I thought she would be all done around 10,000 feet MSL. I was still climbing at 400 feet per minute at 10,000. It was hard to get a good reading on the climb as I circled around. A small reduction in airspeed would make her step up and dropping the nose a little would make her step down.


I don’t have a good answer for you Brian.

The rotor typically spins around 330 RPM and it got up to almost 370 rpm. It changes the whole feel of the aircraft.

Because of the height above the earth it is easy to misjudge distances so I watched my GPS, my indicated airspeed and my vertical speed indicator to stay on track.

I was climbing between 40kts and 55kts. The Predator feels a little vague on the stick at 40kts at any altitude. The winds were around 15kts to 18kts and I was flying a sort of circular course. Because I didn’t have my typical ground reference the aircraft felt a little spooky. It all went away when I pointed her toward SMX.

The stick actually felt smoother to me at the higher altitude.

Perhaps one of the more technically astute can answer your questions more completely.

According to my calculations at 2,350 RPM at 12,500 feet MSL the engine was making around 80 horsepower.

The consumption would suggest that it was a little less.

It would be easy to be off on the fuel quantity to throw the numbers off.

I feel at sea level the engine should be making around 140 horsepower at 2,400 rpm and burning a little less than 11 gallons per hour.

I could have picked up the rpm by increasing the speed but I think that would have been counterproductive. The propeller is over pitched because the first one was under pitched. We are hoping it will be about right for Mariah Gale with her calculated 30% less body drag.

In my opinion Brian more rotor rpm makes for less dissymmetry of lift rather than more. It is about the speed differential between advancing and retreating and with more RPM there is less difference as a percentage of the tip speed.


Hello Paul,

I was actually trying to do just that. I was circling in a 15kt to 18kt wind and even at the end a little pull back on airspeed would get her to 200 feet per minute climb.

She seemed to climb at around 400 feet per minute until almost 10,000 MSL.

I was not at maximum gross weight because Ed was at work.


Hello Ben,

I was wearing my flight suit a sweat shirt and gloves. The Predators windshield protects me pretty well. It was cold but not unbearable. I would say it was not much below freezing. It was a little hard to take pictures with my numb hands. As I got higher I didn’t want to look down or get my finger in the wind so most of the pictures were inside.

The Predator did well, Thank you Mark Givan.

Thank you, Vance

It was an exelent adventure

It was an exelent adventure

Thank you Stan, I found it invigorating.

In my opinion ATC is not enforcement and they were just being helpful.

It happened to be one of the approach controllers at SBA that I work well with

I was above 12,500 feet for about five minutes.

I know enough about hypoxia to feel that for an older out of shape fellow like me oxygen should probably be used around 8,000 feet MSL.

Thank you, Vance

willisbr said:

...But the faster they go, dyssimetry of lift decreases and chance of retreating blad stall is more a risk? Trying to FLex my knowledge that I have learned. Am I headed in the right direction?

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Yes and no. First part is correct - more rotor RPM means less dissymetry, as Vance notes. An increase in blade tip speed (as RPM climbs) or a decrease in aircraft forward speed both decrease the dissymetry, so less teetering is required. Two-per-rev shake will pretty much disappear in a zero-airspeed vertical descent.

Second part - wrong. Flap compensates for dissymetry, so when high RPM creates less dissymetry, it requires less flap, not more.

The risk in overspeeding the blades is not flap, but exceeding the structural ability of the blades to handle the centrifugal force. 370 RRPM is moving right along for a 30' rotor, but probably not a concern.

Thanks Paul and Vance.

That was very informative Paul.
Vance all I can say is I don't have a clue how you put your jeans on over those boulders. That was some fine picture you took.

Hi Vance, it's good to see you being interested in finding out the limits of the Predator's comfort zone. It helps you stay inside that zone with confidence. That's the spirit of flight testing.

The reference altitude for such flights is, of course, density altitude. When I plug in these numbers (you can find a density altitude calculator here):

Altitude on altimeter: 12,500 ft
Altimeter setting: 30.9 in Hg
OAT: -2 °C ("not much below freezing")
Dew point: -20 °C (doesn't have a huge influence)

I get a density altitude of 12,300 feet. That's very close to what you saw on the altimeter.

As mentioned previously, you'd have to be at MTOM to make it a real measurement of the service ceiling. In practice you would do a first rough determination (just as you did). From that you get a good hold on how long it takes you to get to altitude so that you can caluclate the fuel burn. Then you tank that amount over gross prior to taking off for the second (more accurate) test flight. Don't forget to take OAT data during your flights so that you can find the actual density altitude that you reached.

Also, you'd have to know Vy before doing this flight because procedures prescribe a continuous climb at max continuous power at Vy up to the point where the vertical speed has dropped to 100 fpm.

During the ascent you'd best fly a racetrack pattern over ground with long straight legs and shallow turns at each end. Your climb speed will drop when making a turn.

Best of luck and greetings, -- Chris.

Someone ought to ask Dr. Bill Clem about gyro flying at high altitudes, since he holds the record. Perhaps he has already written about it somewhere in this forum.

Dave

Hi Vance, I did that once, in my Bensen.
I didn't have an alt., But I guessed I was about 8k. I was cold.
The lack of reference made it very uncomfortable. I felt as if I was just hanging there.
No sensation of speed at all. I'll stay on the deck.

Vance- In your first picture...the horizon is clearly defined by water....and you can definately see the curvature of the earth.


Stan

Low fear threshold.

Low fear threshold.

Hello Mark,

I have a natural fear of anything I am unfamiliar with and a low fear threshold.

The feel of the Predator at those altitudes and the look of things were very unfamiliar.

I worked to mitigate my trepidation by climbing over an airport and having Santa Barbara Approach watch out for traffic.

I know that altitude is my friend. I reinforced that by coasting all the way to SMX once I was finished. I told the SMX tower what I was doing so he wouldn’t worry about my extra altitude or more rapid rate of descent.

For me it is more intimidating to be directly over something that is at sea level rather than flying high over high ground.

The last time when I did this with the O-290 and the Prince Propeller I thought about how long I would have to think about the impact if my rotor system failed at 8,800 feet and what I would do if we caught fire. I did not have those thoughts this time.

I checked that the temperatures and pressures were in the green often and monitored myself and my speech for signs of hypoxia and hyperthermia. Santa Barbara approach talked to me often and I suspect it was to hear my response to monitor my condition.

I watched my airspeed in relation to the ground speed and used my GPS to stay out of the nearby low altitude federal airway. I used my chart to reinforce this.

I found my trepidation manageable.


Thank you Chris,

I have been meaning to do this but the conditions are usually not as good. I had to fly a fairly small pattern to stay out of the federal airway.

I have been trying to imagine Mariah Gale’s performance based on the Predator and this was a place that was not filled in. I checked my numbers last night and I had Mariah Gale’s practical ceiling at 12,000 feet two up. I feel like having a 12,000 foot ceiling gives us more options on our wanderings across the country. This escapade helped my better quantify the propeller and engine performance at altitude. I had been thinking about an engine driven supercharger to manage altitude. It is now on the back burner.

I look forward to your involvement in Mariah Gale’s test program. I understand testing but I am unfamiliar with the procedures for flight testing a gyroplane. I would like my numbers to have meaning.


I am with you Dave; I would love to read of Dr. Clem’s experiences.


Hello Lee,

I prefer low and slow. When we are flying around the country some altitude capability will expand our options. It seems to me that there is not much altitude required in Florida.


Hello Stan,

I had to hold a straight edge up to the screen to find out that as usual you are correct. That picture was taken at around 9,870 feet MSL. As my fingers became numb I took less time with the pictures and had more trouble pushing part way down to focus.

I have some wonderful pictures in my head. Altitude was more fun than I expected. My horizons expanded in a very exciting way. I felt like I had laid claim to a bigger picture.

Thank you, Vance