An Accelerometer on The Predator.

[Vance]

Based on a post by Paul Plack I checked Ed’s phone and it had a free G meter.

I borrowed Ed’s phone today and did some maneuvering.

I don’t know how accurate the accelerometer on her phone is although it agrees roughly with the aviation accelerometer I borrowed from John Ready.

It certainly was consistent.

The first picture is steep turns and the maximum was just under two Gs.

The second picture after a reset was a pull up from a dive and again it was just under two Gs.

The third picture was all kinds of maneuvering in the pattern and two landings and again it was just under two Gs.

Before someone asks; yes I did reset the min and max before each flight in the run-up area.

I didn’t know it was that consistent till I looked at the pictures when I got home.

More interesting to me was that I was not able to get below .75Gs even with the 12kt gust spread and leveling off from a zoom climb.

The highest rotor rpm I saw was a little over 430 and the lowest was just under 270 rotor rpm.

I will try again when it is less windy, I am more comfortable maneuvering and cloud conditions are better.

I used Velcro to mount the phone at the front of my little glove box thing and I could watch it while maneuvering.

Thank you, Vance

 

[PW_Plack]

There's a seismometer app for the iPhone which continuously records Gs in three axes for display or export to a spreadsheet. I hope to be able to take one flying at some point, and see what it spits out.

 

[ckurz7000]

Hi Vance, your observations are consistent with my own experience. The highest G I was able to pull was coming out of a descent up to 170 km/h followed by an aggressive pullup. I got up to 2.4 G for 2 seconds. In normal turns I didn't get as high.

Looking forward to seeing you at Bensen Days, -- Chris.

 

[Jazzenjohn]

What sort of G loads did you see under normal fun flying? Was your tests for g loading beyond the typical "yank and banking" people would normally do?

 

[Vance]

That sounds like fun Paul.


I didn’t know what to expect Chris and I was not set up to record times, only the minimums and maximums.

I was surprised I didn’t see less than .75 Gs.

It was not a good environment for testing.

It is hard to get Ed’s phone away from her and I don’t maneuver aggressively with a passenger so it will be awhile before I have another go at it.

I look forward to spending some time with you at Bensen Days. I always learn so much.


I just wanted to see how it would work John. It was not a proper test.

It was difficult to do normal flying because of the wind and gust spread.

The tight turns were done at wide open throttle, 60kts indicated air speed and pulling back till The Predator began to lose altitude. I don’t know how normal that is. It is not unusual for me.

The descent with a pull up was at a little over 120kts and that is when I saw the most rotor rpm. It appeared that I was descending at more than 2,200 feet per minute when I began the pull up. This is where I saw over 430 rotor rpm.

The pattern work was limited by what I am permitted to do in the pattern. I feel the just under two Gs was during the round out and flair. We encountered a strong wind shear, descended rapidly and I arrested the descent aggressively.

Most of the “normal” flying appeared to be less than one and a half Gs.

There are lots of things I would have liked to try but it was over my gust spread limit and I felt distracted by the G meter so I made the decision to end the test.

If I can get Ed’s phone away from her again I will post about it.

My fantasy is to get Garmin’s new video camera that will record Gs along with the video.

I just tried Ed’s camera because it was free and easy.

I have long been puzzled by stories of negative Gs in gyroplanes. I doubt if I could achieve negative Gs in The Predator.

I am also puzzled by the angle of bank it appears we can achieve with less than two Gs. The pilot books say that should be good for sixty degrees and I suspect I am seeing more. The video camera will help me understand and quantify that.

Thank you, Vance

 

[brett s]

I am also puzzled by the angle of bank it appears we can achieve with less than two Gs.

60 degrees angle of bank = 2 g's is also assuming you're maintaining a constant speed & altitude. If either of those is changing so is the g load.

 

[StanFoster]

Also to add to what Brett said.....you may have a bank angle of 60 degrees even more, but if you are falling through and not following the true path a 60 degree cone has...you will be flying a larger radius and will have to have less than 2 g's. No other option.

Stan

 

[ckurz7000]

Also to add to what Brett said.....you may have a bank angle of 60 degrees even more, but if you are falling through and not following the true path a 60 degree cone has...you will be flying a larger radius and will have to have less than 2 g's. No other option.

Stan

Stan, any circle you fly at a 60° bank while maintaining altitude willl give you 2g, no matter what speed you fly it at. If you "fall through" your track in the sky will not be a circle but an outward spiral. So the radius doesn't matter. Its being a circle does, though.

Sorry to nitpick but I had nothing more substantial to add...

-- Chris.

P.S.: It would be great to finally shake hands with you during Bensen Days. You coming?

 

[StanFoster]

Chris- Just trying to learn something here by asking this.....If you are maintaining altitude with a 60 degree bank, but are falling through, are you not then flying a larger radius? .....which would lower your G load?

 

[Vance]

60 degrees angle of bank = 2 g's is also assuming you're maintaining a constant speed & altitude. If either of those is changing so is the g load.

That is my understanding too Brett.

Typically I steepen the bank at wide open throttle until I stop climbing at whatever indicated air speed I pick.

I feel it is untidy to gain or lose altitude or indicated air speed in a turn.

Part of why I want the new Garmin Video Camera with the capability to display the Gs and the altitude along the side of the screen is so I can get a better feel for such things.

I feel it will also help me to manage my energy better during airshow routines.

Thank you, Vance

 

[Vance]

Which came first?

Which came first?

I feel it is the old which came first; the G load or the bank Stan?

I feel that a specific bank requires a specific G loading and the rest is just how I got there.

Thank you for jumping in Chris.

I find this all very confusing.

I suspect you and Stan are confused on a higher level than I am.

Maybe we can all three discuss this at Bensen Days.

The thing that actually surprised me the most about this simple test was how little load decreased at the top of a zoom climb.

I have read for many years about negative Gs in gyroplanes and yet the best I could do acting badly was .75Gs. I felt light in the seat and the cyclic felt vague. The rotor speed dropped from around 315 rotor rpm to less than 270 rotor rpm quickly. I suspect my low fear threshold will prevent me from exploring this reduced G experience much further.

I ran into some 15 kt plus wind shear and still couldn’t move the needle below .75. It felt like the bottom had dropped out and I had to aggressively arrest the descent.

We had a 12 kts gust spread most of the day at SMX and two PIREPS of severe turbulence on descent into SBP.

Airmet Tango included warnings of 25kts wind shears below 3,000 feet so I didn’t fly and I gave The Predator her biannual bath. I try to wash her twice a year whether she needs it or not.

I talked to an airline transport pilot this morning who encountered a 40kt wind shear at 2,000 feet on approach to runway three zero.

I just checked the winds at SMX and they are 360 degrees at 19kts gusting to 26kts. Runway two is in use and that means a crosswind component of 8kts gusting to 11kts on the 75 foot wind runway.

The 150 foot wide runway three zero would have a cross wind component of 16kts gusting to 21kts.

I think I will go do a maintenance flight to blow the water out of the predator.



Thank you, Vance

 

[raghu]

60 degrees angle of bank = 2 g's is also assuming you're maintaining a constant speed & altitude. If either of those is changing so is the g load.

Altitude does not matter, after all gliders pull 2 g in 60 degree turns too. As long as you maintain coordinated flight (no slips and skids) and constant airspeed (the actual speed does not matter), the bank angle is related to g force.

 

[ckurz7000]

Chris- Just trying to learn something here by asking this.....If you are maintaining altitude with a 60 degree bank, but are falling through, are you not then flying a larger radius? .....which would lower your G load?

If you are "falling through" your flight path will be an outwardly extending spiral and not a circle. So, yes, your g load will be less, even though you are maintaining 60° bank. What doesn't matter is the radius of your turn or the speed at which you're flying. Just get your bank up to 60°, fly coordinated and don't "fall through", and you will experience 2g.

The "falling through" part, although I experienced it myself many times, can only have to do with the rotor not having reached its equilibrium rpm for the load it is being asked to lift. Because once it has reached the required rpm, it will carry the 2g around the circle no problem. And there will be no falling through then.

-- Chris.

 

[WaspAir]

Altitude does not matter, after all gliders pull 2 g in 60 degree turns too. As long as you maintain coordinated flight (no slips and skids) and constant airspeed (the actual speed does not matter), the bank angle is related to g force.

The g-load is the secant of the bank angle under those conditions (if your calculator doesn't have a secant function, take the reciprocal of the cosine). Your speed will determine the radius. In an SR-71, that could be the whole state of Indiana.