Collective pitch changes hovering over different surfaces

[StanFoster]

When I was making my landing gear fairings....I had to come up with a way to know how many degrees of collective pitch I was applying so that I could repeatedly fly at that same pitch on my data collecing runs. Recording the speed was a given with my GPS averaging groundspeed into and with the wind. I came up with putting a laser pointer on my collective and making a linear degree marking along my door channel.

The first two pictures show 10 and 13 degrees respectively. My linear layout goes from 7 degrees to 17 degrees.

This served its purpose well...but I soon realized how valuable having this information is. On hot humid days...full fuel...and can easily check my performance by hovering in ground effect and noting how many degrees of collective is required.

Just today I decided to do some data on how many degrees of collective it takes to hover over different surfaces. I find this very interesting to prove by actual demonstrations to myself, stuff I read about. Here is the data for HIGE and HOGE for todays already 92 degree high humidity temps.

HIGE asphalt surface 10.50 degrees

HIGE short grass 10.75 degrees

HIGE tall grass 11.0 degrees

HIGE soybeans medium height 11.25 degrees

HIGE tall corn 12.0 degrees

Hovering out of ground effect............12.25 degrees


Now...when those soybeans above reach full height..I expect them to be the biggest power suckers of all. The hovering over tall corn isnt really the same as I am already 10 feet in the air anyway.

But I never will forget during my R22 solo time....I landed down on my mowed lot and had a tall soybean field next to it. I did not have anything but manifolt pressure to watch, so I noted that while I hovered over the short grass.....then drifted over the tall beans without changing altitude. Talk about power sucking vegatation! I expected a necessary increase in collective to maintain my hover height as I went over the beans. The manifold pressure went up of course....but I had no direct pitch reading of my rotorblades like I do in my Helicycle.

I find this information very useful and every liftoff I fire the laser pointer and can instantly tell how much performance I have.

I also recorded my collective pitch setting while transitioning through translational lift which I will post in a thread of its own.

This stuff NEVER gets boring to me! Though I probably bore some with my obsessiveness to experience stuff I read.

The last picture shows some elevated but still very ok temps right after all my hovering tests.

Stan

 

[Jon]

Good information. I too had the same experience with my helicopter while hovering over 2' grass or 2" grass. I takes me about 2" more of manifold pressure to hover over the tall grass than the short. When I start my takeoff run over the tall grass and get over the section that is cut short I get a big boost in lift almost like translational lift twice and the helicopter will immediately climb. One more cool thing to learn and love about our helicopters. Thanks.

 

[rightstick]

Just out of curiosity I did a search for a digital angle gauge that could be mounted on the collective (maybe) and found this one.
http://www.sella.co.nz/general/building-renovation/tools/hand-tools/levelling/bzp83d/
It may be too large to be usable, or too expensive to be reasonable, but an interesting thought none the less.
Scott

 

[StanFoster]

Scott- That wont work correctly showing just the angle of the collective. The Helicycles collective has variable geometry. The degree change to the rotorblades change at different rates as the collective goes from full down to full up. I put an Angle Cube on the rotorblade itself. I cut a mounting jig with the top of it parallel to the chordline of the airfoil. Then I moved the collective and calibrated my degree marks accordingly. I even made sure i was approaching each degree from a descending pitch so as to eliminate any backlash error. I then triple checked each degree marking until I was satisfied I had it right. I have placed my Angle Cube back on the rotorblades just to verify all is still exact, and there has been no change. When my laser pointer is at 11 degrees, I KNOW the chordline of the rotorblade is at 11 degrees. Makes for very accurate data collecting imo. Stan

 

[pallen_001]

Stan,
Very interesting!!! When you get all your data on different surfaces to hover over, please post it. I could definitely use it as a training aid, and aside from that, it's just interesting to see.

Incidentally, the old french helicopters, and a lot of the more modern Russian helicopters use collective position just like you are doing instead of a torque gauge. There is a gauge that directly measures collective position and reads out in either degrees of collective pitch or percent of collective pitch (0=full down, 100=full up). Then there is a chart on the panel. You match Tempurature with altitude and it gives you max collective angle for those conditions. The engineer's tell me it's more accurate than a torque gauge. The MD-902 I'm currently flying has a display on the IIDS that will read out collective position in percent if you select it. Over the next week or two I will record collective positions under various conditions and we will see how they compare to yours. Right now unfortunately, my temps will be much higher than yours (115 - 120 F) and there are no crops in this country to hover over, but I can find grass to hover over every now and then. It should still be interesting to compare. Peter

 

[StanFoster]

Pallen- I did post my results over different surfaces in post #1. Interesting on the Russian copters using collective pitch instead of torqu meters. It sure makes sense to me!

 

[pallen_001]

Stan,
Sorry, I guess I'm getting old, don't know how I missed that. I'll post MD902 info soon.

Here is a picture of an Allouette 3 panel. The bottom right gauge is the collective pitch gauge. Around the outside of the gauge is an E6-B style rotary dial that is used to determine max collective pitch for the conditions. This was used on the SA-315 Lama and the SA-316 Allouette series.

 

[StanFoster]

Pallen- Thanks for posting that panel. Glad you find this interesting as I do. Having hard numbers backing up what we read about makes it more interesting. Stan

 

[anthom]

Nostalgia

Nostalgia

Stan,
Sorry, I guess I'm getting old, don't know how I missed that. I'll post MD902 info soon.

Here is a picture of an Allouette 3 panel. The bottom right gauge is the collective pitch gauge. Around the outside of the gauge is an E6-B style rotary dial that is used to determine max collective pitch for the conditions. This was used on the SA-315 Lama and the SA-316 Allouette series.

Thanks for posting the panel. Very nostalgic picture for me. Both are fantastic machines.

 

[All_In]

Oh I see said the blind man.

Hi Buddy never having flown helicopters your data points really gave me an incite I never had before... most excellent.

Thank you