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High Altitude landings
#1
I have been thinking about how you can tell the power available to commit to a high altitude landing if there is not a MP gauge available in the XE? I am just about solo in the R22 and it has made me consider the performance of various helicopers. I have looked at several postings and the general concensus is that there is "heaps" of power available, but does anyone check at high altitude prior to landing? If so, how do you do it? Do you have to fly at the same height as the spot to land on at the minimum power speed (35??) and note the position of the collective, then estimate the amount of travel left.
I live close to 6000+ft mountains and live at 200m so around home the performance will be fine, but as I will be heading into the scrub and scree slopes at times I thought I would put it out there for comment.
Cheers
Peter
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#2
I'm also interested in the answers from the experienced Mosquito pilots...here in Asheville NC USA we have 6 & 7000 ft mountains....the R22 was scary to fly around the peaks, any advice for playing in the valleys? Downdrafts, etc?....will the Mosquito have enough power?
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#3
Yes I'll join the questioning on this matter.
I actually installed a MP gauge in my Mossie, but have not yet gotten around to connecting it up. Too many other items to attend to first.
And I have been told that it can not work with 2 stroke engines, because the "blow as well as suck". And we know that that is true. But I still want to try it. Surely if one arranged a system of damping chambers, orifice restrictors, etc, it would be possible to damp out that huffing and puffing? I understand that Dwight tried to do this but was unsuccessful.
Rob1
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#4
As you know, the Mosquito, just like the Mini-500 I flew for 100 hrs, has NO WAY of measuring power being applied to the rotor.
As I gained experience flying the Mini-500, I realized that I needed to have SOME WAY of accomplishing this task, which usually
involves a manifold pressure gauge, a torque meter, or a turbine outlet temp gauge. If you don't have a clue how much power
you need to do the maneuvers you intend to do on a particular day and in a particular location, YOU RUN THE RISK OF BUSTING
YOUR ARSE!

I needed a way to do this SIMPLY on the Mini-500. I didn't want to engineer and add complex instruments or devices. What I did
was simple and It worked! I started subjectively rating the little helicopter's performance, EVERY TIME I FLEW IT, on my scale from 1 to 10.
1 as "no fly because not enough power to hover or take off "
10 as "as much power as I need and no drooping RPM no matter what I did, even on max performance takeoffs, etc."

I recorded these values in the log book every flight. In parenthesis beside the number, I'd write the Density Altitude that the flight was
conducted in. After 20 or 30 flights, over a period of several months, there was enough data to make a simple PERFORMANCE TABLE
that showed what RANGE DENSITY ALTITUDE resulted in what PERFORMANCE NUMBER (from 1-10).

This would work for high altitude flights since getting the Density Altitude at such flights is pretty straight forward.
I.E. Say your usual lowland flying on very hot days and at Density Altitudes between 4,000 and 5,000, has given you subjective PERFORMANCE NUMBERS of "3" (Barely Hovers in ground effect and into wind)
Then if you plan to go up in the mountains where it's 45 degrees outside but density altitude is 6,000, YOU WILL NOT HAVE ENOUGH POWER TO HOVER and barely enough to do run-on landings and takeoffs.

I know this is "HOKEY" but I can tell you from experience, it became a pretty good way to do Performance Planning and It kept me from BUSTING MY ARSE more than once.
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#5
Peter,

You'll probably find that there is another issue that will be the limiting factor.

I fly my Mosquito mainly around Auckland, seldom more than 1000ft asl. Even then I need to change jets between summer to winter. Before taking off at one density altitude and flying to a very different density altitude you will need to look at your choice of jets very carefully.

Oskar
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#6
Bryan, are you saying that you are basing your performance chart on impending rotor droop? That sounds like a good system - for a Mossie.
Anything else has TOT/MP/TQ limitations, but the Mossie has none of those considerations. (Not as far as we know at the moment)
Rob 1
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#7
Thanks to everyone for adding to this discussion - I have read elsewhere on the forums, quite a lot of discussion on the jets, so they are a very important thing to keep in mind. How hard are they to change and how do you get hold of spare or various jets?
I like the idea of rating various flights and building up a background to what is possible and what isn't going to work at various density altitudes. I guess at the end of this I will have to keep an eye on the EGT and develop my own scale of a, go, - possibly go, - yea, it may work, - getting dodgy, - no go, range of DA's. Its something I hadn't considered, but I think it is an extremely good idea and able to be developed on the trot. By hovering OGE beside a peak and noting the pressure, temperature and wind speed, it would be able to be calculated once back down at home.
I enjoy reading everyones thoughts and ideas, they are quite inspirational.
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#8
Rob,

About rotor DROOP, I didn't get REAL scientific in developing my very subjective 1 to 10 scale. All I was saying is...
FOR me to record a 10 Performance Number in the logbook from a particular flight when I came back, I would have had to been able to wind the throttle full wide open and pull the collective up in my armpit to the up-stop, WITH NO DROP IN ROTOR RPM.

Smile
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#9
arrow123 - 6/2/2012 6:39 AM

...How hard are they to change and how do you get hold of spare or various jets?...

GENERAL COMMENT: I know ZERO about the MZ engines. I am very knowledgeable about the use of Bing-54 carburetors on a 2-cylinder 2-stroke engine, in a constant RPM helicopter. When I have discussed changing jets on this forum before, I was quickly informed that folks are sick of hearing about my Mini-500 experience because it doesn't transfer to the Mosquito.

First I'll simply answer arrow123's question. The two jets in each carburetor which were intended by the carb designers to be changed very quickly, on-the-fly, at the airport, (MAIN JET & NEEDLE JET **not the jet needle**) are very easy to change. CPS makes a knurled aluminum "thumb tool" that fits both of these jets by flipping the tool over. It takes a couple of minutes to change all four.

The first picture is the MAIN JET. The second picture is the NEEDLE JET.



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#10
The NEEDLE JET lives above the tall, threaded thingy standing in the top left of the tool picture. This thing is called the mixing tube. The NEEDLE JET does NOT screw in, it just rattles around. To remove it, just unscrew the mixing tube and it falls out.

The MAIN JET screws into the bottom end of the mixing tube.

The knurled tool will unscrew the MAIN JET using one side, and unscrew the mixing tube with the other side.

All these threaded parts are soft brass and do not have to be very tight. If you tighten the mixing tube slightly tighter than the MAIN JET, then you can easily change the MAIN JETS without the mixing tube coming loose. The MAIN JET threads are much smaller than the mixing tube threads so making the big one tighter than the little one is DESIGNED-IN.
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