Strange r22 issues at higher altitude

[r44]

Hello Everyone,

 

I am new here so take it easy. I was recently in a r22 beta II and landed at 7000 DA. (2 people, one 180 and the other 140, 10 gallons of fuel). Before we landed, we checked performance OGE at about 500 feet higher and we were able to hold it just fine. We started the approach and clearly we had IGE before we lost ETL.

 

Here is where it gets interesting, while in a hover 4 feet agl, and starting to land, we experienced a cross wind (mild) and inputed left pedal. We immediately had low rotor RPM and set the ship down. We shut the ship down, and chilled for about 30 minutes, got back in and got ready to take off. We had all of the performance in the world, took off no problem.

 

A few weeks later we landed at 7500 DA, check OGE performance, everything good. We landed at 7500DA. About 30 minutes later we started up to a hover and got lower RPM again and set back down. This time we only had 6 gallongs of fuel. The performance charts show we are good and both times winds were mild.

 

Getting to my point, I am concerned that there is a performance issue with the engine making enough consistant power. I know there was compression issues on one cylinder but it was supposed to be fixed. Anyway, I would like to hear thoughts regarding what might be going on here.

 

Thanks in advance.

[Goldy]

Hello Everyone,

I am new here so take it easy.

 

A quartering wind or crosswind can swing that tail around and require a lot of pedal to overcome...7500 DA is pretty damn high for an R22, even if it is a BetaII.

 

Check the mags, check the compression. Pretty sure you would really know it if you had a stuck valve (which Lycoming is famous for).

 

One other tip- don't eat a big meal before you take off.

 

Goldy

[r44]

when robinson put together the performance charts, did they consider having to use left pedal? If so how much, the cross wind was very marginal. Maybe 3-4 knots

[JDHelicopterPilot]

By having even a slight cross wind or a change in wind direction that requires more use of the left pedal will cause more demand from the engine. This will mean less power to keep main rotor RPM where it should be. At that altitude you are operating close to the performance limits.

 

The situation you were setting yourself up for was LTE in addition to Low RPM. By getting that cross wind and putting in left pedal and getting low RPM can then lead to LTE as well.

 

What were the conditions of your landing zone? What type of LZ would provide the best benifit for ground effect? Airport, off airport or a confined area? Now, what kind of conditions do the performance chart represent? Was your Carb. Heat on at anytime when this happened?

 

There are different techniques for flying and landing in a High DA area. Each situation and LZ will be different. For me, I perfer to lose ETL very early and make a very slow approach with a low Rate of desent(200'/min or less). I do this before I get below the highest obstruction around my LZ. This way should I have misjudged my performance, or I am not getting what I thought I have the altitude left to go around. Always have a way out of any approach you are looking to make.

 

Your engine could very well be with in limits, but not performing as well as a new one. When you are operating so high you are really looking for every little bit of power you can find. Power can be found by reducing weight, landing at a lower altitude, change of LZ surface or a different approach(running landing).

 

When that close to the performance edge it's hard to answer you question of a possible mechanical issue. Since you say there was a problem with the compression of one of the cylinders it certinly lends a little more towards a mechanical issue.

 

Be careful up there in the High DA. Things happen a whole lot faster.

 

JD

[lelebebbel]

Don't land a R22 at 7,500'DA - you are asking for trouble..

 

My experience is that the performance charts are generally too optimistic. Maybe they work for factory new machines with smooth, clean blades, perfect engine, clean air filter and plugs... but they certainly don't work for most real world R22s out there.

 

Also, keep in mind that the charts are based on 0% humidity! (I stand to be corrected on this one, but that's what I was told)

 

Real-World Humidity increases the DA, so you would have been even closer to the edge. Any further "imperfection" such as a tiny bit to much left pedal, crosswind, collective, or a situation where the ground effect is not as good as in the chart ("calm wind, 2ft skid height" I think it is?) and you'll bleed off revs.

As soon as you start losing only a few RPM, things immediately go downhill, as your performance and TR thrust is now worse than it was at 104%.

 

Plenty of Robinsons have been destroyed by trying to operate them too close to the limit. You need to add a bigger margin to the performance charts to be safe.

Edited March 21, 2010 by lelebebbel

[lelebebbel]

one more thing: keep an eye on your manifold pressure while doing your OGE hover check. Know how much you can pull before the revs come off, and you'll be able to tell how close you really are to the limit before it happens.

 

(Typically this is outside air pressure minus 1.5"-2". Refer to the full throttle line on the MAP limitations chart, or try it at a safe height before landing.)

 

If there is less than an inch to spare, a bit of left pedal can easily take you over that limit.

[mechanic]

The DA thing is a major concern. RHC puts limits on ferry fights to the East during certain times of the year for R22's leaving the factory to fly over the mountain range. I was thinking it is listed on their website. There have been a few crashes in the mountains with the R22's.

[RkyMtnHI]

Good stuff here, i was going to put something about the humidity.. (but lelebebbel beat me to it) people tend to overlook that and it can catch you off-guard.. i know a pilot with over 5000 hours that forgot to consider the humidity at around 7000' and ended up planting an R44 on a golf course green!! This would be a great subject for Chris and others to put some numbers to.. after the R44 did $30k worth of damage to the green we spent some time trying to figuring out what had happened (of course it couldn't have been pilot error) .. using the Schweitzer POH we came up with some rough figures that indicated the humidity was similar to adding 75lbs of weight to the helo... woops!!

 

also, you have to know where that wind is at all times, even in an r44.. if it's gusting or changing direction, at that altitude, you are throwing the dice..

 

dp

[JDHelicopterPilot]

Some great points! I should have brought up the humidity factor. As another poster said, don't land up that high. Robinsons are not high altitude aircraft.

[Rick McWilliams]

I did a flight in Susie's R22 to look at the snow on Topa Topa. It was very easy to climb to that altitude on the windward side of the steep mountain. It was cold, about -7C. I cruised around at 8000 ft MSL at about 12 to 14 inches manifold pressure. The controls seemed considerably less sensitive. I did not even consider approaching the ridge from the lee side.

[coptermedic]

A practice I put into play and teach my students is to build in a 1000' "FUG FACTOR", when looking at your IGE and OGE charts to help compensate for the humitity that the charts do not take in to account. So if the chart says you can hover a 5000' only go to 4000'. PLAY IT SAFE...

[deerock]

great idea Coptermedic. I'll run with that idea too, thanks

[FauxZ]

One more thing to add, the throttle is less responsive at high altitudes. The correlator is set for sea level performance. At higher altitudes the governor can have a hard time keeping up. I've done IFR flights at 7000 in the AZ summer and any movement of the collective beyond small, smooth movements, would cause the RPM to wander. If you're making large collective movements like you would for landing etc, you could run into issues.

[StanFoster]

I just received my helicopter rating in an R22 last October. I find these threads very informative. Even though I am in the flatlands of Illinois at around 750 ft. and never plan on flying in the mountains...this is good stuff and very much appreciated. Someone is always throwing a gold nugget of a topic in here.

 

 

Stan

Helicycle almost finished.

Edited March 22, 2010 by StanFoster

[r44]

Thanks guys for all the information.

 

The IGE chart for the conditions was 9,500 and the OGE was 8,000. The first landing at 7,000 was almost like an airport in terms of approach... Hard pack snow on the ground. HAD IGE before we lost ETL by a wide margin.

 

To be honest, I am not really sure how to determine the humidity conditions, it was a cold clear day with hard pack snow on the ground. Any help or suggestions on determining humidity and then connecting with performance?

 

I agree the low rpm is super bad, hence the reason I am trying to understand the performance issues...

[JDHelicopterPilot]

Hard packed snow will not give you the same ground effect as smooth blacktop does at an airport.

 

There is a lot more to mountain flying and High DA landings. I will try to find you some information and pass it along to you.

 

JD