Twin Squirril Power loss Question?

[Vfrpilotpb]

Good afternoon Ppruner's,
I wonder if any of you would be kind enough to help me with this question!

If a twin Squirril had a problem, or power loss from one engine, or transfer clutch/shaft, whilst in the hover, would it lose any height, or would the fact that higher power is needed in the hover, cancel out any height loss, from the loss of either engine?
Many regards
Peter B.

[ 07 January 2002: Message edited by: Vfrpilotpb ]</p>

[widgeon]

Might need some other parameters , is it F1 F2 or N , at what gross weight and OAT ?.


<a href="http://www.eurocopter.com" target="_blank">www.eurocopter.com</a> look under civil range ( cant get direct link to work )

Has the OEI charts for N model ,

[ 04 January 2002: Message edited by: widgeon ]</p>

[ShyTorque]

Not sure if I've got the full gist of your question, PB but I'll give it a go. (I note from your profile that you don't appear to have any twin time, so I'll try to pitch the answer as such).

It does depend on WAT and the mark of a/c but generally twin squirrels don't have single engine hover other than at low AUM. In that event the pilot merely cushions to a touchdown from IGE, just like in a single but with less drama.

If IGE there is an avoid curve but it isn't nearly as restrictive as the ones you will be used to. From an IGE hover, in the event of a single engine failure, the pilot needs to merely lower the nose to about 15 degrees and obtain single engine flying speed, about 30 kts IAS on most type of helicopters. Depending on relative wind this may result in a hardly perceptible descent or a bit of a "swoop". From here the pilot can accelerate further to fly away / climb or land straight ahead as he sees fit.

It is therefore possible to operate a twin at low altitude quite safely provided that the avoid curve is respected.

[Droopy]

My experience is that all the variants will involve a certain amount of height loss from a high level hover; at max.aum [2400kgF1; 2540F2 and 2600N] this will be around 100ft, 150ft and 100ft respectively with average pilot reaction times on an ISA still air day [the F2 is the worst case because it has the same engines as the F1 but higher AUM]. The horizontal distance needed to commence the climb following the height loss is around 100-150m.

PB, why don't you speak to the very friendly chaps at your own police ASU?

[Devil 49]

If you had a sudden, total power loss, you'd likely lose altitude as the NR sagged.

At any reasonably likely mission weight, a Twinstar hovering will pull at least 60 (More likely 70 or better) per cent torque times 2 engines equals 120 per cent of the nominal single engine torque. On a good day, you might not overtorque/overtemp your good engine as you landed, if you were low and had good place to set it down.

I have hoovered at total 100 per cent, but the bird was light as possible. NO PAX, no extra fuel, no serious thinking and not much heavy breathing. Flip side-In an F-1, if you're cruising and not very high, she'll usually continue the trip to your choice of landing places. The extra gross in an F2 could be a problem OEI.

[widgeon]

What are the Cat A requirements then ?.

[Droopy]

Not quite sure about what you're after widgeon, but if you mean a vertical takeoff with guaranteed damage-free reject before decision point and flyaway thereafter, both the F1 and F2 are limited to 2200kg at ISA with the N at 2500 ISA. The "clear area" profile for which you need around 220m allows for the higher weights, but depending on national interpretations of "Cat A" you may have to operate below those to allow obstacle clearance.

[Weight and Balance]

When I last worked on 355s, there was no Cat A approved, or performance data published. Has this changed?

In about 1996, Widgeon and I were involved in a brief test program to produce un-official data for a Canadian operator who intended to use a 355F2 to land crews on power towers. We came up with a WAT chart that would show you what weight would permit a transition to forward flight without altitiude loss, after one engine failure. We took advantage of the transient engine and transmission limits. I don't remember the numbers, but it was quite a bit below full gross, even at Canadian temperatures.

[widgeon]

Yes W and B the N model according to the blurb is Cat A ops approved . You may be seeing an EC155 tootling around the skys near you soon . E mail me and I'll give you the details not sure if I have your current one.

[Vfrpilotpb]

Shytorque,
You are right I have only once been in a Twin, and that was a private Squirril.

Droopy, Thank you , I had not thought of the local ASU, at Warton I will try to contact them,

To all thank you for your answers, very interesting.

Many Regards

Peter B