Required performance increase with added weight, AS350B3

[airdoggy]

In reference to performance planning in an AS350 B3; Let's say you arrive over your LZ and it is a "Hover Hole" in and out. You conduct a HOGE power check 500 feet above the LZ and determine you have enough power, at your current weight, to conduct the operation. This, however, is not taking into account how much of a load you are going to pick up(let's say 200 lbs). My question is, how do you account for the increase in power that will be required and by how much? For example, how much more %Ng and %Torque will be required for HOGE with the addition of 200 pounds. I've heard some use the formula that 1% Ng is equal to 200 lbs and 1%Torque is 70 lbs. So in the case presented, it would require 1% additional NG and almost 3% additional torque.

Yes, I know that is what charts are for and I know the B3 has a VEMD screen that lets you performance plan, but I'm curious for impromptu planning, etc. Such as, I'm just out of the yellow on the gauges during the HOGE power check, but how much further will I be into the yellow on take off with the additional weight?

So, I would like to hear your experiences and how you determine the needed power increase. If you can back it up mathmatically, even better. Thanks

[RVDT]

Flight manual?

The numbers on the power instrumentation are NOT linear.

As these are anonymous forums the origins of the contributions may be opposite to what may be apparent.

[Matthew Parsons]

Check the charts in the flight manual.

If you can't, then try the following:
- Note the power required to hover out of ground effect.
- Before you land, note the power to hover in ground effect.
- When you take off with 200# extra, note the increase. -
Apply the increase to the power required to hover out of ground effect (and a little bit extra).

Not scientific, but if for some reason you can't check the charts, then this could help. With a guess method like this, I would want to ensure a good power margin.

[sycamore]

A-D,it would take a few hours in the classroom to show how the power figures are derived and put into the Performance graphs,but perhaps Shawn and Matthew could elaborate at some point on new test methods.Several decades ago I flew Whirlwinds(turbine S-55) and our
only `power` indication was fuel-flow,Ng,and PTIT,before a suitable Tqmtr was developed.The FFmtr also had a `correction scale`,for both altitude and ISA deviation.We would do a power check in level ,stabilised flight at 50 kts(min. power speed/just below best ROC speed) and note FF,then pull max `power` to determine the limit,either FF,Ng,or PTIT.Depending on the amount available,would determine the type of landing one could do,ie OGE,IGE,wheels touching,or run-on,using a `formula`;it could also give one (using another `formula`/rule-of thumb) how much one could lift out in terms of running T/O,cushion creep,200ft/min ROC ,etc. Hwever, it should be remembered that the fuel-flow in-hand (or Tq,or Coll.pitch )at min pwr,is not the same as Tq/ff/cp. in the hover. It also gave a measure of `power` of the particular airframe,in terms of a good ,or crap set of blades,or worn compressor,in this case in tropical conditions.
So,if you can get time etc you can make up your own `formulae`,by preferably in a ballasted a/c,do some hovers at various hover heights,noting `power`,and then at min power speed/best ROC/power available.
Obviously,in certification there is a lot more work/time spent to derive the graphs,to which one should always use !!,however,reality is always different,and manufacturers (and their lawyers) don`t offer the `quick` ways..Hope that helps, but if you want any further info,send a PM...
So,you can do your own set of `formulae`

[Shawn Coyle]

The real problem is that the civilian performance charts don't tell you the information you need to know.
In this case, you need to know two things - power required to hover, and power available. VEMD and the power check chart in the FM can give you power available, but the 'hover capability' chart doesn't tell you the power required to hover. (I gather there may be one or two helicopters that do, but the majority do not have a power required to hover chart).
So unless you know a good rule of thumb for how much more power will be required for the additional weight, you're into the land of guessing.
If you know how much additional power is required to hover OGE vs. IGE then you can do a pretty good estimate once you load the additional weight and hover IGE in the hole.

[airdoggy]

All good answers, thank you. I was just curious, as I've found myself in the green on Torque and Ng when doing HOGE checks prior to landing in some of these hover holes to pick up patients. Then on take off, I've found myself to be mid to high range yellow on the Ng depending on how much of a load I've taken on.

I always do a perfomance check on one of the VEMD screens which takes into account Temp, weight, alt, etc. and it gives you a theoretical weight you can be at to have HOGE and HIGE. I've found it to be pretty accurate, but was curious as to other "rule of thumbs" and if there was some sort of formula. For example, the VEMD is giving a theoretical weight to have HOGE based upon temperature, weight, and altitude, but I was wondering if there is a way to determine how much more Ng and Tq will be required on take off(with additional weight) vs what was displayed when doing the HOGE check prior to landing

Anyways, I was just more curious than anything and found it to be good food for thought. Thanks.

[Shawn Coyle]

It also depends on how the performance charts were made. I know of one helicopter where the HOGE performance charts were made by 'flying in' to the HOGE height. But if you try to climb to it from ground level, you need much more power (even climbing very slowly).
The chart meets the strict requirement of the regulations, but doesn't address reality.

[airdoggy]

It also depends on how the performance charts were made. I know of one helicopter where the HOGE performance charts were made by 'flying in' to the HOGE height. But if you try to climb to it from ground level, you need much more power (even climbing very slowly).
The chart meets the strict requirement of the regulations, but doesn't address reality.

Wow, that's interesting! So in essence, they were able to establish a higher HOGE and then say their "brand X" helicopter has better performance than "brand Y" helicopter due to superior design, etc, etc. That is some good insight and certainly a thought provoker. Thanks.

[sycamore]

Don`t forget,even from an OGE hover,you need an extra thrust margin to climb out of it,unless you are going to sacrifice the height to get fwd. speed..