R22 Performance problem/quiz
 

Looking through my old FAA FI notes, I cam accross this problem which I used to give students to get them to understand various things and get their head in the POH. It may not be 100% accurate but I though i'd post it here and see what answers people come up with. Enjoy.


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R22 Performance Problem


You have to fly from airport A to airport B (a straight line distance of 60 nm), collect some gold bars, and return to airport A.

Airport A


Elevation: 500 feet MSL

Temperature: 21 degrees C
AWOS altimeter setting: 29.52 inches

Airport B


No fuel is available here
Elevation: 7,600 feet MSL
No AWOS

Aircraft


R22 Beta
Cruise speed: 70 kts
Fuel burn: 9 gallons per hour
Basic empty weight: 890 lbs
Pilot weight: 130 lbs

(Assume nil wind)

Each gold bar weighs 11 lbs.

You need to be able to sustain an in ground effect hover at both airports.

How many gold bars can you carry back to airport A, and still remain legal and within all performance limits for the aircraft?

This is an absolutely brilliant question.

With the hindsight of vast experience of those who cheat or couldn't give a flying f*** in a thunderstorm about their A/C performance limitations or hours recorded, will immediately expose themselves with the wrong answer.

there are two ways to conduct the test;

1) via the written medium as you suggest, - they fail.

2) send them out to do it as a practical, - they don't return with the gold bars, the insurance company pay for the lost gold and helicopter and the good ol' taxpayers pay for the police to track it all down.

in both events we are rid of a blight on our industry. Excellent result all round:ok::ok:

Good question. Just to add realism, can you give the info for airfield C? That's where the pilot will actually fly with the gold, never to be seen again;)

So I say the limit is how many you can stuff under the seats.

120 lbs

Wasn´t the limit under the seats 60 lbs each!?

But what about the gold you can strap to your body or place in a holdall on the passenger seat?

Cheers

Whirls

120 lbs?

Any more answers?

How many gold bars?

And where do you put them?

Don't forget you have to remain legal under the POH and under the FARs

I came up with 14 bars!!!!!

Not the answer I got. But I may be wrong!

Don't forget the R22 has a seat weight limit and you need to be able to hover OGE at both airports.

Hang on is it an IGE or OGE hover ?

as if you're not confused already!
 

My mistake, its - IGE!

I guess it's airwork and that you have an Ops Manual which might say something about fuel reserves?? as they do over here. no tempo or Inter?

8, with 4 under each seat (4 x 11 = 44 lbs), to keep you under the cargo limit of 50 lbs/seat.

I didn't find an issue with the HIGE/HOGE for the temps and altitudes given, but the fuel load would be right at it's limit for a Beta w/o the aux tank (with the aux tank you'd load as much as you could w/o going out of CG on the outbound portion of the flight).

Change the question to "Should you take an R22 Beta with no aux tank to pick up a bunch of gold bars at ~8000 PA..." If you didn't have the aux tank, you'd be cutting very close to the required 20 minute reserve.

No aux tank:
depart with full fuel (19.2 gal, 1136 lbs), arrive with 11 gals fuel (1088 lbs), add 88 lbs (1175 lbs), return with 3 gal fuel (~20 mins).

Well, here is what I called the 'solution'. Not sure it's right. But it proved a useful tool to give to (CPL) students. It wasn't the answer that was important, it was the things they thought about on the way.

Feel free to borrow/edit/pass off as your own.

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Solution

Standard lapse rate is 2 degrees c per 1000 ft.
Hence temperature at B is 21 – (2 x 8) = 5 degrees C

Pressure altitude at B is (29.92 – 29.52) x 1000 = 400 ft.

7600 ft + 400 ft = 8,000 ft

Total distance to fly is 120 nm.
This would take 1.7 hours at 70 kts. 1.7 x 9 gallons per hour = 15.3 gallons.

20 minutes fuel is required by law (see FAR 91.151). This is 3 gallons. Add 2 gallons for startup/shutdown.

Total fuel required is 20.3 gallons. Fuel weighs 6 lbs per gallon.

Hence Total fuel weight is 20.3 x 6 = 121.8 lb

See In ground effect chart (POH page 5-5):
Max gross weight at B is 1300 lbs. (8000 feet pressure alt and 5 degrees c)

1300 - 890 - 130 *- 121.8 = 158.2 lbs of gold can be carried back to B

158.2 / 11 = 14 gold bars

BUT…. Max allowable under each seat is 50lbs.

So you can only carry… 100/11 = 8 gold bars. (4 under each seat)

….unless you put more gold on the left seat – but is this legal??

ISTM that you should be calculating your fuel for departure from Point B and subsequent payload: not from Point A.

Of which you will have burnt off 7.7 gallons flying to Point B, plus 1 gallon of the startup/shutdown allowance. Further, you will use the second 1 gallon allowance prior to take off from Point B, so your fuel on takeoff from Point B should be 20.3 - 7.7 - 2 = 10.6 gallons.

Minimum fuel for the return leg is 10.7 gallons, so you need 20.4 on departure from point A. Pt B departure fuel of 10.7 gallons would be 64.2lbs.

The payload available will then be 215.8lb, or 19.62 bars.

If the R22B has an aux fuel tank, minimum pilot weight is 135lb, so an extra 5lbs ballast would have to be carried on both legs, reducing the payload accordingly unless the outbound ballast is discarded and replaced with bullion for the return leg :cool:

I'll just get as many gold bars as I could and land crash! :} :}

Manfromuncle

Is it legal in the US (or UK) to carry a secured load in an unoccupied seat?

Load her up and bounce her down the runway like the kiwis do! Have you ever seen ''The Robinson R22'' dvd that was made in NZ and OZ? :=

John Eacott, you're probably right, it was a long time ago!

There you go ... strap the bullion to your calves with gaffer tape. :}

Cheers

Whirls