couldnt figuere these questions out, could you please help?

Q1. Your flight planned track is 090 degrees M. The present heading and ADF reading respectively are 085 degrees M and 175 degrees R.

Your present bearing from the station is - ?


Q2. AIRCRAFT DATA AND COMPANY POLICY.

NORMAL TAS.......................190 kt
ASYMMETRIC TAS...................110 kt
NORMAL FUEL FLOW.................120 lt/hr
ASYMMETRIC FUEL FLOW.............85 lt/hr
FUEL TANK CAPACITY...............680 lt
FIXED RESERVE 45 min CALCULATED AT CRUISE RATE.
VARIABLE RESERVE OF 15 percent OF THE FLIGHT FUEL.
START UP AND TAXI ALLOWANCE......15 lt

Ignore climb and descent.

Assume a 20 kt head wind at all levels and a charter flight.

If departure is with full tanks, the maximum distance the aircraft, whose data is given above, can plan to fly is closest to - ?


Q3. Your heading is 335 degrees M and your ADF reads 350 degrees R.

The OBS setting you should select to give command indications to fly to a VOR at the same aerodrome as the NDB is - ?

Question No 1
If you read up my Nav book from page 5.11 to page 5.18 you will get a detailed explanation of this type of question.
Heading +or- ADF = Track. so 085 -5from = 080 from. The track is 080°M from the station.
In this question, the flight planned track is irrelevant, the question is asking only for your present bearing from the station. i.e. the magnetic track direct from the station to you.

Question No 2
Find the flight fuel available. [Total fuel - taxi - fixed reserve] ÷ 1.15
[680 - 15 - 90] ÷ 1.15
= 500 litres
@ 120 lph = 250 minutes.
Ground Speed = 190 - 20 = 170 kt.
Distance possible = 250 min @ 170 kt = 708 nm.

Question No 3
Same method as Question No 1 above.
Heading +or- /ADF = track. 355 -10to = 345°M to the station.
The VOR setting is always the same as the track you intend to fly.
So set the OBS to 345 and the flag will say "To".

Hi Ned and BOb. I believe the answer to question 3 should be setting the CDI on course of 325degrees magnetic. 335 + 350 - 360 = 325. that is the correct answer

Hi Bob,

Thanks for that answer, I am still struggling with Question 7 on Nav Progress Test 4 (issue 3) on page 4.49. See if you can see anything the matter with my logic. It could be my understanding of the concept of FLIGHT FUEL.

The Question is based on (ignoring the Asymmetric fuel flows since we are told to ignore climb and descent, and I'm guessing those rates dont apply to climb out anyway as it would be higher, only perhaps descent? (side issue)

Normal TAS of 190 kt
Headwind of 20kt (so Ground Speed of 190 - 20 = 170 kt)
Total Tank Capacity of 680 Litres
Normal Fuel Flow of 120 Litres per hour
Fixed reserve of 45 minutes
Variable reserve of 15% of FLIGHT FUEL
Startup and Taxi Allowance

What I am trying to find is the maximum distance the aircraft can fly based on the above.

So I start with two main factors:

Ground Speed 170 kt
Total Tank Capacity is 680L

680L -

90L (45 mins reserve - 120 lph x 0.75 = 90 Litres)
15L (Start up and taxi allowance which I assume is not part of flight fuel)


So that now leaves us with our FLIGHT FUEL which should be 575L.

We need to subtract a further 15% of 575 L which is our Variable reserve (575 / 100 x 15 = 86.25 L) (same as if we had gone 575L x 1.15)

When we subtract 86.25 from 575 which leaves us with:

488.75 Litres of fuel remaining

If we then divide 488.75L by the fuel flow (consumption) rate of 120 Litres per hour we come up with 4.07 hrs.

If we times 4.07 by the groundspeed of 170 kts we get 691.9 nm range.

The answers presented are as follows:

a) 690nm (this is what I selected but got wrong)
b) 710nm (this was apparently the answer but I still dont know how you arrived at this figure)
c) 720nm (N/A)
d) 680nm (N/A)

Any thoughts on why I got 690 instead of 710?

Brook

Guys, my two cents if I may,

When INBOUND to a VOR station, the radial you are tracking, or 'on', goes to the bottom of the OBS.

Using the HAT trick:

Heading: 335
+
ADF: 350 = (685 - 360) = 325..
=
Track: 325 TO the NDB. (Simply intercept the 325 inbound to NDB)

BUT..

Wouldn't the correct setting on the OBS be the reciprocal of 325 as we're INBOUND to the VOR? The actual RADIAL we're on is 325 - 180 = 145.

I would have thought, then, 145 to be the answer..

Hi Ellzy,

You are indeed on the 145 radial but you are heading 325 to the station. Remember the radials originate and are numbered according to the direction out of the station. If you set the OBS to 145, the VOR needle will centre but with a FROM indication. You are on a bearing of 145 from the station.

However we we want to fly 325 TO the station. With a heading of 325 and an OBS setting of 145, the two are 180 degrees off. The VOR will not behave as a command instrument i.e. it won't give command indications. The VOR only gives command indications when the heading and the OBS setting are in agreement.

So, we set 325 on the OBS and the VOR gives you indications on how to fly TO the station INBOUND on the 145 radial.

Cheers,

Rich

Silly, I've just completely contradicted myself in one post haha.. I said the radial you're on, for an inbound track, should be on the bottom of the OBS.. Correct.. so that would mean 325 would be on the top! My bad!

To be set in the command sense track and heading must be in the same 'hemisphere' as each other and if I could just clarify something, the only time it's 'acceptable' to not be in command sense is when making the turn from an outbound to an inbound track?

Cheers!

Hi Brook,

The problem is the way you removed the variable reserve.

575L is (Flight Fuel + 15% of the FLIGHT FUEL). In other words, 575L is 115% of the flight fuel. The way you worked it was essentially saying flight fuel is 85% of the total (after removing fixed reserve and allowances). This is not correct.

Let FF be the flight fuel:

115% of FF = 575L or, expressed differently, 1.15 x FF = 575 L
Switching the formula around a bit, FF = 575 / 1.15 or 500L

If you continue your calculations using 500L instead of 488.75 you will get the right answer.

Remember:

To apply 15% variable reserve to flight fuel: FLIGHT FUEL x 1.15
To remove 15% variable reserve from some amount: FUEL / 1.15

Check out the answer on page 6.6 to see the working.

Cheers,

Rich

Thanks for this Richard,

This is indeed valuable information. It turned out I was looking to SUBTRACT 15% off something, when in actual fact the 15% was INCLUDED IN the flight fuel figure of 575 L, so the secret trick would seem to be:

When you have your fuel ie:

Tank Capacity - fixed reserve (eg 45 mins) - startup / taxi fuel, TAKE THIS REMAINING FIGURE AND DIVIDE BY 1.15 to get your figure to use for flight calculations.

So in that case, the result was 500 L, which means the ACTUAL 15% variable reserve was only 75 Litres, not the 86.25 I had mistakenly calculated by SUBTRACTING 15% from the total, rather than INCLUDING IT in the total and dividing it by 1.15.

So correct me if I am wrong, I can categorically say that in this case, the FLIGHT fuel was in fact 575 L, but this INCLUDES the Variable Reserve (which is expressed as a % of the fuel), but NOT the FIXED reserve (which is expressed as a number of minutes of fuel burn or normal cruise), which is removed prior to calculation.

So rather that accept my flawed logic that I need to subtract 15%, I accept that the figure is included in the flight fuel and divide it by 1.15.

Sound right to you?

Thanks

Brook

Hi Brook,

No, Flight Fuel is the fuel you will burn on the flight. If you flight plan a trip that will have you in the air for 70 minutes then your flight fuel is the fuel you expect to burn in 70 minutes. THAT is flight fuel. "Flight Fuel" does not, by definition, include the variable reserve. It does however include the fuel you would need to fly to a planned alternate.

On top of flight fuel you add variable reserve, fixed reserve and taxi/holding allowances.

So, 575L is actually FlightFuel plus Variable Reserve and not just Flight Fuel. Perhaps that is why you were having problems removing the 15% variable reserve.

TOTAL FUEL = FLIGHT FUEL + VARIABLE RESERVE + FIXED RESERVE + ALLOWANCES + MARGIN

See Bob's diagrams of the Fuel Cake on page 1.26 in the Nav textbook and in the Perf textbook as well if you have it.