MTOW calculation

[frank marriott]

Remember it is a 'STRICT LIABILITY' offence.

 

Exceed the weight - commit the offence - very hard to defend.

 

 

[motzartmerv]

Andy, those maths would work if an hour was 100 minutes and fuel weighed 1 kilo/ litre. Hehe..

 

 

[Guest davidh10]

for those discussing the "does it include taxi fuel or not"...Im thinking a degree of desperation must be approaching. Last time I checked at an RAA friendly airport the type of aircraft we have would really strecth a 10 minute taxi, which at an OMG burn rate of 10L/hr (Yep that'll test your brakes!!) means you might actualy get to 1kg of fuel use..... Have a pee before you leave, equally effective.Andy

I agree. As I use flight planning software that wants to know taxi fuel allowance and cruise consumption, and won't accept "0" as the taxi fuel usage, I have to opt for 1l or 10min. I opt for 1l, as 10 min at 12l/hr (my cruise usage plus a safety margin) is 2.4l. Reality is, I cannot measure the taxi fuel consumption, as it is so small, so that just adds to my real reserves. The fuel usage rate metering does not even register at the power levels used for taxi.

...and yes, brakes just hold at cruise power on the ground. At full power, I need a chock under a wheel.

 

 

[Guest Andys@coffs]

Andy, those maths would work if an hour was 100 minutes and fuel weighed 1 kilo/ litre. Hehe..

10L hour with fuel being around 0.7kg /litre = 7kg/hr. 10 mins is 1/6th of an hour which is pretty close to 1kg. I accept that my math here is approximate times approximate but the point is in our aircraft its almost inconsequential as we are not taxing at Mascot!!:big_grin:

 

Andy

 

P.S and thats the difference between us and teh mob over at the shriveled plum....who want to argue that its not 0.72 its 0.71 no, no its 0.695 kgs per litre...... to me, given teh 100's of grams involved rough as guts, erring towards underweight is good enough http://www.pprune.org/dg-p-general-aviation-questions/332015-avgas-specific-gravity.html for those in need of a pedant chuckle

 

 

[facthunter]

It's not the amount, just the principle of it. Some engines take a lot of time to reach operating temps in winter. My Citabria was on the ground for 15 minutes at least at Corryong before I would do a mag check and depart over tiger country, in winter. That fuel use shows up nowhere. unless shown as taxi fuel. (A term and concept used in aviation everywhere.) If I loaded extra fuel to allow for the extended taxi ( which IS legitimate, and was ramp checked I could be proscecuted under the current rules even though I would be legally OK as the weight at roll for take-off is all that matters for performance and structural limits. Nev

 

 

[Old Koreelah]

From the new 95.55:For the purposes of sub-subparagraph 1.2 (f) (iv), the minimum useful load for an aeroplane is:

 

(a) if the aeroplane’s engine power is rated in kilowatts — the amount in kilograms worked out in accordance with the formula:

 

(80 x S) + 0.3P; or

 

(b) if the aeroplane’s engine power is rated in brake horse power — the amount in pounds worked out in accordance with the formula:

 

(175 x S) + 0.5P

 

where:

 

S is the number of seats in the aeroplane; and

 

P is the aeroplane’s rated engine power.

 

Could someone please explain what is meant by "minimum useful load".

 

 

[facthunter]

I think it is only used there as an element/concept of a formula. This probably implies a minimum performance capability or requirement. Nev

 

 

[Old Koreelah]

I think it is only used there as an element/concept of a formula. This probably implies a minimum performance capability or requirement. Nev

Thanks, Nev. I was looking for resources to calculate the MTOW of my modified home built.

 

 

[facthunter]

I can only suggest Bill Whitneys Notes. You essentially break the plane into sections, (for calculating) and determine the weight and CofG of each and add the moments. Is that the sort of thing you are after? nev

 

 

[Yenn]

Bit simplified Facthunter, but we should all know how to work out the C of G for take off and landing and any configuration of passenger, fuel and luggage.

 

 

[Old Koreelah]

I can only suggest Bill Whitneys Notes. You essentially break the plane into sections, (for calculating) and determine the weight and CofG of each and add the moments. Is that the sort of thing you are after? nev

Not really, Nev. I have a pretty good handle on CoG. It's the MTOW I'm trying to work out.

 

 

[jetjr]

The numbers for a large jabiru, are 700 kg under VH and 600 under RAA are correct

 

Pretty simple, if you and the aircraft weigh more then appropriate limit your flying illegally

 

You can argue the aircraft will perform ok up to 700 kg and it will, but not whilst being under RAA restrictions of maximum 45 kts stall and therefore you arent qualified to fly it

 

 

[facthunter]

it's just basic weight +fuel carried + occupants + anything else added above basic weight (Baggage etc). UNLESS there is a take-off length limit. or climb weight limit. (density altitude factor).

 

Cof G must use weight and moment. ( distance from datum point) x weight. This can be done graphically and there should be something in the POH. The CofG should remain in the range allowed from total fuel loaded till empty tanks. ( You can't rely on fuel to bring you into balance). Nev

 

 

[Old Koreelah]

it's just basic weight +fuel carried + occupants + anything else added above basic weight (Baggage etc). UNLESS there is a take-off length limit. or climb weight limit. (density altitude factor)... Nev

This could be interpreted as 'set the MTOW to the maximum you want to carry.'

 

If I have ample TO power the resulting number could be humongous.

 

 

[Guest nunans]

This could be interpreted as 'set the MTOW to the maximum you want to carry.'If I have ample TO power the resulting number could be humongous.

The MTOW of an own design, would come as the result of structural testing. I imagine if building from a kit then the kit manufacturer would supply figures from the structural testing they done and the kit builder would use the figures provided.

ALOT of RA aircraft manufacuturers have in the past and currently just done structural testing sufficient to satisfy the RAA rego weight limits of the time as there's no point testing beyond what the legeslation allows right? Then RAA gets approval for a MTOW increase in the legeslation ie 544 to 600 for example and then you have all these aircraft which "just coincidently" ended up being structurally sound for 544.0Kg on the dot and then need to be re-tested and recertified for the new legeslation increase.

 

It would be great if the manufacturer would quote the real max figure and then just let it be limited by the RA exemption.

 

As for the Carbontax BEAST Cub, If cubcrafters can get the paperwork done to allow it RA rego (ie. certify the MTOW under 600kg, allowing for the usable fuel requirement and the min pilot & pax weight which i believe they have,) then anybody can buy one and get it RA registered.

 

If that person happens to weigh 160kegs then it's up to them to work out how they can fly it staying under the MTOW and C of G within limits ie cut back on fuel and pax weight.

 

I've done a W&B for the standard sport cub and it turns out the legal usable weight is fairly slim and hence we never put much fuel in it.

 

However even at MTOW I can assure you it gets off the ground short and has plenty of wing, as i've said before if you stick some floats on the bottom of it, all of a sudden the same wing is certified to fly at 650kg so take from that what you like but legally that's no help at all.