Fuel Economy (what affects it)

[harry200sx]

so i had 6 litres of highly flammable liquid in a sealed plastic container, this, according to the manufacturers specs should have gave me between 1.45 and 2 hours of flight. The plug being a lovely coffee colour shows the motor is running as it should.

 

So im happy to take of with my 6 litres knowing that i am safe for 1.45, i fly, i do my thing, i return, I overshoot my landing and roll on the throttle, to a splutter bang pop, (and thats just my arsehole). It turns out that i had consumed 5.75 litres of fuel in what turn out to be 50 minutes, i manage to nurse it to a safe controlled landing, smiling at the amazing flight i had just had. however on the way home i started pondering. 

A. how efficient is my motor

B.how efficient if the wing

and 3 lol. how inefficient does the wind make us all 

 

so now lets go into a little more detail of the three options 

A I fly a vittorazi fly evo 100cc if creates 56kg of thrust and its enough for me at 75kg. the spec states that it uses 3.-3.5 ltr per hour at around level flight (30kg thrust), so the motor i have if pretty much perfect for my weight, so either

Do the specs lie ( are vittorazi actually in partnership with those sneaky german car  manufacturers that manage to trick the world to believe there engine is more efficient). 

Am i using to much throttle, and by this i mean am i being inefficient in my throttle usage? (maybe climbing at full chat and then going to tick over) kind of like the way  the way our mums would drive causing everyone in the car to suffer small scale whiplash ?

Is my motor not really tuned? I have tuned the motor to where i believe it should be, the plug is a nice coffee colour with a very slight oil build up on the base just near the electrode, showing my oil mix and air to fuel mix is correct. (i also have an in flight tuning mod to the carb, which i have not used since i got the motor running smooth) 

 

B. I fly a 29 synth ( i know the thing is a boat, and last time i saw fabric that size  i decided to leave the canadian girlfriend and head back to england) however i am in the correct weight range of the wing when taking into account the motor fuel reserve etc. 

would flying a smaller wing increase my fuel consumption as i will be flying faster ? 

or will it decrease as the newer wing would be more efficient (even though it would fly faster) 

Or is the fact that i shit myself on every launch the problem? does the shit hit my prob and disturb the airflow causing less thrust and making me use more throttle to fly

 

and 3. going into wind. ok i understand this would slow me down, but it would also create more lift, therefore i would not need as much throttle to maintain a steady flight.

going with the wind would give me more speed but i would need more throttle to maintain height and this is where litres per (distance) would come into play

 

so i will post my flight details below and look forward to hearing some answers back, (i don't mind having a laugh and reading some hilarious answers but some sensible ones would be great to please 

 

Flight location oh fuck .... here we go.... (sorry guys) Parafest.........(i know, i know, but in my defence i wasn't made aware of the summer fly in rsvp so i missed out) 

wind speed 2kph On ground around 12-15 kph in air 

air temp 12 but i was freezing my tits off up there

distance traveled 36 km 

fuel used 5.5 - 5.75 litres

max engine temp 120 - 125

max height 2028 feet

 

so whats the conclusion here.

am i just a fat fucker, 

is my motor letting me down 

or do i need a new wing 

 

look forward to the opinions of others 

and and Paul ....... no talk about your bailey please Lol 

[Hann__]

Picking up on a few points that stood out;

Yep, 6.9L/hr for that motor is far too much.

Do makes lie? Maybe not lie but their figures are probably on a test bed not during actual flying, not that it should make that much difference because a PPG motor putting out 30kg on the ground will be very similar to it doing it in the air (as long as you keep a constant speed and not constantly climbing/losing altitude)

How are you doing your plug chops?

To get an accurate indication you`ll have to run the motor at cruising speeds for a while, then kill the engine and glide down so that the plug shows the actual running conditions during cruising speeds not just the last 2 minutes when you were at idle/low speeds lining up for a landing.

Is it a Synthesis LT (original Synth)? They were renowned for being a bit of a lardy ol` bus with similar efficiency..

Once your feet leave the ground there is no `wind` - you are simply flying in a moving air mass - flying into or with the wind only affects your ground speed, your air speed on a PPG is always the same (for any given trim setting).

Have you got a tacho fitted?

Knowing where you are in the engine power/speed range might help.

 

I suspect that your motor is not as well tuned as you think - an engine temp of 120-125 is very low and is an indication of a very rich mixture.....

[harry200sx]

9 minutes ago, Hann__ said:

Picking up on a few points that stood out;

Yep, 6.9L/hr for that motor is far too much.

Do makes lie? Maybe not lie but their figures are probably on a test bed not during actual flying, not that it should make that much difference because a PPG motor putting out 30kg on the ground will be very similar to it doing it in the air (as long as you keep a constant speed and not constantly climbing/losing altitude)

How are you doing your plug chops?

To get an accurate indication you`ll have to run the motor at cruising speeds for a while, then kill the engine and glide down so that the plug shows the actual running conditions during cruising speeds not just the last 2 minutes when you were at idle/low speeds lining up for a landing.

Is it a Synthesis LT (original Synth)? They were renowned for being a bit of a lardy ol` bus with similar efficiency..

Once your feet leave the ground there is no `wind` - you are simply flying in a moving air mass - flying into or with the wind only affects your ground speed, your air speed on a PPG is always the same (for any given trim setting).

Have you got a tacho fitted?

Knowing where you are in the engine power/speed range might help.

 

I suspect that your motor is not as well tuned as you think - an engine temp of 120-125 is very low and is an indication of a very rich mixture.....

hi yes the engine was running rather cold however it was very cold up there that day, but looking back on previous flights it does look like im using around 6 litres an hour, 

i mean if this is normal then i will accept it and just take more fuel with me but it does seem a little much for a 100cc engine to use 

i have not plug chopped yet but i do check the plug rather often to make sure colour is not greying or white, and i normally run high rpm then stall the engine and check that but what your saying to check at mid throttle makes more sense so although i'm running "right " top end i may be rich in my mid throttle, i will check this one out on the next flight. 

thanks Harry 

[Blackburn Mark]

I did a quick calc the other night... in still air, I am getting between 40 and 50 mils per gallon which tickled me
somewhere between 2 and 3 liters per hour (best calc has me at 2.2lph if I fly like my granny)
23m wing and an old Bailey V2... weighs 45kg with reserve and fuel so its not all smiles  
Because of the "air speed / ground speed" anomaly, its not useful to measure efficiency in distance traveled.

Also, you climb rate will be the same "down wind" and "upwind"... it seems you have hung onto the optical illusion created by the differing ground speed at low level EG: the "climb angle" is steeper into wind and more shallow "down wind" but the rate of climb will be equal given the same rpm etc.

[harry200sx]

55 minutes ago, Blackburn Mark said:

I did a quick calc the other night... in still air, I am getting between 40 and 50 mils per gallon which tickled me
somewhere between 2 and 3 liters per hour (best calc has me at 2.2lph if I fly like my granny)
23m wing and an old Bailey V2... weighs 45kg with reserve and fuel so its not all smiles  
Because of the "air speed / ground speed" anomaly, its not useful to measure efficiency in distance traveled.

Also, you climb rate will be the same "down wind" and "upwind"... it seems you have hung onto the optical illusion created by the differing ground speed at low level EG: the "climb angle" is steeper into wind and more shallow "down wind" but the rate of climb will be equal given the same rpm etc.

oh really ? i wasn't aware that upwind or downwind would be the same climb rate at the same throttle position, thinking about it, it makes sense, as the wing will always travel at a given speed as hann mentions above.

so what your saying is a need a bailey lol 

Im glad i asked the questions now as im learning alot more thanks guys 

[Blackburn Mark]

1 minute ago, harry200sx said:

so what your saying is a need a bailey lol

Not unless you like long xc flights... the weight is a bit of a bitch!
 

[AndyB]

Big wings like mine (28 m) create more drag and hence use more fuel. Likewise, big people require more fuel.

[harry200sx]

21 hours ago, Blackburn Mark said:

Not unless you like long xc flights... the weight is a bit of a bitch!
 

this is the problem i want to do xc and fly low and fast, i guess you cant have your cake and eat it 

 

[harry200sx]

20 hours ago, AndyB said:

Big wings like mine (28 m) create more drag and hence use more fuel. Likewise, big people require more fuel.

so is there a wing that is

easy to launch 

stable in the air (hand off flight) 

fast in the air 

agile when you want it to be 

slow takeoff and slow flare 

i guess if such a wing existed there would be no need for any other wing on the market 

[Blackburn Mark]

11 minutes ago, harry200sx said:

this is the problem i want to do xc and fly low and fast, i guess you cant have your cake and eat it 

 

Bailey's... reliable and economical (both at the top of my list)
"Low and fast" would be more to do with your wing and smooooth air unless you are talking about having more power to climb yourself out of an error...?

I personally become attached to whatever I am flying... hate changing wings.
I am assuming any modern intermediate ought to be enough wing to cruse at 25mph ish and have enough energy retention to pull out of any minor errors while skimming