DrZoos Posted September 30, 2015 Share Posted September 30, 2015 So i know the big guys have magic formulas where they can calculate for example that to load 1000kg of extra fuel will burn say 300kg just to carry it over a trip of X hours... In our aircraft we dont have the historical data and I dont have accurate enough fuel records to knwo for each weight my fuel burn, as my flight routes vary too much. Does anyone here know how to calculate with our smaller aircraft when its feasible to leave home on a massively full tank rather than a half full tank and fill up at the other end... ie in a slippery little ultralight at say 100 knots 560kg MTOW and traveling say 2 hours but having to climb to say 6500ft at 80 knots first at 500ft pm is it more feasible to just take say 3 hours of fuel and fill up before returning or 5 hours and make it home... clearly its always going to burn less fuel with less weight, but often at the other end fuel is dearer, harder to get, or may involve a call out fee. I want to do a few long trips soon, maybe to the Cape, Darwin etc so i want to work out when its cheaper to fill her up and fly max v more regular callout fees and dramas with availability.. my gut feeling says every time you can get fuel just fill her up to MTOW... but by doing so it means carrying a lot less luggage. So after all that the actual question i want answered is using the weights and numbers above is anyone able to give me a pretty good guide, formula or benchmark for the cost of say carrying 70L v 90L v 112L in an aircraft that's say at MTOW 560kg with 112L on board.. Or is this just a stupid question due to the ridiculous variations in flight levels, headwinds etc on such a trip. Im interested to know your thoughts. Especially from those with lots of this type of experience in smaller aircraft on long trips. Link to comment Share on other sites More sharing options...
Head in the clouds Posted September 30, 2015 Share Posted September 30, 2015 As part of my work I have flown many dozens of long trips across the country and to the far north and I can tell you for certain that you don't need any specific weight vs fuel burn formula because it's quite simple ... If you're going inland significantly (the great ol' outback) or to the mid or far north then it's always far cheaper and way less hassle if you carry as much fuel as possible. Forget about lots of baggage, just take the minimum you really need and max fuel and enough survival water and first aid/satphone. As you go further into the bush and further north or remote then fuel becomes exponentially more expensive and so do callout fees and availability becomes less reliable, sometimes fuel quality deteriorates etc. Getting to and from airstrips gets harder too, although sometimes there are strips close to highway bowsers and at some places you can land next to the road but that usually requires local knowledge. There are two slightly different cases where different kinds of folks are concerned - If you're a city slicker then the bush and far north and remote areas are a bit more difficult for you as you don't 'speak the lingo' and so you often get less co-operation however nice you are. If you 'drop-in' to private strips on stations and the like without prior permission or invitation you could well get hunted off the place looking down a barrel if you pick the wrong place, whereas a bushie would always receive a warm welcome. If you are, or have been, a bushie, then you'll 'know the go' and the inland and far north are a lot easier to manage, in which case you'd already know how to go about arranging fuel stocks and a good welcome in advance. Unfortunately that's not something you can teach, you learn it by working in the bush over a long period and getting to know the people and their ways. There are so many ways to cause offence unintentionally - try giving a man's dog a food scrap, touching his hat, or taking yours into the dining room for example ... and of course townies and bushies have such different humour and ways of expressing humility that each often mistakes the other's for arrogance instead. The more you travel those areas the more you might build relationships and so it can get easier each time but for the first few trips I'd recommend you just 'fill 'er up' and take a jerrycan or two as well if space and weight allow. Talking of jerrycans - always take a couple of them in any case, empty if necessary (and you can get collapsible ones), for carting fuel from town to your plane, you can't always borrow them, and if you do then you have to return them to town. Lots of people in the bush have a rack in the tailcone of the fuselage to carry empty plastic jerrycans, you can stow them down there because they don't weigh much empty - check your W&B of course ... 2 1 3 1 Link to comment Share on other sites More sharing options...
DWF Posted September 30, 2015 Share Posted September 30, 2015 I have done quite a bit of flying around Oz over the years although perhaps not to as out of the way places as referred to by HITC. I have almost always had a good reception at the places I have been. Maybe I am just culturally insensitive. As far as carrying fuel goes my advice would be the same as HITC, carry as much as you can, particularly in remote areas. The extra fuel burn would be insignificant compared with the inconvenience and cost of having to get fuel in rural and remote areas. [it also means you have less luggage to lug into town for overnight stays. ] DWF 1 Link to comment Share on other sites More sharing options...
frank marriott Posted September 30, 2015 Share Posted September 30, 2015 Think about it practically, in our size aircraft you are talking about maybe 40kg difference in weight. Important for MTOW and performance from short strips, but wind variation will have a greater effect on fuel used then weight carried. As HIC suggests, carry max fuel permitted by MTOW, 1 Link to comment Share on other sites More sharing options...
Birdseye Posted September 30, 2015 Share Posted September 30, 2015 The variation in the price of fuel enroute would probably have more significance. Link to comment Share on other sites More sharing options...
Nobody Posted September 30, 2015 Share Posted September 30, 2015 The other factor to consider is temprature. At MTOW on a hot day you might not climb all that fast. Say on a colder day you can climb at 500' per mimute average ( low down you may be faster) to 8000. That climb takes 16 minutes. If in the hot afternoon that drops off to 200' that will take you 40 minutes. If you use 30l per hour to climb and 15l per hour in cruise the extra 24 minute is 6 liters or enough for nearly half an hours cruise. This is why departing early is a good move and minimizing the useless stuff in the aircraft to minimize weight. 1 Link to comment Share on other sites More sharing options...
Litespeed Posted September 30, 2015 Share Posted September 30, 2015 With the exception of being on fire, nothing is more useless than fuel on the ground, if you are in the air. Always carry as much as you can in your tank. Plus some of the red plastic cans empty. They are better to carry and don't weigh much. What aircraft is it? 1 Link to comment Share on other sites More sharing options...
DrZoos Posted September 30, 2015 Author Share Posted September 30, 2015 ok thanks guys - yeh thought as much for the outback. @Nobody - you have hit the nail on the head, for me everytime i go anywhere around here other than a local flight I tend to cross the ranges at minimum 6500 foot up to 10000 foot if clouds are around normally i wouldnt bother, but climbing the last few thousand feet in the warmer months is really quiet a lot of work due step climbing for engine temps and just the time it takes to climb when your on mtow... i generally leave with full tanks to avoid the hassle and extra expenses... but yesterday with 2POB at full MTOW and fairly warm temps it was a real effort and i started to wonder about the logic behind it . i had to step climb as my aircraft with its slippery design and cooling inlets on top of the cowl doesnt like climbing for long periods in the warm cond at mtow and i really started to think, 40kg less fuel in these conditions would prob really help Link to comment Share on other sites More sharing options...
microman Posted October 1, 2015 Share Posted October 1, 2015 I understand many P300's have an issue with oil temps on extended full-power climbs - funnily enough my P200 with the same oil-cooler setup wont even get to optimum temp (100 deg C) under the same circumstances, and in fact at cruise the temp sits around 80 degC which is a little cool. The Rotax book says that all 912's should reach 100 deg C at some stage during each flight - in order to burn off any moisture. Actually I generally cruise-climb my P200 at around 5000 rpm - it will still climb at over 500 fpm at MTOW. Great design these Alpis! Even with a fixed-pitch prop (mind you it is a Brent Thompson special!), I cruise at 100 kts at 4700 rpm - 12-15 litres per/hr. 1 Link to comment Share on other sites More sharing options...
Russ Posted October 1, 2015 Share Posted October 1, 2015 Ok.......you're heading off on a long jaunt, why power your way to cruise height ???.....setup cruise revs, set up gentle climb rate 150....250ftpm max, and sit back........you'll get to height with no engine stress / high fuel burn, happining. works for me....... 1 1 Link to comment Share on other sites More sharing options...
DrZoos Posted October 1, 2015 Author Share Posted October 1, 2015 Ok.......you're heading off on a long jaunt, why power your way to cruise height ???.....setup cruise revs, set up gentle climb rate 150....250ftpm max, and sit back........you'll get to height with no engine stress / high fuel burn, happening.works for me....... Wish that worked for me..na too close to mountains.. i can get to 4000 pretty quick but then the next 2500 takes a long time and Im over Tiger country before I have enough height to reach emergency patches.. I did some reading on PPRUNE from some pretty learned folks... they seem to think somewhere around 6% per hour of additional fuel is used to carry the fuel. thus carrying an extra 50L for the return flight of a 2.5h flight means before you start using it you have used around 6L just to carry it there. So a cost of approx $15 In this case when Im heading over the ranges I think Im going to travel lighter if Im coming back via a known good fuel stop with no landing fees. Where as If im going to some tin pot airport, i think i will just allow more time for the initial climb on departure and carry the fuel, plus leave as early as possible and safe to do. Link to comment Share on other sites More sharing options...
Nobody Posted October 1, 2015 Share Posted October 1, 2015 I suspect that 6% is a bit high but it depends on the aircraft and cruise altitude. The graph below plots the data from the J160 POH. It shows the time to climb for a MTOW of 440kg and 540 kg at both a standard day (15 degrees on the ground) and a +20 degree day(35 degrees on the ground). The extra temperature and the extra weight doubles the time to climb to 8000 feet. The data in the POH docent go higher than 8000 feet but is is reasonably obvious that the temp and the extra weight will have an even greater affect above 8000 feet. Link to comment Share on other sites More sharing options...
K-man Posted October 1, 2015 Share Posted October 1, 2015 Obviously you aren't going to be carrying even one jerry can in the Pioneer. We carry a collapsible 20 litre container and sometimes need more than one trip to top up when required. We have never had a problem getting fuel and never had bad fuel and we have never experienced the animosity HITC was alluding to in any out of the way places. Actually it has always been totally the opposite, but we do plan ahead and contact every place where we will be landing. For us, we normally fly with full tanks. I take a small bag for two weeks away (3kg) and my wife goes overboard at an excessive 4kg. That leaves plenty spare for cameras, extra oil, water, tools, first aid, emergency supplies, cover and tie downs. We have never had an overheating problem but we do push the climb to get the oil temp over 100 degrees to remove moisture. Once enroute I normally just climb at 500 fpm. What extra fuel you burn climbing you save at the other end when you come back down. To be honest, I've not noticed any real difference in fuel burn with extra weight. We burn 18-20 litres per hour regardless and would average 130+ cruise at that rate. Depending on conditions the cruise may drop to 120 or might be above 140. Landing fees? Well that's just part of the cost of flying. Most small places don't charge, some do. In the scheme of things it's not a great amount normally and often it's an honour system. Link to comment Share on other sites More sharing options...
facthunter Posted October 1, 2015 Share Posted October 1, 2015 A higher atmospheric temp will reduce performance and fuel flow. so time to cruise level isn't the full picture. All extra weight costs something, but probably much less effect than a head wind component. Cruise alt doesn't appear to be a major factor with piston engines, as it is with jets (and turboprops to a lesser extent). But you might have a mountain range to consider . Better to start out earlier when it's colder to get height and do it quicker. Nev 1 Link to comment Share on other sites More sharing options...
ben87r Posted October 1, 2015 Share Posted October 1, 2015 I'll say the difference isn't even worth considering... Don't carry any fuel considered unnecessary and ALWAYS carry enough. At MTOW I'll get about 5kn less then a light load which would be around 2%, excluding climb which may add a few min extra burning 135% of cruise fuel flow. 2 Link to comment Share on other sites More sharing options...
facthunter Posted October 1, 2015 Share Posted October 1, 2015 Never go past a refuelling stop and cut yourself short just because the fuel or landing charges are a bit steep. Get your priorities right. IF you need fuel You NEED fuel. Nev 2 Link to comment Share on other sites More sharing options...
DrZoos Posted October 1, 2015 Author Share Posted October 1, 2015 Cheers all for your input... So my question was two pronged and I should have explained the original post a bit better... the first part which is clearer and easier to answer is in relation to my long trip around parts of aussie for next year... i think its pretty clear..fill up every opportunity... the second is a bit more questionable... crossing the ranges regularly for short say 4-5 hour round trips , maybe an od over nighter but within a full tank of gas these I now think winter..hell yeh just fill up and go, but summer i think when crossing the ranges, with good fule stops available on the way home Im going to take less and fill up for a break on the way home ...im not convinced the saving of say $10 maybe $15-$20 is worth the effort and risk of climbing so much harder and hotter due to the extra weight Link to comment Share on other sites More sharing options...
Yenn Posted October 1, 2015 Share Posted October 1, 2015 Are your ultralights really that much worse climbers in hot weather. Maybe that is the reason that engines fail. They are overloaded. I don't seem to notice any difference between winter and summer, maybe I just pull the throttle back a bit less in the hot weather. The RV took me from takeoff at 100' to 9500 in 8min 13 sec, but that was in mid 20 degs on ground. Link to comment Share on other sites More sharing options...
Nobody Posted October 1, 2015 Share Posted October 1, 2015 Are your ultralights really that much worse climbers in hot weather. Maybe that is the reason that engines fail. They are overloaded. I don't seem to notice any difference between winter and summer, maybe I just pull the throttle back a bit less in the hot weather.The RV took me from takeoff at 100' to 9500 in 8min 13 sec, but that was in mid 20 degs on ground. But your RV likely has nearly double the HP (180 vs 100 ish) in only slightly more weight. Link to comment Share on other sites More sharing options...
Yenn Posted October 1, 2015 Share Posted October 1, 2015 Nearly right. 160hp, due to restricted rpm to 2600 due to the prop. I was just illustrating the point about underpowering, as well as skiting a bit. 1 Link to comment Share on other sites More sharing options...
facthunter Posted October 2, 2015 Share Posted October 2, 2015 A lot of RAAus planes are sensitive to density altitude at max weight. Not many are overpowered.. Your Corby and the RV are not typical.. The Corby with 4 cyl Jab is a good match. Much better than the original Volksy. Nev Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now