J-160 fuel burn /economy

[lyle janke]

hi all 

i have recently acquired a J-160  on the couple of flights i have had it has used fuel at about 20-25litres /per hr . i  compare this to the J-120  i owned previously  which was in the 13-15 litre range . i know the airframe is different  but when i read on the internet the quote is around  16 litres /hr . i haven`t looked into the internals of the carbie yet to see if jets have been changed or not , how do i determine that jets are worn or what is wrong ? the burn rate seems high based on what i can read it should be 

 your thoughts please 

lyle 

[KRviator]

I agree that "sounds" high for a Jab - I routinely use 25/H in the RV, with the O-340 and scooting along at 2,400RPM & 140KTAS.

The -160 and -120 share the same fundamental engine so the fuel burn shouldn't be significantly (50-75%) greater, though aircraft performance may be for the same power setting.

Which leads to the question - what prop did you have on the -120 and what RPM did you cruise at, vs the -160? Could it be it is pitched quite differently, giving a different cruise power setting and an inability to compare apples with Malus domestica?

[lyle janke]

hi 

 the J-120 hardly ever seen RPM above 3000 & went everywhere at 2800 rpm  i replaced the wooden prop with the Jabiru plastic option 

 the J-160 will go to 3300RPM  full power  easily so cutting the rpm in cruise to  2900 rpm is where it seems to like it  using  20-25 l/phr . using 2800 is slow & 16-18 l/hr approx i have a wooded prop fitted don`t know if it is correct or not 

so have a few variables to consider & weather is windy so not good for comparing numbers 

[facthunter]

If she's richer the oil will go darker, quicker.  A good condition motor will make the carb needle rise more into  the richer range. Try flying a little higher and see if it changes things. Nev

[Yenn]

The plugs should give some idea of how rich or lean an engine is running. Even better is EGT gauges if they are fitted.

[spenaroo]

I did my training in a J160 and I thought we used 15L an hour as the rule of thumb for fuel usage

[facthunter]

Legally you use ACTUAL established figures for your operation, OR the POH whatever is  higher.  Be prepared  to substantiate the former if it comes to the "toss". Nev 

[spenaroo]

Looks like my memory was pretty good, 2900rpm cruise is about 15L an hour

from the Jabiru POH

 

[kgwilson]

From comments I would say the prop pitch is too fine. I have a Bolly Bos-5 with my Jab 3300 Gen 3 and have set the pitch so that WOT straight & level at about 3000 feet it tops out at 3300 rpm which is the maximum continuous rpm operation for the engine. Low level cruising at about 27-2800 rpm gets me 18-19 LPH & 115-120 knots. High level cruising around 8000 feet at 2850-2950 RPM is around 24-26 LPH & 130-135 knots. The J160 I have flown averaged 15-16 LPH & that was with a Jabiru wooden prop. The jabiru Scimitar prop which replaced the wooden props is made by Bolly and is ground adjustable though it comes new with the pitch set to Jabiru specifications. If you have one of these it may have had the pitch modified by the previous owner.

[RFguy]

Lyle

what type of J160 is it - does it have a 6 cylinder or does it have a 4 cylinder ?

 

I would expect you would get 90 kts indicated and 15 lph.

I have some questions : 

 

1) What indicated airspeed does  do indicated at 16 lph ? (what fuel # pax also approx) 

2) What is the static RPM -  RPM at the beginning of the TO toll, WOT . ?

I woudl expect 2850 for the 6cyl, and ~3000 for the 4 cyl. 

3) what fuel are you using ?

 

-glen

 

if the aircraft will easily go 3300 RPM, is MIGHT too fine, and the prop is likely a very inefficient screw in that setup, depending on the IAS

 

 

 

[lyle janke]

6 hours ago, RFguy said:

Lyle

what type of J160 is it - does it have a 6 cylinder or does it have a 4 cylinder ?

i have the std 2200 offering 

 

I would expect you would get 90 kts indicated and 15 lph.

I have some questions : 

 

1) What indicated airspeed does  do indicated at 16 lph ? (what fuel # pax also approx) 

would need to do another flight & record some more numbers  but as i remember quite slow 

2) What is the static RPM -  RPM at the beginning of the TO toll, WOT . ?

I woudl expect 2850 for the 6cyl, and ~3000 for the 4 cyl. 

3000+ a bit variable  most times 

3) what fuel are you using ?

 i use avgas in the bush & mogas 95octane or 98octane if near town & i can cart 

 

-glen

 

if the aircraft will easily go 3300 RPM, is MIGHT too fine, and the prop is likely a very inefficient screw in that setup, depending on the IAS

 

 

 

 

[RFguy]

Hi Lyle

well the static RPM sounds about right for the 4 cylinder.

The wooden prop is a fair way down on efficiency compared the the composite prop- it bends.  the composite prop is a great upgrade.

 

yes, will need those 15 to 16 lph indicated airspeed cruise numbers. Have fuel pump OFF when you are doing this otherwise the facet pump upsets the fuel flow sensor and it reads higher as you probably know. 

 

If you have GPS, maybe do a couple of forward-backward  runs and note down the ground speed (as to check the indicated airspeed sanity check) .

-glen

 

 

[lyle janke]

hi 

"The wooden prop is a fair way down on efficiency compared the the composite prop- it bends.  the composite prop is a great upgrade."

the prop on the J-160  i understand was replaced in recent past so i`m wondering what prop i have fitted  ( are no`s easy to read without removing the prop ) 

i had composite prop on my previous J-120 aircraft  (definitely agree on up-grade )

 will get a set of no`s  next flight  (cost of fuel is not making it easy to fly for pleasure at the moment  in the bush - $3.60 P/L)

[RFguy]

OK will be interested  - suggest adding Decalin Runup to the AVGAS - otherwise you are always up for a 400 hour top end clean.... (ring lands, chambers, guides, valves,) 

[kgwilson]

Simple solution. Change to Mogas 98 & plug fouling, piston, valve and head deposits are a thing of the past.

[RFguy]

as long as it is fresh. agreed. 

[lyle janke]

hi 

this additive is expensive  how many jab owners are using ??

i have always used a bit of upper cyl lube  

no additives seem to have the blessing of the factory  but any use seems to be by popular opinion 

guick search seems to have the blessing of the rotax factory  will like tosee some more opinion on it 

 

[RFguy]

Buy it in the big bottles, not so expensive. small bottles are !

Yes, without using this, and using AVGAS, the Top end (ring lands, rings, chambers, guides, valves) TBO of the Jabiru engine  on AVGAS is about 400 hours . 

Jabiru suggestions ? Pfffsst.

As KG says, run fresh MOGAS and the build up wont happen. It will stay nice and clean ish/ still gets a bit black because of the richness (depends on types of ops of course) , but it doesnt cake up  and cause rings and valves to stick. If the MOGAS is in the airplane for more than a couepl of weeks, freshen up the volatiles with some known fresh fuel (sealed Jerry cans) , at least 25%. or put it in your car ! (you probably have a diesel out there) 

The Jabiru  engines generally run rich (exacerbating buildup) , and not all that hot say compared to a Lycoming (burns some of the otherwise deposits) 

-glen

Edited August 12, 2022 by RFguy

[facthunter]

Often , some of that build up is dust.  Nev

[RFguy]

There's a oil analyser guy in another forum ( for all sorts of engines ) that reckons (on weekly oil changes) he can see when you were operating from a dirt strip for a day ...

[lyle janke]

Hi RF Guy

Buy it in the big bottles, not so expensive. small bottles are !

https://www.skyshop.com.au/shopexd.asp?id=1189   is there a better deal than this 

[RFguy]

to my knowledge not locally. 

you dont need too much. bottle says 0.5oz per 10 gallons to 2 oz per  10 gallons. I ran 1 oz.....

 

[kgwilson]

While I agree that Mogas should be as fresh as possible, it will last in your aircraft tank for about 5 weeks without significant degradation. I have proven this when I did not fly for 5 weeks & just decided to try to start the engine which it did so I flew with no issues.

Some of the aromatics will evaporate off but the octane rating will actually improve slightly. The tests run by BP found after 5 weeks 98 RON had improved to 99.5. The only issue with a Jab engine is that it may prove harder to start from cold. The loss of aromatics will cause detonation in small high revving engines such as used in boats and chainsaws. The light components provide octane benefits under high revving conditions & this is not an issue with a low revving Jabiru engine though would be in a Rotax. Also you do not need to add very much to improve starting & running properties, 5-10% is adequate though I tend to put another jerrycan full in as my main tank is 100 litres & I often only have 20-30 litres left after a flight.

 

The study text is below. The table did not copy properly so the pdf of the study is attached as well.

 

INTRODUCTION
Petrol is a mixture of many components with different properties that contribute to the performance of the fuel. When petrol is left out in an open container exposed to the air it will in time completely evaporate. As it evaporates the composition and properties will change because different components evaporate at different rates. This is a normal feature of petrol and the same process takes place in equipment fuel tanks. Where petrol is kept for more than a week in equipment tanks then it can become stale and it is better to add fresh fuel before using. Examples are classic, veteran and vintage cars and bikes, racing cars and bikes, drag cars, boats, dual fuel vehicles, lawn mowers etc.
Generally petrol will last in equipment fuel tanks for about 3 weeks at a temperature of around 20 deg C, after that it will perform better when fresh petrol is added.
Petrol will last in sealed containers for more than 6 months, while some breathing will take place this is not enough to significantly affect product quality.
In underground storage tanks the rate of replenishment prevents the fuel from becoming stale
HOW PETROL CHANGES IN EQUIPMENT TANKS
Loss of light components – impact on mixture
The light components in petrol are lost first as the petrol sits in the fuel tanks. These components provide valuable octane benefits during cold start. Because they are volatile they compose most of the air fuel mixture during cold start, if they are absent then the mixture becomes lean resulting in higher temperatures, pre ignition, detonation and piston damage. This is generally the cause of piston damage in high revving engines used in boats and small engines such as chain saws etc.
The portion of the petrol that remains has a higher density and higher octane but this is not available during cold start resulting in hard starting. Because the fuel carburetors and injectors operate on a volume metering system the higher density means that more fuel is introduced for a given volume of air and so the air fuel ratio is fuel rich. If all the fuel cannot be burnt then it forms carbon deposits that will foul the spark plug and cause the engine to stop and not start. This is generally the cause of problems in classic cars where the engine stumbles and hesitates or cuts out.
Loss of light components – impact on octane
The light components in petrol are lost first as the petrol sits in the fuel tanks. These components provide valuable octane benefits under high revving conditions such as cold start acceleration and the loss of these components can result in detonation and pre ignition at high speed resulting in piston damage.
The remaining components that have not evaporated are high octane and octane can actually increase with time but this octane is not available for high revving conditions.
Document: Petrol life in vehicle fuel tanks v4.doc Page 1 of 2
Issued: Jan 2010
Supercedes: Feb 2005
BP Australia Limited A.C.N. 004 085 616

Gum and Peroxide formation
With long storage periods, especially in the presence of hot weather or engine heat the petrol can oxidize to form peroxides. These compounds can attack rubber and metal, stripping away the liner on fuel lines or copper from fuel pumps and attacking rubber hoses. These normally take a few months to form in sufficient quantity to cause a problem. This process is faster if Ultra Violet light can get to the petrol.
IMPACT OF ENVIRONMENTAL LEGISLATION ON PETROL PROPERTIES
Volatility restrictions
Current State EPA legislation restricts petrol volatility in the summer period, generally November to March. In that period petrol will have less volatile components than at other times, generally the summer volatility of petrol is 30% lower than the winter volatility which means that the loss of lighter components in summer can be quicker. However this is not usually an issue due to higher temperatures but can create problems in autumn if the summer fuel is held over. To avoid this fresh fuel should always be used in the April May period.
MAINTAINING FUEL IN EQUIPMENT TANKS
It is not possible to provide a foolproof strategy for engines that are used only intermittently, however the following principles help.
1)
Always add some fresh fuel when the equipment is to be used if it has not been used for more than a week. This will provide additional volatile components and protect from cold start high revving detonation and piston damage.
2)
Always keep the tank half full to stop water vapour from being sucked in and condensing.
3)
Use a fuel that contains anti oxidants, metal deactivators and corrosion inhibitors to protect metal surfaces such as BP Ultimate
4)
Using a hotter spark plug will help to reduce carbon deposits

At the end of 5 weeks the fuel is 5% heavier and the fuel air mix will contain more fuel.
For further information, please call the BP Lubricants and Fuel Technical Helpline 1300 139 700 local call
Or visit www.bp.com.au/fuelnews Document: Petrol life in vehicle fuel tanks v4.doc Page 2 of 2
Issued: Jan 2010
Supercedes: Feb 2005
BP Australia Limited A.C.N. 004 085 616

petrol-life-vehicle-tanks.pdf

[RFguy]

Nice info, KG

[sfGnome]

10 hours ago, kgwilson said:

Always keep the tank half full to stop water vapour from being sucked in and condensing.

Thanks KG. That was really interesting. With regard to the bit I’ve quoted, are they saying “don’t leave it empty”, or “don’t leave it full” (or both)? What’s the reasoning?