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Expected fuel burn

HeliCooper

Well Known Member
Hello everyone,
I am looking into the 14 and 9 for a xc IFR machine and was wondering if anyone had any idea how much more the 14 will burn then the 9 at the same cruise speed. Assuming both are standard injected Lycomings.
 
No one would know except Vans, since there is only 1 flying.

But I would bet at the same cruise speed they will be fairly close in fuel flow. I've guess at 8gph they'll both be around 190-195mph....just a guess.
 
HP x .44 / 6 should be close to gallons per hour.

Ie., Lyc 180 at 75% (135 hp): 135*.44/6=9.9 GPH. Not perfect, but close. Assumes leaned with a traditional engine setup. If running EI & LOP, you would do better than that.

Dan
 
You are interested in economy so lets try to compare LOP at 55% power.

Vans figures for the RV14 are 169 mph at 55% at gross. LOP fuel flow at 55%
for a standard 210 hp engine would be close to 7.75 g/h (FF * 14.9 = HP when LOP). So 169 mph @ 7.75 g/h.

Using Vans figures for the carb 9A and the same formula as above gives 166 mph and 5.9 g/h at 55%. So 3 mph slower but nearly 2 g/h less.

Vans uses an unspecified FP prop for the 9A figures and a Hartzell CS for the 14A. CAFE tested Vans 9A with a MT constant speed prop and their figures show significantly better economy.

From my experience and from performance figures others have posted a 160 hp 9A with a Hartzell prop will burn about 6 to 6.5 g/h LOP at 150 kts (173 mph) at around 8,000 ft.

A bit of guess work here but based on the above and if both have a Hartzell prop I would expect that the 9A would burn between about 1.5 to 2 g/h less than the 14A at around 170 mph and 8,000 ft????

Fin
9A
 
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engine efficiency numbers

Hey Fin:

Where did you get the efficiency numbers for the 210HP Lyc? I would have expected something closer to 13.5 or so, as Dan mentions - the TCM crossflow engines (VERY good design - almost modern) don't hit the numbers you mention. Curious.

I would also cast some doubt on the stated differences in the two ships in terms of cruise performance - maybe the RV9 fellas know a shortcut?:eek:

FWIW I ferried an RV9 TD/O-235 to FL from Texas and it would hit ~140MPH GS @ 5.5GPH @ 9500/11500MSL. I figure there was a tailwind component in that equation...

Carry on!
Mark
 
Mark,

14.9 is the figure commonly quoted for a Lycoming with 8.5:1 compression and LOP for example see the last part of post #12 in this thread. The figure could be slightly better for the 8.7:1 engine in the RV 14. Unless I have this completely wrong your figure of 13.5 would give higher fuel consumption.

I stand by the figures I gave for the 160 hp 9A with a Hartzell CS prop. They are not far off Vans figures for a FP prop and I consistently get within the range of these figures. Pete Howell for example consistently gets even better figures than me (damm him).

The bottom line is that the two aircraft have similar speeds at 55% power but this equates to 115 hp for the RV14 and 88 hp for the 9A. It will take significantly more fuel to produce 115 hp than 88 hp.

Fin
9A
 
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Thanks guys,

I just contacted Van's to try and get an idea of their numbers they have been seeing. If I get a response I will share it here.
 
Thanks Mike.

To all, here is the email response I received from Vans. The last sentence is because I mentioned I was 6'6". Hope it helps someone else looking for this information.

"Since there are no owner built 14s flying yet, there aren't a lot of real world numbers. I've
flown the airplane on one 1400 mile trip and a lot of shorter trips, and generally plan on 10
gph overall. In cruise, at altitude we can do a bit less -- around 9 gph for 155-160 KTAS. IT'll
give you 170 KTAS, but the fuel burn will be about 12 -- so we rarely push it that hard. With
the injected IO-390 and good instrumentation, we're quite happy running it lean of peak at
altitude.

For the same 155-160 speed the smaller RV-9 burns about 7.5 and the RV-7 about 8 at
altitude. The 9, with no need for aerobatic roll rates, has a higher aspect ratio wing and it's
efficient cruise altitude is a bit higher, resulting in better economy.

Understand that these numbers are very general. The pilot has ultimate control and one
person's figures can easily be different by 15% -- or more.

While you'd fit in any of them (with the proper seat cushions and seat position) there's no
doubt that the 14 will be significantly more comfortable for a guy your height."
 
From my experience and from performance figures others have posted a 160 hp 9A with a Hartzell prop will burn about 6 to 6.5 g/h LOP at 150 kts (173 mph) at around 8,000 ft.
Running 40F LOP, my 160hp 9A with 3 blade Catto shows almost exactly the same numbers. FWIW.
 
Check with Lycoming, since it is one of their engines. Their site lists 11.1 GPH at 65% power. I can only imagine what 75% power will be.

The -9 is a well known item and Van's is known for listing real numbers for their aircraft.
 
Hello everyone,
I am looking into the 14 and 9 for a xc IFR machine and was wondering if anyone had any idea how much more the 14 will burn then the 9 at the same cruise speed. Assuming both are standard injected Lycomings.

At the same speed, they will be awfully close, with the -14 probably burning slightly more (perhaps 1 gph) due to differences in fuselage cross section and span loading.
 
If it helps, my 76 Cardinal RG with lycoming IO360 200hp engine burns

8000' std temp 22"/2300 65% 9.3gph
8000' std temp 22"/2400 69% 9.9gph
8000' std temp 22"/2500 72% 10.4gph
 
Originally Posted by Finley Atherton
From my experience and from performance figures others have posted a 160 hp 9A with a Hartzell prop will burn about 6 to 6.5 g/h LOP at 150 kts (173 mph) at around 8,000 ft.
/QUOTE]

I noted this number and took it as a bit of a challege:)

This morning I took my EVO rocket, (280 to 300HP?) up to 8000'PA to see what I could do at 150knots TAS.
It took a while to slow down :) but with the autopilot on level flight I was at

2000rpm, 14.5"MP burning 6.1 gph

It takes a certain amount of energy to push and aircraft through the air at 150 knots. Most RVs and rockets share a very similar profile, thus these results were not unexpected and I am sure that the RV14 will be about the same.
 
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