Efficient cruising altitudes

[dlegg]

What altitudes are you guys/gals flying at on long cross countries for best airspeed/endurance combination. Throttle at WOT or a lower power setting. Mainly interested in 3300. I have a sensenich ground adjustable so looking to set up for long distance running....

 

 

[Ultralights]

what ever level gives the best tailwind, or least headwind, with respect to hemisperical levels. if winds are negligable, then i aim for 9500 east and 8500ft west, as this will give a higher TAS. still fly with the same throttle settings and rpm. IAS will be a bit lower, but with temp and pressure calc, you can get a TAS. in the Savannah. at 9500, on a hot day in summer, the TAS will be about 15kts faster. im not sure how it will be much different it will be with a Jabiru engine.

 

 

[viewfromright]

We just got back from a round trip Lismore, NSW - Broome WA.

 

"Tail winds rule" was our motto, our altitude ranged from 2500 to 9500.

 

Our best effort was on our last leg, Roma/Lismore, 149Kts ground speed, 110Kts indicated, 8500 Ft...............

 

 

[Guest Andys@coffs]

With regard your question on throttle......WOT is not IAW jabiru's instruction and will result in a fuel burn that more approximates a GA aircraft than an ultralight (circa 33+Litres per hour instead of 23ish cruise). That said I wouldn't be just tooling along at low RPM either. J tell us that 2850 is a good solid cruise RPM that wont result in problems.

 

Setting up the pitch correctly will I think require you to monitor CHT and ensure that whatever angles you set don't result in too low an RPM but too high a CHT.....Be kind to your engine....they cost a sh!tload to fix........Don't ask me how I know that!

 

That all said obviously a fixed pitch prop is a compromise what ever you set has to still be Ok at climb and Take-off before worrying about fine tuning for CHT.

 

Have you also checked the forced air cooling with pressure gauges to ensure that what you have works? ....... An incorrect cooling setup will kill it faster than any other thing!

 

 

[Yenn]

Wide open throttle, with leaning for economy above about 5000' for normally aspirated engines. Don't lean too much above 75% power, but above 5000' you won't get much above 75% unless turboed. Look for the best wind direction and fly slower with a tailwind and faster with a headwind. Be aware that you can't fly in class E airspace without a transponder and radio contact.

 

 

[facthunter]

Wide open throttle on a CV type carb (as the piston is drawn up by differential pressure). gives a situation. at altitude where the slide will never be fully open. This has ramifications for fuel mixture ratio caused by needle taper. At the levels we fly, altitude, on a petrol normally aspirated motor is not a big effect on fuel use for air distance flown. As stated the main effect to achieve is getting a favourable tailwind or avoid a strong headwind, on the track you fly.

 

If your plane is overpowered it may be capable of cruising at well above it's economic flying speed. Your motor is dragging it through the air well above it's best L/D considerations so a speed lower will save fuel..

 

A heavier plane cruises faster with advantage and as it gets lighter a lower cruise speed is more advantageous for range and economy. Also as Yenn says go faster (airspeed) into a headwind and slower ( airspeed) with a tailwind. Nev

 

 

[dlegg]

Thanks Nev, thats exactly where I was going with the question. With the standard CV bing carby, the throttle cable doesn't directly operate a slide. I only presumed that there would be an altitude where at WOT the engine would be operating at peak efficiency.

 

My aircraft is overpowered so a careful testing regime is in order, but was hoping for a good starting point. I did hear around 7000-7500, so headwinds and tailwinds aside, I'm sure the jab has a sweet spot at a narrow alt range.

 

 

[facthunter]

WOT (Full throttle) is desirable on a direct driven supercharged engine for cruise height selection as there is no point restricting the charge and then compressing it. This is a common feature of radial engines, but to utilise it you need C/S prop to get the power selection more variable. You have to balance RPM and Manifold Pressure within set limits too. Nev

 

 

[mAgNeToDrOp]

Excuse my ignorance but can you explain what is meant by " fly slower with a tailwind and faster with a headwind" are you referring to engine power (rpm) ?

 

 

[Captain]

I agree with ultralights' post # 2.

 

When I had my 230 I always felt that the 230's wing was happiest cruising at about 7,500 to 8,500 or a tad above. It just felt sweet & balanced purring along around 120 knots ....... like cruising a BMW bike at 180 (kph). And at that level the nice cool air was great for keeping the heads happy.

 

But the governing factor for "long cross-countries", which is the key criteria of this question, has to be wind direction vs height (but also perhaps turbulence on rough or marginal days).

 

When on a longie my practice is to plan for the best winds and if not as predicted, or if varying over the 400 - 500 miles of the sector, go up or down chasing best wind and hopefully be able to then move to an appropriate cruising level with that wind. And if that happens to be up near 7500 - 8500 then woo-hoo.

 

But Huey didn't play the game too often and my 230 attracted adverse wind direction most of the time. Why is that?

 

 

[turboplanner]

like cruising a BMW bike at 180 (kph)[/font]

Please see me when you get home

 

Julia Doubtfire

 

 

[facthunter]

For reduced fuel usage have the tailwind for longer (time) reduce airspeed, and the headwind for less (time) increase airspeed. It's the same principle as doing an engine out forced landing. You should have been taught this. Nev

 

 

[Guest Andys@coffs]

......But Huey didn't play the game too often and my 230 attracted adverse wind direction most of the time. Why is that?

And that's with a 230 that has a fair turn of speed across the ground.......

 

When your in a trike, flying into a head wind, and a horse running in a paddock below you is overtaking you.....that's when you really can bemoan the fuel impacts on a headwind....

 

On a 230, the head/tailwind in the main is unlikely to exceed 20% of unaffected speed....On a trike that can be up to 50% of your speed.....don't get caught short....although landing into such a headwind should mean (tongue in cheek) that you need a runway no longer than 2-3 car parking spots, and a precautionary pass can become a precautionary hover......

 

Andy

 

 

[facthunter]

You must have the wrong wind "GOD" Captain. Nev

 

 

[AVOCET]

I agree with ultralights' post # 2.When I had my 230 I always felt that the 230's wing was happiest cruising at about 7,500 to 8,500 or a tad above. It just felt sweet & balanced purring along around 120 knots ....... like cruising a BMW bike at 180 (kph). And at that level the nice cool air was great for keeping the heads happy.

 

But the governing factor for "long cross-countries", which is the key criteria of this question, has to be wind direction vs height (but also perhaps turbulence on rough or marginal days).

 

When on a longie my practice is to plan for the best winds and if not as predicted, or if varying over the 400 - 500 miles of the sector, go up or down chasing best wind and hopefully be able to then move to an appropriate cruising level with that wind. And if that happens to be up near 7500 - 8500 then woo-hoo.

 

But Huey didn't play the game too often and my 230 attracted adverse wind direction most of the time. Why is that?

Your hanging your tounge out of the wrong side of your mouth !!

 

Cheers Mike