O-360 A1A fuel burn at 17,000ft?

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coma24

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coma24
I have some long range flights coming up. Having learned the basics of portable oxygen systems, I'm curious what type of performance to expect if I take my airplane up to 17,000ft.

I routinely fly it at 11k, and occasionally at 12k. The difference in fuel burn between flying at 8k and 12k is pretty significant. I'm wondering if I should expect a linear reduction in fuel burn up at 17k?

The aircraft is a Lancair 360. Based on the expected drop in manifold pressure, I'm pretty sure I'll be able to get it up to that altitude to take advantage of the reduced fuel burn and massive winter tailwinds (it'll be a coast to coast flight, so I'm interested in maximizing range). My question is what fuel burn to expect up at that altitude, wide open, lean of peak. That said, at such a low power setting, I may well shoot for best power instead of LOP as the drop in IAS associated with LOP ops might be significant in terms of TAS.
 
Actually, just remembered there's a YT video of a Lancair 360 up at FL180: https://www.youtube.com/watch?v=Ts7y7rcu0gE

I was initially alarmed at the fuel burn at FL180, it didn't make sense, but it looks like they didn't do much in the way of leaning on the way up. Shortly before the 2 min mark (1:56), there's a shot of LOP ops, burning around 5gph (the top left of the EFIS shows they're LOP). Unfortunately, they transition to back to ROP ops pretty quickly and the FF rockets back up again.

They were showing around 193KTAS at best, with some earlier stints at 191KTAS. It's good to know they're not losing too much in the way of speed up there.
 
You will want best power mixture. If you can take advantage of tailwinds yep it could be worth it.
 
At 17,000, you can't put that mixture knob anywhere to harm the engine. I'd shoot for about 50* rich (~best power) of peak to get the most out of the engine.
 
I'm well aware that you can't hurt the engine at 17k :) LOP generally yields a 20% drop in fuel consumption for a 4-5% hit in performance at the lower altitudes. My concern is that due to the IAS/TAS spread, the TAS hit will be higher doing LOP up high. I'll have plenty of time to find out, I suppose.
 
coma24 said:
I'm well aware that you can't hurt the engine at 17k :) LOP generally yields a 20% drop in fuel consumption for a 4-5% hit in performance at the lower altitudes. My concern is that due to the IAS/TAS spread, the TAS hit will be higher doing LOP up high. I'll have plenty of time to find out, I suppose.
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I would imagine so. I've never had the opportunity to take a NA piston up there.
 
Cpt_Kirk said:
I would imagine so. I've never had the opportunity to take a NA piston up there.
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Me neither, this'll be interesting. Fuel flow of 5-6gph would be helpful for max range. I'll just need to find a day when the winds are howling up there to make the most of it. If I can nab a 70-80kt tailwind component at 5-6gph, it's likely I might be able to drop a fuel stop. We'll see. The descent will also be interesting. Trying to work out if a shallow, longer descent would yield better efficiency than delaying the descent until later and then using a steeper deck angle.

Normally, from 11k and lower, you can't do more than a shallow descent without getting into the yellow arc with wide open throttle.

However, at 17k, the KIAS will be relatively low (135-140, based on the video I saw), I'll have room for a steeper descent, at least initially.
 
I chuckled when I first read the title. I didn't think an 0-360 could get to 17k feet. How long will it take you to get there in the lancair?
 
Anymouse, thanks for the reply. That's a surprisingly high fuel burn, I normally see around 8.5 up at 11k. Where is it running the mixture?

Actually, I suppose a better question is, what is your fuel burn at 8k?
 
rbridges said:
I chuckled when I first read the title. I didn't think an 0-360 could get to 17k feet. How long will it take you to get there in the lancair?
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Honestly, not a clue, but I have a feeling the climb performance is going to be pretty marginal towards the end of the climb.
 
rbridges said:
I chuckled when I first read the title. I didn't think an 0-360 could get to 17k feet. How long will it take you to get there in the lancair?
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I have had my O-320 powered Lancair to 17k feet. Solo it will still climb at a couple hundred fpm.
 
Forane, thanks. What's your typical fuel burn at 8k and what was it at 17k? Where do you run the mixture?
 
coma24 said:
Forane, thanks. What's your typical fuel burn at 8k and what was it at 17k? Where do you run the mixture?
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I had a digital fuel flow meter but removed it at some point; I think when the EFIS was installed. At 8k it used to indicate something like 8 gph if I recall. Rarely would I cruise at 8k so I didn't pay attention to that number. Typical cruise for me was 10-12k where the fuel flow meter would indicate 6.5-7 gph. I didn't go to 17k until after removal of the fuel flow so I cannot comment on flow at that altitude. As far as mixture, for me (and I don't make any claims of being an expert on leaning), I would just lean with altitude until it coughs then enrichen slightly. At 17k the mixture was way out.
 
kgruber said:
Range in a normally aspirated airplane does not increase with altitude!
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I think you mean "max" range, dontcha? Normal cruise range will increase.

dtuuri
 
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I've had IO550ed 206s up to 17.9, F' that noise.

If I need o2 crammed up my nose that just life telling me I should be in a pressurized turbo or turbo prop.

Only exception would be a glider.
 
kgruber said:
Range in a normally aspirated airplane does not increase with altitude!
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If I've got 120kt tailwind at altitude vs 30kts down low it will most certainly increase range.
 
coma24 said:
Anymouse, thanks for the reply. That's a surprisingly high fuel burn, I normally see around 8.5 up at 11k. Where is it running the mixture?

Actually, I suppose a better question is, what is your fuel burn at 8k?
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Actually, it's probably a tad less, but I didn't want to make it sound TOO good. The best numbers I can give you is a trip I did from Scappoose, OR (SPB) to Little Rock, AR (LIT) at 15.5. I did it in 8.1 hours and put 64 gallons back in the plane. This included two climbs. I spotted an unreported fire and spiraled down to size it up before I reported it, then climbed back up again.

I have a FADEC kit on my engine, so it does the leaning for me. I had the throttle full in for the entire flight, so it probably gave me WOT (wide open throttle) power as opposed to high (>65%) or economy power (<65%).

On those occasions where I find myself flying a bit low, I'm seeing 9-10 GPH depending on power setting. Unfortunately I've only recently got my fuel flow dialed in, so I can't give you better numbers.
 
Same engine in my travel air. IIRC 17kft will be about 6.5-7gph leaned for best power (which isn't much power)
 
coma24 said:
However, at 17k, the KIAS will be relatively low (135-140, based on the video I saw), I'll have room for a steeper descent, at least initially.
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I'm interested if anyone has looked at the flutter margin for that airplane at those TAS in a high-speed descent. Aerodynamic flutter is driven by TAS, not IAS, so if you get high enough, IAS can be relatively slow but with the high TAS, you get into flutter. This would be even more of a concern if you're pushing it over for descent to attain higher speeds.

I've read it's one reason Van's doesn't recommend higher power engines or turbos with the RV-10.
 
James331 said:
If I need o2 crammed up my nose that just life telling me I should be in a pressurized turbo or turbo prop.
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Some people don't mind it. I myself cannot do that. The cold dry oxygen blowing directly into my nose just kills me. The masks are better for me but also irritating in a different way. Lots of people out there who don't mind it at all.
 
Well, the OP did mention going high for tailwinds. ;)
 
RussR said:
I'm interested if anyone has looked at the flutter margin for that airplane at those TAS in a high-speed descent. Aerodynamic flutter is driven by TAS, not IAS, so if you get high enough, IAS can be relatively slow but with the high TAS, you get into flutter. This would be even more of a concern if you're pushing it over for descent to attain higher speeds.

I've read it's one reason Van's doesn't recommend higher power engines or turbos with the RV-10.
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Don't know about Coma, but I tested my Tango to 275kts IAS at 10k specifically looking for flutter. It was rock solid and the acceleration was scary fast!
 
bikert said:
Some people don't mind it. I myself cannot do that. The cold dry oxygen blowing directly into my nose just kills me. The masks are better for me but also irritating in a different way. Lots of people out there who don't mind it at all.
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It's not that I didn't mind, I didn't know any better, and it was my job to be up there with an O2 mask. But the day I finally flew a pressurized airplane I never went back.
 
RussR said:
I'm interested if anyone has looked at the flutter margin for that airplane at those TAS in a high-speed descent. Aerodynamic flutter is driven by TAS, not IAS, so if you get high enough, IAS can be relatively slow but with the high TAS, you get into flutter. This would be even more of a concern if you're pushing it over for descent to attain higher speeds.

I've read it's one reason Van's doesn't recommend higher power engines or turbos with the RV-10.
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Russ,

Correct. Putting a turbo or new power plant can keep you below the published VNe (which is in KIAS) but get you into trouble from a KTAS standpoint.

However, my KTAS isn't going to be any better on this flight than it would've been at lower altitudes, so I don't see it as an issue, unless I decide to do some obnoxious descent at VNe while I'm way the hell up there (it would take some effort to get to VNe, too, given how little power I'll have at that altitude).

So, I'm not concerned about TAS-related flutter. If I were to consider modifying the power plant to add a turbo, we'd have a lot more to talk about.
 
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