Demonstrated service ceiling

[tps8903]

Hi folks. I purchased a set of Bearhawk plans for review. I plan a scratch build over about 10 years. Should be finished in time for my retirement. Or soon after. Has anyone demo started a service ceiling limit with the O-360 and the O-540 at or near gross weight? I'd like real life numbers. After building my first homebuilt I don't trust factory numbers..... This stat is important to me as I plan on flying in high level terrain. Thanks, Chris

[tps8903]

I meant demostrated. Darn auto correct......

[jaredyates]

Hi Chris, I don't know of anyone that has yet. I have a spreadsheet for predicting performance that seems pretty accurate when I have been able to verify it. It predicts a climb rate of 500fpm at 7000, and a zero climb rate around 16000, which is obviously into supplemental oxygen territory. I've had it over 10,000 at Max Gross, and I've had it higher than that at lower weights. Those numbers are all density altitudes, and they do not account for any fuel burn to get there. This is with an engine that produces around 185 hp at sea level. At lighter weights, the zero climb rate gets up into the flight levels. For the guys with the bigger engines, I doubt they will have been able to demonstrate an absolute or service ceiling without a clearance to get into class A airspace. If you are truly planning to spend most of your time at high altitude and I weights, I think you'll want to focus your research on the larger engine options.

[whee]

Where you going to be flying Chris? I've had a 180hp 4place up to 14k MSL when loaded to ~2400lbs. Could have gone higher but didn't need to.

[tps8903]

I have every intention of putting around the world in this plane in retirement. So at a bare minimum I have to get over the Greenland ice cap which has a minimum cruise altitute of FL13. If I can't get over that......then I can't access the other side. I could always cheer on global warming and hope it shrinks over the next 10 years... I'd like to stick to an O-360 if possible. I assumed an O-540 would be up to the task. I plan on equipping the plane with old fashion nav equipment for the trip (NDB, HF Radio) etc are common in the north so my panel will likely be fairly heavy and the O-360 will leave a lot of room for the extra weight and I imagine gets better range. That being said this will be a two person trip with no backseats. So I imagine the plane can be at less than gross with all the gear I need. It will be equipped for IFR, but only used when necessary, I prefer VFR flight, and won't depart if I expect hard IFR. That's the mission profile and the bearhawk appears to be the best fit. (It's not a speed trip. It's a see the world trip). On a side note.....I know the dangers of trans Atlantic flying in a single engine plane, so any nay sayers need not remind me. I'm a dreamer and a do'er. It's gonna happen.

[Battson]

I thought I heard a story of someone (for some reason I thought it was Pat?) taking theirs up to 23,000 ft with just two aboard. With O2 of course. Unhelpfully, I can't find it...


The 260hp IO-540 still has plenty left at 13,000 - over 500 ft / min. But the biggest problem is of course the MAP dropping away, at 13k your seeing about 19" or something similar at WOT, which is less than 50% power. If you need to go high as part of your mission, you absolutely need to consider turbo-normalising the engine.

[Enewton57]

My 180hp equipped Bearhawk flew up to the Leadville airport in Colorado, elevation 9927 ft. From there it was flown up to 14000 feet at gross weight and still had a little climb in it (300 for) this was in winter time so pretty cold temps. Eric Newton - Long Beach, MS http://mybearhawk.com

[tps8903]

Thanks for the replies. Looks like I'm on the right track. Regarding the comment regarding turbo normalizing.... I understand how it works and the practical benefits of it. However I have no actual experience with turbo normalized aircraft. Is there a fuel economy penalty for adding a turbo or supercharger? I understand you can operate at a higher power setting at altitude, so yes you burn more fuel. However say we use the above example of 19".

If I run the engine at 13,000' naturally aspirated, vs throttling back to 19" while normalized, will I burn the same amount of fuel? or will I burn considerably more fuel with the turbo engine.

My instinct tells me that 19" burns "x" amount of fuel no matter what is attached to the engine. And if you want to use the benefit of the turbo and push it to 23" you will burn the same amount as a regular engine at 23" at a lower altitude.

Thanks,

Chris

[Battson]

Yes I think you're right. The fuel burn should be very similar.

Of course the air is much colder at higher altitudes, so the engine produces more power at "x" fuel flow. So where 23" & 2300 is about 65% at sea level, it might be ~75% at 13,000 ft; presuming you can get 23" (I can't).

[tps8903]

On a related note there are some interesting options for bolt on updraft superchargers on the market. The one from G3I ignitions looks really nice for $8k. I think I like the simplicity of the supercharger over the turbo (no complicated exhaust routing, and reduced heat of intake air). There appears to be a manual by pass on the supercharger to bypass it at lower altitudes and a vernier control to close the waste gate to engage the supercharger at incrementally at altitude. There is a 4 hp penalty for using it, but that will be made up for at altitude. It says it will operate at sea level up to 8500', then starts to taper off at that point. So presumably 13,000' will be equivalent to about 4,500' performance numbers.

[Pat Fagan]

I just happened across this post. I did do a gross weight climb to determine service ceiling with my normally aspirated O540. I climbed to 17999 but was denied a clearance higher because I happened to be underneath a MOA that started at 18K. That was several years ago so I don't recall any performance details. It was still climbing, but not very fast. Pat