How high can you go in a normally aspirated

[Rickskymaster]

Over this past weekend May26th, I went from Washington DC to pick-up my plane in DuPage.
A friend flew me out in his turbo Seneca.
I won't go into all of the details, but it turns out the Skymaster is still in DuPage and another trip will be necessary to pick her up. I had the new GTX 330 transponder installed.
That got me thinking on the way back. To top all of the clouds, we went up to 15,000 in the Seneca, no big deal in it. But with the
Skymaster, even though my book says Service ceiling is 18,000, what is the practical ceiling I can expect.

In other words, can I get up to 15,000 loaded in a reasonable time period.

I would really like to hear from normally aspirated guys only.

Thanks

Rick

[kevin]

You can get to 15,000 in a fairly reasonable time (I did in my '65 337), but your cruise speed will be pitiful. I did it to get over some weather once (with oxygen). It is not something I would want to do as a regular procedure. I remember a groundspeed of something like 110 kts... I was lightly loaded as well, at full gross, I can't comment.

Kevin

[hharney]

I HAVE A NORMAL AND I HAVE HAD A LOT OF EXPERIENCE AT THE HIGHER NUMBERS. I HAVE FLOWN MY 337C FOR OVER 20 YEARS AND MOST OF THE TIME IN THE WESTERN STATES. WHEN FLYING IN THE WEST YOU ALMOST ALWAYS HAVE MOUNTAIN RANGES TO CROSS THAT ARE ANYWHERE FROM 9 – 12,000 FT. SO MOST OF MY TIME WAS AT 10 – 15,000 FT. THE 337 DOES JUST FINE. I HAVE TO DISAGREE WITH KEVIN, I ALWAYS FIGURED ABOUT 155 KT ON MOST ALL OF MY FLIGHTS AND A FUEL USE OF 18 – 20 GAL PER HOUR. NOW IN THE FLATLANDS OF THE MIDWEST I AM FLYING AT 6 – 9 AND BURNING 23 – 25. I HAVE MADE TRIPS TO ALASKA WITH FOUR LARGE ADULTS AND ALL THE BAGGAGE YOU COULD STUFF IN THE REAR, FULL FUEL AND AWAY YOU GO. CRUISE ALTITUDES AT 10 – 12 ARE NO PROBLEM AND 15 – 18 ARE ONLY TEMPORARY BUT IT CAN BE DONE.

BTW, I HAVE BEEN TO 21,500 FT WITH 4 PEOPLE ABOARD ON O2. NOT ANYTHING I WOULD SUGGEST AGAIN BUT THE PLANE HANDLED IT PRETTY GOOD

[Ernie Martin]

My experience isn't as bad as Kevin's and more akin to HHarney's. I made a trip clear across the continent from Miami, FL to Boise, ID, across the Rockies in my prior 337D. At nearly full load I had no difficulty cruising at 11,500 ft and I made some short jogs up to 13,000 ft to go over mountains. It wasn't a rocket getting up there, but climb rate was decent. For instance, my 337G POH says that at 4630 lbs (max load, yours might be 4400 lbs) rate of climb for a new bird is in the range of 545 to 885 ft/min (depending on climb airspeed) at 10,000 ft, and 265 to 570 ft/min at 15,000 ft, all assuming a standard day.

Regarding cruise speed, I found the speeds acceptable. It's true that you're going to go slower but the economy is going to be superb, so it's a tradeoff. Again from the POH, picking a combo of 2400 rpm and 20 inHg at 7500 ft gives you a cruise of 172 mph and a range of 1155 miles. At 15,000 ft a combo of 2400/14 cruises at 138 mph with a range of 1310 miles. So it's clearly more efficient to fly at the higher altitudes, albeit slower.

Obviously, on a short trip it isn't worth it to climb high (unless weather requires it). But on a long trip (4-6 hrs) I have found that the longer time spent in the climb (especially once you get past 8,000 ft or so, when the climb gets sluggish) and the slower cruise are more than offset by the fuel savings and longer range.

Ernie Martin

[Jim Rainer]

I fly from MEM to EGE (Eagle, CO) on a fairly regular basis in a 1976 337G. First of all, you didn't mention oxygen. For absolutely sure buy a good portable kit. I have a precise flight bottle with four outlets and four canulas. I put O2 on at 10k going up and keep it on until I land at EGE (elevation 6500.) I travel about 10% under gross max. This is reccomended by mountain flying schools for all mountain flight - so should work as well in flatlands. True AS is still 150K+ but fuel burn is in the 16 gph range. I've been tp 15.5K several times and it's been no problem even in July. Climb rate is slow above 11K but you will get there. Plan descent early so as not to supercool the engines.

Climbing to 15K on a regular basis especially at gross (my plane carries 148 gallons so I have a lot of leeway in fuel load.) is probably not practical, however, I have friends who do it on a regular basis to save fuel and get speed eastbound.

Incidentally, I depart EGE with full fuel (only one on board) and climb to 14.5K to cross the passes and fly non-stop to MEM in about 6 hours at 11K buring under 17gph for the trip.

[kevin]

Hmmm... I am confused. I said I was getting a groundspeed of 110 knots. With an average permanent headwind (joke) of 10 knots, that would be 120 kts, which is very close to the 138 mph that Ernie says is book at 15,000'. Are the rest of you saying you get better than book performance? You are lucky folks...

The normals do just fine at 12 - 13, I flew mine there all the time. Getting to 15 took a while, and I got slower ground speeds than I would like, but yes indeed, it was more efficient. Above 15 I think would be impractical.

I guess the only point I am trying to make is that there is a BIG difference in performance between 10-12 and 15+.

Just my opinion, y'all seem to have faster airplanes than mine was...

Kevin

[Jim Rainer]

Kevin - my POH doesn't show anything above 12,000 as far as TAS at higher altitudes so don't have a book number. I was not keeping written records so it comes from memory pretty much and I may be a little optimistic about 150K TAS but my groundspeed dropped off very little from 11,500 to 15,500 (very slight wind effect difference.) I was at least 10% under gross. I'm going back later this summer and will do a little more scientific study.

Incidentally I climb at the top of the green (2600) but cruise at 2450. Climbing at 2800 might have a significant effect as would cruising at 2600.

[Wayne Pearce]

just as a matter of interest, practically speaking, how high do you guys go on a standard or hotter than standard day without supp oxygen, oh and for how long.


Damn cold ...... best regards ........... Wayne

[Jim Rainer]

Wayne, I stick to the regs, no more than 30 minutes if at 12,500 and no higher without O2. Actually, as long as I have a kit on board, I put the mask on at 10K. At night, I'll put it on above 6K. May not be necessary but it makes one feel more refreshed. O2 is cheap. About $15 for a filluip at the scuba dive shop. Incidentally, I am and have been a non-smoker all my life and in good physical codition. I think there is a lot of variation in people as far as O2 is concerned.

[kevin]

Jim is really right about how much oxygen requirements vary by person. Until I got my P, I regularly flew at 12,000 for an entire flight (3 hours plus) without oxygen, and up to 13,500 for periods less than 30 minutes. And anyone who has met me can tell you I am *not* in great physical shape. I have a friend, non-smoker, who *is* in good shape, yet he gets loopy if he flys all day at 10,000', let alone 12...

Individual differences are large here, I think. And erring on the side of caution is certainly best.

Kevin