Well with the old manuals, the bigger problem is lack of data. In many cases, you need to extrapolate as there simply is no data e.g. for take off and landing above 5000 ft. Also a lot of other stuff is missing, other is quite badly misleading (range?) .
Basically, I usually take the manuals and then fly to figure out how accurate it is for that airframe. You are very right, quite a few airframes will have massive performance issues. On the other hand, they also do not take into account mods like in my case thePowerflow Exhaust or in other cases new cowls or windshields, which turn the old cabin into a J type cabin.
In the 10 years I operate my plane now I found it pretty much makes book figures… not least because of the powerflow exhaust. For cruise, the Aspen’s TAS and the Shadin fuel flow meter have helped to determine this, for runway performance, I’ve had possibilities to get pretty accurate results too. For Samedan, 600m is the first third of the runway. You are right it won’t be totally accurate but you can easily see if you are in the ballpark or not.
Apart, being conservative is certainly a good thing. e.g. always go to the higher elevation in the manual (in my case, most airfields of Switzerland are around 1500 ft AMSL, I always use the 2500 ft tables). Likewise, one can compensate for lack of data with an adjustment of temperature. e.t.c.
In cruise you can sooner or later define a bias, a factor to correct the book figures if they are too much off. In my case, my normal cruise and long range cruise figures are pretty much spot on, while it does not quite make the marketing figures for high speed cruise. And obviously, range needs to be recalculated using the regime you are actually flying. Which btw is why a lot of folks think their manuals are wrong, they simply don’t fly the actual power setting they refer to.
I vividly recall one guy who claimed his Grumman Tiger was a 120 kt airplane. Well, when he sent a picture eventually, we found him out… he referred to IAS he was seeing on his ASI. At the altitude he was flying, TAS was 138, which is close to book. His ears are still ringing from that one I think.
Mooney_Driver wrote:
So even the 1965 POH’s are not that far off, as long as the sometimes optimistic top speeds and range figures are ignored :)
I still have my doubts about that. The good thing is that aircraft engines mostly make their book power thanks to the amount of maintenance that is spent on these. That is certainly not so true when it comes to classic cars from that Era. But all the dents, missing wheel spats and so on must make a difference. I believe that when you really compare apples to apples and take off at MTOW at exactly the published conditions you will measure a difference. Probably you will barely notice a difference without measuring because at 60 knots it is hard to determine the exact spot where the aircraft left the ground. But measuring it is going to make a difference.
boscomantico wrote:
Doing the calcs vs not doing the calcs does not change your actual performance one single bit.
No, but obviously doing the calcs should make you aware of the situation. Guesswork doesn’t really help.
boscomantico wrote:
Some people seem to think that if they do these calcs, and the numbers from that thing called manual somehow says that the flight is
possible. I tend to be more cobservative with that.
Me too. I reckon the operative word here is “somehow” or rather how exactly. If the numbers come out “just” then extra care is well advisable. If there is a lot of tolerance, then there should not really be a problem.
boscomantico wrote:
I would not do any takeoff or landing operations in a low-powered non-turbo plane.
Question would be where does low power end and where can you be comfortable. Again, I think that is not only horsepower dependent. Also, mixing for the take off run can make a difference. We did that in the C150 and much more carefully in the Mooney (which is not supposed to be leaned above 75% power as per POH). In the C150 the difference is noticable, in the Mooney about 1-2 Inches MP.
Most people say 180 hp non turbocharged should be ok at these altitudes. Which makes Archers, Cherokee 180, Robins, C/G Mooneys, Grumman Tigers, Jodels/Robins with 180hp e.t.c. the kind of plane which can reliably take off there. And that tends to be true, if of course they are loaded to specification. Most of those give a service ceiling of 15-17k ft, which even with DA’s of 8000 ft on take off in Samedan will mean they can climb to 10-12k ft AMSL. That should be sufficient for most passes and even some direct crossings.
I’ve taken off repeatedly with my C-Mooney, of which once at MTOW and about 7000 ft DA and it was a non-event.
POH figures for this are difficult to get, as it only provides figures to 5000 ft, not 5600. OAT that day was 20°C, practically no wind, so we elected to take off on runway 03 for better terrain clearance. In order to compensate for the 600 missing ft, I took the next higher temp in the POH, which was 26°C, which results in a take off run of 580m and a total distance of 998 m. With an 1800 m runway, that is ample. Climb rate indicated at 7000 ft is around 550 fpm, so actually we got a tad more.
Actual figures: Airborne at around 600m take off roll, climb after clean up was about 550 fpm. We reached 12000 ft at Zernez, which was the turningpoint to the South, direction Ofenpass.
Several times I’ve taken off there on 21 which requires a turn down wind, mostly 2 on board, with DA’s up to 8000 ft. Never was an issue. We had one condition where Malojawind was present, which meant we had to accelerate to a higher climb speed before turning down wind, but we still reached circuit altitude at mid downwind.
So even the 1965 POH’s are not that far off, as long as the sometimes optimistic top speeds and range figures are ignored :)
On the other hand, there is the famous sequence of pictures of a Jodel 180hp which almost relanded after the initial 180 turn after take off on runway 21. There are cases of others which barely made it out. On the other hand, C172’s and Warriors are up there all the time and without incidents. I would wonder how a Cheetah does there, as it has a reputation for low service ceiling and climb rate.
The C150 I had up there when I did my training in 1983 managed to get out of Samedan on an average day with two on board and half fuel on 21 and reach the altitude needed to cross the Furka Pass without needing to do extra miles.
On the other hand, I recall crossing the St. Gotthard in my F150L with 2 on board and about half fuel and we had to fight for every ft until we got to the crossing altitude. That was definitly not comfortable and something I’d like to repeat.
Doing the calcs vs not doing the calcs does not change your actual performance one single bit.
Some people seem to think that if they do these calcs, and the numbers from that thing called manual somehow says that the flight is
possible, it will be possible safely. I diasgree with that and tend to be more conservative.
I agree that if it‘s summer and its in the high mountains, I would not do any takeoff or landing operations in a low-powered non-turbo plane.
I agree Frans, no point in doing such stuff in summer or when the conditions are not perfect.
Actually, most calcs are pretty straighforward. Simply way too many people don’t take into account density altitude. If DA is 8000 ft on the ground and your plane can reach 10’000 ft (DA) on a good day, then climb will end at somewhere around 7000 ft AMSL. That is insufficient to go over most passes. And you are right, C150ties don’t do summer in the alps, or at least only in the early mornings.
And no, nobody is calling anyone cowards or inexperienced. On the opposite. Not doing something may be the result of higher maturity and experience than doing it against better knowledge.
Most Dimona’s flying today, do have 100HP or 115HP, so that is perfectly fine for Samedan. I’m not saying that it is impossible in a 80HP Dimona or Falke, but it feels way too risky for me. All “parameters” must then be perfect, in other words: Low-density altitude, no winds etc. As soon as you’ve high DA, Malojawind etc., you have very less options. For me a clear no-go. Call me an inexperienced coward, but I don’t like to calculate on the last bits of minimum runway length, climbing rates, and learned “tactics” from alpine flying lessons. Looking at Swiss aeroclubs, which are located in the Alps, they all have some good horse-powered airplanes. They don’t do that without some valid reasons.
For sure I wouldn’t have a problem to cross the Alps from Altenrhein towards Venice in a C150, but from Samedan to Münster in Summer? No thanks.
I’ve seen plenty of Dimonas in Samedan and have done my alpine introduction with a C150 there decades ago. I’ve seen 172’s and Warriors up there too. Münster is also quite high and a lot shorter. DA can be 8000 ft or more in Summer. But on a cooler day it should work fine with the right tactics.
Ambri can be sizzling in Summer, but it is actually not that high up, just about 3200 ft. Downvalley the departure is not so bad. Saanen as well.
Les Eplatures is also quite high, it actually qualifies over 1000m too.
I guess in the end most of this can be done with due dilligence and careful checking of the performance calcs. Sometimes it takes a bit of planning or to wait a bit until the temps are not as brutal as they can be in Summer.
This topic seems to be about flying from flatland to flatland over the Alps, but not about landing in the Alps. Thinking of departures out of Ambri, Münster, Saanen, Samedan or so, I would never fly an 80HP Falke SF25 out of it, not even an 80HP Dimona. Even with the most standard-powered C172’s, I would have lots of respect, even when just one passenger with baggage comes along.
You could touch RVSM altitude with the Rotax 914 
europaxs wrote:
Ibra wrote: Does turbo let you fly high with less HP ;) ?Trick is, that the power remains at altitude.
… and it does on Rotax 914, right?
Last time I heard drone operators routinely fly their 914-power machines above FL3xx, so FL380-390 apparently (allegedly?) happened frequently.
