Blu wrote:I guess i was thinking that in the video stol preformace wasn't the issue. The runway was plenty long and he got in the air.

What i was thinking is that a Stitson is a better backcountry/STOL plane than say A36 bonaza. I say this because if i was going into a strip like "mile high" or "vines" with 1/2 fuel and a just me on a cool day the stitson is by far my first choice.

But in the situation we see in the video the stitson was taking off at close to its service ceiling leaving little to no room to climb, while i would submit that the BO would still have at least a few thousand feet of climb left in it and with almost a mile of runway there was ample room to get it off the ground and the wheels up while in ground effect.

I guess im just arguing that a good "back country plane" and a good "high country plane" is not always the same thing when there is plenty of runway.

I have an S35 Bonanza, a few hundred pounds lighter than an A36 but the same wing and engine. I don't know the weights of the folks in the Stinson so I'll just use my plane at gross weight of 3300 pounds, far more than the Stinson could ever hope to be. Using the conditions of that day and assuming no wind my plane gets off the ground in 1500 feet and then climbs at 800 feet per minute per the POH.
Assuming 4 FAA standard folks for 680 pounds and a half tank of gas I would be 350 pounds under gross. Takeoff roll now 1300 feet and rate of climb 1100 FPM. Those are book values, I have VGs so would be slightly better.
Any Bonanza is far superior to a Stinson for that mission. As for what's the better plane the question is what's your mission? I sold my 182 7 years ago for my Bo and have taken it everywhere I ever took the 182. For a typical camping mission the 182 needs a couple hundred less feet for takeoff or landing but then gets smoked in climb and cruise and will use more gas than the Bo. That can be offset if you can use car gas, although the older Bo's can use that too.

As for what's the better plane the question is what's your mission?

Sunbrella, rainbrella, and pass over the sagebrush when the plane is rolling in a slight depression? Look down in flight?

Are there any low wing birds?
lc

Really, Bonanzas are great planes, no doubt about it. I just 'work' at being happy with what I've got.....

If I did my math right?, the 165hp Stinson was making 120hp at 9000ft DA.
Or a 230hp would put out 168hp.

Cary wrote:Theoretically a long wing with a short chord should be less affected by high DA, because that's the sort of wing used on almost all very high altitude aircraft, such as the U-2, high performance gliders, etc.

I am tempted to agree. The Luscombe has a long wing and a fairly short chord and I think it does pretty well in high DA situations. I am quite cautious but there have been a couple situations where I have tested the limits.

Bonanza Man wrote:

Blu wrote:I sold my 182 7 years ago for my Bo and have taken it everywhere I ever took the 182. For a typical camping mission the 182 needs a couple hundred less feet for takeoff or landing but then gets smoked in climb and cruise and will use more gas than the Bo.

That is my impression of the Bo as well, except the 182's climb gradient seems considerably better than the Bo. I've followed one out of Cabin Creek earlier this summer and was smoked getting to Cold Meadows, but I was able to out climb the immediate terrain way better. I was actually carrying more gas and load then the Bo. All things considered, it really doesn't matter for 99% of flying, and the speed and ROC of the Bo are really enviable. The Bo also has a couple more inches of more prop clearance than my 182, which is more of a practical biggie to me than any performance differences.

Does anyone care to conject how much HP either would lose by being excessively rich - like full rich - at high DA? The video seems to show full rich and no leaning procedure during the runup - doesn't mean he didn't do some leaning - hard to tell.

But I would guess 10-15hp additional power loss due to excessive richness. I've no experience with the frank 165 or the o470 - but I routinely lean O and IO360s and see 30-60 RPM delta between excessive rich (not even full rich - just my startup/landing/takeoff rich) and properly leaned for best power at altitude. This seems to translate to 5 knots or so indicated when in flight. 5 knots might have made a big difference on the Stinson at gross and 9000ft DA.

Terry wrote:If I did my math right?, the 165hp Stinson was making 120hp at 9000ft DA.
Or a 230hp would put out 168hp.

Cary wrote:Theoretically a long wing with a short chord should be less affected by high DA, because that's the sort of wing used on almost all very high altitude aircraft, such as the U-2, high performance gliders, etc.

The U2 had a high aspect ratio to achieve low induced drag near the stall speed, where it flew most of the time up high. It's important for climb performance, since they have more HP left to climb with, but DA degrades aircraft performance similarly. For breaking ground, wing area is more important than aspect ratio.

Some of this is summarized at
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083224_1993083224.pdf
"It was found that the shortest take-off distances are obtained with low span loadings, power loadings, and aspect ratios and that air drag and ground friction are relatively unimportant at these low loadings".

No doubt failure to lean is a factor in available power. Years ago when I was instructing in Laramie, a family flew in from somewhere flat and low (I think their last stop had been North Platte) in a fairly new for the time 172, 160 hp. They borrowed a car and drove to town for lunch, and when they returned and loaded up, I made the comment "don't forget to lean". The pilot sort of blew me off as if he didn't hear me, though I think he just didn't understand. So they loaded up, fired up, and taxied for take off.

The slightly visible exhaust was a give-away. He did his run-up and apparently didn't notice anything amiss, took the runway and started his take-off roll. But pretty soon he was taxiing back, everyone unloaded and came in, and the pilot was visibly shaken. "There's something wrong with the airplane. I didn't have enough power to take off!"

So we had a discussion about leaning, the effects of density altitude, expected take-off roll, climb rate, etc. He asked me to show him the leaning technique, so I accompanied him out to the airplane and showed him at the tie-down (no airplanes behind it). Once again they loaded up, taxied out, and this time he leaned for the taxi and obviously for the take-off, because they took off after rolling maybe 2000' or more, made a shallow climbing turn toward the north, and continued on their way.

How much difference proper leaning would have made to the video'd airplane's performance, I can't say, but it's certainly noticeable. Flatlanders/lowlanders rarely get any training in proper leaning for higher elevations, usually something like "lean as appropriate when above 3000'". But they look at the altimeter, not considering density altitude. So a good many never lean at all except to shut down the engine at the end of the flight. And of course, in addition to the sparse information in the POHs/owners manuals, they usually say "full rich for take-off", never mind that that assumes being able to make full power, which can't happen at high density altitudes.

In addition to a full rich take off, a full rich taxi can cause some plug fouling problems, which may or may not have played a part in the video'd accident. I nearly always lean aggressively for taxi, and the one time I didn't (at OSH a couple years ago) is the only time I've had any problems with plug fouling as long as I've owned my airplane (0-360 Lycoming).

Cary

Good post, Cary. I was taught early on that leaning in relatively high density altitudes at lower elevations can be rather useful as well. A 100+ F day at 300 msl in the valley can necessitate a little leaning all the same for takeoff power. Just watch the CHTs on climbout.

How do you lean for takeoff? No egt or cht, how does one lean for takeoff when surely your not going to full power while holding the brakes so you can set mixture. I really don't know. The Luscombe has a stromburg carb so I rarely lean unless I'm pretty high; most people with the stromburg just wire the mixture full rich and don't mess with it. I don't get an increase in rpm when I adjust mixture; I just lean it till it gets rough then richen it back up some.

whee wrote:I just lean it till it gets rough then richen it back up some.

That way.

But the mixture will be different for each throttle position. So you just set it at run up and figure it will be good enough for takeoff??

whee wrote:But the mixture will be different for each throttle position. So you just set it at run up and figure it will be good enough for takeoff??

Good point.

In my case (O-470) at my 5000' msl home base, I run it up to 1700 RPM, lean until the onset of RPM reduction (~10 RPM), enrich to restore the RPM, add a full 1.5 to 2 turns, and continue the run-up. I find that when I'm level at 6000' at full power after take off, peak EGT is pretty close to 2 full turns out while leaning, so I'm convinced the method keeps the engine 'rich enough' on takeoff in my case.

I really don't see a RPM rise at all while leaning out for the run up way down low, and the few times I've been down really low, I just leave it full rich (under 3k').

My 1962 POH says always leave it all the way rich. That seems inadequate since I gain very nearly 100 RPM on run-up at an 8200' msl strip near here (Granby) between full rich and leaning out as described. The EGT check on climb out from Granby gives very similar results to down lower. I think it is probably a reasonable proxy for proper mixture on takeoff.

I have yet to receive first hand training from someone who knows, but the book for high altitude operations says you should lean to maximum RPM (peak power) during any run-up above 6000ft, and leave the mixture there for takeoff.
It wont be the same ammount of leaning required for peak EGT / rough running. Peak power should come a lot sooner.
Apparenty you should "always" do this for takeoffs above 6000ft..... .. .. . . .

whee wrote:But the mixture will be different for each throttle position. So you just set it at run up and figure it will be good enough for takeoff??

I've seen a technique where the mixture is set during the takeoff roll. The max power mixture position is really pretty wide but falls off steeply once on the lean side of peak. So, without EGT, and assuming you are not absurdly critical on runway length, you start the takeoff roll, pull the mixture out until you find the cliff, believe me, you will know it when you feel it, and then push in again until you feel the surge in power. Takes a lot longer to write it down than to do it. The short excursion LOP at full power won't hurt anything and you can get pretty good at doing it without looking inside.

On the fully instrumented Maule, I found a useful benchmark. Many times I flew from sea level to 12,000ft or more before setting cruise. EGT's are useful because they show variations almost instantly, much faster than CHT changes, but they are fingerprinted to each particular plane depending on where the probes are mounted in the exhaust, etc. I went out one day, at sea level, close to standard temp and took off full rich. The hottest EGT was 1280* F. That number appeared every time I took off under those conditions, so that was the gold standard I used when leaning during climb. I would lean until my hottest EGT was 1280* F. Now, I would never recommend 1280 to any other airplane as I believe each plane has its own characteristic temp.

That IO540 was also very kind to plugs IF you leaned it to the point of starving as soon as she started.

YB

Battson wrote:... you should lean to maximum RPM (peak power) during any run-up above 6000ft, and leave the mixture there for takeoff.

Sounds fine. Best power often happens around 50-75f rich of peak anyway. I was interested in the idea that mixture changes with different throttle settings, and setting things up for peak RPM at a reduced run-up RPM might not actually give best power at full throttle (at least in my O-470).

If I run up at 1700 rpm and go a couple turns richer than peak RPM, and then check for mixture pretty soon after takeoff at full throttle, I find I am about 50-75f rich of peak, which I believe gives me the best power from TCM's data. This means the best power mixture control position changed with throttle position. If I were to lean to max RPM at the reduced RPM at run-up, I think that means I would be running leaner than best power at full throttle during takeoff (and not be operating at max power after all).

Good responses, thanks. I didn't figure anyone would go to full power during run up to set the mixture, good way to ding a prop. Sounds like you just have to know your plane and how much fuel to add after setting mixture during run up.

Yellowbelly wrote:That IO540 was also very kind to plugs IF you leaned it to the point of starving as soon as she started.

YB

Do you think that would burn the valves at all, idling really lean (localised increases in combustion temperature)? Obviousy there's no real power involved mind you.
Sounds like a good engine management technique if there's no associated risks to other parts.

whee wrote:Good responses, thanks. I didn't figure anyone would go to full power during run up to set the mixture, good way to ding a prop. Sounds like you just have to know your plane and how much fuel to add after setting mixture during run up.

I've heard of another trick and that's to find the sweet spot while you're still in the air before you land, assuming that conditions are going to be similar during takeoff. Visual setting of the mixture isn't as preferable as actually setting by the rpm stumble, but it would allow you to avoid that prop-dinging high rpm runup.

lesuther wrote:I was interested in the idea that mixture changes with different throttle settings, and setting things up for peak RPM at a reduced run-up RPM might not actually give best power at full throttle (at least in my O-470).

That is true to the best of my knowledge, I was taught to always (and I do) re-lean following a change in power setting - and to never increase power without enriching the mixture first.