They they should absolutely stop doing that. (And it wasn’t just Tex Johnson - I was also told that face-to-face by an airshow pilot who spent 30 years in the business and presumably would know better). That is, of course, a serious problem with “dumbing down” explanations. I am now pissed off with several people I know in real life who should know better but apparently have been spouting misinformation to those of us who aren’t in the “club” called aerobatics. Well, they can now stop whining about how “misunderstood” they are since obviously they’re contributing to the problem. If they can’t honestly explain what they do they should STFU.
Possibly a little of both, as I am not an aerobatic pilot. But I will quibble on one detail - it is NOT a C152, it is a C150 and it is specifically an aerobat - I realize the differences are subtle but they do involve such details as different Vne speeds and different best glide speeds. I hope to never need to use the Vne of an airplane, but when there is a 5-10 mph difference in best climb and best glide speeds between different models of the C150-152 series I think it’s best if the PIC is aware of which number applies to the plane the PIC happens to be in at a given moment. Pretending there is no difference whatsoever between models in that series is on par with making misstatements about the g-force of a aerobatic maneuvers. It’s sloppy. Sloppy and aviation don’t mix well.
It’s also the reason I wouldn’t use the flight manual as a textbook for aerobatic maneuvers - I’d use a real aerobatics instructor for that.
For a C150 you use 130 mph as an entry speed according the flight manual, which would be 113 knots.
(One of the first differences I noted between C150’s and C152’s is that the 150’s have their speeds in mph and the 152’s in knots in the manuals. That’s fine if the instrumentation on the airplane matches, but I rented one such airplane where that was not the case - requiring the pilot to remember to convert figures in the manual to what the instruments on the airplane read. I don’t view this as a good thing. Imagine someone used to thinking in knots for C152’s stepping into a C150 marked in mph and blithely assuming the same numbers apply - hence, I get picky about knowing which model you’re in and which numbers apply to that particular airplane.)
Does that 3 g figure come from actual observation while performing said maneuver, or is it a guesstimate based on the size/power of the airplane? Would a larger or faster airplane have a higher or lower g force involved?
I strongly suggest you use NEITHER if you want to learn aerodynamics (or attempt to teach aerodynamics to people that have studied it and used it all their lives).
In 1988 a pilot named Murilo de Lima e Silva did not only a barrel roll (“tonneau”) with a 737-300 but followed it with a downward spiral. It happened in Brazil and he was trying to neutralize a hijacker who had already killed his co-pilot and wanted to crash the plane. With the manouver he suceeded in saving the plane and the passengers.
It’s been 40-some years since the 747 was introduced. By now, somebody at Boeing must have fed all the voluminous data they have on the planes into a very sophisticated computer and determined whether or not you can safely do a barrel roll with one of those puppies.
A Very Sophisticated Computer? With Very Sophisticated Software? Running a fairly accurate model of the performance envelope and flight behavior of a 747?
C’mon, someone here must own a copy. Fire it up and try a few different barrel roll configurations; see if you can complete one without exceeding max g-loads or airspeeds. Let us know the results.
I have little doubt that a 747 has the power and structural integrity to perform a barrel roll. But I suspect the IMU will not let you command a bank of greater than 60 degrees, nor a pitch of more than +/- 30.
If Microsoft Flight Simulator is regarded as authoritative (or at least highly accurate) by aviation junkies, I’d be interested to know, too. Hell, we have folks who are willing to pan-fry their own semen in response to a request from fellow Dopers - this should be a no-brainer!
I feel kind of puny asking this after the bickering session, but back to Cecil’s column:
Doesn’t it seem like Mr Johnston, at least, would have been confident that a 747 would do a roll w/o any problems? He was so confident of the 707, and the fact that the stress was so minimal, and the maneuver so safe, that he essentiall did the first one live, in front of a world audience.
I know nothing about planes other than a general sense that mine will probably crash, but it seems to me a barrel roll, especially if the corkscrew helical pathway is wide enough (as opposed to a pure aileron roll) is not that big a deal. I’ve sort of always thought even an Immelman (half-assed; maybe but not perfect) would be do-able in one of the big planes I fly every week as a frequent flyer…
One would have to see the control inputs to better gauge what’s going on; it looks like the pilot in that video may have been inputting down-elevator while inverted, which would help to keep the nose up. Also, not much up-elevator during the rest of the maneuver, making it more like a simple aileron roll.
Tacho, do you have a cite for this? I’m Googling and I can’t find anything about it at all… it doesn’t show up in Wikipedia’s list of aircraft hijackings, for example. List of aircraft hijackings - Wikipedia
Properly used, MS Flight Simulator can simulate some aspects of aviation quite reliably. On the other hand, you can also turn down the reality and “cheat”. Although pretty good for what it is, I think that there are many who would refuse to accept results from it whether positive or negative.
Here’s the kind of question I wouldn’t expect MS Flight Sim to answer correctly:
When taxiing (below stall speed obviously), is it possible to raise your gear in a DC3?
It seems to me when aerobatics pilots are describing the maneuver as 1-g, they are talking about the load that the pilot/passengers feel and not the airframe stress. I could be wrong, but that is what I glean.
I also wonder if a barrel roll can be performed keeping the airframe stresses in the range experienced by normal maneuvers such as turns and such. Comments in this thread suggest so. Chief Pedant said:
All that shows is a cartoon of a plane going over. We don’t see any instruments or airframe readings, and have no idea what settings were (are there “cheat codes?”). I wouldn’t hold that video as authoritative of anything.
And it occurs to me that if a maneuver is required to start and end with straight and level flight and not exceed 1G, then pretty much the only maneuver possible is: straight and level flight.
I agree. It’s something I’ve heard a number of times and I’ve heard it repeated by non-aerobatic pilots who’ve taken the word of Tex Johnson as gospel (and why wouldn’t you? He was Boeing’s test pilot and he rolled an airliner, surely everything he says about it is accurate?) I think in his case he’s probably playing down what he did and in his attempt to understate the stresses involved, he’s ended up saying something that is factually wrong.
Sorry, I didn’t see that you’d written C150 rather than C152. I learned on a C152 and subsequently did my initial aerobatics in a C152 Aerobat (they made an Aerobat version of the C152 as well.) I’ve never flown a C150 and recognise there are some differences, albeit minor.
Fair enough. You’d appreciate the concerns our crews had a few years back when we had a new aircraft added to the fleet. Unlike all of our other aircraft, its fuel guages read in kilograms. We used a generic maintenance release form for all of the aircraft, and that form is where we enter the fuel added and used and also where we do our “3% check”, which is a check of the gauge readings against calculated fuel figures. Fuel could only be entered in the form in pounds. So we were receiving fuel from the refueler measured in litres, the aircraft gauges read in kilograms, and both litres and kilograms had to be converted to pounds for the paperwork. We could almost see straight through the swiss cheese before we even started the engines. Thankfully it’s been converted to pounds.
I can’t specifically remember what sort of gs I’d pull in a C152. I know that in the Pitts it was about 4g for a loop and 3g for a barrel roll, though you could easily make it more like 2g if you wanted. But my physical memory of flying the C152 was that it was around 3g.
I don’t think any assumptions can be made about the g force required just from the size and speed of an aeroplane. A faster aeroplane may have more energy available to allow for a gentler pull up without losing too much speed, but a slow aeroplane with a lot of power can do the same thing. A large aeroplane will lose speed quickly in a climb unless it has sufficient power to compensate. I guess it’s more to do with power to weight ratios and manoeuvrability.
Also something that is often neglected with a barrel roll is that although you may be able to perform one with the g meter reading only 2g, there is a twisting moment due to the simultaneous rolling and pitching. The outside wing may be experiencing significantly more g than the centreline of the aircraft. For this reason it’s advisable to maintain a buffer between the g limit for the aeroplane and the gs pulled during a rolling manoeuvre. Also if you’re rolling an aircraft with low g limits, avoid rolling while pulling the maximum gs, that is, do most of the rolling after the initial pull up and prior to the final pull out.
I don’t think the B747 has any means to prevent you from getting any attitude you like. Unlike an Airbus, it’s not fly by wire and the pilot has direct control of the control surface positions.
Sort of. I don’t know about the underlying physics but the accuracy of a particular aircraft model depends on how much time has been spent getting it right. My experience is that it’s ok for normal flight but it falls apart near the edge of the flight envelope, e.g., near the stall. I’ve had to make significant tweaks to the config file to get an FS2004 aircraft to fly to the numbers that I observe in the real aeroplane. There is also a fundamental problem with the way the trim works in PC flight simulators where you can run out of control movement if the trim is not set somewhere close to neutral.
I’m sure plenty of people have rolled the full motion simulators used by airlines for training though.