Thus, for example, when broomsticksays: “Your statement makes no sense.” That’s acceptable. That’s challenging what you said, not who you are. That’s very different from “you’re an asshole” or “you’re a prick.” WHile I agree that broomstick used somewhat provocative language, it was always about your posts, not about you. (Well, almost always, the crack about “skygod” was over the line, too.)
If you want to call another poster an asshole or a prick, the forum called The BBQ Pit is the one where flaming and gloves off are allowed.
Thanks for the tips. The “skygod” comment was absolutely the least of the insults. Broomstick appears to be the master of personal insults just within the limits of forum rules. I suppose I’ll have to learn to do the same when dealing with posters such as him.
Wow. A whole lot of bickering about credentials and erroneous assumptions.
Lemme try and define some terms and conditions. First, for the purposes of this post, let’s define a barrel roll as a maneuver in which the aircraft starts from straight-and-level (or near-level) flight, and follows a helical flight path, returning to its original altitude and direction of flight, but offset from its original line of flight.*
During the maneuver the aircraft’s altitude first increases, reaches a maximum when the plane is fully inverted, and then decreases, returning to the original altitude. Simple physics will show that since the aircraft is pulling 1 g just to maintain level flight, the initial change from level flight to ascent must necessarily incur a g-load greater than that of just gravity; likewise at the end of the maneuver, changing from descent back to level flight will again incur a g-load greater than that of just gravity.
It may be possible to pull a steady g-load during the barrel roll, but that steady g-load will necessarily be something greater than 1 g (and your final altitude will be lower than your initial altitude).
*The helix angle determines the offset of the final flight path from the initial flight path. If the angle is zero, the maneuver is a simple vertical loop, and final/initial flight paths coincide. If the angle is 90 (or the helix diameter is zero; same thing), the maneuver is a simple aileron roll.
Perfectly reasonable. I think it follows that if you’re willing to relax these constraints so the aircraft can recover at a lower altitude into flight that isn’t straight and level, then the maneuver can be done without exceeding 1g.
The plane would have to exit the maneuver at the greatest descent rate it experienced during the maneuver. Even then, I’m not so sure you could do anything that looked much like a barrel roll without exceeding 1G. Maybe I’ll write a simulation and see what can be done within that limit.
To never exceed 1 g, you’d have to gain zero altitude during the initial stages, and as Ziploc noted, finish in a pretty severe dive; indeed, when fully inverted, your downward acceleration (in an absolute frame of reference) is 2 g’s. the final descent rate/angle would depend on how rapidly you completed the maneuver, i.e. for how long the aircraft was not devoting its 1 g of lift completely toward offsetting gravity.
I just ran a quick sim in Excel. Starting from level flight, a 1-g barrel roll which takes 5 seconds would result in a final vertical speed of almost 110 MPH (9680 ft/min). :smack: I finally realized this is essentially the same as freefall: the aircraft’s lift vector makes one complete revolution, and so it cancels itself out for the duration of the maneuver, and earth’s gravity is all that’s held constant for that time. If you perform a 5-second, 1-g barrel roll at 400 MPH (~350 kts), you’ll finish in a 16-degree decent. Cut your forward velocity in half, but still take the same time to do the maneuver, and your final descent angle will be 33 degrees.
Viewing the video (see at 0:54), it looks like it took Tex a solid ten seconds to complete his 707 barrel roll. No way was that particular event a 1-G maneuver; his final vertical speed would have been nearly 20,000 ft/min.
Been a while since I played with a flight simulator, but shouldn’t this be easy to investigate with something like Microsoft’s flight sim? try a number of variations on the basic barrel roll, and record the event so you can observe control inputs, flight paths, and g-loads?
Thought experiment: Consider a plane with no practical limit on its airspeed (a fighter jet would probably work here). Starting from straight and level flight (hopefully from a very considerable altitude), nose the plane over smoothly. Once you’ve reached a vertical dive, you can do a nice round, slow, large-diameter barrel roll with extremely low G-force.
Assuming the barrel roll starts and ends at the same altitude (thus, a “straight and level” roll, or at least a direction of flight), and assuming you have the World’s Greatest Pilot perform the maneuver with the least amount of g-force required at any given point throughout, what is the smallest maximum g-force required by the maneuver?
You can get as close to 1 as you want, with the time needed to perform the roll being longer the closer you are to 1g. (This assumes that you have enough power to not lose speed during the long, slow climb portion of the roll)
It could probably be done so that passengers without windows didn’t know it happened.
Annecdotally, I have done a barrel roll with about 1.5g’s or so according to the G meter.
So… we have empirical evidence that a barrel roll with 1.5 g maximum loading is possible. If I recall, that is within the tolerances of “big airplanes”, and probably wouldn’t be noticed by many hypothetical passengers, particularly if done smoothly, g changes were gradual, and they weren’t allowed to look outside.
True. But let’s say the dive is constant rate. That would give you a constant 1G right there. Now you’re also tracing a spiral path. This would give you centripetal acceleration which would put you above 1G. Perhaps if you were in a continuously accelerating dive…
Given arbitrary time and power you could certainly follow the path of a proper barrel roll while arbitrarily approaching 1G, but it wouldn’t be much like a traditional barrel roll in which the pilot and passengers feel positive G(s) in their seat at all times - at least not if its the maneuver I imagine you’re describing.
Interesting… so that’s identical to what I said earlier about perhaps being able to do one that a passenger wouldn’t detect, but an IMU absolutely would. Remember when you told me I clearly had a very poor understanding of how planes fly? No apology necessary - I’ve encountered your type plenty.
My thought experiment is certainly not assuming a constant rate of descent. If you had such in a vertical dive, the G-force resulting from this would be pushing you forward, not into your seat. So the (rather limited) force due to a large-diameter barrel roll would not directly add to the 1G from your constant rate of descent.
I wasn’t sure, but assumed that’s what you were suggesting.
True, but it would still be 1G at that point.
It would add perpendicularly. So you’d have 1G straight down (in a constant rate dive) + the centripetal G’s from flying the corkscrew. The result would still be greater than 1G. But yes - in an accelerating dive you could maintain less than one G vertical, and perhaps make a full circle without exceeding 1G net.
Sorry Broomstick, but it’s wrong to call a barrel roll a 1g manoeuvre. When people like Tex Johnson say it’s a 1g manoeuvre they’re misspeaking. It should be a positive g manoeuvre and it can be a low g manoeuvre but any time you pitch up from level you must increase the g, and you cannot recover from a dive or initiate the manoeuvre from a dive without exceeding 1 g.
Your C152 flight manual is either poorly worded or you haven’t understood it fully. Assuming a low powered aeroplane like a C152, to perform a barrel roll you’d enter a dive until you had the airspeed you want (can’t remember off the top of my head, 110 knots?) and then you must pitch up through the horizon to commence the manoeuvre. You cannot do the initial pitch up through level without exceeding 1 g and in something like a C152 you’d be looking at around 3g. This is true regardless of whether you start from a dive or straight and level.
Theoretically you could barrel roll or loop an aircraft at 1.000001g, but you’d have an incredibly low pitch rate and would need a lot of performance to maintain airspeed through the roll. The highest g loadings in a classic barrel roll or loop are at the entry and exit.
Xema, I think your thought experiment works but it doesn’t meet the classic definition of a barrel roll where you start and finish in level flight. The act of pulling out of your dive is where the gs come in, and you must pull out at some stage or hit the ground, so by performing your manoeuvre in the dive you are committing to pulling out of the dive and therefore the manoeuvre still must involve more than 1g even if this happens after you consider the roll to have finished.
