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  1. #1
    Airplanes400's Avatar
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    The G forces we put our planes & jets through

    Out of curiosity, I decided to find out what kind of "G" forces my planes and jets are experiencing when I fly them. So I bought a few "G" meters and installed them into my planes and jets. I also added airspeed and altitude sensors since I was curious about obtaining that information too.

    I was surprised at the information I got. First of all, my estimates about the airspeed were within 10 to 20 mph of the actual readings I got. But the faster the jet, the more I, and others were off with our estimates as to how fast it was actually going. We were only off by about 10 mph with our estimates about my slower prop planes that hit speeds of 100 mph. What we thought was 100 mph, turned out to be 105 to 111 mph. When I brought the plane down in a 45° dive it sounded like it was going much faster, but the airspeed reading indicated just an added 5 to 7 mph. Although the engine and prop speed increased quite a bit, the speed of the plane didn't increase by much. But those extra rpm's sure made the plane appear as if it was going an extra 20 mph faster, yet it was just an added 5 to 7 mph.

    The faster jets were averaging 165 to 170 mph when I (and other people) thought they were just doing @ 150 mph. And when the jets were going close to 200 mph, we thought they were just doing 180 mph. The bottom line is, they are going faster than we think, and it is very easy for them to hit 220+ mph from a shallow dive of just 20-30°. This includes turbine and electric jets. We noticed that the size of the jet is also a consideration in the perceived speed vs. the actual speed.

    A big surprise was the altitude. What many people who were estimating my planes (and theirs) to be at 300 to 350 ft., actually turned out to be 500 to 700 ft. in altitude.

    The biggest surprise was the "G" readings I got. Before attaching the "G" sensors, I was thinking the worst I put my planes and jets through was 5 g's. As it turned out, I was putting my planes through 4 g's when I flew them normally. By normally, I mean with the average turns, climbs and gentle loops that we all do. Just the acceleration from take-off of my prop plane resulted in a 2.4 g reading.

    When I did aerobatics, rolls, and hard banked turns with my planes and jets, I got "G" readings that maxed out my "G" meter that was only capable of recording a limit of 8 "G's". I never thought I put my planes through that kind of stress.

    I then bought a "G" meter that records up to 38 "G"s. I installed those meters and flew my planes and jets again. During a flight with normal 60° banks and turns at 120+/- mph I got "G" force readings of 6 to 8, while harder and faster turns and climbs on a different flight resulted in readings of 12 to 16.4 G's. The max reading I got was 18.7 G's. Since the meter records only the highest reading during a flight, I can't tell you during what maneuver it was that this reading occurred. During that flight, I did 90° banked turns, loops, a split "S", vertical climbs, high speed dives at about 60° towards the ground and then into a loop, spins and aileron rolls.

    Also, it was very easy and all-to-quick to climb to altitudes of 600 to 800 ft. within 3 or 4 seconds. The top of my loops averaged 900 to 1100 feet, as with other maneuvers like a vertical climb which easily went to 1500 ft. and more. I wasn't the only one going to these altitudes during normal flights. Even the IMAC guys go to those altitudes. No one was able to keep their jet under 400' AGL. Good thing our fields don't have the 400' limit.

    All I can say is that it's a good thing I build my planes and jets well, and buy high quality jets like BVM. I can also understand why some of the lower-end Chinese jets come apart in flight. I think the Chinese jets aren't made for heavy "G" loads or aerobatic maneuvers. I only see Chinese manufactured jets being flown gently ... mostly high-speed passes, straight and level with normal turns (especially when going fast); never a tight 90° banked turn or a split "S", hardly any loops, and just the occasional roll. Maybe it's the owner who doesn't want to fly it harder, or is still unfamiliar or still nervous about his investment or the jets structural integrity? I don't know.

    Bottom line is that we have no idea of the stress and "G" forces our planes and jets through with just normal flights, let alone what we put them through during high-speed maneuvers. But his should give everyone some idea, and make people aware enough to possibly think to 'beef up" their high-speed planes and jets wherever possible. Especially those ARF's!!

    Secondly, what we think is just 400 ft can easily be 600 or 800 ft of altitude.
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  2. #2

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    RE: The G forces we put our planes & jets through

    Very informative post. Thanks a lot for taking the time to write it. I have to say I am always conscious of G's when flying my Boomerang Nano. That said 120mph turns pulling 6-8G is amazing! Who would have thought!

  3. #3
    MustangAce's Avatar
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    RE: The G forces we put our planes & jets through

    Were those altitudes agl or msl??

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    RE: The G forces we put our planes & jets through

    They were all altitude readings from AGL.
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    RE: The G forces we put our planes & jets through

    Could you list the equipment you used to measure especialy airspeed?
    SidGates
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  6. #6
    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through

    I used Eagle Tree products.

    The "G" sensor was mounted inside the fuselage.
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    RE: The G forces we put our planes & jets through

    I had a Jetcat sensor on my untraflash. measured 16.5 max g's on that with a P120 and 17.5 on my Sprinty power with a P-80 I was shocked to say the least!

  8. #8
    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through

    It's amazing as to how much stronger the airframes are with carbon fiber rods and laminates in the wings and fuselages.
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    RE: The G forces we put our planes & jets through

    Yup, my ultra has pulled 13.6 g's measured by the Jetcat GPS sensor.....quite and eye opener and a good reality check......would you guys go and stand on your jet wings while they were propped up??!!! I know I wouldn't and I know it's not that simple but it does help illustrate the point.

    Craig.

  10. #10
    David Gladwin's Avatar
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    RE: The G forces we put our planes & jets through


    ORIGINAL: Airplanes400
    During a flight with normal 60° banks and turns at 120+/- mph I got ''G'' force readings of 6 to 8, s
    A most interesting post but I wonder just how accurate the accelerometer was ? I ask this because the "G" in a 60 degree banked turn is always 2 (speed is irrelevant). Of course transient Gs "spikes" are always possible in turbulent air but 6-8 G with 60 degs of bank seems very excessive. That said, 4 Gs in a loop seems about right, its a good pull rate in a real jet when starting a loop.

    Beware JetCat Gs. The G is derived from GPS positions and the refresh rate (certainly on the older JC GPS) was not high enough to produce accurate results. In extensive testing, I got some really excessive readings even when flying smoothly and gently in totally calm air.
    Regards,

    David Gladwin.

  11. #11
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    RE: The G forces we put our planes & jets through

    I have a small jet making small loops. The diameter of the loops is about 25meters and the speed at half throttle is about 200mph which makes about 48G's
    /Henke
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    RE: The G forces we put our planes & jets through

    Hi David,

    good to know but my GPS is the newer version and readings seem to correlate with flying style. Even if it is close it still serves as a reality check for how much strain we put these things under.

    Craig.

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    RE: The G forces we put our planes & jets through


    ORIGINAL: Henke Torphammar

    I have a small jet making small loops. The diameter of the loops is about 25meters and the speed at half throttle is about 200mph which makes about 48G's

    I know you do, and its freaking awesome !

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    RE: The G forces we put our planes & jets through

    Very interesting reading indeed, both the G-forces and the altitudes were much higher that I would expect, and
    something to take into consideration when flying. However, I do not agree with the point about Chinese jets -
    I have owned 5 Skymaster jets, 2 of those have been the 1:6 F-16, and I roll, loop and do split S-s all the time.
    What I do not do is yank and bank like some pilots do at Jetpower Fair and other exhibitions . Yes, it may look
    impressive from one single perspective, wondering how it is possible (and how responsible it is) to fly a model
    jet in an extreme high speed 90 degree bank without it breaking apart? I fly every manuever in the book with
    my jets, but I do it like there should be a live pilot in the plane, and therefore it looks smooth and scale instead
    of toy-like flipping around in the sky. I have no idea how many G-s I pull, but I would guess that it's closer to
    what a real pilot would survive, not something that would kill him instantly..
    Tor/Jets of Norway. \" Keep your feet on the ground and keep reaching for the stars\"

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    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through


    ORIGINAL: David Gladwin


    ORIGINAL: Airplanes400
    During a flight with normal 60° banks and turns at 120+/- mph I got ''G'' force readings of 6 to 8, s
    A most interesting post but I wonder just how accurate the accelerometer was ? I ask this because the ''G'' in a 60 degree banked turn is always 2 (speed is irrelevant). Of course transient Gs ''spikes'' are always possible in turbulent air but 6-8 G with 60 degs of bank seems very excessive. That said, 4 Gs in a loop seems about right, its a good pull rate in a real jet when starting a loop.

    Beware JetCat Gs. The G is derived from GPS positions and the refresh rate (certainly on the older JC GPS) was not high enough to produce accurate results. In extensive testing, I got some really excessive readings even when flying smoothly and gently in totally calm air.
    Regards,

    David Gladwin.
    From my understanding, speed and rate of turn are always relevent. Making a turn at 50 mph will produce less G forces than making the same turn at 90 or 120 mph. G forces are proportional to speed and rate of turn (or rate of ascent or decent). I know there is a formula for this, I just can't remember or find it now. Military jet pilots are taught the formula during their flight training. Also, aerobatic pilots know the formula.

    Secondly, I can only estimate that I was making a 60° banked turn at the time because it seemed that way to me. The turn could have been slightly steeper or shallower; and I can only estimate that the jet was doing 120+/- at the time. But the turns during that flight were consistent, as far as I could determine, and I got the 6 to 8 G readings on three different flights where turns were the only thing I did.
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  16. #16
    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through

    Hi Icepilot,

    For the most part, I do fly normally. Yet I'm still surprised at the G's that I get doing the normal maneuvers. Occasionally I'd fly aggressively, but keep it to a minimum during any flight. But I don't yank and bank hard either. I'd enter the maneuvers smoothly, but a little on the quick side, then increase the rate of turn or climb as the jet goes through the maneuver.

    After reading Maj. Woody's experience with servo splines stripping, I won't be doing any steep and high-speed dives anymore, nor any really tight 90° banked turns. Those two maneuvers and a split S, seem to pull the highest G's.

    Although the airframe might withstand the G' forces, the servo splines could give way. Got to think of every part involved with the control surfaces and linkages to make sure nothing fails!

    The G meters don't cost much. Just for fun, install one in your jet and see what readings you get. Even during normal flight, I was surprised at the readings I got. It isn't hard to get 8 or 9 G's just doing steep banked turns and maintaining level flight when the jet is doing about 150 mph.
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  17. #17
    David Gladwin's Avatar
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    RE: The G forces we put our planes & jets through

    ORIGINAL: Airplanes400


    ORIGINAL: David Gladwin


    From my understanding, speed and rate of turn are always relevent. Making a turn at 50 mph will produce less G forces than making the same turn at 90 or 120 mph. G forces are proportional to speed and rate of turn (or rate of ascent or decent). I know there is a formula for this, I just can't remember or find it now. Military jet pilots are taught the formula during their flight training. Also, aerobatic pilots know the formula.

    +/- at the time. But the turns during that flight were consistent, as far as I could determine, and I got the 6 to 8 G readings on three different flights where turns were the only thing I did.
    With respect, you are wrong. (I was a military jet pilot and instructor (of instructors) ) speed is irrelevant. A 60 degree bank level turn ALWAYS produces 2 G regardless of speed, 50 mph or 1320 mph, Mach 2! At constant speed G force in a turn is a function of bank angle only, speed affects the radius of the turn.

    The formula you may be thinking of is G =1 over Cos. bank angle.
    so G in a 60 degree bank turn is 1 over .5 (cos 60 ) =2 ALWAYS !

    Regards,

    David.

  18. #18
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    RE: The G forces we put our planes & jets through

    Airplanes, speed has nothing to do with G forces felt in an aircraft. The only "acceleration" that has to do with speed is Lateral acceleration,or lateral g forces. (like what top fuel dragsters feel). Dave Gladwin is correct.
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    RE: The G forces we put our planes & jets through

    Great post and thanks to all that's added to it. Very informative stuff here.
    Scratch it till it bleeds Convert it till it chokes

  20. #20
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    RE: The G forces we put our planes & jets through

    Let me clarify ...
    I may have used the wrong term, or you may have misunderstood what I was trying to express. But this should clarify what I was trying to express ... Speed and radius of turn have a direct result as to the amount of g's. Thus, the tighter the turn and/or the faster the speed, the more g's.

    An object (let's say a person in a car) making a given turn at 20 mph will experience less sideward g's than that object (person) making the same turn at 60 mph.

    Even a centerfuge ... Spin it at 10 revolutions per minute and you get a small amount of g force. Spin it at 30 revolutins per minute and you get a higher g force reading. Spin it at 60 revolutions per minute (a higher speed) and the g force increases again.

    Here's a graph to illustrate g forces with regard to speed and radius of turn ...
    As you can see, the tighter the turn (smaller the radius) at any given speed, will result in higher g forces.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  21. #21
    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through

    The G meter I have is able to display + and - G loads on all three axis. That is how I got a reading of 2.4 G's for acceleration of my prop plane during takeoff.

    After that, I only concerned myself with the G load readings of the downard vertical (in relation to the meter) axis while flying the jets and prop plane.

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  22. #22
    Xairflyer's Avatar
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    RE: The G forces we put our planes & jets through

    Two things are getting mixed up 2g is at 60deg bank, if you tighten the turn it will no longer be 60 deg
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  23. #23
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    RE: The G forces we put our planes & jets through

    Airplanes, speed and radius determine the amount of bank you would have to bank to make a turn in a prescribed area (whether it be vertical climb or horizontal turn)- thus, if you had to bank tighter, the g-force would go up. It (load factor) is a direct linear equation for any aircraft that has nothing to do with speed (velocity). As the vertical component of lift is lost, it is made up in the horizontal component and thus, elevator is required to maintain altitude. this is the same for all aircraft, and gravity doesnt care how fast you are going. Google "aircraft load factor chart" and you will see. This was one of the hardest things for me to grasp when starting pilot training.

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  24. #24
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    RE: The G forces we put our planes & jets through

    ORIGINAL: Airplanes400
    We noticed that the size of the jet is also a consideration in the perceived speed vs. the actual speed.
    Should be no surprise here at all. A 747 appears to be crawling down final approach when compared to a 737.

    Likewise, a "hot" EDF appears faster than an Ultra Bandit when both are flying at the same speed, i.e. 120 mph.


    ORIGINAL: Airplanes400
    ... and a split S, seem to pull the highest G's.
    This is very true! Too high of an entry airspeed on a Split S is a great way to get a jet to come from together to apart...either from excessive 'g' or the Earth getting in the way of the flight path


  25. #25
    Airplanes400's Avatar
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    RE: The G forces we put our planes & jets through

    In the early 90's, I had a T-38 Talon break in half during a 'split S' as I tried to level it off from the dive. Part of it was due to a design flaw where the top of the intakes were too close to the lip at the top of the fuselage (about 3/4 of an inch as far as I can remember), and there wasn't enough support/structure/fiberglass in between. (Before the days of carbon fiber.) But the biggest part was that I entered the maneuver at full speed (like you wrote sluggo), and pulled too many g's.
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