Most folks are unaware of just how much the G load rockets up as the speed increases. To maintain the same diameter of turn, if you double the speed the G load quadruples, since the equation is related to velocity squared. So if you are in a 2G manouevre and then double the speed while pulling ever harder back on the stick to keep the manouevre the same size, the G load will hit 8G! If you quadruple the speed, the G load will go up 16 times, to 32G. Typical sports models do 50mph. Jets can achieve 100 or sometimes 200mph. I have seen a well known jet pilot try to crank a big jet around tight curves like a sports model, he doesn't seem to realise he is not getting say 4G but perhaps 30G. A few weeks after I saw him do that, the model blew apart in the air, no wonder! So if you double the speed, but want to maintain the same G load as before, the diameter of the manouever must increase by a factor of 4, not 2. If you treble the speed, say from a 50mph sports model to a 150mph jet, the diameter of the manouevre must increase by a factor of 9 to maintain the same G load. Hence gliders at low speed do tiny loops at 4G, aircraft at several hundred mph do huge loops at 4G.

Loops present interesting G load variations. Assume a model flies a loop that is perfectly circular and at a constant speed all the way around. At the bottom the load is 3G. What is the load at the top? 1G. The load in level flight is 1G to start with, so the G meter reads 1 even before you start the loop. If it reads 3G at the bottom, then 1G is normal gravity and 2G is the loop. At the top, you still have 2G from the loop, but now the 1G of mother earth is reversed, so is deducted not added to the loop G. Hence, 3G at the bottom, 1G at the top.

What if the model flies a perfectly circular loop but the speed at the top is half the speed at the bottom? At the bottom, it is 3G. what is the G at the top? Would you believe it is minus 1/2G! Again, G due to loop is 2 at the bottom. The speed has fallen to 1/2, and the speed factor is squared in the calculation, so the load has fallen to 1/4 what it was at the bottom. Therefore the load due to loop is now just 1/2G. But the model is inverted, deducting 1G, the total load is minus 1/2G. So now the load on the plane varies from +3G to -1/2G in a perfectly circular loop where speed at the top is half what it is at the bottom.

In level flight, the wing produces an acceleration of +1G. This is set by altering the elevator, too much produces more than 1G and a pitch up, too little produces less than 1G and a pitch down. Push far enough forward and the wing will produce an acceleration of minus 1G. Roll inverted and the elevator must now be set to produce an acceleration from the wing of minus 1G to maintain level flight, funnily enough being the same setting as it was to produce minus 1G when upright. At a constant speed, the ele setting determines G load whichever way up you are. Now fly that perfectly circular loop at constant speed. At the bottom the ele must be set to produce 3G. At the top it must be set to produce 1G, which is the same as level flight, i.e. not pulling back at all, but at neutral. If you have lost speed and now need less than 1G to maintain circularity, the stick might actually be in the down position at the top of the loop. A lower speed will usually let the nose drop anyway, so the ele will be set at the eqivalent of whatever it would be in upright flight to produce minus 1/2G at the lower speed. Watch most model fliers do a loop, and you will see they hold the stick back a constant amount all the way around. That's why their loops are egg shaped. Now you know what to do, you can ease off the elevator as you go over the top and let your loops become a lot more circular. Don't forget to start pulling back again on the downline though!

Harry