Well its my opinion based on doing RV acro
"Wrong" is a strong word.
You can do loops all day long with 4 or 5 g's at entry & exit (standard don't kill yourself disclaimer applies). You certainly don't need to though. 3-3.5g's works great for just about everything.
We can agree to disagree, but that's my opinion. It sounds like we agree, but certainly you can use 4g, 5g or 6g pull-ups but WHY? Its really poor form. I think you miss my point.
The word "wrong" may be strong, but it's the correct word in my opinion. The other way to say it, there is
"NO NEED" to pull more than 3.5g's to make a good loop.
You say 5g's. OK, why not 6g's? My main concern is if you start at 5'gs you may end up at over 6'gs during the recovery, especially if you screw it up. If you're pulling more than 3 or 3.5's to initiate a loop, you're wasting energy and it's a less elegant maneuver. If you do competition acro in a RV, you do have to pull more g's to say in the acro box. However we are talking about learning and beginners acro.
The bottom line is RV's have a "fat" highly cambered wing that do not like load factors over 3g's. Pulling more than 3-3.5g just bleeds exponentially more speed off. Why does Van say "keep it light"? The lower the angle of attack the less drag, and the drag curve has a slope on it that gets steeper with AOA (load factor). Also when teaching I've made a few observations, one being new acro pilot's almost always over control & pull too many g's. Ask for 3g, they pull 4g.
The IAC (international aerobatics club) says a LOOP is started with a 3-4 g's pull-up;
LINK So that is what the IAC says. Pulling more initial g's in a RV just gets you a tighter loop or a very egg shaped one. My worry is if you're going too fast over the top, the recovery at the bottom can be way too fast, closer to Vne than I personally like or is safe. Now I'm not saying to under do the pull-up or entry speed either.
I find people fly too fast and pull too hard out of fear. Pilots have worries about stalling and doing a inverted flat spin? I'm not sure you can even intentionally do an inverted flat spin in a RV? (any one done this?) Pilots fear being too slow over the top, so they start faster and pull harder (which is counter productive to maintaining speed). Yes you can get slow and stall. So what. What if you stall at the top? LET THE BACK PRESSURE GO AS USUAL. The plane will do what it always does, the nose drops and the plane flys again, finish the loop. If you really mess up, the plane will roll upright (naturally due to dihedral), and than you than recover from a nose low attitude (power idle, wings level pitch up to level).
When I teach a student a loop, I have them intentionally stall at the top of a loop, inverted of course; I tell them to pull back harder on the stick, causing a stall buffet. The plane buffets, and its no big deal. Than I have them release the back pressure. WOW, the plane flys again as smooth as can be with no snap roll or inverted spin. People also worry about "floating" over the top like that is bad, but they don't understand the forces and angle of attack. First again not to "float" is wrong. Stall speed is real low at 0-0.5 g's, which is the ideal over the top pos load factor (according to the IAC
LINK). Some where in the 0-0.5g over the top is correct;
anything more is wrong.
Entry speeds for loops can also be over done. I'm not going to recommend since Van has those, but it can be as slow as 140 mph. I like 140-160 mph, but it varies with plane, weight, density altitude, engine and prop. Like load factor of pull-up you can go faster but you can also exceed Vne if you screw up, but not so much with a loop but stuff happens. Just be careful of the Split-S, the entry should not be over 140 mph, since speed will increase through the whole maneuver which is all down hill.
I rather stall at the top of a loop, upside down (it does not matter right side up or down a stall is a stall), than getting the nose pointing straight towards the ground screaming near Vne. Pulling too many g's at the initial pull-up
can result in high speed and high g recoveries. None of this has anything to do with making the perfect LOOP, just a safe one and giving more margin to the g and speed limits. None of the above is a substitute for a competent instructor and flight training.