Aerobatic Loops

[Ross McWhirter]

I can do a loop but only on a small tight radius. Can anyone offer advice on how to do a relatively slow and wide radius loop, both inside and outside loops.

[Former Member]

[This posting has been removed]

[cymaz]

The size of loop is dependant on the power to weight ratio of the plane. The less power you have the smaller the loop.

I agree with Tom. Set up the plane before you start the loop...wings level, not too close to you.

If the wind is coming from the left.. Enter the loop at full power apply elevator just to your right in a gradual, progressive manner. Slowly start to release elevator over the top and then slowly reduce throttle progressively from about 1 / 2 o'clock. When you have the loop correct you will suddenly realise how much time you have to correct for drift as the plane is coming down out if the loop.

If you try and make the loop too big the plane runs out of speed around 11 o'clock. You then try to keep the loop large by applying elevator. This flattens out the top. The speed drops further and the plane exits the loop almost straight down. Maybe a little over dramatic but I hope you can get what I'm droning on about.

This the plane properly trimmed ? Side thrust and lateral balance ok? This is excellent 

Edited By cymaz on 21/08/2016 06:48:04

[Former Member]

[This posting has been removed]

[Paul Jefferies]

As an aside...... I once met an ex-RAF pilot who had done an exchange with the USAF and had a ride in an F16. He told me they had come burning down the runway before pulling up into a loop........... the top of which was 29,000ft ! (That's 5 1/2 miles!)

As Cymaz said, it's all down to power to weight ratio.

Paul

Edited By Paul Jefferies on 21/08/2016 08:17:08

[cymaz]

Posted by Paul Jefferies on 21/08/2016 08:12:01:

As an aside...... I once met an ex-RAF pilot who had done an exchange with the USAF and had a ride in an F16. He told me they had come burning down the runway before pulling up into a loop........... the top of which was 29,000ft ! (That's 5 1/2 miles!)

Paul

Edited By Paul Jefferies on 21/08/2016 08:17:08

I'm sure you'll find a quad at the top of that loop

[Biggles' Elder Brother - Moderator]

The guys have mentioned most of the main points. Three things I would add:

1. You're not flying everywhere at full throttle are you? Good loops start with more power. You can't have "more power" if if are already at full power! So enter, as Cymaz describes above, then as he says add the power as you ease in the elevator. As you go over the top of the loop, take the power out, gravity is in the driving seat know so you don't need so much power.

2. Your airspeed will vary through the loop; medium to enter, slowing towards the top and then picking up again on the downward side. As your speed varies the effectiveness of your contriols varies too! When you go faster the controls are more sensitive abd effective. Remeber to allow for this. So you need bigger control movements as you go over the top of the loop for example than you will do on the wat down. This is why, you have to be prepared to come out of the elevator slightly on the way down or the loop will tighten on that side and be a sort of mirror image "9" rather than a circle.

2. Don't expect the model to just track straight and perfect through a big loop unaided - you are going to have to fly this one! Watch the wings and the skew all the way round. Be prepared to add aileron and/or rudder as required. (Yes,.... rudder - shock, horror!) This is particularly important at the points where you are changing throttle. As you throttle up to enter the model will tend to pull left - a touch of right rudder needed. Similarly, when you throttle back over the top it might yaw right - it might not! - but of it does some correcting rudder will be needed. And of course any side wind will cause drift and will need correcting. You get the idea, a big loop is not just about circular flight - you have to work, pro-actively, to maintain the track as well as you go round.

Outside loops are just the same but the other way round! There is, I think, an unreasonable fear amongst us of the outside loop, or bunt. Fact is if the model will loop then it will bunt - in terms of the physics they are identical! So things to remember for the bunt:

1. Unlike the loop - which you should enter flying into wind - enter the bunt flying downwind.

2. Throtlle back, push eleavtor. Let the aircraft complete the curve to about the 4 o'clock position.

3. Start to feed in the power, aim to be at full throuttle by 6 o'clock. Watch for torque pull to the left here as you throttle up and if so correct with rudder.

4. Climb up the other half. You might need to feed elevator out as you come towards the bottom, then in again as you come back to top - because of the variation in airspeed and control effectivness as you go round just like in the loop.

In the end - practice makes perfect!

BEB

[Martin Harris - Moderator]

I'm treading on dangerous ground here, knowing your credentials BEB, but I have to disagree with part of your point on bunts. While you're correct that a "0/0" model will find a bunt pretty much the same as a loop, surely anything with an asymmetric wing section will fly it very differently? In my experience, many trainers which will loop OK run out of power to get back over the top with their inefficient inverted wing sections...or even struggle to pull out of the downward stage with very mildly set up elevators.

Just don't want to see sales of bin bags rocketing!

Edited By Martin Harris on 21/08/2016 11:04:11

[Engine Doctor]

Hi Martin . I have to agree with BEB here. If you or you student is still flying a trainer with the elevator still set "mildly" then they are not ready to fly a bunt ! Decent control throws will be needed as will the ability to manage them.It is very challenging  the first a beginner fly's a bunt as it seem wrong for some reason . That is of course if you have to do your own building and repairs. My son's didn't have any fear of flying any outrageous aerobatics as any crashes were miraculously fixed by the " garage fairy" or in this case "Dad".

[Martin Harris - Moderator]

I was just a little worried that relative beginners who had flown a few loops might take BEB's advice that a bunt is as simple as a loop at face value and try it with an unsuitable model. After all, the loop the loop (as opposed to a "proper" aerobatics loop) is so basic that many people let a first timer have a go on the buddy lead to introduce a little extra fun for that first experience!

It's unfortunate but it seems that when a beginner's bunt goes wrong or confidence evaporates with the model plummeting at 45 degrees inverted, they seem locked in one plane and don't realise that recovery using a half roll and up elevator is the better option than bending the elevator stick against the stop or even trying to reverse the direction and pull through - both actions often resulting in extreme disappointment!

Edited By Martin Harris on 21/08/2016 12:11:37

[Biggles' Elder Brother - Moderator]

Ah - but there are two factors at play here - the model and the pilot! I'd stick with what I say, if the model cam loop, then it can bunt. OK at the margin of the very larest circle possible you might lose out a bit with some wings that work less well inverted - but I really believe that is a marginal effect.

When beginners get into troubkle in a bunt I think 90% plus of that is fown to them - their inexperinece and panic - not the nodel. The truely fatal one of course being, when in trouble, to "pull" at the bottom - a big mistake! I always tell anyone learning to bunt tell themselves very firmly several times beforehand hat if this goes wrong they are going to roll - not pull!

BEB

[john stones 1 - Moderator]

Yep biggest danger in a bunt is pilot, usually go's pear shaped right at the start by pushing too hard and screwing out, i would teach bunts by rolling inverted and starting bunt from bottom, build confidence first then onto proper ones, loops ? more power bigger loops.

John

[Martin Harris - Moderator]

We're obviously in total agreement with our second paragraphs BEB, but next time you're instructing with a lowly powered flattish bottomed wing trainer set up for a beginner, try looping and bunting and I think you'll find the bunt very different - if even possible. Or are you saying that sticking a larger engine in and increasing the throws will allow it to bunt? I would then consider that to be a different model, personally. The fact that, as you mention, beginners do get in trouble with the bunt points to the fact that there are differences.

I suppose we should also consider airframe issues - while I'll happily loop my 1/4 scale Cub - with load bearing wing struts, you will never find me trying to bunt it! Any wash-out built into the wing will also become wash-in...

But - I would certainly agree that the bunt is feared unreasonably. It's a manouevre that I enjoy (with the right model!) with only a little more difficulty involved than an inside loop - I will admit struggling a bit with correct roll correction at the bottom while learning them for my B.

Edited By Martin Harris on 21/08/2016 14:42:43

[Peter Christy]

I'm afraid I'm with Martin on this one. I have a couple of models that loop very well, but full down elevator simply produces very fast forward flight! To bunt, the model need enough elevator power to force the nose down and under. Many trainer type models are set up with positive incidence between the wing and tail, and as the speed increases, so does the "up elevator" effect of the positive incidence. At the very least, this may result in a bunt of enormous proportions - maybe bottoming out below ground level! And in some cases (think "Super 60" and similar), all that happens is an enormous increase in forward airspeed accompanied by a loss of altitude, with no indication of the model ever bunting. This latter case is often followed by a sudden loop - possibly accompanied by a folding wing - when the down elevator is finally released!

Again, the advice about throttling back around the loop depends on the model. My current "aerobatic" mount is a "Kingpin", a design dating from 1963. Back then, we didn't have control systems that allowed for the throttle to be operated at the same time as the elevator. They were designed with a thick wing and a very blunt leading edge, which gives a nice constant speed around the loop, without having to jiggle the throttle at all.

In fact the handling is so benign that today it would probably be regarded as an advanced trainer! Back then it was considered a "hot" aerobatic ship - but that was because the control systems available were much cruder than today's!

So whilst BEB's comments may be fair enough for some modern designs, they are by no means universally applicable. I wouldn't recommend trying a bunt with any basic trainer!

John Stones advice about trying it from the inverted first is very good.

Having said all that, the Kingpin bunts beautifully!

--

Pete

 

Edited By Peter Christy on 21/08/2016 14:49:54

[Biggles' Elder Brother - Moderator]

I've bunted; the ePoneer, the Arising Star, the Boomerang, the Irvine40, the Tiger Trainer and many others. I knoiw this because its a standard "party piece" of mine when beginners complain they can't loop the aircraft . I've experinced no issues with these aircraft, beyond the usual which is many of them don't like being inverted at all because of a combination of wing profile and dihedral. But, that is exactly the same problem in the loop as in ithe bunt - it just occurs in a different place and at a different airspeed. So, I reiterate, all my experince tells me - pilot to one side - if it will loop, it will bunt. True - if it loops badly it will bunt badly as well - but it will do it. I have never come across an aircraft that will loop but won't bunt!!

BEB

[Peter Christy]

As I say, I've got one that loops a treat, but full down elevator just produces very fast forward flight. I am quite happy for you to attempt a bunt with it. I guarantee you won't be able!

--

Pete

[john stones 1 - Moderator]

Bunts need more care with your trainer etc than a purpose designed aerobatic jobbie, needs more thought/input from pilot but i'd agree with BEB, i see no reason why your B can't be done with a trainer, i did my test with a clipped wing cub, bunts no problem unless you push too hard, then you're in danger of screwing out. Looped lovely and big as well

John

[Ross McWhirter]

Thanks everyone for all the responses. This is my first post on the forum and I didn't expect so many replies so soon! Some great advice there that I'll try out .

[Martin Harris - Moderator]

I can't argue that many trainers will bunt - they often have semi-symmetrical wing sections and as power is cheap these days, are very adequately powered. But this is digressing from the point that it was claimed that any model that will loop will bunt - and I hadn't considered Pete's vintage style models! Of course, it also depends on your definition of a bunt - if you count a desperate semi-stalled flop over the top with full power and elevator applied then many more will "qualify"...but I'll bet most of those models will loop properly - even if a dive is required before entry.

[fly boy3]

On a lighter note, many years ago I was using my 60 powered Acrowot to do loops and bunts. It did large loops with throttle control on the way down. Not knowing any different all them years ago the Acrowot did large bunts wth throttle wide open all the way round. What a dope I was then, also very lucky on many occasions. I now know different LoL. Cheers

[Peter Jenkins]

Ross, what sort of aircraft are you flying and what is the power plant? That's the first part of the equation when wanting to fly larger loops. If you pull up into a vertical climb with full power applied how far will it climb before it runs out of speed? If the answer is, not far, then forget trying to do big loops because you haven't got enough excess power. If the aircraft just keeps climbing then you have the basis for doing large diameter loops.

[john stones 1 - Moderator]

Important question is did you enjoy it FB3

All the rest is opinions n chat, enjoyable as well, unless we take ourselves too seriously

John

[Former Member]

[This posting has been removed]

[Peter Jenkins]

Alternatively, roll inverted and then push down elevator. At least you know that if you get to the top of the bunt you'll get round it safely!

[Tim Cheal]

The Loop

I am sorry to come back to this topic, but have pondered this from the sidelines up until now and although I wrote this some days ago my computer has been upset about something and running i..n..c..r..e..d...a..b..l...y slow.

You originally asked:

I can do a loop but only on a small tight radius. Can anyone offer advice on how to do a relatively slow and wide radius loop, both inside and outside loops.

The simple answer is ‘don’t pull so hard’, or fly faster and pull the same amount, but this would miss some important detail. About 2 years ago (January 13 issue I think, but I apparently don’t have access to the digital archives anymore) Shahid Banglawala explained how to fly a loop. In it he talks about pulling up and then starting to ‘push’ over the top. I have to say I was more than a little surprised; as an ex RAF pilot, and having taught aerobatics as an RAF QFI for many years the last thing you do on a loop is push. The loop is a positive G manoeuvre. But here I needed to back down and think about the objectives. The loop, as flown by full size aircraft is most usually an egg shape, witness the heart formed by the Red Arrows when flying opposing loops from the same starting point. However, the objective of RC aircraft loops is to fly as close to a circle as possible, and this requires a different skill. But first we need to consider what makes our loops egg shaped if left to their own devices.

Of course, our RC aircraft will possibly slow down as we climb the loop which will change our control effectiveness and radius of turn. But more significantly we need to think about the effect of gravity on out manoeuvre. If we are the right way up (at the start of our looping manoeuvre) our aircraft will be subject to 1G, acting vertically down through our aircraft. To pull our nose upwards we need to increase the angle of attack (pull the stick back), and this in turn increases the G being felt on the airframe. Typically, on a full size aircraft, you need about 4G during the start of the loop. More pull, and you get a tighter radius (OK, this is limited by available lift and/or G, but lets assume this is the case for the time being), less pull, and you get a larger radius (so in theory this answers part of your question). So far so good, but our 4G pull is made up of 1G already acting on the aircraft, so we are, in effect, using only 3G to turn the aircraft.

Now consider our aircraft at the top of the loop. We still have our 1G acting vertically downwards in relation to the real world, but this is now pulling our aircraft around the loop and pulling our aircraft down in the direction we want to pull, in fact to fly level upside down we need MINUS 1 G, so in fact the 1G being provided vertically downwards is effectively 2 G (the difference between MINUS 1 and 1 is 2).

If we can sustain our 4G pull all the way around our loop, we would have in effect 3G turning us as we start the loop, and 5G turning us at the top of the loop. This is known as the combat egg, and fighter pilots use this effective increase in turning performance to great effect to increase their manoeuvrability.

So, to fly our round loop, at constant airspeed, we would need to reduce the pull over the top of our loop. This effect is somewhat compensated for in real aircraft by variations in airspeed, but our model will also be affected. So, as we loop our aircraft the amount of pull we require reduces to keep our loop round, and then increases again as we return to the right way up at the bottom of the loop.

Continued below.......