DLG flying skills

[StraightEdge]

Earlier advice was to get yourself a Radian powered-glider (foam, ready to fly).

That way you can wonder off to a bigger space (lockdown is much more relaxed than it previously was) and learn to fly properly without the stress of handling a mini DLG on super-short flights on hard ground.

The motor will give you the opportunity to climb to a decent height each time you get a bit low ('two-mistakes high' is the expression) and practice basic skills and even try to recognise thermals.

Then, when you come back to your existing model, you'll be much more instinctive on it.

[tomc]

I do have a foam electric plane. can fly that no problem, even from and to the back garden. It just seems to be a big jump to the DLG.

thanks

Tom

[Neil Harrison]

So manufacturers cg settings give you a ‘guide’ to where it should be.

A lot has to do with personal preference on how each pilot likes the model to react to both control input or the way the model responds to lift/sink.  This will change given different conditions, like a calm day cg more rearward and then changing more to the nose when the wind I strong to give more stability.

The best way to derive at the cg neutral position is the dive test, you can then work from there.

You will be amazed when you experiment with different cg positions and how much it affects the way the model flys.  Just remember that a forward cg is safe and the further back you go the more unstable and responsive it becomes.

https://www.rc-airplane-world.com/trimming-your-rc-airplane.html

[thermaldoctor]

4 minutes ago, pete beadle said:

Hi all

I've seen more models diving straight into the ground while the pilot attempted the dive test on their own than I've had salads!

For me, the secret is to get the model flying more or less right before 

I'm intrigued about the "down elevator pulse" though, I would have thought that moving the elevator at that critical point, just after launch, would ruin any chance of "catching" it, if the pilot realised, however quickly, that its dive wasn't going into the "desirable behavior" sector.... hey ho!

Regards

Pete

BARCS1702

I think the diagram is showing the plane in flight not straight after launch..!

[StraightEdge]

With a DLG on could always start the dive at a gentle 30° which should give the OP more than enough time to see what's happening before easing back on the elevator stick.

With a power model of course you need to enter a 45° climb then half-roll...!

[Neil Harrison]

Dive test is not hard!

Just be sensible and make sure you have recovery altitude...you can always pull out of the dive anytime...

Once the dive is initiated it will not take long before you see it’s tendency to either pull out or tuck under.

 

[Martin O]

Tom

Lots of good advice been given. I picked up on the bit where you mentioned flying speed and stalling.  Just wondering if you have dialled in any camber for normal cruise flying? No camber usually means fast flying. I was also wondering if you use the rudder much? It might be something to work on to help get the flying accurate. 

Good luck. 

[tomc]

Hi

Yes, I have camber dialed in for camber and thermal flight modes. It does slow the model down, but it still seems very stally, if anything its easier to fly in speed mode as it generally flies faster so is not so close to stalling. I have added 3g of nose weight and will see how that helps, just waiting for no wind. Due to a heavier boom than the standard one my model is now at a flying weight of 143g, compared to the 125g quoted in the manual, I wonder if it is just too heavy? I do use the rudder, but probably not as much as the ailerons.

Tom

[SilentPilot]

@pete beadle

Are you just messing with us here?
I thought you knew about the Dive Test.

Flying trimmed ‘level’ (no glider can maintain true level) has the attitude, or more precisely the AoA, set to a particular angle.
The Dive test is designed to show what elevator trim you have in order to maintain this. So no it won’t dive or climb out of its ‘level’ state if it is trimmed for a set speed.

Diving increases the airflow over the elevator. This magnifies what the elevator was doing, if it pulls out of the dive then the elevator was up slightly to offset the nose heavy component. If it tucks then that is because the elevator was down due to the tail heavy component.

[SilentPilot]

It sounds like the tests that ended badly were because they weren’t done high enough!

[Marc RC pilot]

 

Question about the dive test/CG if you please:

Can someone explain why the glider goes up on the test if it is nose heavy/CG is forwards? 

 

Thanks

[StraightEdge]

Because, as Silent Pilot pointed out earlier, a nose-heavy plane will need some up-elevator trim to maintain normal level flight:  this will then reveal itself as soon as airspeed picks up in a dive (fingers off the controls that is!).  It doesn't have to be a vertical dive, a fairly shallow one will suffice.

Move the CG back a bit (either by adding a smidgeon of tail-weight or by moving something heavy in the nose, like the battery, backwards a bit) and less up-elevator trim will be needed to maintain level flight.

Move it back too much and down-elevator will be needed in level flight.

All these things are revealed by the fingers-off-the-controls extra speed of the dive-test.

[mikef]

Marc,

I think your version of the diagram is aimed at aerobatic models!  I was typing the following when you posted....

The dive test is a way of judging the static longitudinal pitch stability of an aircraft.  This type of stability is a measure of an aircraft's tendency to return to its trimmed speed after a disturbance in that speed.  In the dive test, we start with the aircraft in steady gliding flight at constant speed.  A pulse of nose down is given and then the control is returned to neutral and left there (Ie back to the steady gliding position).  A speed increase will result.  A stable aircraft will then proceed to pitch nose-up and slow down.  An unstable aircraft will want to speed up more so it will pitch nose down.

The dive doesn’t need to be a long distance, just enough to speed the aircraft up noticeably.

If you built a kit or a proven design and put the cg where advised, you will get no surprises in a dive test as long as you are high enough when you start it.  You can always pull out.  I can't understand why anyone would attempt this test straight after launch - even from a hill.  You need to establish a steady glide first.

CG forward to increase longitudinal static stability and back to reduce it.

You can get a rough idea of where you are by launching your aircraft much faster than its trimmed gliding speed - if it's stable it will pitch up.  DLG flyers know this situation!

There's a lot of confusion around this subject - some of it compounded by the way things are described.    I’ve seen a model that glides nicely with good stability being called “nose heavy” because there's slight up elevator relative to the tailplane in its glide trimmed state.

Pitch stability is a matter of taste and depends on the purpose of the aircraft - aerobatic pilots may well go for an 'aft' cg.

For thermal soaring, I like an almost Free-Flight degree of pitch stability - you can just let the model fly itself and watch it show you the lift.  If the model is marginally stable you will need to make more inputs and this will mask what the model is trying to tell you.
But it's a matter of taste.

 

 

 

[StraightEdge]

Free flight pitch-stability is an excellent comparison.  My other 'hobby' is indoor free-flight scale (rubber, CO2 and electric) where a good degree of positive wing-incidence combined with slight nose-heaviness results in stable, slow flight.  This is analogous to float (or thermal) mode in a thermal glider, where, although one has control of the model in flight,  a CG that is too far back will result in a model that is likely to be far too twitchy and will constantly stall and lose height, whereas with the CG too far forward it'll be too stable, fly faster and not signal lift as well, etc.  The happy medium depends on your skill-level.  As an learner/intermediate I tend towards a CG that is very slightly forward (i.e. a shallow dive test will result in a slight gradual pitch-up) whereas more experienced fliers will experiment with moving it gradually back until they find the sweet-spot that works for them, the model and even the particular conditions on the day.

 

[thechalster]

What Mike f said.   Spot on.  Read it carefully,  then read it again.  Go flying do some tests,  make some adjustment.  Read it again!

 

 

[mikef]

38 minutes ago, Marc RC pilot said:

...

Question about the dive test/CG if you please:

Can someone explain why the glider goes up on the test if it is nose heavy/CG is forwards?
...

I f the CG is moved forward and the model Is retrimmed for a new steady speed, on the test, it pitches up more due to the increased pitch stability.

There's a common misunderstanding In your question -  the use of the term, “nose heavy” is the clue.  It's in another post just above too!

If an aircraft is trimmed for a nice glide (or level flight at cruise throttle if powered), and you then stick a lump of weight on the front, it would be, as some would say, be “nose heavy”.  It would pitch nose down and the speed would increase.  If it was stable in pitch (with its new cg,) it would settle in a faster glide (or powered slight descent).  You now have a new ‘trim state’.  If you want to slow the model down again, some ‘nose up’ trim would be required.  At this new state, it doesn't look “nose heavy” anymore.

 

[Marc RC pilot]

38 minutes ago, StraightEdge said:

Because, as Silent Pilot pointed out earlier, a nose-heavy plane will need some up-elevator trim to maintain normal level flight:  this will then reveal itself as soon as airspeed picks up in a dive (fingers off the controls that is!).  It doesn't have to be a vertical dive, a fairly shallow one will suffice.

Move the CG back a bit (either by adding a smidgeon of tail-weight or by moving something heavy in the nose, like the battery, backwards a bit) and less up-elevator trim will be needed to maintain level flight.

Move it back too much and down-elevator will be needed in level flight.

All these things are revealed by the fingers-off-the-controls extra speed of the dive-test.

That makes sense SE! thanks 

[StraightEdge]

Mike, I bow to your superior knowledge and clear explanation.  But, while the term nose-heavy might be misleading on its own, is it not a useful shorthand as long as its referenced alongside trim (which is how it was in the posts above)?

[mikef]

StraightEdge,  You posted when I was in full Pedantic Anorak” mode - I'm sorry if I seemed to pick on you.  I'm sure I've used “nose heavy” myself in the past.
I come from the aircraft industry and forty years of competition free-flight Model flying, so these things are in my blood.  I'm a newcomer in F3K (14 years).

Each person finds their own way of explaining things, often using their own take on the terms involved, and they all get along with their projects just fine.  Problems only arise when they try to explain things to folks with a different vocabulary/understanding or some 'expert' butts in and confuses everybody.
I'm reminded of conversations I used to have over many years with an Estonian, Andres Lepp World F1A Champion 1989 (Yes - shameless name drop).  We spoke using our schoolboy German it was our only common language and we got on pretty well most of the time.  However, one day we got totally stuck.  Fortunately, there was a real German flyer at the same contest and he was enlisted to help.  It was useless - neither of us could understand the real German and we went on in our own sweet way.

I think between us all we have explained the dive test and how to use it.

[StraightEdge]

No need to apologise Mike!

Your story reminds me of an episode many years ago when I was teaching craft skills to adult students.  Like any good school-teacher I typically used a combination of words, pictures and practical demonstration/practice to impart understanding in each lesson.  I was explaining something to one chap when his body-language must have indicated to me that he wasn't quite grasping it.  I said "Rob, do you see what I mean?", to which he answered "Yes... err... I mean NOT YES... I mean NO... I don't!"  Great answer in fact, as it gave me an opportunity to change how I was explaining it until I was certain he understood it properly.