rudder 'cheat' on snaps?
 

It's been 6 years or so since I last competed in IMAC, and I'm planning on competing again this year (if the old body allows) - have been working on the Advanced maneuvers, and I'm pretty happy with my progress to date. (I am not interested in dropping back to any other class - these maneuvers seem to fit me / my skills pretty well)

But - as I really don't have anyone with whom I can practise (I expect, after getting to a comp or two I'll meet some folks, but), or from whom I can get critiques and help, I am creating my own answers to the problems that pop up - I'm fine with this..

I guess I should mention that I fly at the low(est) end of the speed spectrum - always did this in the past, and plan to do so in the future - the plane(s) I have are all capable of any flight speed I could want, but I happen to like doing things at the low end of the speed - basically I try to fly up lines, down lines, and everything in between at the same 'medium' speed - which mean 1/4 power (as an example) or less on horizontal lines (even points rolls, snaps, etc..). I do know, specially here in the Pacific Northwest, that folks fly A LOT faster than me, and with that standard as the competition, I know my scores will suffer (slow flight shows corrections more clearly, and in fact needs them more too of course - but I am fine with that, in fact it is a BIG part of the fun for me)..

Well, not trying to complain, just sharing some background.

Used to practise with a few unlimited pilots (back in California), and am now drawing on old memories for 'advice'..

The first question I have - regarding snaps - again, remember that because of my lower than usual flight speed, I need a bit more of everything - I mean control input, etc.. So - snaps - to come out on the right line, I find a 'cheat' with rudder (only) in the opposite direction prior to the snap, makes a big difference - for 3/4s of the snaps, I can do this without it (yaw) being too obvious, and therefore I would not expect any downgrade - if they can't see it, they can't ...

But - up-line snap, looking at the top or bottom of the plane - a rudder 'cheat' before the snap is REALLY obvious - so, related to this - is there a downgrade in judging if the rudder cheat is observed? If so, what is the fix / solution / way around this? (I mean, other than increased flight speed)


Cheers,
Bob

RE: rudder 'cheat' on snaps?
 

Bob, if there is an observable opposite yaw just prior to the snap it will be a downgrade. Usually on upline snaps such as #7 on this years sequence the trick is to use little to no elevator input. Your low speed setup may only require more aileron throw.


Shawn

RE: rudder 'cheat' on snaps?
 

I am just beginning IMAC, and attended a judging school in Salinas not too long ago, and it was emphasized by the instructor that a snap starts as an accelerated stall.

If you don't load the wings you can't create an accelerated stall and then initiate autorotation. With a slower flight speed you will just have to use more elevator to get the aircraft to quickly load, and stall, the wings.

RE: rudder 'cheat' on snaps?
 

Ahh yes FT - but I understand what 'blimb' suggests. Elevator is not (actually) needed for this upline figure (usually)

If you think about it - up lines are not flying on the wing - so the 'usual' stall entry doesn't mean much. (to make more sense of this....You don' even need wings to go straight up, so how does elevator help stall? Doesn't really)

It is all about the presentation for / of the snap, and the entry and exit lines - moving to a different up line is OK (actually), but a different axis entry vs. exit is not.

For my flight style I think I do use a fair bit more than normal throws (3d of course is the standard WOW amount).

Blimp - thanks for the suggestion - I don't know why that never occurred to me - I understand what you're suggesting, and will be trying that to see how much better it looks.

Cheers,
Bob

RE: rudder 'cheat' on snaps?
 

Well, if there is no loading on the wings, no matter what your attitude, you CANNOT have AUTOROTATION. It would be something using ailerons, a big no-no in a properly executed snap.

The plane won't know that it is going straight up once you load the wings, then autorotation can be initiated and a SNAP can be performed. Don't be fooled by judges that don't grade properly, a common problem with IMAC, according to Brian Howard (IAC instructor, IAC Judge, TAS judge, former TOC judge) who taught the Salinas Advanced Judging School.

Good luck fighting the good fight and not let poor judging make us fly poorly.

RE: rudder 'cheat' on snaps?
 

I'll ask a dumb question. How do you score a snap with no pitch deviation?
No elevator.....no pitch...... = 0

RE: rudder 'cheat' on snaps?
 

Bob,

What is it that you are trying to accomplish with the opposite rudder before the snap? Are you trying to keep the line before and after the snap without offseting the line of flight?

If so- don't worry about maintaining the same line before and after the snap, it is not a downgrade. When you snap there is an inevitable offset of line of flight (left or right of the plane) before after performing the snap. If you are performing the snap directly in front of you while looking at the side of the fuse then you won't notice it. If you are performing the snap directly in front of you while looking at the top of the plane, you will notice some offset in the direction of the snap. The lines before and after the snap should both be 90 degrees from horiontal- just that the second line is moved over a bit. Hope that makes sense.

I will tell you that I have different techniques for snaps depending on the attitude of the plane. If on a horizontal line, I bump the elevator just before performing the snap. If on a vertical line, I don't bump the elevator and I use much less elevator during the snap. I recognize that the argument can be made that the plane didn't stall/autorotate..... all I can tell you is that I score better that way than by using lots of elevator in my snaps on a vertical line.

Good luck this season.

Dave Michael

RE: rudder 'cheat' on snaps?
 

Hi,
Just to follow up on Diablo's most succinct ;-) (and correct) summarization: Some snap criteria . . .
At the entry to the maneuver the aircraft MUST:
- Abruptly pitch positive or negative to briefly set the wings at a critical angle of attack to cause an immediate semi-stalled condition. In other words: no pitch departure, no points.
- Yaw to unbalance the airflow between the wings, and therefore reduce the critical angle of one wing while increasing the other.
- The initial pitch and yaw (can be made simultaneously, or as a quick one-two) must immediately produce rapid auto-rotation - note: the exceedingly light wing loading of scale aircraft necessitates aileron input combined with pitch and yaw to present the appearance auto-rotation.
- Throughout the snap-roll the aircraft must remain in auto-rotation by continued application of the initiating pitch, yaw, and roll control inputs.
- A translation to aileron rolling at any stage before the required degree of rotation has been completed would mean that the snap has ended early - a certain 1 point / 10° downgrade. - At the correct angle of rotation the roll should cease abruptly, and the aircraft should continue along an axis closely parallel to the extended pre-roll axis. Read as: some line displacement is NOT a downgrade - in fact, some displacement should be expected if the snap is properly executed.
- Check carefully that the last part of the auto-rotation is not turned into an aileron roll to assist accurate end-stop positioning, a commonly adopted ploy that must be penalized. An extreme but VERY common example of this: 1 1/2 snap is presented as 1 snap + 1/2 roll, which = 0 points.


Whether the aircraft is flying fully "on the wing" or not is irrelevent with regard to what must occur in a snap. The fundamental aspect to a snap is autorotation generated by a differential in lift between the two wings - regardless of flight path - up, down, horizontal or otherwise - (your in trouble if its otherwise). That lift differential is achieved by a rapid change in the wing's angle of attack combined with, or immediately followed by, yaw. As noted above, scale models generally also require the application of aileron due to the very light wing loading.
Hope this helps.

Ty

sp. ZDZ Engines, RC Showcase

RE: rudder 'cheat' on snaps?
 

Let's not get all twisted up here. Do not confuse scoring criteria with how to fly a figure. The judge could care less about HOW you fly something. All they care about is how what you fly compares to the scoring criteria. Which for a snap roll are:

1 - The aircraft MUST stall
2 - The nose MUST depart the line of flight in the proper direction of the snap (towards the canopy for positive snaps, towards the belly for negative snaps).
3 - The aircraft MUST autorotate. This really means that the plane must rotate faster than it could by control input alone.
4 - The Aircraft must complete the proper number of degrees of rotation
5 - The entry and exist lines must be parallel to each other. Displacement during the snap roll is permitted, but the lines before and after the snap must be parallel.

These are the same for all snaps regardless of the number of degrees of rotation or the line of flight (vertical, horizontal, 45 degree).

RE: rudder 'cheat' on snaps?
 

Wow - interesting discussion..

For Dave Michael:
<<What is it that you are trying to accomplish with the opposite rudder before the snap? Are you trying to keep the line before and after the snap without offseting the line of flight? >>

Perhaps because of my relatively low speed entry to snaps, the yaw component results in an out line that is not 0degree from the entry line - I know the offset and parallel line of output is accepted from a snap, and my snaps do / have that, but additionally the yaw results in an out line 20-30degrees or so (in the direction of the snap) from the entry line - a quick cheat that amount, in the opposite to snap yaw, results in the exit line being ideal (usually). And, as long as we're looking at the side of the plane (which is 'usually' the case), the judge does not see the yaw offset - which is what I mean when I originally stated that three Fourths of the time the yaw cheat is not visible.

As far as the discussion of what is a snap - interesting stuff (but I think, at this level, most of us already know what a snap is, and how we lose or retain points during judged snaps??)..

I'm wondering if ... If there is a suggestion for this upline snap in there?

Cheers,
Bob

(PS - high speed snaps are A LOT easier IMHO, on all lines of flight, but for me the 'beauty' of this IMAC stuff comes from very controlled flgiht speeds, and presenting everything so the judge has NO question(s) - and FWIW, I have received lots of 10s in the past, and I have ALWAYS flown the slowest of any competitor.)

RE: rudder 'cheat' on snaps?
 

That would not be my experience.

As far as your correction goes, are you saying you do this to ensure that the entry and exit lines stay parallel??

And remember, in IMAC we are judging the TRACK of the CG, NOT the heading of the nose.

RE: rudder 'cheat' on snaps?
 

Bob,

If flying slowly works best for you- and for what it is worth I like the way a sequence looks when it is not rushed even though speed is not a criteria for scoring - then continue to do so. However, if you think you are losing points on your snaps because you fly slowly, you might consider adding some speed when entering snaps.

If by appling opposite rudder I saw that the track of the plane deviated, I would downgrade you. I assume that you feel the potential for lost points is smaller by changing the attitide or track of the fuse when entering a snap because it increases your likelyhood for a clean and "proper" exit where you would have an increased chance for a larger deduction. I would experiment with some more speed, no opposite rudder on entry (unless it is necessary to maintain a vertical line due to cross wind) and then application of immediate opposite rudder after the snap.

Experiment and see what works for you and results in better scores. I can't tell you which way would work better for you without actually watching you fly.

Dave

RE: rudder 'cheat' on snaps?
 

For Phaedrus:

I'm years out of date on IMAC competition, so I'll accept your suggestion that folks in the advanced class don't all understand how to do / score / judge snaps..

My rudder cheat, my 'why'.... again I guess I'm out of date, but 'back when' .. the unlimited guys I flew with taught me this as a way to correct on upline snaps - since I never encountered an upline snap (in my class - not Unlimited) before, I just added that 'hint' to the list of things available to correct problems.

I use the opposite yaw to ensure that I come out of the snap with no yaw offset in flight - yes the plane is on a different out line, but exactly parallel to entry. My snaps (I have 3 IMAC (gas powered)planes right now, and putting together number 4 as we 'speak :D) vary a bit plane to plane, but on my latest IMAC plane -> a little 'cheat' , then usually full elevator (get a big snap stall), an a micro second later full rudder with reduced elevator - the snap end is usually opposite rudder just to track straight, sometimes aileron to help stop the rotation - if I don't use the 'cheat' I find that I have to hold opposite rudder for a few moments after the snap ends in order to correct the line, and in my thinking the chance of downgrade is much greater there than with the chance they (judge) saw the initial cheat. I'll have to spend more time thinking about this I can see, and trying different things - heck, I have the gas!

FWIW - Unless I mess up, or the snap is too slow (I mean flight speed at entry), I don't use any aileron until I get to snaps over a full rotation - for those I am thinking I may need more entry speed, I'm open to that.

Again, my biggest 'challenge' is that I don't have anyone from whom I can get feedback these days- well, I get the local guys saying stuff, but..

(IMAC planes - main one right now is a 4 month old 33% Edge 540, and being built is the QQ 102" YAK)

I expect to get dinged (at least a bit) from my lower than usual flight speed, but for me a lot of the fun is in trying to do the figures with the very controlled speed. Actually, I guess that is A LOT of the joy for me.. I have seen IMAC folks carry so much speed that they don't even use rudder for VERY basic moves, because they're going so fast - fine for them, but not the way I want to fly, and if I lose points, I have no issue or problem - my choice, I know that.

It occurs to me that the rudder cheat I have usually used is not 'the way'. I do know that my first contest this year will teach me A LOT - I just want to be well prepared - or at least feel I am well prepared for it.

RE: rudder 'cheat' on snaps?
 

I've been thinking more about this - and while my original question was about just the up-line snap, you can (I think) tell that I guessed everyone used a yaw 'cheat'. I'm thinking a couple of reasons might explain the fact I am so far off base here - A) everyone does their snaps at a much faster speed than mine (try snaps as slow as you can, and I think you'll see the yaw problem I try to address with the 'cheat' OR ii) many of the responses are not actually advice on snaps as much as what folks have read, heard, or been taught.

I see what I think is a bit of 'textbook advice' here - I mean description of how 'it' should be - but I am actually looking for real advice - I'm not meaning to criticize in any way, I am simply looking for (real) feedback.

On an upline - how do YOU do a snap for IMAC? How do YOU address the potential for a yaw 'issue' at exit? (At this point, as mentioned very early in this, my 'plan' is to try the upline snap with very little elevator to initiate it, and to use rudder and (eek!) aileron to give the right look - haven't tried it yet, so I can't say how it will look or work)

On 45 degree up or down, or horizontal lines - how do YOU do a snap for IMAC and how do YOU address the potential for yaw issues?

I mean, not how have you heard or read it should be done, I mean - actual and real experience - which I guess means competing at Advanced or above.

Cheers,
Bob

RE: rudder 'cheat' on snaps?
 

Diablo, the figure associated with the original post is the humpty bump on the advanced sequence. Flying paralell to the runway pilot pulls vert, performs 1/4 roll so pilot and judges see either bottom or top of the airplane, one opposite direction snap. Because the judges are looking at the bottom or top they will never see the pitch deviation even if it is there, As the airplane travels 1/4 way through the snap the nose will be displaced by the rudder and the judges will preceive this as the required pitch deviation. Remember that the judges have to give benifit of the doubt to the pilot. Obviously this wont work on snaps where the judges have clear veiw of the fusalage profile. In this case you will need a visable pitch deviation at the onset of the snap but the trick is to not hold the elevator in thoroughout the entire snap. I'm sorry but as lightly loaded as our models are, you are not going to get anything that appears to be autorotation without aileron.


Flying Tiger, as you may remember, Brians bulk of experience is with full scale. He mainly touched on what the judges wanted to see. Most if not all of the upper class pilots have developed ways of easing the difficulty of the manuver and still give the judges what they need to see.


Shawn

RE: rudder 'cheat' on snaps?
 

Exactly. Brian, and other hardcore IAC judges often cannot grasp how much differently our planes fly compared to full size. Snaps are one of the most obvious examples. But I will agree with him on the point that for the life of me I cannot understand why a model takes 3 times more airspace to do a roller than does a full size Sukhoi!!!

But for snaps, make sure you show the nose departure in the correct direction and what the judge will perceive as autorotation and you have nothing to fret about. Remember, the key issue is that it is not important what you do or what the plane actually does. It is ALL about what the judge perceives the plane to be doing.

RE: rudder 'cheat' on snaps?
 

for anyone who may have missed snaps 101---
the aircraft is loaded in horizontal flight -but--- it is completely unloaded in perfectly vertical flight
so
any snap up/down/45 - level - must be done with far less inputs of PITCH as the attitude goes from level -to 45-to vertical
also any maneuver decreases speed (energy gets used - so, do the verticals with power ON going up and a little tiny bit of power going down vertically. otherwise the plane slows and in up lines (vertical -it can be dramatic.
You may not see any pitch in the verticals snaps -even when the snap is a true snap -
why?
the wing is not loaded -
If you think it is -raise your hand-and tell me why

RE: rudder 'cheat' on snaps?
 

The wing may not be "loaded" or carrying as big a load but it is still flying. In flight school I was always told that you can stall a wing at any speed and/or angle relative to the air mass when you exceed the critical AOA.

RE: rudder 'cheat' on snaps?
 

exactly -they told you right -
in vertical attitude - it is not loaded -at all - until you start to rotate it with the ailerons - so IF you plane weighs 40 lbs for example - in a exactly vertical attitude --it is not loaded with 40 lbs (lift required to fly level )
this is why it is so easy to over yaw or over pitch in verticals - you are not overcoming the loads from gravity.
just a momentary flick of elevator or rudder will set up the AOA necessary to stall a panel.
You are working against airloads tho -

RE: rudder 'cheat' on snaps?
 

Progress (or .... :eek: activity anyway) report -

Spent nearly an hour in the air yesterday (lots of cold and wind, but heck, I wanted to FLY!) - and spent A LOT of time working on this upline snap.

I am finding that my habit of yaw cheating first comes back if I don't very consciously stop it (years of doing this for snaps where we see the profile of the fuse) - so any time I am mentally relaxed going into the upline snap, I find my plane doing a small opposite yaw first (oops - will stop that with concentration).

I can see the upline speed is the first issue - relative to the amount of control movement used for the snap - too little speed, too much control authority - WAY off line after. So the challenge for me is to keep the speed up higher that I might usually have, and to NOT use as much rudder / aileron as I might usually want.

Related question (I am putting together my new QQ102" YAK ) - in the manual for that plane, discussing rates and flight maneuvers, he (QQ) suggests using low rates on rudder for snaps? (and high rates on rudder for all other IMAC type moves) I have never thought of that - but I can now see the reason why...

Do any of you use low rates for rudder on snaps (as suggested, I mean high rates for everything except snaps)?

My rudder throws tends to be 85-90% of 3D rate all the time, meaning I really don't have a low rate - am I 'unusual' in doing this? I guess, because of slower flight speeds, rudder is a BIGger deal to me..

Cheers,
Bob

RE: rudder 'cheat' on snaps?
 

practice -- what QQ suggested -is what I tried to explain in previous posts above - the plane requires far less control input- as there is far less load on surfaces
Bad news - simply finding an ideal switch position--is about a hopeless task-
you are best of learning to apply a quick input and release it -
there is no ideal "setup"--
If you can't get the hang of it - this maneuver may be the one case where you use a snap button -(I refuse to use them).
Up line -- start with enough speed -then apply full power and try best combos of throw (different quick applications of stick)
do not reduce power on the upline snap -this will kill it quicker than anything .

RE: rudder 'cheat' on snaps?
 

Here's couple things that work for me:

If you have almost 3D throws on the rudder, learn not to push the rudder stick all the way during the snap.

Unload the elevator.

Modulate the elevator and/or rudder input DURING the snap to line up your exit.

Don't be afraid of opposite elevator input on exit of certain snaps. 1 1/4 on vertical upline comes to mind.

Slight opposite rudder just before you exit is very effective for aligning the flightpath for full snaps ( 1 or 2 continuous)

Some additional same direction rudder input (you're not flying full rudder during the snap by now, are you ?) just before exit of 1 1/2 snaps aligns you as well.

P.

RE: rudder 'cheat' on snaps?
 

Bob,
I'm not going to get in too deep here into how to do snaps, there's already been a ton of advice, I don't think I could offer anything of magic that will solve issues. I will tell you that I do leed snaps on an upline with oposite rudder, just a small amount, not enought to change headings, but enough to "load" the inside of the fuse (as related to the snap direction).

As for speed, don't assume because you like to fly slow you'll be scored poorly. Not sure if things used to be different in the NW but there are lot's of guys who fly really slow, some fly faster, but I think it's actually less common than you may think. Once noise and overflight came to the forefront of peoples attention, more effort has been focused on controling those two factors, thus slower speeds.

I see your from Camano Island. I live in the Arlington, Smokey Point area. I fly in Snohomish, if you'd like to hook up and do some flying, let me know. We have a large group of IMAC guys at the Cascade field, so there are plenty of guys to practice with. A couple of us fly in Lyman from time to time as well.

Glad to hear your coming back to IMAC. I look forward to flying with you, let me know if I can do anything for you.

Kev

RE: rudder 'cheat' on snaps?
 

Thanks Kev,

I think you might be the first person to say you also used opposite yaw at entry on up lines - I do know you fly with great success at the Unlimited level.

FWIW - I am very comfortable with snaps, I'm not sure how the thread wondered into 'snaps 101'.. but not a problem. I was really only looking for a solution to the new problem / challenge I have run into.

As far as IMAC up here - I am so far out of date, and I am sure you're much more aware - so ..... cool! I am really looking forward to getting out to a competition.. (Have the new plane and moto (QQ102 and DA100), just 'cause, the new radio(10X), just 'cause', and even a new cargo trailer.... but right now I'll most likely compete with the old plane and radio.. Just funny to me..

As my body allows (JUST got home from 5 days in hospital - scheduled surgery for my cancer) I do want to find the IMAC group out here - but that is the big challenge for me, my body and the cancer.

Cheers,
Bob

RE: rudder 'cheat' on snaps?
 

Bob,
You'll love the QQ Yak, it flies great! I also fly the 10x and love it. Very easy to use which encourages you to get the most out of it.

Any time you feel up to it and want to fly, give me a call and we'll set something up. I hate to hear your having health problems but hope all is as well as can be. If we can ever do anything to help you out, please don't hesitate to let me know.

I'll pm you with my contact info, call any time,
Kev