Plane trimming...no side issues please this time

[Matt Piatkowski]

Hello,
My previous inquires about plane trimming evolved in the end into discussion about something else. Human nature perhaps?

I am trying again and would like to appeal to you to stick to the subject if you please.

My Pattern skills improve very fast now and I am able to see and feel things that I was not able to recognize a month ago.

I have noticed today after seven flights that my eParrot is hunting.

The CG is located where the maximum airfoil thickness is and this represents 29% of the root rib chord line, measuring from the LE.

There is not much of this hunting but it is there.

I will start incrementally moving the CG FWD and will flight test after each change but would be grateful for your comments, ideas and suggestions.

Regards and Happy Flying,
Mat

 

[Will Davis]

With any new model or one that has trim issues , I use the Paul Walker trim chart to resolve my issues.

http://flyinglines.org/index.html

[peabody]

What Will said

[Russell Shaffer]

Go to the Aerobatics section in Flying Lines and scroll down.  There are many of Paul Walker's trim and flying articles. 

[Dan McEntee]

   I would like to offer that the slight hunting that you are just seeing now, might not have been there before you made the slight elevator adjustment. Any adjustment you make can always be put back where it was to double check what you are experiencing. Now that you have some real time of the machine, put it back where it was and fly it five or six plights and see what you think. If you are truly unhappy with it the old way, you can put the elevator adjustment back in and try the nose weight. The side benefit of all this is what you have already expressed, you have gotten some good handle time and you can see and feel the changes. Just keep in mind to keep changes at one at a time. if you leave things the way they are, make sure the controls are not sticking, even just a little. that can initiate a hunt. Also, no gaps in hinge areas. Tape off and seal your flap and elevator hinge lines.
   Good Luck and Have Fun,
  Dan McEntee

[Brett Buck]

My previous inquires about plane trimming evolved in the end into discussion about something else. Human nature perhaps? I am trying again and would like to appeal to you to stick to the subject if you please.
 

  The first law of holes - when you are in one, stop digging.

My Pattern skills improve very fast now and I am able to see and feel things that I was not able to recognize a month ago.

I have noticed today after seven flights that my eParrot is hunting.

The CG is located where the maximum airfoil thickness is and this represents 29% of the root rib chord line, measuring from the LE.

There is not much of this hunting but it is there.

I will start incrementally moving the CG FWD and will flight test after each change but would be grateful for your comments, ideas and suggestions.

    Did you do the previous suggested change, and what was the effect? Did it start hunting after the change, or was it doing it before?  What is the CG position in percent, from the LE along the *average* chord? Knowing it at the root doesn't tell us much if the wing it tapered.

   As a general proposition and to first approximation, almost all hunting is a function of stiction or free play somewhere in the control system - bellcrank, leadouts, lines, hinges, pushrod ends, etc. Electric is vastly more prone to it, almost certainly because the lack of vibration to break the stiction free. Some airplanes that formerly flew OK with an IC engine have begun to hunt wildly when they were converted to electric. That's because any stiction in the controls is continually broken free by the shaking of the engine. If the controls do not drop under the weight of the surfaces or pushrod (when nose down), that is a prime candidate.

     I would suggest very carefully inspecting the control system for friction or drag in the controls, that means, even the ribs touching the leadouts inside the wing, and that sort of thing.


     Brett

[Ted Fancher]

Hello,

snip

My Pattern skills improve very fast now and I am able to see and feel things that I was not able to recognize a month ago.


I have noticed today after seven flights that my eParrot is hunting.

snip


Mat

 

Matt, Glad to hear your pattern skills are improving rapidly.  Any particular maneuvers giving you trouble or are they all falling into place?

Re the second quote above: Are you saying the hunt was not there until the 7th flight?  Had you changed anything prior to that flight?  Had you, for instance, not re-cleaned your lines after each few flights?

Ted Fancher

[Steve Helmick]

Electric planes, it is said, need to have the CG WAY farther forward than an IC version of the same design. Leadouts seem to need to be even farther aft than the IC version of the same design. I'm not sure anybody has a 100% certain reason for this.  Steve

[Ted Fancher]

Electric planes, it is said, need to have the CG WAY farther forward than an IC version of the same design. Leadouts seem to need to be even farther aft than the IC version of the same design. I'm not sure anybody has a 100% certain reason for this.  Steve

Disclaimer: I've zero personal experience with electrics other than flying perhaps a half dozen or so generous flights on OPPs all of which preceded the current CG/line rake revolution.  With the exception of the very first of those flights (back at, literally, the very beginning of the amps/ohms revolution) I found the line tension of these stunters to be excessive for my preferred wrist and finger input style of flying the pattern.  This is one of the reasons the current emphasis on the desirability of drastic trim changes from the historic IC powered set-ups--especially changes that would tend to increase line tension even more--seem counter intuitive.

Per the current discussion, I wonder if the currently vaunted forward CG, aft leadout locations...both of which would be assumed to increase line tension...might have come about as a means to overcome the "reduced vibration/increased stiction" issues discussed by Brett?

Along these same lines I'm curious if any of the committed EC fliers have experimented with solid lines and, perhaps, found them less than beneficial or, even, detrimental in terms of apparent stability of the ship itself?

I've no dog in this fight either way.  Just interested in what it is about the change in power source that has made fliers I admire greatly determine the--otherwise similar in most respects to IC ships--EC ones require substantially different aerodynamic configurations to obtain optimum performance?

Ted

[Matt Piatkowski]

Hello,
I know Paul Walker's trim charts.

Dan,
Wings to flaps hinge line is sealed with the kite rip-stop nylon. It is not 100% air proof (there is some air permeability because it is nylon not tape) but flaps are very effective in my opinion. Elevator hinge line has been sealed with tape but it made hunting worse. The plane was slightly hunting before the elevator hinge line was sealed and, after sealing, the hunting become more pronounced.

The controls are not sticking. They are actually very loose ( not like the loose women of the Victorian Era) but loose. When I move the handle - the control surfaces move easily and predictably.

Brett!
One day we have to shake hands and talk about the most important issues in the universe, namely, the C/L Stunt flying.
Yes...I moved the elevator up w/r to the flaps by turning the Sullivan 4-40-Gold Clevis that I use in the pushrod to the elevator horn connection (please see the attachment) 1/2 of a turn. It had a very positive effect.

Then, I taped the the elevator hinge line and, like I wrote responding to Dan, the hunting become more pronounced. I gather that the elevator became more effective and this only amplified the hunting tendency. The position of the CG is 24% of the average airfoil chord. The control system is loose: I can move the elevator and flaps a bit up and down without LO "seeing" this action and vice versa. I never measured this "bit" - it is small but I can feel it.

There are no ribs at all in the eParrot's wing. It is made of folded ~0.2" PFP (Paper-Foam-Paper board) and has only primary and secondary spars.
LO move freely and there is very little friction in the control system elements.

Hi Ted,
Taking off is too fast. Around 10' and the plane is airborne. When I try to keep the main wheels on the ground, eParrot is, how shall I put it...impatient and wants to fly. It is a bit risky to force it to roll with the tail up as the hunting manifests itself during such rolling.

The hourglass is the worst maneuver but I am working on it. The other maneuvers are, I feel, on the intermediate level with squares, triangles and all the loops quite precise and repeatable.

No...the hunt was always there but I could not properly identify it. I have changed the control system throws ratio many times and also modified the handle spacing thinking that these were the root reasons of high plane sensitivity.

Yes...I clean the lines using the fresh paper towel after each flight and I am keeping the lines as dry as possible. Before the launch, I walk the lines again holding one of them loosely in my hand and making sure they are not twisted. I feel the hunting problem is not lines and the control system related - it must be aerodynamics. Some hard to see warp somewhere or the plane is simply still tail heavy.
 
Hi Steve,
I am moving the firewall with the rear mounted motor 1.75" FWD now. This, associated with the more FWD battery position, will give the CG at 18-19% of the average airfoil chord line.

The epoxy is setting right now and I will fly on Monday, July 31 to confirm if the entire hunting affair was caused by the plane being simply tail heavy.

If I get good grooving with enough maneuverability, the issue will be solved. If not, I will think about something else.

Thank you all for your input,
Regards,
Matt

"A day without learning is wasted"


 

[Peter Nevai]

Hmm. Never had a model that was prone to hunting. The only time it would climb and dive during level flight was when the wind was kicking up. But then the first thing I did was to make sure the CG was where it was supposed to be as a starting point. the rest I figured (except for line tension) I would sort out over time.

[Steve Helmick]

As I understand it, the object of sealing the hinge lines is to make them more consistent, rather than more effective. Having tried my hand at applying the recommended tape with the approved method, perhaps it needs to be tried again? It isn't easy to get it exactly perfect...three hands or more could help.

Your use of the R/C clevis is scary and will likely cause the end of your plane. Another thought...test your controls for hitches with tension on the leadouts. I think you're going in the right direction, but wonder if your LO adjustment range is going to be adequate.

I understand Ted's concerns, too. When I saw Paul flying his PW-47 at Chehelis Muni in June, I thought it was pretty fast, but also near maximum length lines. I didn't get lap times, but it was quite turbulent air, with rollers over the nearby hangars. He discussed the CG and LO locations some. If you're not already using maximum length stranded lines, be prepared to, if you need to reduce line tension. All the electric fliers seem to have hunting problems. Some vibration might help!  Steve     

[Ted Fancher]

Hi Matt,

A couple of things I see in the photo of your elevator horn and the bottom of the stab/elevator concern me.  They may be the result of the photo giving some false impressions.

First, it appears the sealing of the hinge line may not have been done as precisely as necessary.  Item 1, be sure the tape that appears to be going straight across the bottom of the surface directly over the "elevator connector arms" of the control horn isn't sticking and impeding free movement of the  elevator.  The entire span of the tape seal should wrap halfway around the hinge-line itself on both surfaces so that it applies zero sticking friction when the elevators move from full up to full down.  The tape should not be touching the hinges themselves (I seal only between the hinges).  If you hear any "crackling" of the tape as the controls move throughout their travel consider redoing the hinge seal that caused the noise.  I use a ~1/2" thick X an inch or long balsa "wedge" to make the following easy.   Attach the tape first to one surface; then use the wedge to press the tape uniformly "into" the hingeline and only then attach it to the second surface. (Hint, use a rubber band to hold the elevators full travel exposing the bottom gap when applying each seal).  After each seal is in place remove the rubber band and check for freedom of motion...don't omit this step as, if you do them all and then hear the unwanted sticking/unsticking sounds, you'll have no idea which and/or how many sections are sticking.  Use this method for the flaps and elevators.

A second item that may be more important...again noted in the picture.  It appears as if the picture was taken with the elevators at a neutral setting.  However, the elevator horn appears to be tilted aft at least 10 degrees aft.  At worst the horn should be perpendicular to the aircraft center line at neutral ("ideally" it should be tilted forward so that, at neutral, the pushrod exits/enters the horn at 90 degrees at neutral.  This state is necessary to insure uniform control surface deflection for a given amount of pilot input.  As an extreme example to make the problem obvious: if the pushrod with the elevators at neutral was 90 degrees aft of the hingeline no (0) degrees of up elevator would be achieveable.  To the degree that the angle departs 90 toward 180 degrees with the elevators at neutral the amount of up control per unit of handle input will decrease proportionately and, simultaneously, the amount of down control will for the same amount of input will increase.

such disparity in up and down response to the same unit of input could noticeably exacerbate resultant "pitch axis" behavior of the eParrot and be a factor in what you're experiencing.

FYI, most competitive stunt fliers utilize control horns that, to the greatest degree possible, are assembled and designed to compensate for the system's built in angular non-conformities to 90 degree angles at neutral.

sorry for the length of this post.


Ted

[Air Ministry .]

I think it was P Walker , " C.G. 1 " fwd, leadouts 1" aft of infernal combustion engine position , invariably " ( other " are = inch , ' being foot )


Foistly , if your on those 15 thou stainless stranded THINGS ,

decoiling - having a person hold a line in each palm with there thumb, at the Far End - then running down them with a rag -
so Ea Line ROTATES , done 1/2 dozen times, on new lines , untill they DONT rotate , Halves the Stretch .
( or halves the rubbery controls ) ( cant see how anyone can fly on em when its blowing , myself )
Digressing further , First flights on a 60 Oz Whirlwind in good country air ( generous steady varying wind )
it was piching or weaving a tad ( a foot or two ) on a middle handle spacing  , And Thats on 15  thou solids .

Logic would have it as to touchy , & to close the handle spacing. Whereas . . .
further thought - regarding it as line stretch , ' We ' opened the spacing - which reduced the movement % stretch ,
and cured it . Also had it tending to leave one line unstretched , which means at least somethings steady .

The olde fix the line ends to a imovable object at say 3 in apart ( a few nails in a solid fence ) pull the handle
FIRMLY and jigger it about . If it feels like a live trout , decidedly unstable , there you are . Stretchy Wires  .

-------------------------------------------------------------------------------------------------------------------------------

TWO .

Harrased to the pitching , overcontrol , in the P - 51 .
We ' inspected ' several magazines . Nearly ALL circa 1980 ships run 15 % M.A.C. centre of gravitys .
P.W.'s Impact Plan ( thicker Airfoil than most earlier ships ) SHOWS it at 20 % M.A.C.

( The P- 51s flaw is rubbery horns, should have 1/8 wire ones , with its intricate scaleish aerodynamics )
In sweeping ground air , it can delay pull up , so if you feed in more control to overcome the breeze , it pulls around
sharply once out of the wind sheer layer .But this is getting a bit off track .

FREE

INCRIMENTAL ??

You might save a bit of faffing around throwing the C.G. 3/4 or 1/2 Fwd, in one hit , for a few flights .
To See if it steps straight out of the hunting - Without becoming doggy on the controls .

As In one would think , if at 3/4 fwd. , it hadnt stepped straight - there may be a issue other than C.G.

FOUR ( as in Golf )

Currently messing with three ships ( two of em hand me downs ) where if you envision the control loads ,
and Apply THAT FORCE to the Aerodynamic Surfaces , as in a flap or elevator ;
With the leadouts secured - moving one gets the rest shifting too . . .

Which is not a good idea .

---------------------------------------------------------------------------------------------------------------------------------
Id think a firm push with a thumb at a elevator particularly , or a flap t.e. , should see minimal deflection THERE ,
and Particularly of the Other Surfaces .

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But start checking the lines for spring . . .015s uncoiled on a light straight twister .40 and it wont groove ,
whereas after the decoiling treatment its almost steady but responsive .

Some planes will follow every shiver in your hand , whereas you need to trim em groovier , unless youve a delicate touch .

==========================================================================

Wheres the flight video & comentry . 

[Matt Piatkowski]

Hi Ted,
I will repeat the elevator hinge line sealing following your instructions but there is no tape "crackling" and "sticking" at the present moment.
I have taped over the hinges, therefore there are only two continuous tape pieces, each one taping the hingeline on 1/2 of the elevator's span.
Comment: after the tape was applied, I have noticed a very slight increase in the elevator's rotational resistance and I know it comes from the bending resistance of the tape. This resistance is truly minimal and does not impede the elevator's movement that remains smooth when the leadouts are moved.
 
The photo was taken when the elevator was not in the neutral position.
The horn is perpendicular to the elevator's mid surface within (+)1 and (-)1 deg.

Hi Matt,
Yes....eParrot's lines are 0.015", stainless stranded THINGS.

I am decoiling them each time I fly. Also, I keep them clean of dirt and moisture cleaning them thoroughly with the paper towel before and after each flight. When I connect the lines and the handle (I am using Brodak's handle), I make sure they are hooked up without me accidentally rotating them.

I do not think the lines contribute to the hunting problem we are discussing here.

I have changed the handle spacing many times trying to understand what is going on. This spacing is now 3". For your information:eParrot uses 4" bellcrank with the push/pull wire installed in the hole 7/8" from the bellcrank axis of rotation. This wire connects to the flaps horn hole 1" from the flaps horn axis of rotation. The flaps and elevator have 1:1 ratio, with the connecting pushrod using the horns holes 0.75" from the respective axes of rotations.

Like I wrote before, I have moved the firewall with the rear mounted motor 1.75" FWD. There is now more room for the 4S 3000 mAh battery that was moved 1.65" FWD too. This moved the CG of the RTF plane about 3/4" FWD.

Again, I will fly on Monday, July 31 and will report the results.

Thank you,
Matt

[Steve Helmick]

How much doe ePArrot weigh, and what's the wing area? I'm thinking that it might well benefit from changing to .018" lines. You'll expect to burn more electrons, so your current battery size may not be adequate. But you never know until you try it.  Steve

[Matt Piatkowski]

Hello,
Could not fly yesterday but went flying today morning.
Moving the CG FWD had a very positive effect for flight but take-off is still "weird".
EParrot (49 oz. 560 sq.in. wings) grooves quite well now but, at the same time, stays lively and smooth in corners. Triangles and horizontal square eights improved and I can see and feel it. Level horizontal flight improved and inverted is ideal. The elevator hinge line stays taped and I checked this tape after each flight.

Take-off is bad. No change. It is too fast and sort of nervous and there is no smoothness in it. I cannot make this plane roll on the front two wheels for more than 2-3 meters without seeing the tail wagging up and down with the tail gear banging against tarmac and started suspecting the elevator flutter problem.

The elevator can move slightly up and down when the LO are motionless because the elevator's horn hole is larger than the pin of the Sullivan clevis there. The flow around elevator is for sure highly turbulent with air rebounding from the ground and the elevator may simply oscillate randomly affected by this flow.

I am going to change the control system horns connections to completely eliminate the build-in play by replacing the Sullivan Gold clevises with the black nylon ball links. 

Also, I will shorten the tail landing gear wire. This wire is quite long now and keeps the fuselage at +3 deg. when the plane stands on the ground.

Maybe the main landing gear is too flexible? The wire used there is 0.118" dia. I am going to try the carbon composite main landing gear (see the attached photo) and maybe this will fix the "nervousness" of the take off?

Anything else to change or check?
Thank you,
Matt

[Ted Fancher]

Matt,
I'm no expert on electric power.  I do know, however, that achieving smooth, well controlled take offs have been an issue for many.  I've seen this attributed to the instantaneous motor response to load as opposed to the less aggressive recovery of IC powertrains.  I'll let some expert folks talk about this facet.  Just be aware that some part of your problem is not unique to the eParrot.

The one thing I believe you do need to check is the fore/aft leadout position with respect to the CG.  If you didn't recheck and adjust them following your multiple CG alterations (nose length, battery location, ) some squirleyness (sp??) on release could be related to yaw induced by an improper CG/leadout exit relationship.  If, for instance the ship is held tangent to the circle while in the stooge until release the effect of too far aft leadout exits will be an immediate outward yaw and the subsequent responses in all three axes are unpredictable but unlikely to resolve themselves until the ship is finally airborne.  The leadouts appeared to be fairly far aft in your original posted picture and if they haven't been changed consistent with the CG movement doing so might be beneficial.

Ted

[Matt Piatkowski]

Hi Ted,
I am using mostly stooge and eParrot uses KR timer/governor.
This timer/governor starts the motor after programmed delay. I use 30 seconds delay to walk to the handle and get ready.
Then, the motor starts and reaches the programmed RPM within 4 seconds. During these 4 seconds the plane is held by stooge and then I release it.

The plane jumps forward and yes, the outward yaw tendency is visible. Following your advise, I will play with the LO position w/r to the new CG position.

Because of the outward yaw tendency immediately after the stooge release, I am not pulling the lines too hard and also walk two fast steps to the left. This allows the plane to roll almost straight for 6-10 feet and become airborne. I had somebody watching the eParrot's take-off path some time ago and this person confirmed it was almost straight.

I have another electric plane that I call MiniBee (please see the attached). It uses the KR timer/governor having a very similar setup like eParrot's and stooge release. I can force this plane to roll at least 30 feet with the tail wheel up before it takes off but this rolling is stable. There is no plane nervousness, jumping up and down, tail wagging etc.

MiniBee uses shorter main landing gear "legs" but the wire for these "legs" is thinner than eParrot's wire. MiniBee wire:dia=0.1", eParrot's wire:dia=0.118".

The wheels are different too. MiniBee uses a very narrow, superlight wheels with foam "tire", eParrot uses wheels having smaller diameter but much wider so their footprint is larger.

All wheels turn well but I started thinking about eParrot's landing gear and maybe it is simply too flexible in bending and/or in torsion, allowing for some form of shimmy tendency of the wheels generated by friction? In other words: I move the elevator a bit down to keep the plane rolling, the tail goes up, the landing gear wires bend/twist a bit and the wheels tires "brake" a bit. I see the nose of the plane going down a bit so I move the elevator up a bit, wheels release and the plane rolls a little further but the velocity is already so high that it takes off.

Like I wrote,  I am going to try the carbon composite main landing gear and maybe this will fix the "nervousness" of the eParrot's take off?

Thank you for your thoughts and suggestions.
Regards,
Matt
   

[john e. holliday]

Mat, have you thought of trying one of Larry Renger's Expo handles?   So far mine has made a world of difference in take off,  level laps and landing.   It also helped the maneuvers.

[Lauri Malila]

Matt,

I can't comment other possible trim issues but the take-off behaviour is clearly related to pusher propeller. Have you tried a tractor prop?
A healthy, well trimmed model does not need a pusher prop, trimming is much easier and logical with a tractor. L

[Dennis Toth]

Matt,
You have heard from a few of the top trim guys in the hobby and you are making progress. I have had some hunting issues with my e converted Stuka. My ship has solid leadouts (originally built in 1992 we all used them on the east coast). The ship has had Fox 35 power, PAW 19 diesel, OS 20 FS and now electric. As I recall I never had the hunting with the IC power (the vibration thin). Lately I started to adjust the leadouts rear ward and the ship flew smoother and had better up-top tension. I suspect the rearward movement of the leads put them in a better position relative to the angle of the flying lines, reducing any bending and slide friction at the guide.

Your takeoff issue is interesting. One of the first things I noticed when switching to the pusher prop was that with neutral elevator the ship wanted to hold on the ground and needed to be flown into the takeoff. Our field is grass so I normally will hold a little up to keep from nosing over until it starts to roll then feed in a hint of down until I was ready to break ground. I use fixed rpm with a soft start so it doesn't jump when released. Also, for serious takeoff practice and at contests the starting position relative to the wind is important. In reasonable wind I position the ship just off dead down wind. As the wind comes up I mover more down wind and shorten the takeoff roll but try to keep it from jumping.

Best,    DennisT

[Steve Helmick]

As mentioned previously, my SV-11 always jumped off the ground. Mike and Pete told me to adjust the handle neutral, but I was reluctant. When I finally did as they said, 1/16" clip change, the takeoff got very controllable.

Please stop using that "pusher" propeller stuff. It's just wrong. The prop is on the front of the plane, so it's a "puller" prop. It's simply a LH prop as viewed from the pilot's position. The top of the prop goes to the left from the pilot's view.  Steve

[Matt Piatkowski]

Hello,
I have just returned from the field after three good flights with MiniBee as eParrot is undergoing "legs surgery".
MiniBee has pusher prop. now.
I managed a very smooth and long rolling after the plane was released from the stooge in each of these flights. The tail gear was raised and the plane was rolling on the main wheels for about 50 feet before smoothly taking off without tail wagging or jumping.

Remembering Ted's suggestion regarding L.O exit points position w/r to the C.G location and bellcrank, I examined it and....bingo!

MiniBee has the C.G 1/16-1/8" in front of the bellcrank axis of rotation and the point equidistant from both leadouts exit points is only 1/4" AFT from the main spars center plane. The bellcrank axis of rotation is located in this plane.

Consequently, the model does not show excessive yaw tendencies during rolling that leads to the jumpy take-off like eParrot, the wheels are not fighting the side component of the friction force (Y direction of the plane C.S) and the landing gear legs are not bending.

I have already modified the L.O exit points in eParrot - they are now like in MiniBee. EParrot's C.G and the bellcrank axis of rotation are presently within 1/16" radius.

I will fly eParrot this weekend to see of all these changes helped to fix the annoying jumpy and waggy takeoff.   

Hi Lauri,
I have tried both, tractor and pusher props in MiniBee and eParrot and:
1. I cannot see and feel any difference in rolling and take-off.   
2. Both planes fly corners and triangles better with pusher.

Comment: perhaps when I improve my skills further, I will see and feel the difference in take-offs and maneuvers?

Hi Steve,
I prefer CW rotating prop and CCW rotating prop as seen from the model cabin (towards (+)X of the model coordinate system) but many people on this Forum and elsewhere use the terms "tractor" and "pusher". Why don't we all vote?

Please see my newly published thread titled "Terminology of propellers" in the Open Forum.

All this is extremely interesting and I am learning and testing new things daily!

Thank you, Guys!
Regards,
Matt

 

[Brett Buck]

Hello,
I have just returned from the field after three good flights with MiniBee as eParrot is undergoing "legs surgery".
MiniBee has pusher prop. now.
I managed a very smooth and long rolling after the plane was released from the stooge in each of these flights. The tail gear was raised and the plane was rolling on the main wheels for about 50 feet before smoothly taking off without tail wagging or jumping.

Remembering Ted's suggestion regarding L.O exit points position w/r to the C.G location and bellcrank, I examined it and....bingo!

MiniBee has the C.G 1/16-1/8" in front of the bellcrank axis of rotation and the point equidistant from both leadouts exit points is only 1/4" AFT from the main spars center plane. The bellcrank axis of rotation is located in this plane.

Consequently, the model does not show excessive yaw tendencies during rolling that leads to the jumpy take-off like eParrot, the wheels are not fighting the side component of the friction force (Y direction of the plane C.S) and the landing gear legs are not bending.

I have already modified the L.O exit points in eParrot - they are now like in MiniBee. EParrot's C.G and the bellcrank axis of rotation are presently within 1/16" radius.

I will fly eParrot this weekend to see of all these changes helped to fix the annoying jumpy and waggy takeoff.   

   As argued exhaustively in the past, the "bellcrank center of rotation" doesn't affect the yaw angle. It *might* affect the tendency of the leadouts to bind in the guide or rub against the ribs internally. Where the leadouts are with respect to the "main spar center plane" doesn't matter at all, aside from the possible binding issue.

  What does matter is the leadout position with respect to the CG. I would use that as a basis of comparison, rather than the other reference points.

     Note well Ted's observation about electric take-offs, the combination of running the level-flight RPM on the ground and in particular, the mostly-discredited practice of spinning the prop backwards to the conventional IC engine, seem to cause a general problem with takeoffs, and exactly the kinds of problems you describe. I haven't flown that much with electric but the furious acceleration, combined with the tendency to abruptly yaw outboard (probably due to P-factor) right at release, makes it tricky.

     Brett

[Matt Piatkowski]

Hi Brett,
I will remember from your response that:
1. The leadouts position with respect to the CG matters the most
2. Spinning the prop backwards to the conventional IC engine is currently discredited

https://en.wikipedia.org/wiki/P-factor explains that:"..P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for the asymmetrical relocation of the propeller's center of thrust when an aircraft is at a high angle of attack..

At this moment my primary concern is rolling behavior of eParrot from the moment of release to the moment of take-off.

When the stooge releases eParrot or MiniBee, the angle of attack is around (+)3 deg.
In my understanding (+)3 deg. cannot be treated as high angle of attack.

Regards,
Matt 

[Fred Underwood]

Could the landing gear/wheels be part of the issue?  Wheel alignment, wheel drag, and could the gear be too far back since the CG moved forward? 

[Ted Fancher]

NOTE, THIS POST HAS BEEN MODIFIED TO CORRECT AND REPHRASE SOME CONTENT TO BE MORE ACCURATE AND, HOPEFULLY, MORE UNDERSTANDABLE.  I THINK IT'S BETTER NOW BUT THE TERMINOLOGY WHEN DISCUSSING P-FACTOR GETS TRICKY.

SORRY FOR IT'S ORIGINAL FORM, I WAS LATE FOR MY HAIRCUT APPT. 

https://en.wikipedia.org/wiki/P-factor explains that:"..P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for the asymmetrical relocation of the propeller's center of thrust when an aircraft is at a high angle of attack..

snip

Matt, Please note that P-factor can be developed in any direction based on which way the prop's axis of rotation differs from the direction of the plane's flight path due to pitching or yawing or any combination of both. 

The Wikipedia reference to it in terms of "angle of attack" is a conversational convenience in that the primary way the phenomenon presents itself to prop driven pilots is when the aircraft is climbing with a positive angle of the prop's axis of rotation with reference to the actual direction of flight path.  The nose wants to go left due to P-factor and the pilot must "hold" or "trim" right rudder to get the old ball centered in the turn and bank indicator and the aircraft "in trim" for its current status!

You can encounter P-factor affects in any axis by forcibly pointing the nose of the aircraft in a direction other than that at which the vehicle itself is moving.  Push the nose down and you'll get a reverse yaw from what occurs during a climb due to P-factor requiring left rudder to get the aircraft "in trim". 

Push the rudder, yawing the aircraft  left or right, and P-factor will be generated in the vertical axis causing the nose to pitch up with right yaw and down with left yaw.

Important for our discussion please note that a stunt ship tracking tangent to the circle utilizing a right hand rotation tractor propeller operates with a constant "right" yaw which generates vertical P-factor thus requiring either some down elevator or positive stab incidence to compensate: some degree of P-factor in the "pitch" axis is "always" present during tethered flight.  The greater the angle between tangent and the axis of the prop's rotation the greater will be the P-factor that, ideally, would be compensated for via an appropriate aerodynamic adjustment. (Note that a left hand rotation tractor propeller would reverse the P-factor.  This 180 degree change in P-factor which results is almost certainly a factor in level flight tracking when switching back and forth between RH and LH rotation.


Ted

p.s.  I expect you'll hear from Brett about this in greater detail as it is a fairly big deal in a competitive stunter...especially when switching propeller rotations.

[Matt Piatkowski]

Hi Fred,
Please see the attached.
New carbon composite landing gear is installed in such a way that the distance from the new CG to the wheels centers is 2" (it was 3" before change with old landing gear using wire "legs"). The wheels turn well and the plane rolls straight. A moment ago, I used my driveway that is quite long to test rolling.
The leadouts exit points are now moved 1" FWD w/r to the old location. This places the point that is equidistant from the leadouts exits only 1/2" behind the new CG location. If tomorrow morning the plane rolls without jumping and takes off in a decent manner, I expect also better landing.

Hi Ted,
http://wiki.flightgear.org/Understanding_Propeller_Torque_and_P-Factor says that the gyroscopic precession is frequently confused with p-factor but one author maintains p-factor is caused by a combination of factors unrelated to gyroscopic precession http://home.earthlink.net/~x-plane/FAQ-Theory-PFactor.html.

Let me read a little more to understand these interesting subjects better.

Regards,
M
 

[Ted Fancher]

Matt,

Please note that after running off to get my hair cut I came home and re-read my previous post and found it advisable to rewrite much of it in hopes of clarifying the message.  Alas, P-factor is best (and easily, by the way) demonstrated in the cockpit of a single engine aircraft rather than textually...especially text written by a long time user of aerodynamics but one who has not a diploma on his wall declaring his expertise of the subject at hand.

Ted

p.s. I'm curious where you live, Matt?  Some of the data and terminology you've used makes me think you're not an Oakie from Muskogee!

[Steve Helmick]

Matt, when your stooge launches your planes with LH propellers (counter-clockwise flight circle direction when upright), do you yaw it outward 5-10 degrees, as is normal SOP for such a setup? Or straight ahead, tangent, as per IC practice with RH props? If you watch the 2-3 guys    flying clockwise with IC power and RH props, they will do this also. It's not often mentioned, due to the rarity of clockwise fliers, but rediscovered when folks started messing with LH props on electrics. And soon will be forgotten again, since very few are still using LH props on their electric stunters.

If they don't, the plane pulls hard to the outside of the circle, rebounds toward the pilot, then back to the outside. Makes for an ugly takeoff at minimum.

It's not easy to trim a plane on the www, with fragments of information. Steve

[Dan McEntee]

Could the landing gear/wheels be part of the issue?  Wheel alignment, wheel drag, and could the gear be too far back since the CG moved forward?

    One potential issue with carbon landing gear is wheel alignment, which can be an issue and isn't thought of a lot. If the legs of the gear are not made exactly the same, the wheel won't be aligned, and I usually try to have a little toe in on the wheels, just like the front end of your car.. I check how it rolls by rolling it down the driveway or in the street, and tweak until it rolls straight. Wire gear is easier to tweak than carbon fiber. It's just one of the little details to watch out for.
   Type at you later,
   Dan McEntee

[Brett Buck]

http://wiki.flightgear.org/Understanding_Propeller_Torque_and_P-Factor says that the gyroscopic precession is frequently confused with p-factor but one author maintains p-factor is caused by a combination of factors unrelated to gyroscopic precession http://home.earthlink.net/~x-plane/FAQ-Theory-PFactor.html.

     They are two completely different things and dependent on fundamentally different effect. The only connection is that they are caused by the fact that the propellor rotates.

   In this case, it happens that the two are probably both acting in the same direction in yaw - P-factor, the blade on the inboard blade lifts more than the outboard since it runs at a higher AoA with the nose up. Precession wants to yaw the nose out, too, because you are pitching "down" from the nose-up 3-point position to near 0. And there is little or no opposing force due to lack of line tension.

    More interesting is the P-factor and precession effects in *pitch*. I have to think about that one for a while.

     Brett

[Dennis Adamisin]

After hundreds of flights using Pusher (or LH or CW or backwards) props on models ranging from a 6 oz Baby Ringmaster through a 70 oz SV-11 I can pretty well guarantee that your funky take-offs are NOT the result of prop rotation.  More like it is misaligned landing gear combined with high foamie wheels:

* Align the wheels with the airplane without it turning out.  Some folks even advocate turning the main gear IN to track the circle but I do not have personal experience with that.
* If you can introduce some toe-in.  Tough to do on a CF or alum gear but it REALLY helps.
* Make the wheels slippery: apply a layer of vinyl tape (electricians tape is fine) so the wheels are not dragging and hopping across the pavement or grass.

Any or all of the above will help.

Since the tape on the wheels looks kinda funky, longer term you can switch out to vinyl wheels - like Williams Brothers Old Time or Golden Age which are nearly as light as the skinny foam wheels.

[Matt Piatkowski]

Hello,
The newest report from the field.

Six very good flights with eParrot but rolling leading to the take off is equally bad as before.
This plane simply wants to fly too early and I have no idea why.

The leadouts exits move FWD helped only a bit but whatever helps is useful. Thanks, Ted and I am definitely not from Muskogee.

Comment: like I wrote before, my electric MiniBee can roll easily 1/3 of a circle on the front wheels only and in a very stable fashion and then gradually takes off. The same timer, almost the same RPM and pusher APC Multi E prop. The major difference between eParrot and MiniBee: wings thickness.
MiniBee: 17%, eParrot: 24%.   

Hi Dennis,
You wrote: "I can pretty well guarantee that your funky take-offs are NOT the result of prop rotation."
I concur based on my own understanding of things right now. I also agree that the foam wheels play a major part in this "funkiness" and I thought about making the wheels foamy "tires" slippery. The bending and torsional stiffness of the landing gear "legs" is, in my understanding, also very important and I will increase it.

Thanks for the detailed suggestion. I will use the vinyl tape and fly again.

Apart from the rolling problems, eParrot flies ok now. The plane grooves well and, like I wrote before, is simultaneously lively. Corners are very good and there is no tendency to stall in any maneuver. Like I predicted, the landing with the carbon composite landing gear improved but I am landing on the relatively smooth hard surface. Landing on the grass will be a challenge, I suppose, having in mind the landing gear placement w/r to C.G. at this moment.

Conclusion: I will fly eParrot as is and work on my maneuvers as this plane is capable of flying much better but for the plane to fly better I have to fly it better. I hope to find the solution to the rolling problem enigma as I can actually compete with eParrot right now but will loose the take-off points.

Thank you and happy flying,
Regards,
Matt

[Brett Buck]

Hello,
The newest report from the field.

Six very good flights with eParrot but rolling leading to the take off is equally bad as before.
This plane simply wants to fly too early and I have no idea why.

   I can tell you exactly why, and was alluded to above. David PA51 airplane had the same problem for the same reason - it was a full level flight RPM (or very near it) at launch, just like your electric. Whichever way it is aimed at release it pretty much just goes that way.

   The average IC engine picks up from 500-1000 rpm from ground to level flight, it's called "unloading". An electric (and David's PA51) unloads 0 rpm since it is running on a governor. Essentially, it is running ~1000 rpm faster on the ground than a similar IC engine, which creates much higher static thrust. That static thrust cause the airplane to accelerate to flying speed much faster that it would otherwise, so instead of taking 1/4 lap to take off, it takes 10 feet. In David's case, we noted that the "oil plops" left on the pavement became evenly-spaced at around 20-25 feet from launch - meaning it was at nearly full speed in less than a second. The acceleration at launch was about 1.4G's.

    David's PA51 system was an oddball system that worked but was very unusual, but it had the same issue. The PA75, even 50% larger, and plenty strong on the ground,  has less static thrust and much more reasonable launch accelerations. Every electric I launch shows the same thing, release, and it's like lighting a JATO bottle. A lot of electric guys have taken to having the airplane launched while the motor is still coming up to speed to avoid this issue.

      Brett

[Air Ministry .]

* Align the wheels with the airplane without it turning out.  Some folks even advocate turning the main gear IN to track the circle but I do not have personal experience with that.

Think thats a Al trick , at least on tarmac .

Tried it on my P51 ( on Grass strip ) and it stopped the pilot getting the aeroplane in the teeth .
Peviously it was ' free flight ' for a 1/4 lap with the pilot backpedaling .
Tho yet to try it with the 4 blade prop again , more tourque reaction from that .

Definately a discernable diferance in this case . But missaligned wheels LOOK ugh , IF you notice em . Great Circle Alignment ! ./ bias .

[Matt Piatkowski]

Hello again,
It looks that whatever I will do with wheels alignment, wheels type, model alignment at launch, landing gear type, its stiffness and location w/r to the model CG, the JATO bottle behavior mentioned by Brett (https://en.wikipedia.org/wiki/JATO) is here to stay and harass me.

The main reason: "The F2B stunt people that make the rules for competitive stunt do not want programmed take-off’s." This quote is from Keith Renecle e-mail to me.

I was exploring the idea of having the gradual increase of RPM in the governed mode but this "gradual increase" is treated as "programmed take-off" and disallowed. Now, I will try to learn the art of a very subtle input at launch with high acceleration and very high rolling speed.

End of the story? Not really.

Like I wrote before, my second electric model, MiniBee, can roll in a stable fashion with the tail wheel up and exhibiting the JATO behavior for about 1/3 of the circle circumference and then smoothly takes off.
In this situation the basic problem can be reworded as follows: what are the differences between MiniBee and eParrot that make this possible for one and almost impossible for the other? I do not think I will ever know for sure but it does not matter too much. I can practice the pattern with two well flying planes and, if I ever want to compete with both of them, I will simply loose some take-off points with eParrot and regain them flying better corners with it.

Thank you for your comments and suggestions.

Regards, 
Matt

[pmackenzie]

Looking at the side view I would try moving the wheels forward and use a longer tail wheel strut.

Pat MacKenzie

[Matt Piatkowski]

Hi Pat,
I can easily install the existing steel wire gear that will move the wheels about 1" FWD. This wire gear was actually there before I started messing up with the very neat looking carbon composite gear that was installed a bit more AFT because there was no other way without serious surgery on the fuselage.

I was considering the tail gear strut extension to make the line of thrust horizontal or even, say, (-) 1 deg. negative.
Theoretically, this should "glue" the plane to the ground for longer rolling.

I am willing to try it and we will see.

Regards,
M

[pmackenzie]

The longer tail strut keeps the AOA lower, so the model does not tend to leap into the air. See Gieseke  Nobler for a good example of this.
Moving the gear forward will let you hold the model on the ground with less tendency to nose over. Take it too far and the model can pitch back up into the air on landing.

The gear also looks to be longer than needed for ground clearance, so shorter main gear might help as well.

[Matt Piatkowski]

Hi again, Patrick,
Like I wrote before, I know what is happening from the take-off dynamics point of view when the tail strut is made longer.
This solution has a drawback, though. The eParrot tail strut is made of 0.064" piano wire.
To make the AOA around 0 to (-)1 deg., I have to extend the tail strut by 3".
To extend the tail strut by 3" and maintain the present bending stiffness (that seems to be sufficient), I have to use a piece of 0.064" steel wire that will be 7" long and solder it (using thin copper wire for wrapping in, say, five places) to the existing wire. This adds about 1/3 oz. of dead weight at the tail and shifts the CG about 1/8" AFT.

Shortly put: I may fix partially something (or not) in the rolling and take-off department but this will affect a very good grooving and corners that the plane exhibits now.

The prop clearance while rolling with ~0 deg. AOA is only 1.25" and I consider this a very narrow "forgiveness band" considering my present skills and subtle input control.

The wire main landing gear is installed back. The distance from the present location of CG to the wheels axles is 3.15". It is 0.8" more FWD than in case of the carbon composite landing gear.

Summary: the main gear wheels position provide now more forgiveness for the minute input mistakes but landing on the hard surface will take a very delicate touch to avoid "kangaroos". I am leaving the tail strut as is and hope to learn better the art of smooth and gentle input after the plane leaves stooge.

Best Regards,
M

[Brett Buck]

Hello again,
It looks that whatever I will do with wheels alignment, wheels type, model alignment at launch, landing gear type, its stiffness and location w/r to the model CG, the JATO bottle behavior mentioned by Brett (https://en.wikipedia.org/wiki/JATO) is here to stay and harass me.

The main reason: "The F2B stunt people that make the rules for competitive stunt do not want programmed take-off’s." This quote is from Keith Renecle e-mail to me.

I was exploring the idea of having the gradual increase of RPM in the governed mode but this "gradual increase" is treated as "programmed take-off" and disallowed.

      While I am generally out of the FAI loop from now on, I am not aware of any rule like that. I hope, as they are adopting my AMA rule, that they don't "enhance" it any further by requiring full-power takeoffs.

    What you can't do is set the airplane on the ground, hit the timer, and walk out to the handle while the airplane sits there unattended with the system armed and counting down with no helper to restrain it in the case of an unexpected glitch that starts it early.

   You *can* set the airplane down, have your helper hold it, hit the timer, walk to the handle, and THEN have the helper release it, motor running or not. If you want to risk the roll-off from a dead stop and all the things that could go wrong, there's nothing  I know of to stop you. So as far as I can tell, allowing it to slowly spool up and reduce the takeoff acceleration is perfectly legal.   It might be a really bad idea in some circumstances, and I would have the helper hold on till the last second to avoid some of these circumstances, but not illegal.

   In fact, many pilots currently have the airplane released at partial power, during the initial spool-up, to mitigate some of what you are seeing. If I was doing it, I would be tempted to use either a two-stage start sequence that initially spins it up to 1000-1500 rpm below level flight revs for the first 20-30 seconds, then jumps to full level flight revs, just to make the takeoff easier.

    One of the more recent FAI proposals is to set the K-factor for the takeoff to 0 (although that was not particularly well-received), in which case, the takeoff doesn't count any more and who cares how the motor starts.

      I hope Keith is reading this - maybe something else got slipped in with the arming plug/restrained when armed rule, but I would be curious as to the basis of this interpretation.
   
     Brett

[Matt Piatkowski]

Hi Brett and Keith if you are reading this,

I believe that Keith will agree with me that the key word is "programmed". The KR governor is of course programmed and this covers the functions that are accepted, as programmed, by the "F2B Stunt People". Brett wrote: " ....a two-stage start sequence that initially spins it up to 1000-1500 rpm below level flight revs for the first 20-30 seconds, then jumps to full level flight revs, just to make the takeoff easier".

After my recent flights with eParrot, I can only enthusiastically agree with Brett's idea, however I would prefer not jumping but governed ramping to the flight RPM.

I do not know how difficult is creation of such ramp for the existing timers and if this is possible at all but believe the problem is extremely interesting, challenging and worth the effort.

Following another suggestion from the Brett's response: "... many pilots currently have the airplane released at partial power", I will begin releasing eParrot at the moment the motor starts. This will allow the plane to roll for four seconds of gradually increasing RPM what should be a bit less "nervous".

On the other hand, these four seconds are not governed in terms of the motor and ESC protection against the current spikes when the prop. hits something.

Decisions, decisions and more decisions.

Regards,
Matt

"There is no progress without risk" 

[Keith Renecle]

Yes, I am reading this. Looks like I need to word my emails a little more carefully......... I have been the F2 rep for South Africa for many years and there are many things that are discussed but mostly do not get added to the actual rules. This one is not a rule in the F2B rules but something that was discussed many times when e-stunt got better. It was in the interest of fairness to the IC engine folks. This was also at the same time as the problem of programming the landing and eventually the rule was added that the electric brake must be used to stop the prop spinning to "prove" that the landing was not being programmed. Just recently there has been a discussion about using an R/C shut-off for landings instead of an emergency. So if we do create a specialized take-off program and it did actually make a huge difference (which I doubt), there would mostly likely be a cry of "unfair"!

I all practical terms, in world champs we either get a good take-off surface like a hard circle or really bad grass with bumps and holes, so right now I don't see the need for a specialized take-off program for my particular timers. Sure....it's interesting, and from writing to Matt a lot, I realize that he enjoys these sort of challenges, but right now I have more interesting things to play with, like my cnc foam cutter which is quite challenging/frustrating enough for me. 

Keith R

[Brett Buck]

Yes, I am reading this. Looks like I need to word my emails a little more carefully......... I have been the F2 rep for South Africa for many years and there are many things that are discussed but mostly do not get added to the actual rules. This one is not a rule in the F2B rules but something that was discussed many times when e-stunt got better. It was in the interest of fairness to the IC engine folks. This was also at the same time as the problem of programming the landing and eventually the rule was added that the electric brake must be used to stop the prop spinning to "prove" that the landing was not being programmed. Just recently there has been a discussion about using an R/C shut-off for landings instead of an emergency. So if we do create a specialized take-off program and it did actually make a huge difference (which I doubt), there would mostly likely be a cry of "unfair"!

    OK, thanks, I didn't think so, but I wasn't sure.

    Actually, even though I don't fly electric, I don't see a big problem with having a different ramp-rate program to help the takeoffs. After all, to first approximation, you are replicating the performance of the IC system, and it can be pretty ugly to watch the way it is now. I certainly wouldn't outlaw it. I wouldn't outlaw the landing rundown, either. I would get rid of the 1-lap landing requirement instead and let you have the rundown, since there wouldn't be a significant  advantage to it any more.

  I guess I also missed the rule about prop brakes, too. We don't have that and aren't going to - same reason, we don't care if someone lands power-on, since we don't have the 1-lap landing requirement. People have landed with the IC engine running in NATs competition and no one really cared too much.

Sure....it's interesting, and from writing to Matt a lot, I realize that he enjoys these sort of challenges,

    I think I get your drift on that one...

    Brett

[Keith Renecle]

I can only agree with you that all rules should be based on common sense, and I too prefer the AMA ruling on landings. The prop brake thing to me is also silly because if don't enable the esc brake, then the prop spins and acts like an air-brake so you get zero glide. If someone wants to let their prop freewheel then let them. Electric power has been around long enough now to see when the power is still on or being reduced purposely.

If I think about how long it took a few of us to convince the FAI rule makers about some of the maneuver shapes and silly things like not trying to define level and vertical flight paths as being relative to the surface of the circle "even it is a slope" then you can understand the difficulty in getting the rule book technically correct. I have often stated that the rules should be defined from what the model can actually perform and not what certain people think the maneuvers should look like. The math for spherical geometry has been around a lot longer than our toys. Anyway, this is a long story as you know too well, so we don't need to revisit it. This could be construed as a side issue.........sorry Matt!

Keith R

[Brett Buck]

I can only agree with you that all rules should be based on common sense, and I too prefer the AMA ruling on landings. The prop brake thing to me is also silly because if don't enable the esc brake, then the prop spins and acts like an air-brake so you get zero glide. If someone wants to let their prop freewheel then let them. Electric power has been around long enough now to see when the power is still on or being reduced purposely.

If I think about how long it took a few of us to convince the FAI rule makers about some of the maneuver shapes and silly things like not trying to define level and vertical flight paths as being relative to the surface of the circle "even it is a slope" then you can understand the difficulty in getting the rule book technically correct. I have often stated that the rules should be defined from what the model can actually perform and not what certain people think the maneuvers should look like. The math for spherical geometry has been around a lot longer than our toys. Anyway, this is a long story as you know too well, so we don't need to revisit it. This could be construed as a side issue.........sorry Matt!

Keith R

   As I tried to gently point out earlier, the original poster doesn't get to dictate the responses, and is not in charge of "managing" the thread to get only what they want out of it (which is also a feature of the behavior of the ever-lovable "Charles").

   Fortunately, we have already done the work for you, its in the middle of an egregious, endless, run-on paragraph (which is more-or-less my fault for not having properly formatted it) and even has (erroneous) metric dimensions in the proper Continental manner:

11.2.
 At least two (2) laps of level flight shall precede each maneuver, including landing. (A nominal interpretation of the “two (2) lap’’ level flight requirement is the accepted interpretation, allowing the starting point of one (1) maneuver to begin slightly less than two (2) full laps after the exit point of the prior maneuver due to the width of the maneuvers.) The two laps between maneuvers need not be at normal level flight attitude. Except for the Overhead Figure Eights, judges shall not require more than two (2) nominal level laps between maneuvers due to the time limit imposed by these regulations. At least two and a half (21⁄2) nominal laps must be flown between the Hourglass Figure and the Overhead Figure Eights. Level flight at an altitude of from 1.20 to 1.80 meters (3.9 to 5.9 feet) will be considered normal level flight, regardless of the height of the flier. Level, for purposes of Precision Aerobatics, means flight along a horizontal plane (perpendicular to vertical); it explicitly does not mean a constant height above the terrain over which the airplane flies. The portions of certain maneuvers which require normal level flight elevation must be accomplished between 1.20 and 1.80 meters (3.9 and 5.9 feet) for maximum points. The elevation reference shall be the height at the center of the pilot’s circle. In cases where uneven terrain makes this impractical or unsafe, and alternate reference shall be determined by the organizers and announced at the pilot’s meeting.....


       I am less convinced on the topic of the spherical geometry issues, in fact, I would be highly inclined, if I was going to change anything, to remove ANY reference to spheres and define each maneuver in terms of a projection of the 3 basic shapes onto a plane perpendicular to the center of the maneuver - since that is how it is both flown and judged anyway. We have had WAY too many bizarre "it has to look wrong to be right" type interpretations over the years, and it's entirely moot because it's judged as if you were seeing 8-year-olds drawing a square on a blackboard.

   I have also been *sorely* tempted to add a paragraph at the beginning to the effect of:

   "There is no intent to insert subtleties of interpretation or "hidden meanings" in the rules. In almost all cases, the rules are explicit. In cases requiring interpretation,  the simplest and most facile reading of the rule is correct.   The rules do not contain anything that requires extensive study or any form of cryptic hidden meaning or complex logical or rhetorical constructs. Anything appearing to be of that nature is either a simple mistake or a figment of the reader's imagination, and any such conflict is correctly resolved by application of simplest possible interpretation and/or common practice.

    But based on doing this forever, it wouldn't make any difference, there would still be people pouring over the rules for years,  looking for secret messages like the damn Da Vinci code.

     Brett

[Howard Rush]

If I was doing it, I would be tempted to use ... a two-stage start sequence that initially spins it up to 1000-1500 rpm below level flight revs for the first 20-30 seconds, then jumps to full level flight revs, just to make the takeoff easier.

Available in the TUT, as used at the 2014 world championships.

[Keith Renecle]

Tut, tut Howard................!  Hmmm......so that's how you got such good scores! 

Keith R