skillet92

Guys I have just finished my second ESM Corsair and she is dialed in!!! Take offs are great, and landings have no tendency to nose over! So far a lot better set up and flier than my first one. My question is now that I have really been able to fly her and wring her out I notice what to me looks like the plane is moving the tail side to side when doing fly bys. I have read some info on here that call it a waggle. What I am wondering is it normal and do I need a stronger rudder servo? What is the cause of it?

Chad Veich

My Feedback: (60)

Typical of almost every Corsair model I've ever seen fly. It is something in the aerodynamics of the airframe and I doubt it will change no matter what servo you put on the rudder.

skillet92

Thanks Chad, I wonder since it is modeled after a scale real plane did the real one do it? It does not affect the way the plane flies or handles. Mine is over 19 pounds and the G-38 pulls it GREAT!!

yard-dart

My Feedback: (35)

Mine does it too, mainly during high-speed flight. From what I'm told, this is a characteristic of all Corsairs.

denoferth

My Feedback: (71)

I have to admit my only experience with gull wing models has been the upright kind and they display no such tendency. Tail wagging would seem to make it a very bad gun platform, a fatal flaw for a fighter, and that’s certainly not born out in its record . It would also seem to be an uncomfortable ride for the pilot and I can find no complaint in any pilot reports I have had access to. Literature on other aircraft, like the B35 Bonanza for instance, almost always mentions the tail wag, especially in turbulence. Some say it’s caused or acerbated by the short coupling combined with the wing span being longer than the fuselage.

Scale Specialties

Corsairs are indeed prone to this phenomenon, but the fullsize was not. The fullside did indeed have some propensity to dutch roll, most of this was attributed to the forward placement of the vert stab/rudder and the relatively small vertical stab in relation to the rudder which was much larger in proportion. In models a culprit could be a rudder with static balance issues. Most modelers in my experience never bother to do this. Or it may very likely be a dynamic balance issue related to the hinge arrangement the model has and the way the small top "flag" on the rudder goes into the wind to help push the rest of the rudder the other direction. If this arrangement is off just a little bit, the rudder may tend to "hunt" during normal straight and level flight. Remember, that front portion of the rudder goes into the slipstream opposite everything behind the hinge line. The rudder servo will tend to mask this but any slop or give in the setup will be reflected negatively.
Hope that helps, sorry for being so wordy.

denoferth

My Feedback: (71)

Sure sounds like a logical explanation to me.

Chad Veich

My Feedback: (60)

As noted by denoferth any tendency of the full size to "fish tail" would have been very detrimental to good marksmanship and would have surely been addressed by the manufacturer if it had been an issue. I've been priviledged to see at least 8-9 different full size Corsairs perform at airshows over the years and have never noticed this characteristic in any of them, even at high speed and in windy conditions. It has also been my experience that, in most cases, as the scale of the model increases the tendency to fish tail decreases.

Experten109/40

My Feedback: (-1)

Its called "dutch roll" caused by not having enough vertical fin. You will not see this on a real airplane because it has been engineered out.
Moving your CG forward will help because that will increase verticle axis stablity. If thats a problem, suggest you go with a gyro.

another thing, if the weight was scaled porportionally, most of the "waggle" would go away.

skillet92

I understood everything else that you guys said but this. I am at 19 pounds, maybe a little over, for a plane the the manual says should weight 15. Now in saying that everybody that built it came in in the 18-19 pound range. For a 74" wingspan plane are you saying that I should have been lighter or heavier? I only ask because I can not imagine this plane being any heavier! I can deal with it if it keeps performing like it does. And it looks so good in the air!!!

Experten109/40

My Feedback: (-1)

' scaled ' weight would be around 42lbs. obviously not practical or recomended to do.
but the wag would go away mostly. weight= stability when momentum is envolved.

thats the problem with scaled rc models, the weights never work out.

cheers.

dionysusbacchus

My Feedback: (25)

I'll quote the best explanation I've read on this subject, and it goes back to one of my pet peeves, keep the outer extremities of a model as light as possible. When I see servo's in the tail and wing tips along with other equipment in a Corsair especially, I just cringe. The full scale Corsair had bell-cranks for it's plywood ailerons and fabric covering on the outer wing panels. Also if you look in the rear fuselage of a full scale corsair there is absolutely nothing back there but a tail wheel. I could be wrong but none of my planes have ever exhibited Dutch Roll.

Whassa Dutch Roll ???


From : Don Stackhouse

It's a maneuver that combines yawing and rolling motion, sort of like a falling leaf. The model wags its tail side-to side, and rolls in concert (but out of phase) with the tail-wagging. It's sort of like a falling leaf's motion, but regular, with a specific frequency. It's the result of a number of parameters, the main ones being the wing dihedral, the effective fin area, and the inertia about the yaw axis. In general, too much dihedral and/or not enough fin area will result in a dutch-rolling tendency.

Spiral instability is the tendency of the model to wind itself up into a "graveyard spiral" if held in a sustained turn (such as a thermal turn). It's generally the result of not enough dihedral, or too much fin. Also, it's not unusual for a model to have positive spiral stability (i.e.: tends to roll out of a turn, back to wings-level) for some bank angles, and slightly negative spiral stability for others (typically for steeper banks)

Note, the fix for one problem is the opposite of the fix for the other. Depending on how much inertia the model has about the yaw and roll axes, the ranges of dihedrals and fin areas that result in one problem or the other may:

1. Overlap. No matter what fin area and dihedral you use, it will either dutch roll, have spiral instability, or both. This is usually the result of having too much inertia. That's one more reason for trying to keep the weight out of the model's extremities!

2. Touch at one spot in the middle. There will be ONE, and only one, combination of wing dihedral and fin area that has neither dutch roll nor spiral instability problems.

3. Have a range of dihedrals and fin areas that are free of both dutch roll and spiral instability. Once again, keeping the inertia to a minimum is usually the key to the size of this "sweet spot". Because they tend to have slightly higher inertia, the size of the sweet spot for a conventional tail tends to be a little bit narrower than for a V-tail.

SCALECRAFT

My Feedback: (13)

My 54" all composite Corsiar did the same thing. I would be willing to bet that a straight wing on a corsair model would stop the wag.

I have other warbirds with short tail sections and they don't wag.

Just a thought.

Steve

SJN

My FMS foamy does this too.

Anyone tried a rate gyro on the rudder ?

dauto

My Feedback: (10)

I have a 86" TopFlite gold edition and it weighs 36 lbs. with 5lbs of lead being on the nose.I am using a BME44 for power and the tail wags.But the plane flies great and lands fantastic at this weight.I have a parkzone corsair and it wags too.

GaryM

My Feedback: (14)

This is a question that is often brought up but never seems to be answered as to whether or not the full scale did it and why it occurs. I thought who better to ask than someone who flys a full scale. So, I shot an email off to the Lone Star Flight Museaum in Galveston, Tx. and ask them to direct my inquiry to the pilot of their F4U-5. Keep in mind he reminds us he is not an engineer and this is just a quess on his part as to why our models waggle.


Gary,



My name Is Tom Gregory, I am the chief pilot here at Lone Star. The -5 Corsair is a joy to fly and I have been lucky to have flown her since the mid 90’s. It requires a lot of rudder trim after takeoff as your speed builds. There is no tendency for the nose to “waggle” around throughout the speed range. I surmised by looking at your pictures that there is no rudder trim in your rudder system. This certainly could have something to do with the flight characteristics you are experiencing. I am not an aero engineer and please don’t hold me at gunpoint if you find that I was wrong. You have a beautiful model and I wish you the best.



So this is one report from a full scale pilot that the real thing does not waggle, and she requires more rudder trim to hold a heading the faster she goes.

chistech

Both me and my buddy have the old Kyosho Corsairs and neither of them have the waggle at all. They fly straight and true yet my Kyosho P40 and Spitfire does waggle quite often. I find that there are times when the waggle is present and other times when the same plane really grooves. To me it seems to be because of wind speed and different temperatures. Just my experiences.

scubajohn

my corsair is not finished so i have not flown one i do fly afull scale 172 and ruder is always a factor the turn and bank indicator has a ball in it and if you are in uncordanated flite this tells you what rudder input is nessasary you can also feel it in the seat of your pants but as they say trust your insterments
with rc we must use or eyes to determine control inputs so i am thinking ruddrer inputs may change througout the flight envolope as the pilot from lone star stated
ruder is one of the most overlooked or not used properly controls

tfarmer96

Its just happy right?