Flaps geometry

[Matt Piatkowski]

Hello again,
Almost everybody flying stunt agrees that full size stunt plane (~60" span, 650-700 in.^2 and 62-65 oz. RTF weight) performs corners better with narrower flaps.
A little wider flaps allow for better execution of round maneuvers, but corners will be a little worse. This general rule is of course affected by other parameters of the model like the flaps to elevator ratio, hinge-to-hinge (h-t-h) distance, horizontal stabilizer size, horizontal stabilizer to elevator ratio, wings airfoil and shape, C.G location, RTF weight and many other parameters. 

What should be the length of the flaps to work well in corners? Some of the very successful stunt planes have flaps stretching to the wing tips (let's call them "Full Length Flaps": Max Bee II, Impact, Thundergazer itd.), some have shorter flaps (for example: Yatsenko's Shark, Solomianikov's Maestro itd.)

I would like to concentrate on corners because they are simply more difficult to fly well than round figures.

Is there any connection between wings shape and the length of the flaps? For example: if wings are trapezoidal, flaps are full length, if elliptical or semi-elliptical (Shark again), the flaps are shorter.

Is this a matter of...fashion or there exists some, aerodynamic based, justification for that?

Regards, stay safe and fly stunt if you can.
M

 

[jfv]

Check out this thread.  I think it is what you are looking for.

https://stunthanger.com/smf/stunt-design/flap-design-pros-and-cons-of-extending-flaps-all-the-way-to-tips/

[Matt Piatkowski]

Hi Jim,
Thank you for the link.
I collect the parameters and geometry of modern stunt planes in order to better understand the C/L stunt and the length of the flaps is one of them.
Please note that only elliptical or semi-elliptical wings have partial flaps. These flaps are usually w bit wider close to the fuselage when compared to the "Full Length Flaps" and their width does not go to zero in top competition models from Ukraine and Poland.
Most of the currently flying stunt models use the configuration shown on top of the page. Wingtips may vary, the trim tabs may be installed or not, flaps may be trapezoidal or almost rectangular...
Please see the attached.

Hi Motorman,
I will write to David Fitzgerald. Thundergazer wing is a bit smaller than the wings I prefer in 2020.

Regards,
M

[Howard Rush]

When in doubt copy Thundergazer.

The Thundergazer is an attempt at compromise. It has one full-span flap and one partial-span flap.

[Matt Piatkowski]

Hello Howard,
Please see the attached. One set of flaps in semi-elliptical Sea Fury wings is clearly visible. I have noticed that these flaps extend almost to the tips.
This, in my opinion, represents a derivative of the flaps for semi-elliptical wings from my previous attachment (Wings Shape, Stunt Planes).

The other attachment shows Thundergazer in 2008. The photo is rather small and it is hard to see the extend of the flaps but I think they are Full Length.

Regards,
M

[Brett Buck]

I will write to David Fitzgerald. Thundergazer wing is a bit smaller than the wings I prefer in 2020.

  I agree with that if you are going to use electric power. If you were going to use a 40-75 tuned pipe engine, it hasn't shown any real limitations as long as you can keep it below 70 ounces (dry)/78 ounces (fueled). David's is 63-64 (dry). I think you could probably get it to the electric equivalent of maybe 56 with no battery with no real problem, but it would require significant changes to accommodate the battery, since there's not enough room.

      My electric design is *substantially* bigger than the Thundergazer, 675, which is the same as my current IC airplane, but with a thinner airfoil and higher aspect ratio - about like a scaled-up Imitation in general dimensions. I have the wing built (complete and then split into in two parts - twice), but still not reassembled and currently, no controls

     Brett

[Matt Piatkowski]

Hi Brett,
The 1/2 wing you see in the attachment has the Tiger Shark airfoil. Total span of the wing is 62" now, without the tips.
The flap you see is too narrow close to the wing tip and it is also too thin. The thickness of the flaps changes from 0.250" close to the horn attachment reinforcement to 0.158" at the tip.
The trailing edge of the wing has constant height: 0.370"
The width of the flaps at the horn attachment is 2.76".

Comment: the wing was designed for the profile fuselage stunt plane, therefore the flaps horn is asymmetrical w/r to the wings center to allow for the pushrods attachments and regulation.

The total surface area of the wing (without tips) and the existing flaps is 715 in^2.

The wing was intended for large profile stunter with 60-65 size glow engine.

Should I only increase the width of the flaps at the wing tips by 0.40" and leave the flaps base width (2.76") as is and the thickness as is?

Should I replace the existing flaps with the flaps wider by 0.40" at the tips, having 2.76" at the base and make flaps as thick as the TE of the wings along the length ?
Such flaps seem to me impossibly thick and beg for shaving some weight by sanding to wedge airfoil.

Even in the level flight in quiet air, the flow over any flaps is turbulent but the sudden "step" that exists right now behind the wings TE will cause, in my opinion, additional re-circulation and turbulence, both contributing to drag and decreased efficiency of the flaps.

Thank you for your input,
Regards,
M

[Will Davis]

What Howard said

[Matt Piatkowski]

Hi Will,
The photo of Thundergazer you have attached indeed shows the inside flap shorter, I would say by 3",  than the outside flap.
This is interesting because the inside wing and flap generate slightly less lift than the outside surfaces.

I do not have any plausible explanation of consequences of this aerodynamic imbalance.
Regards,
M
 

 

[Brett Buck]

Hi Will,
The photo of Thundergazer you have attached indeed shows the inside flap shorter, I would say by 3",  than the outside flap.
This is interesting because the inside wing and flap generate slightly less lift than the outside surfaces.

I do not have any plausible explanation of consequences of this aerodynamic imbalance.

      The tail is centered on the fuselage.

     Most airplanes with asymmetry in the wing end up with tabs or larger outboard flaps, to compensate for the fact that the airplane tends to hinge worse in tight corners than it does in round loops. Effectively, it acts like it needs less tipweight in hard corners than it does in round maneuvers. The nearly universal solution is to make the outboard flap larger than the inboard. I think this is probably because, while using asymmetry in the wing will result in the CG being in the center of the fuselage, the inboard half of the tail also goes slower than the outside, meaning it applies torque in proportion to the control deflection - which rolls the airplane in the direction of hinging.

     From what little I have studied equal-span wings, they have other issues (like requiring heroic amounts of tipweight), but not this one to the same degree. With equal-span wings, the CG ends up offset well to the right/outside of the circle, which is why it takes so much tipweight, with effectively add the same asymmetry to the tail as it does to the wing. Unfortunately, the tail needs about half as much, so it tends to have the opposite problem.

     There have been some epic arguments over asymmetry (most of them displaying the mathematical and critical thinking failings of the American and European educational systems) but as far as I can tell, you can make any of them fly about the same, and acceptably well, as long as you work in the range of about 0 to 1.5".

     Some people have made them the wrong way around, too, which is intended to "carry more tipweight", which makes no sense whatsoever, and is based on a very basic misunderstanding of something Al Rabe wrote in about 1969, as far as I can tell. However, it you adjust everything to be as good as it can be, it doesn't seem to hurt anything too much. Which just goes to show that, like a lot of the stuff we tend to argue about,  it is not a critical parameter.

     It's in the same category with the tail moment, changing it by 2" doesn't make a big difference if otherwise optimized, as long as you don't get it too short.

     I have flown both of David's Thundergazers, and they were perfectly acceptable with the arrangement he came up with. 3" seems like a lot of flap asymmetry to me, I would not use anything close to that, Thundergazer or otherwise, but be prepared to add a tab or replace the outboard stab with one of a different chord to adjust the differences between rounds and squares. My current airplane has 1" of asymmetry and about 5 square inches more outboard flap area. A typical number is anywhere from 1/16" to maybe 1/8 more outboard flap chord.

      Brett

[Brent Williams]

Matt,  here is a low-res view of the ThunderGazer plans.

[Matt Piatkowski]

Hi Brent,
Thank you for the plans.
I am trying to reach David Fitzgerald for comments.

Hi Brett,
"Critical thinking failings of the American and European educational systems.." is, in my opinion, one of the four horses of the Apocalypse in the modern world.
The other three, in no particular order: corrupt and irreparable political systems, idolatry of money and extreme selfishness.

Could you, please, comment on the issue of flaps geometry in the wing showed in the attachment to my message sent Yesterday at 01:12:26 PM?
Thank you,
M

[Brett Buck]

"Critical thinking failings of the American and European educational systems.." is, in my opinion, one of the four horses of the Apocalypse in the modern world.
The other three, in no particular order: corrupt and irreparable political systems, idolatry of money and extreme selfishness.

     One thing I am pretty sure about - kids aren't really any different than they have ever been. The failing is what and how we are teaching them.

Could you, please, comment on the issue of flaps geometry in the wing showed in the attachment to my message sent Yesterday at 01:12:26 PM?

     I prefer full-span flaps, because I don't want to create the transition from the deflected flap to the fixed "filler" at the ends. Just think about what is happening there - air is supposed to be flowing over the deflected flap, and 1/16" away, it's supposed to be trailing straight off the wing. That means there is shear and a vortex coming off the edge. That has to create control non-linearity, that is, it has to change the flow radically as the flap deflects.   And additional problem is if the flaps are tweaked, or if there is a trim tab with deflection - then it lines up differently on the left than the right, with uncontrollable trim effects.

     Another David airplane (Trivial Pursuit/"Star Gazer")  had this in droves. It had a small warp in the wing, and David used a trim tab to "correct" it. We could never get it calmed down in roll/yaw, it acted like it had too much tip weight on insides, not enough on outsides. One day we just bit the bullet and tweaked it with a heat gun. Straightened everything out, trim tab went straight, too, everything was fine. Next flying session, the warp came back, we had to tweak it with the tab instead, back to the same problems. Eventually we got it to be "ok", not great, by tweaking the flap and the trim tab to get the wings level while also having the trim tab and flap lined up at the same time on either wing. The entire flap and tab lined up on the inside while being deflected down a bit, and the flap and fixed section was lined up at neutral one the outboard. Then it was pretty good (although still not as good as the others).

    The Yatsenko types end up with a similar situation if you have to tweak the flaps (which, jig construction or not, you still have to do), but flap chord is so narrow where the interface is that it doesn't appear to cause tremendous problems - although none of them that I have assisted with of flown  was really "right", even though it was good enough.

  Subsequently, at some team trials, I talked to Paul about it, and he showed me his airplane, where he had the adjustable tabs with the adjuster removed, and taped to the rest of the flap, so the entire thing moved as one piece, for similar reasons. I subsequently experimented with the same thing on one of my airplanes, and it flew almost exactly the same as it had before, except that all the little roll "glitches" around neutral (particularly in the vertical just went away. Both airplanes I have built afterward have the flaps extended to the tips (since I don't need adjustability, my wings are straight) and at least the first one has absolutely none of the these sorts of little hitches around neutral.

        So, I think it is a bad idea to use the "fixed section" of the flaps as an adjuster, because of the differential effects, and I think it's a less-than-ideal to have the unmoving sections at the ends even if they aren't adjustable.

     As always, people can make do with a remarkable number of problems and bad ideas, and still be successful. As long as it stays out on the lines and you are willing to thrash hard enough, you can overcome almost anything.

    But stunt is hard enough without building in problems.

     Brett

   

[Howard Rush]

Some people have made them the wrong way around, too, which is intended to "carry more tipweight", which makes no sense whatsoever...

Sure it does. You can calculate it from nose moment and density altitude.

[Brett Buck]

Sure it does. You can calculate it from nose moment and density altitude.

Now Howard, what are we going to do with you?

    The real point is that even making it go the wrong way can be worked around to some extent, so the bizarre and quite lengthy arguments that have taken place in the past over 1/4" differences seem, well, more than a little pointless.

    Brett

[Igor Burger]

     Most airplanes with asymmetry in the wing end up with tabs or larger outboard flaps, to compensate for the fact that the airplane tends to hinge worse in tight corners than it does in round loops. Effectively, it acts like it needs less tipweight in hard corners than it does in round maneuvers.

All my Max Bees (all beside the first are done from CNCed parts, so mostly identical) need trim tab (for Mat - it is on building plan so you should know about it - and it does similar thing like that asmymetric flap on that David's model) ... except for model I had in Perth. I was not able to trim it well until I dismounted that tab. The only difference of that take apart wings was, it had tabs of the same span, so the wing was symmetrical. 

But I am not 100% sure with that elevator offset reason. During time with my first Max Bee I tried many different trims in yaw direction and I did not find difference (size of necessary tab area) between tangent and extremaly yawed trim. And it should, if the tail offset is the reson and yaw moves it relative to the wing. Or at least I do not remember well.

[Matt Piatkowski]

Hi Igor,
Indeed, the Max Bee II plans show the trim tab on the outside flap.
I have never used it in my version of Max Bee II named Big Red but I will give it a try.
Unfortunately, Big Red is in Poland and I am stuck in Canada until the pandemic ends.

The first item on the Big Red "to do" list is to make it "turn better". To do this, I am going to move the C.G of the RTF plane back as far as I can and fly.
C.G cannot move back more than 10-12 mm. (0.40-0.47") without serious internal surgery on the plane, cutting into the wing etc. - I sent you the photo showing what I am going to do with 6STP2800 battery to achieve this. 
Like I wrote in my email to you, perhaps I need to make hundreds and hundreds of flights to adjust my input to the response of the logarithmic control system in Big Red and then it will start "turning better"?

Now..I know that the phrase "turn better" is somewhat vague but this is what I heard from a very good F2B flier who had flown the pattern with Big Red.

The issue of "turning better" is actually a very good subject for a separate thread. We are all searching for the elusive combination of many parameters to see our models flying "clean and tight" through the corners, "tracking and grooving" well and being "controllable". 

The quest to achieve this combination never ends and this makes the C/L stunt so interesting.
Stay Safe,
M

[Igor Burger]

Yes I saw those pictures and I also wrote you that you not need any surgery to move CG back, simply attach some balast to tail,  2, 5 or even 10 grams is no problem, takes only seconds, battle with model with wrong position of CG is lost time and weight of model gained by wrong CG position is counterproductive and something like flaps geometry, magic bellcranks or 1000 flights will not solve it.

Here is model of our former world chamion Jozef Gabris. When I was kid I was suprised by that heavy brass wheel on tail, he told me that when he trimed model, he simply add lead solder on tail wheel until it flew well, then removed and made wheel of the same weight. It was aproximately 15 grams and still that model 2x won worlds so I think you can also fly with 10 grams of dead weight on tail  

[Matt Piatkowski]

Hi Igor,
Before I left Poland last year, on September 11, 2019, I made five full patterns with Big Red having 15 grams of lead attached at the aft end of the fuselage, very close to the rudder's hinge line.
The RTF weight after adding this 15 grams was, I believe, 1837 grams. I left all the notes pertaining to Big Red in Poland and I am not sure about this weight right now.
Unfortunately, I could not see nor feel any changes in model's "turning agility" in corners.  Round figures were ok., level flights both ways stable as before adding the weight, gliding in the end of flight stable.
All this with 100 mm. lines distance on the handle. B-crank has 100 mm. lines distance so handle to b-crank is 1:1.

If I can travel to Poland this year, I will start adding the weight in 5 grams increments at the aft end of the fuselage until this thing is more pitch sensitive.

I have a question for you: what is better from the turning agility point of view: some weight at the tail area or c.g of the battery moved back if BOTH allow to place the RTF model's C.G in the same place?

As of today, I have only one opinion of the very good F2B flier that agreed to fly-test Big Red and, based on this opinion, I am trying to make the plane more pitch sensitive.
I would prefer to get other opinions from the very good F2B flyers as the guy who flew Big Red was using geared contra in his main competition plane for a long time and his perception and reflexes were optimized for that.

One way or the other, I will discover what is going on, learning to better use the logarithmic control system in the meantime.

Thank you for the historical photo.
Stay safe,
M
 

[Howard Rush]

Although it’s not far behind the CG, perhaps a gram or two of tape between the fixed part of the wing and the flaps could help.

[Matt Piatkowski]

Hi Howard,
I will tape both gaps if I can get to Poland where Big Red gathers dust - this is #1.
If this works, and it actually may despite the fact that Igor does not do it in his Max Bees, #2 is more tail weight.
If this works, and I will be still able to control the flight line without "waving", I will increase the deflection of the elevator by about 3-5 degrees. This is #3.
If this works without tendency to stall the model in corners, I will try the outside flap tab. This is #4.

I am using the Rabe Rudder in Big Red and it was generating from time to time something funny in the yaw channel in some corners. Perhaps the gyro effect was saying hello from the dark side of the C/L flying?

Please note "time to time" and "some corners". Here I am at loss as I do not remember the weather or/and my hand and wrist movement when this "funny" happened.

Everything must wait for the borders to open but when...?
Regards,
M

[Howard Rush]

I’m looking forward to seeing you there.

[Igor Burger]

Hi Howard,
I will tape both gaps if I can get to Poland where Big Red gathers dust - this is #1.
If this works, and it actually may despite the fact that Igor does not do it in his Max Bees, #2 is more tail weight.
If this works, and I will be still able to control the flight line without "waving", I will increase the deflection of the elevator by about 3-5 degrees. This is #3.
If this works without tendency to stall the model in corners, I will try the outside flap tab. This is #4.

I am using the Rabe Rudder in Big Red and it was generating from time to time something funny in the yaw channel in some corners. Perhaps the gyro effect was saying hello from the dark side of the C/L flying?

Please note "time to time" and "some corners". Here I am at loss as I do not remember the weather or/and my hand and wrist movement when this "funny" happened.

Everything must wait for the borders to open but when...?
Regards,
M

I am not Howard, but I do not understand - you mean I do not have taped gaps? I do on all my models. YOu saw it, so if something was not clear, you had to check it. Including CG position. BTW you still did not write where you have it so hard to suggest something.

#3 - tell us what is actual maximal deflection I have it 30 degrees
#4 - all max bees need it, so why do not you simple attach it, it has TE of flap 6mm high so simply tape there 6mm thick 150x15mm tab I had sometimes even larger .. if you feel it helps, glue it there permanently, taped tam can move in corners and it can spoil quality of somtrolling

and ...

#5 also tell us radius of stab, your picture you sent me shows blunt LE, if I see well, it needs minimally 5 or 10 mm CG aft of optimal CG for sharp LE as I use

#6 I also see you have leadouts moved extremely forward, I even thing front of CG, but if not, your CG is shifted extremely forwad


... looks like I will need to wrote trimming article for MaxBees 

[Matt Piatkowski]

Hi Igor,
Ad.1)    Indeed, in your email to me (matt.piatkowski@gmail.com), dated Apr. 12, 2020 you answered >>> Yes <<< to my question "Do you seal the gaps in your Max Bee II ?".
I missed this >>> Yes <<<...My apologies...Old age perhaps...??

Ad.2)    The current position of the C.G for the RTF model is 83 mm. from the L.E of the wing measured along the outside surface of the fuselage. This is with 15 grams of weight added on the fuselage end, along the rudder hinge line. Before adding 15 grams the C.G was exactly like showed on your plans - 80 mm. The precision of this measurement is probably (+) (-) 1 mm. - I do not have the 3D laser equipped rigid fixture and I used rulers, right angle triangle etc.

Ad.3)     Here I am not sure. The model and all the notes are in Poland and I simply do not remember. The elevator's deflection in Big Red is larger than the flaps deflection for certain.
The flaps deflection is limited to the maximum allowed by the logarithmic mechanism, I think it is 30 degrees. The elevator's horn arm is 19 mm. what is the minimum possible (please see the attached). This horn has a slider (not shown) that allows for mini-adjustments using the hex head screwdriver.

Ad.4)     I will attach the tab to the outside flap. After discussion about flaps in this thread I began sensing the need for the flaps generated moment CORRECTION in the yaw channel while executing corners.

Ad.5)     Please see the second attachment: this is the best photo I have of the Big Red tail area. The radius of the horizontal stabilizer LE is larger than on your plans but the LE is not blunt. Again, I cannot measure this radius now. The radius of the stabilizer can be decreased almost to the knife edge by sanding the LE area and replacing about 50% of the balsa sheeting along the width of the stabilizer. I have used foam as the stabilizer's core and it can be sanded easily.    Comment: you say interesting things about RELATIONSHIP between the RTF model C.G position and the SHARPNESS of the stabilizer LE.  Further explanation of this phenomenon will be appreciated.

Ad.6)      No. The leadouts are not "extremely forward". The centerline of the leadouts at the inside tip is 16-18 mm. AFT w/r to the current location of the RTF model C.G (83 mm. from the L.E of the wing measured along the outside surface of the fuselage).

Thank you for your comments - I look forward to meeting you in Wloclawek if the circumstances allow.
Stay Safe,
M

[Igor Burger]

Ad.2)    The current position of the C.G for the RTF model is 83 mm. from the L.E of the wing measured along the outside surface of the fuselage. This is with 15 grams of weight added on the fuselage end, along the rudder hinge line. Before adding 15 grams the C.G was exactly like showed on your plans - 80 mm. The precision of this measurement is probably (+) (-) 1 mm. - I do not have the 3D laser equipped rigid fixture and I used rulers, right angle triangle etc.

80mm is safe position for sharp stab and first flights. I have it 85mm. I think your blunt stab easily need 90 ... if everything else is the same. I affraid not.
However I am surprised, I have gap aproximately 20mm between battery and wing fuselage rib. If I add your screws and take apart harware on stab, something is "different" here, my take apart Max Bee had gap proximately 50mm. 

Ad.3)     Here I am not sure. The model and all the notes are in Poland and I simply do not remember. The elevator's deflection in Big Red is larger than the flaps deflection for certain.
The flaps deflection is limited to the maximum allowed by the logarithmic mechanism, I think it is 30 degrees. The elevator's horn arm is 19 mm. what is the minimum possible (please see the attached). This horn has a slider (not shown) that allows for mini-adjustments using the hex head screwdriver.

As far as I remember, flaps should be limited to 27 and elevator to 30 degrees and that is enough for tight corners. Elevator horn should be 20mm.

Ad.5)     Please see the second attachment: this is the best photo I have of the Big Red tail area. The radius of the horizontal stabilizer LE is larger than on your plans but the LE is not blunt. Again, I cannot measure this radius now. The radius of the stabilizer can be decreased almost to the knife edge by sanding the LE area and replacing about 50% of the balsa sheeting along the width of the stabilizer. I have used foam as the stabilizer's core and it can be sanded easily.    Comment: you say interesting things about RELATIONSHIP between the RTF model C.G position and the SHARPNESS of the stabilizer LE.  Further explanation of this phenomenon will be appreciated.

It was discussed several times here, try carbon rod 2mm diameter and tape it on LE and you will see if here is difference. You not need solve everything with first minute surgery 

Ad.6)      No. The leadouts are not "extremely forward". The centerline of the leadouts at the inside tip is 16-18 mm. AFT w/r to the current location of the RTF model C.G (83 mm. from the L.E of the wing measured along the outside surface of the fuselage).

So move CG back, move LO minimally the same distance and try, then try to move it even more aft , retrim model  and see if it is better I think it will be. I guess it should be aproximately 25mm, I have it much more, but most flyers here (Alex for example) have it there.

[Matt Piatkowski]

Hi Igor,
Ad.2.) To move the RTF model C.G back 7-10mm. (from current 83 mm from the L.E of the wing to 90-93 mm.), I must position the battery (6S TP 2800 mAh.) the way it was shown in one of the previous attachments.
          I would not need 15 grams of lead at the tail area if the battery is vertical and close to the rib. The main structural fuselage rib is according to your plans. 

There is no way I can achieve 20mm. gap between the battery (362 grams) in the horizontal position and the main structural fuselage rib without who knows how much lead at the tail to achieve 90 mm. distance for the C.G.

The possible differences between your Max Bee II and my Big Red are listed below:

1. Motor: you are using AXI 2826/xx weighting bare about 187 grams.
               I am using Plettenberg 15-22 with cooling fan weighting bare ~200 grams. with the centrifugal cooling fan. The fan standalone weights 11 grams and I have found that its presence lowers the surface
               temperature of the motor by ~15 deg.C.
               With this fan, after 5 minutes and 10 seconds long pattern flight in 33 deg. C, full sun, almost no wind weather, the motor's temperature was acceptable (again, I do not have my notes and do not remember
               the exact ##). Without fan ( I have made only one flight like that in similar weather), I could not touch the rotor's surface and the battery use was higher. Having this in mind, I have decided to use the fan.
 
2. The volume of balsa wood, carbon fabric and plywood is probably larger in the front of the fuse in Big Red than in your Max Bees. The reason: Big Red has much larger front inlet and more volume in the motor and
    battery compartment to allow for better cooling and required about 15 grams of extra carbon-epoxy reinforcement around the motor.

I cannot think of anything else having the major impact on C.G location.

In addition to changes in battery position, I can replace the Du-Bro 2" nylon spinner with the carbon composite 2" - this will remove about 7 grams from the very front of the plane.
Again, you say interesting things about RELATIONSHIP between the RTF model C.G position and the SHARPNESS of the stabilizer LE..where can I read more about it?

Ad.3.)  Then it is 27 degrees for the flaps. I will change 19 mm. to 20 if my plane starts turning better.

Ad.5)  The idea of the carbon rod crossed my mind too. If I can get to Poland, I will try carbon tube 2 mm. OD - it is fractionally lighter.

Ad.6)  Will do if...I can get to Poland.

[pmackenzie]

FWIW, I made Matt the logarithmic "metal bits" for his model, based on a paper print drawing, and images on the Max-II/netax web site.
Seeing Igor's image above everything is within about 0.1 mm, except for the forward arm of the mixer. 38.5 mm in the image, mine were 39.3 mm.

I checked in CAD and this would very slightly reduce flap travel, but only by about 1/4 degree. 

One dimension missing above is the length of the slot.
Mine was about 20.5 mm (outside to outside) allowing for 10.5 mm of bearing movement and  +/- 28 degrees of flap travel.
The table in the link below says 27.1 degrees max travel, so I figured I was in the ballpark:)
http://www.netax.sk/hexoft/stunt/the_max_ii.htm
I doubt I ever hit full deflection in flight, I certainly never felt it hit the hard stop, or had any sense that the model was hanging on one line.

I have the exact opposite CG problem on mine, the battery has to be quite forward to get the CG correct.
I had to extend the battery tray a couple of inches.  But I am (so far) running 5S 2800, and no cooling fan on the Plett.
And I guess my elevator must be heavy 

Pat MacKenzie

[Matt Piatkowski]

Hi Pat,
Good to hear from you!
I still hope we will all meet in Wloclawek but...yeah...this virus changed everything.

Your 5S TP2800 is 60 grams lighter than 6S TP2800.
Your Max Bee fuse front is lighter than mine because you followed exactly the "tight and narrow" geometry from the Igor's plans and I have made the fuse front "bulkier" (~15 grams extra weight in front of the wings).

The cooling fan for Plettys weights 11 grams.

You were running kv=755 Pletty and I was running (in Big Red) kv=685 Pletty: the weight of these is almost identical.
You used 11x5x3 Igor's prop. and I used 12x5x3 narrow blade Igor's prop - they have the same weight. We use SPIN66 and active timers.
I do not know what spinner and the prop.adapter you use...I used Scorpion X-long prop.adapter and Du-Bro 3 blade nylon spinner with nylon back-plate (27 grams). I will switch to the carbon composite spinner with aluminum back-plate that weights cpl. 17 grams. 

I think that the main reason you had to move the battery forward is 60g +11 g +15 g that you DO NOT HAVE in your Max Bee in front of the wings. Our models hinge-to-hinge distances are the same and tail surfaces weight probably almost the same.

When I get (if I get...) to Poland, I will methodically modify Big Red and I am sure it will, in the end, turn on a dime. What interests me the most is the relationship between the C.G location and the shape of the horizontal stab.airfoil in this particular case when the wings airfoil is so forgiving for the C.G location like the one used in Max Bee.

Regards,
M

 

[Igor Burger]

One dimension missing above is the length of the slot.
Mine was about 20.5 mm (outside to outside) allowing for 10.5 mm of bearing movement and  +/- 28 degrees of flap travel.
The table in the link below says 27.1 degrees max travel, so I figured I was in the ballpark:)
http://www.netax.sk/hexoft/stunt/the_max_ii.htm
I doubt I ever hit full deflection in flight, I certainly never felt it hit the hard stop, or had any sense that the model was hanging on one line.

Well ... life is hard ... I for got that distance, but those vertical lines show end positions of wheel axle, That slot allows 10mm movement of 10mm ball bearing wheel, so end to end opening is 20mm. If you have longer, no problem. I can esily feel and hear when the wheel goes to end of the slot and I also never heard and did not feel that, so I am sure 30 degrees deflection is enough also for panic input.

[Igor Burger]

Ad.5)  The idea of the carbon rod crossed my mind too. If I can get to Poland, I will try carbon tube 2 mm. OD - it is fractionally lighter.

That is great idea, you can fill that tube with some heavy metal, CG will finally come to proper place     

[Matt Piatkowski]

Igor,
One way or the other I will improve the "turning agility" of Big Red.
I hope that we will meet in Poland and you will find ten minutes to test fly this plane after modifications.
Stay Safe and Fly Well,
Regards,
M

[Brett Buck]

That is great idea, you can fill that tube with some heavy metal, CG will finally come to proper place     

   Oh, geez, now you are getting to be as bad as the rest of us....

     Brett

[Matt Piatkowski]

I can fill the carbon tube with unobtanium and use the maglev effect.
Big Red will levitate easily and fly the pivoting corners having 0.25 m. radius.

Isn't this, by any chance, the best idea of last ten years in the C/L stunt?
M


 

[Brett Buck]

I can fill the carbon tube with unobtanium

   Don't be ridiculous, just fill it with Uranium. Depleted or not depends on your relationship with the Iranian government.

    Brett

[Matt Piatkowski]

Brett,
I am sure I can find some Iranian ancestors in my family if I go back 2500 years to the times of the Darius' Empire.
The rest will just a family matter..