CG and Airfoil suggestions - Twin Boom Pusher

[phibru]

Hey Guys!

I already asked here (http://www.rcgroups.com/forums/showthread.php?t=448682#post4686704) because I haven't seen this subforum before. I only saw the Foamies (Discussion about plans, designing, building, assembly, power setup, flying wings and other RC planes related to foam.) forum. But my intention has nothing to do with foamies, so I put my question in the "Electric Plane Talk" forum.

I'm going to build a twin boom pusher plane for Aerial Photography.
The fuselage is made of wood and the wing is made of polystyrene and covered with wood. It shall fly very slow.

A sketch of my intention is attached.

-> Which airfoil would you suggest?
-> Where is the CG with the suggested airfoil?

Thank's for any advice!

[hul]

using Gordon Whitehead's formula for CG position:
CG pos = MAC/6 + (3*tail area*tail arm)/(8*wing area)
you get about 31% at the root.
This does not take into account the large forward fuselage, which will make it necessary to move CG forward some.
And move it forward some more for the first flight. I'd probably try 25%.

Airfoil: you'll have pretty small Re numbers at only about 100mm tip chord and flying very slowly. Others will have to give advice what airfoil would work well in these conditions.

Hans

[Bill Mixon]

I can't offer much help on the airfoil, as there are many, many good ones to chose from which will work well. I would like to share my thoughts on the design though.
The CG location will not really change regardless of the airfoil you select, and as Hans posted 25% should be a good starting point and you can go forward or aft with the Cg after the first flight depending on how you want it to fly.

If you intend to fly slow and carry camera equip, I think you need to change the design a little. With the high aspect ratio wing you have drawn the speed will be fast, and stall characteristics will be ugly.
I would decrease the aspect ratio (make the wing chord much longer) along with a larger horizontal stab mounted further back (longer booms) to help out with pitch stability.
For slow flight speeds the AUW needs to be as low as possible. And for that reason I would use a built up wing structure, as they are typically easier to build light compared to sheeted foam construction.
It would be a good idea to get an estimated weight figure for the airframe, camera, and rc gear first to see approx. where you will be at in terms of wing loading.

Regards

[BMatthews]

Something with a high camber and moderate thickness will fly slowly. If you're making this with a foam core and sheeted after then a more agressive shape is possible. The Eppler 212 as used on the old Dodgson Windsong is a very nice flying airfoil that slows down very nicely. Another option that I have on one of my old timers is the Goetingen 501. It's a thick and highly cambered airfoil that should be able to fly slower then the Eppler but will not have a higher speed like the Eppler would.

As for the design I see that the fuselage is quite long behind the wing. I would suggest that shortening that so the engine sits just behind the trailing edge will make balancing the model easier by not needing to use so much nose weight. To avoid a siren like sound the prop should be 2 or 3 inches behind the trailing edge.

That is also a very large model. What sort of weight do you expect your payload to be?

And finally low speed comes mostly from low weight. Even with all the wing area this model will have the weight will be very important to lower flying speeds. A higher camber value in the airfoil will help the wing to fly easier at high lift coefficients but it's low weight and thus wing loading that will be the real aid to slower flying.

[phibru]

Hey Guys!

Thank you very much!

@hul:

What do you mean with 25%? 25% of the wing chord measured from the wing leading edge?

@Bill Mixon

Ok I'll draw a new sketch with a longer chord and shorten the fuselage behind the wing and make the wing with wood ribs. Or is a foam core wing good too?

I have no idea, how heavy it will be.

What means AUW?

@BMatthews:

I expect that the payload is about 150g.

@all:

Would you prefer a twin boom or a single fuselage construction? The twin boom is heavier isn't it? Is a carbon fiber tube a good choice for the boom? Is it stable enough?

Is such a construction (Sparky Paul) (http://static.rcgroups.com/forums/attachments/1/7/2/0/662883.attach?ESAQEwNjAwDhnaOaBmL7Zwt9ZmgcoJSaMFHl EzcjMJp=) better? (single fuselage)

Oh and one more question, would you make the leading edge or the trailing edge straight or both? (wing tip chord smaller than the wing chord at the fuselage or not?)

Regards

Is this better: (attached picture)? I streched the wing chord with paint (180%). The 2nd picture is the plane, which I wanted to copy first.

[hul]

the 25% are from the leading edge at the root.

AUW = all up weight

I think you need more tail area and/or tail arm now. The new design is pretty close to a flying wing, which would need a reflexed (S-Schlag) airfoil.

A few more thoughts.
Low aspect ratios are easier to build light, their longer chord improves Re number (makes the airfoil perfom better), they have more drag though. More drag means lower flight times at the same weight. Lower weight compensates at least part of that.
Narrow tip wings are more prone to tip stall. Rectangular wings (same root and tip chord) don't tip stall. But they don't look as nice...
Ages ago, I guy at my club (possibly your current club: MFGL) had a very good thermal glider called Paragon (I think). From memory: about 7ft span, 1ft chord, Clark Y and very very light.

Hans

[BMatthews]

150 gms of payload is not much at all. You do not need such a large model to successfully carry that small a payload. Not by far. You could easily carry that much payload and still fly at a very low airspeed by using a model of about 1.2 to 1.5 meter span built up lightly using an open frame style of construction and lightweight covering. Either glow or electric power would be easily accomadated with such a model. If electric I would suggest making it twin motor powered and then your model could follow the pattern of the old C119 Flying Boxcar. Keeping the motors on the front end of the booms would encourage a more easily achieved CG location.

http://www.bermuda-triangle.org/assets/images/C-119.jpg

[John O'Sullivan]

The optimum size and configuration of model depends on what you intend to achive with the model. Simpler is better in most cases.
A 150 gm payload can easily be handled by a Speed 400 sized airplane of about 45" wingspan and the size model you are proposing is probably a bit large and more cumbersome than you need.
As an example my Eyespy (with over 2 years testing on a half a dozen airframes) is a single boom pusher of 54" span weighing about 36 ounces bare and 42 ounces with camera, altimeter, FMA copilot and a few other bits and pieces. With an AXI 2808/24 it will climb at 1200 ft/min on full power and with a 2100 three cell Li-Poly battery at cruise speed (about 1/3 throttle) will fly for 40 minutes. It is an ideal size compromise in terms of portability, ease of setup and performance for general flying.
The larger model you are visualizing fits in a different class and will require a more rigid attention to setup detail and flight maintenence than the smaller models. If you have the requiremnet for a system which requires autonomous flight (autopilot, without pilot control input) or data transmission to ground, this more elaborate system may be justified.
As an example of each type, I am appending PDF files of my Eyespy single boom pusher which I use for regular airphoto work with paylloads under 200 gm and my Heatseeker, a twin boom pusher currently under construction. The Heatseeker will be an autonomous aircraft with air to ground data transmission and capable of flights of 10-15 mile radius. As this model is currently in development, I am a little hesitant in presenting the plans here. However, I do have enough confidence in the basic design that I know that it will perform to specifications.
Bruce Marshall recommended the Eppler 212 section as used by BoB Dodgeson on his Maestro. It was in fact an Eppler 214 section that he used and it is a high lift efficient and very forgiving section. I have used it on sailplanes up to 15' wingspan and use it with slightly reduced trailing edge camber on the Eyespy and Heatseeker, where it gives slow to medium range airspeed with lots of stability.
Have a look at my drawings and if they can be of use, feel free to use them.

John O'Sullivan

[phibru]

Hey!

Thank you all! You helped me alot.

@hul:

No I'm not in the MFGL - there are 2 clubs in Liechtenstein and I'm in the other one. You were in the MFGL in Bendern?
Thank's for your information, sorry but John O'Sullivan's plans look great - maybe I'll build one of them.

@BMatthews:

I planned to build a large plane because I intend to fly high and take photos from higher alts too. And 2 motors are heavier than one single engine, aren't they?

@John O'Sullivan:

Thank you very much for these nice plans. They are great! I also visited your homepage. Maybe I'll build one of those but a bit bigger - maybe with a wingspan of 70". Aren't ailerons necessary? Is it well steerable without ailerons?

Best Regards!
Philipp

[John O'Sullivan]

Phillip:
My background is in Free/Flight competition flying, where model stability and performance are a priority. I then got involved in R/C sailplanes where the skills are similar, but give the satisfaction of being able to bring the model home.
In Aerial photography, the prime requirement of a model is to have a wide range of flying speeds and a built in stabilizing ability. This allows the pilot to trim out the model to a hands-off stability, which allows him to concentrate on the photography.
The Eyespy is a product of my Free/Flight and R/C sailplane background and even without ailerons handles very well.
Larger models in the 2 metre + range will benefit from the addition of ailerons, however even here they are not really necessary for high level flying (remember, the simpler, the better). Where ailerons give the advantage on the larger models is to allow increased manoeuverability in flying from and landing in small areas.
John O'Sullivan

[Sparky Paul]

For photo work, manuverability takes second place to stability.
A polyhedral wing with rudder is more than sufficient.
Two motors frees up the front of the plane for a forward looking camera, as does a pusher setup.

[hul]

You were in the MFGL in Bendern?
yes, 20+ years ago

Hans

[BMatthews]

For photo work, manuverability takes second place to stability.
A polyhedral wing with rudder is more than sufficient.
Two motors frees up the front of the plane for a forward looking camera, as does a pusher setup.

What he said....

And two motors turning separate props can be set up to provide more thrust. I would say from an electric standpoint that the amps to thrust efficiency is probably better with two motors than one larger one that consumes the same current. But of course that would depend somewhat on motors and props.

But achieving a good CG without needing a lot of nose weight would be far easier with the motors up front on the ends of the booms than with it back at the rear of the pod.

As for the model size I go along with our need for the larger platform if the use will often involve higher altitudes. But how high do you need? A semi wide angle of f = 35mm equivalent will cover a lot of ground at 800 feet up and a 4 foot model is still quite usable at that height.

Why not compromise with something in the order of a 2 meter wingspan? Easier to build and transport and just as usable at higher altitudes. And pleanty of wing area to carry that payload.

I also concur with Paul about the idea of building in free flight like stability by using the polyhedral wing so often found with beginner to intermediate glider designs. When flying far away it is far easier to fly smoothly with that level of stability than with straight wings and ailerons.

[phibru]

Hey!

@John O'Sullivan:

Where is the CG of the eyespy?

Regards

[John O'Sullivan]

CG of the Eyespy, I usually set at 38% chord. Most of the guys around here use 33% (on the spar). It is pretty forgiving and some times when I use batteries of somewhat varying weight, I don't worry as long as the CG is in the 30-40% range. It just requires a little trim change on the elevator.

John O'Sullivan

[Vince inTX.]

With reguards to comments by Hul.

I second the recomendation to use a wing similar to that of a Paragon. I did just that earlier this year to build my twin boom pusher photo plane. It worked out great! One thing nice about it is that it can be flown with or without the outer wing panels depending on the wind. In gusty conditions I can remove the outer panels and double my wing loading and the plane still flies and glides nicely.

Good luck and keep us posted.

Vince

[alexcmag]

Paragon style is an excelent choice.

For AP you usually need low sink-rate, but still capable of flying against the wind if necessary. I like the S4083 or S7035 for this mission, but there is a lot of different airfoils that can do the job pretty well...

I made several pusher designs that can carry 150g payload and several pusher with twin boons.

Since you're planning to use twin boons, if your radio can do V-tail mixing I suggest using inverted V-tail. This tail design supports bad landings very well and is out of propeller airflow.

To make it easier to set CG on a pusher, swept wing is a good choice.

For AP it is a good idea to make a self-stable design, like like polihedral wing with rudder/elevator controls or V-tail. When trimmed properly my polihedral wing airplanes can keep attitude by itself, without pilot interference. This is good for AP because you can align to the desired heading, turn off motor and take some pictures while the airplane is stable enough to avoid shaking pictures.

[phibru]

Hey Guys !

Thank's for your advice! Now I decided to use the wing of the eyespy with another fuselage.

Isn't the twin boom harder to put into practice than a single boom? The wing has to be very solid because it has to withstand forces of the tail, doesn't it? And a solid wing means more weight.
And another problem is, how to mount the booms (carbon fiber tube?) to the wings and how to attach the tail to the booms?

A single fuselage would be easier to put into practice, isn't it? Would a single carbon fiber tube work too? What would you prefer?

Regards Philipp

[John O'Sullivan]

One thing you might consider for a twin boom model is an Eyespy wing, with a flat 20" long centre panel added between the existing wing panels. This panel would be constructed as for the regular wing panel, but with full 1/16" sheeting top and bottom. The twin booms could be attached below the outer ends of this panel, which would provide sufficient torsional rigidity to support the tail group. A wrapping of Kevlar tow around the spar unit would also provide additional wing strength and prevent possible separation of spars from the web.

Using this layout and keeping same tail moment will require a tailplane area increase. You would need in the vicinity of 100 sq. ins. As your boom spacing is 20" a mean tailplane chord of 5" would suffice (make it 5.5" for stability).

My tail halves are built directly onto each of the booms and have a small vertical fin on the ends, which come together and are connected with nylon bolts.

The boom attachments to the wing are done by fitting an additional rib inboard of the CPanel tip at the same distance as the thickness as the boom. This rib and the CP tip rib are extended downwards to accommodate the depth of the boom. This forms a box, which can be padded with scrap balsa to provide a "nest" for the boom. Simple screw locking plates secure the boom. If I get a bit of time in the next week, I'll make a drawing of this fitting.
John O'Sullivan

[Sparky Paul]

I'm flying these right now, swapping motors and engines.
With the OS 15FP, 8x4 Zinger pusher these fly fine.
With an AXI 2820/10 and a 9x6 prop, they fly way too well!
About 60 oz average weight, using a GL or Spirit wing.

[phibru]

Hey Guys!

Thank you very much! Another question: (I don't know how to explain it in English) Is it necessary to cover the front part of the wing with a thin (1.5mm) balsa wood plate? Or is the wing rugged enough without the planking/covering?

I like your design Paul. What's the wingspan of yours? Maybe I'll build something similar with the eyespy wing.

Regards Philipp

[John O'Sullivan]

Balsa sheeting of the leading edge of the wing adds extra torsional strength and toughens up the model considerably. However there is also a weight increase and a resulting increase in airspeed. Sparky's Spirit wing has sheeted leading edge, top and bottom the full wingspan, and the Gentle Lady is sheeted in parts of the centre panels only. This is fine for these wings which are 2 metres wingspan.

The Eyespy wing is lower aspect ratio wing, quite a bit smaller at 54" (1.37 m) and with a thicker than usual (12.25%) wing section and a webbed spar is considered strong enough and has plenty torsional rigidity without any sheeting. Lightness was one of my design parameters on this model, and in spite of the lack of sheeting is tough enough for the purpose.

If you stretch the Eyespy wing, it would probably benefit from 1.5 mm sheeting on top of the centre panels on the centre panels as far back as the wing spar. This is not a major modification, as the wing ribs are already the correct thickness. Just replace the cap strips with the sheeting.
If you really want to make a tough wing, sheet both top and bottom of the wing, forward of the spar, but for normal flying this should not be necessary.
John O'Sullivan

[Sparky Paul]

The two planes above fly too fast when making videos!
The 2M wings are too efficient.
i'm pondering how to slow them down.. probably a thicker wing.. about 14-15% thick.
Phibru, the wings are straight out of the kit boxes as John mentions. GP Spirit and Goldberg Gentle Lady.
The Spirit wing easily handles a 70 oz load.. it's 58 oz on the airplane above.
I expect the GL wouldn't take that much.. installing it on the heavy plane, it just didn't feel right so I didn't fly it that way.
Sheeted leading edges are much stiffer than open structure anyway. For load carrying planes they're better.

[phibru]

Hey!

I'll make a compromise with the size. I'll make a 1.7 m wing.
How thick carbon tubes would you recommend for a twin boom?

Regards Philipp

[Sparky Paul]

For mine, I've migrated up to at least .3" in diameter for twin booms. I've had problems with the booms bending down at speed, with anything less.

[RSteel]

Hi Phil,

May I suggest a NACA 64A-315? It is the same airfoil as on an OV10 and works extremely well at low speeds.

Ray

[phibru]

For mine, I've migrated up to at least .3" in diameter for twin booms. I've had problems with the booms bending down at speed, with anything less.

Hey!

What do you mean with .3"? I'm sorry, I'm not good in the American art of measure :rolleyes: . Means .3" 0.3 Inches (7mm)?

Thank you and sorry for this dumb question.

Regards Philipp

[Arvid K. Gromhol]

Bill, see below

[Arvid K. Gromhol]

Bill Mixon

If you intend to fly slow and carry camera equip, I think you need to change the design a little. With the high aspect ratio wing you have drawn the speed will be fast, and stall characteristics will be ugly.

Please explain why the stall characteristics on a high aspect ratio wing "will be ugly".

[BMatthews]

Hey!

What do you mean with .3"? I'm sorry, I'm not good in the American art of measure :rolleyes: . Means .3" 0.3 Inches (7mm)?

Thank you and sorry for this dumb question.

Regards Philipp

That would be inches for sure. So 7mm.

Even at that size I think you will be better with a larger diameter or a built up box that has more depth than width. To achieve sufficient bending stiffness to avoid this flexing size really helps more than what it is made from. A simple box made from 2 mm sheet balsa that is 50 x 30 mm is going to be stiffer than a carbon tube of 7 mm diameter. Note this is STIFFER and not STRONGER. They are not the same thing at all. Stiffness is a measure of how much bending you get if you apply a load. Strength meaures the max load you can hold before it breaks. But at the max load just before it breaks the carbon will be bent like a horseshoe while the balsa box will still be almost straight. Even at the load just before the box breaks the balsa box would be flexing less than the carbon tube would be flexing. And that is the weakness of using carbon tubes. It's not that the carbon is weak, far from it. It's that it is not used in the right way. If you made a box boom out of carbon fiber cloth the same size as the balsa box then it would be both stronger and stiffer than the balsa box.

Higher aspect ratio wings tend to have a more clearly defined stall point. Depending on the airfoil choice this can often show up as a harsh stall charactaristic. As with most things there's usually a happy medium. Sailplanes already know this and you generally see moderate aspect ratio wings in 2 meter sizes and higher aspect ratios in the open class designs. The idea in this case being to retain a reasonable wing chord and avoid the very low reynolds number effects where airflow can become mixed up at lower speeds.

Wing "efficency" is relative. Sparky's 2 meter wing is not that good for a camera plane because it's fairly low camber airfoil was designed to operate nicely in the range of low to higher speed flight so the glider can move around on windy days. If you substitute an engine for gravity as the power source you can forget about the need to use the wings to speed upwind. At that point going slow is the primary task and an airfoil with more camber will provide the higher lift coefficients you need with less fuss. This is why the SAE load carrying designs are all using airfoils that look like they fell of a bannana tree. They are designed to carry high weight at the low airspeeds that are mandated by the relatively low power available under the rules. If larger engines were allowed in the SAE competition there would be no real need for the high camber airfoils since the models could just simply fly faster and lift off normally with "standard" airfoils. But when you limit the power you limit the speed and you need to compensate for this with the proper design.

And that seems to be what this thread is all about....

[Bill Mixon]

Bill Mixon
Please explain why the stall characteristics on a high aspect ratio wing "will be ugly".
Bruce has answered already.
High aspect wings typically have a less forgiving stall characteristic. The stall will be without much warning, and take a good bit of altitude to recover from, compared to something with a lower aspect which will have a more noticeable and less harsh stall.
When I first saw the sketch I assumed Philipp would be carrying a lot more weight than 150 grams.

[Arvid K. Gromhol]

Bill

Ok, I understand. But I still wonder what aerodynamic reasons it is for this less forgiving stall characteristics. Do you know?

[Ollie]

The flow around a real wing is three dimensional. Two dimensional flow is for the airfoil. The three demensional flow is spanwise due to coefficient of lift squared. In a high aspect ratio wing, mostly flow around airfoil and lesser spanwise flow. In a lower aspect ratio wing, mostly flow spanwise (vortex tip) and lesser flow around airfoil.

The real wing has airfoil (2D) angle of attack plus induced (vortex tip) angle of attack.

[Arvid K. Gromhol]

Ok, thanks, I follow you, Ollie.
But, why the abrupt stall?

[Ollie]

There are three types airfoils of stalling. Read about Soartech #8, Airfoils At Low Speed (A11501) Selig, Donovan, Fraser.
http://www.carstens-publications.com/
From Book Hanger above.

I will show three examples.

S3021 has maximum AOA from about 10 to 16 degrees with maximum coefficient lift or mushing stall. This type is the best for your purpose.

E374 has abrupt stall for a snap rolling aerobatic purpose.

NACA2312 (if I recall) has abrupt stall but recovers after stall at much lower coefficient lift and at lower AOA (hystersis). It is bad for models.

The wing planform that is too tapered, loads the tips and stalls at the tips first. You must design the wing so the stall is due to elliptical lift distribution. See:
http://aero.stanford.edu/WingCalc.html
or
http://www.amadistrictii.org/cjrcc/wing2/wing.html

[BMatthews]

Arvid, the stalling thing is all relative.

Mostly at our model sizes it's related to reynolds number scale effects. A higher aspect ratio wing stalls earlier and deeper because the chord is shorter and it's operating down in the range where the air gets confused easier. That's the simple explanation.

But the stall effects you see when you fly are also affected by the airfoil chosen, the constrution method and trueness of the airfoil (leading edge misshaping, turbulator spars, sheeting, etc) and the airfoil chosen. Beyond that the other factors mentioned already come into play.


I think it's fair to say that the only time you would be able to tell the difference is if you had two wings with the same airfoil and construction method but with widely differing aspect ratios.

A few years back this came up with the sailplane community. The final outcome was that the chord length for smaller 2 meter models was more important than aspect ratio just so they could better utilize the airfoils to achieve overall speed range and thus REAL performance vs the theoretical advantage of higher aspect ratios. At the time the stall didn't enter into it as a good glider pilot avoid stalling. But in any event this is why the 2 meter designs these days all look a bit "thick" compared to the open class models.

[phibru]

Hey guys!

Thank you very much for your help!

How big would you make the angles α and β between the wings?

Regards Phil

[Ollie]

Read this:
http://www.rc-soar.com/tech/spiral_eda.htm

[Airboatflyingshp]

Take a look at the M55 Mystic :cool: :D ...if you want more info /links drop me a PM but my other sugestion is go to one of the big sites in the the Freeplans and Links section in Waterplanes and look for Big brother ;) or XPO4??? its a motor glider in the same layout one versions glow the others Electric both pushers bith similar size and both free ...just google free plans and the name it should come up..youcan use the wing plan whole or adapt to your idea...M55 is just my personal all time favourite their is a smaller PSS version out there and it flies very well so does Big Bro as it was designed for novices.

[Airboatflyingshp]

Big Bro zipped Auto Cad DFX file...you may need to find a viewer....but its here..Electric version.

[Rick D]

I've been wanting to build a twin boom pusher for ap. I notice a lot of people using an inverted v-tail, is this to simplify the links to the control surfaces or does it have other benefits as well? I really like the look of the M17/M55 and I would like to use that style of tail if possible. I was thinking of using a 72" constant chord clark Y wing, not cool looking like the M55 but easy to make and I hope slow and stable to fly. does anyone know what would be good dimensions for things such as boom length and spacing, pod size and wing and tail chord?

[Airboatflyingshp]

Rick its Clive that is U as of the piaggio gull isnt it?
you could scale big Bro its a very stable design, linking the rudders is a bit of a pain but not that hard Jamara do a kit called Easy Riser ..it used to be available through Flair it was based on an earlier version...Sunriser both geared 480 pusher powered and with very good flight endurance.

Then theres also this one boomerang its used by one guy as his his Avtar and its old but beyond that and this pic i know nothing.
I do have stuff on EXP R1 the last one RED though................let me know if you want more info. :)

[John O'Sullivan]

The A tail gets yout tail out of the way fot landings and depending on the height of the thrust line can help get it out of prop wash. It is better aerodynamically than a Vtail too.
I posted a sketch of the comparison at
http://www.rcgroups.com/forums/showpost.php?p=4504581&postcount=4

John O'Sullivan

[Rick D]

Yea Clive its me, I did a search for twin boom ap planes and found this thread.
I was pleasantly suprised to see you posting here.
I really want to try out the wireless video stuff I got for christmas so I'll have to put my other projects aside for now and get this done.
I had been using a zagi for ap which worked ok but was too fast.
thanks for the pics of the rudder and elevator stuff, that's what I had in mind.
I downloaded the bigbro plans, looks cool. I have my own basic design drawn out but still have to work out the proportions.
what do you think about my wing choice? I have the same basic wing design on an old glo powered trainer that worked quite well. I guess I'm going more for utility rather than good looks.

[Rick D]

Thanks John that makes sense, do you think that design would work better than seperate elevator and rudder?

[Sparky Paul]

The inverted vee is easy to setup, with the twin booms it's a bit stiffer than a single boom normal vee.. and there's no linkage problems with the rudder.
I use the configuration a lot, with polyhedral wings for simplicity.
No ailerons, the rudder-vators work fine.
I've had boom twisting with vee-tails on single boom planes.
The tractor setup puts the camera in the least risk location behind the wing.