Which Park Jet for me? - Part 9 - Stabilizers and control surfaces

Hi Everyone -

I will caveat this article with a bit of my personal opinion about where I think park jets fit into the grand scheme of things as it applies to control surface size.  If you strive to fly park jets in a scale manner, in other words similar to how the real planes fly, I think they fall into the sport/aerobatic realm.  Unfortunately for awhile many park jets were being designed with 3D size control surfaces.  Certainly if you want to fly a park jet non scale and opt for crazy tumble flips and rifle bullet rolls, that is your choice, but if you are a beginner or want to fly with more precision, over sized control surfaces can make your flying experience more difficult.  I certainly did this type of flying when I first got into park jets, but found it not terribly satisfying after awhile as I was just slamming the sticks around doing crazy non scale maneuvers and my true flying skill really didn't improve.  As soon as I started trying to focus on smoother flying, more scale turns, loops, rolls and other aerobatics, my skills and confidence improved and I found my level of satisfaction increased greatly.  I am still constantly trying to fly the perfect loop, roll and keep my turns silky smooth, overall it has just made the flying experience much better for me anyway.

Essentially there are two types of stabilizers (not the electronic kind that acts as a gyro😉) that are popular in most park jets.  The horizontal stabilizer to which the elevons are attached and the vertical stabilizer to which the rudders are attached.

There are the three control surfaces, elevons, ailerons and rudders.  As mentioned very early in this thread, most park jets will fly quite well with elevons only, but for more advanced handling and aerobatics, a builder/pilot really needs to consider activating ailerons and rudders.  

In this article, I won't be discussing other control or lift devices like leading edge flaps/slats or canards, those will get their own article.

Depending on your transmitter's capabilities and your imagination, the mixing possibilities for ailerons and rudders are considerable.  The ailerons can be used as spoilers/spoilerons where they deflect and stay up to help keep the nose up for advanced flying like high alpha.  They can also be used as flaps/flaperons to enhance the lift capability of the wing for better slow speed or to slow the landing approach.

Rudders can also be mixed to act as "V-tails" on twin tail park jets where when you pull up on the pitch input, they both deflect inward increasing the upward deflection of the plane's nose and vice versa, they go out when the stick is pushed forward increasing the downward deflection of the nose.  Also, they can be programmed to be switch selectable to act as a form of air brakes where they both deflect in or out depending on what you want the plane to do.  From my experience, I would experiment with with these mixes up high first as they could cause your plane to pitch up quickly and stall or pitch down quickly and make it difficult to recover, both behaviors you want to avoid down low or on approach to landing.

So back to the beginning.  One of the first things to look at in my experience again is the size of the control surfaces in comparison to the wing.  While many people argue that you need very large/over sized control surfaces for better handling at slow speeds, I personally disagree with that theory based on thousands of flights with park jets that have smaller control surfaces that are closer to scale size.  Granted with any model of a real plane, control surfaces and stabilizers may not be exactly scale, often without the support of on board computers like the real jets have, designers need to take some licence with the size and sometimes placement of park jet control surfaces and stabilizers to optimize the flight experience.  Just based on common sense, the larger the control surface, any time it is deflected, it causes more drag, more turbulence and greater instability, all properties which can take away from the airplane's handling and performance.

Horizontal stabilizers/elevons

For a very long time, park jets were all designed with "flying" or fully functional elevons similar to the real plane, meaning there was a considerable amount of control surface moving anytime you touched the sticks and no stability features built in.  This picture below is of the RC Powers Mig-29 V2 which is no longer available.  This airplane was my park jet nemesis 😒  I built three of them and between those three accumulated less than 50 flights, two of them crashing in less than ten flights.  Makes you wonder why I love the Mig so much?!😳

One of the first things that strikes me as I look at this old picture is how huge the elevons are on this plane.  They are very close to the same "span" as the wings, very large outboard surfaces and massive amounts of area in the prop wash.  No wonder it felt so twitchy 😵 Also of note is how large the ailerons are and how the moving surface extends all the way to the wingtip.  In contrast, if you fast forward to the Mig-35B, Stephan designed the elevons to be of scale size, incorporated fixed horizontal stabilizers and the ailerons are much smaller and don't extend to the wingtip (more on that later).

The idea of fixed horizontal stabilizers is certainly not a NAMC idea, RC Powers first introduced the idea with the Mig-29 V4 and Su-34 V4 and I think it is one of the best innovations to come along in park jet design in a very long time and this has been carried over into the V5 lineup by RC Powers as well.  When you look at the back end of a park jet, there is already going to be a lot of "dirty air" caused by air flowing over the plane and prop wash, so anything that can be done to improve stability in the back end of the plane is crucial to improving the airplane's handling and performance.

When assessing elevon size, if the span from tip to tip is too large and the surface itself over sized, not only does it cause more frontal drag and slows the plane down, every time a big surface is deflected, it causes more drag, turbulence and instability.  With the unique design of a mid mount "prop in slot" over sized elevons can also act as speed brakes, get too slow, pull back too hard on the stick, they act more as speed brakes, parking the plane in the air and on comes stall quite quickly and hammering the power just worsens the problem unless you have enough wherewithal to also let off pitch input as you accelerate.

So since almost any park jet I have ever flown flies quite well elevons only, these are very important to consider from a standpoint of size and whether the design has fixed horizontal stabilizers.  Smaller, scale size elevons work very well, you obviously need to add a bit more throw in the roll axis since you don't have ailerons helping in turns and rolls.

Fortunately, since the RC Powers V2s, many designers are starting to produce planes with much more scale size elevons and are even incorporating the horizontal stabilizers that RC Powers introduced.

Ailerons

As you can see from the first picture above of the Mig-29 V2, the ailerons are quite large and extend all the way to the end of the wing tip.  They are essentially what you would see in a 3D plane and make precision flying very difficult as there is so much control surface entering the slip stream every time roll input is made.  What also happens with these full length ailerons is as you get slow and give roll input, having that area deflected close to the wing tip can bring on tip stall much more quickly.  If you look at this plane below, the ailerons are actually wider at the tip, I found this plane had a tendency to tip stall quite quickly if I got slow and put in any roll input, the wider aileron at the tip caused more force and would tip the wing over quite aggressively compared to more uniform size ailerons.

When Stephan and I were tinkering with the RC Powers Mig-29 V4 which led to the NAMC Mig-35, we experimented with several different sizes and shapes of ailerons and found the ones you see in the picture of the Mig-35B above seem to work the best.  In essence they are probably "maneuvering flaps" more than anything else and not exactly scale in size, shape and position, but give great flexibility in increasing roll rates, and in use as flaps/flaperons/spoilers/spoilerons.  They are certainly not needed, but for more advanced aerobatics, they certainly do help out.  We have found that having inboard ailerons/maneuvering flaps that are about 60% of the total trailing edge of the wing seem to work the most efficiently.  

Vertical stabilizers/rudders

In my experience, twin tail park jets like Migs, Sukhois, F-15, F-18, F-22 tend to be more stable in the yaw axis than single tail planes like the F-16, Rafale, Eurofighter.  Obviously, having almost double the area of stabilizer helps as does allowing for a more clean flow of prop wash without it being split and made even more turbulent by a single tail cutting it in half.

In general, planes with vertical stabilizers that are perpendicular to the wing plate like Migs, Sukhois, F-15 are more stable than planes like the F-18 and F-22.

In the picture above comparing the RCP F-18 V3 and NAMC Mig-35B, you can see what I mean by the difference in placement angle of the vertical stabilizers.  Planes with the angled stabilizers like the F-18 tend to be less stable in windier conditions.  The tail will tend to "wag" like a dog's tail going into wind and in turns.  It definitely helps having rudders on planes with this sort of tail configuration to help keep the nose tracking true through corners.

Another thing to consider with the vertical stabilizers is whether they are completely parallel to each other or "toed in".  RC Powers introduced the idea of toeing in the vertical stabilizers to create a slight "wedge" to improve yaw stability with the Mig-29 V3 (now discontinued) Again, it isn't exactly scale, but another minor innovation that makes major improvement.  I found this picture that allows you to look from the top down on the vertical stabilizers and I think makes it very easy to see the "wedge" created by the toed in vertical stabilizers on a NAMC Mig-35B.

Again, not the most scale look, but it is a matter here of what the wind "sees" as opposed to what the eye sees.  This wedge creates a noticeable increase in yaw and overall stability versus planes that do not have this feature.

When discussing rudders, they can be a very polarizing topic.  Much of the community feels they are not required and never uses them, which is fine.  I would say that in general I use rudders about 5% of the time, but when I need them, I am very glad I have them.  Since I started using them full time about four years ago, my left thumb certainly uses them probably more than I realize to feather in just slight amounts of yaw control as I fly.  Certainly if you like to fly very slow or want to practice high alpha, I would say they are pretty much a must have.  Another area I find them very useful is flying in windy conditions as turning in crosswinds sometimes the tail will drop or slide high, so being able to feather in a bit of rudder really helps keep the turns smooth and the plane under complete control.  So regardless of the extra weight of a couple of servos, I always like to have rudders when I can.

When Stephan and I first met and started sharing ideas, he was tinkering with the RCP Mig-29 V3 in a project he called KnEX (Knife edge experimental) where he was working on a rudder configuration to get the Mig-29 to knife edge.  He had some very good success, but what came out of that experimenting is that the orientation of the rudder hinge line is very crucial to the effectiveness and efficiency of the rudder in the yaw axis.

In the picture above, the plane on the left is the stock RC Powers Mig-29 V4, on the right is one of the first prototypes of the NAMC Mig-35A.  You can see quite a difference in the rudder hinge angle.  What happens with the angled hinge line is that with rudder input, considerable roll is also induced in the direction of rudder deflection meaning opposite roll input has to be applied to keep the plane from doing a "rudder roll".  Not an efficient or effective form of yaw control as it can cause real issues especially when slow, inducing tip stall much more easily in high alpha.  With the hinge line being vertically oriented, this tendency is greatly reduced, yaw control is much more effective and efficient with minimal to no opposite roll input being required.  Rudder control at slow speeds and high alpha is greatly improved.

Although this is a bit of an aside perhaps, but I wanted to mention the unique "under rudders" on the RC Powers F-22 V5. They are definitely not scale, but work really, really well with the unique stealth layout of the F-22.  You can see them here in this picture, not big, but very efficient at all angles of attack whereas conventional rudders on a stealth plane like the F-22 can get blocked from the airflow by the wing and horizontal stabilizers.

​So I know this has been a rather lengthy and involved article, but certainly stabilizers and control surfaces are very important to consider in choosing a park jet.  They are either working well with the rest of the overall package of the airplane or working against it in my experience, but are also fairly simple to modify if you like to tinker with your planes to maximize your flying experience.  

In the next article, I will discuss my experiences with some more advanced things like leading edge flaps and canards.  I don't have a lot of experience with these, but will share my thoughts on how they have impacted my flight experience with planes I have built and flown.

Park Jet noise...the "other" sound of freedom😎
Cheers,

Scott

Which Part Jet for me? - Part 8 - weight distribution

Hi Everyone -

I have already touched on this somewhat in previous posts, but wanted to discuss it a bit further and combine all my thoughts on weight distribution in a park jet either by design or by choice when building your plane.

I would suspect weight and balance has been important in air planes since the Wright Brothers first took flight.  Unfortunately, over time, some serious aviation accidents have happened either due to incorrect weight and balance calculations before flight or weight shift during.  Of course not that anything that dramatic applies to your foam park jet, but hopefully it drives home the idea of how important weight distribution is to the proper balance of your plane and most importantly it's overall performance.

Perhaps I should have covered this a little earlier, but I like to use this definition of center of gravity from this NASA website.

In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft. 

Although a bit simplified (sometimes simplified is good 😊), this diagram shows how theoretically all the axes of pitch, roll and yaw intersect through the center of gravity.

I will use one of my average park jet builds to discuss the weight of the electronic components, all of which are flexible in their placement to show the importance of their layout to try and achieve best balance and best performance.  On average, most of my park jets all seem to fall around 21.5 oz/610 gr.  When adding up the total weight of the motor, ESC, receiver, 2200 3S battery and 6 servos, the total weight of these components is 377 gr/13.3 oz, so over 60% of the plane's total weight.  The battery alone weighs 198 gr/7.0 oz, so almost one third the total weight of the plane.

For the longest time, I only thought of a plane's weight distribution along the pitch axis, to get the plane to balance so that it wasn't nose or tail heavy.  Then as my NAMC partner and chief designer Stephan continued to do more research, he taught me the importance of vertical balance or how the weight is located in relation to the wing plate top and bottom.  Stephan made this video awhile back to figure out how to design the plane to be as neutrally balanced in the vertical axis as possible.  This science went into the Mig-FA and continued into the Mig-35B and later the Su-27.

So let's get back to how the design of the park jet can affect how you are able to distribute the weight of your plane.  In the last post, I discussed motor location, this has a very significant impact on how the weight is distributed along the longitudinal axis of the plane, affecting pitch balance and performance.

Other design factors are where you are able to place your servos, servos of course are not as heavy as a motor or battery, but the further back they have to be placed in relation to the CG, more weight has to be placed ahead of the CG to compensate.  For example, the rudder servos for the unique "under rudders" on the RC Powers F-22 V5 have to be placed behind the prop slot in order to be able to run the linkages without interfering with the prop and/or the elevon linkages.

I tried to compensate by placing the elevon and aileron servos as far forward as I could, they actually "straddle" where the CG is located, which seemed to work out OK, so these are things to consider when looking at a park jet design or planning out your build.

So back to vertical balance as discussed in Stephan's video above.  Some park jet designs have all the weight on top of the wing plate, the wing plate actually acting as the bottom of the electronics bay.  This tends to make the plane very "top heavy".  This can cause the plane to want to roll over aggressively on it's back in turns, loops and other vertical maneuvers.  I have also found it causes issues in the yaw axis at the top and bottom of loops as the plane will "dart" sideways one way or the other.  Tip stalls also come on much more quickly when slow in turns or when coming in to land, so it is important to keep more speed on the air plane than the wing loading would normally dictate.

Here is a picture of a plane that has all the electronics (other than the elevon and ailerons servos) on top of the wing plate, over half the weight of the plane is above the wing plate in this example.

​Planes that are top heavy are not impossible to fly, but much more tricky to fly because of the behaviors mentioned above, they are much less relaxing to fly in my experience than a neutrally balanced or "bottom heavy" plane, so that is definitely something to keep in mind.  The RC Powers Su-27 V5 is an example of a "top heavy" plane, which is a very good flier, once I got it dialed in and got used to it's behaviors, but it still occasionally demonstrates the behaviors mentioned above if I get too slow in turns or on landing.  From my experience, top heavy planes definitely benefit from having rudders activated to counter act some of the yaw behaviors I mentioned above.  

As mentioned above, lowering the battery on the Mig-35B was important to us after seeing the improvement in stability and forgiveness it provided the Mig-FA.  The Mig-35A (the first Mig-35 we designed and sold), was in fact a bit top heavy which was one of the reasons it was for more intermediate to advanced pilots as it was not quite as forgiving as the Mig-FA and Mig-35B.  By lowering the weight in the Mig-35B along with some other changes, it became even more stable, more forgiving and the low end of the speed envelope was improved.

To get a sense of how a plane that is neutrally balanced handles, this picture has the battery installed, so just as it would be for flight.  I am holding it by the prop nut and the nose so that it can rotate just like when you would balance a prop.  As you can see, the wings are perpendicular to the ground.  This plane is about as neutrally balanced as you can get, so it's movement in all three axes in quick and effortless with very little control surface deflection required.  For a precise, agile and highly aerobatic flight experience with almost no bad habits, neutral balance is ideal in my experience. 

As I have mentioned in my table talk videos about the RC Powers F-18 V5 and the RC Powers F-22 V5, "bottom heavy" airplanes tend to be quite stable and forgiving as they always have a tendency to want to right themselves.  They can be a bit slower in responding to roll inputs, but not something that is a huge negative to the overall flight performance.  In the case of the F-22 V5, it made an inherently unstable platform far more stable, forgiving and relaxing to fly compared to any other F-22s I have ever flown.  Picture the above where you do the same test and the plane wants to roll partially or all the way onto it's belly, this provides a lot of stability, excellent tracking in turns and pitch maneuvers as the centrifugal force of that lowered weight helps the plane really carve around the sky while staying stable.

I think it also important to have a plane or set up the plane where the battery can be as close to "straddling" the centreline as possible.  For a very long time, I always flew with my battery well over the right of the electronics bay to counter torque roll because I was stuck in a mindset that I always had to have "zero trim".  This actually caused me to set my planes up so they were unbalanced with far too much weight to one side making rolls and turns unbalanced and the plane more tricky to fly.  I now always try to put my ESC on the right side as it is heavier than the receiver and wire bundle of servo wires, then place my battery along the centreline.  Hopefully you can see what I mean in the picture below.  This gives my planes a much better balance and more even, predictable performance.  Sometimes depending on the design, the electronics bay may be too narrow for this type of layout, so it is something to look at when choosing a plane or when building your plane depending on the performance you are looking for.

​So while it is hard to tell just by looking at pictures of a plane you have never built before where the weight is distributed in relation to the center of gravity in all three axes has considerable impact on how the plane will handle and perform.  As such, it is a very critical consideration to make depending on what sort of performance you seek from your park jet and worth doing the research on the design and considering your approach to the build with respect to where all your components will be placed.

In the next article, I will discuss stabilizers (horizontal and vertical) and control surfaces.

Park Jet noise...the "other" sound of freedom😎
Cheers,

​Scott

Which Park Jet for me? - Part 7 - motor location

Hi Everyone -

There are essentially two styles of park jets when it comes to how the motor is located.  The most popular seems to be the mid mount "prop in slot" style and coming in second, the tail mount where the motor is mounted at the back with no hole in the middle of the fuselage.  Pictures below show the two types.

I have not ever built and flown a tail mounted plane, so I'm only basing my ideas on that style of plane from build and flight reviews I have read as well as common sense.  Both styles have their advantages and disadvantages, some of which I will discuss now.

Tail mount

Disadvantages

More difficult to balance the plane with the motor weight right near the very back.  From most build logs I have read, it also requires some extension wires between the motor and ESC in order to get enough weight forward to balance the motor location.  This adds a bit of complexity and weight to the build.  Performance wise, there is no plane structure blocking airflow coming off the prop, but the entire length of the plane is blocking air getting to the prop.

Additionally, you won't have any moving control surfaces in the prop wash, so no advantages of any "thrust vectoring" you may experience with mid mount planes.  The longitudinal moment ends up being quite long in order to counter balance the motor.  I have read build logs where folks have reported almost 24" difference between the front of the battery and the motor which puts a lot of weight distributed over a very long portion of the longitudinal axis, making pitch maneuvers slower.  Greater weight overall, with more 3D structure the whole length of the plane and no hole in the middle, the amount of foam is greater as is the weight.

Advantages

More scale look, no big hole in the middle of the plane, allows for more 3D structure over the length of the plane.  I have read and watched video that performance may also be a bit more scale without the thrust vectoring.  As mentioned above, no obstructions to the airflow from the prop, so I have also read reports that they might be faster than prop in slot park jets.

Mid mount "prop in slot"

Disadvantages

Non scale look, big hole in the middle of the plane and really no 3D structure rear of the prop slot.  Airflow to and from the prop are affected by air frame structure.  Prop size may also be prohibited more than with tail mount planes due side structure of the fuselage.

Advantages

Normally, at least one or two sets of control surfaces (elevons and rudders) in the prop wash, allowing for quicker maneuvering and more advanced aerobatics at slower speeds.  Easier to place the electronics and battery closer to the motor and CG to get better balance, shorter longitudinal moment of inertia, makes for much more effortless and efficient movement in all three axes.

Since I have all my park jet experience with mid mount "prop in slot" planes, I will focus on this primarily, but as I discuss behaviors with respect to planes with motors too far back, you hopefully will see how those may relate to tail mounted planes and what behaviors which might be present affecting the plane's performance.

As Stephan and I started modifying the RC Powers Mig-29 V3/V4 working unknowingly at the time towards the first Mig-35A, one of the major things we started playing with was moving the motor forward to shorten the moment of inertia by being able to concentrate the CG (center of gravity), CM (center of mass, primarily the battery location) and CT (center of thrust or motor mount location).  

What we started to find along with other modifications we were making was that the plane felt much better balanced, moved more quickly and effortless in all three axes with the CG, CM, CT so centrally located and condensed in a smaller area of the plane.  This meant much smaller control surface deflections to get the plane to move meaning more precise flying, reduced turbulence with small deflections and better overall stability.  With other planes I have tinkered with since then, we started to see some numbers come forward that translated to excellent performance no matter the air frame.  

We started to discuss the motor mount location being located at a percentage of the overall length of the plane.  We discuss the wooden motor mount location as the datum point rather than the prop location as different motors and shaft sizes would make for inconsistent measurements between us.  I took this picture from the planview of the RCP Mig-29 V1 to hopefully demonstrate what I mean.

You can see that the tip of the nose is 0%, the very tip of the elevons is 100% and where the motor mount location is on the Mig-29 V1 is located is at 56% of this length.  

Also to note on the diagram is the large black dot, of which the very center is the CG point.  The rectangle highlighted in orange is where a 2000-2200 mah battery would normally be placed to get best balance.  From the front of the battery to the motor mount, it covers only 20% of the length of the plane and is all very centrally located and condensed in the longitudinal axis of the plane.

So based on some testing I did with my modified RC Powers F-18 V3 (this link will take you to a video discussion of my mods) the RC Powers Su-30 V4, Parkflyers International Su-35, RC Powers Su-27 V5  and F-22 V5, I started to see a correlation between the motor location and the plane's overall handling and performance.  I took several measurements and found that the best motor location is between about 55-65% of the plane's overall length.  It is very difficult to get much further forward than that due to plane structure and still being able to place battery, receiver, ESC to balance the plane properly.

Much further back than that and I started to notice that my moment of inertia became much longer to balance the plane which slowed the pitch performance down slightly and made the nose feel a bit heavier when maneuvering.  What happens as this moment of inertia between the very front of the battery and the back of the motor gets longer is that it is like trying to balance a yard stick on your finger instead of a 12" ruler.  As the nose starts to move around, it can get a bit sloppy in pitch maneuvers like loops where the nose will wander a bit more than it will with a plane a tighter moment of inertia.

I have flown planes where the motor has been 70% or further back from the nose of the plane which required the battery to be sometimes 12-18" ahead of the motor mount in order to balance this difference.  This very long moment of inertia made the plane feel sluggish in the pitch and when pulled up in the vertical as it slowed down, the nose would get sloppy and wander around on it's own, bringing on stall quicker than normal.
​
So, after all that scientific stuff, I know that sometimes without having access to the plans you may not be able to tell where the motor is as a percentage of the length of the plane, but it is certainly something to consider.  Too far back, the moment of inertia gets longer, the plane can be more of a challenge to balance and maneuverability suffers.  It is certainly something to consider if you have already built the plane and want to tighten up it's balance and maneuverability by modifying the motor location on a second build.  

In the next article in this series, I will discuss weight distribution, much of which I have touched on already in a couple of articles, but I will focus more on why it is so important and how you can perhaps adjust your builds to optimize your plane's performance by where you place your electronics other than the motor and battery.

Park Jet noise...the "other" sound of freedom😎
Cheers,

​Scott

Which Park Jet for me? - Part 6 - wing shape and size

Hi Everyone -

Of course a plane wouldn't fly without wings, but how the wing is shaped and sized on a park jet design has significant impact on how the plane will fly.  I haven't flown any real exotic winged planes like the F-117 or a flying wing like the B-2, but have covered pretty much all the other wing shapes and sizes in my park jet journey thus far.

Here are the four wing types and their characteristics that I have flown and experienced in my park jet career.

• Moderately swept - I often refer to the F-18 as being a "straight wing" plane, but it is moderately swept at the leading edge and essentially a straight trailing edge;
• Delta - planes like the Eurofighter, Rafale and F16XL, all a form of delta wing where the wing shape is essentially a large triangle.  These planes are normally single fin tails and have the elevons incorporated in the trailing edge of the wing without benefit of horizontal stabilizers and elevators as on "conventional" jets.;
• Stealth - modern stealth planes like the F-22, Sukhoi T-50 and F-35 have a very unique wing shape, the F-22, T-50 and the NAMC Mig-FA have very similar wing shapes with the horizontal stabilizer almost blending into the wing.  One characteristic all the planes in this category that I have flown including the F-35 is that the leading edge sweeps back and the trailing edge sweeps forward, making for very unique look and flying characteristics; and
• Swept wing - in this category I am referring to wings that are fairly aggressively swept rearward at both the leading and trailing edges like the Mig-35, Su-35, F-15 to name a few, although the F-15 does have a more unique trailing edge, they all have very similar wing characteristics.  I will discuss this one last in this post as I think this is the most popular and versatile wing in my park jet experience.

Straight/moderately swept wing

I have flown two park jets with moderately swept wings, the RC Powers F-18 V2-V5 (pictures below are of a modified F-18 V3 I built awhile back) and the F-16 V5.

Since the F-18 V3 has been and is still such a successful park jet (plus the plans as this post writing are still free👍), I will focus on the F-18 V3 from this point on.

Like some of the more aggressively swept wings such as on Mig and Sukhoi aircraft, the F-18 has LERX (leading edge root extensions) which certainly act as part of the wing and promote much better stability, smoothness and slow speed handling, especially when extending the KF airfoil all the way forward.

​Although there is considerable wing area, due to it's design, this wing does not handle high wing loading as I mentioned already in part 4 of this series.  However, I did find in my most recent build pictured above, that a wing reinforcement plan like this one shown below does make for a very strong, stiff wing, the strongest of all F-18 V3 wings I have built thus far.​

The wing shape does tend to be a bit more "draggy", so not a great design if you are seeking blinding speed from your park jet.  It also tends to slow roll rate down somewhat, requiring more throw in the roll portion of the elevon and aileron.

With the LERX assisting however, it does make for a stable platform for slow speed and high alpha flying if that is something you seek.  I pretty much taught myself high alpha flying with the F-18 V3 and it is one of the most stable high alpha park jets around, flying very scale high alpha when compared to the real F-18. 

Overall, good stability and handling characteristics, combined with all the other features of the F-18 V3, this wing shape makes for a good starter park jet in my experience.

Delta wings

I don't have a lot of flights with delta wing planes, they are certainly unique and simple to build, only three servos with rudder.  Pitch and roll is elevons only along the trailing edge of the wing.  I dug into my photo archives for pictures of the Rafale (a semi profile plane I built from a plan on parkjets.com) and the Parkflyers International F-16XL "Garuda".    Also shown is a recent picture of the RC Powers Eurofighter V5 that I built.

All the planes above were relatively stable, although I found the Rafale and Eurofighter to be more of a handful in any wind above 10 mph, but perhaps some of this was due to the canards.  If choosing to build a delta wing plane, I would strongly recommend activating a rudder.  Given that most scale delta wing park jets have a single fin tail, yaw stability can suffer somewhat.  Couple this with the fact that there are elevons only that are not directly in the prop wash to help with "thrust vectoring", it can be tough to get the plane to track smoothly through turns without assistance of the rudder.  Often when turning in a crosswind, I found the tail to drop more than it would on a conventional "twin tail" park jet, so rudder was needed to track straight and true through turns.

Although most delta wing planes in real life have been pretty fast (F-106, Concorde, etc), I never noticed that delta wing park jets were any faster than others.  Even though it is larger with a much bigger leading edge, I would say that the F-16XL was the fastest of the bunch, again, not having the frontal drag of the canards probably helped with this.

Slow speed stability of these delta wing planes is about average, not as good as a straight wing or aggressively swept wing, but better than a "stealth" style wing from my experience.  The "cranked" delta wing of the F-16XL has the best slow speed handling as the wing was specifically designed to try and blend the improved high speed of a delta while still allowing for good slow speed maneuvering and stability.

Simple setup with three servos, but limited for advanced aerobatics, not very good for any sort of high alpha, although I have played around a bit with flaperons for slower speed.  Roll rates are slowed by the large wing, so roll input in the elevons needs to be relatively high to get crisp roll rates, but pitch rates are quite good as the elevons have a much longer span than they do on non-delta planes.

Wing loading with this style wing is good, although none of the planes above were over 22 oz, but the wing was very strong and solid, so could probably handle more weight if you really wanted a faster delta wing park jet by adding a more powerful motor setup.

"Stealth" style wings

The stealth wings and profile of planes like the F-22, T-50, NAMC Mig-FA and F-35 are very unique and have their own unique set of characteristics.​

In all cases, you can see in the above pictures that the leading edge of the wing sweeps back, while the trailing edge sweeps forward.  In the cases of the F-22, T-50 and Mig-FA, the wing flows directly into the horizontal stab and elevon structure which depending on the angle of attack, tends to block out the airflow over the vertical stabilizers, causing some instability and control issues, especially at slow speed.  The F-35 not so much, but it is still not a terribly stable plane at slow speeds as the wings tend to be a bit "stubby".  These stealth style planes are difficult to replicate as models as the models lack the high speed flight computers that help make the real planes fly and do the incredibly aerobatic things they can do.

The F-22, T-50 and Mig-FA can handle a pretty heavy wing loading without too much trouble, the F-35 not as much.  All of them because of their very "thin" frontal profile from top to bottom or completely flat bottoms in the case of the F-22 and F-35 have extra lift (perhaps about 15% more) due to this extra flat surface.  This can make the plane feel lighter than it is, but can also cause the plane to want to "zoom" at higher speeds, so trimming the plane properly or shimming the motor down can sometimes be needed to stop the plane from wanting to climb on it's own at full throttle.

To make the plane more stable at slower speeds as we started to learn with the Mig-FA, one of the biggest secrets is to get the weight distribution (ie the battery) as low as possible.  This was further proven with the RC Powers F-22 V5, even though their design called for the battery to be low, I lowered it even further and it is the most stable, well behaved and forgiving F-22 I have ever flown.

What I found with extensive testing of the Mig-FA is the stealth style setups like the Mig-FA, F-22 and T-50 are very prone to adverse yaw at slow speeds.  In other words, as the plane gets slow and you try to give it roll input to turn one way, it will actually yaw quite aggressively the other way, normally after almost reaching stall.  This can be quite catastrophic if you are low as you need some altitude and to be very quick on the throttle to get it to recover before it starts spinning opposite to the direction you wanted to turn.

RC Powers has touted the F-35 V2s and V3s and good trainers, I have never flown the V3, but I found the V2 to be a bit of a challenge as a trainer, not just because of the wing shape, but other issues I will discuss further in later articles of this series.  I would not recommend any of the other stealth style planes as a plane to tackle early on either although the F-22 V5 is one of the best stealth style planes I have ever flown with the couple of mods I made to it.  These type planes are perhaps good for a third or beyond park jet as they can be tricky to fly for someone just starting off.

There are a couple of tricks to try if you do want to fly slow or attempt high alpha.  Flaps/flaperons work the best as lift aids.  They help deflect "dirty air" away from the elevons rather than using spoilers/spoilerons which lift the dirty air and them dump it on the elevons, making the plane very unstable and hard to control at slow speeds.

But at 50% throttle and higher, stealth style planes are very happy, stable and quite aerobatic, especially with full controls.  Even without the computers, you can do some really good scale aerobatics with most of them and they are very stable as they glide in to land as long as you don't try to get too slow and just let the plane establish it's own sink rate.

Swept wing

In this category, I am referring to wings that are swept fairly aggressively at the leading edge and trailing edge like the Mig-29 and Su-27 family of airplanes and to a certain extent the F-15.  For this part of the discussion, I will refer to the Mig and Su wings primarily as about 50% of all my park jet flights over time have been with Mig-29 and Su-27 style planes that rose from these two iconic fighter jets.  In this picture, you can see the first prototype of the NAMC Su-27 with the NAMC Mig-35B.

Obviously, having been part of NAMC, the North American Mig Consortium, I am quite partial to the Mig designed wing.  However, long before Stephan and I ever met and started tinkering with the RC Powers Mig-29 V3/V4s, it became one of my favorites because it is such a versatile plane and wing.  Of course there are several other factors in the overall designs of the plane, but the Mig and Su wings are capable of a broad speed envelope from quite slow to very fast while remaining stable through this range.  Additionally, they are capable of handling considerable weight and wing loading without huge amounts of reinforcement or concern about wing flex.  Overall the Mig and Su are plane designs that translate well from real world to models and the simple yet very versatile wing design is a large part of that.

The two planes above have overall quite similar speed envelopes from quite slow to quite fast.  You will notice a difference in how the LERX are shaped, the Mig's flare away from the nose, making the LERX and "shoulders" of the plane larger which does help the plane fly very smooth, but compared to the Su, a little less snappy in the pitch and roll.  With it's LERX flared in more, the Su responds more quickly and aggressively in the pitch and roll without the extra surface area in the way, so these are considerations to keep in mind between the two wing shapes.  Both these planes are quite capable of very scale maneuvers and if you watch videos of the real planes on You Tube, you will note that the Su does respond more quickly and aggressively in the pitch and roll.

Either way, this wing shape as I mentioned is the most versatile from the stand point of their speed and stability envelopes.  If you want a really fast plane with the potential for lots of aerobatics, this wing shape is the best to choose in my experience, but it will still allow for good slow flying and rather forgiving characteristics, with the Mig wing shape being slightly more stable and forgiving when slow, probably due to the bigger LERX.

So each wing shape has it's strength and weaknesses depending on the flight envelope and performance you seek from your park jet.  This is certainly one of the more important considerations to keep in mind when selecting a park jet as the wing shape and size is so key to the plane's overall foundation of performance.

In the next article in this series, I will discuss the importance of motor location in selecting the park jet that is right for you.

Park Jet noise...the "other" sound of freedom😎
Cheers,

​Scott