I am passionate about building and flying scratch built foam park jets and passing on my experiences and lessons learned from more than five years of experience. Blog is purely based on my own opinions and experiences. If you have questions, please e-mail me at scott.parkjet@gmail.com. Park Jet noise...the "other" sound of freedom :) Happy flying! Cheers, Scott
Welcome to my build log series of the Ground Control RC (GCRC) F-22 Mini V3.😊
Here is some flight video of this little steed in action😎
As I mention in the video, this plane is build with Dollar Tree foam (also known as Adams Readiboard) but could with the necessary adjustments to the slots on the plans be built with just about any foam you have available. You can see much more information about this awesome little park jet at GCRC's You Tube channel and his Patreon site.
Here are the basic dimensions of this park jet.
Wingspan - 22"/559 mm
Length - 28.75"/730 mm
Height - 4.75"/120.7 mm
In the video, my AUW with a 1050 Mah 3S 75C battery is 326 gr/11.5 oz.
Between us to this point, GCRC and I have accumulated well over 200 test flights with this plane with different props, motors, ESCs, batteries, KF (Kline Fogleman) airfoil combinations. Therefore it is a very well tested and evaluated park jet right from the plans through to the finished flying product😊
In the video, my plane is equipped with the following inexpensive components.
This is a very agile and fast park jet with the current setup and I would say is in the intermediate category, so I would not recommend it as a beginner/trainer park jet. However, if you check out GCRC's You Tube channel and Patreon site, he has some better options if you are just getting started in the hobby or park jets.😊
This summary has been a long time coming and if you already follow this blog and my You Tube channel, much of what you are about to read or watch has already been covered. However, I wanted to do a bit of a wrap up to review some of the more important points and some of the items I may not have discussed to this point.😊
I have certainly become a convert to using quad motors in my single motor, prop in slot park jets. Their light weight and incredible power certainly fits the way I like to fly. Of course this power does come with a cost in both money and amp draw and requires some consideration about which plane to choose and how to build it, but for me it has been worth it.
Here is a video I shot that this blog supports.
I mentioned three major sources of information that I found very helpful making the correct choices to achieve the power setups I was looking for. Here they are.
You can also find all the my bench test data on my motor test spreadsheet. Each motor I tested has it's own page, so if you scroll along the bottom you can navigate to whatever motor you want to view. Also on this spread sheet is test data from the 2212/6 2200 kv and 2212/5T 2700 kv motors which are the two most popular park jet motors around and what I replaced in all my planes. I put this data there for info and to compare. Also, rather than providing links to every motor, prop, ESC and battery I used in testing in this blog post, you will find links to all of these on the motor test spreadsheet. Where applicable, I also put what custom settings I selected on certain ESCs to maximize performance. All these setups have been thoroughly tested at the field also.
I also started a thread on the RC Powers forum which may also cover some items missed in this blog post or videos.
From the first post of the RC Powers forum thread, here are the advantages and disadvantages of using quad motors over the more conventional 2212 motors in 2200 and 2700 kv.
Advantages
quad racing motors tend to be much lighter, saving anywhere from 15-25 grams just in motor weight alone;
paired with the right prop and ESC, they can produce equal to or often far more power than the standard 2212 2200 kv or 2212/5T 2700 kv motors, so very high thrust to motor weight ratios;
with so much time and effort being put into the development of lighter, more powerful quad racing motors all the time, the performance is increasing in leaps and bounds whereas the 2212 2200 kv motors other than perhaps becoming cheaper, have not changed much in the last several years from a standpoint of weight and power output;
although quad motors are often more expensive, because there are so many different companies making them, the competition is fierce and you can often find them for a very reasonable price. For example, I have only paid full price on about 25% of the motors I have purchased in the last year, the rest were all picked up on sale (although one could say I might have gone broke saving money😏);
many quad motors are designed to be run on batteries from 2-6S, so a wide choice of battery options;
if you find a motor you really like, they are often sold in bunches of four at a more reasonable price.
Disadvantages
due to their smaller physical size, they often might not have the torque of a 2212 2200 kv motor. Even though the test bench numbers might show incredible performance, sometimes because they are about half the physical size of a 2212 size motor, they just don't have the "muscle" to push a larger, "draggier" plane around or deal with windier conditions. Therefore airplane size and weight becomes very critical. I have found that planes with about 27" wingspan or less and under about 21 oz AUW work the best, as always, the lighter the better;
when you build your "prop in slot" plane, you do need to adjust the front of the prop slot quite a bit to compensate for the much shorter "bell/can", otherwise the prop will run far too close to the leading edge of the prop slot causing a lot of noise and causing the prop to run much less effectively/efficiently;
with a couple of exceptions, I have found that motors with a stator size of 2306 or better (2406, 2307, 2207, 2208 for example) and greater than 2600 kv seem to give the best power when looking for equal or better power than produced by the 2212 2200 kv motor setups;
they are often considerably more expensive than 2212 2200 kv motors which can often be found on Ebay for $5 USD, but there are some fairly reasonable options available that are pretty peppy and much lighter than a 2212 2200 kv motor setup; and
they are considerably more "amp hungry" than the 2212 2200 kv motor, normally requiring a 40A ESC on 3S whereas you can often run the 2212 2200 kv motor with a 30A ESC.
As mentioned in the first video, here are the final reviews I did organizing the motors into "budget", "middle of the pack" and "serious power where cost doesn't matter"😉
Budget/value
Middle of the pack (includes a couple of motors to avoid)
My top five choices where cost and efficiency isn't an issue😎
I have also created several playlists to organize other "table talks" about motors, ESCs, batteries that I tested during this process. As time goes on and I have evaluated these components more thoroughly, these play lists will be updated. Also is a playlist of all the flying tests at the field.
Thorough reviews of individual quad motors can be found here.
One thing I should mention that I did not mention in the video, if you don't want to spend money on new ESCs, experiment with higher timing and different PWM settings if you can. Even if you don't have a thrust stand to evaluate, normally the quad motors I tested all seemed to like a pretty high timing setting for max performance. Having said that, monitor the heat build up carefully in your ESC as often most ESCs will run warmer with a higher timing setting.
So certainly none of this information is exhaustive and I will continue to evaluate and learn as my park jet journey continues. I may still test the odd motor that comes along but for now I am pretty satisfied with the setups I have discovered and will continue to use quad motors in my park jets for the foreseeable future😊
You can find the detailed and updated spreadsheet by clicking on this link.
Motors tested today with the numbers at 100% throttle -
DYS MR2205 2750 Kv (Hobby King) currently $15.60 USD (thanks to rcplanepirate, I got mine on sale for $8.60👍) 29.8A/358.6W producing 820 gr/28.9 oz of thrust;
Multistar Viking 2208 2600 Kv (Hobby King) currently $28.14 (again thanks to RCPP, I got mine on sale for $16.10 😊) 31.9A/384.7W producing 960 gr/33.9 oz of thrust;
RC Timer FR2306 2650 Kv (RC Timer) $11.99 USD 30.9A/351.7W producing 878 gr/31.0 oz of thrust; and
RC Timer FR2205 2550 Kv (RC Timer) $10.99 USD 28.0A/322.5W producing 849 gr/29.9 oz of thrust.
Interestingly, the motors below 2700 Kv all have thrust numbers that match up in order with how I rated them in this blog post compared to the Racerstar BR2406 2600 Kv motor with the same prop. Just for comparison, at 100% throttle, the Racerstar 2600 numbers are 31.7A/385.7W producing 982 gr/34.6 oz.
The DYS MR2205 2750 Kv numbers are disappointing, but not surprising. rcplanepirate and I had discussed this motor off and on after he tested his second one that perhaps DYS had produced a bunch of 2300 Kv motors but put the 2750 Kv bell on by mistake 😒(if you click on the highlighted 2300 Kv, it will take you to the HK website where the DYS MR2205 2300 Kv motor is listed).
Comparing it to all the other quad racing motors I have tested, it is actually less powerful than the RC Timer 2205 2550 Kv motor as it produces 1 oz less thrust and is supposed to have 200 more Kv!😲 I put it in the category of motors above 2700 Kv because of how it is labelled, but the closest motor to it in that category is the Racerstar BR2306S 2700 Kv motor which pulls two more amps, but produces 6.3 more oz of thrust! Something not quite right there. The DYS 2205 2750 Kv might still be a good light little motor if you weren't looking for a ton of power, but I certainly wouldn't pay full price for them when I can get a Racerstar 2700 for $8.99 that produces a whole bunch more power.
Still waiting on three more quad racing motors to test on the bench and in the air
Sunnysky Edge R2305 2800 Kv (again on sale, regular price at AliExpress $41.80 (what?!😲), I got mine for half price at $20.90, current price at Banggood is $23.71 (regular price); and
KF orKline Fogleman airfoils are one of the most significant additions/innovations to flat wing park jets in my opinion. They can take a very simple flat wing and add stability, improved wind penetration, increased lift, increased speed and really help to give that "locked in" feeling if you want to fly your park jet with precision. Much has been tested and written about Kline Fogleman airfoils, yet they still seem to be misunderstood or incorrectly applied in the park jet community. I am certainly not an expert by any means, but between Stephan (NAMC chief designer) and I we have done considerable field testing to dial in the correct KF configuration for our NAMC planes. I have also taken these findings across to other designer's planes and have had the same very good results, so it leads me to believe that for swept wing park jets we have a pretty good idea of what works and what doesn't backed up by thousands of flights worth of experience. So how does a Kline Fogleman airfoil work? Well, essentially, here is a simple (simple is good for me😏) description from the Wiki link above. "The purpose of the step, it is claimed, is to allow some of the displaced air to fall into a pocket behind the step and become part of the airfoil shape as a trapped vortex or vortex attachment. This purportedly prevents separation and maintains airflow over the surface of the airfoil."
There are numerous varieties of KF airfoils as shown in this picture below, I will be discussing KF2 and KF4 in this post as they are the most popular for park jets. I know it is difficult to read the description below each one, but looking around Google, you can probably find much more information about the more exotic or complicated setups.😊
This video hopefully gives you some visual idea of what is happening as air flows over a wing with KF airfoils.
The video above shows a straight wing where the normal rule of thumb is that the KF extend to 50% of the total chord of the wing at the root and tip. Through considerable testing, experimentation and some discussion with Scott Lott and Dave Powers (Scott Lott was the primary designer of all the RC Powers planes up to and including the V4 lineup), once you start to sweep the wing even slightly, this number decreases to about 40%. So if you are adding KFs to a plane where the designer has not included them or you want to modify existing KFs on a plane, 40% is a very good starting point for most swept wing park jets, even a moderately swept wing like the RC Powers F-18 V3. At about 0:55 in the video below, you can see/hear Dave Powers discuss the 40% starting point which just seems to work well on almost every wing configuration I have ever tested.
With our NAMC planes, we actually took this a bit further as we fine tuned things at the field, our KFs are very close to 40% at the wing root, tapering down to about 35% at the wing tip, but if you are playing around with KFs on a plane, 40% of wing chord overall is a very good starting point.
A few things of note from Dave's video that my experience has taught me. While I agree to a certain point that the addition of KF airfoils do help strengthen the wing, I would never use them in place of recommended carbon or other reinforcement in a wing, there will still be too much flex. I have found that when really dialing in a plane for best precision and performance, that a few mm between trailing edges top and bottom when using KF4 do make a difference in how the plane performs. Having said that, you can certainly trim KFs down to really optimize the plane for how you want it to feel as we all seek different feel and performance from our park jets. Lastly, we found through testing that KF2 while popular with RC Powers and others degrades the precision and handling of your park jet by about 15-20% as the increased and unbalanced lift cause the plane to "float" and the controls to be "mushy" and very slow to respond in turns if you get too slow. I'm not saying your plane will fly "horribly" with KF2 airfoils, I'm simply passing along what I have seen in extensive testing with many KF configurations. More discussion on that later. Actually most park jets will fly quite well without any sort of KF airfoil, so if in doubt, cut them out, fly it without the KFs, then add them on and experiment later to get the feel and performance you seek. Without the KFs, you do lose some added lift, wind penetration and speed, so for some inexpensive foam, KFs can really add another level of performance to your park jet. KF2 does seem to be a popular setup as some folks like their planes to feel "floaty" and have better slow speed characteristics. Fair enough, KF2 will give you that if that is what you seek. However, I know this flies (pardon the pun😏) in the face of what most folks say, I personally think and have found through hard earned experience that KF2 are not a good set up for beginners and here is why. This is a bit of a repeat of what I have already said, but I'll drive it home anyway. KF2 causes the plane to "float", but also at times when slow have a mind of it's own. The first park jet I ever built was the RC Powers F-35 V2(no longer available) as you may have already seen in the intro post of this thread. I followed RC Powers advice and put KF2 on the plane as I didn't know any better and as I was losing control of my plane in turns, still didn't know any better as I put it down to me being such a new and not very good pilot. As my experience grew and I tested them further on our NAMC planes, I realized that compared to no KF or KF4, the KF2 made the plane feel very "mushy" and slow to respond in turns, in fact if I was to put a number to it, the response and crispness of the plane was reduced by about 20% over no KFs or KF4s. So I ask myself and I guess I ask you, is that a good thing when learning? I personally don't think so, we all tend to panic and over control a lot when learning, especially if our plane doesn't respond when and how we want it to. I "over controlled" my F-35 V2 numerous times into the trees/ground, etc because it was very slow and sluggish to respond to inputs and would float/slide itself around turns. Then I would hammer harder on the controls, it would stall or go the opposite direction and normally a "walk of shame" would then ensue 😳. Although this video is using a flying wing, it is a swept wing like a park jet and I think shows how much more stable and precise the plane is with KF4 versus KF2.
So getting back to why starting the KF depth at 40% of total wing chord at the root and tip and why it just seems to work and why getting too much less or too much more than that doesn't.
I have flown planes with 30% KFs up to 60+% KFs and the results were not great. To keep it in context, from this point on I will be discussing KF4 as I think they are the best overall configuration for speed, balance, stability, wind penetration and precision for 99% of park jets. In all honesty, you are better to go smaller than larger. If you go smaller than 40%, you start to lose a little bit of the stability effect to the point if you make them too small, there really isn't any point in having them at all. What I have experimented primarily with in our development of the NAMC Mig-35B/Mig-FA as well as other designer's planes is when the KF gets too big and what happens to the plane. I found it easier to start off slightly large and then trim off foam as I went rather than start small and try to glue small strips back on. Obviously, I don't have wind tunnel data or video to back this up, but rather lots of hours spent at the ultimate park jet laboratory, the flying field. What I have found happens is that the further the trailing edge of the KF goes in relation to the wing chord, flying straight and level it does become super stable, but as you start to maneuver the plane, this over stability starts to fight back with some very negative behaviors. Stephan and I have discussed it at length and our thoughts are is that as you manipulate the "bubble" of the KF further back, the center of gravity (CG) and center of lift (CL) start to work against each other and not in harmony. Back to something I mentioned in the last post, as you start to push a plane's setup too far in one direction aerodynamically, other aspects of the performance envelope are bound to suffer and this holds true with KF size as well. Here are some characteristics I noted with KFs that are too large. In turns, the plane almost fights back, becoming difficult to keep tracking straight, it can get "floaty" or "mushy" or just as quickly be too precise and twitchy. I know this sounds over simplified, but the plane almost acts like a toddler throwing a temper tantrum, just not a smooth or fun flight experience and very unpredictable at times. Second and perhaps most significant is it can require much more effort to get the plane to pull out of dives or loops. Having the KFs too big really effects the ability of the plane to respond quickly in the pitch axis which if you aren't ready for it can lead to a walk of shame as your plane theoretically pulls out of the loop too low 😨 A couple of other notes we found through testing KF4 airfoils. You can use up to the same thickness as the foam you built with, although slightly less seems to work best as it reduces the thickness of the wing and reduces drag. However, whatever you choose whether it be 6mm MPF, paperless dollar store foam (about 4.5mm thick) or even 3mm foam, use the same thickness top and bottom. Stephan and I have both tried what I have heard referred to as "KF 3.5" where the top layer is thicker than the bottom layer (6mm top and 3mm bottom for example). The claim is that it uses the best of both KF2 and KF4 properties. For how I like my planes to fly, I disagree as I find it is much closer to KF2 than a compromise of both and also causes even more imbalance between the top and bottom of the wing. If you do decide to try out KF4 airfoils, another important note I have learned the hard way is to ensure that the trailing edge of the top and bottom airfoils are as close to even as possible. I know the angle of the picture below might show these as being off a tiny bit, but they are equal along the trailing edge. If either the top or bottom trailing edge is even a couple of mm further back than the other, it can cause your plane to unexpectedly dive or zoom as speed increases and the difference in the "bubbles" is amplified. If you do put KF4s on your plane and you find it has these tendencies as it accelerates or decelerates, this would be one of the first things I would check.
You may also note that the leading edge has been shaped so that it is symmetrical. I have used a more "chisel" type of leading edge early on in my park jet career and found it to cause a lot more drag and instability, so having a symmetrical leading edge like in the picture seems to work the best for overall performance with KF4 airfoils. There are also arguments that having the leading edge rounded works best. Honestly I have not tried that, perhaps because the setup above has always worked for me and I don't want to mess with success😉 So there is certainly lots to consider and to experiment with concerning KF airfoils on park jets. They are a very simple and inexpensive performance upgrade requiring some inexpensive foam glued in place and will transform your plane into a whole new "animal" at the field 😊 For testing purposes, you can even tape them on to try out, just don't affect the step along the back or you defeat the purpose of the airfoil. On the reverse side though as hopefully I have explained, they can also take your already decent flying plane and handcuff it, like putting a speed and handling governor on a high performance sports car, probably not something any of us wants to do 😏 In the next and final installment, some final thoughts to wrap up this thread. Not to "name drop", but when this article first appeared on the old NAMC blog, I was honored that Dick Kline himself (The "K" in KF) commented on that post, I have pasted our conversation below as a post script.
Park Jet noise...the "other" sound of freedom😎 Cheers, Scott
Chat with Dick Kline
Scott... Enjoyed reading about your research on the KF concept. KF airfoils are designed for power because it takes energy to create the vortex. With the vortex employed, you have excellent control over your aircraft. Thank you for exploring this subject. Did you ever complete your final installment? ~ Dick. The K in KF
Hello Dick - Very honored that one of the inventors and innovators of such a simple yet amazing addition to model airplanes would find this article. Thank you so much for your kind words and response. Very interesting insight as to how the power affects the vortex, KF4 have certainly been one of my absolute favorite addition to foam park jets, so I like many others am in your and Floyd Fogelman's debt for this invention. I did write a wrap up article to this thread about "Which Park Jet for me", you can read it here http://www.migsrus.com/blog/which-park-jet-for-me-some-final-thoughts All the best to you and Floyd and thanks again for taking the time to write to me. Cheers, Scott
Dick - Sorry in my excitement I forgot to make a very important acknowledgement. Much of what I know and have learned about the proper thickness, depth in relation to wing chord, etc about KF airfoils on foam park jets has been the result of hard work, knowledge and testing by my NAMC partner Stephan Moran. He is the scientist and chief designer behind all our NAMC airplanes to date and I have learned an incredible amount from him and through lots of fun flying and testing at the field. Again, all the best! Cheers, Scott
Reply
Dick Kline
7/29/2017 02:43:33 pm
Scott... it is great to acknowledge Stephan Moran for his contribution to your knowledge base. He also showed that he believes in you which gives you permission to believe in yourself. We ALL need that in our lives when we are young. And, we are all creative because creativity is all about problem solving. Always acknowledge your own creativity to yourself. It empowers you to be even more creative. ~ Dick
Hi Everyone - I don't have a lot of experience with leading edge flaps (only tried them once) or canards as they don't fit that well into my flying conditions and flying preferences, but I have tried them, so will relate my experiences. If they are something that interests you to suit your flying style and conditions, there are certainly folks who have written considerably about them on the RC Powers forum, so not to pass the buck, but I would direct you there to start searching for more info if my thoughts don't satisfy your curiosity 😊. Where I fly, I have dead calm still days or days with less than 5 mph wind less than 20% of the time. I fly primarily in conditions with winds of 5-10 mph, so having a plane that can handle wind well is pretty important to my flying situation. What I mean here is having a plane that I can still fly relatively smoothly and perform basic aerobatics while it is a bit windy. I suppose I could throw any plane in the sky in these conditions, but I don't like being in a situation where I am basically "surviving" the wind and not having any sort of fun at all. Not a relaxing way to fly and enjoy myself in my experience. As you read through the rest of this post, you will probably realize why I rarely build and fly planes with LE flaps or canards. Leading edge flaps When I read posts on the RC Powers forum from those who are big supporters of LE flaps or who design them into their airplanes, essentially my takeaway is that they enhance slow speed flight. I would agree with that, but my experience is that having these fixed flaps on the leading edge narrows the overall flight envelope quite a bit as a sacrifice to enhancing slow speed flight.
The RC Powers F-18 V4 pictured above is the only plane I have flown with fixed LE flaps. It is difficult to see, but this plane also has KF2 airfoil (KF added on the top of the wing only). I do agree that in calm conditions it did improve slow flight handling compared to the F-18 V3. My initial thoughts on this plane were that it was an amazing improvement over the F-18 V3, but the more I flew it in varying wind conditions, the less I liked it. I'm not hiding anything here, I have discussed this all privately with Dave Powers of RC Powers, but this setup became one of my least favorite park jet setups of all time and after about 50 flights, I retired her, beautiful paint job and all 😳, it was just not much fun to fly for what I expect out of my park jets. Here is what I found was happening. The leading edge flap was causing drag and as speed increased more turbulence and less stability. With KF2 as it got slow, the controls could also get a bit "mushy", not a feeling I like in my park jets. In windy conditions, with those angled flaps, it would get bounced around unexpectedly in a way that was hard to predict and often hard to handle. So I realized for conditions in which I normally fly and my flying preferences, leading edge flaps were not for me. When the RC Powers Su-27 V5 was first released in Oct 2015, as soon as I saw leading edge flaps, it went on the "I doubt I will ever build this" list for me. However, I continued to follow the thread on the RC Powers forum with mild interest as it was an Su-27 and I hadn't had one of those in my hangar yet. Unfortunately, it got a lot of bad press initially, one of the key things that I saw was that more than one person reported it was a calm wind plane only. Again, this confirmed for me that perhaps the leading edge flaps were contributing to problems with how this plane flew and handled the wind. After several months, I noticed that guys were modifying it to fly without the LE flaps with either no KF airfoils or KF4s, so I figured I would give it a try and it has turned out to be just an awesome flying plane. I never really treated her to much of a paint job, but I put over 300 flights into this great flying plane 😀
Canards I have flown three different planes with canards, Su-37, Rafale and the recent RC Powers Eurofighter V5.
If you read through the RC Powers threads, there are a few guys who set the canards up to be moving to provide better airflow over the wing when slow in high angles of attack. From what I have read it does require more weight with linkages and a servo and far more complexity in plane and transmitter setup, so it has been nothing that has interested me. But if you are looking to have a plane that is fully optimized for slow flight at high angles of attack, by all means experiment. However, like about 90% of the rest of the folks who build park jets with canards, I have always had them fixed (ie non-moving). When flying in dead calm to very light wind conditions, they do reduce wing loading, making the plane feel a bit lighter on the sticks and when comparing a Su-37 to a Su-35 (same plane but without canards), the Su-37 does feel smoother in calm wind conditions. I do find the canards slow down pitch and roll performance slightly over non canard planes as they do create drag and resistance in these axes. Additionally, even in calm winds, having that extra lift further forward can contribute to the plane wanting to "zoom" or climb on it's own as speed increases. I found this tendency to be the worst with the Eurofighter V5 as the canards are quite large and quite a bit further forward of the wing than the Su-37 and Rafale. Bring on the wind and in my experience, planes with canards can start to become a real handful as the wind hits them and really pushes the nose around. Whereas I fly many of my non-canard planes in winds above 10 mph, I rarely fly a canard plane in those conditions, I find they become too unstable, unpredictable and not much fun to fly. So that essentially sums up my experience with LE flaps and canards, in calm winds they are fine, certainly canard planes look very cool and modern in the air, but what the eye sees and what the wind "sees" are two completely different things in my experience. LE flaps do perhaps improve slow speed handling and stability, but with many things to do with aerodynamics, if you push one part of the flight envelope too far one way, you pay penalties in other ways. So certainly give them a try if they interest you, I would strongly suggest doing your maiden flight with LE flap or canard planes on as calm a day possible before experimenting with any wind. These are just my experiences, perhaps yours will be completely different 😀. In the next article, I will discuss KF airfoils, something we have done a lot of testing with in the development of our NAMC planes and I have tested on other designer's planes as well.
Park Jet noise...the "other" sound of freedom😎 Cheers, Scott
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 inpart 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 V5that 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
