RCPowers - F-22 Raptor

F-22 Raptor

Development

In the Spring of 2006 I had officially made plans to design and sell a depron F-22, with vectoring thrust of course. At the time I was busy building the first prototypes of the F1 Hydro and designing the SkyRider, so I didn't have any time to actually "work on it." Which was fine as I already had about 6 other kits lined up before it and was not planning to release it until fall or winter of 2007.

Once the F1 project was complete and the SkyRider was underway in late summer of '06, I finally had enough time (and space in my head) to start designing it fully. I had some rough ideas of what I wanted but was curious to see what was out there first. I searched RCGroups and the other RC forums every night to see what kind of F-22s were made.

There was very little in the area of manufactured kits, only really a few scratch builds here and there. I came upon one that I liked in particular that was a nice simple plane with a "doubled up" nose and cockpit. This gave it more of a real three dimensional appearance, rather than the profile look that I was trying to get away from. I imaged that I could use some cheap-o foam from Home Depot or something like this.

Then it was on to the thrust vectoring. At that time, there had been very little done on this idea of moving the motor with the elevators for improved (and scale) extreme handling.

Still not having a whole lot of time to design it, or real sense of urgency, I came up with a few different ways to make the back motor move. All the different techniques, ideas, designs, sketches, quick models, were just too complicated for me. They were like many that I have seen that involve specially cut parts, pivots, hinges, dealies and thing-a-ma-bobs. All of which I did not want to have to mass produce.

I would make another design and tell myself, "That's great, now make a better one with less parts." I must have invented 4-5 different ways to vector a motor around. After a few weeks of thinking about it on and off I FINALY came up with just mounting the motor to the elevator! How easy is that, genius?!

That second I knew I had it. Vectoring thrust with no moving parts. It's just piggy-backing on what the elevators are already doing anyway! I loved the idea, that’s what I was pushing for.

It's still late summer of '06 and I have to just sit on the idea. Then early October,Jetset44's (Steve Shumate) F/A-22 Raptor with vectoring thrust plans came out on RCGroups and everybody loved it. I happened to be up the night he first posted and I stalked the thread almost every night. Of course he is the KING of foam jets and made the most spectacular, scale, well designed F-22 ever. http://www.rcgroups.com/forums/showthread.php?t=579681

I then went back to the board of advisors (Keith and Al) and talked about redoing the order of kit releases for 2007. I proposed that I better get this F-22 kit out quick before someone beats me to it. We all agreed that the 22 needed to be next on the list after the SkyRider.

So by the time the SkyRider kit was released in December I was able to get to work right away on the F-22. I started construction of M-1 on December 10th and flew it the 13th.

These were my goals in designing the construction and flight performance of this new jet:

1) I want the VT maneuvers to be somewhat scale. If you watch full size fighter jets such as the real F-22 or even better, some of the Russian Migs, you will see that they have a very unique, graceful flow to them as they vector around in the air. They are so big and heavy that when they are flying straight and yank the stick back they slam their tail down, jam their nose up and keep moving forward belly first! It's like a train that gets derailed while it's moving at high speed. There is so much inertia that it continues to move forward even though the nose is facing another way!

Now this is close to impossible with foamie RC because the planes are so light, and have such dramatic control that they have very little weight and inertia bossing them through the air. That’s why they can instantly stop, flip on a dime, and then continue flying. Not something you ever see real fighter jets do.

So what I was NOT looking for was the fastest, most flippy, agile, super light, jet I could make. Any good 3D stunt plane can go up and do 5 flips in a second, that’s not what I was looking for. I want some scale looking VT that has some inertia to it. Watch the below 3min video to see what I am talking about…

3 min: http://video.google.com/videoplay?docid=-1994695142386399860&q=russian+jet&hl=en
13 min: http://video.google.com/videoplay?docid=-2979344652803798315&q=russian+jets&hl=en

I wanted to find what the ideal size and weight/wing loading the plane prefers to pull off somewhat scale thrust vectoring. I expected that it's going to want to be a heavier plane so it has more of a real jet commanding presence in the air. So to get the wing loading heavier, where I need it, I either have to have a big plane with lots of weight on it… or a smaller plane that automatically has a higher wing loading cause it's smaller. Did you get that? This is very important.

2) Another goal I am wanting is for the construction to be very simple and strong. What I am not is a "ground pilot" I get planes to fly. I am not too concerned about the paint, the weight, the build and all that stuff that makes it look good on the work bench. I am concerned about how does it look in the air, how does it perform in the air, and how much abuse can I put it through. The worst thing you can do to me is send me home early when I still have batteries to fly at the field. I want to be the last guy flying even though I might have crashed a couple times today.

3) It needs to work off of very common parts, somewhere in the small 400 motor class. If I am building a bigger plane I need to have a bigger or faster motor. Which means I have to either use a larger prop or a more expensive speed motor. Then I will need bigger more expensive servos to vector that big motor and prop around. I want to keep it as simple and inexpensive as possible.

Those 3 points are what I was setting out for:
1) The right size/wing loading for the most scale thrust vectoring maneuvers.
2) Simple and strong.
3) Uses common parts (motor, battery, servos, etc).

M-1
The first one I made the same size as Jetset44's and went from there. This plane was about 22x36 and weighed between 20-23oz. It did everything it was supposed to do! The VT worked, the construction held together, though the front nose and battery compartment was thin and weak. It was a great start, and all the theories are working out.

It did fly like an "airplane" and not a "jet". It would sail and float around real nice, but it didn't have the mean jet feel that I was looking for. The VT maneuvers all worked but they did not look all that scale, as the plane was just too light and would "float" rather than move with inertia.

M-2
The second one was pretty close to the first and had a redesigned and strengthened nose and battery hatch to it. Using magnets for the canopy didn't work cause the Home Depot foam was too weak to hold together. The magnets just pulled the foam out. So I switched to Velcro and anchored them with pins and epoxy.

It flew nice and would work with the Hacker motor as long as I had a 9x6 prop on it. Which is, if you ask me, just way too big of a prop for a jet. The problem is, if I were to get a motor to spin a 5x5 to 6x4 on such a large plane I am greatly narrowing what motor can be used. Most guys want to spend about $40-50 on a motor and get something that is pretty common and can be used on other planes. This larger size plane was limiting what motors I could use for it and stay within the smaller budget I am shooting for.

M-2.5
After many experiments with the F-117 Stealth I found that a smaller version flew MUCH more jet-like than the larger one. The reason was the wing loading really. The smaller one was heavier per square inch even with the same components inside. The plane had more weight and inertia to penetrate through the air like a real jet.

A large super light F-117 starts to act like a kite when it's too light. I want my 3D planes to be light and kite like, not my jets. Lighter is simply not "the best" every single time, on every single plane, depending on your goals. And for my goal of having a more scale-like jet in the air, I needed a heavier wing loading!

So the simplest and cheapest way to do this is to make the plane smaller. What I did to save myself some time and foam, was to just cut M-2 down to what a smaller version would be. I do this a lot on experimental planes. Start big, sturdy, and simple, and then cut it down inch by inch at the field. It's like flying 5 test planes in one day.

M-2.5 worked good, just as I thought it would. It was all chopped up and full of duct tape but it gave me a trial run of the dimensions I was looking for. And the best part was I was able to put a $39 motor on it with a small 6x4 and have ballistic power! That’s more like it.

M-3
So with that info, I built the 3rd one. This one is about 95% of what the kit is today. The only changes were 1/8" here and there as far as the construction, stress distribution, parts notching, etc. Not much to do with flight performance.

This one started to fly just as I originally wanted it to. It was not too light and kite-like, yet was very aerobatic and would glide real nice. I don't ever want a plane that falls like a rock when the motor is off! That’s too heavy! Even though this one was smaller and heavier per sq in, it still glided real nice.

One day that really confirmed it was when I was test flying it with a light 1320 3oz battery in it, then landed it and put in a larger 1650 4.8oz battery in it, plus 2 smoke bombs that weighted a total of 3 oz between the 2 of them. It had a payload increase of 4.8, going from 14.2oz to 19oz with smoke bombs on it and a heavier battery!

Now, with all this weight loaded up, and 5 bystanders standing around watching, I gave it a running toss and launched it… now 3 out of 5 of them were people I didn't know, nor did they know I was experimenting with wing loading… The instant I threw it, they were all amazed and said that it actually flew BETTER with the extra weight on it (some were expecting it to crash). It did in fact fly much better as far as scale-like jetness with the extra payload on it. This only triple confirmed to me that I was on the right road to put some meat on this thing to get it to fly like a jet. In fact, watch the video and take notice how well the plane performs with the smoke bombs on it. That’s because it's heavier.

So in summary, here is what the data showed for a smaller F-22 compared with a larger one:

- More scale performance. The smaller design has a more scale jet-like performance in the air especially when it comes to thrust vectoring maneuvers because the heavier wing loading gives it some weight, mass, and inertia to push it through the air.
- Assembly. With the smaller parts I don't have to cut the wings in half to get them in the box. The smaller parts are also inherently stronger.
- Electronics. A big issue with a big 17-23oz plane is finding a motor that will spin a 6 to 7 inch prop to move a plane that big and be under $40-50. The F-22 needs to have enough power to go vertical when you come out of the dead stop maneuvers. Having a bigger plane forces you to buy a hard to find, expensive motor, or swing a larger more torquey prop. The smaller plane works perfect with a large variety of inexpensive, common Outrunners on a 6x4 prop. Perfect.
- Price. Having a smaller plane means it uses less foam, less carbon supports, less expensive electronics, faster to cut out, etc.
- Versatile. The plane can still be flown light and floaty if the pilot prefers or is going to be flying indoors. The plane can instantly be transformed to a lighter jet by using a smaller battery. Also, a lighter motor can be used as well. The F-22 is not picky about what motor and battery you give it. You can easily fly a wide range of flight characteristics.

M-4
The 4th one is about 99% of what the kit is today. At this point I am experimenting with different flight modes and construction. I learned from Jetset44 that spoilerons might help me in the high alpha maneuvers. I finally figured out how to program my radio to do spoilerons (upside-down flaps) and boy, did it work nice.

When the plane is flipping around and you go to recover it, your air speed is real low or totally stopped. So you go to fly it but your wing stalls and you tip stall. Hitting the spoilerons up help regain stability and control at low air speeds and high angles of attack.

After I learned how to fly the silly thing, I continued on to perfect all the construction, parts fitting, and strength. My thinking is, the more work I go through, the more over-thinking I do in the development stage, the easier it will be for the guy who buys it. I went on to make 4 more planes each one getting 1/16" closer to perfection.

For this project, all the planning, research, and experimentation really paid off. I was able to meet all of my goals in only 4 major prototypes. I accomplished more than expected as far as flight performance and kept it all very simple. I'm happy with how it turned out and best of all its something new and exciting.