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04/05 JDC: F-22 Raptor

Ed Waldrep's F-22 Raptor, 04/05 Jet Design Contest entry.

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Introduction


Weight:2523 g (89 oz)
Length:120.6 cm (47.5 in)
Wingspan:87.3 cm (34.4 in)
Wing Area:18.6 dm2 (289.2 sq. in.)
Wing Loading:135.7 g/dm2 (44.5 oz/sq. ft.)
Fan:(2x) Wemotec Minifan 480
Motor:(2x) Kontronic Fun 400-28
ESC:Kontronic Smile 40-6-12 /w BEC
Battery:Thunder Power 4S4P 8000 mah
Power Draw:50 amps, 700 watts
Retracts:Jet Hangar Hobbies Mini Retracts

This F-22 design of mine sprang from a desire to have a scale outline model powered by an electric ducted fan. Although there was the Wattage F-22 pusher on the market and I successfully converted one to EDF power, the lack of a scale outline and the rough foam surface finish really left me wanting something more. No such kit was available so as I have in the past, I had to design my own model. Initially the model was to be a replacement balsa and ply fuselage for a foam pusher F-22, but was never built. Later on I enlarged the plans to fit two Wemotec Minifan 480 fans or a single 90mm Wemotec Midifan (the midi version may be built later but the prototype uses Minifans). Link to Ezone discussion forum build thread is here.

Construction

The design of the model was performed with an older version of Designcad 2D. I chose balsa and lite ply for the fuselage since thatís the material I have the most experience with and those materials are less work overall than building a plug and making molds. Parts were cut on a scroll saw by hand, but eventually I plan to have parts laser cut. Balsa sheeted foam wings were hand cut with a hot wire as I find foam wings much easier to construct accurately.

There are 3-views of the F-22 on the net, but most are small and cross sectional drawings were nowhere to be found. Some cross sections can be derived from the front view but not all of them. I chose to buy a plastic model and cut it into sections and scan the parts. I later found a website where someone did the same thing as I did, but his drawings were fairly small so I used what I already had. These bitmaps were then imported into cad, traced, and imported into the drawing. The side and top view from the model kit was used as the basic outline, with many tweaks, and the tracings were used as a guide to design the bulkheads. Then the hard work began, designing holes in the bulkheads for ducting, battery trays, gear mounts, etc. Parts were printed out on paper and that was attached to lite-ply and cut with a scroll saw. Most balsa sheeting was cut to fit as I went.

I wanted an airplane small enough to use my planned 700 watt power system but big enough to carry Jet Hangar Hobbies (www.jethangar.com) mini-retracts. Later I tried to fit Springair retracts but there was so little room between the inlet ducting and the side of the fuselage due to the twin fan design that the 602 series would not fit since they are about 1/16 inch deeper than the Jet Hangar retracts. To make up for the lack of room, a somewhat scale retraction angle was chosen, with the main gear retracting outwards and upwards so that the wheel lies in the horizontal position within the wing and fuselage when retracted. When extended the main gear strut lies at about a 45 degree down angle. This worked fine and even enabled the main gear door to be attached to the strut and cover part of the gear-well.

The prototype was finished with Ultracoat Lite Clear iron-on film, and then sprayed with Testors Model Master spraycans (I plan to finish the scheme and add details later when I have time). Iíve used this finish in the past and it works really well and is probably lighter than any fiberglass and epoxy finish that I could apply. The paint scheme was modeled after schemes that have been applied to F-16s at the USAF Weapons School at Nellis Air Force Base here in Las Vegas. Their schemes are sometimes designed to emulate potential enemy aircraft paint schemes that the students of the Weapons School may someday encounter in actual air to air combat. There are no F-22s painted in this color scheme currently but I suppose someday it could be possible! With the advanced systems of the F-22 though, itís likely, just as it is today, that the Raptorís prey will never even see itís killer coming!

Flying

The first test flight attempt was not error free, the plane rotated too much after a long takeoff run, lost itís energy in the high angle of attack attitude it was at, and fell off to the right and hit the ground nose down, crushing the nose. The accident investigation board determined later that the center of gravity was too far aft. I was holding too much up elevator when the plane rotated and the plane over-rotated since it was tail heavy. The long takeoff roll was due to the main gear being located too far back behind the CG. This is a common mistake made in models of modern fighters that are balanced tail heavy to improve agility. The full size fighters have gyros and flight stability systems, which our models lack, so we have to balance our models at a more forward location. I should have caught this mistake but over the long gestation period of the model some facts get lost or overlooked. With the rearward gear location, more down-force needs to be generated by the tailerons to lift the nose (the moment arm is effectively shorter with the gear farther back), so a higher speed and thus a longer takeoff roll is needed to rotate. When the model finally did rotated, I had a lot of up elevator held in so the tail heavy plane over rotated and lost speed at the high angle of attack, dooming my takeoff attempt.

I went back to my Wattage F-22 and checked the balance point and it was at about eight percent of the MAC (mean aerodynamic chord)! Thatís a lot farther forward than I flew my prototype at. During the nose rebuild, I moved a bulkhead forward so that I could lengthen the nose gear strut and have the model sit at a higher angle of attack, hoping to achieve a shorter takeoff run. I also shifted the battery forward to change the balance point and removed the tail ballast I had on the first flight.

The second flight was much better than the first attempt. I let the plane roll almost to the end of the runway and slowly eased in some up elevator. It rotated and climbed out at a shallow angle. With a few clicks of trim I was flying level. The gear was retracted and the speed increased. I checked the stall up high, performed an aileron roll and a loop, and made some low passes close in for the camera. The plane was probably nose heavy a bit but it behaved well. I dropped the gear and landed after about 4 minutes, using about 3600 mah of battery capacity. The sticky right main gear wouldnít come down due to loss of air pressure so I have an air leak to hunt down, but damage was limited to a scraped wingtip. I could always use more power but right now at 125 watts per pound Iím happy with it..

Conclusion

Overall my F-22 had a long gestation period, but seeing it in the air made it all worth it, the plane has an unmistakable profile that is only done justice by being replicated accurately, with the correct shapes. Cartoon scale Raptorís need not apply! I hope to refine the design, make corrections, and have laser cut parts made, but thatís still more work. A laser-cut semi- kit may be made available in the future but that remains to be seen. Iím even thinking of a smaller version for single MF480 or a big twin Midi powered version.

Discussion

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Old May 05, 2005, 06:24 PM
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RCParkflyer's Avatar
Racine, WI AMA# 809291
Joined Nov 2003
5,856 Posts
The F-22 Raptor

First off I'd like to congratulate Ed on his successful Maiden flight, and the RC Groups for hosting and promoting this contest, and to the vendors who have donated prizes to the contest.

Having followed his build thread from the beginning, I know all of the hardships he has gone through to see this bird fly, including a total rebuild of the nose in one weeks time. He put a LOT of hours into this plane and I'm glad to see it succeed.

I considered building an F-22 for the contest myself, but I knew that Ed was planing on building one also, so I chose a different jet instead. The Aurora Spy Plane, which I never finished, as I built it way too small for the heavy weight it needed to carry. I'll probably build a larger version over the winter, as it is really a cool jet and it deserves to fly, much like the Raptor.

I'm really suprized that no "big" model companys have steped forward and built an Electric RC version of the Raptor yet. A few companies have worked on YF-22's but no one has built a F/A-22 yet. There are a few turbine versions out there, however, but at several thousand dollars a copy it will be a LONG time before I can afford one.

The F-22 seems to be the "Black Sheep" of the R/C world. I suspect this may have more to do with Lockheed-Martin's band of "Intelectual Property" lawyers than anything else, however. It's really a shame that a huge company receiving Billions of our tax dollars, would choose to go after someone making a "Toy" airplane, and force them to purchase a licencing agreement. You would think it would be just the opposite, that they would try and PROMOTE the flying of THEIR aircraft by hobbyists. I'll get off my soap box now.

Ed mentions in his write-up that he would like to see a twin midi-fan version of the jet produced. I too think this would be a great idea, as it can incorporate many of the items that make the Raptor such a unique aircraft.

Things like leading edge and trailing flaps, alerons mixed as flaperons, full flying elevons, and a "scale like" set of retracts and doors. (things found on the high end turbine models.)
Coupled with the Raptors undercambered and anhedral wings, this would go a long way in eliminating the "bad" slow flight problems a number of previous models have shown. The "real" Raptor can fly slower than an F-15 (and faster too) and there is no reason why a scale twin Midi-fan (or larger) R/C Raptor can't do the same.

Ed Waldreps F-22 Raptor gets my vote in the contest, hands down!! Way to go Ed!!!

Tom - Milwaukee
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Old May 05, 2005, 09:57 PM
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Las Vegas, NV
Joined Dec 1996
7,940 Posts
Quote:
Originally Posted by RCParkflyer
..this would go a long way in eliminating the "bad" slow flight problems a number of previous models have shown.
Actually, the only other F-22 I've flow is the Wattage, and it flew very well if you upgraded the power sytem. It had excellent stall characteristics, it wouldn't tip stall at high angles of attack, and if you put it into a highly banked turn and pulled lot of elevator, it would roll level and mush toward the ground, wings rocking slightly side to side but that was it. No uncommanded snap roll followed by a vertical nose dive into the ground like some models. The big problem with the Wattage is the looks, the nose is wrong as are a lot of the fuselage curves. That and the foamy look really detracted from the appearance, but I guess it inspired me to design my wood version.

Thanks for your kind comments Tom! Now off to work I go to finish covering so I can get some paint on this beast, I've got to get ready for the Dixie Jet Rally in St. George, Utah in just over a week. I'm still debating weather to do the grey scheme typically seen or continue with my desert scheme.
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Old May 05, 2005, 10:28 PM
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Racine, WI AMA# 809291
Joined Nov 2003
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Hi Ed,
What I was talking about in my comment was some of the turbine models I've seen video's of, a few of them really have trouble on take-off, I guess I should have phrased that better.

My first jets were Wattage Raptors and I managed to ding both of the up really nice I have a lot of wing and vert stab repairs to do on them before they see the sky's again.

The desert camo sounds great, I'd go with that!!! If your going to put the airbase code on the jet, the big base in Saudi Arabia is "ZZ" and Raptor production numbers are in the 4000 series and current production has about 50 aircraft made. There building 4 a month now with something like 275 ordered through 2012.

Punch a BIG hole in the sky next weekend!! We need video's!!!!!!!

Tom - Milwaukee
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Old May 09, 2005, 10:50 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
7,940 Posts
I've added some pics of the painted airplane to my thread in the discussion forum here:
http://www.rcgroups.com/forums/showt...0&page=8&pp=15
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Old Apr 30, 2010, 06:27 PM
RaptorManiac
Joined Apr 2010
1 Posts
Hi, i was wondering if you could e-mail me the plans of your marvelous F22 Raptor model. I am new to this and i was hoping i could make a F22.
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Old Mar 27, 2015, 01:32 AM
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Joined Dec 2014
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Are plans available?

Ed, great work! Beautiful jet. Is it possible to obtain build plans or print copies?please shoot me an email at justin.lareau87@gmail.com . Thank you very much it's a beauty I'd love to attempt to build! Best regards, Justin from Wisconsin
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