|May 24, 2005, 12:20 AM|
F-14 Tomcat Park Jet
Here’s my latest contribution to the Depron park jet series, the Grumman F-14 Tomcat. This design is similar in concept to my other park jets, and uses similar construction methods and power setups. Like the other jets, it’s intended to be a semi-scale parkflyer that uses simple construction methods and readily available components. Here are the specs:
Wing area: 220 sq in
Span: 40.7” fully unswept, 24.7” fully swept
Length: 39.8 in
Weight RTF: 22.3 oz as shown painted
Wing loading: 14 oz/ft2
Motor: Himax 2015-4100 with 4.4 gearing
Battery: Thunder Power 11.1V 1320 mAh Lipo
Prop: APC 9x6 SF
Current draw: 12.3 amps static
Power input: 128 watts
Power loading: 100 watts/lb
Radio equipment: Berg 5 receiver, GWS Pico servo (rudder), Hitec HS-55 servos (tailerons), Hitec HS-81MG servo (wing sweep), Phoenix 10 speed control
Flight controls: Tailerons, rudder, wing sweep
The flight performance of this model is fantastic, and far exceeded my expectations! It has a wide speed range and excellent handling characteristics, and is very smooth and predictable in flight. It is very aerobatic and is well-mannered at both low speeds and high speeds (and with the wings both swept and unswept). Landing speeds are slow enough that I can easily hand catch it, yet the top speed is as fast as I’m comfortable flying a sheet foam airplane, about 50 mph. But my favorite part is how well this model captures that distinctive look and feel of the Tomcat in the air. It sends visions of “Top Gun” through my head whenever I fly it… ;-)
If you haven’t already seen it, here’s a link to a flight video of this model before it was painted (this is the same video I posted 2 weeks ago in the F-18 thread):
And here’s a link to a short video of the model on the bench showing how all the controls work:
F-14 Flight Controls Demo
Because the F-14 Park Jet has a little less wing area than the other park jets (220 vs 250 sq in) and a heavier AUW (22 oz versus 18 oz), it needs a little more power. My F-14 uses the same brushless Himax 2015-4100 setup as my F-18 and Gripen park jets and it performs extremely well with this setup (21 oz thrust). But unlike the other park jets, I doubt the F-14 would fly well with a stock brushed GWS EPS-350C motor setup (15 oz thrust). However, if you want to use an EPS-350C on this model you can install a simpler and lighter fixed sweep wing, which I’ll describe in an upcoming post. Keep in mind that this is the first park jet I’ve built that required ballast in the nose to balance (4 quarters), so it will certainly pay to use as light a motor as you can!
|May 24, 2005, 12:22 AM|
As you would expect, there are significant differences in how this model handles with different wing sweep angles. With the wings fully unswept, it responds quickly in pitch but is a little sluggish in roll (since the tailerons don’t have much moment arm). With the wings fully swept, it is a little sluggish in pitch (since sweeping the wings aft significantly increases pitch stability) but lightning quick in roll. Interestingly, I’ve found that a mid-sweep position seems to offer the best control harmony in pitch and roll. This model is noticeably faster with the wings unswept in level flight and especially when maneuvering—which shouldn’t be surprising to anyone. When you sweep the wings aft on this bird, you’re trading a very small reduction in frontal area for a huge increase in induced drag and trim drag! But then again there’s no beating that awesome arrowhead-like look of the F-14 with the wings fully aft…
Mixing is required to keep this model trimmed with different wing sweep settings, but this is very easy to do and works like a charm in flight. Just set up a 5% mix so that ¼” up elevator is added as the wing sweeps aft. The reason for this is because as the wings sweep aft, the center of pressure moves aft a lot but the center of gravity doesn’t move aft nearly as much. This results in a nose-down pitching moment that requires up elevator to compensate. But with this mixing, I can change the wing sweep at any time in flight and the airplane always stays trimmed.
Here are some more pictures of the finished model.
|May 24, 2005, 12:24 AM|
Here are some pictures showing construction of the Tomcat. Note that the wing sweep mechanism is entirely independent of the rest of the airframe. This is nice since it allows you to build, test, and tweak the mechanism to get it working perfectly BEFORE you install it. I used a Hitec HS-81 MG servo for the wing sweep, and while this servo does strain a bit to sweep these wings, it works well enough that I don’t think a stronger (and thus heavier) servo is necessary. But there’s plenty of room to install a larger servo if needed.
Note that a simple nylon bolt and nut is used for the wing pivot pins. The initial design of this model was intended to use a carbon tube running inside aluminum tube bushings and Teflon bearings for low friction. But after building and testing the mechanism, I was quite surprised to find out that none of that complexity was required—it worked great with just simple plywood bearings and a nylon bolt pin. Simpler is always better in my book! But I did find that the plywood bearings have a lot of friction in flight due to the flight loads on the wing (which press the bearings together). However, I was able to solve that problem by covering the root of the wing and the insides of the wing slot with slick low-friction packing tape. Again, very simple.
Note that the F-14 is much more complicated than my other park jet designs and is quite a bit more difficult to build, so if you haven’t built a Depron jet before I’d HIGHLY recommend building an F-18 or F-15 park jet first before tackling this model!
|May 24, 2005, 12:28 AM|
Plans and Construction Guide
Here are the plans for the F-14 Park Jet. As usual, these plans consist of two files—a scaled assembly drawing that shows how everything fits together and a full-scale parts template. The parts template is posted in both tiled and non-tiled formats. Previews are posted below to show how the plans should look when assembled.
I've also put together a construction guide that provides photo illustrations and step-by-step instructions on how to build this bird. It's available at either of the links below. Please Right-Click these links to save the PDF file to your hard drive. Note the file is quite large (5.1 MB), so it might take a while to download.
F-14 Park Jet Construction Guide (on RC Groups server)
F-14 Park Jet Construction Guide (on parkjets.com)
PLEASE NOTE: Although I have been very happy to freely distribute the plans and build manuals for all my previous park jet designs, the F-14 required so much more work to develop that I decided it would be nice to make a little something back for all the time and effort I put into it. I did not want to simply sell the plans, since I thought that would severely limit how widely the plans would be shared. So I decided to go with the voluntary contribution route. You may download, print, use, and share these plans as you like, however, if you enjoy them please consider sending a small contribution to the designer to show your appreciation for all the work that went into developing them. The suggested contribution is $10, and can be sent via PayPal to firstname.lastname@example.org. Thanks for your support!
Enjoy, and as always, post pictures if you build one!
Edit #1: If anyone would like a copy of the Jolly Rogers decals I used on my bird, they're available at the link below:
Edit #2: Platinum has put together an excellent parts list showing all the parts and materials required to build this bird. It's available at the link below:
|May 24, 2005, 12:30 AM|
Fixed-Sweep Wing Conversion Parts
Realizing that not everybody will want to tackle the complexity of a variable sweep wing, I went ahead and designed the parts necessary to convert the F-14 park jet into simpler fixed wing sweep versions. Plans for those parts are posted below. Note that this model can actually be built 5 ways:
1) Full in-flight variable sweep – As shown on the plans above
2) Ground adjustable sweep – This could be done by building the wing sweep mechanism but not installing the servo or linkages. Wing sweep can then be adjusted on the ground by loosening the nylon nut on the wing pivot pin, and then tightening it down tight after you’ve selected the sweep angle. The advantage of this is that it eliminates the weight (1.0 oz) and cost of the wing sweep servo, yet still allows you to fly with different wing sweeps. Plus, if you prepare the fuselage for the hardware when you build it, you always have the option to install the servo later.
3) Fixed wing with low sweep – For this version, you can eliminate the wing swing mechanism entirely and permanently install a simple one-piece wing. All the parts necessary to make this version are posted in the files below. This option will provide all the excellent maneuverability of the low sweep wing and eliminates the weight (3.0 oz), cost, and complexity of the wing swing mechanism. This is the lightest, quickest, and least expensive way to build an F-14 park jet! And if you’re planning to use a brushed GWS EPS-350C motor setup and/or NiCad or NiMH batteries, this would be the best way to go.
4) Fixed wing with high sweep – Same as option 3 except the wing is in the high sweep configuration. This version won’t be as maneuverable as the low sweep configuration, but if you like the looks of the F-14 with the wings swept aft this may be your bird! Note that if you go this route you should move the CG aft 0.5” from the location shown on the plans.
5) Swappable wings – Because the interfaces to the two fixed sweep wings are identical, you could build both and install a nylon bolt wing retaining system that allows you to bolt on either the low sweep or high sweep wing. I don’t show this in these drawings, but I know it could be done!
The diagram below shows how both the fixed sweep conversions look. Note that the only parts that need to be replaced are the wings, inlet tops, and inlet sides—everything else is the same as that shown on the original plans.
Edit #1: And now there's a 6th way to build this wing! For those of you that would like to build a mid-sweep fixed wing, I've posted templates and a preview pic in the post below:
Edit #2: It was brought to my attention that a couple of additional parts modifications are required for this--to the strake upper and lower pieces. Revised parts templates are attached.
I've found that mid-sweep is my favorite wing position for general manuevering--it provides the great roll rate of the fully swept wing and the great pitch response of the forward swept wing.
|May 24, 2005, 12:38 AM|
Joined Jul 2004
Nice look plans
Plans look awesome as usual Steve.
The plans have just finished on the plotter.
I've been saving some depron just for this bird.
Will start slicing this evening, and keep you up to date with the progress.
|May 24, 2005, 12:49 AM|
Thanks guys, and thank you, Matt! I'm REALLY looking forward to seeing how everybody's Tomcats turn out!
By the way, I just found a small error on the fixed wing conversion plans and just posted revised versions (Rev A) in the post. I accidently left out the slot for the rudder in the inlet tops...
|May 24, 2005, 12:54 AM|
thank you again for that wonderful Jet you construct for us !!!!
I opened a thread at RC Online (Germany) about your F-14 !
Regards and thank you again
Greetings from Vienna (Austria)
P.S. I have no paypalaccount and I would not have one so please be so kind and send me a PM with you livingaddr. that I can send you 10 Euro .- in a letter for your fantastic work now and from the past !
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