F-18 XL Park Jet Build - RC Groups
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Oct 09, 2005, 01:29 AM
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LBMiller5's Avatar
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F-18 XL Park Jet Build


I saw the thread that Depron Dave started about his Icarus SU-27 XXXXL over in the Foamie section a few days ago. I got inspired and thought it would be cool to scale up the F-18 Park Flyer that Steve Shumate (aka JetSet44 ) designed. I emailed Steve and got a couple PDF drawings of the parts for the F-18 that were seperated into 2 different sheets. I took these PDF files and blew them up 166% and re-printed them on one of the big plotters at work. At this scale, the plane will have 48" wingspan (including the missle launch rails) and an overall length of about 70".

I am going to build the entire plane from BlueCor Foam, and hopefully the finished weight will be somewhere around 26-28 ounces. I think that I will use 2 thicknesses of BlueCor for the wings and tail surfaces, with a 3/8" carbon fiber tube spar inside of each for strength. I will go with a brushless pusher motor with 36-40 ounces of thrust to get good performance from the beast.

Here are a couple photos of me standing next to each of the plans sheets to get an idea of the scale of this plane. I am 6 foot tall, and each of the plans sheets measures 3 feet by 5-1/2 feet. The first one is me next to the fuselage pieces. It is a little tough to see the lines on the drawing, but the fuselage runs almost the entire length of the sheet, and then you have to add the nose cone.





This one shows the wing and tail surfaces. I am holding my hands at the wingtips to get an idea of the size. There are a couple full 2' x 4' pieces of BlueCor standing up behind me that also help define the scale of this project.





It will almost take a full sheet of BlueCor just to do the wing on this one! I will probably get started tomorrow cutting out some parts and creating a kit. It will be fun to see how a foamie this size performs.

If anyone has any good ideas or suggestions on building one this size, please post your comments. I think this will be a great flying plane when it is finished, and will have a great "Wow" factor with the spectators.

Stay tuned for progress reports.

Till next time ...........

Lucien
Last edited by LBMiller5; Oct 09, 2005 at 04:32 PM.
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Oct 09, 2005, 02:48 AM
Live to fly, fly to live!
DCobra's Avatar
Whoa...thats gonna be way cool.

Have you come up with a power system for it yet?

One suggestion is to go with a Typhoon 15/10 or the larger Typhoon that DAF is using.

The 15/10 should be capable of giving you at least 1:1 thrust to weight if propped right with a lipo capable of giving out the needed amps.

http://www.warbirds-rc.com/Merchant2...tegory_Code=WH

Paul
Oct 09, 2005, 10:55 AM
Registered User
RCParkflyer's Avatar
Hi Lucian,

Wow at 6Ft. long F-18 How are you planning on launching this? I can't wait to see this one come together!!

Tom
Oct 09, 2005, 11:30 AM
FoamyFactory.com
Tim H.'s Avatar
Cool Project!!!!!

Another suggestion would be the Mega 22/20/4 on 3 cells, APC 9x6, APC 8x6. I used that combo on my 50 oz. MB339 and it rocked!

Tim H.
Oct 09, 2005, 12:26 PM
Or am I...
Cool.!!! Landing gear?? or better yet Retracts??
Oct 09, 2005, 01:18 PM
Registered User
awesome!!! can't wait to see what she looks/flies like! my 130% mig-23 will have a 42" wingspan when unswept... still smaller than your monster. one suggestion: i read somewhere long ago in one of the jetset44 f-14 threads about someone building a 100% f-14 but used 2 sheets of depron for the wings and sanded a nice airfoil into it. he/she never posted details of the flight, so i don't know if it helped or not... but just a thought. good luck.
-beanie
Last edited by beanie; Oct 09, 2005 at 01:32 PM.
Oct 09, 2005, 03:34 PM
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ARCHER7153's Avatar
I want to see this
Oct 09, 2005, 04:20 PM
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JCaste's Avatar
With such scale, I'd take the time and added weight of making the F-18 "less-squared" (i.e. simulating engine pods, intakes, etc.). I second the idea of the double layer wing. At such a big size, a single 6mm wing will look lake a razor!
I'm quite curious about the final result, it must be a very solid flyer!
Oct 09, 2005, 04:30 PM
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LBMiller5's Avatar
For the first one I plan to keep it simple and light. No landing gear, just hand launch it!

The original size plane had a wing area of 275 Square Inches and a flying weight of 15.6 ounces, giving a wing loading of 8.2 Ounces per Square Foot. Now, if I subtract the weight of all the "Guts" of the plane, I will be left with the weight of just the foam parts & glue. Based on Steve's reports of his prototype build, the following equipment was used: GWS 350C Geared motor W/8x6 prop (2.4 oz), 3-cell 1200mA Li-Po Battery (3.2 oz), GWS 6ch Receiver (0.3 oz), 4 HS-55 Servos @ 0.3 oz each (1.2 oz), 10 Amp ESC (0.5 oz) and I can probably figure another 0.5 oz for pushrods & connectors. Adding all that stuff up gives a total weight of 8.1 oz, and if we subtract this number from the flying weight of 15.6 ounces we are left with 7.5 ounces for the bare painted airframe.

Steve also mentioned that the paint and decals on the plane added 1 ounce, so if we subtract this from the above total, this leaves us with a total bare, unpainted airframe weight of 6.5 ounces. Since I am going to build the F-18 XL out of the same BlueCor foam, it is easy to get an estimate of the flying weight of the bare airframe of the bigger one by doing a little math.

The scale factor on this plane is 166%, which means every linear dimension of the plane is multiplied by 1.66 to get the size of the big one. For example, The original wingspan was 28.4 inches, and if we multiply this by 1.66 we get 47.14 inches. The original length was 41.7 inches, and when we multiply this by 1.66 we get 69.22 inches. When you want to calculate the new wing area you need an extra step. Since the wingspan AND the wing chord both increase by a factor of 1.66, to get the increase in wing area, you must multiply the original wing area by the square of the scale factor. In this case, with a scale factor of 1.66, the multiplier factor for area calculations is 1.66 x 1.66 which equals 2.7556. With this number now we can calculate the new wing area.

According to the plans, the wing area on the original plane was 275 square inches. If we multiply 275 by the area constant of 2.7556, the new wing area will work out to be 757.79 square inches, which I will just round off to 758 square inches. This area constant also come in handy to estimate the bare weight of the larger airframe. Since both planes were built from the same BlueCor material, each piece of the larger plane will weigh exactly 2.7556 times as much as the pieces in the smaller plane, since the area of each piece of the larger plane is 2.7556 times as big as the smaller one.

So using this method, with the bare airframe of the original plane coming in at 6.5 ounces, I can expect all the pieces of the new plane to weigh 6.5 x 2.7556 or 17.91 ounces. This is assuming that all of the surfaces will be made from a single layer of foam. Now, in the case of this plane, making the wings and tail surfaces from a single layer of foam would be a little thin, so I plan on doubling up the foam for these pieces. So lets figure out the weight of these extra pieces.

To do this, we first need to calculate the weight of the BlueCor foam. This is actually very easy to do if you have an accurate digital scale. First I took an entire 2 foot by 4 foot sheet of BlueCor that I had cut from the stack and measured the actual dimensions. I got 23-1/4 x 47-3/4 inches for the piece I used. If you multiply these 2 numbers together, you get the total area of the sheet in square inches which turns out to be 1110.1875 square inches, which we can safely round off to 1110 square inches. Next I placed this piece on my digital scale and got a weight of 5.6 ounces. This means that BlueCor foam weighs 5.6 / 1110 or 0.005045 ounces per square inch. Now granted that is a very small number, but the foam is also very light.

Now that we have a weight for the foam I can calculate the extra weight that will be added by doubling up the thickness of the control surfaces and wing. Earlier we calculated the area of the new larger wing, which came out to be 758 square inches. This figure includes the area of the leading edge strakes on the wing. By measuring the plans, I came up with the area of the rudders and stabilators. Each rudder has an area of 98 square inches, and each stabilator has an area of 70 square inches. Since there are 2 rudders and 2 stabs on this plane the total rudder area is 196 square inches and the total stab area is 140 square inches. So if we add up the area of the wing (758) plus the rudders (196) plus the stabs (140) the total additional area equals 1094 square inches. Now if we multiply this area by the weight constant we just calculated for the foam, the total extra weight added will be 1094 x 0.005045 which equals 5.5 ounces. Now adding this number to the previously calculated total bare airframe weight of 17.91 ounces gives a total calculated bare airframe weight of 23.43 ounces!

(Does your head hurt yet?!)

What can I say, I am an engineer and I do this kind of stuff all day long for a living, so I think in numbers all the time.

So the bottom line of all this number crunching is that based on the scale factor, and if I double up the thickness of the wings and tail surfaces, I can expect the total weight of the bare airframe to come in around 23.4 ounces. Because of the way I calculated things, this includes all the glue and little pieces of plywood and the carbon fiber wing spars.

By adding back in the guts of the big plane now I can calculate a flying weight for the finished plane. I will probably use a geared brushless motor for the plane that is capable of putting out around 40 ounces of thrust. I am still looking at motors, and if I find an outrunner that would work well I would go with that as well. In either case, the motor will come in around 4 ounces. I will probably end up using a 3000 mA 10C 3-cell Li-Po battery pack or a 2200 mA 15C 3-cell Li-Po battery for the plane. The motor will more than likely draw around 25 amps at WOT so having 30 amps available would be about right. The 3000 mA 10C pack weighs 9.2 ounces, and the 2200 mA 15C pack weighs 5.8 ounces, so my vote is for the 2200 pack! If I figure an ounce for a 35 amp ESC, the total power system weight will come in at around 11 ounces.

Moving on to the radio, I will need to use mid size servos with around 35-40 oz-in of torque in a plane this large, so the servos will weigh around 0.65 ounces each and a good dual conversion receiver will weigh around 0.5 ounces. Based on these numbers the radio gear will come in at around 3.1 ounces.

Now adding all this stuff up, with an airframe weight of 23.4 ounces, a power system weight of 11 ounces, and a radio system weight of 3.1 ounces, the total weight of the unpainted, flyable plane would estimate out to be 37.5 ounces, or 2 pounds and 5.5 ounces. Based on this weight, with 758 square inches of wing area (5.26 square feet) the wing loading would be 7.12 ounces per square foot! It would actually be lower than the original plane which had a wing loading of 8.2 ounces per square foot. With a motor putting out 40 ounces of thrust, the power to weight ratio would be 1.06:1, not great, but still more than 1:1.

I would really like the finished weight of the plane to come in at 2 pounds or less. Is that do-able? If every effort was made to lessen the weight, I believe that it could be done.

As a test, I took a piece of scrap BlueCor that I had and cut it to 18 x 9 inches giving a piece with 162 square inches. I put this on my digital scale and it weighed 0.9 ounces. I peeled off the skin from 1 surface and placed it back on the scale and it weighed 0.8 ounces. Then I peeled off the other skin and put it back on the scale. Now it weighed 0.7 ounces. For a double check, I put the 2 pieces of skin on the scale and they weighed 0.2 ounces. I would need to skin an entire 2' x 4' sheet to get a good accurate reading, but based on this test sample, the core of BlueCor makes up around 76% of the total weight, and each of the skins weigh about 12% of the total weight.

Based on these numbers, if I skin the inside surface of all the fuselage pieces, skin both surfaces of all the bulkheads, and skin the inside surfaces of the wings and flying surfaces, I should see a weight reduction of somewhere around 15% for the bare airframe weight. This would cut the bare airframe weight down from 23.4 ounces to about 19.9 ounces for a savings of 3.5 ounces! Looking at the plans, there are several places where I can cut lightening holes in the bulkheads and inner fuselage sides, as well as building up the nose and canopy in a hollowed out fashion. This could save an additional couple ounces getting the bare airframe weight down to around 18 ounces. With these weight savings, I should be able to get the complete plane down to 2 pounds.

Painting the plane will probably add around 2-3 ounces, which I will probably do after the first few test flights, so I guess we will see how it all adds up in the end.

Well I think that is enough theoretical rambling for one session. I need another cup of coffee!

Thanks for the input guys, it is good to see that there is some interest in this project. I would like to thank Steve Shumate for his incredible contribution to the R/C hobby with the original design of this plane, and his help in obtaining the PDF files that I used to make my plans for the larger version. If any of you guys download his plans and build one of his planes, please be kind enough to send him a donation through PayPal. $5.00 or $10.00 would go a long way to help with the amount of time he spent designing all these great planes. I know that I am going to. (With the new baby girl in the house that is 3 months old now, I am sure he could use the money to buy formula and diapers! )

Stay tuned for more updates coming soon!

Lucien
Last edited by LBMiller5; Oct 10, 2005 at 01:06 AM.
Oct 09, 2005, 04:57 PM
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JCaste's Avatar
Quote:
Originally Posted by LBMiller5
...
Hehehe... Nice way of setting the basic lines for a new craft!
If you let me make a suggestion, I'd consider a heavier airframe weight (glue, small repairs, scale details etc. will add some ounces), and thus aim for a slightly more powerful motor.
BTW, isn't a 3s1p pack way too much for a 250-300W motor? how long do you expect to fly with that?
Last edited by JCaste; Oct 09, 2005 at 05:24 PM.
Oct 09, 2005, 05:18 PM
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LBMiller5's Avatar
JC,

I think a 3-cell Li-Po is the perfect battery for a plane like this. As an Electrical Engineer, I am used to de-rating everything to ensure long life and reliability. If I have a motor that draws 25 amps at WOT from a freshly charged 3-cell Li-Po battery, I will get around 11 volts to the speed controller. A freshly charged 3-cell Li-Po will measure 12.6 volts, but under that kind of load it will drop down to 10.8 to 11.0 volts. This will provide 250-270 watts of input power to the motor.

Granted I will probably only be flying at WOT for short bursts, but even then I do not like to draw more than 80% of the batteries rated max current. With a 2200mA 15C battery pack I would have 33 amps available for a max current draw. If my motor pulls 25 amps, this would be 25/33 or 76% of the battery capacity which is right where I want to be. If I were to run at WOT for the entire flight I would be pulling 11.3C from the battery and get a 5 minute flight. Running at 2/3 throttle for the majority of the flight would pull around 10-12 amps and would pull around 5C from the battery and give me a flight time of 10-12 minutes.

Based on these numbers, the 2200ma 15C battery would be, in my opinion, the perfect size battery to use.

What do you think?

Lucien
Last edited by LBMiller5; Oct 10, 2005 at 04:45 PM.
Oct 09, 2005, 05:42 PM
DIY user
JCaste's Avatar
Quote:
Originally Posted by LBMiller5
What do you think?
1) You're an electrical engineer, and I'm still at the first year of an engineering degree, so I'd better shut up and listen for a while!

2) Your explanations have made me understand many concepts, thanks! (electric flight is a bit scary for glow guys like me ). I figured that a 3s1p lipo would have to work seriously to make the motor have +200W, and probably would overheat and reduce its service life. Anyway, I'm glad things are this way, I think I'm going to buy that same batt for my project...
Would you mind PMing me with the details of your setup?
Thanks!

Juan
Oct 09, 2005, 06:11 PM
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LBMiller5's Avatar
Juan,

No problem! Keep watching here as I will post everything in this thread as the project progresses. I enjoy passing on my findings to other modelers, as we all benefit from the sharing of ideas.

I have been a technician since 1983 and an Electrical Engineer since 1990. I have also studied a LOT and with the work experience I have acquired over the past 20 years consider myself to be a non-degreed self-taught Mechanical and Aeronautical engineer as well.

For this first plane, I want to keep it simple. I will round things off a little, but I do not plan on adding any fancy extras on this one. Besides, things like missles and bombs on the plane just add unnecessary weight and always break off when you make the unexpected "Landings" in the tall grass. I have always been a fan of the orange and white color scheme used on prototype #6 that was used in spin testing. Here is a photo of a similar F-18 that I found on the web.



This one is real easy to see in the air!

Well, if I don't quit writing things here I will never get the plane built, so I will sign off and start cutting foam!

Later!

Lucien
Oct 09, 2005, 06:31 PM
Registered User
lucien- i love your detailed explanations. being a former chemical engineer, i hear ya on a lot of your engineering philosophy. any way of posting the 166% sized plans so others can build along with you? thanks.
-beanie
Oct 09, 2005, 08:13 PM
Registered User
RCParkflyer's Avatar
Do you have a favorite technique for skinning the FFF sheets. I've tried pulling it off, using dowels, but the stuff always rips, and it takes forever to get it all off. Depron is much nicer to work with


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