|Dec 26, 2012, 11:50 PM|
65 inch Boeing 247 inspired by Cleveland Model and Supply plans
The Boeing 247 has been on my “to build” list for about 15 years. I really like it's art deco good looks.
I also like that it is not “over modeled.” 2013 is the year when I am actually going to start building.
My plans are as follows
1. I want to keep my hobby in perspective. Model aircraft are a very enjoyable cherry on the cupcake of life. Often times I get over absorbed in my model airplane projects. Hopefully I will achieve the goal of “proper perspective” on the 247 project.
2. I will take my time. I expect I will spend two years on this project. I am a famously slow builder. It took me 10 months to finish the excellently designed and quite complete Dumas/Tritle Dragon Rapide kit http://www.rcgroups.com/forums/showthread.php?t=1650419 . Experience gained on the Rapide will really help on this build, but there are still a lot of decisions to make and I am slow. Two years might be optimistic.
3. I will use the Tritle design philosophy of light weight and scale flight appearance first and scale fidelity second.
4. I don't expect that I will post more than once a week. There probably will not be enough progress to justify more frequent updates.
CLEVELAND PLANS: I purchased Cleveland Model and Supply plans originally drawn in 1935 and revised in 1974 as the basis for my build. http://www.clevelandairline.com/ASP/PRODUCT.asp . With the help of fellow RCG members, the plans were modified to suit my desired wingspan of 65 inches. Thank you very much for your help. A 65 inch wing span would put the 247 at the same scale as my De Havilland Dragon Rapid. I will make further modifications to accommodate modern RC equipment, electric power and electric retractable landing gear. I will use stick and tissue style open bay fuselage and wing construction. I may use balsa infill in places on the fuselage to smooth out some of the contours.
TRITLE AND PETTIGREW PLANS: I purchased Pat Tritle DC6 plans and Ivan Pettigrew De Havilland Mosquito plans to help make design decisions. I also welcome suggestions from fellow RCG builders.
A FULL SCALE 247: I am fortunate to live 20 minutes away from a full scale, airworthy (as soon as the landing gear is repaired) Boeing 247. It is located at the Payne Field Restoration Center Annex in Everett of the Museum of Flight in Seattle Washington http://www.rbogash.com/Annex.htm
PLASTIC MODEL: There is a plastic model of the Boeing 247 by Williams Brothers
REFERENCE BOOK: There are very excellent drawings in the book, "The Boeing 247: The First Modern Airliner" by van der Linden. It has three views with cross sections, lots of photos and black and white drawings of different 247s in the livery a number of different airlines. http://www.amazon.com/The-Boeing-247.../dp/0295970944
OTHER BUILD LOGS: There is currently a wonderful 247 build log in progress. http://www.rcgroups.com/forums/showthread.php?t=1766141
Don Olsen is using his own plans and a different design philosophy. He is building a fully sheeted internal combustion powered model. He builds rapidly and very well. http://www.rcgroups.com/forums/showthread.php?t=1766141 It looks to me like his plans were derived from the diagrams in the van der Linden book.
I also have carefully followed WAGliderGuy's and payne9999's multi-engine builds. I have completely read every one of Pat Tritles' build logs and many of the BIMBO Pettigrew build logs.
|Dec 26, 2012, 11:55 PM|
Best of luck on the build Robert, if it it will be anything like your Rapide then I know it will turn out great BTW I need to see the 247 up in Paine someday, I haven't been to the Everett restoration place in ages!
|Dec 27, 2012, 11:26 AM|
Beautiful plane and a great choice. .... ( a DH Dragon....???? really?... ) this time Oh.. just kidding, beauty is in the eye of the beholder and all that, just ask my wife.
I'm staying tuned, please get it done before I croak, if I died first the disappointment would kill me.... ahhh.... eh..whatever.
|Dec 27, 2012, 03:12 PM|
Im In! This should be a nice flyer with the fat airfoil, ample wing and tail that the plans have. Is prop size going to be a peoblem? the nacelles are quite close, I had to move mine out a smidge to clear
|Dec 28, 2012, 01:32 AM|
Thanks everyone for your interest. It is quite encouraging I will spend the next few days making rough estimates of wing and power loading, cleaning up a work area and deciding what balsa to order. Don asks a great question. Will the nacelle spacing allow for a big enough propellers? I am prepared to slide the nacelles outboard a bit if I need to. As is, they will allow an 8 inch diameter props. Also, I would like to use three bladed props like the Everett prototype. That should help as well.
|Dec 28, 2012, 02:02 AM|
|Dec 28, 2012, 06:09 AM|
What will the wing span be? The Blenheim that I'm building has a 50" wing span and that uses 9" x 6 props on 2 x 2215/25 950KV 15A brushless motors, running off a 3s gives 109 watts per pound, (340 watts total) which I'm told is going to be very powerful.
|Dec 28, 2012, 09:51 AM|
Hi Robert, As a heads up also look at all the 3 views! the one I chose makes the plane look fat" in the middle(top view) you may want to alter the center formers to slim it some.I didnt notice till I put the sheeting on then it obvious Just depends on how True you to scale you wish to be. Mine was an experiment and was to be "fun scale" from the start Your the builder do what makes you happy
Enjoy the build
|Dec 29, 2012, 03:27 AM|
Power System Choices
Don, thanks for the heads up. I will stay pretty close to the Cleveland outlines. My stick and tissue style build will be much more "fun scale" than your fully sheeted beauty. We have a chosen two good but different build philosophies from one another.
Daz393 answers to your questions below.
DD scale outlines allow for an 8 inch prop which will make power system choices a lot easier. I hear you on preserving the 247s good looks.
On my previous electric builds I have simply done what the designer said to do when choosing the power system. There is no such recommendation for this build. I have made some preliminary estimates using the data below and a very nice online RC aircraft power calculator called WebOCalc http://flbeagle.rchomepage.com/ I don't really have a very good common sense feeling for what systems will work or not yet, but this is what I have come up with so far. I will run these calculations by my fellow builders as well at the kind people at Heads Up RC for a reality check.
Wing Span 65 inches
Wing area 639 in sq
Total weight: 40 oz (same as WAGliderGuy's completed DC6b ) = 2.5 lbs
Wing Loading: 40/639/144= 9 oz ft sq
POWER SYSTEM CALCULATIONS
What kind of power system would be appropriate?
Watts: 70 watts per pound = 174 watts
Amps x Volts = Watts
at 7.4 volts need 24 amps
at 11.1 volts need 15 .3 amps
According to WebOCalc http://flbeagle.rchomepage.com/
8 inch props with 4 inch pitch, APC-TE
1100 KV motor at 15 amps
Battery 3S 1800 mAh 9C lithium polymer (x2)
20-25 Amp speed controllers x 2
Stall speed – 15 mph
Prop speed – 37 mph
Wing loading – 9.01 oz/ft sq
Power loading 64 Watts per pound
8 inch props with 6 inch pitch – APC – SF
Motors 1300 KV at 9.5 amps
Battery 1220 mAh 2S, 8C lithium polymer (x 2?)
12-14 Amp ESC x 2
Stall speed – 15 mph
Prop speed – 37 mph
Wing loading – 9.01 oz/ft sq
Cubic wing loading, 3.42 oz/cubic foot
Power loading – 70 Watts = 27.5 Watts per pound
Although the 2S system yields a total thrust of 30 oz which should be fine for a 40 oz plane, the power loading is 27.5 Watts per pound which seems very low.
The 3S system is said to have 50 oz of thrust which seems ridiculously much for a 40 oz plane but the power loading seems fine at about 70 Watts per pound
In either case an 8 inch propeller looks like it will work so there is no need to move the nacelles outboard.
|Dec 29, 2012, 03:44 AM|
I highly recommend a 3S setup with (at the very least) 70 watts/lbs. Remember I have four 7'' 3-bladers shoving air over my DC-6 wing while you only have two and also I am not sure if the plans you are building off are designed like Tritle planes. I mean in no way to offend your building style sir, I am just wondering if 40 oz. is a realistic goal because the 247 wing as you know has a lot of wing area and a lot more material at 65''.
The four Power-Up 25 Plus motors I am using give off a total of about 28 amps at WOT (7A each) and at 11.1 volts (discharged 3S) that means 124 watt/lbs. With a fully charged 45C 12.6v LiPo, my climb rate is rather extremely scale and sluggish (141s watts/lbs) and although it is what you and I shot for from the start, I would not want to fly it anywhere I am not comfortable with because there is no power to be spared.
If I were you, I would try and get at least 100 watts/lbs (the extra wing area will have it more them the draggy DC-6 wings) on a 3S with a higher KV motor to still achieve an 8'' prop.
Best match I could find is the Firepower 450 sport on a TP 8X6. 48 ounces of thrust combined and 171 watts/lbs at 12.6v (what Jeff tests them at) and assuming the plane weighs 40 oz.
BTW I have always been a non-believer of the whole 'watts/lbs' thing because it dosan't take into account the features of the plane itself such as the wing thickness and area, amount of stuff hanging out in the breeze (like nacelles) and most importantly, type of prop. It seems it was designed over a .40 sport plane but I have converted two of those and at 125 watts/lbs they don't do anything close to the power they are supposed too.
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