stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: Bob Hunt on February 28, 2010, 08:42:35 PM
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Hi all:
Just thought I'd give a progress report on my new twin electric design. I'm working on it quite a bit and hope to have it at the Nats.
It will be powered by either two E-Flite Park 480 motors or two E-Flite Power 10 motors. Provisions will be made to mount either set. The projected weight - with battery on board - is 59 ounces and... it has retracts!
Attached are a few photos of the model under construction.
Later - Bob Hunt
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Lookin' good! y1
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Hi Bob, That looks stunning so far. I love the wing. Can you let us have the weight of the wing as it is so far in the pic with the carbon veil? By the way.....where is the pic with the rudder fin?? VD~
Keith R
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Hi Bob,
Thanks for the info. That wing is certainly very light. It sure looks light, so that's why I asked. This is a marvellous project, and something in true "Bob Hunt" tradition. I can't wait to see how it looks when its put together. I've also drawn plans for twins, but that's as far as it goes. I spoke to Gilbert Beringer at the 2004 world champs in Muncie, and although his twin 4-banger was beautifully built and very innovative, it did not fly very well in my humble opinion. Gilbert is a top-notch pilot, and the model certainly did not perform to his usual standard. Maybe his design was just too close to being a scale model.
What I would also like to know is how you calculate the required power. If you would normally use a .60, do you simply divide by 2 and use two .30's? Is there some basic formula that you use? If I think about Paul Walker's famous B-17 that I saw in France in 2000, the four .15 engines sure looked more powerful than a .60. I'm pretty sure that a single .60 wold not fly the bomber like that.
The last twin that I drew, was a twin boom style twin with a push-pull arrangement like the Cessna Skymaster. The nice thing about this, is that you can use a standard tractor prop running backwards in the rear. Pusher props cost more and the range is also limited, so this made some sense to me. Anyway, your project will maybe inspire me to actually have a go at this. I'm sure that you will keep us posted. Thanks for sharing.
Keith R
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Very cool Bob!!! Looking foward to seeing the finished product, especially a twin with retracts!
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WAAAAAY cool! Guess we'll find out just what all this cool stuff CAN do
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Very cool, Bob.
I just realized that I am now 62 and really should start using that stuff!
I'll be 64 in a couple weeks. Send me the rest of the good balsa.
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Bob and Keith:
The C-337 layout sounds like the "Two Bits" stunter from a few decades ago, that looks like a good electric planform. But what do you all think about a D0-335 type twin layout, with one tractor and one pusher in the tail, maybe different size motors and props? Less overall drag and centerline thrust. I know a semi-scale 335 has been flown, but I am envisioning a clean sheet of paper type twin, not a semi scale anything.
Since I too am 62 and have been hoarding good wood for ages I better use it while I still can hold a hobby knife steady. Sort of.
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Hi Mike,
The DO-335 is interesting, but the rear motor so far from the C of G would maybe cause a few problems like Len Neuman's "barbell-effect". The tail end would also have to be beefed up as well. You could of course, stick the motor further forward and use a long shaft to the rear prop, but I think that would be too much like hard work. I also prefer the looks of the C-337 layout. I would still like to know about how to work out the power needed and prop size on twins.
BTW.......I turn 60 in August, and then I'll start feeling like Bob and Howard..........I just don't have hoards of good balsa!
Keith R
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Bob, is this plane based on a full-sized airplane, or just your own design? I can't wait to see the finished product!
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Hi Keith:
Every time Dean comes over I have to sweep up a bunch of mathmatical symbols that are left lying on the floor... :-[
Bob
If you leave a couple of blank spreadsheets lying around, most of that stuff will stick to them - then just delete them .... y1
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Put the symbols in the box with the balsa and send them out. I'll put them to good use.
Bob, you are causing a little family friction here at the Rush household. My wife has been using you as an achievement example, e.g. that I haven't won the World Champs or had my own spy plane business, or the relative effort between your Lost Foam method of making slanty ribs and my Lost Time method. Just this morning she said, "Have you seen how clean Bob Hunt's shop is?" Slow down.
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You guys should have seen that shop just a week before. VD~
signed,
the troublemaker
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Yeah......it's amazing what you can do with Photoshop these days! S?P
Jealous
So Dean...........how do we work out what size motors and props for twins??
Keith R
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A clean shop is a sign of a sick mind LL~
John W
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To see Bob clean up the shop ............ amazing!
To have Howard by the short and curly's ............. Priceless!!!
Kim.
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Hi Matt:
I guess nothing is "totally original." This one is my interpretation and blending of many things I've liked about twins that I've seen over the years. You are far too young to remember the twin engine designs that were modified by the Army and Air Force in the 1960s. They, and a few dedicated twin designs, were dubbed "Coin Fighters" (Short for: Counter Insurgency Fighters). I was going to do this one in an aggressive pseudo military scheme and call it, "Coin Return." Alas when I bounced that name off of some friends - who were around in the 1960s - even they didn't get the connection and so that name was scrubbed.
By the way, your Oriental Plus is looking great! Just don't put on too much paint...
Bob
What goes around comes around. Aviation Week had some recent articles about the COIN aircraft being brought back again to help in Afghanistan...
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now that is just SICK!!! Awesome looking twin - LOVE IT!!!
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Here is an early drawing of the side view of the twin. I've made a few subtle changes since this was drawn. I'll save those as a surprise for the Nats. Just imagine this design with an agressive military-like paint scheme...
Later - Bob
That is an INSANE twin!!!!!! Very slick, and cool looking
Edit: What airfoil is that Bob?
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In this photo I see you've put the Foam Brick(s) to use. Great idea.
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Hi Keith:
The wing - ready to install - with flaps, tips, leadout guide, tip weight box, controls and carbon weighed 9.9 ounces. The fuselage with all the molded shells ready to install weighed 2.7 ounces. Yes, I'm using up a good portion of my best wood on this project. I just realized that I am now 62 and really should start using that stuff! ;D
I'm planning on using the new Hyperion batteries in this one. They are reputed to be able to be charged at a C5 rate. Not sure that I will go that far, but maybe i'll give C3 a try. Should be able to cut back just a bit on how many batteries I need to take to the field. The 4S2P 4000 mAh pack they have is priced around $100.00. That's far less than the Thunder Power 3850 V2 extremes that I'm using now. They are getting a great reputation with the RC Ducted Fan guys...
I'm not sure if I'm going to use the tail assembly pictured. It is light for its size at 2.5 ounces with horn and hinges, but it may be just a bit twisty. I'll have to carbon it and see how stiff it gets before I make a final decision.
Again, the projected all-up weight is 59 to 60 ounces with battery on board. That equates to a 53 to 54 ounce glow ship without 6 ounces of fuel on board... y1
This is a project that I've had in mind even before electric power became viable. I have been sketching twins for 50-plus years, but just never took the leap. I've spoken with Gordan Delaney - the recognized twin expert in the glow world - on several occasions and picked his brain on the technical aspects of designing one. It was, however, our moderator, Dean Pappas who finally convinced me that this is the time to try one. There are so many advantages to an electric twin. You can counter rotate the props and try them in both opposing directions. There were several full-size twins in which the props rotated outward on either side of the fuselage. The P-38 is a good example of this. I'll try them both ways and the beauty of this setup is that I can try that experiment right at the field. It is no big deal to reverse the rotation of the motors and just switch the props. Also, the spiral airflow problems ahould cancel out. I'll get 22 inches of "wetted" area of air blast due to the 11 inch props I intend to use. This disk area comes without the attendant problems of spiral airflow and prop ground clearance issues.
All in all this is a project that is keeping my interest peaked!
Later - Bob Hunt
P.S. Attached are a few more photos. I needed to get the wire harness for the motors and the retracts out to the nacelles. I rolled a balasa tube araound a dowel and than used that dowel wrapped with sandpaper to make a perfect radius in the nose of each of the cuffed area's ribs to accept the tube. It is now actually an additional spar! The "cuffed" area was employed to put the wire harness tunnel well ahead of the bellcrank and leadout so there would be no interference issues. Besides, it looks cool! - Bob
So, are you running that retract battery out to the tip or is it part of the motors power supply? By the way...I have been waiting a few years on you to come back to this project! I must assume it was an on going research saga during the lapse? :P
I see that you have a flat stab platform for a tapered stab. Are you making this removeable?
I am using an airfoiled stab/ el assy. also. Got the wings skinned you sent and will be getting some pics together of this build and down load to a disk...based on the request you sent H^^
Hey one more thing, I see you are not using geodetic construction in the fuse...or atleast not yet.....?
Lookin' sweet Bob!
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Here is an early drawing of the side view of the twin. I've made a few subtle changes since this was drawn. I'll save those as a surprise for the Nats. Just imagine this design with an agressive military-like paint scheme...
Later - Bob
This reminds me of a cross between a Phoenix V and VI...Dave Browns stuff.....slick ship! ;)
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Your model looks terrific Bob! As usual your building techniques are very clean and well done. I'll be watching this project with great interest.
Rob
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Bob super Shop but i have to one up you.
This is the new age foam cutting. This is a machine that i have designed from the ground up. The precision is 99.96% accuracy and it is CNC controlled.
Enjoy.
Dorin 8) 8) 8)
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Dorin,
I am going to ask, even beg, you to start a thread in either the Engineering or Design fora on the CNC cutter, especially the software.
Thanks,
Dean
P.S. I will also start a new thread on extending the subject of motor/prop and battery selection to include twins, sometime soon. This next week is going to be way too crazy.
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Bob,
can you please describe your retract system - what gear/servos etc - I would be interested in how to do this also as I want o build a Jet with retracts
Thanks
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Here is an early drawing of the side view of the twin. I've made a few subtle changes since this was drawn. I'll save those as a surprise for the Nats. Just imagine this design with an agressive military-like paint scheme...
Later - Bob
Apparently I'm not familiar Bob, what Military scheme uses white with copper and orange??? S?P :##
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I got my hands on this " Bronze Dawg" a few years ago. No matter what you think of the paint scheme....this is a beautiful model and you will never know just how beautiful... until you fly it.
When the Genesis was first electrified, Bob stopped through Columbus to visit with my Pop on his way to Muncie. Naturally the ole Man got some shots under the hood. When I got my ride I was completely sold on E power, but had to much on my plate to do anything about it.
This year I can play a little......ahhhh...its going to be nice to hang with stunt gang again!
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What are the dimensional specs Bob?
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Bob,
How many sq.inches. is this twin? Hope to see you at VSC. I`m here now.
Gordy
PS. I brought my little twin down.So you can fly it. A Pair of 15teens on it.
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The twin Bob. What's the wingspan?
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So Bob, VSC's over, let's get back to work on this twin! #^ :##
...Oh yeah, CONGRATS too!
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So Bob, VSC's over, let's get back to work on this twin! #^ :##
...Oh yeah, CONGRATS too!
I'll bet he ain't writun cuz he's buildin! :o Plus i'll bet he got a dose of twin-envy @ VSC... y1
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Spot on, Dennis!
He's working on that twin-envy problem. Shop time is much better than couch time, right compadres?
Dean P.
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AMEN, Unca Deano!
BTW. APC has now brought out the 9x4.5 as a PUSHER, they will be going on my PF twin. Hope we can get APC to do pushers of the 10x5 and the 11x5.5 too.
Hope to lobby them next weekend at Toledo...
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Dennis,
By all means put on the hard sell for an APC 11x5.5 thin E pusher. That would be perfect for my electric Ringmasters and I would not have to cut down those 12x6 pushers!!
John
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What's the latest Bob??? #^
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Attached are a couple of photos of a model sporting the most elegant paint scheme ever devised. ;) Of course, Billy Werwage doesn't see it that way...
Later - Bob
Yes, we know. The ole BD paint scheme.
Did you buy a 55 gallon drum of that bronze paint Bob? #^
I think Billy probably still has some of the Day-Glo pigment left that you could use! ::)
Hope it is ready for the Nats.
Paul W
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Excellent project Bob. I understand you flew Gordy's wet twin. Impressive isn't it? That plane has 640 sq inches, roughly nearly the same as your project. I believe that over the years, twins have been over built, over powered, and too large. Watching Paul W. fly his B-17 was an eye opener, and proved that multi engined models can be powered by engines smaller than most would consider.
I beleive that one of the advantages of twins, has to do with the smaller dia. prop, but because there are two of them, you still have a lot of prop diameter to do the job. The smaller dia. prop seems to have less moment to impart prop forces so the turns seem to be much better, but the area allows it to have the traction to pull the plane through.
Using a pair of .15's instead of a single .40 or .46 on what is basically the same plane, the Pathfinder, seems to show that propped correctly, great performance can be achieved with engines, and I'll presume, moters as well, 60 to 75% the size, (when added together) for the same design, running a single engine.
Dennis A. has built and is currently flying one of Gordy's twin Pathfinders on e-power. At first he was running larger engines, and bigger props, but recently has gone to something much closer to what Gordy is running. Smaller motors, turning 9" props. I believe he has reported that the plane flies extreemly well on the smaller motors and props. If my memory is correcct, it flies better on the latest set up.
Best of luck and success on your twin Bob. It really looks great, and i love the lines of your sketch. Impressive Master Bob. H^^
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QUote from John M's post:
"I beleive that one of the advantages of twins, has to do with the smaller dia. prop, but because there are two of them, you still have a lot of prop diameter to do the job. The smaller dia. prop seems to have less moment to impart prop forces so the turns seem to be much better, but the area allows it to have the traction to pull the plane through."
John's assesment on twins is very accurate and it is based on his background with a numerous twins. Electrics make the twins a LOT easier to handle too - opposite rotating props are just the icing on the cake!
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bin wondin , if the TRIM alters gear up / gear down , but if its straight up & late down , youd have to reprograme it to see if it was worse Gear Down .
Which would be counter productive in effect . :(
Good to see it DID go in the Nats .
indeed , the ' prop disc area ' Vs prop inirtia PLUS the Thrust over the Flaps gets it all going good .
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Thanks for that information, Bob (and John). This is a very interesting and significant thread!
SK