Design #207~ B-17 stunter!

[Pat Johnston]

Ole' Allan Perret requested a B-17 stunter and now it morphed into a 595 inch profile powered with four "1/2A" electric motors.  One of these motors will pull a 10 ounce Shark 202 around like it is not even there.  At the B-17's target weight of 50 ounces, that will not tax the electric motors much.  Plus, I have observed a synergy of multiple motors acting like they are more powerful than expected.  The electric package will be powered with a 3S/2800 battery and have each motor with it's own separate timer and ESC.  Starting will be a matter of pushing four start buttons from the inside motor progerssing to the outside.
The airfoil is similar to my "+P" series.  The TVC is a whopping .525 which is a bit more than PW's Impact.  Without flaps, the tail will be super effective and very stable.  I expect this will be a fun plane to fly and be a real show stopper.  PDF's attached. . .
Pat Johnston
Multi Engine Design Studio
Skunk Works

[Tim Wescott]

No flaps?.  OMG.

Starting will be a matter of pushing four start buttons from the inside motor progressing to the outside.

Or using a TUT in engine sequencing mode.  If I can be made to be interested in doing another production run.

[Tim Wescott]

Wait -- why not one timer with a 1-to-4 Y cable?  Then you just start all the motors at once.

[Pat Johnston]

Tim,
Could, but initially it seems simple to have separate timers.
Pat

[Bill Adair]

"Starting will be a matter of pushing four start buttons from the inside motor progressing to the outside."

Pat,

I'm confused (as usual)? 

Don't you want the outboard motors to stop first?

Bill

[wwwarbird]

 Wow, very cool Pat! Kudos for taking the time and working this one out. It's a very tempting project but I'd have to do IC, I just can't stand all that garbage that goes along with electrics hanging all over the outside of what are otherwise good looking models. 

 On another note my previous offer about this potential offering still stands, I'll send a fresh can of Brodak Olive Drab to the first one who shows us photos of one of these built, finished, and ready for color. 

[Pat Johnston]

Bill,
You are right.  The outboard motors should be the first to quit.  I was thinking about the safety of starting the inboard motors and progressing towards the outside so you are not leaning over the ones already running.  A person can set the timers to account for the timing issue and get all the advantages of safety and sequenced stopping of the motors.  Thanks for pointing this out.
WW,  The offer of the OD dope is generous.  In actuality, I was heading towards a silver scheme as used on later samples from mid 1944 on.  I like the brighter look.  I have had P-40's with camo which when flying in front of trees get a little hard to see on the pullout of square loops, etc.  I quickly realized that the visuals in this regard is a good consideration.
Pat

[Paul Walker]

Pat,

I'm confused (as usual)? 

Don't you want the outboard motors to stop first?

Bill
[/quote]


From one who has flown 2 different IC B-17's, the shut down sequence is just not that critical. In fact, mine would fly with just only the outboard motor running.

Don't get carried away with the shutdown sequence. The starting safety aspect is much more important.

[Tim Wescott]

I'd be concerned that an all-silver ship would just look gray on an overcast day, and mix in with the clouds.  If you're worried about visibility and authenticity both, search on "assembly ships" or "formation ships".

https://www.warhistoryonline.com/war-articles/formation-ships.html/2

[Steve_Pollock]

Pat, if you really want to do something crazy, do a mod to add a single larger engine in the nose, as in the test bed B-17 for the 4000hp+ Typhoon turboprop.  The test plane had the cockpit section moved back 47 inches to allow installation of the engine and exhaust.  It might make an interesting single-engine stunter.

[Bruce Shipp]

Pat, very cool project. Looking forward to seeing how consistent 4 EP motors on one plane will be.

Paul Walker, given the current state of EP technology, if your were building your B17 PA ships today, would you go IC or EP?

Tanks,

Bruce

[Paul Walker]

Pat, very cool project. Looking forward to seeing how consistent 4 EP motors on one plane will be.

Paul Walker, given the current state of EP technology, if your were building your B17 PA ships today, would you go IC or EP?

Tanks,

Bruce

Electric motors without question.
Too many options for rpm adjustments on individual motors.
Reliability is no issue. Not sure why that is a question.

[Dan Berry]

Pat, if you really want to do something crazy, do a mod to add a single larger engine in the nose, as in the test bed B-17 for the 4000hp+ Typhoon turboprop.  The test plane had the cockpit section moved back 47 inches to allow installation of the engine and exhaust.  It might make an interesting single-engine stunter.

Mark Troutman has one.

[Paul Smith]

Impressive with piston engines.

With electrics, no better than a $39 quadcopter.

[Paul Walker]

Impressive with piston engines.

With electrics, no better than a $39 quadcopter.

Yes, and yours was a very "impressive" response.

[Pat Johnston]

PW, I agree with you 100% about the stopping sequence.  The beauty of the electric setup is that they actually don't start till the flyer is at the handle.  Love those electrics.  But as always, safety is job #1. 
Also, after seeing your B-17 fly, there is about the same likely-hood of lightening striking twice that anyone will compare it to a quad-copter.  My ex (Julie) remarked about your B-17 that it was worth the whole 500 mile trip just to watch it fly.  Personally, I felt it was the single most impressive effort in any modeling field.  Hands down.  When you get down to it, making a B-17 fly that well is not only an enormous effort, but flying it with precision as you did made it even better.  Can't hardly tell I was impressed.  Thanks for leading the way for all of us in so many areas.
Pat Johnston
Humbled in Boise
Skunk Works

[Frank Imbriaco]

Nice looking design. Lots of promise.
Some possible givens:
-4 ESC
-1 Timer( to my knowledge, the only available on the market is the Hubin and it is currently suitable just for two motors)
- 1 battery  required because of the single timer. Two would be better. You'll  likely need the nose weight.
- Some combination of tractor and pusher props. There are limited prop size options for smaller motors ; particularly with pushers.
- Long stretches of wire for the ESC ( battery and timer). That adds weight .

I just completed a twin with retracts. Will maiden in the Spring.

[Paul Walker]

Pat, are you sure you want to make this without flaps?
With your projected weight of 50 ounces and 585 of wing, it might not want to make enough lift to corner very well.

[Tim Wescott]

Nice looking design. Lots of promise.
Some possible givens:
-4 ESC
-1 Timer( to my knowledge, the only available on the market is the Hubin and it is currently suitable just for two motors)
- 1 battery  required because of the single timer. Two would be better. You'll  likely need the nose weight.
- Some combination of tractor and pusher props. There are limited prop size options for smaller motors ; particularly with pushers.
- Long stretches of wire for the ESC ( battery and timer). That adds weight .

I just completed a twin with retracts. Will maiden in the Spring.

AFAIK there's no need for one battery.  You should be able to put a battery and ESC in each nacell.  Just be sure that only one ESC powers the timer, with just ground and signal going to the other three.

Pat's suggested setup with one timer per motor should also work fine, and be less of an "interesting educational experience" (i.e., less hassle learning how to do multi-motor electrics).

[Pat Johnston]

Tim,
I put the battery in the nose to get the CG to work out better.
Here is a flapped version of the wing for anyone wishing for flaps.  With the improved Reynolds # of the larger B-17, it should maneuver well, in my opinion.  Of course this is a SWAG.
Paul, when we get the trimming setup on its way, it would be fun for you to fly it to provide your input and impressions.  I'm sure we will be at some contests together, or I can even meet up with you and Mark at the Stunt Ranch for fun.
Pat

[Allan Perret]

When I first asked Pat to take on this project, I was not thinking in terms of a competitive stunt bird, but a sport scale bird.  I wanted it to be capable of inverted flight and round maneuvers, but square corners not required.  Now that's just for me.  If Pat wants to take the design to a competitive level, that would just be icing on the cake.  I wanted a semi-scale B-17 about the same size as our "60 size" stunters that would work good on 63-65' lines. Have had this project in back of my mind for 15+ years.
My Dad was a B-17 Bombardier, 33 missions into Germany.  His bird was the "Lady Velma" named after the Captain's wife.  He flew out of Framlingham Field near Ipswitch, England. The original control tower on that field was converted into a museum for the 3 (maybe 4) Squadrons that flew from there. On the second floor of the museum is a B-17 static model.  Several years ago my brother Jeffrey runs across a YouTube video taken by someone visiting the museum.  The B-17 model seen in that video is the "Lady Velma".  Don't have a clue how or why its my Dad's bird, but hope to make a trip there someday and maybe find out.  Will locate that video and post link here later. 

"Lady Velma" model is around the 3:10 mark in video.  I realize now that the base was actually called Parham Airfield, Framlingham was the nearest small town..

 

[Frank Imbriaco]

AFAIK there's no need for one battery.  You should be able to put a battery and ESC in each nacell.  Just be sure that only one ESC powers the timer, with just ground and signal going to the other three.

Pat's suggested setup with one timer per motor should also work fine, and be less of an "interesting educational experience" (i.e., less hassle learning how to do multi-motor electrics).

Tim :
 It would be swell for you to do a complete build thread on this ship ; much the same as Bob Hunt did under the "Amped Up" banner with his "Electric Twin Back On Track ". If it's not too much trouble,  please include step by step photos and a flight  video .
Frank

[Tim Wescott]

I put the battery in the nose to get the CG to work out better.

D'oh.  Of course.

[Paul Walker]

Tim,
I put the battery in the
Paul, when we get the trimming setup on its way, it would be fun for you to fly it to provide your input and impressions.  I'm sure we will be at some contests together, or I can even meet up with you and Mark at the Stunt Ranch for fun.
Pat

Sure, just let me know when!

[Howard Rush]

Wait -- why not one timer with a 1-to-4 Y cable?  Then you just start all the motors at once.

And you can run light wires among the engines.  Would separate timers be lighter?

Hey, you EEs, what’s the minimum wire gauge from battery to speed controllers?  Alternatively, can all the controllers be in the middle and the long wires run to the motors?  Which would be lighter?

[Jason Greer]

I’m far from an EE, but I’ve read that’s its best to put the esc as close to the battery as possible and extend the motor leads. If the battery leads are excessively long, then voltage spikes will eventually kill the capacitors on the esc which will allow the esc to see excessive voltage and eventually cause esc failure. If the motor leads must be extended, then more capacitors can be added to the battery leads. I believe Castle Creations actually sells a capacitor “pack” that can be added to an esc for this.

Jason

[wwwarbird]

 How about just using four of these? 

 

[pmackenzie]

FWIW, I would put the four ESCs in the middle and run motor wires out.
Long ESC to battery leads are generally a bad idea, for the reasons mentioned above. (I do have an EE degree )
Might be heavier than running the battery wires out to ESCs in the nacelles, but at least you know it won't end up causing the ESCs to fail.
(battery wires would need to be thicker than esc-motor wires, so it might be close)

Example below is a "flying beer cooler" B17. Size is very similar to what is being discussed here.
It uses two batteries, so ESCs are connected to them in pairs. Inner motors on one battery, outers on the other.
3 standard Y-connectors to connect all three ESCs to the receiver, or in a C/L example the timer.
With a bit of soldering you could make up a 4 to 1 connector that would be lighter.

Pat MacKenzie

[Paul Walker]

It might be lighter to use 4 smaller batteries, and keep the heavier gage wire to an absolute minimum. The mass distributed like that would keep the wing root bending moment down also.

[Frank Imbriaco]

And you can run light wires among the engines.  Would separate timers be lighter?

Hey, you EEs, what’s the minimum wire gauge from battery to speed controllers?  Alternatively, can all the controllers be in the middle and the long wires run to the motors?  Which would be lighter?

According to Castle Creations, best to  run the same gauge wire as the comes  ESC  equipped with. I've seen as low as 16 gauge for ESCs that are suitable for the motors we use in electric control line.

[Scott Richlen]

Whoa!  When you take the "lid" off it looks like a flying spaghetti factory!   

[John Rist]

For sport flying why not use 2.4 gh radio control for the motors.  Would add the fun of power-on landings and motor shut down by the pilot. Lots of info in the scale section. 

[Tim Wescott]

It might be lighter to use 4 smaller batteries, and keep the heavier gage wire to an absolute minimum. The mass distributed like that would keep the wing root bending moment down also.

I think that makes sense if the batteries are in the nacells, but I'm not sure, for the same current-carrying capacity and the battery (or batteries) in the nose that you'd save weight.  (I don't know if you wouldn't, either).

[john e. holliday]

Sure getting complicated for what was to be a sport scale aerobatic air craft.

[John Rist]

Sure getting complicated for what was to be a sport scale aerobatic air craft.

Any time you have 4 engines it is more completed.  That's the challenge and fun of it all.  As an retired electoral engineer the electric setup seams simple.  What I have trouble with is getting consistent piston power.  You piston poppers find it easy.  So all 4 engine setups are more difficult.  If you are up for the challenge go for it.  If not enjoy watching those who can make it work.  When it ceases to be a challenge whats the point?       

[Tim Wescott]

Sure getting complicated for what was to be a sport scale aerobatic air craft.

Only if you pay attention to the water cooler talk -- if you just build it like Pat tells you, it'll probably work just fine.

[wwwarbird]

Whoa!  When you take the "lid" off it looks like a flying spaghetti factory!   

 Ahh, the "beauty" of electric, and on a profile there's nowhere to hide it. 

[Paul Walker]

 Ahh, the "beauty" of electric, and on a profile there's nowhere to hide it. 

Ah, the beauty of IC, and on a profile there's nowhere to hide the engines!   

[wwwarbird]

Ah, the beauty of IC, and on a profile there's nowhere to hide the engines!   

 Ha! At least with IC it presents like a "MAN"S" airplane and doesn't sound like a hair dryer. 

[Paul Walker]

Ha! At least with IC it presents like a "MAN"S" airplane and doesn't sound like a hair dryer. 

Unbelievable! 

[Scott Richlen]

I'd try electric except I don't know where I'm going to clothespin that playing card......

(I know, I know.  But if I ever build a twin I think that electric is probably the best way to go.  I'd love to build an F5F.  But with ic's I'd have to load a bunch of lead into the front of the cowl.  With electrics I'd just have to figure out how to mount the batteries as far forward as possible.)

[wwwarbird]

 Anyway, IMO, Paul still holds the record for building the ultimate "MAN'S" airplane, and probably always will. 

 Here's hoping someone gives Pat's version a try, it'll be a fun project to watch.

[John Rist]

Ha! At least with IC it presents like a "MAN"S" airplane and doesn't sound like a hair dryer. 

However it won't grease your hair - so you don't need to wash and dry it. 

[Pat Johnston]

With all the talk about routing wires, I did a little soul searching and decided to see what simplifying the approach and installing the 3S/800mah batteries with the motors similar to the way I did the Shark 202 looks like.  The only problem is that the mass of the batteries is pushed back and not it will need about 2 ounces of lead in the nose to make it CG out properly.  Also, the batteries weigh another 3 ounces more in total so there is an additional 5 ounces overall weight.  Still need to contemplate this all and see if it is worth adding an additional 10% weight.  Probably still be best to go to plan "A" and put one battery in the nose and probably 16 guage leads to the ESC's.  Voltage loss on 18" of 16 guage wire is non existent and the weight of the wire is not all that much.  Think I've talked myself into keeping the one battery in the nose.  Any decent source for nice 16 guage wire?  Anyone?
One nice thing about this little exercise is that I have a really clean setup for a single engine "1/2A" electric setup.
I'll attach the PDF's anyway.
Pat

[Allan Perret]

  Here's hoping someone gives Pat's version a try, it'll be a fun project to watch.

If Mr.PJ releases a design I am confident it will be right.  And if he delivers me a kit it will get built !

I will do a posting of the build, but debating whether to do it here or on facebook (probably MikeGriffins "Control Line Flying" page).   
Any thoughts about that ?   

[Gerald Arana]

 Ahh, the "beauty" of electric, and on a profile there's nowhere to hide it. 

Wrong! It can be hidden in the wing.............

Jerry

[Tim Wescott]

16 gauge seemed too fine, but I checked your math: the voltage drop for that 18" (I'm calling it one meter round trip) 16-gauge wire is around 80mV, so, yes, probably negligible.

Too lazy to look up the weight, but it's probably better than the excess due to individual batteries (should check, though).  You'll want to do the calculations with the ESCs in the fuse, so three wires per motor out the wings. 

Hobby King has wire; I suspect everyone does.

[Allan Perret]

  Any decent source for nice 16 guage wire?  Anyone?

Test lead wire is nice and flexible.  I have a roll each of red and black, but 12 guage for the 40-60 motors.   Its easy to source from any of the online electronics suppliers.  Or order from your local Radio Shack.

[Fred Underwood]

I have used Motion RC for wire and a few other things.  I got my last wiring from there.  Very good to deal with, quick service, and good communication, and some good prices.

https://www.motionrc.com/pages/about-us

https://www.motionrc.com/pages/search-results-page?q=silicon+e+wire