Twin IC engine setup

[John Carrodus]

My next project will be a semi scale, profile stunt Tigercat  throttle control. What is the best engine setup and why please? Both engines with heads facing the centre of the circle, or facing the outside of the circle , or both glow plugs facing the cockpit. OR- phew- one facing in and one facing out! The choices are simply overwhelming!!
Any other hints for setting up a twin would be a great help.
Many thanks in advance

[Jake Moon]

My father, Steve Moon, built an extremely semi-scale Hughes XF-11 with twin Saito 40s. It was a big plane and flew well. I don't remember many specifics but he wrote an article about it in the June 2007 issue of Flying Models if you can scare up a copy.

[Dan McEntee]

 Look for and read the article on setting up the engines for the twin Pathfinder by Gordon Delaney and John Miller. It was published by Flying Models but has been discussed thoroughly here on the forums. If you are going to have throttles, you want the exhausts pointing down so the engine doesn't load up at low RPM. The Pathfinder Twin article also lays out engine thrust angles and such. It will have everything you need. That along with XF-11 article will get you through.
  Type at you later,
  Dan McEntee

[Dennis Toth]

John,
Multi IC engines are a challenge but have been done, check out the ships by Windy on Youtube, also Paul Walker's bomber (I think he used 4 OS 15FP's). But the most reliable is the electric twins that Bob Hunt has done. There is a lot of information on Bob's ship on this forum.

Best,    DennisT

[Steve Dwyer]

The GD Pathfinder Twin's preferred engines have been either the OS FP 15 or OS LA 15. It's been reported some will use higher nitro with the 15s to achieve a bit more umph while the 25 size works well but tail weight may come into play. I plan to build the PF twin this winter and have already fabricated small aluminum interchange pads to swap out either size engines. As Dan has said there has been much published on twins including much from Bob Hunt who favors electric as Dennis said.
Steve

[Jim Hoffman]

I had great success with OS 15s on a twin.  Ran both on separate uniflo tanks and a shared bladder with individual pressure regulators

These motors were reliable and quite powerful

The bladder system is the same as the Paul Walker IC B-17

[john e. holliday]

My B-25 design by Don Hutcheson has Fox 25's.  Heads pointed to out side of circle. In board no off set.  Inboard has about 3 degrees off set to out side of circle.  Both metal tanks are uni-flo with out board a 1/4 ounce smaller.  I start both engines separately before getting ready to fly.  Top off both tanks.  Start in board first then the out board.  Needles set at about 9800 rpm before hand in initial start of engines.  So far the out board quits first and the inboard a lap or two later.  As I learned the hard way make sure you clip the glow plug clip from top side.  If using one of the plug igniters make sure to reach from top side.  I have a scar to remind me.   Also who ever is helping make sure thair job is to hold the plane only and you wil yake care of every thing else.  But, I have successfully used my stooge.  Twins are fun and a show stopper when flown.  I could almost hear the oohs wnen I did a reverse wing over with the B-25.  It will do the whole pattern and be a winner in the right hands..

[gene poremba]

. Not sure if its the best set up, but this works for me,2- OS 25la s , sullivan 4oz tanks on tongue muffler pressure. No off set and no rudder offset. Been flying it on .015s x60'. Great performer and allways gets attention when flying. Will do the pattern better than i can fly it. It doesnt matter ( so far) if either engine quits first. Once one does, i fly circles til the other one quits shortly afterward. Its basically a bashed Twister to resemble a HE-129...Gene

  PS, there is a video somewhere  on the web of me flying the pattern with it, but wasnt posted by me. I believe i did a build thread on RCG awhile back....Gene

[wwwarbird]

 You can check my Reply #17 in this thread for some suggestions that have proven to work for me.

 https://stunthanger.com/smf/open-forum/twin-engine-question/msg623213/#msg623213

[Dave Hull]

You may want to use full bodied nacelles instead of profile nacelles. That would give you more options about correct tank placement for upright and inverted running. You could still use the profile method of construction on the fuselage. The tradeoff might revolve around keeping the nacelles short (more scale-like) and therefore stiffer (a very good thing) but now not having room for a good tank setup on a profile nacelle, or longer than scale for the pattern-sized tank but accruing all the disadvantages mentioned above.

If you go with built-up nacelles, then you have the option of canting the engines at any angle you want. Especially easy if you use a plastic bulkhead-style R/C engine mount. You might want to look at the F7F Navy Carrier design by Ray Randall (Plans by Netzeband and Plecan), which was an award-winning plane if I recall the article correctly. Lots of good details. It would likely be at one extreme of "scaleyness" whereas you will have to deviate a good bunch if you are going to achieve "stuntyness."

As always, I find myself compelled to say that building a very stiff wing--including torsional modes--between the nacelles is paramount. Of all the different multiengine CL ships I've seen, nearly every one has some mode where the structure gallops off if one engine or the other is running a bit different. Fuel feed issues, foaming, random stoppage, structural cracks, etc. then ensue. I think this is the major reason most multiengine ships get flown a few times for the novelty and then hang on the wall. It shouldn't have to be that way--they are too cool....

At our recent 1/2A fun fly, one member had very good success running his profile B-25. But he spent a good amount of time getting the engines healthy before the event.

Other places to look at for ideas would be some of the Johnston Epiphany Twin as a full-stunt configuration. Saw a couple of those at our recent contest. They fly very well. Didn't Hutchinson have a P-38 profile stunter? Or, go way back and look at McFarland's P-38 full-bodied sorta-scale stunter. Close enough in looks to make it real.

Sounds like a fun project!

[Fred Cronenwett]

I have buillt and flown CL scale models with 2 and 3 glow motors. For throttle control get a 2.4 Ghz set-up, either the RC car units with the trigger or a std transmitter. I hang the transmitter on my belt with a metal clip. With the RC car transmitters, I hold that in my left hand and fly with my right hand.

The model will have a reciever, on-off switch, battery and the servos. Control each motor with it's own servo. Adjust the length of the pushrod by turning the clevis in 2 turns at a time to slow down or speed up an engine so that they are in sync when you shut down the engines. There will be straight, short pushrod between the servo and the motor.

[944_Jim]

I love twins!
Working out the tanks was an exercise in frustration. No throttles, small tanks, short flights...and great line pull! The build log is on CEF.
So is the unscheduled re-kitting.

[Ian Hewitt]

I was advised to avoid synchronising the engines  to reduce the opportunity for resonance. I fitted different sized props - pitch size.

Last time out I ran into problems with one engine cutting out on take off (pretty scary) and noted that the profile nacelle was shaking pretty badly at take off power settings on the ground.

I have put some more glass cloth on the nacelles in the hope that this stiffens things up and alters the response of the airframe to engine vibrations.

Have yet to try it out - the profile Mosquito has been a hangar queen for some time now..

Ian
Nottm, UK 

[944_Jim]

Mr. Ian,
Which Mossie kit did you build? The one shown was a Black Hawk Models profile with slab wings. My next will be a custom-cut Frog Mosquito with (most likely) Cox Medallion .09s. This one is bigger then the first one by nine inches (36" total).

[Paul Smith]

I started building a Black Hawk XF5F Skyrocket and found that when I replace the weak and underside parts there was nothing left of the kit.
I started with twin TeeDee .020's and upgraded to Black Widows, then TeeDee .049's.
I was always able to get them running well enough to do well in contests.
The inboard quitting first happened sometimes and caused no trouble.

The issue of strong structure between the engines and the fuselage is huge and cannot be ignored.

[Paul Smith]

Mr. Ian,
Which Mossie kit did you build? The one shown was a Black Hawk Models profile with slab wings. My next will be a custom-cut Frog Mosquito with (most likely) Cox Medallion .09s. This one is bigger then the first one by nine inches (36" total).

The problem with BOTH the Skyrocket and the Mosquito is they can come out tail heavy and there's no place to put the nose weight.
That's why Grumman dropped the F5F Skyrocket in favor of the F7F Tigercat.

[Dan McEntee]

I was advised to avoid synchronising the engines  to reduce the opportunity for resonance. I fitted different sized props - pitch size.

Last time out I ran into problems with one engine cutting out on take off (pretty scary) and noted that the profile nacelle was shaking pretty badly at take off power settings on the ground.

I have put some more glass cloth on the nacelles in the hope that this stiffens things up and alters the response of the airframe to engine vibrations.

Have yet to try it out - the profile Mosquito has been a hangar queen for some time now..

Ian
Nottm, UK

     In the article for the twin Pathfinder, it is explained that you want the outboard engine to be running a bit faster than the inboard when on the ground. Once in the air and at speed, the outboard engine will experience more centrifugal force than the inboard and will richen up that little bit and be closer to being in synch with the inboard. I don't think it's a critical issue.

  Type at you later,
   Dan McEntee

[wwwarbird]

My next will be a custom-cut Frog Mosquito with (most likely) Cox Medallion .09s. This one is bigger then the first one by nine inches (36" total).

 That thing will be a rocket ship with twin Medallion .09's. 

[944_Jim]

The BHM one had twin Norvel .074 BigMigs...it was nose heavy. Shoot, it was just heavy! But the line pull was amazing! I think the nacelles and fuselage were 5/16 or 3/8 inch, the wings were 1/4 slabs, and the tail was 1/8 inch, maybe 3/16 inch. Since the engines were sidewinders, the tanks were little flat rectangles under the wings. They were very shallow so they were centered on the NVAs. The pickups were in the outboard wedge, and the full tubes pointed just about straight ahead. Fueling had to be done nose down until the fuel was pushed to the NVAs. Sadly, the second "accident" was irreparable. An inside engine flame-out just coming off the deck, upwind. The plane continued to climb, but kept turning in on me as it barrel-rolled to port. I had two choices...hope I could back up out of the way, or dive below and out. The debris field on concrete was worthy of an FAA investigation.

[wwwarbird]

The BHM one had twin Norvel .074 BigMigs...it was nose heavy. Shoot, it was just heavy! But the line pull was amazing! I think the nacelles and fuselage were 5/16 or 3/8 inch, the wings were 1/4 slabs, and the tail was 1/8 inch, maybe 3/16 inch. Since the engines were sidewinders, the tanks were little flat rectangles under the wings. They were very shallow so they were centered on the NVAs. The pickups were in the outboard wedge, and the full tubes pointed just about straight ahead. Fueling had to be done nose down until the fuel was pushed to the NVAs. Sadly, the second "accident" was irreparable. An inside engine flame-out just coming off the deck, upwind. The plane continued to climb, but kept turning in on me as it barrel-rolled to port. I had two choices...hope I could back up out of the way, or dive below and out. The debris field on concrete was worthy of an FAA investigation.

 You won't have to worry about any of that running the Medallions on your new one, the launch should be akin to shooting a rubber band. 

[John Carrodus]

Many thanks to all of you. I appreciate the advice. It's great being able to call on literally thousands of hours ( if not years!) of experience. Stunthangar offers great depth of CL stunt knowledge. Well worth a designer coffee a day!!

[Fred Cronenwett]

I have never had a problem with the larger glow motors being in Sync. I always set up my glow powered multi-engine engines to shut down at the same time when the throttle was reduced to kill with the throttle trim. The Actual RPM at full power might not be the same, probably within 500 RPM. remember, with the 2.4 Ghz throttle control you have one throttle stick and two or more motors. The servos that controls the engine speed for both motors receive the same signal from the receiver and act the same. It's best to have the same brand and size of throttle servos, especially the servo arms so that the control throws are the same.

But....if the inboard engine quits during the flight throttle back very slowly and land. Any throttle surge from the outboard will turn the model inwards towards you. Taxi will be affected if either of the two motors are down.