running twin engines off a single fuel tank

[Miotch]

I've always wanted to build a twin something or other.  One of the reasons I haven't is because of a fear of always having a problem starting an engine which would lead to a differential in available fuel once it's in the air.  Has anyone built a twin-engine CL where the engines share a tank ??

[Dan McEntee]

I've always wanted to build a twin something or other.  One of the reasons I haven't is because of a fear of always having a problem starting an engine which would lead to a differential in available fuel once it's in the air.  Has anyone built a twin-engine CL where the engines share a tank ??

   I don't recall any one doing a multiengine feeding off of a single hard tank, but it has bee done with a bladder. Search out on the forum here about Paul Walker's B-17 stunt model. I think he had built three over the years, each one an improvement of the previous model. he used a single bladder that was in the fuselage on the balance point and it fed the four OS.15 FP engine ( i think) and each engine had it's own pressure regulator to help with keeping things even. I would also like to do at least a twin engine stunt model and most likely use two tanks but keep this bladder/fuel regulator thing in the back of my mind!

   Type at you later,
   Dan McEntee

[Paul Smith]

I have built and flown two two engine CL models one with .049's and one with .25's.

Both engines flew without a problem on the outboard engine alone.  While this is not good, it is not certain death either.

In lieu of a single tank, assuming you have no throttles, a common fuel shutoff might be a better idea.

[Paul Walker]

I have. Don't do it. The centripetal acceleration will make the inboard engine lean, and the outboard rich.
 Nice idea,  but it doesn't work

[Paul Walker]

Yeah, I dud it with the B-17..It required 4 pressure regulators, filters, switches and other monkey business to make it work. Too much work, and a good reason it hasn't flown for over 20 years now.
 

[Dick Byron]

Paul,
      That is the most dynamic stunt ship I have ever seen. Your skills are beyond belief.

Dick Byron

[Dan McEntee]

I have. Don't do it. The centripetal acceleration will make the inboard engine lean, and the outboard rich.
 Nice idea,  but it doesn't work

     I still want to do a twin, just because! When Gordon Delany and John Miller developed the twin Pathfinder, they covered this a little bit in the magazine article and how to set up the thrust angles during construction, and needle setting for flight. On the few twins that I have messed with  that belonged to others, I have found that the needle setting work. One guy was kind of perturbed at how the engines sounded on the ground, because he saw enough war movies about getting the engines in sync and didn't understand what I was trying to tell him, but got over it when the model was in the air and up to speed and the settings came in. Still a little bit of luck involved but I have have seen enough first hand to keep my interest alive. No more that a twin, though!!! I talked a since deceased flying buddy out of building a profile scale B-17 several years ago, because I knew he couldn't get all  4 Fox .35 engines running correctly and was gonna bug me to help!! And that if he tried to fly it he wouldn't be able to hang on to it!! We reached a compromise, where he reduced the size of the airplane to be powered by two Fox.35s, and just have the outer props installed for display. The result was pretty pleasing and it impresses most people that saw it fly. All together, he did the B-17, a B-25, and a B-26. All profiles and for a guy his age at the time, working the way he had to, they came out OK. Not competition models, but pretty nice to the average person. And setting the needles according to what Miller and Delany described work pretty good and we often got them where they came in to pretty close sync when in the air. This is all just gonna be for fun and a bucket list item to check off after seeing Delany's Two Much Too fly on a couple of occasions and two Jack Sheeks Mosquito's fly. I better get going because I ain't getting any younger!
    Type at you later,
      Dan McEntee

[Dave Hull]

Antone Kephart flew a King twin in the stunt contest last weekend. He was a bit off his usual precision, but it sounded like the plane--both tanks and all--was working well.

[wwwarbird]

I've always wanted to build a twin something or other.  One of the reasons I haven't is because of a fear of always having a problem starting an engine which would lead to a differential in available fuel once it's in the air.  Has anyone built a twin-engine CL where the engines share a tank ??

 I've tried it, it doesn't work.

[M Spencer]

A inline push / pull plane , it should / could work .  Wondered if the rear engine goes rich , uphill .

You have your good days & bad days with twins. A series of near identical ' stops ' & one & two lap max differances .
And days where its a dozen laps or more , Theyre generally light on the lines on the outer . Offset on outboard engine ,
on a profile at least , Thrust vectors & suchlike .

A few things've had ' cut outs ' triggered by a mighty grab on the handle . Like 50 Kg I saw on a Kolsnikov thread .
Sliding bellcrank platform , with a mighty tough spring . 1/4 inch od side movement ( wouldnt've been more than 10 m.m. )
and it ' throws ' a fuel line pinch . Twos as good as one , there . Or better . Youd usually land with fuel onboard .
THEN what do you do with it .

Or just - check the inner ( bump ) . Fire up the OUTER - Thenwhack the inner over . Your didgits aimed at a fuselage or running prop .
So inner props best flat so your flicking UP . But ' Bump ' back against comp. is saner . Or a electric finger .

[Miotch]

Thanks everyone.  How about trying to top off both tanks after the second engine is running ??  I don't recall ever tried topping off a tank with a running engine.  My feeble mind tells me I'd probably just enrichen the engines during the fueling process, maybe to the point of killing the run .....  But I'm guessing someone has tried this before.

[M Spencer]

To many propellors & wobbly  things vibrateing everywhere , and the pressure can get it going to slow or fast or stopping , AND it spills everywhere . Usually Anyway . Pre Flight prep. & it'd be unecessary .

Wotcher gotta do is . . . .

Fire one up . Hold the nose up vetical . Lean the needle till it drys off , then out two of three clicks . S H A K E the daylights out of it - to see its all marvellous & Wont STOP . Like wotcher doona  Combat Wing - with a steel tank .

Then you stand it on its NOSE so it STOPS . Unless the noseisnot longenough . Standing it on the inner wing tip , wing vertical , works . IF youve got things o.k. there .

REPEAT on the Other Engine .
I drain off the fuel , or it can get messy . ALSO evaporation & mayhem . If theyre BOTH drained & your fuels well shaken , then both filled , both fuels will be matched , Rather than the  methanol evaporating so theres To Much Castor . Or Something .

Therefore & thereafter ; When BOTH are Fired Up , The r p m 's should be near rather close . You can leavem or ' synch ' em , Maybe the break is better a tad rich on the inner . or not . You want the Inner Strong . The Better Engine ifin there the same .
Better Runs on the 88 were 25 & 18 Foxes with strong 25 Inb'd on full 10 x 4 & ' racing clearances ' 19 outer with the clipped 9 1/2 prop . On that day . 25 booming  & responding mildly to load , the 19 coasting but snapping up when needed uphill .
Like a Hound & a Terrier , perhaps . Way bigger leap on the 19's rpm's or Ex Note anyway . Wailing while its working but loafing when its just being towed around ! BUT its run with strong 25s both and loose & snappy 19s both And Others .

So , Dont use a motor thats a monkey , use a dependable pradictable one , or two , even if theyre not the same , as long as theyll swing the same prop soundly . 

Generally thats V close , Useable . Change in the barometer over a month & you might want to retry it , unless youve got the needles sussed . Clear engines well .
Give them a BURST on a PRIME , Tanks Empty . As a Preliminary , each session - and it should be problem free . Check the bolts occasionally too .

Much better if you have plug leads for / on Each Engine . Long Ones . And Dont Panic . Cool Calm & collected . All unpredictable jumpy types behind the fence . If you damp each motor . Fuel Each , see each FUEL LINE isnt empty ,
if the batterys good they should crank up straigght off . Generally it just Two Times every proceedure . Duplicted each step , Paired  . And theres no distractions  / ANYWHERE NEAR , tellem to Clear Out . To many propellors for distractifiers .

Putting a NOBLER & this into the blender ( throw the wing up there & throw ten inches onto the span and youve gottit , or otherwise . . .)



GOTTEM , Thems the Ones !   

from Chris McMillan .

Rick Loomis re-drew and built his latest Two Bits all over again in 2007. I think he had Eric Rule laser cut the ribs, which I believe are Palmer Thunderbird. It has two Aero Tiger 36's and weighs a good bit but not excessive. Bob flew it at VSC '08.
I flew it at the Palmer Classic at Whittier Narrows, CA in '08. The practice was a thrash and eventually the model was withdrawn for technical issues. Later found to be a battery lead problem!
The airplane flies very well, doesn't pull too hard yet is "right there" all the time, never gets loose. Turns well, very docile and easy to fly accurately. Even with three flights I was confident enough to enter the contest with it.
Worth a look.
Chris...

Pics are of Bob helping get 'er going at Whittier.

[Steve Dwyer]

Dan, I'm sending you a PM

Steve

    I still want to do a twin, just because! When Gordon Delany and John Miller developed the twin Pathfinder, they covered this a little bit in the magazine article and how to set up the thrust angles during construction, and needle setting for flight. On the few twins that I have messed with  that belonged to others, I have found that the needle setting work. One guy was kind of perturbed at how the engines sounded on the ground, because he saw enough war movies about getting the engines in sync and didn't understand what I was trying to tell him, but got over it when the model was in the air and up to speed and the settings came in. Still a little bit of luck involved but I have have seen enough first hand to keep my interest alive. No more that a twin, though!!! I talked a since deceased flying buddy out of building a profile scale B-17 several years ago, because I knew he couldn't get all  4 Fox .35 engines running correctly and was gonna bug me to help!! And that if he tried to fly it he wouldn't be able to hang on to it!! We reached a compromise, where he reduced the size of the airplane to be powered by two Fox.35s, and just have the outer props installed for display. The result was pretty pleasing and it impresses most people that saw it fly. All together, he did the B-17, a B-25, and a B-26. All profiles and for a guy his age at the time, working the way he had to, they came out OK. Not competition models, but pretty nice to the average person. And setting the needles according to what Miller and Delany described work pretty good and we often got them where they came in to pretty close sync when in the air. This is all just gonna be for fun and a bucket list item to check off after seeing Delany's Two Much Too fly on a couple of occasions and two Jack Sheeks Mosquito's fly. I better get going because I ain't getting any younger!
    Type at you later,
      Dan McEntee

[M Spencer]

This is actually a Gieske Nobler ! .
as in , two OS .15s & a few Nobler Bits , and Your Off !


Blue planes  long so room for extra things in places . Like nacells or booms with two engines !!!!!!!!!!!!!!!!!!  Thinking of doing a + 25 % ( 60 inch ) Oriental Wing profile Mosquito or Beaufighter for two old 35 S OSes . maybe perhaps one day . 

 !#^% No 100 is something like a 60 inch Nobler wing with something like a 28 inch tailplane , so if you put the booms there , or threw a nacelle each side . I just measured something for two .40s at 16 1/2  between , , itd be something like right .
Maybe with a yard stick or double sheeted under or a absorbtious ! undercarrage . AS IN the stressings greatest BETWEEN the nacelles / the center section . The outer panels are just there , just double spars or C F sheeted to the powerplants
perhaps , But you gotta watch the WEIGHT as theres plenty of pieces that weigh something . A 60 inch Nobler with two FSR 25s or old OS 35s , or better , two old Max 25's from the 70's would get THE WEIGHT DOWN to sumint reasonable .