stunthanger.com
Design => Stunt design => Topic started by: beercamel on April 17, 2016, 10:04:37 PM
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Gentlemen..
I have a lot of experience with control line flying.... but all single engine stuff..
I have been thinking about a twin engine F-82 profile model for fun flying... fun aerobatics.. NOT scale.. .. but I have no experience with multi engine MODEL aircraft ( I have tons of real multi experience ..LOL)..
Questions:
-How do you keep both engines running for about the same time?
-Do you run one engine , the noncritical engine, with slightly less gas so it quits first?
-How bad do they fly on single engine?.. meaning when the critical engine quits..?
I imagine a lot of engine offset is utilized, as well as significant 'outside' rudder.. but I don't know for sure
Any advice is welcome!..
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Gentlemen..
I have a lot of experience with control line flying.... but all single engine stuff..
I have been thinking about a twin engine F-82 profile model for fun flying... fun aerobatics.. NOT scale.. .. but I have no experience with multi engine MODEL aircraft ( I have tons of real multi experience ..LOL)..
Questions:
-How do you keep both engines running for about the same time?
-Do you run one engine , the noncritical engine, with slightly less gas so it quits first?
-How bad do they fly on single engine?.. meaning when the critical engine quits..?
I imagine a lot of engine offset is utilized, as well as significant 'outside' rudder.. but I don't know for sure
Any advice is welcome!..
Find and read all you can about Gordon Delany's Twin Pathfinder. I believe it was published in Flying Models. John Miller did the cad work for the plans and helped with the article. He goes into the set up of the plane in great detail. He has figured out stuff on setting the needles and such I would have never thought of. It's way more than I can post here. You might do a search here on Stunthanger and on Stuka Stunt on the same subject, as I believe he has recounted the same information several times on the forums. The short story is, you set the engines where the out board engine is slightly faster, because it travels farther and faster than the inboard and gets richer in flight. Fuel the engines the same so that they quit at about the same time, trial and error if you have to for proper amounts. The engine off sets are covered also, but I can't recall that exactly. John and Gordon's set up should work well with any twin. I hope to put it in practice with a Twin Pathfinder and/or a Sheek's Mosquito.
Good luck and have fun,
Dan McEntee
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Youve been beaten to it . !
http://www.airplanesandrockets.com/airplanes/f-82-twin-mustang-june-1968-american-aircraft-modeler.htm
(http://www.airplanesandrockets.com/airplanes/images2/f-82-twin-mustang-plans-jun-1968-aam-1600x1134_small.jpg)
Dick Sarpolus. did a fox 35 F 82 too.
(http://media.airagestore.com/media/catalog/product/cache/14/image/265x265/602f0fa2c1f0d1ba5e241f914e856ff9/f/s/fsp03763.jpg)
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I kit the F82 in four sizes. here are the .35 and .15 sizes. Full size .pdf files with templates of all parts are available for $5.00 per set.
Pat
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I've only had one twin and it was back in the early 1960s. It was a Sterling P38 with .09 engines. What I remember: It flew straight and level with both engines needled the same and "hung" in the air with the inboard engine alone...and not as easily controlled with only the outboard engine running. I fueled the outboard less and started it first so the inboard would be the last running. Several of us kids built these and flew them on short lines...if memory is right they were short (40'?) to keep tension for single engine flight. It was fast with both engines running and I never looped or did anything other than level flight and wing overs.
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I've only recently had the opportunity to see some multi-engine CL stunt planes fly, and have learned how tricky they can be. Not only synchronizing the fuel supply and having both engines draw at exactly the same rate, but the fact that no two of the same engines behave in an identical manner. And any difference in their mounting structure and vibrations can induce small differences in behavior that wouldn't be an issue on a single engine plane.
I recently listened to some guys discussing twins, Alan Buck, Steve Fitton and Bob Zambelli. Earlier that day, Bob had lost his twin Fox .19 Jezebel when the inboard engine cut off at a very bad time, causing it to turn in. That one engine had a history of being quirky and cutting off first. They were each on separate tanks, and he would top off the inboard tank after both were needled and singing in harmony. But that inboard one would invariably shut down early.
So before flying in Huntersville, he switched sides, so the if the supposed quirky power plant shut down, it was on the less critical side. But that's not what happened. The early shutoff did not move with the engine. The previously dependable engine now became the first to shut off. They discussed regulators and other things outside of my range of knowledge. But If I wanted to try it, I'd probably start with both engines feeding from the same pressure bladder.
Rusty
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From what I've seen, the world does not come to an end if the inboard quits first. I've seen it happen several times and the model just flew on the outboard until it ran out of fuel.
Don't underestimate the stresses between the engines and the fuselage. Things are A LOT farther apart on twin than on a regular single engine model. I HAVE seen some twins come apart. That's one reason why twins come in heavy and don't stunt as well as singles.
I'm building a twin profile scale now. I recommend carrying a couple of extra ounces and using a 2.4 RC setup as a fuel shutoff. Use the battery as tip weight. That way you can just use BIG gas tanks and stop both engines any time you want. You will look a lot cooler with an on demand stop than flying around on one. All the engines come with throttles and muffler pressure. All this stuff is off-the-shelf. No EE needed.
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you want at least 10 % nitro . 15 or 20 % and you can setem rich , & use the tourque .
Fire up the outer first .
Test , when unflown , is to burp Ea Engine on the prime , to see if theyre there .
Tank & fire one , Hold nose up and lean off , then 2 or 3 clicks out . Then same on the other .
Damp the engines with a prime and finger the props , BEFORE refueling. then theres just seeing the fuels up to the needle .
Often get one flick on Ea . IF THE BATTERYS GOOD . Often gettem cutting near simultaeneously .
Just gave away the Mosquito Today . Was a Wunderbar , buts had many misshaps and repairs . Recover and He should get another firteen yeers outve it .
Dispute your ' never as good as a single aerobatically . On 60 of .018 with the Veco BB 19s and 9 x 4s or 8 x 6s , on 15 % and with the Rossi R5 plugs ( unsilenced :o)
at 50 Oz. the Oriental Wing benifits from the prop wash , so was ( is ) a lively and accurate machine. If the pilots up to the mark .
Found you always need say 3 deg. outhrust on the outer . The 262s got FP 25 Clones these days . 70 Ft of .018 and 72 Oz. ( OUCH >:() on the same wing , its good to fly .
When Ive Refinished it . :-\ as its all stripped back to bare wood , to aim for 55 Oz. with thatr setup . The Flying Wing Fence trip makes them V good on the outer only - ( side area of Fuse & Nacelles )
The Modern ABC things are likely to be less crankey on low nitro , though back in 74 the original at 38 Oz was good for wingovers and loops on the outer OS max 20 on No Nitro . Silenced . 70 Ft of .012.
Wed test it on 60 ft. of .015 , and if it was calm ( summer ) and it was behaving , it'd go onto the 70's of lite wt.
If youve a good wing ( the Oriental Main Wing is 384 od bare plus another 50 for the flaps & tips .
THRUST LINES equal about fuse , gets the nacelles offset left .
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Thanks for all the great replies!
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I could claim to have flown Gordan's original Pathfinder twin several times this week and to have come up with a device that enabled all four engines of a bladder-fueled stunt plane to quit at the same time with no sissy timer or radio, but nobody would believe me.
Nevertheless, I have some observations about the twin Pathfinder. It has OS .15 FPs (as did the four-engine plane). They are mounted with no offset. If one engine quits first, it is difficult to tell which one quit. I could tell if I looked closely at which main wheel was forward of the other. The outside engine takes 1/4 oz. more fuel per flight than the inside engine, per Gordan's instruction. It takes 66-ft .015" lines (handle C/L to airplane C/L). It feels woozy at the top of the circle if flown with .018" lines and inadequate nitro. It is an excellent stunt plane.
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I could claim to have flown Gordan's original Pathfinder twin several times this week
Was that the plane you had at Chehalis, that you "forgot" to bring the lines for?
... and to have come up with a device that enabled all four engines of a bladder-fueled stunt plane to quit at the same time with no sissy timer or radio, but nobody would believe me.
Yes, you do have credibility problems.
Y'know, if it were possible for this twin engine stuff to work, someone would have, like, flown a multi-engine plane in some major stunt competition, like the Nats or the Worlds, and done well with it.
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If you wish to wuss out, you can always go electric. If I recall correctly, Will Hubin has done a special version of his timer for a twin; again, if my memory doesn't fail me, it lets you set the RPM of each motor individually (I only know this from comments that Bob Hunt has made about his CL twin -- apparently setting the motor speed differential becomes an item on the trim chart).
With electric not only can you get both motors out at the same time much more often, and get controllable RPM on each one, but the vibration will be lower, putting less stringent structural requirements on the center section of the wing.
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If you wish to wuss out, you can always go electric. If I recall correctly, Will Hubin has done a special version of his timer for a twin; again, if my memory doesn't fail me, it lets you set the RPM of each motor individually (I only know this from comments that Bob Hunt has made about his CL twin -- apparently setting the motor speed differential becomes an item on the trim chart).
With electric not only can you get both motors out at the same time much more often, and get controllable RPM on each one, but the vibration will be lower, putting less stringent structural requirements on the center section of the wing.
That makes very good sense, I would seriously look at electric for a twin, That is the single biggest advantage I see for electrics..multi engines
Randy
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Here Here . or is it hear hear . Could always fit speakers . S?P
No Excuses for not building a Dornier Do X or Spruce Goose NOW , is there . ;D
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That makes very good sense, I would seriously look at electric for a twin, That is the single biggest advantage I see for electrics..multi engines
Randy
Well, it is certainly one of the major advantages of electric power. There are many other advantages as well. The pitch CG does not shift throughout the flight; the vertical CG is easily adjustable; the center of the mass of the weight that is balancing the model is closer to the CG; virtually no noise so more lost fields (This one is undeniable!); no castor smell on clothes so the wife is much happier (and you can go flying during the day and she will have no clue that you did...); you can make one up to five one-minute test flights per battery charge to achieve a proper handle setting, level the wings, etc. much quicker than with glow; virtually no vibration means that your model will last longer.
Attached are couple of photos of the Second Wind thing that I designed and built a short while back. It's a hoot fly.
Later - Bob Hunt
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Here's a couple more: Jack Sheeks AT-9 Jeep, and Dick Sarpolus' TC-Two
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Well, it is certainly one of the major advantages of electric power. There are many other advantages as well. The pitch CG does not shift throughout the flight; the vertical CG is easily adjustable; the center of the mass of the weight that is balancing the model is closer to the CG; virtually no noise so more fields (This one is undeniable!); no castor smell on clothes so the wife is much happier (and you can go flying during the day and she will have no clue that you did...); you can make one up to five one-minute test flights per battery charge to achieve a proper handle setting, level the wings, etc. much quicker than with glow; virtually no vibration means that your model will last longer.
Attached are couple of photos of the Second Wind thing that I designed and built a short while back. It's a hoot fly.
Later - Bob Hunt
Another advantage seems to be that it needs no undercarriage either ;)
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Chris,
The landing gear (under carriage down under) retracts.
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Model airplane news has the Sarpolus F-82 plans- twin .35's
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There are few that have the experience with competitive twin designs to rival that of Gordan Delaney.
He has been at it since the sixties flying and refining his twin designs. Two Much, Gemini, ect.
The Pathfinder Twin has received some very good accolades, by some some very notable fliers.
my choice for the best profile I've ever flown - and quite possible the best airplane of any kind that I've flown... - is Gordan Delaney's Pathfinder profile twin. Ask anyone who has flown that ship and you're likely to hear the same story.
Bob Hunt
I had the opportunity to fly Gordan Delaney's Pathfinder Profile twin. That ship is powered by two 15's and is fitted with two 8.5-inch diameter props. It has effectively 17 inches of prop disk span providing a huge amount of that (as I call it) artificial air blast. Gordan's model was among the very best flying models that I've ever had the pleasure to pilot. It had plenty of line tension (but not excessive) everywhere; it flew at virtually one speed everywhere, and it was easy to fly anywhere on the hemisphere. I was sold at that point.
Later - Bob Hunt
The Pathfinder 2 is one of the best stunt planes I have flown.
Here's another vote for Gordon Delaney's Pathfinder Twin. I was so impressed by it that I got the plans and bought two OS FP15's and I'm building one.
I usually don't get very excited about profiles.
When I flew it I was expecting it to be pretty good because a lot of guys like Bob Whitely flew it before I did and Bob was really impressed and He doesn't impress easily. Then I flew it and truly couldn't believe it!
It did everything as well as anything I've flown (and I've flown some pretty good airplanes).
Of course it was in wonderful trim...no less would be expected with one of Gordy's airplanes, but it flew like a larger very competitive competition stunter!
If you really want a profile and can deal with two engines (a little more work), I really believe there is nothing better. Actually it's an easier build than most also.
Randy Cuberly
Sounds like an infomercial for the twin Pathfinder, but it does make a compelling argument.
(http://flyinglines.org/pathfinder.twin.jpg)
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Seeing the Fuse SIDE AREA , thinking thats definately a sound proposition ,
My two ' short sided ' twins , the Mosquito & Whirlwind are definately yaw susceptable .
The Me 262 just sits out there , the Flying wing fence . All on Oriental Wings .
As was a Meteor NF 11 , 58 in length o.a. .
(http://img.wp.scn.ru/camms/ar/204/pics/89_3.jpg)
This had enough ' directional stability ' to stretch the lines to blazes ,
where new .015 stranded gave 1/4 loop control delay .
60 Oz IS a satisfactory WEIGHT for these on the Oriental ving with two injuns .
Braced pushrod , 3/32 horn wire . 7 in engine - crank to fuse c/l .
Scale outline of fuse & nacelles , scaleish outline on Oriental size tailplane .
Seem much better without the undercarrage drag , and fly accurately .
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Ensure the WING stays straight while the dope cures . ;D a couple of bricks & a 3 in vice , should do it . LL~ LL~
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The Resurection ! .
Wind & Nacelles are 24 Oz. :P Shows WHERE some weight can be saved . (bearers, doublers etc need minimaliseing ) Fuse Assy is 9 1/2 Oz .
with empenage , just pinned on the wing here . Mods inc. rebates for inset tanks . New pushrods & Leadouts , recover & refinish .was 70+ Oz.
still flew the pattern well ( excellently ) with two Fp clones on 70 Ft circle, .018s . So maybe 10 Oz less , will fit tubes to accept a undecarrage >:(
as allways " wheres the wheels " ? . Its an AEROPLANE ! it doesnt NEED wheels ! . If it flys ok withim will give it a whirl in a comp.
Original was 38 Oz in 74 with OS 20s ! , so balsa ( not spuce ) spars & a few other considerations in the next one . A Beaufighter perhaps .
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OOPS .
63 Oz ready to GO .
Still , its 10 Oz LESS than previously . I may have to ballast it up to match its best . ;D LL~
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At last years Tucson 1/2a scale contest Jim Hoffman flew a tri motor where all three engines were feed from a single bladder so they stopped simultaneously.
Jim
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I just finished Gords Two Much twin! Aero Tigre 36s, electric retracts just like the original in 66. Still trimming... But so far it's been lots of fun! Flies fine and the trim is progressing nicely
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The only piece of twin engine advice I can give you is to always start the outboard engine first as things will alway end happier if the last one running is the inboard one.
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The outside engine takes 1/4 oz. more fuel per flight than the inside engine, per Gordan's instruction.
Why is that ?
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On my twins I make the in board tank larger than out board. I also start in board engine first when ready to fly. Before flight I set each engine with a tack individually at about the same RPM. I also now tell the stooge or helper all they do is hold the plane. I will take care of battery cable and starter. JUust don't le plane move when engine starts, even when I am also holding the plane. So far no problems with in board quiting first.
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(http://www.retroplane.net/forum/images/uploads/Jacquot/Caudron_C_670-1_847.jpg)
(http://www.retroplane.net/forum/images/uploads/Jacquot/Caudron_C_670-2_298.jpg)
(http://www.retroplane.net/forum/images/uploads/Jacquot/Caudron_C_670_-_3_188.jpg)
J'ai moi-même souvent volé seul en utilisant un système ficelle-goupilles. J'équipais mes modèles d'une roulette de queue en bois percée d'un trou au travers duquel passait la goupille reliée à la ficelle.
Jacquot
PS : Limousin a raison, attention à ne pas se prendre les pieds dans la ficelle...! C'est comme ça que j'ai planté mon Caudron C 670( plan encart du MRA) : Sad Sad
I was just saying the same thing , myself . :-X