We know you will just buy another...

We know you will just buy another...

Great, you've found me out. Hey, would you like to build two instead on one?

Sung

Sure throw in the second P-120 I need and get the kit coming!

I would think that a P-200 or an Olly would be the only way to go if it were to be a single.

I understand there will be more weight with a twin P-120 plane, but how much more are we talking compared to a Olympus? The motors themselves only weigh 1.2 lbs more than an Olympus. The P-200 burns 24 oz per min, the P-120s burn 12 oz per min so I don't see the need for more fuel. Am I missing something?

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Kenny, I agree. having seen two Hornets fly with engine combos of 160/pegasus I guarantee you'll wish you had the 200/Olly in there after the flight. there is just no comparison. the thrust / drag component on this airplane is fairly high and the 160/pegasus performs ok IMO just not gonna blow your skirt, so to speak. the 200/Olly provides a better margin of thrust vs drag but the airframe is the speed limit no matter what you install.

go with the twins (Coors so to speak) and you'll be cappin' it off after every flight. but...the 1.2lb heavier margin is not what should be your focus. thrust vs wt will be a non-issue. the engine install would be my limiting factor. the bypasses will sit directly over the landing gear area. which incidently is where all the door cylinders will reside. not to mention what type of framework will be required to mount the bypasses?? Better not dork the landing or you'll be driving the gear into the bypass etc etc. We all know it can be done so go for it but I would give Tom a shout and see what he has to say about it. I'll argue that the ease of maintenance and overall higher AUW of install will be your largest headaches.

200oz of fuel sounds great but how much is usable?? 100oz per engine of which 80oz is probably your usable fuel which leaves you with 20oz for go arounds etc. how long does 80oz last @ a moderate throttle setting? more importantly how much does 20 oz last when you're in the pattern with every other Tom/Richard and Harry trying to land? 200oz forward of the CG (granted it's not that far) makes me nervous but honestly I wouldn't carry less than 248oz. 100 in the pancake tanks, 20oz hoppers feeding a UAT per engine.

not trying to be a Holly Homewrecker (figured the "female dog-Betty" would get bleeped) but merely offering another viewpoint. It's a big project any way you slice it and two engines don't sound much different than one BIG one except at start up. Safety factor?? maybe but you better be ready with rudder trim. the plane doesnt' like yaw or X-winds.

seriously fellas good luck with the project it'll be fun to watch the progress

Buck

I gotta agree with Buck here.

I saw my first twin turbine powered F-18 at Florida Jets and I have to say I was disappointed. If I had not known it was a twin, I would not have been able to tell. It sounded like a single turbine. I was expecting a big difference like with twin D/Fs. You didn't have to be told it was a twin to tell it had 2 D/Fs in it.

Yep I have seen a few twins and to me it is impossible to tell they are twins from the sound.

PMFJI guys. I have a twin P-120 powered Y/A F-18 and have not flown it because the total weight wet is more than 55lb. I have gutted it out and in the process of converting it to a single turbine. I am contemplating purchasing “shiny� one or a P200 as a new single power plant.

Regards

Ben

I agree. They (twin turbines) don't sound any different to me. You can't tell it's a twin unless you ask. Then again, there's a big sound difference when one engine quits. In that moment, you'll probably still hear an egine going, and not just exclamations of "*****". Having seen the big twin climb out of a high-speed low pass downwind, make the circuit and land like grease on one DF engine, I'm pretty confident that one P-120 could get this bird home safely (even on full fuel) in the event of a flameout. That's what I'm thinking.....

Sung,

You're right. If that had been your F-15 at BITW that had the flameout, you'd probably have just limped home. I've got that flight, and it's subsequent landing, way out in the front of my mind as I'm looking at this big Hornet.

Buck,

Thanks for the thoughts on the hydros! I'm sure I'll be talking to you lots about this project. Question: Didn't you tell me that the Bug is well-behaved in single-engine situations due to it's close-to-center engine placement? Or am I thinking of something else? Thanks Bro!

I am telling you a twin has to be at 42 pounds dry to work under AMA rules.

The weight police will nail you in an instant.

yup, but it still requires a boot full of rudder to minimize the sideslip. remember this plane doesn't like yaw. I've got a wicked smart video of what I'm talking about.

in addition, despite all those ponies coming out the back certain configurations and fuel states (full bag, 4 pylons lots of drag etc) it won't hold altitude no matter how much you pull on the elevator until you "adjust gross weight" we don't have that luxury in R/C.

happy to help in any way I can. the hydros are a no brainer and despite leaking ever so slightly they are worth the effort.

you want to talk about scale presence? ever not see a puddle of fluid under a BUG?

c'ya

buck

matt's got a valid point. build it light to make weight and you're gonna rip the wings off. build it stout and you can kiss any AMA field adios. just a thought.

Matt,

Out of the box, the new kit is a lot lighter than the polyester one. I'm confident I'll be in compliance with whatever regs the AMA sets forth.

Buck,

What's your empty weight?

32.5lbs

Buck,


Really? Cool! I'm thinking that the second engine won't add another 10 pounds, even if I butcher the install. That's the best news I've heard so far!

well don't get too excited. the shell of the plane minus engine, bypass, servos, extensions, airlines, hydraulics, fuel tanks, tires and brakes was 17lbs.

I told bill I was going to make 30lbs easy because the engine only weighed 5lbs and how heavy could the servos be??? he laughed, thank goodness I didn't bet that case of Corona.

Little did I know at the time. 15.5lbs from one engine, 9 servos, 50' of airline, count up the extensions, fuel line etc etc I was suprised @ how fast it added up.

you might be able to make 40lbs dry with the extra engine. dunno

The F-4 is proof positive anything will fly with enough thrust.

c'ya

buck

So.....


Anybody wanna bet a case of Corona??

I just got off of work and had to do a little reading to catch up. There is a lot of different opinions and fact in the post already. That is what I was hoping there would be.

I think Matt is correct when he says that it will have to weigh less than 42 lbs dry. That leaves enough room for fuel that will allow a decient flight time.

I hear what Buck is saying about everything adding up. If his plane is 32.5 lbs with everything installed than the only added weight would be the difference in the weight of the second motor and some more fuel lines. The Olympus weighs 6.9 lbs with everything. The Jetcat website says 3.1 lbs, but does not mention if it is for everything. If it isn't for everything, I can't imagine the acc. weighing more than 1 lb per motor. That puts the P-120s around 1.3ish lbs heavier than the Oly. The extra fuel lines may add some but probably not much.

I believe the finished dry weight will be in the 36.5 - 40 pound range.

What about the difference in weight of the split vs. straight pipes, which is heavier?

How much does the inlet weigh?

Is there anything else that will change the dry weight between a single and a twin?

We are going to be flying a new 18 with a P200 in two weeks. I will let you know what the performance is compared to what been going on. I have not built a twin ver, but there are only a hand full out there, which should tell you something. In addition to the design and engineering headaches, fuel and weight. There are also 2 fuel pumps, two ECU's, Two ECU batteries, two complette sets of wireing and so on. The two engines is only one part of the equation.

The twin is nice, but I can't see any benefit in it.

I will take you up on this one. Build it with two P-120's, make the weight, fly and land it and you have 10 cases of Corona.

Kenny,

I'm inclined to agree with you on your suppositions. As far as design and engineering headaches go, I don't intend to design or engineer anything, I'm just gonna build the airplane relatively stock. I will add a few reinforcements here and there, along with a couple of shortcuts I learned on the last one, but otherwise I plan to build it stock. Part of the point is that I won't have to make the design mods to convert a twin to a single. The only unresolved question at this point is whether or not to bypass. Stock JetCat mounts can be used on the stock DF motor mounts easily if I don't try to incorporate a bypass system.

Dice,

Here are my perceived benifits to Twin V. Single:

Fewer construction mods
Better speed
2nd chance if a flameout occurs

Lets see, if the Olympus weighs over 6 lbs. complete and the P120s weigh say 3.6 lbs complete, then 2 P120s adds up to 7.2 lbs. So you pick up an extra 1.2 lbs from the engines, another 1 lb from the extra fuel tank and tubing. Don't forget addition bulkhead and support for the other engine, say another pound. You'll probably carry an entra 2 lbs of fuel, I think 40 oz., for a total of 240 oz of fuel. Thats 120 oz of fuel per engine, good for any 8 minute flight with reserve. So if you add it all up, you have an extra 5.2 lbs at take off and landings around 3.2 lbs more then Buck's F18 which weighs in at 32.5 lbs. I think some of the F18s out there probably weigh in around 35 or 36 lbs and still fly well. All that considered you have the safety of two engines instead of one and your added cost is that of the engine, fuel tank (a 40 oz Dubro for $15.00), and an extra pipe (according Shaun the two single pipe would be cheaper then the split). I think it's just a cost and time issue. Do you spend the extra time and money to make it a twin and have plane that will make it home should you lose an engine. I have had planes come home safely after a flame out and I have had planes that did not make back so gracefully after the engine quit.

Sung

Shaun,
Make sure you reinforce both main bulkheads (wing spar mounts)

Don't AMA regs require bypasses on a twin?

Gary,

I did. I added carbon plate doublers to those bulkeads, and the spar receivers bolt through the carbon plate. Do the AMA regs require bypasses for twins?

You're on!

I'm too lazy to look it up but I think Gary is correct regarding the bypasses. something about keeping the engines seperated or their vapors or something.

Shaun I forgot about the stock DF mounts but you're still putting the tires, brakes and associated airlines pretty close to the hot section of the motor.

I'm good for a case of Corona, @ 36lbs. as AD jr would say, "bring that weak *****"

besides how much more can one more 120 and the associated components weigh?? we'll find out in say 6 months??

c'ya

buck

Not sure if this means both motors have to be in separate bypasses or if they just have to be installed with separate tailpipes.