trumpetjet

My Feedback: (12)

Has anyone built the profile p 38 with two four stroke engines? The manual only talks about two strokes. I am thinking of putting two Saito .30s in one. Any thoughts?

Nathan

William Robison

My Feedback: (3)

Nathan:

In another thread a fellow is discussing this exact engine selection for the plane.

Bill.

Robby

My Feedback: (18)

Bill,,
Might wish to provide the URL of the thread when referencing another thread..

Robby


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William Robison

My Feedback: (3)

Robby:

I'm lazy, OK? I figured Nathan could do the search for himself.

Turns out the reference is for Saito FA-40 engines, but the FA-30 engines should do very well also.

Postigs on the Saitos start [link=http://www.rcuniverse.com/forum/m_895473/mpage_9/key_/tm.htm]here[/link].

Bill.

trumpetjet

My Feedback: (12)

Thanks, I did find the other post. I was wondering about specific performance issues with these engines. Will it fly with one out? Will the RPMs match easily? How long will they run with 4oz? and so on...

The other thread does not address these issues.

Nathan

William Robison

My Feedback: (3)

Nathan:

Twins are unlike singles, in that if overpowered they can be much harder to fly in an emergency situation then any other type. Even a four engined plane can be a lot easier with one dead than a twin with only one running. And the more powerful the twin is, the worse this characteristic becomes. This is not just because of the tendency to firewall the throttle on the remaining engine, just letting your airspeed decay can kill your plane. The more power, the higher speed necessary to maintain control on a single engine at full power. Vmc (Velocity, minimum, control) is the correct term for this.

So, for a first twin, less power is better than more.

Your Saito FA-30 engines should fly the plane very well, and while not have sparkling performance, they will be more than adequate for scale flight. And safe flight.

Absolute synchronization of the engines is nice, but not necessary. Within a couple hundred rpm is fine, get your twinsane experience before you worry too much about it, get the linkages as close as you can and fly. Worry about the finer points after you have a few hours stick time on twins.

Run time should be at least eight minutes at high throttle with the 30 engines and four ounces fuel, up to twelve or more with lower throttle settings. Don't worry about it, you'll find even five minutes seems like an eternity on your first few flights.

Hope you enjoy it, and welcome to the twinsane asylum.

Bill.

trumpetjet

My Feedback: (12)

Thank you for the info William,

I usually fly jets. I just want something cool that I can bring to the field, fuel up and fly without the worry of crashing a $3000 model.

I gather from what I have read in this forum that if one goes out you shut down the other and dead stick it (at least in the case of the P 38). I was thinking of using an onboard glow mixed into the throttle so that at lower RPMs the glow always on, this combined with the impeccable reliability of Saito engines should keep both motors humming. Ill definately be around to ask more questions! Thanks again.

Nathan

Ed_Moorman

My Feedback: (1)

When it comes to twins and engine out, I think configuration has a lot to do with it. The twin engines on the wing and a single tail would seem to be the worst configuration. Obviously, a pusher-tractor configuration would be the best with regard to yaw. For separate thrust lines, I would thing the twin fuselage set-up would be the best. It has a tail behind each engine for better rudder control and the fuselage also helps straighten out the air flow.

About 15 years ago I had a simple twin, an Airplane Factory Kombat Twin. You remember, the Airmodillo guys. Square metal tube fuselages and Coroplast wings. Their twin was specified for 2 .25 engines and I didn't have a .25. I did have 2 Fox .50s with tuned pipes. These were the only matching engines I had and I wasn't going to buy new engines for that plane so in went the Foxes. I had to bend the engine mount area to fit them in and the plane came out fairly nose heavy, as you would imagine.

It did fly. The tails fluttered like mad until I put a wire between them. It also flew well on 1 engine at full power. With the piped .50s, 1 being out didn't seem to change the airspeed at all. I did acro of all types with 1-engine out. Rolls both directions, point rolls, big loops, but the best was the spins. Let me tell you, a twin with 1 engine out will flat spin and really wrap up.

Here's a photo, circa 1992. I finally bounced it and bent the tubes up too much to fly.

lear31A

My Feedback: (123)

All of this is good info, however, you will find that if you have an engine failure, you will do what it takes to keep the airplane level from instinct. If it starts rolling, you will naturally add opposite aileron, if thats not enough you will begin to feed in rudder. At the end of the day, you will have done all the right things without even realizing it and stressing about how much or in what order these things should happen. Alot of twin guys,especially, the newer ones will tell you that they are hard to fly etc.etc. Now the disclaimer: All of this is assuming that you are an avid and current pilot. Just put your engines on the airplane, go to the field,crank one up and tune it,leave it running and crank the other, now tune that engine by ear, when the props sound close to one, you have it within a couple hundred RPM, go flying. The profile P-38 lands fast but is a great airplane.

pault

My Feedback: (34)

nathan......i m just about finished with mine using saito 40s...i keep you posted how it flies....thanks....pault

Jimmy Bananas

My Feedback: (13)

Trumpetjet:

Glad you brought up the subject..I intend to build one this winter and put 2- Magnum 30- 4 strokes in it..Engines are well broken in..should have some fun with it next spring...Beleive it'll be Ok,until one engine goes out, then it's 'O S&$# Time"....just gotta know what engine is out...then throttle back and land it safely...Easier said then done, as they say....

trumpetjet

My Feedback: (12)

Sweet...

Keep me posted guys. I think the Saito 30s would be a little more powerful than the Magnums (and way more expensive I guess) I just want to get scale flight out of mine plus the sound of 4 strokes can't be beat! I can only imagine what two of them sound like! As a musician the sound of my planes is almost as important to me as the way they fly! Go figure...

Nathan

rc74

My Feedback: (6)

Did you end up building you p38 using the magnum 30s. I am starting back on mine using the same engine. If so how did you hook up the throttles since there on the top.

SIMCO

My Feedback: (33)

I have flown mine on one and zero running(os25's). The trick with this a/c is land a little fast. The elevator poops out and drops like a stone. Nose high and power will also save you from rebuilding the nose structure. Double the crappy ply mount for Nose gear. Sounds like its happened before!!! 4:30 total time flying with tip tanks installed full throttle.

MinnFlyer

My Feedback: (4)

Something that might be worth mentioning:

The one I built had 2 - OS .25 LA engines. At that, it needed a good amount of tail weight - so much so that the wing loading was really getting high.

I think having 2 4-strokes might really turn that thing into a Lead Sled

laker500

My Feedback: (2)

I just started this kit this weekend. It's been on the shelf for over two years, time to get it done. I have two Magnum 30 four strokes I was intending to use. This post was fairly old and it sounds like several other's have had the same idea in the past. Do any of you guys have anything new to add? If it is going to be way over in the weight department I will use two strokes instead. I am intending to have a nice flying sport model when I am done. The mention of a "lead sled" really has me thinking twice about the four strokes.

jrf

My Feedback: (551)

The OS 25LA weighs 9.5 ounces. The OS 25FX weights 10.8 ounces. The Magnum 30FS weighs 9.6 ounces.

You will find that most of todays 4-strokes are lighter than their 2 stroke equivalents if you include the mufflers.

Jim

laker500

My Feedback: (2)

Hey Jim,
Thanls for the info. After reading it my memory joged and I believe that I looked into that as I made the FS decision a couple years ago. Do you or anyone else have any input on the power output of the Magnum FS vs. say a 25 FX? I know two strokes generally turn higer rev's, hence more HP but less torque. In your opinion would the 30FS perform about the same as the two stroke?

jrf

My Feedback: (551)

Somewhere in between the 25LA and the 25FX. Closer to the LA. But you could run three blade props on the 30s and still get good performance.

Jim