Ron McGrath

My Feedback: (10)

I have been watching some of the posts on the yellow p38 and was thinking of running 2 os 120 sp it has the same HP as your g 38 and I was wondering what rpm they turned the 18x10 props at I would think that a lighter pitch smaller diameter prop might be better even as small as a 16x8 this would give you more RPM that might mean more speed for example if you increased RPM by 20%you would maintain the same speed and have better vertical performance if you turned 7000 RPM on a 18x10 and 8400 on a 16x8 the plane would be just as fast with a better climb out rate I was also wondering what the weight of the plane was I would also be interested in the airspeed on any of the yellow p38's with the engine and prop size and RPM I am not sure if the engines that I am thinking of using are good enough the airplane that had the 3w 24's turned 6900 RPM and had a pitch of 10 If you do the math I would not think that the airspeed on that combination would be much over 70 mph the max RPM on that engine is 8400Rpm so I would try a smaller diameter same pitch prop a 900 Rpm increase in RPM could pick up almost 8 to 10 mph in the air the G38 with the 20x10 at 5300 RPM would not go much over 50 MPH so that is why you did not get off the ground I am thinking of 16x 8 that should be in the low 70 mph range or 15x10 s that should be in the 80 MPH range this has always been one of my favorote airplanes and I am a 4 cycle only kind of guy and want to find a good size P38 for my engines (plus it would be cool because they are supercharged just like the real ones)

eulgeneral

I got new exhausts and now I turn the 18x10 average 7000 RPM. It'ss really better and now this P38 flies like a P38 !!! More power in vertical flight would be better but it's already a progress. I will have new exhausts in seferal weeks to increase RPM's (perhaps 500-1000 rpm) so it will be wonderfull.

This plane is wonderfull in flight !!!

Another question: how did you install (and wich) exhausts and tanks in the Yellow P38? I have some difficulties to find the good installation.

Thanks.

Yannick

kram

My Feedback: (7)

My 3W24's are now fully broken-in and turn 18 X 10 APC's 6,900-7,200 rpm, depending on altitude and temp and what humor they're in. I've always said they have 90% the power of a G-38, but they may be closer than that. They certainly are as LOUD as G-38's!

I run them inverted with Pitts style mufflers, but I would never be happy with inverted glow engines on a P-38, altho some guys are. Bisson makes really nice Pitts for glow engines.

My Yellow weighs 31 lbs empty, with 13 oz of lead in the nose.

I agree, the fuel tank placement is difficult. Don't do what I did and struggle in the closed space! I used some techniques like building a ship in a bottle. Cut a big hatch and hinge it. It'll look good, if carefully done, and save you a lot of hassle. I plan on doing that this winter when I re-plumb my tanks.

I have no experience with 1.20's. 15" or 16" props are gonna look awfully small on the Yellow....I'm not sure they would generate the amount of thrust necessary to pull it, even at acceptable rpm. RC Report has engine review for the 3W24 where they list static thrust with different props. I'd look through their compilation book and see if they did the 1.20 and how it compares. The 18 X 10's at 7,000 are good power for the Yellow, but I wouldn't want much less. May I suggest you see how much you can get out of the 1.20's with 18 X 10's ?

On "bad engine" days while breaking in my 3W24's, I flew the Yellow with as little as 5,400 rpm on the 18 X 10's, but take off and climb out were NOT FUN !!

All I can find is a 1987 review for a non-Surpass 1.20 that lists thrust on a 16 X 8 prop as 156oz @ 7,300 rpm. The 1999 review of the 3W24 gives a thrust of 223oz @ 6,500 rpm (not broken-in). So, unless the modern 1.20's are a HUGELY better engine, I would say that they are not in the same class as G-38's or 3W24's, so should not be used for the Yellow.

mt

Ron McGrath

My Feedback: (10)

Why do they say you have to use 18x10 props ????? I have a Cap 232 that weighs 12.5 lbs and will hover and then pull out and go straight up with a OS 120 supercharged I would think that 2 of the same engines on a 30 lb airplane would be enough (the 120s weigh over 30 oz less each) that is about 4 pounds for 2 of them that might mean a weight of 27 pounds with the 120 supercharged I think 13.5 lbs per engine would be great!!! I would like to see how a yellow p38 with the g38 would fly with 16x8 graupner or apc props I think that it would fly better than the g38 with 18x10 props

Ta-152

Myvwtruck, I'm using two Ys 91's in a 94 inch 38, 21lbs. The 91's swing 14x10 apcs very well, about 8900-9100 rpms. The plane flies with authority and really scale at half throttle. I would think that Ys140's would be a good combo for the Yellow 38. I believe they will swing 16-17" props pretty good. You would most likely have to keep the weight to 25-26 lbs. Did I mention that two Four strokes sound much better than two, two strokes. JMHO. JG

Ron McGrath

My Feedback: (10)

I ordered a APC 15x11 to see what it might turn at on the 120 I will let u know

kram-RCU

My instincts tell me 1.20's will not fly this plane.

I did consider 1.80's when I was building it, but they were newly-out and un-reviewed then.

Has anybody asked Yellow Aircraft? He's never been shy to offer opinions to me.



mt

Ron McGrath

My Feedback: (10)

ta-152 what kit is your p38 If it is as light as you say It might be a better choice for me to use with my 120's I could tell that I would have to run more pitch than a 16x8 to get to the same speed as your 14x10 on your 91 but a 15 or 16x10 might work you say that it flies scale at 1/2 throttle could you tell me what it tacks on the ground at that setting ? I might get a 18x10 just too see as far as the saito 180 my 120 has about the same power as the 1.80 saito and more reliable

Ta-152

Myvwtruck, The 38 is my own design, I have had three ships built with one still flying in Florida along with the one I'm flying. I did plan to kit the plane but have put it to the side for now, time and business. I designed this ship for OS 91's and Ys 91's not to say that 60-90 two strokes wouldn't work. 120's would be much too much for this one. I opted for 4 strokes because,I think they are a bit more reliable than the two strokes. If you are going to fully dress out a Yellow AC you most likely not be able to use 140's. I think that the YS 140's with their power to weight and throttle response would out perform the 150's and 180's jmho. If you could get the Yellow in at 25 26 lbs I don't think that you would have a problem with 140's. Keep in mind that you'll be inverting both engines and you want as much reliability as you can get. YS's don't mind running upside down. I think that 120's are marginal for anything much above 23-24 lbs. Just some thoughts JG

Ron McGrath

My Feedback: (10)

I do not know if you are familiar with 120sp they are the supercharged version of the OS 120 I have been running one In a hanger nine cap 232 and I love it very reliable I have it almost inverted slightly to the left side. so that the exhaust valve is at the bottom. I am not sure of the output of the ys 140 but my 120,s are 2.5 hp and will swing a 16x8 at 9400 RPM and take the cap at 12.5 lbs straight up so I think that 25 lbs for the p38 would be great but up to 29 or 30 would be OK It seams that with 4 lbs of weight savings in engines that to weigh under 30 lbs should be easy to achieve if everything that can be moved forward is I would think that the fuel tank could be in the center section on the cg because with the pumps on the 120s it would not be a problem and one tank would mean there would be less of a chance of engine out failure due to one engine running out of fuel before the other.

clugo4

I have a Yellow AT-6 and I need to know the AT-6 CG. does anyone knows?. Also can you help me on choosing a servo for the rudder and elevator. how many oz of torque do I need. I'm thinking of 2 JR 811 (66oz) for the rudder and 1 1/4 scale 3302 Futaba?
Thanks

DCGayhart

My Feedback: (22)

I pulled my Yellow P-38 down from storage last month, been ten years! I never really liked the Moki 135's I had used, to messy. I replace them with DLE 35 RA's with twin sync .

I replaced all the old Futaba radio gear with coreless MKS digital HV servos and a Jeti DS 16 radio with Central Box 200 and Cortex Pro.

I had the CG marked but wanted to double check the location. It's about 3.5" back from the leading edge outside the engine nacelles. I don't have the plans but the pictures at the beginning of the thread match my location.