What are your current lap times, and line length? Are you taching the engine each flight to know what your ground RPM for take off is?  If the engine is happy, you can play with line length a bit.
  Type at you later,
   Dan McEntee

I may play with line length also but wondered about less pitch than the 9-4. Thanks

And the other question is whether you have one of the "good" LA .25s or not.  I bought a blue LA .25 at a swap meet and it will only turn up a maximum of 13,000 rpm  with an APC 9 x 4 and Brett Buck has posted that the "Good" LA .25s turn up to 14,000 rpm leaned out with an APC 9 x 4.  It would seem to me that if you lean out a "good" LA .25 and back off to the audible change in rpm you will probably still be at a much higher rpm than an FP .20 would turn the APC 9 x 4.  That may explain your fast lap times.

I bought a blue "not good" LA .25 at a swap meet and it will only turn up 13,000 rpm fully leaned.  I recently put the "not good" LA .25 with an APC 9 x4 on my Skyray 35 (32 ounces without fuel) and it had the same power and lap times as my FP .20 ABN because it turned the APC 9 x 4 at almost exactly the same rpms when backed off of full lean.   But the LA .25 used a little more fuel per flight, so I put my FP 20 back on.

Also, my Skyray 35 has a lap time of about 4.8 seconds on 60 foot lines (eyelet to eyelet).  I've got 75 flights on my Skyray and the plane likes lap times in the 4.7 to 4.9 second range.  Whenever I have not set the needle right and had 5.1 second laps (or slower) she doesn't fly as confidently and crisply.  This may not apply to all Skyray 35s but unless yours is really light don't expect her to fly well on 5.3 second laps or slower.

Joe Ed Pederson
Cuba, MO

I have a Skyray with a 25LA and 9-4 prop that I would like to slow down for stunt flying. Is trying a 9-3 prop likely to slow it down and still run well?

I would not bet that changing from a 4-pitch to a 3-pitch will slow down this airplane or any other.
Lower pitch makes higher RPM, higher power, higher fuel consumption, and often higher SPEED.
The 3-pitch could very easily be closer to true helical speed and make the plane faster.

Al Rabe figured it out.  You can have BOTH high power and low speed by making a plane with a fat wing and a fat body.

My 25LA is stock with a stock muffler Brett. I havent clocked the lap times but am hoping to slow it down. Lines have been 60 ft eyelet to eyelet. Maybe the lines should be longer.

Also, the engine is not blue. However I recently obtained a blue 25LA which doesn't seem to rev as high as the other one. Haven't had it on an airplane yet. 

Thanks to everyone.

NOT LA 25 , But Brett has us discourseing on our own observations . Hold On tight . Pay Attention . and Dont Let Go , as it were ( see below )

Used Al's Mk V Mustang airfoil on the MB3 . Sent him some drawings & pictures . his Comment " Your Airfoils seem a bit thin , for modern F2B " seemed amusing . As they were HIS Airfoils .

As for efficancy ? U Tube ' reveals ' nearly all flights ARE 5.0 to maybe 5.2 , IF the ' dubbing ' speeds correct . Get a watch on a few & check , if you doubt it .

The MB3 at TWO KILO , 71 once odd . ' well built ' as far as stiffness goes , and controls , at 50 in span & 530 ish area , wasnt good outside 5 / 5.1 on 60s if I recall right . .018 Laystrate 7 stand steel .
HOWEVER , in a Gale , it was like being bolted in a 440 Dodge on a wet skidpan with a stuck throttle . ( HENCE relateing the Info for Paul - If he went Electric He could put a Igor G thingo in it .  )
G 51 on a 10 x 6 black 3 blade , Tried a K&B 40 with the pump for a  10 x 4 three blade . As eventually the billowing air up past 20 windspeed , anything start kiteing . In Hill Country so theres rolling waves
in the wind flow & pressure .

Id back then , start the Vertical eight from inverted downward . a leap of faith required . The Aeroplane see4med to find its own consistant bottoms AT the right altitude . As you seemed to be feeding full up in , and hanging on and hopeing , I could never figure how it could do clean & accuratre squares . The second Day of flying just squares , with the K&B , about 25 windspeed , the jolts at the bottom corners were cracking
the underside wing sheeting . it was all built from F'ing stiff Wood . Some'd been ten years in the rafters of a tim roof . The wing sheeting .

So , LIFT , which hev seemed obsessed with , evidently was produced , under " Full deflection " , as he had evaluated .
Your Hair'd be near standing on end , and the impulse was to find a stiff drink , Particularly after it cut loose ovehead with the G 51 Hard Out . Due to no Yaw Counter . No moveable rudder hooked up .
Instant ' wheres my crash HELMET , and arm over head . But impulse to SPRINT was stronger . Despite these ( into Clover & across Top of Hourglass , took away the impulse to ' hammer ' the turn ,
it had to be ' flown ' . BUT windspped past 20 it was evident a rudder was required , as it was interfering with a accurate pattern , up there , then .

the General impression was say akin to being stuck in a Grand Priix car  . one of these ground effect things , and told to STEER , " we'll work the brakes & Throttle " No Proplems . Yea Right . alright for you to say .
Id found all the junk flown , the 18 knot ( estimated ) windspeed was where one had to start paying attention , as things began to happen quickly , and you stasrted looking at the 4.5 lap speed .
the WIND would kite it to that lapspeed , needle untouched .

The plane NEVER hit the deck . Tho the pilot hit the roof several times each flight . BUt the performance was , in general ( we already coverd rudder misshaps ) TO THE BOOK .

So , I figure one at 45 Oz with a Como 40  , on a 10 x 4 would do the trick . scale Planform . SOLID SHEET flaps & empenage .
I can see why He'd put FIVE LAYERS of Glass Cloth on the FLAPS , but im not sure it was necessary for attaching the canopy .  on his Big Saitio 72 etc Ships .
If He'd found the Como 51 in the 70s ( probly a 80's motor ? ) He woulda been fine . His stroked 51 had WEIRD timing , low rpm's .
He Did Not Find , or think he should , go to a low pitch , for wind flying .
Where Id strongly dissagree THERE . and Folow Bretts Lead .

As for PIPE's . Fine , great , governings brilliant .
But they dont fit in a semi scale wotsit easy , and dont grow on trees , for back yard experiments . Wot got a guy airbourne in NZ as soon as anyone with a plane way more current than over there .Bleedy farmers .
Solid Stiff Torsionally very stiff straight even grained 12 lb  wood flaps , or harder . bout that almost for tailplane & elevators  . If anyone doubts it , thats there problem . Al's Stuff isnt totally appaling ,
And Anything in a gust rolling 20 knot wind , is going to buffet & judder a bit , unless the airs pretty smooth ! . AND will be down close to 5.0 a lap , with the ' wind behind it ' ( as a GENERAL rather than aeronautical term )
As In It will be Kiteing , even if all the modernisms halt & control the kiteing , the forces they are dealing with , ARE the forces generted BY the ' Wind Force ' , the energy generted by the ' windage ' =
moving atmosphere transversing aeroplane .

SMOOTH Air is a differant game . Draw your own conclusions. BUt a ' scale planform ' built ridgid , can deal with those conditions SMOOTHLY .
YAW on a Diheadral wing , if acute , presents the TOP of one wing , and the UNDERSIDE of the other , to the airflow . and is not advised .
Measures to counter yaw , might be considered adviseable .
Or take a helmet , and youll need to run foking quick , to get the lines tight again .
AND if you ' catch ' it upwind , inverted , and low airspeed . IF you Dont Keep the Nose Low , it'll blow in up and across , and you gunna hafta leap like a kangaroo upwind to catch it as its headed for the other side .
good Exercise ,
but if inept there FIT A MOVING RUDDER . Hammering the Turns , the restraint translates the force into yaw . if brief & positionings favourable , its manadgeable .  If conter productive forces combine cumulative ,
Oh Sheet .


Run Forrest , Run . 

Scuse tha splenink .
Horses for courses . Of course , every Jockey has the Best Horse . But . Differant configurations have their strenghts and weaknesses . FSR 25 , whick IS a LA 25 , Almost , id Down from a 9 1/2 - 6 ,
as it was kiteing ,
and try a 9 x 6 black tornado .
Sometimes it worked better than others. When the Wind was over 18 knots .
Latter i found one of the two 9 x 6's was a 9 x 4 .
I wonder why oneoffem worked better .
Thats onna 47 Oz nobler size Thing .
The FSR is a ball race with the SAME TO END as a FP 25 , which is like a FP 25 . The BLACK Tornado 9 x 4 will haul ass . Used 55 ft of .018 , so gotta bout 58 Foot . Like wot Bob Gieske was once ,
HE worked IN the WIND . The Ball race ones got a bit more reserve , under load it can keep coming on . I had a 7.5 intake & a 3.5 ? odd spraybar ( Taipan ) Tank Inboard of intake . Worked Good.
Only hit the deck one or two dozen times in ten gallons . 30 knot winds it was a hanfull , and would STOP sometimes , in gusts , overhead . But stay going .    No room for innatention in gales .

My 25LA is stock with a stock muffler Brett. I havent clocked the lap times but am hoping to slow it down. Lines have been 60 ft eyelet to eyelet. Maybe the lines should be longer.

Also, the engine is not blue. However I recently obtained a blue 25LA which doesn't seem to rev as high as the other one. Haven't had it on an airplane yet. 

Thanks to everyone.

John, I would just try out an APC 9-3 for a couple of flights to test out the model's performance. If not to your liking in the air, just go back to the 9-4.

On my Flight Streak w/ stock OS 25LA, I prefer the APC 9-3 vs a 9-4. On other models w/ 25LA, the 9-4 works best. It may or may not be optimum for your Skyray. But easy to test out in the air.

Also, I have three stock 25LA's (w/ stock tube muffler) and all run pretty much the same. If you experience different performance, 'maybe' it just has to do to with time on the particular engine. I find the engines run better and settle in as time on them goes up.

Thanks Collin and Dan. I have only flown this airplane alone with a stooge but I will need to get a lap time when I have someone with me. I shouldnt guess but my hunch is 4.0.

OK Colin. I will post here if I find a 9-3 and try it. I have to say that it does run great on the 9-4.

Steve my lines are .015 and 60ft eyelet to eyelet.

You should try a 10 x 4 and use 5% nitro   fuel

You should try a 10 x 4 and use 5% nitro   fuel

   I was boing to buck the trend and suggest the 10-4 also. It's what I use for the most part on LA.25 powered stunt models. Takeoff ROM is in the 9800 to 10200 range depending on the model. I find the wider blade makes for better line tension. Sometimes I but them down one quarter of an inch at a time to get the run I want. Just cut it off square and rebalance.
  Type at you later,
   Dan McEntee

Thanks for your question Brett. I am trying to get it to a pace that is more comfortable when flying the AMA pattern. As soon as i have someone with me when flying I will get a lap time and post it.

Happy to answer your question Brett. I can fly each maneuver most of which would be recognizable, none of which would score well. I flew in beginner stunt at the Nats in1990 and that was my first and last contest. Sporadic flying since then. Not much handle time. Its always been a passion of mine. I retired 12/31/22 and now have time to fly on my own property here in Michigan. I'm like a 67 yr old kid in a candy shop. I have purchased some airplanes that I can fly now and am learning to build. I'm also teaching and flying with my 8 yr old grandson. Learning to build through repairing his crashes. We plan to be at the Nats. The Skyray was purchased and I'm trying to dial it in for my flying now and hopefully for my grandson when he is ready. It weighs 36 oz. I'm working on a Nobler ARF but turned it into a marathon because I am modifying it to replace the bellcrank with a suspended bellcrank, add adjustable lead outs and adjustable controls along with fortifying the engine/tank compartment. I suffer from paralysis by analysis. I really appreciate the information and guidance from you and others with tremendous experience and expertise.
Sorry for rambling.   

Thanks for the valuable information and the video Brett. I guess I need to dismiss the idea of my Skyray performing well at 5 second + laps. It's pretty cool that these "little" engines can drive a 35 size stunter well in stock mode. You talked about the 20FP. Does a stock 40FP work best with this low pitch high RPM approach? Assuming the 40FP is good on an airplane larger than the Skyray?     

   Yes, the 40FP can run similarly, but it is *far too much* power for most "35-sized" airplanes. In fact, people trying to use 40FPs on airplanes like Twisters, Coyotes, etc, is what led me to try the 20. The speed of these airplanes were way too fast, and, when I calculated the difference in the power required compared the power I was getting (the cube of the ratio of the speeds), I found that I need about half the power of a 40FP. So I got one that was more-or-less the same, but half the size - a 20FP. Then I tested a whole bunch of similar engines available at the time, ALL of them were easier to handle and more reliable, and with the right prop, could be made to work better than a Fox/McCoy 35. As luck would have it, the 20FP was the best of the bunch (better than the contemporary 25LA {more power}) and the 25FP (which has more power but was less stable with the available props). But even the lowly Brat 28 was better than either a 40FP or a Fox/McCoy on these types of airplanes.    Only much later, a quarter of a century later, did we get a "new" 25LA, it is better than the 20FP, with a little more power and just as stable.

  Note that the "excess speed" from the 40FP in these situation is more-or-less a matter of the engine running the way it was always intended. But people who don't "get it" interpret this as the dreaded "runaway" and then start grinding on it and putting in extra head gaskets to try to "tame" it to run like a traditional stunt engine - by which they mean a stunt engine from the 50s-60s. 4-2 break "chug mode" running 8500 RPM with a 6" pitch prop hasn't been a competitive system since about 1988, which is a lot longer than the "traditional" era of Fox 35s.

    I have never attempted to find the right sized airplane for the 40FP (or the 40LA, either) but I did at one time try a 35FP (original iron-liner version) on my 1985-style ST46 airplane, and while it ran very differently than an ST46, the overall performance was about as good as the average ST46, and it was a A LOT more reliable/predictable. Now, for this size airplane (630 square inches and upper 40's-low 50 ounces), if I didn't have a 40VF, I would use a 46LA for a tremendous performance and reliablity improvement over an ST46.

   My guess ,without any other information, is that your engine/prop is running as it probably needs to run and that you are going to start running out of corner if you try to slow it down very much. But, with a 9-3 running at near full-tilt, you have a lot better chance because the reason it will hold the speed better in the corners.   I *have* experimented with 9-4 APC depitched to about 3.75, that was a useful change for my 30 ounce all-balsa model. But you have to have pitch gauge and the experience of depitching propellors.

    Brett

I have an APC 9-3 on my Flite Streak w/ 25LA. Interesting that APC markets it as a 'combat' prop. The APC 9-4 as a 'sport' prop. The APC 9-3 airfoil shape is much different compared to the 9-4. It did slow down my Streak. Not sure how it might perform on a Skyray 35.

Today I tried out an APC 9-3 (combat) prop on my Skyray 35 with stock OS 25 LA. I was previously running an APC 9-4 sport prop.

A few notes:

I was running the 9-4 sport at around 12,500 rpm and 60' lines. Model was flying a little fast for me, but still flew well.

Then I ran the APC 9-3 combat at around 13,000 rpm. I did notice the model was fling a bit slower. But still plenty of thrust for maneuvers while being slowed down a bit. Model flew better to my liking.

Unfortunately, I did not take lap times. But it was easy to tell that the lap was a little slower.

I had the same basic experience with my Flight Streak. The APC 9-3 combat prop is well matched for an OS 25 LA. 

     Was it cold outside? Air temp and density come in to play at lower temps. Make note of all you data and save it and repeat the test when it's solidly over 75 degrees and see what you get. This is another reason why you need a prop box with a decent selection to choose from.And you gotta test fly them to know what they do and don't do.
  Type at you later,
   Dan McEntee

  I found the APC 9.625 x 3.75N to be the best prop for a LA 25 in stunt after lots of testing.
Al