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Author Topic: 25LA prop  (Read 6977 times)

Offline John Skukalek

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25LA prop
« on: June 04, 2023, 12:59:49 PM »
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?

Online Dan McEntee

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Re: 25LA prop
« Reply #1 on: June 04, 2023, 01:05:12 PM »
  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.
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Offline Colin McRae

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Re: 25LA prop
« Reply #2 on: June 04, 2023, 04:54:03 PM »
I would just try the 9-3 and keep the rpm up on the 25 LA. Adjust to peak rpm (lean) and then open the needle maybe 20-30 deg. You will notice the rpm decrease a little. Just like the OS owner's manual says.

I have a Flite Streak w/ OS 25LA (stock) that I fly on 60' lines. I was originally running an APC 9-4 sport prop and it too was flying fast. The Streak is a very light model. I tried an APC 9-3 (labeled a combat prop by APC) and it flew much better. Slower but still plenty of power. You can always go back to the 9-4 if needed.

The OS 25 LA likes to spin fast for best performance. Probably around 12,500 rpm or so.

I am also currently building a Skyray 35. I too have an OS 25LA planned.
« Last Edit: June 04, 2023, 05:30:36 PM by Colin McRae »

Offline John Skukalek

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Re: 25LA prop
« Reply #3 on: June 04, 2023, 07:29:08 PM »
I may play with line length also but wondered about less pitch than the 9-4. Thanks

Online Brett Buck

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Re: 25LA prop
« Reply #4 on: June 04, 2023, 07:31:26 PM »
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?

   How fast is it going? And is the engine entirely stock, including the muffler?

    Brett

Offline Joe Ed Pederson

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Re: 25LA prop
« Reply #5 on: June 04, 2023, 08:03:09 PM »
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


Online Brett Buck

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Re: 25LA prop
« Reply #6 on: June 04, 2023, 10:53:09 PM »
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.

  That's about what mine does, too. The nice thing is that when it is set properly on a *stock* engine with all the original parts, its fast in terms of lap times but so predictable it seems like you have forever in the maneuvers. I have flown piped airplanes at 5.9-6.0 second laps that felt "rushed" and others that were flying 5.0 that felt like you had forever (although that is A LOT of pull on a 4-lb airplane). It's all about power delivery in the maneuvers, the more predictable and smooth, the easier it gets to fly.

      Brett

Offline Paul Smith

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Re: 25LA prop
« Reply #7 on: June 05, 2023, 11:49:17 AM »
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.
Paul Smith

Online Brett Buck

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Re: 25LA prop
« Reply #8 on: June 05, 2023, 03:52:06 PM »
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.

  Your statement is true under certain circumstances, some which are probably not true here. The intent is to take advantage of the descending HP curve as the RPM goes up, so, 25% faster will have less HP than it currently does. Additionally you are probably right about the true helical speed, that is what we want, because "true helical speed" (for those not following, how fast it would go a speed of "pitch x rpm") also has an efficiency of 0% - that is, produces no thrust but uses copious amounts of shaft HP. That is in fact the key to low-pitch, high RPM setups, the prop is run inefficiently as possible in level flight, so running closer to the "true helical speed" is likely less efficient, which will also obviate the speed in level flight.

    If you run on the upslope of the HP curve, *the system will be unstable*, period. It may well do that on the ground but the premise is to get it past the peak in the air. That is why you want less pitch and how these systems (and piped systems, where you can adjust where the peak falls in terms of RPM) work

  Mitigating factors include the fact that the 9-3 may or may not have less actual pitch than the 9-4.

   I note that the system (Skyray/9-4 APC/25LA) as described *is not an experiment*, we know exactly what it needs to work from very extensive testing by myself and other competent stunt fliers. That's why I think there is something else amiss or unstated, it goes about 4.6-4.8 second with a stock engine on appropriate lines (.015x60-62 feet) which is what you want for stunt.




Quote
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.


   Al Rabe figured it out when you are using a ST46, his approach has long been obsolete. He did not understand, even a little bit, how how a conventional system works. I know because I spent hours on the phone over the years trying to explain it to him. He understood all the parts of it, but didn't (or refused to..) put it all together.

  And, in any case,  the typical 46VF setup from, say, the 1995 NATs, flew much more slowly in many more conditions than anything Al ever built, wing thickness notwithstanding. And, his wing is nothing to write home about, thickness-wise, hardly any more than an Impact airfoil, and definitely much thinner than Trivial Pursuit, Infinity, or even a Patternmaster. Note that at least I *did* get the basic idea from Al's Sea Fury article, so did everyone else, and you don't see too many Xeroxed Nobler airfoils from the late 4-2 break area.

   Brett


Offline John Skukalek

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Re: 25LA prop
« Reply #9 on: June 05, 2023, 05:16:50 PM »
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.

Offline Air Ministry .

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Re: 25LA prop
« Reply #10 on: June 05, 2023, 09:01:38 PM »
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 .  S?P )
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 . :P

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 .  S?P

It is due to them , and their kind in the other services , that Britain today is not a mere slave market in a Nazi empire .That was the Plan.
Never forget it.

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Re: 25LA prop
« Reply #11 on: June 05, 2023, 09:38:16 PM »
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 .  S?P )
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 . :P

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 .  S?P 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 .  ;D

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 .  LL~  ;D No room for innatention in gales .
It is due to them , and their kind in the other services , that Britain today is not a mere slave market in a Nazi empire .That was the Plan.
Never forget it.

Artur T Harris .

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Re: 25LA prop
« Reply #12 on: June 05, 2023, 09:40:38 PM »
They loosen up a bit with use , and get ' more comfortable '  steadyer pottering about . just get some time on it , so youve a bit of  a field of observation . And avoid trees and concrette cricket pitches . Planting It .  :o
It is due to them , and their kind in the other services , that Britain today is not a mere slave market in a Nazi empire .That was the Plan.
Never forget it.

Artur T Harris .

Offline Colin McRae

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Re: 25LA prop
« Reply #13 on: June 06, 2023, 08:07:31 AM »
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.

Online Dan McEntee

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Re: 25LA prop
« Reply #14 on: June 06, 2023, 09:14:02 AM »
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.

   We need to know what the lap times are. You say you want to slow it down for doing stunts, but we have nothing for a reference. Most airplanes flying on 60 foot lines need to fly close to 5 second lap time, maybe even 5.5 seconds if everything is in trim. You must have a certain speed for enough centrifugal force to keep the lines tight to maintain control.  You may already be at that speed.. Your stop watch will be your best friend throughout this process, so it's important to learn how to time your laps. A tachometer will be handy also. Slowing down to anything approaching 6 seconds is not desirable for anything other than flying around in level flight.
  Type at you later,
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Offline John Skukalek

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Re: 25LA prop
« Reply #15 on: June 06, 2023, 10:11:37 AM »
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.

Offline Colin McRae

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Re: 25LA prop
« Reply #16 on: June 06, 2023, 10:47:48 AM »
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 shouldn't guess but my hunch is 4.0.

I am really interested in this post as I am currently building a Skyray 35 w/ same OS 25LA planned. I plan to initially use an APC 9-4 sport prop and fly on 60' lines.

If you do try out the APC 9-3 as a test, your experience would be interesting information.

Offline John Skukalek

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Re: 25LA prop
« Reply #17 on: June 06, 2023, 11:41:06 AM »
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.

Offline Steve Helmick

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Re: 25LA prop
« Reply #18 on: June 06, 2023, 01:08:19 PM »
Ordering the more obscure sizes of APC props is easy if you go directly to the factory, and service is excellent.

I'd be interested in your line size and length. Some will go on about .012" lines stretching, and .015" lines being much better, but IMO we're not talking about enough line tension to make that a valid concern. Line weight and bow is more of a problem, I think.

With the OS .25LA, the APC 9-4 worked, as did a Graupner 9-4...about the same, actually.  H^^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline John Skukalek

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Re: 25LA prop
« Reply #19 on: June 06, 2023, 06:17:20 PM »
Steve my lines are .015 and 60ft eyelet to eyelet.

Offline john e. holliday

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Re: 25LA prop
« Reply #20 on: June 06, 2023, 06:24:47 PM »
I have read through this again and I'm going to post.  Is the plane happy at the speed you are flying?  If you fly more you will get used to the speed if it is consistant.  I let the plane do the talking ,not the stop watch. D>K
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Offline RandySmith

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Re: 25LA prop
« Reply #21 on: June 07, 2023, 11:29:20 AM »
You should try a 10 x 4 and use 5% nitro   fuel

Offline John Skukalek

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Re: 25LA prop
« Reply #22 on: June 07, 2023, 02:07:34 PM »
I was about to ask about a 10-4 Randy. Thanks.

Online Dan McEntee

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Re: 25LA prop
« Reply #23 on: June 07, 2023, 03:49:32 PM »
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.
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Online Brett Buck

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Re: 25LA prop
« Reply #24 on: June 07, 2023, 04:34:13 PM »
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.

   I can't really tell if it is otherwise right without lap times, but, again, try a 9-3, that should have a rather drastic effect on the speed. It may not have much line tension if you try to slow it down too much. You can certainly try longer lines, but the airplane will not like full-length lines even though you have enough power.

    Just out of curiosity, what makes you think it is too fast, and what are you trying to do when you "get behind" it?  If you are just trying to fly level, it's pretty easy to slow it down since you don't have to consider what happens in the maneuvers.

       Brett

Offline John Skukalek

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Re: 25LA prop
« Reply #25 on: June 07, 2023, 05:16:44 PM »
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.

Online Brett Buck

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Re: 25LA prop
« Reply #26 on: June 07, 2023, 07:52:37 PM »
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.

   Forgive my next question - can you do the entire pattern, some fraction, etc? I am not trying to cast aspersions on your piloting, I just don't know, and allows us to adjust their advice accordingly.

   Brett

Offline John Skukalek

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Re: 25LA prop
« Reply #27 on: June 07, 2023, 08:47:55 PM »
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.   

Online Brett Buck

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Re: 25LA prop
« Reply #28 on: June 07, 2023, 10:53:07 PM »
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.   


  Not at all, that is very good! So, you are more or less where I was with the stock model, also about 36 ounces with a 20FP (and maybe 27 with a Fox 35)*. Once mine got crashed, all the plywood parts in the wing just got pulverized. I rebuilt it with full balsa ribs at each station and it ended up at 30 ounces. Surprisingly, with the 20FP, that made *nearly no difference* in the performanc, but was much more durable. That was 1995 or so, the airplane is still in use (by someone else) after about 40-50 crashes of varying severity, and still flies very well.

    I would, however, suggest that the speed is going to be in the 4.6-4.8 second/lap range on 60 foot lines to get decent performance. At 36 ounces, it will be on the edge as far as wing loading goes in thin air, and you need all the speed you can get. If the engine is running properly ,this will not be a problem because the power delivery is so good that it will seem very controllable in the maneuvers, in particular, I find it does square maneuvers very easily, and  can nail square 8s with it with no practice for years. It does less good in the "easy" maneuvers, like round loops, because the lack of flaps makes it hard to correct without very obvious corrections.

    See innumerable posts on this topic, no airplane.angine combination has been more excruciating detail over the last 30 years or so. Bottom line is that with a 20FP or "new" 25LA, I have done numerous legitimate 500-550 point flights, with sometimes literally brand-new engines and with zero practice for years beforehand.

    Brett

* it started with a Dixon 40FP that was loaned out (apparently permanently...) before I ever flew with it, then a Fox 35 (disaster) and then the 20FP. Going from the Fox to the 20FP was like gravity was cancelled, it was borderline miraculous. It was the primary engine in a very long series of experiments with small engines that is described at lenght in numerout threads. The bottom line was that any of the engines available in the early -mid 90s from about 15 to 28 were very usable and worked way better than a perfect running Fox. The 20FP was the standout, and better and more powerful than the original 25LA. Much later, 25 years later or so, I tried the "new" 25LA and I think that is even better than the 20FP, although a bit touchier on the needle.

  Skyray/"new" 25LA/APC 9-4//015x60/15-18 mph wind/4.8 seconds:

https://youtu.be/VS6v8y7F4QA?t=257


Offline John Skukalek

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Re: 25LA prop
« Reply #29 on: June 08, 2023, 06:31:12 AM »
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?     

Online Brett Buck

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Re: 25LA prop
« Reply #30 on: June 08, 2023, 10:36:37 AM »
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

Offline Colin McRae

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Re: 25LA prop
« Reply #31 on: June 08, 2023, 01:30:25 PM »
   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.

Offline Colin McRae

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Re: 25LA prop
« Reply #32 on: February 11, 2024, 04:23:49 PM »
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.  

Online Dan McEntee

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Re: 25LA prop
« Reply #33 on: February 11, 2024, 08:30:18 PM »
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
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Offline Colin McRae

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Re: 25LA prop
« Reply #34 on: February 12, 2024, 08:54:01 AM »
     Was it cold outside?

Yes, it was cold, around 45F at 8:30 AM, and I do understand air density effects. I usually fly earlier in the morning at our field as the winds typically pick up later in the day. And I do have lots of various props and do indeed experiment.

The original author of this post was simply inquiring on possible ways to slow down his Skyray w/ 25LA. My personal experience on a couple of models is that the APC 9-3 (combat) prop performs well on a 25LA. The APC 9-3 has a very different airfoil shape compared to the APC 9-4 sport. But definitely the APC 9-3 is a prop some might consider for a 25LA application. Works well for me.

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
« Last Edit: February 12, 2024, 09:31:28 AM by Colin McRae »

Offline Al Ferraro

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Re: 25LA prop
« Reply #35 on: February 20, 2024, 08:04:19 AM »
  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


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