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Author Topic: Strega with Saito 72 RPM and prop advice sought  (Read 8971 times)

Offline Ivan Bolton

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Strega with Saito 72 RPM and prop advice sought
« on: December 11, 2012, 04:17:59 AM »
Hi all.  I posted about his build in the General section so I'm posting here about specific RPM issues with the Saito 72.  I am using a UHP C/L conversion on the motor with the smallest diameter venturi supplied.  I have just ground run the motor so far but I am not happy with the RPMs with the motor dialled in. 

On a 13 X 6 APC I l was getting around  9500 rpm.  Okay that was only  the first start to see where the motor was at.   I then switched to a 14X5 Zinger and the rpm dropped to 8400.  A Friend who has a Strega with a Stalker 75 in it says his ground rpm is around 6400 on a 14X 6 which is about right in the air.  I am considering turning a new aluminium manifold for the UHP conversion with thicker walls  and a little taller so that I can put a nylon bolt in place to restrict the venturi size and thereby reduce the rpm as has been posted by Bob Reeves.  Will restricting the venturi in this way work?  I'm not keen on tackling the R/C carb as I may wish to sell the motor in its R/C form,  which is why I got the UHP C/L manifold in the first place.  I also have 14X7 and 14X6 wood props to try.  Those of you running the 72 in the Strega what props and ground RPMs are you using??  This Strega weighs 73 ozs all up and is scratch built

Offline Claudio Chacon

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #1 on: December 11, 2012, 06:50:47 AM »
Ivan,
I have never used the UHP carb conversion with my Saito .72, so I know nothing about it. What I do know is that the carb mod that Bob Reeves suggested works like a charm, EVERY time.
Here are my specs:

Engine: Saito .72
Model weight: 65 oz.
Prop: Top Flite Power Point 14"x6" (stock) or Rev-Up 14"x6".
Glow plug: OS type "F"
Fuel: 10% nitro - 20% oil (70% synthetic-30% castor)
Fuel consumption: 3.5 oz for a 6' 30" flight.
Ground rpm's: 8.4/8.5 K with the Top Flite prop and 8.8K with the Rev-Up prop.
Lap time: 5.1/5.2

If you want to control the engine rpm's, you'll need a venturi restrictor of some sort. If you don't want to modify your RC carb, install it in the engine and use it as is. Maybe it won't give you very consistent runs, but it works (again...not always). If you are not happy with it, ask Steeve Moon about the mod you want to make to your UHP carb. If for whatever reason none of the two above possible solutions works for you, get an extra Saito RC carb (or CL carb, as in my case) and follow Bob Reeves's advice. You'll love it...

Offline Bob Reeves

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #2 on: December 11, 2012, 10:28:55 AM »
Steve and Doug Moon are both friends and I have allot of respect for both, however the UHP intake was developed quite early in the 4 stroke time line to what we know today. If you have a gazillion props and the time to experiment you can match the prop to the intake and make it work. I would rather have two or 3 props that I know are in the ball park then match the intake to the prop.

As I have stated many times I have no direct experience with the 72 but the numbers Claudio posted fit right in with my findings on the 62. Figure out a way to restrict the choke area and make it adjustable. A nylon screw down the throat or one through the side will work. You will find the adjustment pretty critical and sometimes you simply won't be able to get there. This is the setup I have in my Latency and ended up removing a 62 and installing a 56 simply because I wasn't able to choke the intake down enough with the 62 turning the prop I wanted to use.

Modifying the RC Carb is by far the best CL setup for a Saito. It puts the restriction where it should be, right at the fuel inlet and uses that fantastic Saito needle valve. Not sure if the larger UHP intakes still use an OS needle or not? The OS needles used on the UHP for the 40 are not near as good as the stock Saito.. If you wiggle the OS needle without even turning it you will notice an RPM change and more often than not one click is too much one way or the other.

Sorry Steve, I love ya but them is the facts..

Offline proparc

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #3 on: December 11, 2012, 10:35:58 PM »
It just occured to me that, I have been flying the "big block" for over ten years and designed and built 4 or 5 ships just for that one motor. I have been flying and running 4 strokes for so long that, I actually forgot how to run my ST46 the other day!!

I plan to pick up some Evo 60's to re-establish my 2 stroke mojo and get back with it. Cranking up the old ST46 reminded me just what an incredibly good motor it is. Got to be one of the all-time absolute greats!!

I am kind of ashamed of myself. Instead of focusing on Ivans question about the 72, I have "oogling" the pictures of Claudio's ship. LL~ LL~
Milton "Proparc" Graham

Offline Ivan Bolton

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #4 on: December 12, 2012, 12:38:40 PM »
Thank you all for the advice. 

Claudiio's ground RPM is similar to what I have on the 14X5 so I'm going to go ahead and fly the beast as soon as I can.

Bob if I can't get reliable runs I'll then go with your advice.  I've sent the money on the UHP set up so I may as well try it   

Weather here can be flyable even in mid-winter but it takes waiting for a clearance and 'going for it before it closes in again.'   I did succeed in getting out for a session on Monday last with my Bear Nobler but didn't take the Strega, I'm sorry I didn't now!! 

Proparc, as a matter of interest, what size props do you use with the 72?  I too have a ST,  46 Tom Lay tuned, fine motor.

Ivan

Offline proparc

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #5 on: December 12, 2012, 07:18:05 PM »
Right off the bat Ivan, If Bob Reeves decides to run for Presidential office, vote for him. When it comes to 4 strokes, he knows what's up.  Unlike a lot of people who run the big block, I am not down with swinging the big lumber. 12x6 APC on a well setup 72 is devastating and IMHO, can hang with ANYTHING in the world today.
Milton "Proparc" Graham

Offline Bob Reeves

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #6 on: December 13, 2012, 03:13:08 AM »
Milton, you are giving me allot more credit than I deserve, I just happen to be the guy that was stubborn enough to stick with Saitos long enough to have made all the mistakes.

Ivan, Be extremely critical of the run and look for the following faults. When it's right you will think you have a tractor on the end of the lines that can claw it's way through anything.

If you notice any slow down in the overheads at all.. Your prop doesn't have enough pitch and isn't loading the engine enough. Move to the next higher pitch and adjust the intake to get your lap times back down. Never try to adjust lap times with the needle, it should always be set just to the rich side of peak.

Wind-Up. Again the engine isn't loaded enough, more pitch or bigger prop and the intake is too big. I would never try to run a 4 stroke with anything less than a 6 pitch prop and try to keep the take off RPM between 8000 and 8500. I have had success running a 7-1/2 pitch prop on a 56 below 8000 but 8-8500 seems to be the sweet spot.

Inconstant between flights, run time and or just acting weird. Have seen this with a restricted Saito CL intake, the fix was a modified RC carb.

If you are seeing more than a 0.2 second speed up from start to finish of the flight you are probably setting the needle a little too rich.

If it isn't smoking it isn't burning enough fuel. More pitch and smaller intake.

Start with a 6 or 7 pitch prop and adjust the intake to get your lap times where you and the airframe are happy.

I'm running a 13-6 reverse pitch on a 56 in the Latency at about 8400 and 11.3 X 6.5 on my 40's at about 8300. Before I switched to reverse pitch I was running a 13 inch 3 blade on a 62. Can't imaging what size prop the 72 will actually turn...

Offline proparc

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #7 on: December 13, 2012, 08:13:03 AM »

Can't imaging what size prop the 72 will actually turn...

Practical max on the 72 is 14". Practical max on the 91 is 15". The 40A is from another planet and it seems to make its own rules concerning props.
14" max on the 72 is a helluva lot of prop if you consider that a supercharged YS 175 can turn a max of 17x12.  Again, I run my big block with APC 12x6-devastating.

Tony Naccaratto of Burbank,CA launched one of my ships for with the above combo, and after the flight commented that the ship accelerated like a rocket! That said, Windy Urtnowski made the Walker Cup flyoff at the Nats flying his 4 stroke powered Typhoon with a monster prop-16". I have video of his flights-looked good to me!!

Windy's own comments on his Saito 91 powered Hawker Typhoon: "Sorry, I don't have any photos,Saito 91,first 4 stroke ever in top 5 flyoff,first with ZTRON to taxi and have engine control in flight,CARBON FUSE,TANK,16 by 4.5 prop,BRODAK DOPE FINISH,CARBON COWL,this list could go on forever. Removable cockpit was another cool feature!!!!!!!!! Full take apart,Windy"
« Last Edit: December 14, 2012, 10:19:49 AM by proparc »
Milton "Proparc" Graham

Offline Ivan Bolton

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #8 on: December 15, 2012, 08:45:37 AM »
I got a brief chance to fly the Strega this morning.  Only one flight as the prop broke after a soft landing on our rough grass strip.  The prop was Master 14X6 wood, fuel 20% coolpower all synthetic pattern fuel. Launch RPM circa 8200.  The flight was a non event really although it was windy 15  MPH  gusting  to over 20 MPH.  Lap time was comfortable and the model just powered through manoeuvres without any significant wind up in the wind.  I was cautious as it was a first flight and so windy  but verticals were fine and it turned nicely.  Motor cut at around 8 mins on 5 oz of fuel and there was a good amount of  exhaust smoke at all times and the Saito 72  sounded very happy.   It did not lean out at the end of the tank  (Dubro 6 oz, muffler pressure - vent at the middle of the front inside corner), it slowed briefly for about 1/4 lap  and  stopped.  With the prop broken,  and no replacement in the field box,  there was no repeat flight to try it out further.  As it was bitterly cold with the wind chill so I went home a relatively happy camper. I didn't get to time the lap speed but it was, as I have said, very comfortable on the 66' lines.

Offline Martin Quartim

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #9 on: December 15, 2012, 12:05:41 PM »
Ivan,

I use  JXF 14x6 Electric prop with my Saito 72 and OS 70 Ultimate engines. Yeah it is electric, but it still stronger then Topflite Power Point.

For me this prop worked the best.

Good luck,

Martin


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Offline Claudio Chacon

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #10 on: December 15, 2012, 03:58:00 PM »
Ivan,

I use  JXF 14x6 Electric prop with my Saito 72 and OS 70 Ultimate engines. Yeah it is electric, but it still stronger then Topflite Power Point.

For me this prop worked the best.

Good luck,

Martin




Hi Martin,
Where do you buy the JXF electric prop? What were your findings in terms of performance with it compared to the Top Flite PP?

Offline Martin Quartim

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #11 on: December 17, 2012, 10:00:53 PM »
Hi Claudio,

The JXF electric props are thicker at the root and thinner towards the tip compared to TF. Before I found out about the JXF electric prop I used the Top Flite and rework most  of them to adjust pitch and make thinner blades. It took many work hours to get the prop the way I liked it.

The TF ones did not have accurate pitch, some of the props I measured had 7.8" pitch in one blade and 5.5" in the other.  So it was hard to have two props that work the same. The JXF are a lot more accurate in true pitch.  Also most of the JXF props have less pitch at the tip, which I like because it seems they do no wind up in the wind as much.

You most likely will save fuel, as this JXF are more efficient. I found the JXF electric better in all aspects.

Xoar and JXF are the same thing. I good place to find them is www.himodel.com

Cheers,

Martin

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Offline Claudio Chacon

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #12 on: December 18, 2012, 03:43:09 PM »
Thanks Martin.
Have you ordered from Hi Model before? Any comments on this? What shipping method did you choose?

Offline paul winter

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #13 on: December 25, 2012, 02:20:14 AM »
hi
i have been flying a saito 72 powered model for ten years and the best prop is a 13x5.25 flat back Brian eather carbon prop ,the saitos like to be loaded
paul

Offline Bob Reeves

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #14 on: December 25, 2012, 05:02:04 AM »
hi
i have been flying a saito 72 powered model for ten years and the best prop is a 13x5.25 flat back Brian eather carbon prop ,the saitos like to be loaded
paul

Merry Christmas..

That's close to the same prop I was running on the 56/62 before I started running reverse pitch props. 13 X 5.5 three blade with a slight undercamber. Bought 3 of them from MODUSA when I was trying to get a Stalker 61 working in my first Legacy. Sure wished I could get that prop in a reverse pitch but have no idea who made them.

Anyway, thought it interesting you are running more or less the same prop on a 72 I run on a 56. Makes my pea brain wonder just how much prop the 72 can actually handle.

Offline proparc

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #15 on: December 25, 2012, 09:53:27 AM »
hi
i have been flying a saito 72 powered model for ten years and the best prop is a 13x5.25 flat back Brian eather carbon prop ,the saitos like to be loaded
paul

Paul, I would very much like to welcome you here. You have been at the 4 stroke game for a long time, and I was always hoping you would grace us with your presence. Paul like myself, was one of the early adopters of the Saito 72 for stunt.

If anyone is not familiar with Paul Winter; Paul is a world class stunt flyer from from England who builds at the world class level. He has or had his own stunt company importing stunt supplies to England.

Paul has what may be the nicest Supermaster classic Stunt ship in existence today, and has had some us the best Strega\Saito 72 powered stunt ships anywhere. His work on control line stunt has seen publication, and I consider him to be one of the worldwide experts on the Saito “big block” for control line stunt.

Paul can usually be seen partnering up with long time British stunt stalwart John Benzing, and the two of them have traveled extensively abroad to compete at the highest level.
Milton "Proparc" Graham

Offline Ivan Bolton

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #16 on: January 06, 2013, 08:02:18 AM »
I got a window in the weather this morning to try out my Strega/Saito 72.   I had four flights and I am very pleased indeed.  The motor was totally consistent throughout and pulled perfectly everywhere, never missing a beat.  I'm delighted with the model also.  I grooves perfectly upright and inverted and tracks nicely though manoeuvres. (lots of time to think)  I  tried an APC 14X6 for these flights and can see no difference between it and the Master 14X6 wood I tried and broke on our rough grass field last time out.  Needle setting was not altered, fuel is 20% Omega Coolpower.  Temperature was around 12 degrees Centigrade (unseasonably mild) and wind was light.  It will be interesting to see how everything performs in heavier wind!!  So far I am delighted

Offline SteveMoon

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Re: Strega with Saito 72 RPM and prop advice sought
« Reply #17 on: January 06, 2013, 08:19:25 AM »
Hi Ivan, glad to hear you had some good flights with your new rig. When I've run the
72 in the past I preferred a 13 inch prop as Paul described in his earlier post. But, I
was flying a plane a bit smaller than the Strega and with a thinner wing. So, this may
account for some difference. If you're having good luck with the 14 x 6 prop then go
for it.

Steve


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