Rojett 61 prop

[Richard Speer]

Rojett 61 prop size:
Presently using a 12x4 apc. Is a 13x4 apc going to be too much? What about a 13x4 wide? Airplane is 64 oz.
Thanks in advance!

[Dave_Trible]

Hello Richard.  How are you my friend?   I'll ask a question to your question.  You say you are currently using an APC 12-4.   Is it on pipe or muffled?  What are you hoping to accomplish with a prop change, ie, what is it doing now you want to improve?  Have you timed your laps?  What lines are you using?  Launch RPM? 

Dave

[Brett Buck]

Rojett 61 prop size:
Presently using a 12x4 apc. Is a 13x4 apc going to be too much? What about a 13x4 wide? Airplane is 64 oz.
Thanks in advance!

   First of all - no matter what, a 13-4 APC is not going to be much of a load on a Jett 61. I have run a 13.5-4 *3 blade* and the engine had no issue with it (although the airplane certainly does...)

    But, depends on what pipe, pipe length, venturi, fuel. you are using.

     Brett

[Richard Speer]

Dave, Good to be in touch! Engine is muffled, 60 ft .018 lines, lap time varies w rpm but at about 9500 five seconds. Not confident about  the vertical 8. So I juiced up the rpm ( do not know exact rpm)and lap time went to 4.6. Plenty of power then But at that rpm I’m running a rojett entirely 2 cycle. That can’t be right? Also at that lean setting the  six ounce tank ran 11:50 minutes. Need to get back in the four cycle slot. But then not enough power.
PS: Dub Sez as a general rule use a smaller prop rather than a larger one…

BrettThanks for your reply!

[Brett Buck]

Dave, Good to be in touch! Engine is muffled, 60 ft .018 lines, lap time varies w rpm but at about 9500 five seconds. Not confident about  the vertical 8. So I juiced up the rpm ( do not know exact rpm)and lap time went to 4.6. Plenty of power then But at that rpm I’m running a rojett entirely 2 cycle. That can’t be right? Also at that lean setting the  six ounce tank ran 11:50 minutes. Need to get back in the four cycle slot. But then not enough power.
PS: Dub Sez as a general rule use a smaller prop rather than a larger one…

BrettThanks for your reply!

     Dub is generally right, but 13" 2-blade, particularly an APC, is still not much prop for this engine.

    If you leaned it out, it was in a 2-stroke, and 4.6 second laps, it seems you can just richen it up to get a decent speed (maybe 5.2) and you might be fine. Dial it up and down until you have a comfortable speed, then see where you are.

    Failing that, find a 13-5 APC or something like that, you will slow the engine way down for the same speed. As I recall, when Ted was running his on a muffler, he was running a 13-5 Rev-Up - but that was a long time ago.

     Brett

[M Spencer]

Any off the .45s will turn a 12 x 4 , or better . a Rojett 51 too . Seen em on the 12 1/2 x 5 three blades , o.k. .
So asan outsider , the S Tigre 60 13  cut to 12 1/2 sounds ' appropriate ' , The .295 / 320 intake - to get a bit of fuel thru it . say 300 for a normal plane . .300 thereabouts .

Posts: 4

the Rojetts a mega grunter , if you want it . Down .280 it'd be ' controlled ' , you could run any rpm & pitch , depends what your after .
 a 12 x 6 ? ?  You say " no four stroke " . If set deep four stroke with that prop , then go up to the break & pitch to suit .

A DOZEN DIFFERANT ' SAME SIZE ' PROPS WILL GET HALF A DOZEN DIFFERANT MOTOR LOAD / RESPONSE oops . thinned trimmed and fettled , timber . ??

take a half dozen sizes along , try the extreemes ( your 12 x 4 is extremely undersized , unless it started as a 14 ) say a 12 & 13 , in 4 - 5 - and 6 pitches . maybe . Depends on the plane .
but a 14 x 5 cut down to 12 or 12 1/2 and cleaned up & thinned , reairfoiled , swings fine on a s tigre 51 & FSR etc 45 / 46 schneurles , And dosnt get big P & tourque reactions . in hard corners .

As In a 14 x 5 cut to 12 1/2 and thinned & reprofiled ( my one  ) wont load up your Ro Jett at all at all . Tho most timber props are big thick clunkey things , theres a world champs photo of
Bob Barons Super Tigre 60 with a 12 x 6 Zinger . STOCK .

And Im Sure Brett will say ' Anything a S T 60 can do , a roJett 61 can do better ' , EH .

If youve got a big prop , and it baulks , cut it down till it switches fine . The olde ' ground break '  , as it swings Nose Up past 30 degrees - it should get a clean break to a clean two stroke . IF your after a 4 - 2 run  .
( hold plane Securely . mongrels well clear . Should switch 4-2 20 to 30 degrees Nose Up . Upright & inverted , both . Same angle . Tank Hight verification . And setting preliminary .

Youd think a big nasty two blade fourteen inch CARBON prop , would be the thing . AND KEEP YOUR FINGERS    OUT  OF  IT > Step Back , Walk around CLEAR , dont get anything sucked into it .
https://www.worthpoint.com/worthopedia/brian-eather-carbon-fiber-f2b-stunt-487197213 look like that in a 14 . See its High A / R . long narrow blade . a .46 S Tigre prop . ( here ) perhaps .


orrible tourque reation . The 12 1/2 x 5 ish three blades are quite commmon , old things , some cloth & resin . Euro & Eather F Glass . same . Ive cut one to 11 inch For the liddle injuns , and its darn good. UNEXPECTEDLY . Diameter ONLY . as yet . no rework .

So chewing up props with 60 Wt Paper on a stick , goes quick . Nail in 4 x 3 plank, square cut end  - push so anchored , and sand ends matched . No worries . Decked props , on them things . Toss Them !
DONT carry it by the prop blade / s . or itll fall off . Which dosnt help . See ' Operating Safty Proceedures  ' keep small children and dogs WELL AWAY . Its a one H.P. buzz saw .

But a steady four , with it ' nibbling ' a two , occasionally , could get it good , when it blows , it should hold the two stroke longer . And even have leeway in the two stroke , rev variation to load / work ,
in the gusts . The other , pinch the fuel line . release . Instant rev drop ' Test ' might get you somewhere . With Glow Plug suitability etc etc .

[M Spencer]

You can see , if you Cut Down these , all to the same Length / Diameter , theyed all be a bit differant . No matter what the pitch .

https://www.etsy.com/uk/listing/1273973884/maple-wood-propellers-top-flite-super-m?dd_referrer=https%3A%2F%2Fwww.google.com%2F

thus & therefore , if you THEN , made them all the same THICKNESS , theyed ' turn ' more alike . Shaveing T E's thin - altering high point , fore or aft .
Leading Edge radius , and hight ( Philips entry , more airfoiled forward - or Low & Sharp - ( or high & sharp ) ) Sharps only to unload motor  , perhaps .

Bit Like WINGS - Theyre not all the same .  This toikey goes onabout PROPS , and Ro Jetts , to a degree . Their RoJett 90s were turning 16 inch . Urtnowski & Adamusko .
So a wide 12 or a high A/R 14 would get about the same blade area , which is a starting point to look at  . Cut a 13 & 14 down to 12 1/2 maybe . What Aeroplane is it in . What Weight .

https://www.youtube.com/results?search_query=windy+u+.+props

the 3 blade I was prattling on about , is in the heading picture . Cloth Weave Carbon .  and if you think I prattle on , your in for something HERE :

[Brett Buck]

And Im Sure Brett will say ' Anything a S T 60 can do , a roJett 61 can do better ' , EH .

   Certainly, and be a lot more reliable doing it since it is AAC vs ringed. But you have a lot better chance running it with a competitive prop (i.e. 4" pitch) than you would with the ST.

    Brett

  p.s. the props in the Windy video are Eastern Block copies of Eather props, and good choices for piped engines, maybe not so much for muffler engines. The argument I heard was that the Eastern block versions were stiffer and therefore better, they are definitely stiffer, but I have never had any detectable problem with the real Eather props being "too flexible" and very highly recommend the originals.

[Dave_Trible]

Hi Richard.  Hope I've had enough coffee to make sense this morning.  I totally agree with Brett that your RO Jett CAN swing a bigger club-a lot bigger however in my way of doing this I wouldn't.   I actually run all my larger RO Jetts , .61s, .67 and .76s on the same prop.  It is a three blade carbon of my making that is about 12.25 x 6.4 pitch.   I tweak the pitch a little to acquire the lap speed I'm after down on the 8200-8600 rpm range.  When I do this I can either keep the engine in mostly a solid '4' or have a gentle break at the tops and still have all the grunt I want in the 5.2 second lap range.  What I don't want is the effect you are getting-breaking into a moon shot which they can do if you give it too much leash.  If you set it in a slower range it will stay there if your tank is working well.   I use the pipe to help with that but it will also operate OK with the muffler.  (pm me your address-doubt I can still find it-  I'll get one to you)  I haven't tried them in this way but I wouldn't be afraid to put on an APC 12-6 and turn that rascal down into the mid 8000 range and see what happens.  I do not favor going to a larger diameter for two reasons.  First the larger diameter 'loads' the engine quite a bit and therefor CAN cause it to break sooner and come back slower as the engine runs a little harder/hotter.  Bigger props can yield bigger trim problems as well.  Finally (did I say two reasons?) when you change to a bigger prop it acts the same as adding nose weight to the airplane.   It will slow your handle response and then you may wish to put on tail weight which we try not to do.   You could overcome that with spreading your handle line spacing a bit wider.  My running methods are a little different than the mainstream but have worked well for my Jetts for quite a while.  My main point is for you to move up in pitch instead of diameter,  figure out a needle setting that works in the laps speed range that feels comfortable for you and keeps the ship in orbit.

Dave

[Brett Buck]

  I totally agree with Brett that your RO Jett CAN swing a bigger club-a lot bigger however in my way of doing this I wouldn't.   I actually run all my larger RO Jetts , .61s, .67 and .76s on the same prop.  It is a three blade carbon of my making that is about 12.25 x 6.4 pitch.   I tweak the pitch a little to acquire the lap speed I'm after down on the 8200-8600 rpm range.

    Point being is that no one it anywhere close to running "max" props (now that Al has left us...*) on these engines, because you don't need to in order to get the necessary vertical performance, and running larger-than-necessary props kills the cornering too much.

    Brett

p.s. *in one of my phone discussions/45 minute combination of arguments, mutual admiration,  and dirty jokes with Al, he told me that he had run a *16-6* wood 2-blade on his Jett 76, and, that this wasn't the max it could handle, just the biggest he could find!   People forget that even a muffled 60 is a HUGE engine for use on an airplane that is necessarily limited to about 700 square inches due to the 70 line limit, and you can't really use anything like the full capabilities on a muffler engine this large. As Windy found out the hard way, it becomes harder and harder to deal with the bigger the engine gets, if you don't have some other way to control it.

[Steve Helmick]

The 12-4 APC is a prop I've used on my PA .51 and ST G.51 with good performance, so I'd think a 13-4 APC would for sure be worth a try on the .61. APC props are great, IMO, especially if you are forced to fly off public park/soccer field type of grass surface. I'm reluctant to break a $60 CF prop on the average grass circle, cheap guy that I am.

The interesting thing about APC props is that they have multiple blade shapes with significantly different blade areas, yet IF they are an appropriate size for the engine, they work very well. Compare a 12.25x3.75 to a 12-4...wildly different, but both work great. But if I was walking down a dark alley, I'd want a 12-4!    Steve

[M Spencer]

p.s. the props in the Windy video are Eastern Block copies of Eather props, and good choices for piped engines, maybe not so much for muffler engines.

Ive one glass Eather ? I got with a engine , redish translucent . Rest are the Eastern ridgid ones . Look to be 5 - 5 1/2 maybe , pitch .
With nothing better to do , I chopped a Eastern one to 11 inch diameter .

In the ST 60 p.d.p. 85 Oz. Typhoon !  It dragged it round nicely, on 70 ft of .016 single strand . THIS has finally ( the lines ) cured THEM of whip , tourque roll , yaw ( almost )  and shenanagins
in the bottom of the hourglass , and when similarly pressed . The PROP on the G -51 72 maybe Oz. Spit , 4-2-4 drags it nicely too .

Prop merely ' clipped ' to 11 inch diameter .
I didnt narrow , rework or alter it other than that .
So thought it may oveload , no sign off that .

For anyone who has a draw full off them . Start at 11 1/2 maybe .

Al & 16 " , Vindy vas clowning with 16 inch 4 blade toothpicks on the Spit 90 . https://www.youtube.com/watch?app=desktop&v=xjjqtSO8Tds
you cansee there .

The real boys gottit downto Blade Area Vs Horsepower . As in if you wanted to get off the deck , youd got to transfer the grunt . Limited Diameter meant more blades .

BUT , According to Issac Newton , you have a problem . If the propellor was as big as the aeroplane , they wouldnt know which way to turn . 

So , looking at the scrawny 16 inch windy blades , if they were twice as wide , it could be a problem . so youd have to cut a few inches off the end . Which we did on the three blade .