rambler53

My Feedback: (494)

4 strokes are truly habit forming. Once you go to a 4 stroke, you tend to leave the 2 strokes home a lot more often. You can swing a nice big prop with the higher torque, and the sound keeps me off the electric power end of the hobby altogether. I've used these in Cubs, Four Stars, Astro Hogs, Telemasters, and other slow planes. I never thought to remove a Rossi or OS SF piped off an Ultra Sport or Cosmic Wind Minnow, and fathom a Surpass is going to give me more top speed. I hear you can pitch the props over 12 with a 4 stroke, but haven't seen it happen here locally, ever. How many do this? I'm too much a Rossi guy to believe a Surpass is going to beat it on the same plane. Am I wrong?
Have any moderators or other pillars in the forum tried 4 stroke for speed and what speed plane, prop, and fuel did you use? I see videos on Tower suggesting 4 stroke for speed but never gave Tower much credit for any recommendations. I'd really like to know to get motivated to experiment with one, for speed. Generally I over power the faster 2 stroke planes, which is why .51 and .75 are for my .40 and .60 size planes. I wouldn't want to cut up a cowl for a 4 stroke just to pull it off again after one flight, so I'm asking for someone with experience doing this.

4 strokes I could prop are Saito 72, Saito 100 or Surpass 91, if you had experience with these, that would be most helpful in your reply.
ARFs at my disposal are GP Minnow, Revolver 60, World Models Midget Mustang 60, and I'm ready to throw one of these together but wanted to get input for a 4 stroke engine.

asmund

Forget the surpass, YS, YS and YS!!

Check out this video: http://www.youtube.com/watch?v=dburR...layer_embedded

w8ye

My Feedback: (16)

You need to try a four stroke in a speed type plane with 12" of pitch. You will find that it honks along pretty good. Just run without a muffler, they are not much louder.

frenchie79

Time out-I tryed a OS91 Surpass with a 12x12 in a Midget Mustang ARF.(60 size)It was deceptively fast not hearing a screaming two stoke at 16K+. But the above post is correct-YS if you really want to scream.
My Corsair 60 with a YS110S is extreme for a Warbird anyway.
To answer your question-Their fast and will pull big high pitched props and thats what you want.

earlwb

As already stated, you go with a smaller higher pitched prop to take advantage of the lower RPM torque and power curve on a four stroke engine.
Besides YS, there were some rather exotic overhead cam engines that might work too. I don't know if they make them anymore though.
But there are a lot of factors involved. Different planes may need a different prop, One plane might use a 12 inch pitch prop but another plane works with a 10 inch pitch prop. You have to keep the max RPMs under the max rpm limit for the engine still.

w8ye

My Feedback: (16)

This year, I just flew one plane - Ultra Stick 40 with a Saito 62.

It moves along at a pretty good clip if you open it up at full throttle.

I run a APC 13 X 6 prop.

mike early

I just cried a little.

mike early

I have a 13x8 TF powerpoint on my Saito .72 in a GP Revolver. It goes over 95mph.

I've tried over-square props and for some reason it just doesn't fly any faster. I put a GPS in it and tried about 8 props one day. 13x6, 13x8, 12x9, 11x11 and a few others

Them higher-pitch props making taking off and landing a lot more exciting, though.

MJD

My Feedback: (1)

Depends what you interpret as speed though.. 6" of pitch even at 12,000 rpm is only good for a bit under 70mph.

earlwb

There is a lot of aerodynamic drag with a Ultra-stick, plus the thick constant chord wings have a lot of drag to them too.
so yeah a higher pitch prop will not gain anything.
But if you had a really slick low drag airframe, a higher pitch prop would work as the plane can go much faster, so it needs a heavier pitch prop to keep up with the speed.

yeah a high pitch prop at idle can give you a much higher landing speed. I have one plane, sort of a pattern plane design. that with the Saito 80 and a high pitch prop, you have to fly it on in to make a landing. Easing it in doesn't work as the plane just does not slow down at idle enough to land like one would expect..

jeffie8696

Ifind you need a balance of thrust and speed to get the plane to perform. Putting on a smaller prop with a higher pitch may not provide enough thrust to overcome the drag. Ihave done some prop testing with my draggy trainer and a couple of 4 strokes.

SpinnerRow

I've run a 13x10 on a Saito 1.00 that is on a World Models P-51. Moves it pretty good.

I have a YS 1.10 though and that thing is in a different league and could probably spin a 13x12 at 9500+

jeffie8696

YS engines make excellent power. Ihope to own one of my own some day.

Rudolph Hart

I have a cmpro 55" midget mustang powered by a saito 115 and 14x10 prop,very fast and good acceleration.

MJD

My Feedback: (1)

That is the whole trick - for max speed you need to know where the engine makes the most power. Then you iterate through props that allow it to run in that range, adding pitch and reducing diameter as needed to maintain rpm until you hit the wall and start losing speed. Every different airframe takes x horsepower to go y speed. Your speed is limited by the max power output of the engine, and to achieve that top speed the prop must work most efficiently as it approaches that airspeed. Something to remember in this whole process is that for a given rpm, the angle of attack of the prop blades reduces as the forward speed increases.. think relative wind.

The onlne pitch speed calculator is useful for estimates of where to start, or to know what the limit is for a given rpm and prop pitch, i.e. a reality check. For the prop to work most efficiently you need to top out somewhere approaching the pitch speed of the prop, which means the airfoil on the prop blade is working at an efficient angle of attack. Too much pitch is like flying with a small wing at high angle of attack - inefficient. It will work but you waste power fighting excessive drag. And conversely, every prop will top out at a certain point, like an 11-6 at 9500rpm will never move your pylon racer at 110mph no matter how much static thrust it might make, since it stops thrusting beyond a much lower airspeed than that.

pe reivers

Fourstroke on speed planes?
First get rpm up to above 20,000! To do that, you need different camshafts and square props. Nobody but you will do that for you.
So for speed, stick with two stroke engines that can be made to 30,000 rpm and up. For the layman, 25,000 rpm can be bought off the shelf.
Example:
A prop 10x14 narrow blade will need between 5 and 6 hp to run at 20,000 rpm for a speed of about 400 km/h IF the plane will allow that, so it will need a very small frontal area with extremely low resistance.
Doable with a 4-stroke? certainly, if you know what to do, and how to do it, and have the funds to do it.

MJD

My Feedback: (1)

Much depends on your definition of speed... for some people "speed" is faster than all the regular stuff at the field, say perhaps 100-120mph. Get used to flying fast stuff regularly and 110mph seems pretty normal.

2 stroke or 4 stroke aside, it starts to take effort to achieve numbers much above 150, although that is still an off-the-shelf number reachable by many for a reasonable budget. In terms of prop pitch and rpm, 150mph needs 12" pitch at >13,000 rpm. Now think of that compared to available props and typical four stroke engines.. hmm, what to do. Whereas 120mph at 12" pitch translates to a more reasonable figure of a bit over 10,500rpm. Theoretical numbers of course, but then again most props have aerodynamic pitch higher than the listed number anyway, so it tends to come out in the wash.

There's little stopping the production of a higher rpm model four stroke, but of course that is not where the market = money is.

Konrad

Speed
When we went from the 16k rpm Rossis to the 10K rpm Webras in FAI F3A Pattern many of us (myself included) were surprised that the speed of the ships actual rose.
The prop doesn't care about the power source. But you will need much the same power. Maybe a little less as there are less losses (drag and vortex) with the slower prop. But the Reynolds number the blade is operating at will be lower. So going with allow RPM set up I'd look for a wide blade prop with high pitch. The APC prop with respond to heating to facilitate re-pitching (you have a pitch gage?). This is not a recommended practice but I have done it successfully. Do this at your own risk!

Yes, I have re-worked the HP 49VT for more speed running 9X8 to 9x10 props (no poppet valves to limit RPM). But I have to say I liked the Irvine 4cc engine on pipe (heck even on muffler) to the four cycle for the same size plane. The Irvine was much lighter.

With the VT changing the valve timing is just as easy as changing the timing of the inlet rotor on a two cycle engine.

Give it a try and report your findings.

All the best,

Konrad

Sorry, I had no intention of bashing the HP brand or the VT model. Or even the Rossi!

earlwb

I was going to say that it isn't really the RPMs that get you the speed as much as the engine being able to turn a high pitched prop well at a certain RPM. When you think about the old propeller driven fighter planes before and during WWII and afterwards for a while. The engines weren't turning much faster than maybe 2,500 RPMs yet they could get a fighter plane to go over 350mph. yeah they had some huge props with variable pitch blades on them, but they weren't using outrageous RPMs to go fast.

TimT2000

My Feedback: (1)

110mph is what my Little Toni will do with the new OS 110 four stroke.
What a great combo,, just a joy to fly. I am running a 12x12 APC on 15%
fuel.

cheers Tim

TimT2000

My Feedback: (1)

RCER88

My Feedback: (25)

Weight is always an issue with a "go fast" plane. "Power to weight ratio" comes to mind.

Speed on a forty size plane I have had real good luck with a Rossi 45 with a mini pipe. Keeping the plane lighter. A four stroke engine in that class I could never get any speed out of it. The added weight was not worth the trouble or hassle.

Does not matter how many rpms you get or how much thrust. If the plane is heavy it makes it more difficult to make it go fast.

A five pound Sig Kougar with a Rossi 45 will get you in the 115 mph range quite easily, a five and a half pound with retracts 120 mph easy. That is where the added weight becomes an advantage because you reduced drag. A four and half pound electric Kougar can get the same speed. Both using a 10x6 prop.

Food for thought.

TimT2000

My Feedback: (1)

To get 120mph on a 10x6 you will need 21,200 rpm. That is a lot to ask of a rossi 45,, now their pylon
engine will make that on a 8x7 but that would not fly the Kouger very well. A saito .82 would be a good
four stroke for that plane too. On a 11x11 prop @ 9000 rpm you could get 93 mph. The Rossi 45 on a 10x6
@ 16,000 rpm would be right at 90 mph. So speed is doable with a four stroke. just my 2 cents

I hear you on the weight issue, It can slow you down in the turns but it can be made up in the dives and carried
futher if you manage the energy. I would guess the weight of these two engines are with in a few .oz 's ,, never
looked this up.

Fast is fun!

cheers
Tim

Iron Dog

Rambler,

If you look at the majority of the scale racing eventsout there right now, the vast majority of the racers in the faster Silver and Gold classes are using YS 4 stroke engines. Theengine/plane/prop/fuel combinations vary somewhat, but probably the most common that I see is as follows:

[*]YS 110 or YS 110S 4stroke engine (which will likely soon to be superceded by the new YS 115) we findYS engines handle the higher nitro levels a bit better than the other 4 strokes[*]World Models P-51 seems to be the most common choice (Kyosho's Spitfire, Hein, & P-40 are also excellent choices)[*]APC props: if running 20-30% nitro, a 13 X 13N runs well and easily gets mein the 120mph range; if running higher nitro, some of theother racers say they are using 14" props. (But I've only been in the 120 - 125 mph range, so I haven't personally experimented with the 14" props. To go Gold speeds . . . in the 165 mph realm . . . most of these guys are either kicking up the nitro to 55 - 65% &/or modifying the wing with a thinner, specialized racing airfoil.)[/list]To see for yourself, or do some extra research, check out the threads in that forum at the link, below:
http://www.rcuniverse.com/forum/forumid_183/tt.htm

If you go back into that forum (another page or two), you'll find other threads where those interested in getting started have asked the questions you've asked above. Some of these threads are dedicated to specifically answering those questions. Others are threads about specific races, and throughout many of the guys are talking about the plane/engine/etc. combos they are using, and often discuss how these combos have been working for them. Furthermore, if you want to hunt for them, on some of the SAM Warbird Series races, TommyGun often posts videos of some of the races, so you can see these planes in action.

If you just want to get an existing ARF from your stable in the air to just start getting a feel for it, forget the Saito 72, and use either the Saito 100 or OS 91. I don't think these engines are going to be as consistent running using higher nitro levels, so my advice is stick to 20%, for now. But, this will give you a "taste" of speed; and just as importantly, flying with the oversized-engine will give you experience flying with the heavier wing loadings that your future racers will force you to deal with, too. My advice: Keep the landing speed up a bit more than you are used to, or may feel initially comfortable with. . . fly them down and land a bit "hot", otherwise, they stall all too easily with the higher wing loadings!!! (Trust me, I've learned this the hard way!)

Speed is addicting . . . have fun!

Iron Dog

This page has some video from one of our races:

http://www.rcuniverse.com/forum/m_88..._4/key_/tm.htm

(And I was wrong, this was a bigger hunt than I thought . . . is was about 5 pages into the forum. Boy, I got lazy and didn't film many of the races this year!)