Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

fastest 4 stroke plane

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Old 02-10-2014, 09:01 PM
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airraptor
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Default fastest 4 stroke plane

What is the fastest recorded four stroke plane speed? This is for radio control model aircraft not man carring and not a UAV, drone and so forth.

has anyone hit over 200 straight and level with one?
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Old 02-11-2014, 04:54 PM
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I won't say that it hasn't happened or that it isn't possible, but 200 with a four cycle is unlikely.

Getting to 200 requires a clean airframe and an engine that was designed with speed in mind. Four cycles are typically very good at transmitting a lot of torque to the prop, but they just don't spin the high RPM that a Jett, Nelson, or similar can turn.

To take advantage of the four cycle torque curve to take a real stab at the 200 mark, you'd have to have a VERY over-squared prop. And you'd have to have an incredibly clean airframe to allow that much of an over squared prop to unload in the air.

Again, I wouldn't say "impossible," but I will say "unlikely."
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Old 02-11-2014, 06:47 PM
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As far as I know there is no specific category for four stoke vs two stoke for speed, just prop driven with a max AUW of 6.5 lbs (26-29 oz/ft wing loading not sure about the actual #s). But the record set by the German speed cup guys for SLF was something like 304 mph last year (and it was electric the glows were in the 290 range). There are several guys who have posted videos of planes flying in excess of 200 mph with the speeds being confirmed by using Doppler, Radar, or both.
Actually a year or two ago there was a plane called the Rare Bear using a 4 stroke that was in the 225 mph range if I recall correctly (sounded like a Harley). C Roundy I think it was the guys name tricked out motor and custom made composite prop and lots of hard work to do it.
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Old 02-11-2014, 07:35 PM
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Fact: a YS 115 WS can spin an APC 14x14 just over 10K. I have seen very draggy Stilettos do 180 mph. A custom 12x15 or 12x16 prop and a speed design and 200 would be a piece of cake. With some work I would say 230 is within reach. Look at the props and RPM that those 300 mph electrics are using, large dia, deep pitch and much lower RPM then the glow airplanes.
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Old 02-12-2014, 08:53 AM
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I was thinking of a Miss Ashley with a YS 70 spinning a 9x14 or 9x15 at 12-13,000 on the ground. thoughts?
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Old 02-12-2014, 09:43 AM
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With the 9X14 static thrust calculator says about 160 mph at 12K rpm, the 9X15 is about 170 mph as far as prop pitch speeds. If you have a very clean airframe you will yield around 85% of the prop pitch speed. Speedracetrixie made a good point as far as what you need to look at as far as getting some real speed up it going to take a fairly high pitch prop to do it, as well as enough power to spin that prop as well.

Last edited by iron eagel; 02-12-2014 at 09:48 AM.
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Old 02-12-2014, 05:29 PM
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iron Eagle not to pick on you but those pitch speed calulators are not that accurate at all for our model planes. I have ran a few planes on GPS and pitot tube sensors and they showed a higher speed than what the pitch speed calc reported.

The propblem is that the just base it off the pitch alone. they dont account for the airfoil and the difffent pitchs of the props out there. Some of these also showed less than the pitch speed also.

My 12,000 as above is also the ground speed i will expect some unloading.

Either way I will try to see what i can come up with.
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Old 02-12-2014, 06:34 PM
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I have to agree somewhat here. My fastest airplane to date ran a Rossi 61 that was set up to spin a 11x11 at 12,500. According to the calc it should have been in the 125-130 mph range. It was way faster then that. I should do the math but our race course is a two pylon course 700 feet apart. Each lap would be about 1600 ft flown so 10 laps is 16,000 ft. My best time with that airplane was a 1:27 . That ends up being an average of around 140 mph. Remember, two turns per lap and I doubt an 700 ft strait is enough to get to top speed. I'm currently building a duplicate of that airplane with the addition of retracts and a YS 115. I'm hopeful it will see 180 mph.
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Old 02-12-2014, 06:55 PM
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Originally Posted by airraptor View Post
iron Eagle not to pick on you but those pitch speed calulators are not that accurate at all for our model planes. I have ran a few planes on GPS and pitot tube sensors and they showed a higher speed than what the pitch speed calc reported.

The propblem is that the just base it off the pitch alone. they dont account for the airfoil and the difffent pitchs of the props out there. Some of these also showed less than the pitch speed also.

My 12,000 as above is also the ground speed i will expect some unloading.

Either way I will try to see what i can come up with.
I agree there good for indication only, what you actually get will be different. FWIW I have a chart which just uses rpm and pitch not taking diameter into account which has a 15 pitch prop at 12000 rpm having a prop pitch speed of 200 mph. When you get to the point where the prop unloads your RPM will climb, even 1K rpm will give you about 8-10 mph more speed.
There have been many cases were a good clean plane outran the prop pitch speed by considerable amounts.
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Old 02-12-2014, 07:53 PM
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Originally Posted by iron eagel View Post
There have been many cases were a good clean plane outran the prop pitch speed by considerable amounts.

Thats what I'm hoping for with this bad boy.
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Old 02-13-2014, 07:24 AM
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Isn't the prop pitch speed caculated @ the static RPM? The prop will unload in the air & the more streamlined the airframe, the more RPM in the air, thus more speed.

How can static RPM calculate air speed when the aerodynamics of the airframe is a variable?
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Old 02-13-2014, 07:31 AM
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All they can do is give you a rough idea of what your speed will be, they are close but not perfect.
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Old 02-13-2014, 08:31 AM
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Originally Posted by speedracerntrixie View Post
Thats what I'm hoping for with this bad boy.
Why bother with a 4 stroke? go with a 2 stroke, you're only going to get so many RPM's out of a 4 stroke before the valves start to float.
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Old 02-13-2014, 09:21 AM
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Originally Posted by airega1 View Post
Why bother with a 4 stroke? go with a 2 stroke, you're only going to get so many RPM's out of a 4 stroke before the valves start to float.
Because the 4 stroke is faster. RPM is not everything.
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Old 02-13-2014, 10:18 AM
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Originally Posted by airega1 View Post
Why bother with a 4 stroke? go with a 2 stroke, you're only going to get so many RPM's out of a 4 stroke before the valves start to float.
Because I like a challenge. I like to do things that others or not many have tried. I have been flying since the 70's and done most everything RC.

Some say that a four stroke engine makes more torque but in fact the TWO stroke engine makes more torque if close to the same displacement and have the same type of aspriation.

I want to make a four stroke plane that does 200 mph on the level.

Oh I have an four stroke engine that turns 20,000 rpm on the ground also so they are not RPM limited only in stock form they are.
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Old 02-13-2014, 01:07 PM
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What I like best abut watching speed demons is how fast they disintegrate when they hit the gorund.
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Old 02-13-2014, 02:50 PM
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Originally Posted by airega1 View Post
Why bother with a 4 stroke? go with a 2 stroke, you're only going to get so many RPM's out of a 4 stroke before the valves start to float.
Originally Posted by speedracerntrixie View Post
Because the 4 stroke is faster. RPM is not everything.

Propellers are more effecient @ lower RPM.
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Old 02-13-2014, 02:52 PM
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Originally Posted by iron eagel View Post
All they can do is give you a rough idea of what your speed will be, they are close but not perfect.
All they can do is estimate speed @ the static RPM. How can they predict what an SE-5 & a P-51 will achieve for top speed @ the same static RPM W/O the drag factors?
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Old 02-13-2014, 03:45 PM
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Originally Posted by SrTelemaster150 View Post
All they can do is estimate speed @ the static RPM. How can they predict what an SE-5 & a P-51 will achieve for top speed @ the same static RPM W/O the drag factors?
That's an entire different set of calculations that you have to do, and even then there are dynamics which can change things.
The only way you know for sure is put it in the air and see what happens.
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Old 02-13-2014, 03:48 PM
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Originally Posted by rgburrill View Post
What I like best abut watching speed demons is how fast they disintegrate when they hit the ground.
LOL! They do that well.
Sometimes they do it in the air with nothing around for no apparent reason.
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Old 02-13-2014, 06:15 PM
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Originally Posted by iron eagel View Post
That's an entire different set of calculations that you have to do, and even then there are dynamics which can change things.
The only way you know for sure is put it in the air and see what happens.
That's my point. Just using static RPM tells little about actual top speed.
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Old 02-13-2014, 07:16 PM
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Exactly!
Not much better than a guess, but it can give you a bit of an idea of what type of performance you may get.
The calculator I used is really just a design tool it gives you a rough idea of what type of performance the prop may deliver. For example one thing it is good for is, it said the required HP needed to achieve those type of prop pitch speeds would be 1.2 and 1.4 Hp respectively to spin the prop up to those rpms (I would guess that is using the drag of a average type model for a reference). Now that is something that's worth knowing if you wanted an electric motor to spin those props, now you know it would take a 900 or 1050 watt power system to do that.
One of the other things you can glean from it as well is that (at least with a speed plane) if you can't get to at least 80% of that figure something is wrong.
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Old 02-13-2014, 07:46 PM
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Cool idea, I've wondered about a 4st in a speed cobra or similar. You're welcome to use my cnc mill if you want to cut some prop molds or something. Passed my ppl check ride this tue so I will have a bit more spare time.
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Old 02-13-2014, 08:07 PM
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http://www.youtube.com/watch?v=LYwqJtJ34xc#t=153

This would be one of the quicker 4 stroke models around I think.
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Old 02-13-2014, 10:05 PM
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Thanks lance. I will need to do just that. i will need to make some 12x7 thru 12x19 props for the 115WS I have. i just picked up planes from pat like a bunch of Q40 designs and some formula one planes.

Get some Ti valves cut and some stiffer springs will allow me to rev it more.

Also congrats on the PPL. i would like to get mine some day also.

lower rpm isnt always more effiecient but it uses the available power better.;-)
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