fastest 4 stroke plane
02-11-2014, 04:54 PM
#2
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."
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."
02-11-2014, 06:47 PM
#3
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
02-11-2014, 07:35 PM
#4
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.
02-12-2014, 09:43 AM
#6
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
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.
02-12-2014, 05:29 PM
#7
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.
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.
02-12-2014, 06:34 PM
#8
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.
02-12-2014, 06:55 PM
#9
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
There have been many cases were a good clean plane outran the prop pitch speed by considerable amounts.
02-13-2014, 07:24 AM
#11
Senior Member
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?
How can static RPM calculate air speed when the aerodynamics of the airframe is a variable?
02-13-2014, 10:18 AM
#15
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.
02-13-2014, 02:50 PM
#17
Senior Member
Propellers are more effecient @ lower RPM.
02-13-2014, 02:52 PM
#18
Senior Member
02-13-2014, 03:45 PM
#19
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
The only way you know for sure is put it in the air and see what happens.
02-13-2014, 03:48 PM
#20
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
02-13-2014, 06:15 PM
#21
Senior Member
That's my point. Just using static RPM tells little about actual top speed.
02-13-2014, 07:16 PM
#22
Join Date: Jul 2004
Location: Middleboro, MA
Posts: 3,275
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
02-13-2014, 07:46 PM
#23
My Feedback: (18)
Join Date: Jul 2002
Location: Fairfield,
CA
Posts: 254
Likes: 0
Received 0 Likes
on
0 Posts
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.
Lance
Lance
02-13-2014, 10:05 PM
#25
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.;-)
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.;-)