Need to Make New 2-Stroke

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StarJar

Well-Known Member
OK here goes.
I've been mulling over engines for a less-than-200 lb. ultralight, that has a 14-1 glide ratio.
To cut to the chase I want an engine that is less than 50 lbs, puts out at least 30 HP, is direct drive, has low fuel consumption, and doesn't have terrible vibration.
After wandering around this site, the internet, and YouTube, what my idea is is this;
A 2-stroke, with through-the-case induction, an exhaust valve at the top (head), and a cam that is also a balance
shaft.
I also though a longer/narrower bore would be a good feature, to give more torque.
I'm a Powerplant School graduate, and have experience as an engine machinist and engine builder (Type I VWs).
But if I do this I'll probably be learning new things like a kindergartner.
I wish I had experience in John Chotia's shop because I want to cast the case and heads (when everything is layed out).
Any thoughts, comments, or applicable references for a kindergartener would be useful. Thank you.

Aviator168

Well-Known Member
Don't understand the reason you want a new 2 stroke for this class of planes. There are existing 2 strokes that fit the bill except they are not direct drive.

TFF

Well-Known Member
A 30 hp direct drive two stroke will be a thumper; even with a balance shaft. The weight of the balance shaft could be converted in to a piston. It has been done as a 4 stroke with the crankcase induction and valve exhaust. I dont think there is going to be enough filling of the cylinder without the normal two stroke porting . It is where the direct injection works; no fuel is squirted until the ports are closed, but the charge air does flow. I think it would be cool to make an engine. I have always wanted to make one on the model airplane size; mainly radial. I dont really see how a valve will help when it comes to flow and holding combustion. You cant delay the opening too long as the intake will be opening and you dont have the extra stoke to clean out the exhaust.

StarJar

Well-Known Member
The horsepower is too marginal on existing 2 stroke singles, and they suffer from high fuel consumption.
The Polini has the HP but the fuel consumption is typical two stroke and the price is high.
Also to get the 14-1 l/d ratio, I had to keep the prop hub low, so I don't want a longer prop.
With a taller narrower bore, and an exhaust valve at the top, mixture thrown overboard can be avoided I believe.
I was also glad to hear that C. Racer felt that such an arrangement would keep the piston cooler, and keep the rings and case cleaner.

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StarJar

Well-Known Member
A 30 hp direct drive two stroke will be a thumper; even with a balance shaft. The weight of the balance shaft could be converted in to a piston. It has been done as a 4 stroke with the crankcase induction and valve exhaust. I dont think there is going to be enough filling of the cylinder without the normal two stroke porting . It is where the direct injection works; no fuel is squirted until the ports are closed, but the charge air does flow. I think it would be cool to make an engine. I have always wanted to make one on the model airplane size; mainly radial. I dont really see how a valve will help when it comes to flow and holding combustion. You cant delay the opening too long as the intake will be opening and you dont have the extra stoke to clean out the exhaust.
It would have normal 2 stroke porting as far as induction is concerned.
As far as mixture escaping through the exhaust, the idea is to time it so the exhaust port is closed before the raw mixture reaches the top. You can't do that with a normal 2 stroke.
As far as being a thumper, why wouldn't the cam/balance shaft make it smoother than all the thumpers that don't have one?
Thanks for your input though.

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TFF

Well-Known Member
I understand what you are wanting. but some of the two stroke cylinder filling is boosted when the exhaust is opened even if some fuel makes it out the exhaust. Also with a valve in the top, the expanding gas is driving the piston down, I assume you want late exhaust to get the most power, but now the exhaust gas has to reverse direction without the help of an exhaust stroke. It will have a lot of hot exhaust when the intake port opens. As for the balance shaft, it would be smoother. Just lot of weight for smoother when you could be putting the weight to work as a piston. http://www.optimum-power.com/Virtual 2-Stroke.htm might be fun to play with. I bet a 3000 rpm direct drive two stroke would be 45 cid. About a Chevy 350 cylinder worth.

StarJar

Well-Known Member
I understand what you are wanting. but some of the two stroke cylinder filling is boosted when the exhaust is opened even if some fuel makes it out the exhaust. Also with a valve in the top, the expanding gas is driving the piston down, I assume you want late exhaust to get the most power, but now the exhaust gas has to reverse direction without the help of an exhaust stroke. It will have a lot of hot exhaust when the intake port opens. As for the balance shaft, it would be smoother. Just lot of weight for smoother when you could be putting the weight to work as a piston. http://www.optimum-power.com/Virtual 2-Stroke.htm might be fun to play with. I bet a 3000 rpm direct drive two stroke would be 45 cid. About a Chevy 350 cylinder worth.
Well you've caught the arguable point about the mixture burning downward and then exiting upward, but there is another way to look at it. During combustion its the burning that creates pressure which is much more dominant than how the charge was moving when compression began.
Also the part burning first is the first to exit, so when the exhaust valve opens just a little, all the mixture has a chance to burn and still create some power until the valve is fully open.

The exhaust will start opening sooner on the downstroke, especially if you go by piston travel, rather than crank degrees, because of the narower, longer bore, as compared to what's happening on a conventional 2 stroke.

The exhaust also can still pull mixture into the cylinder.. except more in the direction of filling the cylinder than a normal 2 stroke.

As far as the balancer it's using the same bearings and space with the cam.
On the single it can be placed, I think, 45° up from the crank, opposite the intake port to save casting weight..
It going to add some weight but not nearly a much as another piston, cylinder, head, and larger case and crank, IMO.

And thanks for the link. Will go there.

Edit: I know you think I didn't understand you about the timing of ports, and how normal 2 strokes work, but this is a whole different animal with different cylinder dimensions and 'valve' overlaps. Probably no overlap, which is more doable with a longer stroke, at least in my imagination. (I need to make model myself to so I can see this all more clearly.)
And...with this size prop, a 3500 - 4000 rpm redline is what I was thinking.

edit II: Oh wait there will be valve/port overlap, which depends on when fresh mixture gets pulled/pushed up to the exhaust valve. Actually all that was used on a Detroit diesel if I recall another thread correctly.

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cheapracer

Well-Known Member
Log Member

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Armilite

Well-Known Member
OK here goes.
I've been mulling over engines for a less-than-200 lb. ultralight, that has a 14-1 glide ratio.
To cut to the chase I want an engine that is less than 50 lbs, puts out at least 30 HP, is direct drive, has low fuel consumption, and doesn't have terrible vibration.
After wandering around this site, the internet, and YouTube, what my idea is is this;
A 2-stroke, with through-the-case induction, an exhaust valve at the top (head), and a cam that is also a balance
shaft.
I also though a longer/narrower bore would be a good feature, to give more torque.
I'm a Powerplant School graduate, and have experience as an engine machinist and engine builder (Type I VWs).
But if I do this I'll probably be learning new things like a kindergartner.
I wish I had experience in John Chotia's shop because I want to cast the case and heads (when everything is layed out).
Any thoughts, comments, or applicable references for a kindergartener would be useful. Thank you.
=============================================================================

You would be much further ahead, and Cost you much less , if you just Read, and Learned How to Design and Build a 2 Stroke first. Then just make upgrades, some call them Mods, to these many older 2 strokes to make them even better, and make more HP. To make only 30hp is not that big a deal today. Almost all 2 Strokes ever made for Sleds could be built to make that. Those Engine companies spent millions on R&D perfecting them. If your taking CAD in your Class's, draw some of these 2 Strokes into CAD, and make upgrades to them. A good engine to upgrade, and parts are cheap to buy to Reverse Engineer, would be a Skidoo/Rotax Single. Mate the back half of a 335 Case to a 277 Front Case, then Upgrade the 277 Front Case to Provison 8. You have 246/247/250, 277, 292, 299/300/302, 318/320, 335/340's to chose from. A 1971 Stock Blizzard 340 Single was 36hp, the Stock Blizzard 292 was 31hp, the Stock Blizzard 246 was 29hp. The Stock 277 was 26hp, with a better Tuned pipe made 30.5hp.

Lot's of older 2 Strokes didn't use a Tuned Pipe which can add 20-30% HP over a Muffler. Some were rated at Lower Rpms for the day.

Most 2 Strokes were never Race Prepped for making Maximum HP. So Porting and Polishing the Case and Cylinders for better Air/Fuel Flow can add another 10-15% HP.

Some 2 Strokes used low Compression. To be Efficent you need to use a CR somewhere in the 11.2 to 11.8 CR Range.

Industry Standard today for 2 Strokes used on Planes is 6500rpms. At 6500rpms it takes on Average 7cc to make 1hp. A 70's Yamaha 292cc Single made the most HP of any Singles, 70hp at 9200rpms, it was 50hp at 7000rpms for Oval Racing. It was Reed Fed, Skidoo's Piston Port 292's were best 50-55hp.

Blair and Jennings and Bell were the guru's of 2 Strokes, they all wrote Books.

http://www.amrca.com/tech/tuners.pdf

http://iheartstella.com/resources/manuals/tuning/Graham-Bell-Two-Stroke-Performance-Tuning.pdf

http://edj.net/2stroke/BellPerformanceTuning/Bell Chapter 3.pdf

http://www.2-stroke-porting.com/Port_Work.html

Read all thin Info above, and you will be able to Design, and Build a very healthy 2 Stroke. Look at many different Engines to see what each Company did to make them better. Look where they Fail. All of these different Engines have a History of upgrades.

Rotax held over 80% of the World Market in the 2 Stroke category on Airplanes, so there more abundant. Kawasaki 340/440's are also good engines, but not much in aftermarket parts for them, or upgrades. Some Yamaha's are being used with good results.

The only 2 Stroke that I know of that was used in Direct Drive was the 185UL 9.4hp at 5000rpms. A Simple Belt Drive is a much better option, a Gear Drive is even better.

Some Dyno Prints of some Rotax motors, some Stock, some with R&D's Tunned Pipes.

There is No Such Thing as a Free Lunch, to make HP, it takes so much Fuel. Take a new 670cc 4 Stroke 22hp Single that People want to say it sips Gas, and still weighs more than the 670cc Sled motor, and compare it against a 670cc 2 Stroke that maes 92hp at 6400rpms. Of course, the 2 Stroke is burning more Gas Per Hour, it's also making way more HP!
Match motor's who make equal HP, and there Fuel Burn with be closer. A 277(26hp) with a 2.0gph, the 670cc 4 Stroke making that Max 22hp, would probably be close to that same 1.8 - 2.0 gph. It takes so much Power to move so much weight so fast. A 277 at 5000rpms makes 23.2hp with a 1.8gph.

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BBerson

Light Plane Philosopher
HBA Supporter
A large two cylinder such as Rotax 532 is 64hp with gearbox or 30hp direct drive (around 65 pounds). Probably low priced.
Search for "direct drive" two stroke to read Mark Stull's experiments.

Armilite

Well-Known Member
A large two cylinder such as Rotax 532 is 64hp with gearbox or 30hp direct drive (around 65 pounds). Probably low priced.
Search for "direct drive" two stroke to read Mark Stull's experiments.
A 532 would not make his 50lb requirement. You also got Cooling weight and drag.

BBerson

Light Plane Philosopher
HBA Supporter
A 532 would not make his 50lb requirement. You also got Cooling weight and drag.
Might not get to 50 pounds but maybe close or with another similar lighter engine.
I figured at 25-30hp Max direct drive and cruising at just 15hp after a brief takeoff it might have a small cooling load.
With big fins bolted to the heads the liquid cooling could be small or almost completely removed to save weight. The rope start and alternator and the flywheel removed also for direct drive. I haven't studied it yet, but the idea is to get a two-stroke like a large direct drive model. No flywheel. Minimal muffler.

The Rotax was designed for a gear box and requires a flywheel with the gear box but not direct drive because the prop becomes the flywheel. (need some alternate ignition)
Hacking it to direct drive requires some surgery, but might be easier than designing from scratch. I guess an air-cooled 503 would be the lightest with no flywheel, but less hp.

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StarJar

Well-Known Member
That's some impressive stuff Armalite, and I'm amazed at the way you put those 2 strokes together. I think you could write a book yourself.
The most influential thing you said is the R&D that goes into an engine.
I just wanted to focus on a few concepts, that together would create an entirely new type of performance. Not many planes would benefit from it though.
My plane design is a freak though. It can't use a large prop because it sits low to the ground. It's a low drag design and should climb and cruise with a 50" prop.
If it burned 1.5 gal or less I could make the trips in it I want to make, with about 200 mile legs.
I guess I could hide some fuel in the wing and build a modded engine like you describe (and make it DD as BBerson suggests), or see if I can get the Vegas Carts 460 to work out weight wise and durability wise.
Or screw around with my concept engine to see what it can do.
Thanks for the options. For short term a modded 2 stroke would be hard to beat, I think.

Edit; Thanks for the reference links Armalite. I already started on the first one!

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Armilite

Well-Known Member
Might not get to 50 pounds but maybe close or with another similar lighter engine.
I figured at 25-30hp Max direct drive and cruising at just 15hp after a brief takeoff it might have a small cooling load.
With big fins bolted to the heads the liquid cooling could be small or almost completely removed to save weight. The rope start and alternator and the flywheel removed also for direct drive. I haven't studied it yet, but the idea is to get a two-stroke like a large direct drive model. No flywheel. Minimal muffler.

The Rotax was designed for a gear box and requires a flywheel with the gear box but not direct drive because the prop becomes the flywheel. (need some alternate ignition)
Hacking it to direct drive requires some surgery, but might be easier than designing from scratch. I guess an air-cooled 503 would be the lightest with no flywheel, but less hp.
==========================================
The only engines that would even come close to his Spec's of 30hp, Weight 50lbs or less, and get good GPH, is a 2 Stroke Single with Fuel Injection! Belt Drive don't weigh that much, and would be much better than Direct Drive for a 2 Stroke to be Efficent!

185UL - 184cc/7cc = 26.2hp. 184cc At 100% efficent could make 28hp at 6500rpms. If Bored Oversize you could make 30hp.

246/247/250 - 250cc/7cc = 35.7hp. 250cc At 100% efficent could make 38hp at 6500rpms.
'
First off, you also have to Design the Airframe right for Part 103 254lbs. A Lazair with Twin 185ULs was only 220lbs! A New 2017 Phienoix 103 with a Hirth 50hp makes 254lbs. A T-Bird I tail dragger even makes 254lbs with a 277. It's 280lbs with a 447.

Armilite

Well-Known Member
That's some impressive stuff Armalite, and I'm amazed at the way you put those 2 strokes together. I think you could write a book yourself.
The most influential thing you said is the R&D that goes into an engine.
I just wanted to focus on a few concepts, that together would create an entirely new type of performance. Not many planes would benefit from it though.
My plane design is a freak though. It can't use a large prop because it sits low to the ground. It's a low drag design and should climb and cruise with a 50" prop.
If it burned 1.5 gal or less I could make the trips in it I want to make, with about 200 mile legs.
I guess I could hide some fuel in the wing and build a modded engine like you describe (and make it DD as BBerson suggests), or see if I can get the Vegas Carts 460 to work out weight wise and durability wise.
Or screw around with my concept engine to see what it can do.
Thanks for the options. For short term a modded 2 stroke would be hard to beat, I think.

Edit; Thanks for the reference links Armalite. I already started on the first one!
==================================================================
You say Ultralight, is that a USA Part 103 Ultralight? Max it can weigh Dry is 254lbs, Max Gas it can carry is 5 US Gallons! Max Speed is like 67mph. Minimum Stall Speed is 24 knots. So you have to live in them guidelines. The Best you will probably get is 2hrs of Flight with a very little Reserve with 5 Gallons. SPEED and Good GPH don't go together! I would say most True Part 103 Ultralight's average 35-40mph, so that 2hr Flying envelope is 80 miles and you would have to refuel.

If, you need a Plane just for Transportation to Travel 200 miles quick, that's Cheap to Build or Buy. I would look at a Quickey(Q1) originally with a 22hp Onan, I believe it does 120mph, made of Foam and Fiberglass. They have put everything from a Onan 22hp to a Skidoo 583(97hp) on one. Plans are on ebay cheap, Free on the net if you look around. But you would need at least a Sport Pilot license, maybe a Private.

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Armilite

Well-Known Member
277 PTO Case mounted on a 335 Case to make a Free Air engine. Only the 185UL and 277/277UL have the four holes for a Gear/Belt Drive on PTO Case. It Bolt's up ok, the Decks need leveled. Old Skidoo's had Straight PTO 1" Shafts, the 277 and later Skidoo's had bigger 30mm OD PTO Shafts with a 1:10 Taper. You can make about any Stroke you want for a Single, out of a Skidoo Twin Crank, 61mm, 64mm, 66mm, 68mm, 70mm. You can also change Rod Lenghts.

Some where, I read once, a long time ago, a 2 Stroke should always use a Rod Lenght at least twice it's Stroke. All Skidoo's use to short of Rod lenght, that's one of the reasons they Viberate a lot, and take out Crank Pin Bearings. Cranks being out of True is also part of the problem. Racers true them to .001" or less. Skidoo says .0035" is ok. Many New Replacement Cranks come .007" Out of Wack! Do we blame Rotax or the UPS guy? Racers either Weld, Pin, or Epoxy Glue, them after truing. Skidoo/Rotax doesn't Balance the Assembly either.

277(72mm x 66mm) 268cc use's 120mm Rods, 66x2= 132mm
377(62mm x 61mm) 368cc use's 120mm Rods, 61x2= 122mm
447(67.5mm x 61mm) 436cc use's 120mm Rods, 61x2= 122mm
503(72mm x 61mm) 496cc use's 120mm Rods, 61x2= 122mm

532(72mm x 64mm) 521cc use's 125mm Rods, 64mmx2= 128mm
582(76mm x 64mm) 580cc use's 125mm Rods, 64x2= 128mm
618(76mm x 68mm) 617cc use's 125mm Rods. 68mmx2= 136mm
670(78mm x 70mm) 669cc use's 132mm Rods, 70x2= 140mm

Most newer 2000+ Skidoo's use 132mm Rods.

A longer Rod will put less Force on the lower Bearings and Pistons sidewalls, with more Dewel Time at TDC for a better Fuel Burn!

Notice the Case Port on the 277 Case are much Bigger than the 335(78mm x 70mm) Port! This Oly 335 was rated at 22hp with a Muffler, a Blizzard 340(78.5mm x 70mm) had the bigger Case & Cylinder Ports, and used a Tuned Pipe for 36hp.

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StarJar

Well-Known Member
My design looks something like this.

...

The wings are laying on the floor but it's a mid wing. It has a long way to go to becoming a real plane.
Tests show it goes pretty well on low HP.
A 50 lb. engine could put the empty weight below 200#. But an engine above 50# makes problems. The pilot is too far back.
I want to use a monowheel. Much easier on this plane, and cleaner!
Anyway, I'll figure out something for the engine.
Armalite (and I guess a everyone else) has got me thinking of messing a bit with existing stuff.
I think Mark Stul broke the crank on his DD engine. I'll have to consider that.

BBerson

Light Plane Philosopher
HBA Supporter
I don't think Mark Stull broke a crank with direct drive. Direct drive is more suited to low drag designs such as your design.
But he used direct drive on his high drag designs and was still successful.
All the RC engines* are direct drive. The prop rpm isn't a problem at low power.
The Lazair and Chotia was direct drive.
There was a four cylinder Nelson direct drive.

* that I see

StarJar

Well-Known Member
Thanks guys.
And Armalite, that is cool stuff.
But my new question, if going the DD single route (or perhaps small twin), what would an expert change if he had to operate with a 4,000 rpm redline. Probably never's been done. But port placement is like the camshaft. So what I'm going to try to find is port mods for low RPM operation....and maybe do it more to make 4,000 rpm as good as possible.
Just an idea. But I need to read more.
'

Aviator168

Well-Known Member
I would look at a Quickey(Q1) originally with a 22hp Onan, I believe it does 120mph, made of Foam and Fiberglass.
The Quckey is canard. Anyone know a conventional layout aircraft can do this? 22hp and goes 120mph is incredible.