# Tillotson 212cc and 225cc on efficient ultralights?

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#### patrickrio

##### Well-Known Member
I had been looking at the least expensive 4 stroke engine options that might be used in high efficiency ultralights and had identified the Tillotson 1 cylinder 4 strokes as very likely options. They are promising enough that I think they should have their own thread. There is not a good place to put this in the Engine section, and since they really are not likely to be useful anywhere but on an ultralight I have put the post here.

Even the $200 base model comes shipped with crank and valve mods normally done to handle aircraft use, and it also comes with a mechanical fuel injection option which is interesting. And the weight is not too bad either, at 42lbs shipped with a likelihood of reaching mid 30s pounds in weight in the most lightened aircraft versions.... For flying aircraft, they might be a great option for cheaply replacing the dual motors on a Lazair??? Can an ultralight be designed that is light and efficient enough to fly right around 55 knots top speed while retaining a 500ft/min climb for takeoff and downdraft safety, all on the 9+HP of a single Tillotson 212cc? Seems like a worthy challenge..... And it seems that there is already a member testing. REVAN, who I believe is the son of Jedi Has been doing this: My Tillotson 212cc test engine has the electric starter and the steel fuel tank on top. It is stock, with the only modification being a prop flange and propeller attached to the engine shaft. On the test stand, I've got about 40 hours on the engine so far. The test engine as it stands weighs in at 42 pounds with oil. I'm intending to just use recoil start on my ultralight (at least in the beginning). Dropping the starter, steel fuel tank and oil from the engine's empty weight should get it down below 39 pounds. Then if I want to shed more weight, I'll replace the iron fly wheel with an aluminum one. That will cost about$100, and should bring the engine+propeller weight down into the 35 to 36 pound range. Cost for the engine with aluminum flywheel and propeller will be around $500 for about 10 Hp, or$50/Hp.

If it is too underpowered, one option is to upgrade to the 225cc engine. I figure I can prop it to de-rate the 17.5 Hp engine down to about 14 or 15 Hp and still direct drive the propeller. This will provide more margin on heat rejection than running it at 17 Hp. The downside is the 225cc engine is more expensive and drinks premium fuel instead of regular. I'll be looking at more like $1000 for engine+propeller, or about$70/Hp. So, for about double the installed cost and also more noise and more expensive fuel, I can get about 40% to 50% more power.
In any case, I think these engines need their own post so information on them can be grouped in one place.....

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#### Daleandee

##### Well-Known Member
Can an ultralight be designed that is light and efficient enough to fly right around 55 knots top speed while retaining a 500ft/min climb for takeoff and downdraft safety, all on the 9+HP of a single Tillotson 212cc? Seems like a worthy challenge.....
Interesting engines and quite a challenge. I don't know of any ultralight flying on 9 HP but I'm not one of the smart ones.

#### patrickrio

##### Well-Known Member
Theoretical bottom end HorsePower needs roughly calculated:

1HP=550lbs lifted 1 foot in a second=lifted 60ft in 1 minute
10HP lifts 550lbs 600ft/minute so 500ft/minute climb in an airplane that has a sink rate of 100ft/min

550lbs * 0.70= 385lbs maximum gross weight when counting 30 percent efficiency loss in propeller etc...

so, 170lb pilot, 30lbs fuel and 35lb engine equals 150lbs for everything else.

It would be quite a challenge for sure. My TLAR investigation says that such a plane will be so aerodynamically efficient in order to have a 100ft/min sink rate that it should maintain level flight at 55knots with around 2HP..... as long as it's structure is strong enough and resists flutter/resonance enough for the forces!!

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#### TFF

##### Well-Known Member
When you called it a challenge, you got the exercise right. It’s a challenge. You would have to afford to fail while you honed in on it working. Overall it would be pretty expensive compared to going with more horsepower. World record holders will work for years to get their name in the book. Those craft are never meant for fun flying.

#### Dana

##### Super Moderator
Staff member
Can an ultralight be designed that is light and efficient enough to fly right around 55 knots top speed while retaining a 500ft/min climb for takeoff and downdraft safety, all on the 9+HP of a single Tillotson 212cc? Seems like a worthy challenge.....
I would say... no. Build a plane that can fly on 9HP, sure. Build one durable enough for everyday use, safe to fly in anything but dead calm... not gonna happen.

#### patrickrio

##### Well-Known Member
My thought is that you would iterate. First you start with a light and efficient existing airframe that can operate on around a 25HP engine, and then you iterate it to be more light and efficient until it will operate on the 17.5HP 225cc Tillotson (17.5HP only used for takeoff and downdraft emergencies...) and continue to iterate until it can fly on 10HP at which point you switch to the lower cost Tillotson and hopefully have an aircraft that can be reproduced at a reasonable cost.

So you would start with an existing airframe that would work well as a test frame as you iterate.

A Skypup is already not too far off of requirements at 22HP and 195 empty weight including a 42lb Cuyuna 215RR (everything else besides fuel, pilot and engine is already 153lb on a Skypup....) You might be able to get a skypup to work on the 17.5HP Tillotson just as it is if the pilot is light.

But while the Skypup is an amazing airplane, I'm not sure it would make a good starting point for iterative testing. It IS a good place to look for inexpensive and light building ideas though.

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#### WonderousMountain

##### Well-Known Member
Yeah,
I'm going to have to ask you for a turbo.
Sir,
CK LuPii

#### jedi

##### Well-Known Member
I had been looking at the least expensive 4 stroke engine options that might be used in high efficiency ultralights and had identified the Tillotson 1 cylinder 4 strokes as very likely options. They are promising enough that I think they should have their own thread. There is not a good place to put this in the Engine section, and since they really are not likely to be useful anywhere but on an ultralight I have put the post here.

Even the $200 base model comes shipped with crank and valve mods normally done to handle aircraft use, and it also comes with a mechanical fuel injection option which is interesting. And the weight is not too bad either, at 42lbs shipped with a likelihood of reaching mid 30s pounds in weight in the most lightened aircraft versions.... For flying aircraft, they might be a great option for cheaply replacing the dual motors on a Lazair??? Can an ultralight be designed that is light and efficient enough to fly right around 55 knots top speed while retaining a 500ft/min climb for takeoff and downdraft safety, all on the 9+HP of a single Tillotson 212cc? Seems like a worthy challenge..... And it seems that there is already a member testing. REVAN, who I believe is the son of Jedi Has been doing this: In any case, I think these engines need their own post so information on them can be grouped in one place..... That is correct. So, I thought you might like my generalized opinion. The twin engine Lazair configuration would be a good place to start. I am not sure how the Lazair would handle the additional weight. The 9+ hp stock engine in a single engine UL will have marginal performance and / or be too delicate and expensive. The advantage of the stock engine is that it can swing a good size prop on a direct drive and get a reasonable propulsive efficiency. When you put money in upgrades for more power you generally get more rpm and the noise goes up and the propulsive efficiency goes down. It gives you everything you do not want. It is much better to put another$200 in engines and keep the efficient direct drive with the low disk loading on the propeller and get twin engine safety (if there is such a thing) as a byproduct. You could even do a tri-motor and have better engine out performance.

There is another option that is an interesting concept IMHO. The concept applies to the industrial V twins as well as the Tillotson 212cc engine. That is a single engine configuration with some upgrades for additional power. Even with a clean light airframe electric (or other power boost) would probably be needed for takeoff and climb. With sufficient electric boost you could do some upgrades on the engine but pitch the prop for the low power stock rpm to allow a WOT low rpm cruise mode. Use the electric power assist for takeoff and climb to allow the engine to rev up to the higher rpm. The system gives the advantages of a variable pitch prop but with an inexpensive fixed pitch prop that falls within LSA limitations. In cruise use any excess power available to charge the batteries and reduce WOT rpm to the desired cruise speed. This would hopefully help with the FAR max speed limit and perhaps give some power redundancy.

Of course the power assist could also be used on a multi-engine configuration if the max weight is not exceeded.

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HBA Supporter

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#### patrickrio

##### Well-Known Member
A slightly different approach. The engine creates thrust moving the airplane forward. Drag retards the plane and the climb angle is the determined by (thrust - drag)/weight in radians. If the Skypup has a takeoff weight of 400 lbs and an L/D of 10 at 40 mph, then the drag might be 40 lbs. To climb, thrust has to exceed 40 lbs. If the engine produces 15hp and the efficiency is .7 then the thrust at an airspeed of 40 mph might be (375 lb-mph/hp x 15 hp x .7)/40 mph = 98 lbs. And the reserve thrust is 98-40 = 58 lbs. And the climb angle is 58/400 = 0.145 radians. The climb rate is then .145 x 40 mph = 5.8 mph or 510 ft/min, a reasonable number. Use 9 hp and one gets a feeble 165 ft/min. Similarly, the minimum sink rate of the Skypup can be estimated to be about 350 ft/minute.
Yep. My TLAR Minimum required HP calculations are only approximately right at the specific airspeed where min sink occurs too. Max Glide ratio usually occurs at a different speed than min sink, so it will have a faster sink rate than at min sink speed.

The Skypup only has a 12/1 glide ratio per wikipedia, so it probably is not close to being a candidate for 9-10hp and MAY be a candidate for a 17.5hp engine with a light pilot. It is already at 450ft/min max climb (likely at or near min sink speed) with 22hp at max throttle and a 175lb pilot (400lbs gross full fuel). All of this, and even BobDaly's post are just greater/lesser levels of TLAR until an actual design is tested and succeeds anyway.

My TLAR calcs for required airplane stats to get to a 9-10HP capable aircraft are: 190lbs empty weight, Pilot 160lbs, L/D of 30/1 or better, min sink about 100ft/min. Really hard to get to these stats I think, but not impossible I bet.

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#### REVAN

##### Well-Known Member
My TLAR calcs for required airplane stats to get to a 9-10HP capable aircraft are: 190lbs empty weight, Pilot 160lbs, L/D of 30/1 or better, min sink about 100ft/min. Really hard to get to these stats I think, but not impossible I bet.
Though it could be done, I don't see the point of using a single 212cc engine. The engine is inexpensive. Just use two of them. It is much easier to make something that can fly on 20 HP than it is to make something that can fly on 10. If using this engine because it is inexpensive, it does not make sense to use only one cheap engine, thus forcing you to integrate it into an expensive high performance airframe. This is not a viable path to an affordable ultralight aircraft.

I'm planning on using two of these engines with an option to step it up with a third engine. With three engines at 30 HP total, attaining good performance starts to look pedestrian. Minimum acceptable performance on 20 HP is doable.

#### patrickrio

##### Well-Known Member
I think an aircraft similar to the "American Eaglet" would be a better starting point for a test aircraft than the SkyPup. Link: American Eaglet

Note that the aircraft as kit sold did not hold enough fuel (5 gal should be standard on an ultralight I think, not half a gallon) It also did not meet the 24 knot stall speed requirements of part 103. It was built for a 200lb pilot though, so a lighter pilot could swap in a larger fuel tank....

It weighs 160lbs empty including the McCulloch 101b engine 12.5HP (I could not find a weight for the engine...) and has a 25/1 L/D and gets a manufacturer reported 400ft/min climb at max weight on 12.5HP (Maybe....Maybe)

I think an aircraft in this form with carbon pultrusion spars built cantilever wing, and about 100sq ft wing area instead of this planes 72sq ft might be in the vicinity. And maybe build the propeller to rotate around the tail tube so the prop diameter can go up for efficiency... maybe belt drive from engine to a carbon tube drive shaft around the tail tube. (wild ass TLAR thinking here)

There were supposedly 400 kits ordered with 20 completed aircraft out there somewhere and an undetermined number of kits delivered so maybe one could be found.

BIG caveat... the nest of dragons website has a pilot report that says it lacked sufficient stability to be safe.......

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