POLINI THOR 250

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Mark Roberts

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I am about to buy a Polini Thor 250 engine for a puller style ultralight. From everything I have seen it seems like the engine should work but does anyone know of any problems with that engine that I overlook. Thanks
 

Victor Bravo

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Armilite is 100% correct here; common sense tells us running ANY high performance engine at its maximum possible power level for any length of time is going to shorten its lifespan a lot.

It must be understood that the people writing the brochures for these engines are part of the sales department, not the engineering department. The Polini, Simonini, and probably other hi-po 2-stroke engines will probably make their 36HP as advertised, but the engines were designed for a "duty cycle" that is nowhere near 100%. I have no experience in paramotoring, but the videos I have seen SEEM to indicate that they are flying around at cruise power after takeoff, not "wide open throttle".

When we translate this from sales language into aviation language, what it means is that the engine is safely rated for 36HP for takeoff and maybe a minute or two, then the "maximum continuous power" from that point onwards has to be accepted as something less than 36HP.
 

billyvray

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They are good looking engines. Polini has a LOT of experience in the high performance scooter market (don't scoff, some of those things FLY!), but I agree, scooter duty vs airplane at WFO throttle alot of the time is not great.
 

Bille Floyd

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Polini Thor , has a Very good reputation ; for building dependable
ultralight aircraft engines. They even go so far as to tell ya, how
much time, each component in the engine ; should last, under
normal usage.

Bille
 

cgifly2

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Good advice! Always try to use an engine thats rated for 1/4 more hp then you need. So at cruise it is at 3/4 of its maximum output. Especially 2 strokes. I am a definite proponent of 2 strokes and have successfully flown behind them on that principle for many trouble free hours. I use as an example my Hummelbird that I flew with a McCullogh engine rated at 72hp @4200rpm. The Hummelbird flies fine on a 36hp half VW but must run at or near full power. and there are plenty documented engine failures. Not that the Mac has a perfect record, but most 2 stroke failures are traced back to quitting under full power or right after being run full power and having the throttle shut off creating a lean condition. But I ran the Mac at 3800rpm cruise without taxing it and never had a problem. Point being never plan on needing a 2 strokes maximum output and you will good!
 

Flyguyeddy

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Good advice! Always try to use an engine thats rated for 1/4 more hp then you need. So at cruise it is at 3/4 of its maximum output. Especially 2 strokes. I am a definite proponent of 2 strokes and have successfully flown behind them on that principle for many trouble free hours. I use as an example my Hummelbird that I flew with a McCullogh engine rated at 72hp @4200rpm. The Hummelbird flies fine on a 36hp half VW but must run at or near full power. and there are plenty documented engine failures. Not that the Mac has a perfect record, but most 2 stroke failures are traced back to quitting under full power or right after being run full power and having the throttle shut off creating a lean condition. But I ran the Mac at 3800rpm cruise without taxing it and never had a problem. Point being never plan on needing a 2 strokes maximum output and you will good!
I bet that was a LOUD bird
 

PMD

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I realize that this is not a 4 cycle forum, but just wanted to add a note as to engine design vs. engine use power levels. When we build things that are supposed to be "high performance" in the automobile world, they will seldom see 100% at all and can expect to cruise on as little as 10% of their design/rated power. BUT: if you go back to the immediate post-war period, there were a lot of cars (and motorcycles) designed with marginal power, need 100% to move from rest and cruised at very high percentages. In 36 and 40HP VW days, I (and almost everyone I knew) had a standard throttle position for all operation except under braking - WFO. That is why VW engines can be viable direct drive aircraft engines.

Fast forwarding to the 2 cycle world of today: Many 2 cycle installations fall into that same "high performance" category where their huge power output (and fuel consumption) are only used on acceleration (thinking snowmachines now, but watercraft would come close) part of the use cycle. The SMALL outboard motor world probably comes a lot closer to aviation duty cycles than anything else out there (OK, weed whackers would be a good exception, but not too many one HP a/c designs flying with people on board).
 

Armilite

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They are good looking engines. Polini has a LOT of experience in the high performance scooter market (don't scoff, some of those things FLY!), but I agree, scooter duty vs airplane at WFO throttle alot of the time is not great.
=========================

Good Looks doesn't make them dependable. Doing good Maintenance and Using Good 2 Stroke Oil and using Fresh 91+ Octane Gas for 9.5cr - 10.8cr and 93+/100LL for anything higher than 10.8cr are what makes them reliable. Polini is pushing them Small CC Engines too High of rpm for Airplane use, even burning 100LL they don't last. 36hp @ 8000rpm is too High! With a 450hr TBO and used at that High rpm on Trikes they only last about 250-300hrs. Using Max 6500rpm with 93+/100LL and 40:1 Conventional Oil or 90:1 Synthetic with the different Engine Coating could extend the Engines Life. I would use the Evans Waterless Coolant also.

2 Stroke Engines Main Failures.
#1 Detonation, easy to Solve use Fresh 93/100LL.
#2 Seizures, mainly from people using Poor 2 Stroke Oils with low Flash Points.
#3 Leaking Rubber Carb Boots & Case Seals. Use the best Seals and Carb Boots. JBM.
#4 On Water Cooled Engines, Head Gaskets causing Hydro Lock. Use Evans Waterless Coolant, it doesn't Boil.
#5 Carb Ice. Install Carb Heat or use EFI.
#6 People messing with the Jetting.

A burnt Hole in the middle of a Piston is a jetting issue.

Small Pin Holes on the Piston Top or pitting around the Edges. or broken Edges of a Piston is a Detonation issue. Here is a 583 Skidoo I bought still running but with low compression on one side. This is what Detonation looks like.
 

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Armilite

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You are Correct Dana, but you can also upgrade that Time by using Higher Octane Gas, and using the better High Flash Point Oils and these Engine Coatings. HP + BTU's made. You have both BTU Heat made and you also have Friction Heat made from rpm used. Do you ever notice you hardly ever see the Top of the Piston Melt unless someone is messing with the Jetting and then melts a Hole in the Center of the piston, it's on the Side of the Piston that Melts to cause a Seizure. Aluminum Melts at 1221 F. If you use all of the Engine coatings you can reduce your overall Temps by 20% and if you use say 100LL it should be even lower say 22% Cooler. IF your Continuous cruise is at 75% Power, with the Higher Octane and the Engine Coatings you could run it at a higher rpm = more hp. Example 50hp at 75% = 37.5hp = 1,591.687 BTU/min. 37.5hp + 22% = 45.75hp = more Speed.

582UL = [email protected] = 2,758.923 BTU/min (Water Cooled).
503UL = [email protected] = 2,122.249 BTU/min
447UL = [email protected] = 1,697.799 BTU/min
Thor250 = [email protected] = 1,528.019 BTU/min (Water Cooled).
377UL = [email protected] = 1,485.574 BTU/min
MZ34 = [email protected] = 1,273.349 BTU/min
277UL = [email protected] = 1,188.459 BTU/min
277UL = [email protected] = 1,103.569 BTU/min
 

cluttonfred

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Of possible interest...

 

Armilite

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Of possible interest...

==========================

Badlands doesn't show a 303 Price yet!

Polini Thor 303, 38hp at 8000 rpm!
(76mm x 62mm) 281.3cc at 6500rpm is probably 30-31hp Max!

$???????

Polini Thor 250 DS, [email protected]!
(72mm x 60mm) 244.3cc at 6500rpm is probably 29-30hp Max!
$4,900+


Polini Thor 202, [email protected]!
(64mm x 60mm) 193.0cc at 6500rpm is probably 27hp Max.
$3,175.00


I did notice they have the best Price I have seen on a Hirth F33 [email protected]
At (76mm x 69mm)
313.1cc it has more hp potential. 313cc/7cc= 44.7hp, probably 42hp with the lower 9.5cr.

Possible Big Bores for an F33:
(76mm x 69mm) 313.1cc Stock!
(78mm x 69mm) 329.8cc
(80mm x 69mm) 346.9cc
(82mm x 69mm) 364.5cc
 

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n3puppy

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Wish I knew about the flight characteristics of powered parachutes.
Example: If fixed wing aircraft reduce to 75% power to cruise - what do PPG's use?

Polini Thor 303 gives full power 120kg thrust @ 8000rpm -
but lists fuel consumption at 30KG thrust (25% power)
Thor 202 - 90kg thrust @ 8000, fuel consumption @30kg (33%)

Vittarozi Cosmos -124kg thrust at 7500rpm but fuel consumption [email protected] 40kg (32%)

Simoni Mini 250 [email protected], but fuel consumption @ 5000rpm
With prop load - 8000rpm vs 5000rpm = roughly 25% power.

From just those numbers - seems like PPG cruise might be only about 25-30% power which would greatly reduce wear over 75% cruise settings commonly used on fixed wing
 

Dana

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It's going to depend on the motor. Since there is no pitch control (trimmers and speedbar notwithstanding), "cruise" is whatever power setting gives you zero rate of climb.

I don't remember the rpms I saw, but my Solo 210 (15HP) powered Walkerjet did about 250fpm climb at WOT at a flying weight of 250# (motor, pilot, & wing). A back of the envelope calculation says that takes about 2.7HP to climb assuming 70% prop efficiency, so level flight needed 12.3HP or 82% power.

With a more powerful engine, say, 25HP, if the weight is the same you'd cruise at 49% power.

If you let the trimmers out or use the speedbar it'll take more power, as will a smaller or faster/reflexed wing.
 
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