# Lower budget engine options for a low budget UL

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#### Jay Kempf

##### Curmudgeon in Training (CIT)
I get 0.3sqft of drag area...
That would be a record low for something carrying an actual human. Having said that Mike Arnold was working with cruise numbers under 1 sq foot and certainly Lars Giertz', Vmax Probe would have been verified under 1 sq foot with a conservative margin. Those plus most modern racing sailplanes make it under the 1 square foot mark in inter-thermal cruise if you inspect just by speed and best glide ratio. Not sure about thermaling trim but probably there as well, mostly just by exploiting high AR, laminar flow, interference flow management and extreme wetted area management.

I would guess that the DA-11 was somewhere close to the AR-5. They have about the same numbers except HP.

#### Armilite

##### Well-Known Member
so here go's...…..

I believe simple low budget ultralights like my weedhopper still have a viable place in the market (even more so today with so many prospective pilots being budget limited). A weedhopper can be scratch built for 1k or less in tubing and another $900 for a set of solid color sails, the problem is engine costs in the 25 to 30hp range are 3k plus so now you have invested 5k in a simple easy to construct and fly airplane that has a resale value of around 3.5k. To many budget constrained people this makes no sense whatsoever. John Chotia realized this and created the Chotia 460, 18hp at a price point of$750 and it fit the bill for the weedhopper perfectly, I know as I have 300+ hours sitting behind one! with my 180lb but in the seat, climb was only about 400fpm but it was reliable, sipped gas, and got the job done!

so the question (or challenge) is, what off the shelf engine can be purchased and converted for 1k or less (minus the prop) either direct drive or belt reduction is acceptable as long as the cost of the redrive is factored into the 1k overall cost. all mod work needs to be doable with basic tools (drilling ok but no machining). the end product should be capable of producing 20 to 30 hp. both 2 and 4 stroke options are acceptable.

Chris
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First, the Weed Hopper has had a Rotax 277 (28hp) to a Rotax 503 (50hp) put on it. The Rotax 447 (40hp) keeps it in Part 103 Status at 250 lbs. At MTOW of 550 lbs it needs 33.5hp! A Rotax 277UL is 268.8cc/7cc = 38.4hp@6500rpm if Built Right with a Tuned Pipe. A Stock 377UL is 35hp and is 368.4cc/7cc = 52.6hp@6500rpm! A 447UL 40hp is 436.7cc/7cc = 62.3hp@6500rpm!

A 2 Stroke using 6500rpm, 11.5cr, Proper Size Carb, with a Good Wideband Tuned Pipe it takes on Avg 7cc to make 1hp. So 33.5hp x 7cc = 234.5cc minimum needed! So even a Cheap Skidoo 250 Type 247 (69mm x 66mm) 246.8cc could be used. JLO/Rockwell & Sachs alone made 14 different Singles each with Bolt Holes on Front/PTO Case where you could adapt an ACE Belt Drive $669 Shipped to the USA! There were about 20+ different Engine Manufactures for Snowmobiles that made Singles. The 292 Single was made by everybody. Skidoo/Rotax's 292 was (75mm x 66mm) 291.6cc/7cc= 41.6hp@6500rpm! Hint, the 277F/277UL with 30mm PTO 1:10 Taper and the 292 with a Straight Shaft PTO both used the same 66mm Stroke! All Skidoo 292's were TNT's or Blizzards(Rare) with the better Ported Cylinder. The Newer 250 Type 253 Singles also use the 30mm 1:10 PTO Taper and were 61mm Stroke, so use an Older Skidoo Single Case with the 250 Type 253 Crank with a Newer 550F 76mm Cylinder and you have a (76mm x 61mm) 276.8cc/7cc= 39.5hp Hybrid Reed Fed Single. 550F Cylinders have been Big Bored to 82mm. The 277 can also be Big Bored to 82mm, both with a Custom made Sleeve. A New Rotax B Gear Drive is$835. An ACE Belt Drive is a few Pounds lighter is $669 Shipped to the USA. Weedhopper Standard Basic Model with a Rotax 28 hp (21 kW) Rotax 277 engine had an empty weight of 235 lb (107 kg) for the US amateur-built category. Doesn't say if with Belt or Gear Drive. Specifications (Weedhopper Model 40) General characteristics • Crew: one • Length: 18 ft 6 in (5.64 m) • Wingspan: 28 ft 0 in (8.53 m) • Height: 6 ft 97 in (4.29 m) • Wing area: 168 sq ft (15.6 m2) • Gross weight: 550 lb (249 kg) • Empty weight: 250 lb (113 kg) • Useful Load: 300 lbs • Fuel capacity: 5 US gallons (19 litres) • Powerplant: 1 × Rotax 447 twin-cylinder, two-stroke aircraft engine, 40 hp (30 kW) • Propellers: 2-bladed Powerfin ground adjustable Performance • Cruise speed: 55 mph (89 km/h, 48 kn) • Stall speed: 20 mph (32 km/h, 17 kn) • Never exceed speed: 65 mph (105 km/h, 56 kn) • Rate of climb: 1,000 ft/min (5.1 m/s) #### WonderousMountain ##### Well-Known Member I get 0.3sqft of drag area... I got .72, which would beat Arnold's. Another possibility is Davis got a touch more HP than stated. #### sigrana ##### Well-Known Member Go to this page and have a look: I have three of these and they are exceptional: The manufacturer's contact page: Marc Motor "engine for emotion": contact us #### Armilite ##### Well-Known Member Go to this page and have a look: I have three of these and they are exceptional: The manufacturer's contact page: Marc Motor "engine for emotion": contact us =========================== While Small & Light Weight, Web Site is terrible, I didn't see Engine Prices. Most of them are turning way to a high an rpm, 9000 to 10,000rpm to last very long. Machining looked Good from the limited Photos. Part 103 needs 26hp to 40hp today. Compare them to the Hirth F-33 (28hp) 45 lbs with Electric Start and a 1000 hr TBO. (76mm x 69m) 313.1cc. I don't know the Hirth's Head/Cylinder Bolt Pattern, but I'm guessing it's at least 100mm which would allow for a Big Bore up to 82mm. (82mm x 69mm) 364.5cc/7cc = 52hp and maybe even larger if Bolt pattern bigger. #### sigrana ##### Well-Known Member =========================== While Small & Light Weight, Web Site is terrible, I didn't see Engine Prices. Most of them are turning way to a high an rpm, 9000 to 10,000rpm to last very long. Machining looked Good from the limited Photos. Part 103 needs 26hp to 40hp today. Compare them to the Hirth F-33 (28hp) 45 lbs with Electric Start and a 1000 hr TBO. (76mm x 69m) 313.1cc. I don't know the Hirth's Head/Cylinder Bolt Pattern, but I'm guessing it's at least 100mm which would allow for a Big Bore up to 82mm. (82mm x 69mm) 364.5cc/7cc = 52hp and maybe even larger if Bolt pattern bigger. If you believe Hirth specificatgions, you need to rethink. I had two Hirth engines and they are FAR BELOW specifications. #### Bille Floyd ##### Well-Known Member If you believe Hirth specificatgions, you need to rethink. I had two Hirth engines and they are FAR BELOW specifications. I'm glad you said that ! A few months ago, i nearly hit the send button, at Paypal , for a dual ignition, Hirth F-33 , with E-start ; decided to go for the Polini Thor 202 , with it's liquid cooling instead ! Even with the radiator ; it's lighter than the Hirth. The TOB , "should" be longer ; because it's liquid cooled ? Page 18 here ; they give the servicing table , for the Thor 202 : Bille Last edited: #### Armilite ##### Well-Known Member I'm glad you said that ! A few months ago, i nearly hit the send button, at Paypal , for a dual ignition, Hirth F-33 , with E-start ; decided to go for the Polini Thor 202 , with it's liquid cooling instead ! Even with the radiator ; it's lighter than the Hirth. The TOB , "should" be longer ; because it's liquid cooled ? Page 18 here ; they give the servicing table , for the Thor 202 : Bille ==================================== The Polini Thor 250 FWF Install is 54-55lbs, and at 36hp@7500rpm it usually needs rebuilt at 200-250 Hours! The Polini 200: 30hp@8100rpm isn't going to last long!  Polini Engine 2 stroke monocylinder Cooling Forced air Bore for stroke 64 x 60 Displacement 193 cm3 Power 30 HP R.P.M. max 8.100 Cylinder Aluminum with Gilnisil coating Compression ratio 12:1 Says  Engine weight 17.5 Kg (18.5 Kg = 39.68316 lbs with electric starter) You still have the Exhaust, Prop, and maybe Redrive Weight to add on. The Hirth F-33 313cc is 28hp@6500rpm, and is 45 lbs Complete. While they say, it has a 1000 hr TBO, I have never heard of one making that. The Hirth F-33 with more CC to play with 313cc vs 193cc would have been a better choice. #### Protech Racing ##### Well-Known Member I can build 2 of the small block Twins, if some one want the second engine. This build could also apply to the Big single . I can do a cost estimate and contract if desired . Time frame is 6 months from Oct 30 . Specs are . Clone case at 670cc. Honda case is additional 500$ . Forged crank tho..
Total seal gapless second ring.
10/1 compression by milling heads ,Mild porting . 3 angle valve job .
custom cam to operate at 5000
HD valve springs and roller rockers
Steel pushrods
Billet rods
Twin 34 mm carbs , maybe some provision for heat and mixture control .
Light flywheel with charging and crank trigger with electric start may be an option. I 'll have to take a good look at the stock wheel . I hate exploding parts.
I may use a rev limiter to stay under 6000 RPM

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#### pictsidhe

##### Well-Known Member
You forgot the two most important numbers. Weight, and the weight to be removed from wallet.

#### Bille Floyd

##### Well-Known Member
====================================

The Polini Thor 250 FWF Install is 54-55lbs, and at 36hp@7500rpm it usually needs rebuilt at 200-250 Hours!

The Polini 200: 30hp@8100rpm isn't going to last long!
 Polini Engine 2 stroke monocylinder Cooling Forced air Bore for stroke 64 x 60 Displacement 193 cm3 Power 30 HP R.P.M. max 8.100 Cylinder Aluminum with Gilnisil coating Compression ratio 12:1
Says
 Engine weight 17.5 Kg (18.5 Kg = 39.68316 lbs with electric starter)
You still have the Exhaust, Prop, and maybe Redrive Weight to add on.

The Hirth F-33 313cc is 28hp@6500rpm, and is 45 lbs Complete. While they say, it has a 1000 hr TBO, I have never heard of one making that. The Hirth F-33 with more CC to play with 313cc vs 193cc would have been a better choice.
YEA -- BUT :
I didn't make ANY mention , of the Thor 200, or the Thor 250 ; i
was referring to the 33hp Thor 202 , and it is 37.6-Lb complete with
radiator, reduction unit, and muffler, (no E-start).

Liquid cooled, should out-last an air cooled engine , shouldn't
it ; especially if i only need 25 of those 33 horses ?

Bille

#### Protech Racing

##### Well-Known Member
The single will cost around 1700$. The Twin will cost a little over 2200$ at this point. It may come down or up a little depending on what breaks or what I dont like . I dont ship anything that I dont like .
Both look to FWF at around 80#

#### mullacharjak

Yamaha KT100S Go cart engine. 750$brand new added to VJ24W ultralight.Perfect for Local flying in a 50 mile radius. #### pictsidhe ##### Well-Known Member #### Armilite ##### Well-Known Member YEA -- BUT : I didn't make ANY mention , of the Thor 200, or the Thor 250 ; i was referring to the 33hp Thor 202 , and it is 37.6-Lb complete with radiator, reduction unit, and muffler, (no E-start). Liquid cooled, should out-last an air cooled engine , shouldn't it ; especially if i only need 25 of those 33 horses ? Bille ========================== A 2 Strokes Engines LIFE has more to do with Maintenance and the Oil you use and the Octane Gas you use, and the rpm it is used. Water Cooled vs Fan Cooled has the same Life, hence Rotax's TBO was 300 hrs or 5 Years on all of their 2 Stroke Engines. On 2 Strokes there are many Variables. On Sleds today, Fanners are usually rated at 7000rpm, Water Cooled at 8000rpm today. But on Planes there all derated to 6500rpm! I didn't see a 202 when I did a quick search, so I assumed it was a Type O, only seen a 200 & 250. The 202 real displacement is 205cc with a 66mm bore and 60mm stroke. The cylinder has a better-Ported cylinder with 5 Transfers to give you more performance! It's 3.5 lbs lighter than the 200. A +2mm Bore over the 200, and turned 8,500rpm vs the 200 8,100rpm. I did see a 400hr TBO for the 202. 11.5 vs 12.0cr. It has a Small Carb. I didn't see a Power Chart of the Power Band. It would be better to use a Larger Carb with a lower rpm.  Polini 202 Engine 2 stroke mono-cylinder Cooling Liquid cooled Bore for stroke 66 x 60 = 205.3cc Displacement 205 cm3 Power 33 HP *Max trust 90 Kg with Ø 130 cm propeller R.P.M. max 8,500 Cylinder Aluminum with Gilnisil coating Compression ratio 11.5  Polini 200 Engine 2 stroke monocylinder Cooling Forced air Bore for stroke 64 x 60 = 193.0cc Displacement 193 cm3 Power 30 HP *Max trust 85 Kg with Ø 130 cm propeller R.P.M. max 8,100 Cylinder Aluminum with Gilnisil coating Compression ratio 12:1 #### Armilite ##### Well-Known Member Liquid cooled, should out-last an air cooled engine , shouldn't it ; especially if i only need 25 of those 33 horses ? Bille =========================== If the 202 makes 33hp@8500rpm, it probably makes 25hp@6500rpm. It has a 28mm Carb. A Skidoo 250 Single rated 12.5hp@5500rpm has a 30mm Carb and most people upgraded them to a 34mm carb. My 292 TNT Single has a 38mm. The 277UL 268cc has a 36mm. Find a power graph chart for it. #### Armilite ##### Well-Known Member The single will cost around 1700$.
The Twin will cost a little over 2200\$ at this point. It may come down or up a little depending on what breaks or what I dont like . I dont ship anything that I dont like .
Both look to FWF at around 80#
============================

An ACE Belt Drive for the GX 390/420/460 is 2.85 kg / 6.3 lbs!

The ACE Belt Drive for the 623 cc = 3.9 Kg / 8.6 lbs. For the 993 cc = 4.2 Kg / 9.3 lbs.

With the Bigger CC Engines, you have the Option to run Direct Drive.

An HF Predator 420 13hp@3600rpm Single dry weight says 73 lbs!
A Duromax 440 is 18hp@3600rpm.

The Small Block Van Guard 627cc 23hp V Twin is 77 lbs!

The Big Block Van Guard 993 40hp@3600rpm V Twin says 125 lbs, but that may be Shipping Weight. Dry Weight can be less. A 460 Single upgraded can make 37hp@5000rpm! So a 440 would be about 35hp@5000rpm upgraded.

On All (3) Types of Engines, you're going to take off about 12-18 lbs of Weight for Airplane use. but you have to add back whatever Redrive you use.

#### Bille Floyd

##### Well-Known Member
===========================

If the 202 makes 33hp@8500rpm, it probably makes 25hp@6500rpm. It has a 28mm Carb. A Skidoo 250 Single rated 12.5hp@5500rpm has a 30mm Carb and most people upgraded them to a 34mm carb. My 292 TNT Single has a 38mm. The 277UL 268cc has a 36mm. Find a power graph chart for it.
Thanks for your time ; that was Awesome of you !!

Could i hook up a control, to adjust rich / lean, for altitude compensation
on that 34mm carb? I plan to mainly use the engine, at King Mt Idaho
and the elevation at the glider port is 5,500 ASL ; i may want to motor
up the side of King Mt, at 10,000' ASL . That is quite the elevation
change ; and on a calm morning flight, i may need all of it !!

The main mission for this devise is soaring ; the engine and
folding prop are mainly there to get me up to thermal altitude.
Would be a Lot easier, if the Thor 202 had an EFI ! -- (sad)

Bille

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#### Armilite

##### Well-Known Member
They appear to be the same Engine with just different Bores. What would be interesting is what is the Max they can be Big Bored too. Also what Stroker Cranks are available for them.

(74mm x 60mm) 258.1cc
(76mm x 60mm) 272.2cc
(78mm x 60mm) 286.8cc
(80mm x 60mm) 301.7cc

 Polini 200 Engine 30hp 2 stroke monocylinder Cooling Forced air Bore for stroke 64 x 60 = 193.0cc
============================================
 Polini 202 Engine 33hp 2 stroke mono-cylinder Cooling Liquid cooled Bore for stroke 66 x 60 = 205.3cc
============================================
 Polini 250 Engine 36hp 2 stroke monocylinder Cooling Liquid cooled Bore for stroke 72 x 60 = 244.3cc Displacement 244 cm3 Power 36 HP

#### n3puppy

##### Well-Known Member
It may come down or up a little depending on what breaks or what I dont like . I dont ship anything that I dont like .
How are you planning to test to see when things break and the TBO if they don't.
Standard prop?
Wood bar Dyno?
Standard engine dyno loaded to approximate flight conditions?