OS 91 VRDF experts wanted
03-11-2014, 08:23 PM
#52
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I guess round head is a renewal and improvement of the square head.
03-12-2014, 07:52 AM
#53
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All of the parts for the engines should be pretty much interchangeable. As a matter of fact I can't see why the Square head couldn't be machined into a round head if you really wanted to do it.
03-30-2014, 02:22 PM
#56
Last time I looked there were a lot of these engines for sale on ebay.
04-01-2014, 05:11 AM
#60
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04-01-2014, 05:40 PM
#62
There is probably $50,000 worth of engines owned by all of the guys combined who have posted here over the past 10 years and I've no memory of any project threads that featured this engine.
Maybe Rocket Rob had a OS .90 in his ME163....but other than that this engine has not had much "face time" at this forum.
Maybe Rocket Rob had a OS .90 in his ME163....but other than that this engine has not had much "face time" at this forum.
04-01-2014, 05:59 PM
#63
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I had one in a P-80 with a dynamax fan unit, sucked fuel like a vacuum cleaner.
I have a brand new one with a pipe and a rnv but have never used it because of cost of glow fuel the past few years. I should either use it or pass it on to someone who doesn't mind the "low miles/gallon" factor.
I have a brand new one with a pipe and a rnv but have never used it because of cost of glow fuel the past few years. I should either use it or pass it on to someone who doesn't mind the "low miles/gallon" factor.
04-01-2014, 07:31 PM
#65
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When selecting an airframe make sure you have room for 24 oz or so of fuel close to the COG.
04-01-2014, 07:55 PM
#66
Methanol should be $5 per gallon or less from a racing fuel dealer. Sig Castor and Klotz synthetic would be the most expensive ingredients, but you can mix your own 80 / 20 for less than $10 gallon. If you can use APC 10 x 10s and keep the rpm at 19,000 or less [APC safety margin is 190,000 divided by prop diameter], then this could be a fairly cheap engine to run compared to other engines capable of powering high speed planes.
A home built delta could be framed up pretty easily if you use the Diamond Dust / Screamin' Demon style of construction. I'd make the first attempt 38-40 inches of span with the intention to slow landing speeds and keep accidental prop breakage down. I wouldn't make the elevons any longer than what you see on the 32 inch deltas though.
A home built delta could be framed up pretty easily if you use the Diamond Dust / Screamin' Demon style of construction. I'd make the first attempt 38-40 inches of span with the intention to slow landing speeds and keep accidental prop breakage down. I wouldn't make the elevons any longer than what you see on the 32 inch deltas though.
04-02-2014, 02:52 AM
#68
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The only thing I see about using a prop that spins up 19,000 RPM on this engine is that the HP doesn't peak until it's spinning 22,000 RPM. Why would one want to use less than optimum power?
NOTES FROM OUR TECH DEPARTMENT
The O.S. Ducted Fan Engines are designed to develop high power at high RPM.
These are used in Jet (ducted fan) Models where the engine drives a turbine-
like impeller (compressor) that draws a large quantity of air through a shroud
to create thrust. These engines are NOT covered under the O.S. 2-year warranty.
Because this is a high-performance engine, reliability is sacrificed.
The Ducted Fan does NOT come with this engine. One must purchase the fan to fit
BOTH the engine size and the specific plane (these fan units are typically
manufactured by the same people who make the plane kit - a company like
Jet Hangar Hobbies (562) 467-0260 )
FEATURES: Rear Exhaust .
Schnuerle Porting
2-piece Crankcase
2-Crankshaft Ball Bearings
Rear-Mounted Carburetor
Drum Rotor Induction
ABN piston/cylinder (aluminum piston with a nickle plated brass
cylinder
INCLUDES: One Assembled .91 VR-DF Engine w/small head
One Set of Instructions and Poster
One Exhaust Adaptor w/screws and O-ring (OSMG2709)
Bellcrank for use with the remote needle assembly (OSMG7258-comes
with the engine!)
SPECS: Construction: Aluminum and Aluminum alloys
Displacement: 0.91 cu in
Bore: 27.7mm (1.09")
Stroke: 24.5mm (.97")
Max Output: 4.8 PS, 4.73 HP at 22,000 RPM
Practical RPM Range: 2,500 - 25,000 RPM
Weight: 662g (23.4oz)
Length: 133.5mm (5.26") from carb intake to front of drive washer
Width: 43.5mm (1.71") neglecting the engine mounting flanges
52mm (2.05") distance between mounting hole centers
Height: 103.3mm (4.07")
Crankshaft: 5/16-24
Needle Settings: High Speed: 2 turns out from fully closed
Low Speed: 2mm gap between the needle and spray bar
(looking down neck of carb) at full
_ throttle.
REQUIRES: Glow Plug (O.S. #8 or #9 (OSMG2691 is recommended)
Tuned pipe (we don't carry, contact the manufacturer of the kit).
Fuel with 20% MINIMUM lubricant content and 20%-50% Nitromethane
Wildcat Ducted Fan fuel exceeds these requirements
COMMENTS: This engine is the "small head" version of the .91 VR-DF engines.
This engine is designed to operate where space is at a minimum.
This engine works w/ Dynamax or Turbax fan units.
JBN 9.23.93
ir/jl
ADDITIONAL COMMENTS: It is suggested that the cutomer uses a Ramtec fan unit
as opposed to the Dynamax unit. The Ramtec has a much
higher pitch which "loads" the engine better.
updt lmm 4/14/09
– If you need more information, use
The O.S. Ducted Fan Engines are designed to develop high power at high RPM.
These are used in Jet (ducted fan) Models where the engine drives a turbine-
like impeller (compressor) that draws a large quantity of air through a shroud
to create thrust. These engines are NOT covered under the O.S. 2-year warranty.
Because this is a high-performance engine, reliability is sacrificed.
The Ducted Fan does NOT come with this engine. One must purchase the fan to fit
BOTH the engine size and the specific plane (these fan units are typically
manufactured by the same people who make the plane kit - a company like
Jet Hangar Hobbies (562) 467-0260 )
FEATURES: Rear Exhaust .
Schnuerle Porting
2-piece Crankcase
2-Crankshaft Ball Bearings
Rear-Mounted Carburetor
Drum Rotor Induction
ABN piston/cylinder (aluminum piston with a nickle plated brass
cylinder
INCLUDES: One Assembled .91 VR-DF Engine w/small head
One Set of Instructions and Poster
One Exhaust Adaptor w/screws and O-ring (OSMG2709)
Bellcrank for use with the remote needle assembly (OSMG7258-comes
with the engine!)
SPECS: Construction: Aluminum and Aluminum alloys
Displacement: 0.91 cu in
Bore: 27.7mm (1.09")
Stroke: 24.5mm (.97")
Max Output: 4.8 PS, 4.73 HP at 22,000 RPM
Practical RPM Range: 2,500 - 25,000 RPM
Weight: 662g (23.4oz)
Length: 133.5mm (5.26") from carb intake to front of drive washer
Width: 43.5mm (1.71") neglecting the engine mounting flanges
52mm (2.05") distance between mounting hole centers
Height: 103.3mm (4.07")
Crankshaft: 5/16-24
Needle Settings: High Speed: 2 turns out from fully closed
Low Speed: 2mm gap between the needle and spray bar
(looking down neck of carb) at full
_ throttle.
REQUIRES: Glow Plug (O.S. #8 or #9 (OSMG2691 is recommended)
Tuned pipe (we don't carry, contact the manufacturer of the kit).
Fuel with 20% MINIMUM lubricant content and 20%-50% Nitromethane
Wildcat Ducted Fan fuel exceeds these requirements
COMMENTS: This engine is the "small head" version of the .91 VR-DF engines.
This engine is designed to operate where space is at a minimum.
This engine works w/ Dynamax or Turbax fan units.
JBN 9.23.93
ir/jl
ADDITIONAL COMMENTS: It is suggested that the cutomer uses a Ramtec fan unit
as opposed to the Dynamax unit. The Ramtec has a much
higher pitch which "loads" the engine better.
updt lmm 4/14/09
– If you need more information, use
04-02-2014, 05:47 AM
#69
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Two reasons could be that they beat the tar out of the bearings at full rpm, and the prop/airframe choices are more limited.
Here's a "Speed Cobra" with what looks to be an OS .91, they are often used overseas for 15cc speed models. This is an older speed design that is considered a Porky Pig these days in the speed circles. It takes some serious power to get it to 200, and current speed models better it by a large margin. Still flown as sport speed, after all 180-190 ain't so bad.
Here's a "Speed Cobra" with what looks to be an OS .91, they are often used overseas for 15cc speed models. This is an older speed design that is considered a Porky Pig these days in the speed circles. It takes some serious power to get it to 200, and current speed models better it by a large margin. Still flown as sport speed, after all 180-190 ain't so bad.
04-02-2014, 06:42 AM
#70
04-02-2014, 11:00 AM
#71
Just about any engine can be made to run good on zero% nitro if you are able to raise the compression enough. The optimum pipe shape changes some..but that only matters if the "nitro" pipe can't be made to work adequately on 0%
Don't forget that with a 10 x 10 running 19,000 on the ground, that could end up being 21,000 in the air if the air frame allows good unloading. Just speculation, but this would be my approach if I owned one of these engines. At least to get acquainted with it with a conservative starting point.
Last edited by combatpigg; 04-02-2014 at 11:05 AM.
04-02-2014, 11:35 AM
#72
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I'm just proposing a set up that people would actually get some use out of and enjoy instead of seeing all of these NIB engines sitting in people's closets.
Just about any engine can be made to run good on zero% nitro if you are able to raise the compression enough. The optimum pipe shape changes some..but that only matters if the "nitro" pipe can't be made to work adequately on 0%
Don't forget that with a 10 x 10 running 19,000 on the ground, that could end up being 21,000 in the air if the air frame allows good unloading. Just speculation, but this would be my approach if I owned one of these engines. At least to get acquainted with it with a conservative starting point.
Just about any engine can be made to run good on zero% nitro if you are able to raise the compression enough. The optimum pipe shape changes some..but that only matters if the "nitro" pipe can't be made to work adequately on 0%
Don't forget that with a 10 x 10 running 19,000 on the ground, that could end up being 21,000 in the air if the air frame allows good unloading. Just speculation, but this would be my approach if I owned one of these engines. At least to get acquainted with it with a conservative starting point.
I really think to take full advantage of the engine this is one that cries out for a carbon fiber prop.
Bottom line here is that it is kinda a sin to have one of these engines and not use it. Although I will mention that they are not a good choice if you have had complaints about noise where you fly, although they are not as bad as some gas powered 3D planes I have seen flying lately.
Last edited by iron eagel; 04-02-2014 at 11:38 AM.
04-02-2014, 12:50 PM
#73
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If a timing change could deliver that much more power from the existing fuel, then couldn't we achieve the same performance as 50% nitro fuel just by using electronic ignition with FAI fuel? I agree there are timing changes as a result of NM content, but I don't believe for a minute that is the sole cause of increased power. I would say it is symptomatic of the properties of the fuel. It is a monopropellant - although underoxidized - so a percentage of it can undergo a redox reaction without additional oxygen from the atmosphere. So with the density of liquid versus air, you can inhale enough mass of A/F mixture that the total energy released per stroke is higher = more power. If it works differently than that, I'd like to know how.
If you run 9" or 10" props on the .91 they best be CF composite.. the tip speeds and hub stresses are pretty serious.
If you run 9" or 10" props on the .91 they best be CF composite.. the tip speeds and hub stresses are pretty serious.
04-02-2014, 01:00 PM
#75
IE, I was [also] aiming my observation at the dozens of ads I've run across of these engines that are either NIB or very little time / bench runs only for $200 or so.
It's pretty clear to see why so many of them have never seen the light of day. Horsing around with a big DF model would be more aggrivation than fun at a lot of fields, plus the reality of running costs adds up quickly.
This is why I visualize a plain, simple, un-cowled delta, cheap fuel, cheap prop, 2 top notch servos, BFT [big fuel tank] and see what comes of it. If this idea turns out too slow to be fun, then there's always plenty of ways to crank things up from there, but this is where the cost per run starts to get prohibitive for people like me.
I bought a 55 gallon drum of methanol 4 years ago for $3 per gallon at the local Standard Oil distributor. I think it's price follows the price of gasoline fairly closely.
I think back to the video of the guy [from Finland or Norway] flying his Laser Arrow with this engine and it was very impressive even though you could hear that he was only getting 3/4 power out of it. He might have been running zero nitro.
Nitro % is like chemical supercharging. It's not as much a fuel as it is an oxidizer. It does a better job of extracting power from the methanol than what plain air molecules can do. The advancement of the timing is a detriment past a certain point [40 degrees or so BTDC]..so regulating the mechanical compression ratio and combustion chamber shape is how model engine folks handle that.
Too much load ALSO will [effectively] advance the timing..usually bad if you are running everything else at the upper limits.
If our engines didn't have such a need for oil content in the fuel mix and didn't have such limited room to carry fuel, we could run 95% nitro if we were trying for every last ounce of power possible.
Nitro % above 50% doesn't mix well with castor, so then you become dependent on synthetic oil.
I've got a Nelson FIRE .40 that was set up by Dave Shadel for nitro. It runs pretty good, but still not as powerful as the FAI .40 that uses 0% nitro. The nitro version just needs more work, possibly a better pipe design. I don't know.
It's pretty clear to see why so many of them have never seen the light of day. Horsing around with a big DF model would be more aggrivation than fun at a lot of fields, plus the reality of running costs adds up quickly.
This is why I visualize a plain, simple, un-cowled delta, cheap fuel, cheap prop, 2 top notch servos, BFT [big fuel tank] and see what comes of it. If this idea turns out too slow to be fun, then there's always plenty of ways to crank things up from there, but this is where the cost per run starts to get prohibitive for people like me.
I bought a 55 gallon drum of methanol 4 years ago for $3 per gallon at the local Standard Oil distributor. I think it's price follows the price of gasoline fairly closely.
I think back to the video of the guy [from Finland or Norway] flying his Laser Arrow with this engine and it was very impressive even though you could hear that he was only getting 3/4 power out of it. He might have been running zero nitro.
Nitro % is like chemical supercharging. It's not as much a fuel as it is an oxidizer. It does a better job of extracting power from the methanol than what plain air molecules can do. The advancement of the timing is a detriment past a certain point [40 degrees or so BTDC]..so regulating the mechanical compression ratio and combustion chamber shape is how model engine folks handle that.
Too much load ALSO will [effectively] advance the timing..usually bad if you are running everything else at the upper limits.
If our engines didn't have such a need for oil content in the fuel mix and didn't have such limited room to carry fuel, we could run 95% nitro if we were trying for every last ounce of power possible.
Nitro % above 50% doesn't mix well with castor, so then you become dependent on synthetic oil.
I've got a Nelson FIRE .40 that was set up by Dave Shadel for nitro. It runs pretty good, but still not as powerful as the FAI .40 that uses 0% nitro. The nitro version just needs more work, possibly a better pipe design. I don't know.
Last edited by combatpigg; 04-02-2014 at 01:27 PM.