rmenke

My Feedback: (13)

Flyboy Dave suggested a rear piper OS 91 or similar for the AC., no model type mentioned. How would a OS VRDF-65 do as to rpm and power?

slowmo777

Talking ducted fan engines:

Well, if you want to look for the best power available for your Alley Cat, you have to look for a .60 to .105 DF or C/L speed engine.

(Formerly) available .60 to .105 DF engines are:

K&B (not too powerful)
PICCO (no parts any more)
ROSSI (no parts any more)
OPS (parts available directly from Italy)
BVM (very expensive),
OS (only .91 VR-DF),
WEBRA (not too powerful, no parts any more)
CMB (no parts any more)
JETT (no parts any more)

Except for the OS .91 VR-DF and OPS .60 to 80, spare parts are quite rare for those engines.

The OS .91 VR-DF does offer much torque for a .90 sized DF compared to the BVM for instance and considerably more than the OS .65 VR-DF. But some mods have to be done to bring the OS 91 over 24K in flight. It needs a Performance Specialties ABC or AAC liner (which can be modified nicely compared to the nickel plated stock liners of OS) and the very rare RPM connecting rod to make it run reliably above 24000 rpm. Replacing the OS 9B carb with a venturi also adds rpm. The liner timings (of boost, schnuerle ports and exhaust) have to be changed. Replace the stock M3.5 cylinder head screws with grade 12.9 ones. Changing the intake drum duration also adds top end (drum must again be balanced dynamically after that). Please use only 5 % nitro fuel and an oil percentage of at least 20.

Many of the .60/.65 DF versions are/were used for C/L speed as well – equipped with an integral spinner, venturi speed carb and altered sleeve timing.

Looking for the correct prop size: The Alley Cat – since semi scale – is not optimised for pure speed. It’s a big sport airframe. A 10 or 11” diameter propeller sure would be nice to use, but these diameters are too large for the rpms the above listed engines want to turn – bearing in mind transsonic prop tip speed “devouring“ precious top end rpm.

Generally spinning below 20 thousand rpm on the ground should be avoided to benefit from the huge power these engines can provide. For that reason only 9” diameter props (or even smaller diameter for pure speed airframes with minimised parasitic drag) should be used for .60 to .90 DF engines.

A combination of the Alley Cat and a DF engine asks for a 9*9 or 9*10” prop. Take-off requires more runway but once airborne nothing will be faster.

Let’s remember – PROPS MUST BE MADE FROM CARBON FIBRE. Besides all sport props even the APC pylon props are too weak for this application!

A non-muffled tuned pipe guarantees best top end output.

Here’s one highly modified OPS .60 speed engine pulling 26 thousand rpm in flight if combined with a non-muffled tuned pipe and a matched speed prop. Good luck!

_King_Pin_

slowmo, where do you buy those carbon fibre props?

slowmo777

Hello King_Pin_

I make them myself (see pic) non-commercially. But here's a suggestion:

Take the APC 10*10 prop and make a mold of it. After producing temperature cured carbon fibre "clones", shorten their diameter to 9" or less - depending on your airframe. Re-balance them.

The slimmer the fuselage is, the better for speed (less prop diameter possible thus higher rpm). For a .60 to .90 sized engine the maximum fuselage width should be about 65 mm.

rmenke

My Feedback: (13)

Slomo777:

Outstanding info, will try not to bug you for knowledge. I may have gone the wrong directin with the 91 OS, but if it will give me 20K on the ground, think thats all I am going to need for my original appliction, I hope. As usual, someone will get tired of being killed and respond with similar, maby faster stuff, such the life in racing, sport club racing in this case. I have a OPS 8 port 60 something I bought from fellow German Helge Puestow, whom you probably know, about a year ago. Never been in a bird as it is very heavy, and the thing apppears highly modified to make reliability suspect. It sort of seems strange to me that the fast stuff available is coming out of Europe as to larger bore engines. To this point, Jett has been and probably will stay on the consertative side of his sports engines, afterall thats why they are called "Sports" They are great user friendly, reliable engines, and I assume will build you a real one off screamer if you are willing to pay a reasonable buck. After all, he needs to make a living out of his work. I think he is off the mark with the 90 L and LX. A more agressive porting would make them a little more cranky, but why not offer, say a 90-scooter?

As a matter of interest, you recommend fuel with no more than 5%, where the heli guys here run at least 20, a 30% can is not unusual. I will run the thing stock on pipe for a while and go to the better piston-sleve after I peal the nickle off the thing. In the event (likely) that I end up uusing it for a fishing sinker, Is there a web site over there that offers the OPS line. Not able to find anything this side of the pond. Again, thank you guys so much. Maby a clipped wing AC in the future?

Cyclic Hardover

My Feedback: (3)

I have a "NIB" OPS .60 with a NIB tuned Pipe, rear exhaust. $150 (Carb is on the front)

slowmo777

Hello Cyclic Hardover,

if it is an OPS .60 RIRE (be it read or gold head), it is high timed for DF or speed application. If your engine is a FIRE or FISE, then you have the low timed (high torque) liner for sport & pattern application of 16 thousand rpm maximum with the right prop.

Regards

slowmo777

I guess it is this .60 pattern engine.

slowmo777

Well- just rising the liner timings does not turn a .90 FIRE or FISE performance engine into a rpm monster. Why? Because the front intake crank rotor of those .90 engines (in a .60 case) does restrict the volume of the intake fuel/air mixture much more than a rear disc rotor, Zimmerman valve or drum valve induction. Also the “free” lower case volume of RIRE engines is smaller promoting a faster gas flow – the case is better “stuffed” by fresh air fuel mixture.

So why not offer a .90 scooter? – I believe there are only few hobby people around the world wanting to squeeze the very last rpm out of their .90 engines. So no real market here since DF power seems to be dead today.

From a pure subjective point of view I think for many speed addicts it is no problem to fly fast with a prop driven speed plane – but to fly REAL FAST (maybe ridiculously fast for some folks ) demands a high degree of brain work (speed plane aerodynamic solutions, engine rework, propeller design etc). There’s almost nothing on the commercial market serving this little speed market – so we are “forced” to make many things on our own initiative – just take a look at the CL speed guys. It is sad but true: Speed is not cheap.


Well, if running a non-modified DF engine with 30 % nitro you'll most likely smash the connecting rod due to the too high compression. In addition to the danger of too high temps "detonation" is most common destroying the piston.
Yes, the heli engines usually run much more than 5% nitro – to ensure best throttle sensitivity and for “cooling” from inside. For that their compression ratio is set lower compared to DF engines. Last but not least the timings of heli engines are adjusted for a much broader pipe resonance providing much torque and less peaky behaviour – very user friendly for the part-load operational range. For this reason heli tuned pipes are only little suited for ambitious speed plane applications.
On the contrary most DF engines and CL speed engines in particular are super peaky meaning they are intended to run best at full throttle – quite user unfriendly for many folks.


The nickel on the OS .91 liner does hold well – I was surprised myself. But it is not recommended to modify these nickel liners.


There are several OPS marine shops in the internet. However if looking for aero OPS engines and parts you should contact the factory in Italy.

r-c-guy

My Feedback: (37)

Hi,
Try an os 91 vrdf (Only 1 odel available) on 15-40% fuel with an 11-8 apc. I know that the prop's strength is marginal, but I have only broke 1 in 4 years, 22,000 static on the ground. My 'ok' mustang does 180 level.....

randy

slowmo777

Hello r-c-guy,

focussing nitro contend: The bigger competition nitro marine engines often run with 40% to 60% nitro fuel. But their combustion chamber geometry + volume is optimised for that as well as squish band width and angle. You can modify the OS .91 VR-DF head volume for that too providing a long lifespan. Reducing compression: If just trying to raise the cylinder head clearance by adding head shims exceeding a certain limit - which is cc dependant – then the squish velocity starts to decrease resulting in too high combustion temps.

Please re-calculate your prop tip speed – it’s simple physics. We must keep the prop tip speed below mach number 0.8 at the ground to make any speed engine run freely unloaded. You’ll do your engine a favour.

So I think as long as you don’t show us a small video of your OS .91 engine running a 11 diameter prop at 22 thousand on the ground, that will be hard to believe.

Anyway - you are very welcome to attend the German Speed Cup in September this year in Osnabrueck. Speeds of 250 mph are very likely to meet or exceed. The assessed speed is the mean speed measured electronically during an FAI conformous 200 m speed trap in both wind directions, and verified twice by a secondary speed measurement device (for controlling). That’s little comparable to a certain flight speed measured at a certain point in time - so in many respects much harder to achieve than radar gun derived speeds for instance.

International participants are more than welcome to present their speed machines. The Speed Cup should be named “European Speed Cup” at least, shouldn’t it? Randy, your Mustang would start within the class of speed planes powered by 10.1 to 15 cc engines. As for regulations: Besides the obligatory insurance there’s only a 5 kg (wet) weight limit (no prob at all) and the permitted 35 MHz transmitter frequency.

BTW, during the last Speed-Cup several stock “sport” and even “pylon” APC props broke while tuning the engines on the ground. Mainly 10 to 15 cc DF engines were concerned. Can you imagine how deep a gone prop blade can penetrade the turf? – Really frightening. And this was no bad prop production batch. I hope only carbon fibre props will be allowed in the future for certain engines.

Cyclic Hardover

My Feedback: (3)

Just curious, how do i tell. It does have a gold head and the barrel opens sideways. The carb is on the front though. I have had this a year in the closet trying to sell for a friend. Maybe I'll just keep it if it is a DF timed

slowmo777

Hello Cyclic Hardover

The OPS .60 gold head FIRE and FISE engines were developed in the beginning of the 80s for RC1 pattern planes. In contradiction to the rather big current F3A planes those RCI machines where much sleeker and quick to fly. The wing span was only about 60 inches and the engine capacity was limited to 10 cc at those times.

To verify your engine’s liner timing (DF timing versus sport/pattern timing) you must measure the exhaust duration explained in degrees. Use a degree wheel for that.

Because you obviously own the gold head OPS .60 FIRE, your exhaust timing will show something like 150 to 160 degrees delivering a nice compromise between good rpm and torque. If piped 16 thousand rpm with a 10*8 prop is realistic.









Last but not least here’s a speed tip if you want to exceed 190 mph with ease (BTW, the MAGNUM hardly reaches 170 mph):


1. Buy a .40 sized RC1 kit having a glass fibre fuselage and low wing layout. But we need only the fuselage. Those RC1 fuses are quite slim providing acceptable drag.


2. Make a NACA 0009 airfoiled foam wing – reinforced by a strong spar and 50 g/m² glass fibre in 45 degree direction + covered by 0.8 mm plywood. A wing span of 50” is more than enough. Double trapezoid layout. Ailerons length of about ¼ of the wing span each, positioned at the inner part of the wing. Angle of attack should be 0.3 degrees.


3. Horizontal stab: sandwich construction of three layers: strong 3 mm plywood in the center part plus 2 mm thick balsa outside. Remind the wood grain direction. Light 25g/m² glass cloth in 45 degree direction outside to improve torsion. Span about 15 inches.


4. The wing/aileron gaps and the horizontal hinge gaps must be covered. All linkages completely hidden within the fuselage using heavy duty torque rods.


5. No retractable landing gear – too much weight and drag. Take-off by throwing + belly landing.


6. No rudder: too much weight + drag.


7. Servos of 60 to 70 N of torque for ailerons and elevator. No metal gear servos.


8. 10 to 15 cc RIRE ducted fan engine mounted upright or inverted. Tru-Turn spinner, well balanced. Fully concealed non-muffled tuned pipe. Pipe tunnel recommended. The fuse must feature 2 inlets for tunnel air cooling and one outlet whose area is slightly larger than the added inlet surfaces – no temperature probs any longer. Fuel tank size of max 300 ml.


9. carbon fibre prop 9x10


10. The final weight should not exceed 2.8 kg



Good luck! [sm=tongue.gif]

Mike Connor

My Feedback: (5)

11" prop turning 22,000 rpm static would be 719 mph tip speed. Additional calculations needed for inflight tip speed.

The "helical" tip speed in flight Vtip is obtained by adding the airspeed V to the rotation tip speed Vr using the rule of vector addition, viz:

Vtip = SQR( Vr ^ 2 + V ^ 2 )

Now we have a prop tip speed of 741 mph before we consider any unloading of the engine. Hmmmm

I used to run a 10x6 MAS prop at around 18,000 rpm and the prop noise was so loud that one guy covered his ears as it flew by. As mentioned in another post, the prop is not very efficient at tip speeds above Mach .8. I would also like to see and hear a video of this setup.

MJD

My Feedback: (1)

I have one of those OPS Super .60's, purchased in Germany in the early '80's IIRC - it is a very sweet running engine of respectable power output. Not the lightest engine around. I had it in an old Pulsar bipe that weighed a bloody ton, perhaps 8 pounds or so, and it provided good power. Vertical lines were long but hampered a bit by the bipe's drag and the fact that thrust to weight was not too much in excess of unity. It runs like a dream on 5% fuel, and has the nicest idle of any of my glow engines, and starts easily with a small backwards flip of the spinner. But alas, no, it is not a high rpm monster.

MJD

_King_Pin_

slowmo, do you have pics of anything like that? or pics of some really extreme fast planes
It should be a pretty plane! (speed planes are always beautifull)

rmenke

My Feedback: (13)

WONDERFUL, WONDERFUL,WONDERFUL

You guys are simply great. Now I have a reasonable direction to go with a good motor base. It also brings reality of the basis back in full focus. Don't know how many of you out there have experienced a high rpm prop failure, or structural airframe failure at speed, but its just flat scary. Motor is going to stay stock, 20K ground is way good enough for my needs, the carbon prop is a known must, but now I know where to start. The Alley Cat structure is yet to be proven. Mine is stock with the center section of the wing glassed, all gaps sealed, metal pin hinges etc. I am looking for around 160 mph, existing project intended setup appears to be on the money as is, acomplished with your much appreciated help. Now, we just need a little information regarding these things flight character and related strength, will they stay togeather at 160-170? Have a little time to look for structural failures out there, then do it. Thanks again for all the help.

bob27s

My Feedback: (19)

Good posts there Slow-mo.

Hit on the head. Not much demaind for a .90 size F-1 engine. Heck, there is no demand for a .40 size F-1 engine any more for that matter.
And the information on the crank passage and volumes is correct. Remember, the 90L is a .60 on steroids. Its pretty much maxed out on flow volume, and stretched to the limits of physical strength. The 90LX is about as far as one would want to take that design.

The old cast case FIRE-95 ........ now that was a different story That was indeed a front intake fan engine. And with the fan sleeve and the right pipe, it could really howl. And.....yes.... that too is now gone.

Randy there seems to have the handle on the fan engine setup. Id be checking out his layout for your alley cat rmenke

slowmo777

Well, the pure speed machines can be experienced in person when visiting the German Speed Cups.






So, one of the easiest (and quite inexpensive) ways to get hold of a slim enough fuselage nicely suited for .60 to .90 ducted fan engines is an “old” .40 RC1 design.

For example take a look at the Curare .40, also known as the MINARE .40, the small brother of Hanno Prettner’s famous CURARE .60. Sadly the .60 sized fuse is MUCHO TOO BIG for our wanted speed of at least 190 mph. That would require a too large prop size accompanied by a too small prop pitch.

The MINARE .40 pictured below was powered by a piped Supertigre .45 ABC running 16300 rpm with an APC 10*7 prop. This setup was not intended for speed, just for regular pattern flight. Speed was only about 110 mph.

So, while looking closely you can identify many details NOT recommended for our speed project:

- plastic spinner
- a non-carbon sport prop
- the retractable landing gear
- the very fat wing
- the too thick and too large horizontal stab
- the exposed hinge gaps
- the too long ailerons (50% length are enough)
- the antenna outside the fuse
- the elevator linkage being not fully situated within the fuse
- the outside situated ON-OFF radio switch
- and of course the side exhaust engine with external pipe.

You can copy the original wing’s trapezoidal layout featuring a reduced wing span of 45 to 50 inches. NO swept back wing design which would add induced drag. Please do not incorporate an anhedral horizontal stab, it does not make your ship faster.

Everything producing drag and weight (yes - even the retractable landing gear) must be avoided.

If following the speed recommendations already mentioned in this thread – especially the DF engine size of .60 to .90 with fully concealed non-muffled tuned pipe – then you’ll own a real bargain 200 mph prop plane. Provided that a 9*10 carbon prop is mounted!

Let’s bear in mind - this nice speed project still is a converted pattern plane NOT COMPARABLE to the pure speed “breeds” to be seen at the German Speed-Cups for instance. Those are specialised constructions not available commercially.

Enjoy!

Cyclic Hardover

My Feedback: (3)

So if my 90L is on Steroids, whats my Sport 50 on ? Altoids? Hey its early.

rmenke

My Feedback: (13)

Cyclic:

So, you have a old OPS sports engine on your hands you would off for $150.00 I have a hot old OPS in need of various parts. Want to part with yours for $75.00? Dont ya just love our overseas German speed brethern?

Cyclic Hardover

My Feedback: (3)

MIke-Curious here, Always wanted to build a DD, would that OPS.60 I have be to much in weight? Verses a jett .50 or similar



quote]ORIGINAL: Mike Connor


11" prop turning 22,000 rpm static would be 719 mph tip speed. Additional calculations needed for inflight tip speed.

The "helical" tip speed in flight Vtip is obtained by adding the airspeed V to the rotation tip speed Vr using the rule of vector addition, viz:

Vtip = SQR( Vr ^ 2 + V ^ 2 )

Now we have a prop tip speed of 741 mph before we consider any unloading of the engine. Hmmmm

I used to run a 10x6 MAS prop at around 18,000 rpm and the prop noise was so loud that one guy covered his ears as it flew by. As mentioned in another post, the prop is not very efficient at tip speeds above Mach .8. I would also like to see and hear a video of this setup.


[/quote]

Cyclic Hardover

My Feedback: (3)

Thing is it's not mine although i have possesion of it. He wanted $150 for it. Sorry , I am debating whether or not to buy it myself

rmenke

My Feedback: (13)

Hi Slomo:

Am going to follow your directions, recommendations to the letter respecting your obvious knowledge on the subject. My only outstanding item is the pipe system. Will go to Mac's for most of my stuff and recommended pipe, 1190. I have a 15-1/2" pipe from Helge I may try prior to the Mac's. My question is the RE header. A bolt on type seems to be the common system. Am wondering about the preference of a O ring type header as it seems less prone to vibration and stresses, but absent of any real positive bolting system. In your view, which type would be the way to go, if O ring type, where can they be found? Much appreciation for the help!

Mike Connor

My Feedback: (5)

The DD is cheap, quick to build and fast to fly. My favorite adrenaline rush airplane. With a Jett 50 on mine I had to add 2 oz. of lead to the tail for the best CG. Even though I built the plane knowing it would be nose heavy. I cut the motor mount out to move the engine back but could have gone even further back. Mine came out 2 lb. 12 oz. ready to fly (dry). The wing area would probably be good for a little over three pounds. If you build one with a OPS 60 I would sure like a flight report and video