Prop on an OS 91 ducted fan
 

Hi

I was wondering if it would be possible to put a prop on an OS 91 ducted fan engine running at 23000 rpm. I was hoping to use a 12 inch diameter prop. If anyone has done this, what prop? Thanks

JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

It's been done before but I don't think with a 12" prop, it's too big even for carbon. The tip speed would be 821MPH, thats over Mach 1.
And it depends on the plane for size & pitch.

RE: Prop on an OS 91 ducted fan
 

freakingfast

Thanks for the info. Any idea what prop was used

JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

It depends on the plane for size and pitch and it will take testing to find the right one for your app. But getting the prop is your problem. You can’t use an off the shelf APC prop, it’s not safe. Some guy are getting a much larger APC prop for the large hub size and carving it down. Some are using a fine grain hard wood prop. Both can be dangerous.

Carbon is the way to go, guys are using APC props as a pattern to make their own molds. I can't recommend anyone that makes them. Sorry

RE: Prop on an OS 91 ducted fan
 

I was going to be putting it on a direct connection F-18. Finding a carbon prop is going to be hard and I don't want to get into moulding my prop. Thanks

JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

A 90 size heli or Jett would use stock props;)

RE: Prop on an OS 91 ducted fan
 

I realize that a heli or Jett engine would work. I just happen to have many OS 91 df engines lying around after crashing my twin df. I only have a single Avro Arrow. Funds are kind of tight after purchasing a turbine. Thanks again for all the help.

JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

There are a bunch of threads in this forum about a prop on that engine. I would do a search and see what others have done. I know a 12 inch is too big.

RE: Prop on an OS 91 ducted fan
 

Hi,

I used an APC 10x10 and 12x10 with that engine without any problems although I liked the 10x10 better. The plane was soooo fast, scary.

Ulrich

PS: Although I used the prop without problems, you are doing it on your own risk.

RE: Prop on an OS 91 ducted fan
 

Hi
I used an 11-9 and a 10-10 apc on a stiletto mustang and hit almost 190mph. Using the BVM 96, we did break 200mph with the same props and increased nitro fuels. The engines we turning over 23 in the air read by Eagletree systems.

RE: Prop on an OS 91 ducted fan
 

Thanks for the replies.

It has given me hope to at least try a prop in a caged test stand. What RPM and pipe were you guys using. I read about 17000 RPM and I have only BVM pipes. I think this engine could really make the DC
F-18 come alive. I have a buddy who has a Webra 80 in his and I've always wanted to beat him with a prop jet.

Thanks again
JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

Just be careful! A standard APC prop is a potential grenade at those speeds. Check the hub for white marks on both sides of the blades near the hub before every flight. Keep in mind that if the prop throws a blade, the second blade can be thrown in almost any direction as the engine may not be mounted in the plane at that point.

Have Fun and BE SAFE!

RE: Prop on an OS 91 ducted fan
 

Bolly has a variety of CF composite props geared towards pattern fliers, of which some of the 11-13" varieties may be good candidates for trimming down to get the rpm up. Just a thought. Supercool props does not appear to have anything suitable.

MJD

RE: Prop on an OS 91 ducted fan
 

Good idea MJD

A state side distributor for Bolly

http://www.aeroproduct.net/

It looks like the 12X8 or 12X10N could be candidates for trimming down.
Pricy at $37 each!

A BVM remote needle would be a great idea, so you can peak it at a distance on the ground as well as in the air.

RE: Prop on an OS 91 ducted fan
 

Jett Crazy:

See if you can contact "Combat Pig", I recall he has had a lot of experience with the VRDF engines, he is a great source on the go faster engines used in Europe and does know his stuff. There are several USA guys using that engine in warbird racing, seem to end up with props in the 10 X 10 range, cutting down a 12 X 10 I think. Let us know how that engine works out in the DC (Juno) F18. You may have a few CG issues, thats a heavy engine but gobs of rpm power second only to the BVM which is big bucks. Am now covering a Juno Tsunami, Jett 60LX powered. Will not get more than around 130-150 out of it, but can also sport fly well and hover yet. I do have a VRDF NIB that needs a home, so am interested in your results. Its gotta turn without skidding out or of no use to me. ENJOY

RE: Prop on an OS 91 ducted fan
 

IIRC 8-12, 9-10, 10-10 seems to the range of speed props folks have used with success on these .90/.91-ish fan engines. $37 seems like a normal price for a CF prop this size, ILJ estimated the value of CF copies of APC 10" props at about $40 - they're not trivial to make. The trick is not to break one every 5 flights.

http://www.rcuniverse.com/forum/m_80...mpage_2/tm.htm

Post #33 talks about what some Euro folks are using on their .91's; while they are going for all out speed, the info is useful.

MJD

RE: Prop on an OS 91 ducted fan
 

Even though DF engines are timed for high rpm they have pipes that are also tuned for that rpm to drive those
tiny DF impellers. Tuning it for a longer pipe will yield a different rpm and power curve.

Im thinking a .80 - 90 DF engine might drive a 10x10 carbon at about 20k or so and with a little longer pipe
the engine will not be struggling to get on the pipe if its tuned for a little lower rpm.

I have a couple of Rossi's .81, .90 and a 1.05 I was planning on testing out this winter.

I think Freakingfast had a OS .46 that was shredding APC's, so for testing
gloves, goggles, face protection and maybe a flak jacket might be in order
just in case these monsters bite:D

RE: Prop on an OS 91 ducted fan
 

Treat them like testing rocket motors, i.e. assume it could and possibly may blow up at any moment when it is functioning and protect yourself accordingly. Saved my ass a few times before. I suggest remote starting from a bunker with video surveillance. RC mixture control, throttle, no sweat.

I think you could stretch the pipe length a bit and possibly run in the 18-20k range with decent performance. I recall people have done this before and mentioned it here somewhere, but I ain't done it personally. Nothing a test stand and a few props wouldn't tell you pretty quick.

MJD

RE: Prop on an OS 91 ducted fan
 

Hey guys i didn't even knew if this was even possible!, i had a guy asked this same question and i told him it's not possible as these DF engines are designed to perform inside the ducting chambers with super high air velocity going at them. Now what i read here is surprising as it sounds very risky and hazardous at the same time. I am not sure if APC props can take the super high rpms from these engines w/out breaking!, but i guess i was wrong as it's been done and is possible. I know i wouldn't try doing it but i guess it's "Ones to it's own" scenario with this one...

Wow learned something new today, good thread;)

RE: Prop on an OS 91 ducted fan
 

Hi Guys

I am thinking of getting a header from Macs Products and tuning the 91 to 17-17.5K. That way I am under the max RPM for an APC 10x10. I can try this on a stand and see if it will have enough static thrust to get the DC F-18 in the air off grass. As far as safety, I treat every prop as if It's going to explode. I have great respect for model aircraft and know what kind of damage they can do. I've been in this hobby for over 10 years. But thanks for the constant reminder of safety. It's the most important thing. (next to going as fast as possible!! LOL).

Are the Bolly CF props hollow inside or solid. Don't want to buy one and start carving away to find it's hollow.

I will post my progress and findings, but may not get to this project till spring. The snow has started to fly here.

Thanks Again
JetCrazyCanada

RE: Prop on an OS 91 ducted fan
 

snow? i am still picking the last of the tomatoes from my little tomato patch.

david

RE: Prop on an OS 91 ducted fan
 

I live in SW Ontario CANADA. we'll have snow till March.

RE: Prop on an OS 91 ducted fan
 

just ribbing you a little.

david

RE: Prop on an OS 91 ducted fan
 

I like the snow. If I had flying weather all year round I'd never get anything built. LOL

Steven

RE: Prop on an OS 91 ducted fan
 

Okay, here's the deal - you get that thing ready, I'll get my Whip and whatever else ready for spring, and I'll make the gruelling 1-1/2 hour drive to Cambridge from Orangeville and we can break fast airplanes together some day - howzat?

Yeah, there's 3" of wet, slushy cloud spooge all over the place here. Time to winterize the toy collection.. [&o]

MJD