sonicboom

Can anyone help me with some advice. I have been told that running an OS91 in the Dynamax fan will overspeed the engine and reduce its life. Is this true? Is the better alternative the Ramtec fan due to its course pitch?

Shok

My Feedback: (28)

The Dynamax does let the bigger motors turn up alot. The Ramtech is good but I think it has a bit too much pitch. I used to give my Ramtechs to Mickey Edmunds and let him re-pitch them. Happy medium.
He posts on here as Jetdriver I believe.

Thomson

I have 4 Dynamax fans with OS 91s and have 1000s of flights in all conditions. Yet to "overspeed" the engine. I have a remote mixture control and always monitor the mixture before every flight to ensure the engine is running appropriately. I run a little rich when flying in 100 degree weather. Lean it out a little more when it is 50 degrees.

Hope this helps.

Dave

JohnnyA

My Feedback: (1)

I remember in the early 90's seeing Mickey & others lose a connecting rod after a speed run with a clean airframe. I think Mickey started re-pitching Ramtechs & Dynamax's because of this situation. I'm sure the OS 91's of today are much less prone to that sort of thing than they were then.

On another note: I watched a NEW K&B 1.00 go extremely quiet in a repitched Dymamax after 2 tanks of rich running to break it in. To K & B's credit, they replaced the engine with no question. Lesson learned...Don't put a K & B 1.00 in a Dynamax..
JA





reason for edit:spelling

patf

My Feedback: (4)

depends on the application. you can really rev a ramtec with an os 91 in a limited inlet situation as well in a blade stall. what aircraft are you using the fan in? rule of thumb is 14 or 17 sq in. I am second guessing myself. if the inlet area is smaller than 17 sq inches use a dynamax, larger use a ramtec.

since you are down under, the ramtecs are much more plentiful since they grow them there.

Shok

My Feedback: (28)

haha I wish I had a ramtech tree

sonicboom

The Jet I intend putting the Ramtec into is a Jet Hanger Hobbies Mirage thus OS91 with Ramtec. I have a Yellow Aircraft Skyhawk with this setup currently but indend replacing it with a Dynamax and an OS77.

I have these two combinations currently. Is this the best choice? The inleta rea in the Mirage is larger than the skyhawk and I fly of a grass field.

Thud_Driver

My Feedback: (1)

I've flown a JHH Mirage (mine was built as a Kfir C2) with both the Dynamax and Ramtec. Liked it best with the Ramtec. I also closed off the cheater hole after the Ramtec was in it for awhile. Mine was an old kit. I think JHH has recently changed the inlets on this kit. Anybody know for sure???

GrayUK

I flew hundreds of flights with a Dynamax, powered by OS91. While at a competition the Dynamax failed (no complaints it was years old and well used) I needed a new unit to fly next day and all that was available was the Ramtec. This i fitted overnight. I can tell you that the difference in performance was dramatic, top speed well up and general performance throughout the range better. The engine seemed less strained and quieter. I never went back to Dynamax, as good a unit as it was. I fly turboines now, but if i was to build a DF again i would use the Ramtec and OS91 combination every time. Hope this helps.

Vampire

My Feedback: (2)

Flown for YEARsss with both, I prefered the RAMTEC.