I'm looking to get a new fan unit and am up in the air about the Ramtech or Dynamax. Which one is prefered? Does one produce more thrust than the other? Also, are they both identical sizes so either will slip into my inlet duct?

Thanks

Russ

Russ, The even thou the ramtec and Dynamax fans are 5 1/4" fans, I believe the ramtec is just a smidgen larger in diameter. The Ramtec fan will give you more top end speed and the Dynamax will give you more low end thrust power.

Dynamax fans are better on heavy aircraft and Ramtec's are best suited for lighter planes (speed). Both fans will fly the DF kits out on the market that require a 5.25" fan, if just depends on your application.

I thought it was the other way around, but I have only used the Dynamax so I can't make a comparison. I can say that I have had very good luck using the Dynamax with either the OS.77 or .91 in a wide variety of airplanes.

It may be the other way around Gary. Now I'm confused. Can someone else please clarify. Thanks John

Well,

I've used both and saw no difference in performance at all. Even in the same airframe. The Dynamax fan is built better, IMHO, and, depending on the airframe, can be less of a hassle to install. Jedi, you're right, the Ramtec is a hair bigger, so if you've got certain airframes (like the Y/A F-18 single, for example) you'll have a hassle getting it in and out.

Go for the Dynamax.

i,m just about ready to start scratch building an avonds 1/10 scale f-14 & have been checking on those two fan units as to which pair to install! Jet Model products state that the dynamx can give u up to 15Ibs static between 21 to 23,000rpms, true?

the ramtach fan is stated to have a high blade pitch & o.s. recomends the ramtech for its 91 VR-DF engine, as it loads the engine better. you are suppose to get a higher jet efflux velocity than the dynamx at flight speeds, thus higher top end speeds.

i myself will most likely choose the ramtech as they will be paired in the f14 & the combination should give good climbing power & all out speed!

does anybody know where is the best & most secure online site to purchase the ramtech unit? best prices etc..
plus the os 91 VR-DF!

Although opinions seem to vary... The Ramtec in my opinion is the faster of the two in the air but the Dynamax is better at getting you up-there.
Much depends on airframe and engine combo, not to mention setting up with a good pipe... So with this in mind, this is why we have the two schools of thought as to which may perform better than the other.
If you really want to open up a can of worms try asking how much thrust each can produce : )
Not much difference at the end of the day really... Both are very well made fans IMHO and very good products. Give Ed and Kevin at Great Northern Models a call if you want further info on the Ramtec as they are the North American distributors for Trim/Ramtec

Cheers-

hey what abou the turbax 3? is it even around anymore?
any other good 5 1/4" fan units around?

What's the pitch on the Dinamax and Ramtech fans.

CARS II

I have both and did some research a few years ago as to which is good for what. The Dynamax was designed around the OS 77. The Ramtec was designed for the OS 91. The Dynamax will run with an OS 91. I have a Dynamax in a JHH Cougar with a KB 80 and it runs/fies great! While I was stationed in Whidbey Island I flew with Jim Crane (Since deceased) who taught me most of what I know about DF. He had a Ziroli Panther which he built around a Dynamax. He said getting off the ground was always iffy. He tried several engine/fan combos. He finally settled on the Ramtec/OS91 combo which provided the best performance for the 22lb aircraft. Takeoffs were very scale, except for the engine sound!
The quality of both fans are comparable. Neither is "better" than the other.
The Ramtec/OS91 setup is a little cheaper. You can even get an area rule tailpipe from Trim/Great Northern that is ready to install.
BTW Great Northern is an outstanding company to do business with!
Hope this helps.
Jeff Stultz
Representing nobody

Don't want to start a war here but how does the Ramtec/O.S. .91 compare to the Viojet fan/engine combo?

Reaaz, Tower has the .91 VR-DF on sale for $254.49 + you get like another $20 off for an order over $250 so that would make it $234.49, I'm thinking of getting another just for the heck of it.

I am picking one up next week for a backup fror my JHH Phantom an OS 91 VF for less than 240:00 shipped in an incrediable price. I cant afford to buy it till Wednesday so I called to see how many the had in stock. They couldnt tell me but the person said it was a fresh shipment and that they where not selling to hot so I am getting one and BTW the website price goes down by a couple of dollars each day or two
Viper

The guy who designed the Dynamax would disagree that it is designed around the .77. Also, did O.S. recently start recommending the Ramtec? With the dozen or so that I've owned, I never read that. The notion that the Dynamax over-revvs the .91 is an urban legend.

As far as the Dynamax vs. Viojett question, I'm pretty convinced it's a question of inlet design. In non-BVM designed planes, retrofitting of the Viojett system hasn't made any performance difference at all except when you're able to change the inlet too. With the BVM fan AND inlet, you see a noticeable difference in performance.

Another interesting point when it comes to D/F brand's and combo's and performance output of any said particular fan/engine combo, is the often overlooked tuned pipe.
I use to race hi-performance 250cc 2-stroke supercarts for a few seasons many years ago and learnt very quickly that 2-stroke pipe design is where the real power is created and fine tuned, as pipe design is very critical.
The same principals of course apply to all 2-stoke engines and pipes regardless of size, So do not over look correctly selecting a tuned pipe design to suit your application. Tuned pipe design along with fuel mix/plug chosen is where performance can be gained or lost.... It certainly can pay off to do some pipe research as well

Cheers-

Just FYI here you can see the visual differences like blade profile and blade count

2

The Dynamax was actually designed around the OS .65 if memory serves me. Way back when Tom Cook designed the Starfire 1, he had a pair of them at the Sepulveda Jet Rally flying on the Dynamax/OS .65 combo. I also remember seeing a JHH A-4 powered with this combination at the Miramar Airshow in 1984 or 85. Nice thing is it happily soaks up the additional power from the OS .91 as well though. Never heard of an overspeed problem with the Dynamax honestly. There's just too many of this combination out there flying every weekend to say otherwise. They work, work well, and are the bargain in DF for performance/$$ ratio.

I am picking up a Ziroli Panther kit from someone here on RCU. I have been contemplating whether to go with the Dynamax or Ramtec fan with an OS .91 VRDF. Based on this thread, it sounds like either one is a good candidate. I have read some threads that mention inlet area is a determining factor as to which fan is better in a particular aircraft. Does anyone have any specific thoughts as to which fan is better for the Panther?

Thanks!

Paul

Nick originally flew his Panther on a Dynamax/OS .91 and it works just fine.

I dont know what OS really recommends but....

From Towers Site...

Cheers.
James

When it was designed, the most popular engines used in it were the OS.77 and the Rossi.65. Both worked well. Then OS came out with the .91. The .65 was actually introduced after the .91.

I have run OS.77s and .91s in the Dynamax and liked them both. The .91 is more powerful. I have never had a problem with the .91 overspeeding. The OS.65 was the best of all the motors as far as reliability. It really did well in twin fan kits like the JMP F-4.

Hi,

Well, ya know, there's that 'urban legend' thing again :-)

I'd defer to the information on here before I would information from Tower. Those are the same guys who recommend 'Power Point' propellers. I think that's just someone repeating what they heard (as is the megatrend when it comes to this hobby.....)

okay, Yellow aircraft guy, tower might be hawking myth! then lets get some real data in here if possible like:

setup 1 Dynamax & 1 Ramtech with everything being equal! same pipe, same engine & same exaust ducting, inlet duct & same fuel.
then go measure!
1. maximum static thrust!

2. which delivers higher rpm. fan A or Fan B

3. RPM bench mark test! If "fan A' gave lower rpm, set fan B to same rpm & get trust reading for the 2 at equal rpm

4. Exaust velocity!, which one gives higher velicty (airflow measuring instrument needed!

5. Weight! which one is lighter!

6. Fuel consumption, which one gives the best economy for the same engine! (depends on ratio between thrust/rpm)

all of the data collected would give the modeller a chance to sift throught the myth & make educated choices of the 2.
eg, IF the Ramtech unit was lighter by 10% than the Dynamax, but its thrust was 4% less, then overall it might still be the better choice!
And lets say the Ramtech RPMS were higher, thus greater fuel consumtion rate, well one might want the thing to stay in the air as long as possible! so he might choose the dynamax

so anyway before i start sounding like a mad scientist, does anyone know where to find info like this or is anyone up to the challenge for the good of all rcers?
lets gets some replies on this one! yeah right!!

That data does exist, and was published in a German magazine several years ago. Ralph Ploenes conducted the experiment in a wind tunnel, and compared the static and dynamic thrust performance of the Dynamax and Ramtec fans /w OS 91 at various forward air speeds.
The conclusion(s) could be summarized as follows: With a correctly sized/match inlet and thrust tube area, the Ramtec did, indeed, deliver more static and dynamic thrust when compared to the Dynamax with identical inlet/exhaust geometry.
However, if the inlet area dropped below a certain value (can't remember the number) the Dynamax would produce higher thrust levels than the Ramtec.
So, if the inlet area on the jet is on the low side, the Dynamax is probably the better choice. But for installations that can provide the required inlet/thrust tube area, the Ramtec is the way to go.

Peter