Super Sniper

flying saucer · January 29, 2013, 10:46:24 PM

Did a bit of research today and it appears there have been cases of 70mm sniper wings folding in flight...even on 4S

Any ideas on reinforcement?

thehaze · January 30, 2013, 07:37:01 AM

Embedding some carbon strips might help. Is there a wing tube or can you find room to add one?

flying saucer · January 30, 2013, 09:25:36 PM

Unfortunately the two wings halves have already been epoxied together by the original owner. I think the only option at this point would be to somehow reinforce the outside.

Wingnutz · January 31, 2013, 07:29:45 AM

Hi Jeff,
Amps, volts, watts, whatever's, seems to me what's relevant is thrust generated in the model and Ronnie and yourself have a system for figuring that out. Have you measured the thrust yet?
Good luck Snipering!

Wingnutz · January 31, 2013, 07:39:38 AM

Quote from: Ededge2002 on January 24, 2013, 07:55:24 PM
Ugg ducted fans... a proverbial vacuum of efficiency!

The fan is likely unloaded or stalled due to poor ducting. Having internal ducting would smooth the airflow into the rotor and vastly improve its performance. I don't much EDF stuff but I believe there is a calculation based on fan sweep area/ intake area also. High blade count fans might make airframes designed for 6904 style rotors worse.

Wondering if an EDF unit which is "unloaded or stalled" when bench tested will generate more thrust when it's moving through the air at 100+ kph?

Ededge2002 · January 31, 2013, 08:29:02 AM

I suspect in air measurements to be HIGHER watts when the fan actually has some air to push! Thrust is important but the pitch speed produced is also a factor. A big scale plane has much different requirements than a slippery sport model. We would not use the same propeller why should the same fan apply.

Bobmic · January 31, 2013, 01:22:43 PM

I was looking for a while for usable information about EDF's, especially some kind of relation between power in vs power out but there are so many variables that I guess it is not an easy task.
Beside the different fans, the inlet shape, duct and exhaust have a significant effect especially in the air so just measuring static thrust is only part of the equation and will not necessarily mean that the plane will end up flying faster. Just opening a large cheater whole will create a lot of thrust on the ground but can create quite a turbulence in front of the EDF and when combined with airflow around the plane and through the ducts can cause the opposite effect.
The size and shape of the inlet lip together with any sharp corners in the duct will also mess things up so only increasing power does not necessarily solve the problem.
There is a reason why jet engines cost millions of dollars....

At the end of the day there are too many variables to play with compared to the models we are flying.

So just put a 10s and see what happens maybe instead of Jet/EDf propulsion you will end up with Rocket propulsion

flying saucer · January 31, 2013, 04:20:57 PM

Quote from: Wingnutz on January 31, 2013, 07:29:45 AM
Hi Jeff,
Amps, volts, watts, whatever's, seems to me what's relevant is thrust generated in the model and Ronnie and yourself have a system for figuring that out. Have you measured the thrust yet?
Good luck Snipering!

Hey Bill,

I've helped Ronny on his models several times, but to be honest I usually don't bother measuring the thrust on any of my 70mm jets. I just install the most powerful fan/motor I can find, or basically way more power than the model is specified for. Mind you I have only been flying EDFs for about one and a half years, and most of that time has been smallish foamies. Just in the last few months I've been getting into balsa/composite EDFs. And when you start getting into 90mm composite jets, the game changes again. These can get quite expensive ($800-$1200) with a lot of modelers using proven (pricey) high end power systems and getting accurate installed thrust readings is a must.

In the case of the Sniper I'm using a power system which exceeds the capability of the airframe so thrust reading become redundant. Sort of like Bentley when they list horsepower numbers for their vehicles as "more than adequate"

There's an old saying about EDFs:

When in doubt, add 50% to the amount of power you think you'll need..

flying saucer · February 07, 2013, 08:31:53 PM

A few members in the past have inquired on ways to balance EDFs (myself included). This allows for a much smoother, reliable and better sounding fan.

Well I came across a really good post on Rc Canada that details the process (it's actually fairly simple) on Changesun high blade count fans, but the balancing method follows for all EDF units.

http://www.rccanada.ca/rccforum/showthread.php?t=193115