Picked this one up a few days ago. Not really a lengthy build, but there is some finesse and fine-tuning involved to ensure it works and fly's properly. The fuse and vertical stabilizer is fiberglass, the rest is balsa.
Waiting patiently on the work bench is old Panther power system. This one should be fairly light and fast, and will be strictly setup for bungee assisted launch.
It also has a sparkly paint job ;D
that should be much faster than the Panther was!
The wings are so short, I can hardly see them! You're going to need to keep the speed up for sure. ;D
Very nice, Jeff!
And very sparkly ;D
It definatly has an Evel Knievel look to it!
Quote from: Ededge2002 on January 20, 2013, 05:22:02 PM
that should be much faster than the Panther was!
I know, the Panther is a bit of a slow poke. Well at least I can use it as a nice relaxing flyer in between the Sniper and the Rifle.. ;)
Did you get a Rifle? :o
Yes, courtesy of Mr. Edge. Its been sitting on the shelf armed with 450watts, waiting for a nice day...
:o
450W on a Rifle should make it haul a$$!
Sniper is nearly finished, but will probably have to order a small capacity zippy compact 6S, as this model is designed for and usually flown on 3-4 cells.
Just need to adjust a few things and add a satellite rx.
Couple more pics:
I'd go 8S Jeff, to overcome the drag from those servo horns and control rods!!!
I don't think that will do much good, I did a watt test with the fan unit installed. I'm getting over 500watts less in this airframe vs. the Panther. :o Seems large cheater hole(s) are a must when using high power setups, or you need huge intake ducting.
The good news is it's only pulling 53amps, so at least my flight times should be decent, although I'm hoping the power may increase in flight due to ram-air effect?
Jeff - you missed a great workshop last night, on power systems. Your lower "watts" figure means it's consuming less power, not necessarily making less power. It could be that your installation is more efficient this time.
Maybe Ed can shed some more light on this?
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.
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.
Hey Ed, this model actually has full internal ducting. However as you mentioned, the problem I think is that it is simply too small to move the required volume of air. Seems like it was originally designed for 600-800watts using a 4cell setup. I'm still getting over 1000watts out of it, but the fan is definitely starving for air, similar to the Panther before I gouged out 2 large cheater holes in front of the fan. To make matters worse the exhaust exit diameter is only about 53mm. This further reduces static thrust which should be about 80% of total FSA.
Did a bit of research today and it appears there have been cases of 70mm sniper wings folding in flight...even on 4S :o
Any ideas on reinforcement?
Embedding some carbon strips might help. Is there a wing tube or can you find room to add one?
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.
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!
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?
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.
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 :)
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" ;D
There's an old saying about EDFs:
When in doubt, add 50% to the amount of power you think you'll need..
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 (http://www.rccanada.ca/rccforum/showthread.php?t=193115)