Thrust test unit

Tom M. · September 22, 2013, 05:14:42 PM

A couple of days ago the power system components arrived for a F-18 I've just started so I put together a test rig to try it out. It all had to be run up and tested anyway so I thought I'd just put the rig on wheels so thrust could also be measured. Entire airplanes- EDF or prop- can also be secured to the cart for thrust numbers. I don't think this method is super accurate for true numbers (because of wheel friction etc.) but should be pretty close for comparitive purposes. This fan produced about 8lbs.2oz. thrust today so it'll be interesting to see what the numbers are once it's in the airframe with full intake and exhaust ducting.
The fan is a Wemotec 90mm with their new 11 blade Evo rotor on 4s 5600mah 70-120C. batteries (2 in series) through a 100 A. ESC. Peak Amps were 97 at about 2800 watts - I'm liking the nice whooshy sound it produces.

I hope to do a bit of a build thread on the Hornet but for now here's some pics of the test rig (Mk. 1)
Tom

sihinch · September 22, 2013, 05:31:55 PM

That's awesome Tom - thanks for sending the pics.

And I'll be interested to hear your thoughts on the new Wemo "Evo" fan - I've been following the thread on RCGroups with interest. I'm planning an 90mm EDF build this winter and will be using the "standard" 90mm Wemo fan.

Ededge2002 · September 22, 2013, 07:39:35 PM

I think your thrust test rig is quite good. Any friction should be erased by the vibrations of the fan. Please don't take this as criticism but personally I would consider 5mm bullet connectors. Deans are good connectors but at 100amps they might be near there limit.

Welcome to the forum and thanks for posting your rig/results

Wingnutz · September 22, 2013, 08:24:55 PM

Tom,
Thanks for posting. I'll be watching the bug build with real interest.
Neat rig! Your thrust figures are impressive! Much better than my whooshy Lander ...if I can talk my bank manager into a loan, think I'll order the same as yours.
I like the "shrapnel shroud"...just in case.

The only one I had "blow up" on the bench was a 90mm Changesun on which the tester had forgotten to tighten the reassembled rotor...rotor unscrewed, departed the shroud and sprayed fan blades everywhere!
Like Simon, I'm planning another 90mm EDF this winter but I think I'm going to leave "the Bug" to you.
Have fun and thanks again for keeping us in the loop.
Bill

bfeist · September 23, 2013, 10:26:44 AM

Very cool. Are you putting two into the F18?
One suggestion: move all of the taped down bits to the side of the fan. They look like they're one piece of tape away from being sucked into the fan

Tom M. · September 23, 2013, 05:39:08 PM

Quote from: sihinch on September 22, 2013, 05:31:55 PM
That's awesome Tom - thanks for sending the pics.

And I'll be interested to hear your thoughts on the new Wemo "Evo" fan - I've been following the thread on RCGroups with interest. I'm planning an 90mm EDF build this winter and will be using the "standard" 90mm Wemo fan.

I think this new rotor will fit in the standard shroud, Simon, with only a 2% loss in thrust, or so says Wemotec. What jet are you thinking of?

Quote from: Ededge2002 on September 22, 2013, 07:39:35 PM
I think your thrust test rig is quite good. Any friction should be erased by the vibrations of the fan. Please don't take this as criticism but personally I would consider 5mm bullet connectors. Deans are good connectors but at 100amps they might be near there limit.

Welcome to the forum and thanks for posting your rig/results

Ed, I hear you re: the connectors. I was feeling the connectors, solder joints, ESC etc. during the run ups and nothing was very warm, but for the ESC finned heatsink. I've done a fair amount of reading about Dean's and feel comfortable using them. A 4 min. flight would be below 70 A. most of the time, but I'll certainly keep an eye on them.

Quote from: Wingnutz on September 22, 2013, 08:24:55 PM
Tom,
Thanks for posting. I'll be watching the bug build with real interest.
Neat rig! Your thrust figures are impressive! Much better than my whooshy Lander ...if I can talk my bank manager into a loan, think I'll order the same as yours.
I like the "shrapnel shroud"...just in case. The only one I had "blow up" on the bench was a 90mm Changesun on which the tester had forgotten to tighten the reassembled rotor...rotor unscrewed, departed the shroud and sprayed fan blades everywhere!
Like Simon, I'm planning another 90mm EDF this winter but I think I'm going to leave "the Bug" to you.
Have fun and thanks again for keeping us in the loop.
Bill

Hiya Bill!-how's it going? I had the thing assembled and balanced by Mark at Extreme RC- 22 bucks seemed a good deal to have it done by a guy who does it all the time, and indeed it runs super smooth. I'm not usually such a slave to safety concerns (preferring to learn the hard way) but I had the roof flashing on hand and it didn't take long to make a shield. Have you decided on a jet yet?

Quote from: bfeist on September 23, 2013, 10:26:44 AM
Very cool. Are you putting two into the F18?
One suggestion: move all of the taped down bits to the side of the fan. They look like they're one piece of tape away from being sucked into the fan

No Ben, just the one. Cost and weight being the deciding factors. As for the tape, there's virtually no suction out where those things are (and it's good tape

). Anyway, I got the numbers and the rig is now disassembled. Next time it should have a whole Hornet strapped to it!
Tom

Papa · September 23, 2013, 08:47:37 PM

Hi Tom, I've always thought if I made something like that I would use model railroad track and bogies to reduce friction. If you are just looking at comparisons it should all cancel out.

Nice rig.

Jack.

sihinch · September 24, 2013, 08:08:30 AM

Hi Tom, All,

I have (had for at least 8 months) the Jepe "FastFoam" F-4 Phantom to build this winter. Hopefully! It is fairly low down in the queue!

For those that don't know, Jepe is in Europe and does modified versions of FlyFly 90mm EDF jet kits. I am planning on 6S with the Wemo Pro 90mm fan. Not the Evo, although I may succumb to the temptation of the nice "whoosh" noise!

Tom M. · September 24, 2013, 06:00:01 PM

Jack, your track idea would work very well, the rolling resistance being almost nothing. I've also seen drawer slides (the kind with bearings) being used to good effect. Maybe the Mk. II version will use one or the other.

Simon, move that baby to the front of the line!- the Phantom is one of my favorites. I still remember building a plastic model of an F-4 at the age of maybe 12- still love them.
Jepe seems to know what he's about and you probably won't go wrong following his instructions. He also does a build of this Haoye F-18 I'm doing (though a 70mm twin) and I've gathered some good ideas from it.
Tom