frisconick

Made some progress on a couple of fronts tonight. wekenav8r, I think you're right about the CG being measured from the front of the intake; not the LE of the canard. I think the shoulder in front of the intake threw me off looking at the picture in the manual. I took the first image from the same perspective in the manual. The leading edge of the intake clearly lines up with the rear of the canopy. The second image shows where my "calculated" CG range falls (8.6 - 9.5 from the LE of the canard) compared to 290mm aft of the intake, which is pretty much where Curtis said to set it: "1/2 to one inch in front of the manual".

frisconick

Also got the fan and thrust tube mounted tonight. Really pretty easy. It would help at times to have another set of hands around as you try to tape the tube together. The end that fits around the fan is a different diameter than the exhaust end. I ran a length of clear packing tape along the length of the tube once rolled to the proper diameter (outside the plane, of course). I then "mooshed" it into a "C" shape to insert it into the plane from the tail. When it popped back into a circular shape, it hugged the round formers nicely. Slip the rear of the fan into the tube, tape the tube to the rear of the fan, then slide the fan/tube assembly back to the mounting holes in the rails and you're good to go. Trim the excess tube from the rear of the plane. I hooked up the ESC and battery. Ran the fan up full throttle for a few seconds; then spent the rest of the evening trying to find the dog......scared the crap out of her !!

Nick

mpope1

Looks good!

kmp647

what diameter is the end of the exhaust tube?

also is ther an intake ring you can fit on the front of the fan>?


might help scare the dog less!

frisconick

KMP,

I don't remember exactly what the diameter was, but it was something like 3.6". You can measure the ID of the last former.

I wasn't satisfied with the elevator setup. First, I drilled out the last hole in the control horn to accept the clevis pin, but I must have opened it up a bit too much. There was a lot of play in it, begging for flutter. I move the clevis to the next hole in, but with the long moment arm of the elevator, it was overpowering the servo. I mounted some new, longer control horns and cut some carbon fiber tube to slip over the control rods (not in picture yet). Should be rock-solid now.

Nick

dw_crash

My Feedback: (6)

Gents,

If you send me a PM, I can send you a Excel spreadsheet that calculates C.G.s for regular and canard aircraft. It even seems to work for forward swept. I downloaded as a promotional item from one of the Jet magazines.

DW_Crash

frisconick

Here's a shot of the final elevator linkage with the carbon fiber tube. Very light and rigid.

Nick

frisconick

I epoxied a light ply plate across the supports for the canards to hold the battery. I have one 6S-5000mAh (huge) battery. The airflow will really be disturbed by it, but it's the only one I have right now. Should be OK for the first few test flights. It won't give max perfromance, but.... The ideal setup would be 2 3S in series, or 2 6S in parallel on each side just forward of the fan.

This setup, along with 2 oz. of weight in the nose, put the CG just forward of my 9.5" mark. This will be it for the first flight.

Nick

frisconick

Well, I think she's done; at least until I can get out to the airfield. Good temps here, but 20-30 mph winds. Won't be this weekend. I hooked up an E-Flite Power Meter to get a few readings. I'm still concerned with that big battery in front of the fan. I measured wattage with the battery out of the plane and no hatch, battery out of the plane with the hatch, and battery in the plane and hatch installed. Here's what I got:

1,738 watts - battery out of plane, hatch not installed
1,850 watts - battery out of plane, hatch installed
1,820 watts - battery mounted in plane, hatch installed

I really expected the wattage to go way down with the battery in front of the fan. Just like if you put your hand over the suction end of your shop vac, the motor revs up because there is less air to move and less drag on the impeller. Dropping only 30 watts is encouraging; not that I'm recommending putting that huge battery in the air flow. But it may not be as bad as I thought. The system is drawing 79 amps which is right at the limit of the ESC (80). Should be OK. I'm sure it will unload a bit in the air.

If you try this at home, I have a couple of recommendations:

Lock the dog up

Wear ear protection. This setup is extremely loud close to the plane.

Nick

slevin1

My Feedback: (23)

Nick,
Why not just put the battery under the canopy?

Saul

frisconick

Saul,

The way I have the canopy set up, there is no access through it. Also, it would be too nose heavy that far forward. Since I can't fly it this weekend, I may cut out the center part of the former forward of the battery and mount it lengthwise in the middle.

Thanks
Nick

slevin1

My Feedback: (23)

Nick,

I see.

I have this plane so please post pics.

Sounds like they did not think the battery location through when they designed the plane.

Thanks,

Saul

frisconick

Too windy to fly, so I did hack up the center support on the forward former to mount the battery length-wise. I made a saddle for the front of the battery out of light ply and triangle stock so the battery could slide fore and aft to achieve balance. Just for grins, I'll run another set of watt tests to see if there is any difference.

Thanks,
Nick

PhilLin

Hi, Nick! Looking good. Hope the weather clears up soon so you can maiden.

If you got a chance, can you please post your AUW? TIA!

Phil

bruff

My Feedback: (18)

That is how I'm setting up my battery mount also. Mine should be ready in about a week. Here is a link to my [link=http://www.rcgroups.com/forums/showthread.php?t=1022739]X-29 build[/link]
Yours is looking good!
Bob

frisconick

Thanks for looking in Bob. Hope you're not running into too many issues on your builds. After my "battery mount surgery" yesterday, I just need to button everything up again, rebalance, and should be good to go for a first flight this weekend (weather permitting!). From one of your images it looks like you're running the elevator servo arms in the same direction, but the canard servo arms are in opposite directions. How are you handling that as far as "Y"s, reversing "Y"s, or mixing in the radio? I'll have to figure out how to subscribe to your thread.

Thanks,
Nick

bruff

My Feedback: (18)

I have a MC-16 radio going to use mixing to work everything.
Bob

frisconick

Phil asked what the AUW was. I didn't have a scale, so I bought a digital fish scale. Ready to fly weight is 6 lbs. 14 oz.; just under advertised weight. I tried to use the scale to measure the thrust. I know it's crude, but I just set the plane on its landing gear and tied the scale between the garage and the plane and cranked it up. 3lbs. 2 oz is what it read. I'm sure that between the thrust vectors and friction of the sponge wheels, something was lost. Maybe real thrust in the 4 lb range ?? If anyone has a neat way to do this other than hanging the plane with the nose pointed down somehow, please let me know.

Also measure the wattage again with the battery re-arranged: 1690 watts at 78 amps. A bit lower than previous readings. Not sure if it's because I ran the thrust test first and the battery wasn't 100% ???

Nothing left to do but fly it !!

Thanks,
Nick

mpope1

I get more acurate readings holding the scale and hooking it to one of the struts or landing gear wires. I think you lose alot when you have a length of rope.

PhilLin

Thanks for the weight data, Nick! 3Lb2oz static thrust is a bit on the anemic side for that AUW though. I measured the rolling resistance before on my Ke-E-Cat conversion, which came to about 0.5ozs/lb. I'm guessing you are losing a lot of thrust due no inlet ducting. If you decide to try measuring static thrust by hanging your model on the fish scale, just make sure there is a stop on a wingtip opposite the fan rotation to counter torque twist.

I'm thinking of doing a couple of things to study the effect of no such ducting for this model (:
- First, I'm going to try "S" shape opposite hand inside flat walls (as previously mentioned), which are attached flush to the inside straight part of the inlet openings. These wud also act as aft end battery box support; but wud mainly act as inlet air flow open guides based on Coanda principle. I've been granted 2 patents (one for a passive & another for an active devices ) in industrial apps. I'm sharing this one pro gratis as I don't think there is enuf money in this hobby to pay for a patent I'm curious how such a simplified flow guid compare vs.
-Second, a regular ducting merged from 2 inlet branches c/w extended median wall downstream of the merge.

PhilLin

I was side tracked a bit in my above reply to FriscoNick's post#69; sorry! I meant to say that at ca1700watts for a 4" fan, you can expect about 6.5-Lbs of static thrust. Since you're getting ca3.5-Lbs, allowing for wheel loss, you're netting about 54%, or 46% loss My twin 90mm F-4 with 34" long area ruled fullducting had less than 5% loss, or almost undetectable with a fish scale. So IMHO it is worthwhile to see if this loss can be minimized for this X-29 model.

Also, I wud be very interested to hear if you see some improvement when the model gets in motion.

Cheers

Phil

frisconick

Phil,

How do you convert watts => thrust?? I don't know that much about fans, but I do know that 1700 watts (input) is a bit over two HP. But without knowing the rpm or pitch of the fan, I don't see how to get there. A 2HP motor might turn a 16x8 prop to generate a certain amount of thrust. The same motor would turn a 14x10 prop, but develop a lot less thrust, but a much greater air speed. It seems one would have to know the diameter, pitch, and rpm, no?

Thanks,
Nick

PhilLin

You're right on about calculating fan or prop performance from scratch, Nick. I'm not an expert on fans, so I take a "black Box" approach to it; as has a few folks, notably Carl Rich & Whistling watts. We kind of test a fan/motor/pack/Esc system on the bench, measuring the amps,volts,watts-in fed into the black-box, while at the same time take measurements of the static thrust, fan rpm & sometimes exhaust velocity, to try quantify the performance of the black-box. Some will argue static testing is almost irrelevant while emphasizing inflight measurements. Note also that the block-box results areaffected by factors inherent, such as use of rounded intake lip or proper exhaust pipe, motor or ESC efficiencys, & yes even pack internal resistance. I don't want here to get into fan loading in flight, etc.; but I find good static test data very useful for picking suitable motor & packs for my EDF apps, for instance, by using charted data to predict the outcome.

Carl Rich has published various tabulated data including the HiMax 96mm fan in his threads on the RCGroup forum. I've tested a Haoye 4" fan up to 26550rpm (12s 20C packs, 66.1amps, 8.31-Lbs S-thrust). & I'll attach the chart below; as it shud give very close figures for other 4" fans:

Note the Formula in chart:
...Haoye4 = -0.0675(Kw-in)^2+3.7887Kw-in+0.2335 has kilowatt unit for watts in.
... Chart shows one can get almost 1.5-lb S-thrust diff between a 90mm fan vs a 120mm fan at ca2.3kw

Cheers,

Phil

ps: edit to correct amps & thrust figures due reading cross lines in spreadsheet

PhilLin

Sorry about the size of chart in above post. I'll try again as I cud not find way to delet the previous one. Okay! Much better.

frisconick

Mike,

You might be right. I'll try again tonight to get a better reading. I just saw your post on the other thread about your thrust reading. Can you tell me more specifically how you did it?



Phil,

Sorry, but I must be dense today. I still don't get what "x" is and the other magic numbers?? With all the different motors available with different KV ratings and different sweep areas and pitches, I still don't get how one can extrapolate the thrust without more info, or am I still missing something basic?

Nick