frisconick

Also, Phil, how do you measure the RPM??

bruff

My Feedback: (18)

I measure RPM by putting two white stripes on the fan spinner. Then use a optical tach to measure RPM.
Bob

PhilLin

Nick, the X is the x-axis variable, which is Kwatts-in, as I tried to note in the text portion of the post. As I also stated, the outputs from the "balck=box" is slightly affected by the variables mentioned; e.g. motor effcy changes can raise or lower the curv a bit, & 40C packs will have lower internal resistance, decreasing pack loss slightly; but 40C packs will have bigger effect in raising max end performance due to higher voltage under load.

Have fun.

Phil

PhilLin

You can use better laser tacks and do as Bruff. I measured mine using the frequency counter function on a $25 multitester. WW had data showing it gives about same ballpark rpm as Bruff's method, without risk of disturbing airflow or being sucked in by the big vacuum cleaner

Phil

frisconick

Phil,

I'm with you on the kilowatts in and some adjustments for motor efficiency, but the formula in the graph for the Haoye fan is: -0.0675 times x(squared) plus 3.7887 times x plus 0.2535 leaves me with some questions:

did I get it right where the parens should be; e.g., is it ((-0.0675 times x) squared); or (-0.0675 times (x squared))?

how do you get negative KW input?

Still not sure what "X" is

how do you get the 0.2535 that is just added to the rest?

Sorry; I'm no math major, just trying to understand.

Nick

frisconick

Thanks Bob,

I never thought my optical tach would keep up with that high an RPM. Do you have the typical tack you would use on a prop plane, or is it a bit more "special" ??

Thanks,
Nick

bruff

My Feedback: (18)

Standard tach nothing special.
Bob

PhilLin

Hi, Nick! I did not mean to complicate things. You can just use the graphics & not bother with the math, since the equations is merely a curve fitted thru the discrete test points. So for example for your 1690watts reading, change it to Kilowatts to avoid dealing with a lot of zeroes, so 1.7Kilowatts. For the graphic method that is 3 & half divisions between 1.0 & 2.0 on the x-axis. Go vertically up from there to intersect the pink curve & read the thrust off the y-axis; which is about a quarter of the division between 6.0 & 8.0 or 6.5-lbs. Close enuf since this curve is for a Haoye 4" (or 102mm) instead of say a HiMax 96mm.

Have fun,

Phil

PhilLin

Hi, Nick! In case you did not receive an alert, Bruff posted on his RCGroup X-29 thread that his install is having less entry loss most probably due to having a round lip ring in front of the fan. Don't know if you agree that without an rounded lip ring, airflow into fan will form an eddy which restricts total or mass flow, resulting in less static thrust & lower watts than your rpm wud otherwise consume. Don't know if you wud want to try a rounded lip ring?

Maybe I was not totally getting the jest of your question above; thus my response may not be totally satisfactory. What I found from much static testing show that watts-in is more directly reflecting actual work your fan is doing. AS can be observed in my charts above, the watts vs thrust curves for different fans, motor, packs configs all tract close together with small differences.; generally the larger diameter fans showing a bit more than the smaller ones.

Hope this helps. Happy Easter.

Phil

mpope1

I am setting up the throws on mine, this is my 1st model with canards. Any suggestions on the amount of throw on the elevator in comparison to the canard. Also the rate of travel up and down. I usually dial the throw down as compared to up, or backwards for the canard.

frisconick

I'm going with the recommended 15mm on low rates. For the high rate, I'm putting in all I can get (just in case).

I put a few of the included decals on the plane, including the ones for the wings that say: "U.S. Air Force". At least that's what I thought they said. My wife walked into the shop and said: "What's 'Aif Force?". Do yours say "Aif" or "Air"? I can't believe I didn't see that !!!

Pretty breezy again here this weekend. Might not get to fly it.

Nick

mpope1

My stickers are like yours, I didnt notice either. Gonna fix it with a little black paint.

frisconick

No go on flying it this weekend. We had a 90 degree cross wind Saturday, and today was rainy and windy. I did get to do the range check Saturday and some taxi testing; all is well so far.

Anyone else get a first flight in??

Nick

bruff

My Feedback: (18)

Not yet.
Bob

frisconick

Well, I wasn't going to "measure" anything else, but being bored with nothing to build or fix and too windy to fly, I tried the thrust thing again with a more "robust" system. This time the scale read 5 lbs. 6 oz. It was still on its own landing gear, so I'm sure there is still some loss due to force vectors and such. Thrust really doesn't mean too much without knowing what the airflow speed is, so like Vic said on the other thread......if performance sucks, it's not efficient !! Just another datapoint to throw around.

I may have to play hooky one day this week if it's decent weather. Still planning on video'ing the first flight.

Thanks All,
Nick

frisconick

Still bored, so I tried a different way to measure thrust. I hung the model from the fish scale through the loop in the front landing gear strut. The scale read 6 lbs., 15 oz. One ounce above my previous reading for AUW. Under full throttle, the scale read 3 lbs. 1 oz.; a difference of 3 lbs. 14 oz. The plane wasn't hanging perfectly verticle, so that might be affecting the reading, and we had to hold the plane to keep it from spinning around the axis. So the readings have gone from 3 lbs. something, to 5 lbs something, back to just under 4 lbs. Bottom line: go fly it.

Thanks Vic,

Nick

slevin1

My Feedback: (23)

Nick,

Here is a link to BVM Jets. You'll see in the photo that they are using some type of scale on the nose of the jets to measure pounds of thrust. You should call BVM Jets & ask them if they sell that scale. Hope this helps.

Saul

http://www.bvmjets.com/Pages/electric.html

PhilLin

Nick, I sent you PMs via RCGroup in response to your quiz re inlet efficiency. Too long to post here. Just a heads up in case you don't visit that forum too often or notice the PM alert. Just go to the personal mail near top right hand corner then click on the PMs.

Your latest hanging thrust measurement shows a thrust to weight of about 56%. Hope the ram air effect moves that ratio up near 80% or it will fly like an airliner[] If you need a quick & economical way to fab a rounded inlet ring, I posted my method c/w photos in www.rcgroups.com/forums/showthread.php?t=963957. Bruff indicated that using a round lip ring cut down his entry losses to provide significant free increase in static thrust.

Waiting to hear about your maiden. Hope the weather cooperate.

Phil

frisconick

I did get the first flight in today... or maybe I should say the first take-off, of sorts. It was pretty overcast, but only slight breeze right down the runway. I throttled all the way up. The plane picked up speed quickly, but would not begin to rotate on its own once it reached what I thought should be flying speed. So I started adding elevator. The closer I got to the end of the runway, the more I dialed in. I had full up (low rates at recommended throws) at the end of the runway when it literally jumped into a vertical position. I immediately tried to push the nose over, but it already lost most of its energy by exposing the flat bottom of the airframe. I got the nose over, but it was too late. Not enough airspeed left to fly. No prop moving air over the surfaces and not enough forward motion left. It basically just fell back to the ground from about 20 feet. Airframe is a total loss, but all else seems OK.

I think I mentioned earlier in the thread that it sits on its gear in a slight nose-down attitude. The front fixed strut is not long enough to give it a positive incidence. With the slight nose-down attitude I think it had to "break free" from the ground before it could get airborne. I think that if it had a slight positive stance, it would have lifted off nicely and still be here today. I did have someone video it and I'll try to get it posted soon, but it lept off the ground so fast, the photographer missed the main event. Here are a couple of stills of the remains.

I'll probably get another air frame, but will substitue a longer front strut. I think all else would have been OK.

Thanks,
Nick

Phil, saw your post. Will get to the PMs later tonight.

Thanks,
Nick

Arbo

Nick,

That sucks.

If the front gear is too short, then yeah, a longer one needs to be used, or the rear ones cut down.

Not sure about this model, but a good bit of the wing on the real one has a built in negative incidence as well (and it washes IN out to the tips). If they built it with negative
at the root and a good part of the wing, that might have contributed to what happened.

slevin1

My Feedback: (23)

Nick,
That blows!!! Nothing worse than when you crash a new plane on it's maiden. Did it seem as though it had enough power?

Saul

bruff

My Feedback: (18)

Bummer about the take off attempt. Mike and I are to try the X-29 on Monday morning. Any comments on CG?
Bob

mpope1

Sorry to hear about your x-29, Where was your c.g. at. I have been taxi testing mine and I am having the same problem, it seems to need a ton of speed to get the nose to lift. I am worried if I get it in the air I may not have enough elevator to keep it flying, or not have enough to pull the nose up on landing at a decent speed. I have aded some down trim to the canards to help lift the nose on take off, hopefully it will not be to much.

dw_crash

My Feedback: (6)

Frisconick,

Bummer about the test flight. I hate to see anyone loss a bird on its first attempt to fly. I find it REALLY interesting though. A distributor on another forum has made claims of superb performance out of the box. You find it requires some tweaking etc. to get right. Is this Chinese R&D again?

Keep us posted on your mods and upgrades. I have always loved this plane....Guess that's why I bought the Russian rip-off, the Su47. The original always intrigued me. I'll jump in when the time is right.

Thanks again for the fair and honest reporting. It is apprecieated.

DW_Crash

frisconick

Bob and Mike,

This is the first plane I built that did not survive the maiden. I think it would have been fine had it sat at even a slightly positive attitude while on the gear, or just neutral would have been OK. I came so close to buying a longer front landing gear several times, but blew it off. Do yours sit with a nose down attitude? I think it had plenty of speed to get airborne on its own. It just took so much UP to overcome the negative stance that once it crossed over to positive, it just went vertical and lost all energy. I couldn't push the nose over quick enough. I'll try to figure out how to post the (short) video !!

Nick