PART III- More 1/2A Test Flights- Report

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sgilkey
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PART III- More 1/2A Test Flights- Report

Post by sgilkey »

My previous thread "Hat Trick 1/2A Arrow build" showed that a plane could be economically built for Limited 1/2A from readily available kits/materials/radio gear using standard construction techniques, yielding a RTF plane that is well below the proposed 18 ounce weight minimum. The next thread, "Hat Trick 1/2A Arrow Test Flights" showed that a box-stock Norvel on relatively mild fuel could readily turn the proposed props well in excess of the proposed 20k rpm. Thus the first objective of this series, namely to demonstrate that a competitive plane could be put together by virtually anybody, was met.

However, during the first series of test flights, the 16.2 ounce all-up weight combined with the 21.5k rpm on the APC 5.7x3 prop demonstrated remarkable performance, well above what I believe would be the objective of a "limited" 1/2A class. Therefore another series of tests was undertaken to see what a plane operating at the performance-reducing levels proposed in the rules, namely 20k rpm and 18 ounce minimum weight, would perform like. Further, the testing was done to try to see which has the greater impact, rpm reduction or weight increase.

First, a new baseline flight was made, since we had a new day with slightly different atmospheric conditions (temps about same at high 30s, but humidity lower with skies clearer). Since I threw a rod yesterday, I also added another 1% castor oil to my 25% nitro fuel. Otherwise nothing was changed. The Norvel u/c engine with one head shim and stock head turned the APC 5.7x3 prop at 21.4k rpm. The first test flight went well and reconfirmed yesterday's stellar performance. To try to document the claims of incredibly tight turning radius, a streamer was tied to the plane. We also wanted to see how much performance would degrade with a streamer. The streamer was not measured before testing, but after test flights it was paced off at 35 feet length, with about an 8 foot string. This overall length of 43 feet would make a circle of 13.7 feet diameter, or about 6.8 foot radius.

First flight with the streamer, it was quickly apparent that performance was not noticably degraded. Brian flew while I tried to take a photo of the circle made by the streamer.
Image
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My camera is not real good at action photos but these pictures get the idea across. Brian had to try to fly in a corkscrew in order to not cut his own streamer. Several times he still hooked the streamer on the wing (but it could be shaken off with violent maneuvers- no sticky stuff!). It was obvious that cutting one's own streamer was no problem- this is a turning circle of less than 7 foot radius! What you can see in the first photo is how the streamer could have been cut at not much more than midway along its length. THe second photo shows how the continuous turning made the streamer trace multiple concentric circles- the plane could loop and turn this tightly without stopping. Vertical performance was virtually unlimited straight-up climb from level flight (at least until the plane was a small speck and way outside of normal combat radius).
sgilkey
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Post by sgilkey »

Now that we knew the plane could still turn tight even with the streamer, we first added lead weights (pre-weighed at home on a gram scale to get the right amount) to the plane to bring it up to the proposed minimum of 18 ounces. Engine performance was not changed. Here is how the weights were attached.
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Here are the resulting turns, the first one shows we would still able to cut our own streamer as evidenced by the streamer hooked on the wing tip...
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the second photo is not one of my better efforts (dang camera has an enormous delay between pressing the button and taking the photo) but shows that despite the significant weight increase the turning radius is still tight and the streamer could be cut at well less than it's total length.
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Vertical performance was noticeably affected, we estimate the plane would climb vertically about 100 feet from level flight before it stopped.

CONCLUSIONS: 18 ounces by no means turns these planes into poor-flying pigs. The plane was still capable of continuous turns though the radius had gotten larger, yet still it was below 7 feet (what appears to be lack of roundness in the loop in some of the photos such as the second one above is because Brian was trying to fly corkscrews while I took the photos at an oblique angle, so the loop looks distorted).
sgilkey
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Post by sgilkey »

Next we removed the ballast, going back to the 16.2 ounce weight, but detuned the engine to the proposed max of 20k. This was done by adding two head shims (total now three) which got us to 20.8k, and changing to 15% nitro fuel, which got us to 20.2k which was close enough for our purposes. Here's the resulting turn:
Image

At this point we had realized a horizontal turn photographed better/easier than vertical loops. This is actuall a CLIMBING spiral, not descending, so gravity is working against us. It is clear from the photo that the turning radius is once again very tight, tighter than the ballasted flights and getting back to close to the baseline flights. Continous turns were still no problem. Vertical performance was estimated at 100' straight-up climb from level flight. Overall the plane felt cripser and more responsive in this test than with the addition of weight in the previous test, and had a tighter turning radius. CONCLUSION: Reducing power by 1200 rpm has a moderate impact on performance, mostly in vertical climb. Performance is still very impressive at the proposed 20k power level, and tuning the engine with shims and nitro is an easy way to adjust power.
sgilkey
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Post by sgilkey »

Next test flights were with power detuned to 20.2k rpm AND ballast added to bring weight up to 18 ounces. Here are resulting turns, again the plane was able to cut itself as evidenced by streamer on the wing:
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N0tice turn radius in climbing spiral:
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Vertical performane was estimated at 50 to 75 feet vertical climb from level flight before the plane stopped. Turning was still tight and continous turns could be made without stopping. Performance, while certainly below what was seen in the baseline, was still excellent. Had this been our FIRST flight with the 1/2A Arrow, we would have been thrilled!

CONCLUSIONS: the proposed 20k rpm max and 18 ounce weight min on a plane within the proposed max wing area will result in a plane with stellar performance. This is by no means a boring plane to fly, nor is it a wallowing pig. It flies out of my hand with a gentle underhand toss, just like i launch a B ship. The plane is stable, forgiving to fly, and an absolute BLAST.
drewjet
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Post by drewjet »

Scott, very nice report. I believe it pretty well confirms what I said in my "1/2A, is this what we really want?" thread.

I think your tests show that we need less wing area. A higher wing loading would decrease the looping ability. I think we also need the lower engine performance to keep the speeds down. I really believe an RPM around 17,000 would be more than sufficient to produce a good flying plane.
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Post by sgilkey »

Final test in the series was with a Cox engine. Reasons for running this test: 1) availability problems with Norvels may limit engine choices for this class, and due to the abundance of Cox engines in the world, there are many potential combat fliers who may want to try this class with an engine they have on hand, and 2) to see if the noise of an unmuffled Cox, along with the lower power, was a problem.

Due to the lower anticipated power/performance, we removed the ballast weights. We would have run another test with the weights added but we ran out of time....

Engine used was a stock Tee Dee .051 (.051 and .049, by all accounts, are equivalent, I've never really understood why Cox offered both...), stock venturi/suction tank, Galbreath head/Nelson plug with one shim, same prop as Norvel tests and 25% nitro fuel with 21% oil. RPM were 19.0k. The Cox really barked on the starting stand, but in the air, the noise is not nearly as objectionble and is really not a lot louder than the Norvel (louder, yes, but not a lot and not as bad as expected). Here's the resulting turns:
Image

As can be seen in the photo, the plane could still turn within the streamer radius. In fact, it got too close and cut itself, cutting off the last 6 feet of the streamer:
Image
As with the other tests, continous tight turns were possible and performance was still excellent. Vertical was about 75 foot straight-up climb from level flight (Norvel at 20.2k rpm and same weight was capable of est. 100'). Speed was still good, plane still a blast to fly.

To try the concept of "handicapping" the Cox, we took a test with the Grish 5x3, no other changes. Engine tached 22k (Norvel turned that prop 24+k yesterday). PLane flew nice but at the higher rpm the Cox needle kept creeping and richening the mix, we were out of time so I could not get a fix made and another flight. I note this test only for the rpm data point.

CONCLUSION: Even at 19k on the APC 5.7x3, outstanding turning performance and climb are attainable. Unmuffled Coxes are not as loud as expected in the air and may be an alternative if engine availability is a problem, as well as to encourage folks who have them to give this class a try.
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Post by sgilkey »

FINAL CONCLUSIONS: We must keep in mind that the proposal is for a LIMITED 1/2A event. An OPEN 1/2A class is already on the books and folks interested in such a class are encouraged to fly it. Naturally, a lighter plane with more power performs noticeably better. A plane built to the proposed restrictions is still an amazing performer with turning ability equal to or in excess of many (all?) top-performing Open B, SSC, or 2610 planes. If our first flights had been at 20k and 18 ounces we would still be thrilled with this performance level. Flying planes with greater performance naturally leads to higher expectations and a sense of "loss" as performance is decreased, thus we believe in the need to cap performance now before higher levels of performance become "expected." Please make any comments relative to the rules proposals in the thread already started in the Members Section for provisional class rules proposals.

Based on this testing I believe the proposed limits actually still provide too much performance potential for a LIMITED class. HOwever more data is welcomed as we try to find the ideal compromise in the proposals.
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boiler
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Post by boiler »

Thanks for the test report Scott. I believe you are right about finding the right limits for limited events from the start. Perhaps 25% less wing area would help. Did you try the apc 6x2 prop in flight yet? I bought a used Norval today and I have a cox .049 as well. Gotta get some planes built and some are going to be SCALE.[:p]
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Post by sgilkey »

See the first test report thread for results with the 6x2 APC. I did not get a chance to try that prop at 18 ounces, at heavier weights that prop may perform better, who knows?

At this time I do not think less wing area is the answer, I think less power and/or prop (i.e. lower rpm and 6x2 rather than 5.7x3) and more weight is better than lowering area. Reason being that lower weight drives less armor, and small/fragile micro servos. With more wing area and weight we can build with some armor and use mini servos such as the HS81MG which are very robust compared to the micros. That's just my thinking at this point, i'd like to hear others' opinions. I mostly want to avoid driving the use of the unproven and seemingly fragile micro servos.

One other observation, my first test flights, I forgot my 1/2A starter. I managed to remember it for later ones. WHile you can use a "normal" starter for 1/2A, if you're at all serious about trying 1/2A then the smaller starter is worth the investment, it works much easier.
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Post by Thaman »

we should think about increasing the flying mass also increases the damage to the planes. would you rather be hit with a 1 lb hammer or a 20 lb hammer if they were going to be travleing at the same speed. Hmmm
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Post by sgilkey »

The key is they won't be. Kinetic energy goes up with the square of velocity but only directly in proportion to mass. Would you rather walk into a wall wearing a backpack, or jog into it with no backpack? As weight (and therefore wing loading) go up, turning radius opens and turning speed (especially in sustained turns) goes down. Most impacts happen in the turns. If turning speed is down, impact energy goes down. NO DOUBT weight is a factor in impacts, and an important one. We need also to try to manage speed as well. It is a tradeoff. Also I'd rather carry around two more ounces if it means I can use tough mini servos that can take the hit, rather than more fragile micros that are more prone to strip.

Bob, I may have misunderstood your suggestion, I still think the 18 ounce weight is in the ballpark, but perhaps less wing area, in conjunction with that weight, is called for. I at first thought maybe you were suggesting, say , 15 ounces but less area.
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Post by Cajun »

Great report Scott. Thanks for the time and effort. That's the only way good reliable data can be obtained.

I totally agree with your conclusions on RPMs, speed and weight. It would be interesting to see what the 6x2 prop would do in direct camparison with the 5.7x3 (same day-same plane). Theoretically (I hate that word) it should slightly improve the thrust and vertical while reducing speeed, but we all know actual and theoretical don't always go hand in hand.

It would also be interesting to see what reducing the span slightly and possibly inceasing the chord would do. The wing loading would not suffer but the speed and turning ability should degrade some. In your opinion is the speeds of the setups you ran excessive for what we're looking for in this class?

I have a AP and a Norvel, both new, and I'll be trying to duplicate your results next weekend when I have a plane completed. I also have an old TD, but my experience with these is one can't get two good runs in a row.

<font color="red">Again THANKS for this fine report</font id="red">.[8D]
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boiler
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Post by boiler »

Yes Scott, I was thinking of keeping the weight min at 18 ounces but have less wing area. Perhaps a glass rod or two could be added to the shorter wing.
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Ed Kettler
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Post by Ed Kettler »

Scott and Brian,

Outstanding work! This is very valuable information!
sgilkey
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Post by sgilkey »

I think the speeds are good, seem about same as SSC, i don't think the speed is a problem so much as the climbing and especially the sustained tight turning which no doubt makes it fun to fly but i suspect will make for major furballs and therefore midairs.

i did test the 6x2, see results in the first "test flight" thread. The 6x2 gives over 1000 rpm more on otherwise identical setup, which may be good since the Norvel seems to like to rev. it gives slower straight-line speed and better climb but, surprisingly, worse turning- it will still turn continousously but the turn radius goes up a bit. This seems contrary to the better climb performance I admit. Also I suspect the better climb performance may also equate to better launch performance to address the downwind launch concerns.

Overall at this point I consider the 6x2 to be a marginally inferior performer to the 5.7x3, though with certain key offsetting advantages.. Which might just make it the ideal spec prop for this class.

Our Tee Dee ran fine with the 5.7x3 at 19k but with the 5x3 at 22k, the rpm hit some kind of sweet spot in the air that caused the needle to keep backing out from vibration. i could have sworn i balanced that prop...guess that's why Kustom Kraftsmanship did a brisk business in aftermarket TD NVAs. don't know if they are still available....ours is a stocker.
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