PART IV- More 1/2A Arrow Test Flights

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sgilkey
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PART IV- More 1/2A Arrow Test Flights

Post by sgilkey »

Weather cleared a bit today which gave me a great opportunity to try some more test flights. it was also rather breezy which was helpful for testing one aspect of performance. objectives of today's tests: 1) test recommended 18 ounce min wt with smaller wing, 2)try downwind launch with significant tailwind at 18 ounce weight 3) try a different prop, 4) try the all-flying stab

All tests were done on the same Hat Trick 1/2A Arrow built as per Part I of this series. THis round of testing was done with a new Revlite Big Mig .061 R/C since i did not want to deal with the u/c shutoff issue right now. This engine was taching 20.4k on 25% nitro/21% oil fuel on the APC 5.7x3 prop. I richened it up a bit for the test flights since it is new. Temps were high 30s, sky clear, wind about 10 mph.

In the PART III tests, we found that, with an engine turning the proposed rpm max of 20k (and even with one turning only 19k), even at the proposed LIMITED 1/2A rules min weight of 18 ounces, the stock Arrow could easily turn contiuous tight turns and could cut its own streamer. This level of performance seems a bit high for the objectives of a LIMITED class. FOlks have expressed reluctance to up the min weight further due to impact damage concerns, therefore as an alternative to further increasing the min weight, we decided to try testing a smaller wing.

For this series of tests, the stock Arrow wing was replaced with the flat-bottom airfoil wing (also detailed in Part I) cut for me by Mark Schofield. This wing is 40 inch span, about 300 sq inches, for an area reduction of about 40 sq in or about 12%. This wing is lighter than the stock Arrow wing, so additional ballast had to be added to bring the weight up to 18 ounces.

First flight was with no ballast, just to re-establish baseline and make sure the new engine was running well. The plane would turn very tight (Brian did not come along today, for some reason not seeing standing around doing test flights in windy 37 degree weather of interest- so sorry, no photos) and could have easily cut its own streamer. Vertical virtually unlimited. Landed and added ballast to bring weight up to 18 ounces (about 2.3 ounces of lead added to wing). takeoff was still easy, but it was immediately obvious that the turning performance had degraded. the 300 sq in wing does not carry 18 ounces as readily as the stock Arrow wing. Turning radius probably doubled over the unballasted condition, and was marginally but noticeably larger than the stock Arrow wing at 18 ounces. However, continuous turns and loops were still possible without stopping. I did not have a streamer on the plane but i would guess it still could have cut itself. Although the plane was mushier than the stock wing, it still flew very smoothly and was still a blast to fly. Vertical was still good, probably a good 75 feet+ straight up from level flight. Basically, if this had been the first flight i had ever put on this plane, i would have still been very pleased, it was still a nice flying and easy-handling plane. landings were a breeze with plenty of glide to a nice gentle plop. Overall performance of the plane in this config was about equal to a good SSC plane, with a little bit better turning. CONCLUSION: 300 sq in is probably a good target for max area for this class, even at 18 ounces the plane flies very well at this weight.

2) Concerns have been expressed about downwind launches at the higher weight. Today we had a chance to try launching straight downwind with a solid 10mph+ tailwind. Despite the 18 ounce weight and 300 sq in wing, plane flew out of a conventional underhand toss with no problem on two attempts. Did not see any concern with these launches that was any greater than with a similar SSC launch.

3) Master Airscrew 5.5x4 prop test to see if this might be a good spec prop for this class. Engine turned this prop at 19.0k. at 18 ounces, performance with this prop was slightly but noticeably poorer than the APC 5.7x3. Turning was degraded (though still very good), vertical was about same as the APC or slightly worse. We then removed the ballast and this prop performed much better, probably at least as good overall as the APC. In the cold weather, the MA prop maintains its flexibility, while the APC seems to get brittle (i broke two on pretty smooth landings). I also like the correctly-sized center hole on the MA prop rather than the silly bigger one on the APCs which require some type of spacer. CONCLUSION: has potential as a durable prop which further limits performance at 18 ounces, on lighter planes that can take advantage of its small diameter and greater pitch it might actually improve performance.

4)All-flying stab. In Part I I showed an all-flying stab conversion based on the shape and proportions of the AVENGER unit. I wanted to see how this stab performed. I started off at a conservative 25% bal pt. First launch was a piece of cake, plane flew fine. Needed to significantly increase elev servo throw to get turn radius as tight as possible. The A.F. stab is much smaller than the stock unit, i scaled it down using the TLAR method but may have gone a bit too far. WHile the conv stab needed 53% servo throw, the AFS needed 98%. THis would probably improve if i moved the bal pt back. A second test flight was made at about 27% and the plane was still plenty stable, so bal pt could be moved back further. Overall, the AFS turned at least as tight as the stock unit, with more tweaking of area (next one i make i will increase area about 20%) and moving bal pt back i suspect it would improve turning a bit. BUt the stock stab works so well it's really not needed, just a novelty (plus it is so easy to install and set up). low speed and low altitude handling was very stable and secure with the AFS, just like with the stocker CONCLUSION the AFS weighs less and is easy to set up, flies at least as good as stock and maybe slightly better. No clear advantage either way.
AIM
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Post by AIM »

Did you build any of Hattricks wings without the balsa trailing edge? I'm just wondering if it's needed.
sgilkey
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Post by sgilkey »

i built the first Arrow wing with the balsa TE, but i think it is not necessary. for future wings i will just use a strip of strapping tape on the TE. On the 'Roid wing i did not use a balsa TE, just tape.
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boiler
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Post by boiler »

Thanks for the test report. You are doing a great job.[:)] Since the smaller wing had the desired effect on furball potential, do you have plans to go to a 36 inch wing for testing?
sgilkey
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Post by sgilkey »

no, i think the 18 ounce weight and 300 sq inch combo at 20k rpm on 5.7x3 looks like it is a good balance. it still might be too hot, it's certainly not too cold in my opinion, but at this point i think we just need to see how it all shakes out with further flight testing from other folks. If somebody else wants to build and fly different wing planforms and area, weights, props/rpm, i'm all ears. Based on 30+ flights in various combos i think the proposed Limited rules (amended) strike a good balance, but that's just my opinion, want to see others post more flight data and impressions.
Captain America
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Post by Captain America »

I hope to finish mine this weekend. It will be elctric though so it may be hard to compare.
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boiler
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Post by boiler »

I'm trying to get color/fuel proof combinations for USAF camo colors. My 2548's are all re-worked and need paint before test flights. I have a light and dark combo but I need to let them cure for at least a week before fuel proof testing and then flying. I got two new AP engines today and with the used Norval I got last week - it's time to start building three 1/2 A planes. One will be a scale zero about 32 inch span and the other two will be a 36 and 40 inch open similar to the Arrow. Target weight on all will be 18 ounces. I hope I can do at least half as well as Scott in giving reports.
cipoll717
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Post by cipoll717 »

Scott- great work! Sounds like your converging towards an ideal spot. Can't wait to compete in some 1/2a meets this year. I am trying to work out the details on scheduling one or more meets here in Cincy/Northern Kentucky. Need to find out what is happening with the Havoc's this year first.

Bob- Fantastic, really glad to hear your buildign a scale bird. One note for scale- you really need to be more sensitive on your finished weight. For all the scale birds we've built and flown, you really need to be at max weight of about 16 oz. This includes many different WW2 planes- P-39, zero, P51, Hellcat, etc. We build mostly to about 32-36" wingspan. As stated earlier, we flew almost exclusively scale 1/2a planes all year, and just recently got into open designs. The scale planes were just awesome. They did, not surprisingly, fly more or less like scale planes though! Much less furball-ability with these things, and very high 'cool' factor. It seems we got a lot more interest from the general flying public when we flew these, versus our open designs. We even had a bunch of die hard helicopter pilots ask us to build them some scale combat planes! So, again, I encourage all scale flyers to consider 1/2a scale planes as a possible new class.

MC 'the Hammer'
Captain America
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Post by Captain America »

The plastic strapping works great on the TE. I cut the TE at a little bit of an angle for aleron clearance and it fit without trimming.
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