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Old Nov 08, 2005, 11:01 AM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,685 Posts
What a trip, just pricing this plane from here in CA it is $155, but if ordered from the parent company in Aus. it looks to be $133! The exchange rate with the AUD and not having to pay our 8.25% CA tx makes a big difference. It is strange that they list the express shipping as less than standard. At least $133 is getting into normal ARF range . The prices they have on large brushless motors is . Wonder how good they are?

John and Christo
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Old Nov 09, 2005, 01:57 PM
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Boston, MA
Joined Aug 2004
103 Posts
Freebird:

"Re-maidened" yesterday without incident and got another 25 minutes in the air this morning. I've been gradually moving the CG aft since as I mentioned previously, it seemed nose heavy. I'm now at 90mm and the plane seems to fly better. It still drops the nose on power off but less so and inverted flight needs only a touch of down elevator. Cruises on 1/4-1/3 throttle, 13 minutes to LVC with some throttle management.

I am having some trouble getting it properly trimmed out. It climbs ferociously on high throttle settings, which might suggest some downthrust is needed. But I also need a noticeable amount of down elevator trim to maintain level flight even at modest cruising speed. These properties actually did not change much when I moved the CG from 75 to 90mm. I wonder if my wing/stab incidence might be off but have no easy way to measure, nor do I know what they should actually be!

By the way, I also experienced the tip stall or snap that you reported on doing a series of very tight turns. Oddly enough, the plane became more resistant to that when I moved the CG back. Snaps need rudder, aileron and elevator input.

I'm enjoying flying this plane - it just looks so great on those low passes! Just can't figure out how to trim it. Any thoughts would be appreciated

DP
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Old Nov 09, 2005, 03:20 PM
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DougC's Avatar
New Hampshire, USA
Joined Sep 2004
489 Posts
Might want to read through this.

http://www.nsrca.org/trimA.htm

A Google on Trimming a plane, or Trimming a model will bring others, but seem to me to be similar.
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Old Nov 09, 2005, 04:34 PM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
Joined Jul 2004
3,199 Posts
Yeah this model was a gret deal two months agao, but no way am I paying Grand Hobby or Raidentechs current rates.
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Old Nov 09, 2005, 04:54 PM
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Boston, MA
Joined Aug 2004
103 Posts
Thanks DougC, I've read that chart and other similar ones. I'm a relative noob, flying for about a year, electrics only and completely self-taught. I can fly and enjoy the plane, but probably the best thing to do is contact a club and get some hands-on advice about subtle (or not so subtle) issues relating to trim.

DP
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Old Nov 09, 2005, 08:45 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,685 Posts
Congrats dpaul!

That you are self taught and can fly a plane like this is really something . You are doing the right thing to get some help and experience from a club. One quick and dirty way to check incidence is to lay the wing on a flat surfase and measure the difference in gap to that surface from the leading and trailing edges. Then, do the same with the wing mounted to the plane. Compare that diff. side to side. Our ARF SuperSportster EP had the RH side higher than the left causing a pronounced dip to the right at level flight. This was almost completely eliminated by putting a bit of counter twist in the wing and taking a covering iron to it with the covering showing a wrinkle. Also, measure the distance from wing tips to stabalizer tips and to the forward centerline of the fuse say with a pin at the forward edge of the battery box. They should be equal. Since you are getting a climb, it may be the wing mount is allowing too much up angle. One way to test that is to space the forward mounting portion of the wing to the contact area of the fuse with say some tape. Use a thin section to start and add to it each test to see if you get a more level flight. That is what I did with our Sportster before I did the wing twist.

John and Christo
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Old Nov 09, 2005, 10:00 PM
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Boston, MA
Joined Aug 2004
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John and Christo;
Thanks for the good suggestions. I'm guessing too high an angle of incidence on the wing (or too low on the stabilizer) is the problem. I've decided to bite the bullet and buy one of those incidence meters. Just another $20 + the usual obscene postage! On this plane it is easy to increase but difficult to decrease the wing incidence so I want find out exactly what the setting is before I start hacking away at the wing mounting. Possibly I can dial it out in a crude way with more downthrust, which I'll try tomorrow, weather permitting (doesn't look good right now).

One thing though, all my issues seem to be related to pitch. Level flight is attained with rudder trim at neutral and aileron just a couple of clicks away. It is the elevator trim that seems to be excessive, compared to the other models I've been flying. And, of course, this strong tendency to climb on throttle.

DP
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Old Nov 09, 2005, 10:34 PM
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Bradbury, Australia
Joined Mar 2002
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DP,..I seem to have opposite probs , iv had to keep moving battery forward to maintain level flight.The 8 cell 3700mah pack is now poking out through the firewall-motor mount cavity i installed.Spit not flying to badly now,i havent really given this model a thorough testing just enjoying a few scale like manouvers and maybe some low fast passes.
Landings are still an ordeal when weather is dead calm.I prefer it to be a little windy and Spit does too. Have you used the spoilerons you added and if so howd it go.
Do you think it could be a side thrust ,down thrust issue with regards to perfect trimming. The supplied motor mount appeared to have it built in ,but i didnt measure, just cast eye over.
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Old Nov 10, 2005, 05:59 AM
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Boston, MA
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Hi Freebird;

I'm surprised to hear that you've moved the CG even more forward than the Ripmax spec. When you say that you needed to move it forward to maintain level flight do you mean that the plane would climb or dive in the original position with neutral controls? Does it nose-up on power off or power on? Have you tried any of the tests on those charts DougC mentioned? Just curious.

Well, I'm confused too! Not to overstate the problem because the plane is really fun to fly, just hard to do precision aerobatics, which it was not really designed for after all. My motor mount had no obvious (by eye, not measurement) downthrust or sidethrust and I think that may contribute to the problem. I'll add some downthrust to see what happens but unfortunately its raining now and that tends to go on for days at a time around here.

I haven't tried the spoilerons yet because I've been focused on these other problems but in fact, I'm not finding it difficult to land in a relatively small area. To be sure, some wind shortens the approach but even in dead calm, the glide is not nearly as flat as my Alfa MiG. One possibility is that this reflects the difference in our AUW; likely my landing speed can be slower than yours. That's my guess. I've used spoilerons in my TM400 and Corsair, in fact have dual aileron servos in the MiG as well. In the TM there is a clear advantage; with proper elevator trim, the angle of glide steepens noticeably without much gain in airspeed. So you can drop in over a tree line for landing with a very short approach. In fact, it helps set up a three point landing because a slightly nose up attitude is required to keep from gaining airspeed. The stall speed increases but not much and there is no loss of aileron response and no tendency to tip stall (not much in a TM anyway). In the Corsair, I see the same effects but they are much smaller so there is only a little benefit. In the MiG, you lose some aileron response without an obvious change in glide ratio. Not worth the effort. I've no idea how the Spit will respond. I'll play with it as soon as I can and let you know

DP
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Old Nov 10, 2005, 09:49 AM
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drksyd's Avatar
USA, HI, Honolulu
Joined Jan 2003
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With plane trimmed put it into roughly a 45 degree dive and cut power. If it pulls up it's tail heavy, if it dives more it's nose heavy. I would say trim the plane at about half throttle or where you normally would fly at.
It's normal for a plane to climb at higher throttle levels, especially with more powerfull motors. The way to counter this is to add right and down thrust as necessary. The more powerfull the motor, the more you add.
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Old Nov 10, 2005, 11:07 AM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,685 Posts
Well I bit the bullet (20mm ?) and found one from the store on E Bay. I placed my first ever bid one dollar over with about 30 min. left thinking, "I'll never get it". I got it . I did not want to pay more than my 'Sportster ARF at $120 so I figured that below $80 plus tax and shipping would be okay. Total came out to be $114 . Now, start to think about fitting retracts. This and the orig. Ripmax look to be the only 600 size war bird ARF's out there.

John and Christo
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Old Nov 10, 2005, 11:39 AM
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Boston, MA
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Trimming the Spit

Quote:
Originally Posted by drksyd
With plane trimmed put it into roughly a 45 degree dive and cut power. If it pulls up it's tail heavy, if it dives more it's nose heavy. I would say trim the plane at about half throttle or where you normally would fly at.
It's normal for a plane to climb at higher throttle levels, especially with more powerfull motors. The way to counter this is to add right and down thrust as necessary. The more powerfull the motor, the more you add.

Drksyd;

I'm sure you have more experience than I in these matters but I'll need help understanding the rationale for the test you describe. I've been trying to read about this and it appears that there are three variables affecting response to inputs on the pitch axis; CG, incidence (or decalage or rigging angle) and the angle of thrust. Since they all interact, the best way to assess the effect of a change in one would be to minimize the changes in the others. If you cut throttle in a dive, you have no way of knowing whether a pitch up is the result of a forward CG or excessive downthrust

All the tests I've performed suggest the CG is too far forward. 1) trim for level flight at slow speed, induce shallow dive and neutralize the stick - it pitches up=nose heavy 2) trim for level flight at cruising speed and roll into near vertical (no elevator input, only aileron) - it drops the nose=nose heavy. 3) inverted flight - needs down stick to maintain level flight (not that much but it is not neutral) = nose heavy. So I've been moving the CG back in steps and I'm not done yet.

This morning, I decided to make some measurements. I figured that if I used a level to set the stabilizer exactly horizontal, then I could measure the distance from wing TE and LE to the table and use good old trigonometry to obtain the angle of incidence (relative to the stab, not the centerline of the fuse but that's the best I could do). The same should work for the thrust angle. I found the wing incidence was a little more that +2 degrees. I'm guessing that is too much for a pattern plane or precision aerobat but who knows what the Spit will be happiest with. Worse, there is 2-3 degrees upthrust at the motor! That should explain the climb on throttle, which by the way is not just excessive. After a few seconds on full throttle, the plane is vertical and rapidly disappearing from sight!

The thing that's confusing me is that if I trim for level flight at cruising speed, and cut the throttle, which is the test on the charts for thrust angle, it pitches up, an indication of too much downthrust. That cannot be, according to my measurements. So I'm guessing that the incidence and thrust angle are so far from where they should be that the simple tests are not giving mutually consistent results.

I'm going to bite the bullet and reduce the wing incidence to 1 degree and return the motor to 0 degrees (all relative to the stab of course) and see what happens.

This is proving to be a frustrating but hopefully educational experience.

DP
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Old Nov 10, 2005, 08:19 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,685 Posts
Fiberglass fuse?

Hey all,

Wondering if you guys noticed the description of the product says the fuselage is fiberglass . So, I asked the seller about this and their reply via e-mail was "the fuselage is made by fiber glass, the wing is balsa wood". The pics from the store and the parent company show an unskinned wood plane as is Freebird's. Certainly the Ripmax is built up so hope I don't get dorked here . I did notice they have a P-51 of similar size pictured on the parent company site that does have a fiberglass fuse, so maybe the guy I e mailed really does not know.

It also looks like this model has proper fillet from the fuse which is a nice detail.

John and Christo
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Old Nov 10, 2005, 10:08 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
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For those still interested in getting this plane there are a few more at auction on ebay through Grand Hobby. Just FYI.

John and Christo
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Old Nov 10, 2005, 10:18 PM
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Boston, MA
Joined Aug 2004
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John and Christo;

No worries! The plane is built up balsa/ply with a fiberglass cowl. It is fully covered (although I could not tell you what material this covering is).

There is a fillet between the fuse and wing, nicely made.

DP
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