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Old Nov 10, 2005, 10:42 PM
Warbird crazy!
new2rc's Avatar
United States, CA, San Mateo
Joined Sep 2004
3,685 Posts
Quote:
Originally Posted by dpaul
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
Thanks DP
That is very reassuring. I am paranoid in general especially as I have only purchased two buy it now items on ebay. I guess Grand Hobby Calif. does not know fully what they are selling . It looks like if I waited a bit, I could have done better on the price based on how many they now have at auction . Oh, well...time to start planning a retract mod.

Thanks again DP and best of luck with your Spitfire trimming .

John and Christo
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Old Nov 11, 2005, 03:09 AM
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Bradbury, Australia
Joined Mar 2002
159 Posts
DP.. I checked out the motor mount and there is only 1mm side thrust and no down thrust
Its something that i have totally overlooked in my haste to get Spit airborne. .Will definately add downthrust before next flight and see how it performs.Could be why i have had to move battery forward to compensate for no downthrust
My AUW is now at 1472 grams with 8cell 3700 nimh pack and theres more scale work to be done
Good to see youll have this Spit soon John and Christo.Good luck with the retracts, you must be an exceptionally good pilot to be able to land Spitfire with undercarriage
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Old Nov 11, 2005, 04:05 AM
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USA, HI, Honolulu
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dpaul
Sorry don't have time to explain now, need to get up early and catch a flight. Will be back Sun evening.
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Old Nov 12, 2005, 09:59 PM
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Boston, MA
Joined Aug 2004
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Drksyd;

Thanks - I'll be here!
DP

Freebird:

I'd really like to know more about why you moved the CG even more forward. How exactly was the plane behaving with the CG in the original position?

I restored the downthrust to 0 degrees (from 1-2 degrees upthrust) and the climb on throttle is much more reasonable! I'll try a little more downthrust tomorrow. My CG is at 90mm and frankly I think it can go further aft. I wonder if the 98mm specified in the instructions might not actually be correct? Anyways it is far from tail heavy; it still recovers to level flight when elevator is neutralized in a shallow dive with constant throttle, indicating a fair amount of pitch stability. I have no trouble landing at fairly low speeds. I know that's a pretty subjective evaluation but certainly no faster than an overweight (575gm) GWS Corsair. By the way, I've used one of those Great Planes CG machines to measure the CG so I think it is a fairly accurate measurement.

I also reduced the decalage angle by notching the wing dowel and adding some 3mm depron to the top front of the wing but that did not produce much change in the down elevator trim required for level flight. I have subsequently read in various posts that the importance of decalage setting is greatly overstated. OK fine. It appears that there is an amazing amount of disagreement over how airplanes actually fly and which parameters are critical. Up to this point I just threw them up into the air and kept the faith.

I've also added the main gear that came with the model. Kind of small wheels but I've just got to try it! Getting some nasty grass stains on the belly.

AUW up to 1125gm, thanks to various "fixes".

DP
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Old Nov 13, 2005, 12:48 AM
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Bradbury, Australia
Joined Mar 2002
159 Posts
Your not gonna beleive this DP but my Spits CG is now measured at 60 - 65mm. I put 2mm downthrust in and now have good pitch control at higher speeds.
Got a few good flghts in this morning, and i did a couple of those tests .
The one with the shallow dive and then neutralise ,well the Spit slowly started to climb back to level.
Inverted flight involved just holding in a bit of down stick for level flying.
Still having minor difficulties with landing.Bumbed the cowl savagely again,more repairs. Im just going to glass the whole underside of cowl to stenghthen.
The fierce Australian sun is making the covering wrinkle up severely on the fuselage whilst at the field, kinda like huge varicose veins.YUK.Its like very- very thin vinyl.
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Old Nov 13, 2005, 07:48 AM
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Boston, MA
Joined Aug 2004
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Freebird - I'm completely mystified! You like it with the CG at 60mm and I like it at 90mm? Oh well, it flies either way. Maybe it's just personal preference. I don't think the stock landing gear will be easy to use with the CG at 60 tho...

DP
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Old Nov 13, 2005, 10:22 PM
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USA, HI, Honolulu
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Ok, I'm back.
Addressing the cg, I think (from what I've read) it should be around 75mm. When you put the plane into the dive and cut power it should stay on track in the dive. Thrust line is not an issue at this time since no thrust is being generated, if it noses in it's nose heavy and if it pulls out it's tail heavy.
The only way to fix the thrust line is to keep adjusting it until it gets within a tolerable setting. The more power to weight ratio will require more down and right thrust. I have this problem with my GP Corsair so will adjust my thrust line again.
DP, since you've changed your incedence you're pretty much on your own with the setup as your plane is unlike the others now. If your plane flies as is it's all good, if it tends to balloon while trying to land then the cg is too far aft. I usually like to have the cg up a little and move it back if necessary.
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Old Nov 14, 2005, 07:54 PM
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Boston, MA
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[QUOTE=drksyd]Ok, I'm back.
Addressing the cg, I think (from what I've read) it should be around 75mm. When you put the plane into the dive and cut power it should stay on track in the dive. Thrust line is not an issue at this time since no thrust is being generated, if it noses in it's nose heavy and if it pulls out it's tail heavy.

Dyksyd;
I'm still not really getting it. Thrust line is an issue because when you induced the dive, you had the throttle on and were generating downthrust. When you cut throttle, you remove that downthrust and the model must compensate for that loss by changing pitch. Regardless of whether you are in a dive or level flight, too much downthrust and you pitch up when you cut the throttle; too little, and you nose down.

From what I've read, the point of putting the plane in the dive is to assess pitch stability i.e. the tendency of the plane to return to level flight from any disturbance in the pitch axis. If you trim for level flight, leave the throttle setting as it is, put the plane in a dive and release the stick (neutralize elevator), if the CG is ahead of the neutral point (center of lift) then the plane will gradually nose up until it regains level flight. This I can observe in most of my models, including the Spitfire, even with the CG at 90mm.

So again I don't understand how you can separate the effects of downthrust and CG in the test you describe. Both will influence pitch responses.

Finally, incidence, as I've recently read and also now observed, doesn't have a major role in pitch stability. It appears that changing the elevator trim (or adding reflex to the aileron) has the same effect as changing wing incidence (or more properly stated, decalage; the difference in angle between the wing chord and horizontal stabilizer). The major problem with "incorrect" decalage in this situation would be the need to carry elevator trim which is to some extent speed-dependent and also induces drag at non-optimal airspeed. I'm not very worried about drag with unlimited vertical! The only result I noticed from changing the incidence was that I needed a little less elevator down trim for level flight. It did not change the pitch stability of the model.

DP
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Old Nov 15, 2005, 02:57 AM
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Bradbury, Australia
Joined Mar 2002
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DP...I have no intention of fitting fixed landing gear as i think it looks ghastly in the air hanging from that beautiful shaped wing .(thats my excuse).
Actually im just not good enough to consistently land with landing gear at moment.Ill put up with a bit of dirt stain on underbelly Vs constant repairs

It will be very interesting to read a 3rd persons opinion of this Ebay Haikong Spitfire.
The CG difference really is perplexing. Could it be the weight difference and then apply that to flight characteristics?Like in the movie Saving Private Ryan,in one scene with the injured glider pilot describing how they crashed.With the jeep loaded and armour being welded in for the protection of Colonel.Upon release of the tow plane the glider reacts due to the added weight and the trim all messed up....FUBAR.

Anyway my Spit is gaining weight again,im changing receivers and the replacement one is 12 grams heavier.Still have to repair cowl and that will push the AUW to 1500g
How heavy to you think you can load up a 48" Spitfire?
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Old Nov 15, 2005, 03:47 AM
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USA, HI, Honolulu
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[QUOTE=dpaul]
Quote:
Originally Posted by drksyd
Dyksyd;
I'm still not really getting it. Thrust line is an issue because when you induced the dive, you had the throttle on and were generating downthrust. When you cut throttle, you remove that downthrust and the model must compensate for that loss by changing pitch. Regardless of whether you are in a dive or level flight, too much downthrust and you pitch up when you cut the throttle; too little, and you nose down.DP

Inducing the dive and cutting the throttle is to find the correct cg. From my understanding there is no thrust line if power is not applied. Maybe think about the plane as a glider, set up correctly it should fly straight hands off. Same thing with powered planes I believe, none of my planes pitch up or down when I cut the throttle, however they will pitch up at higher throttle settings. Anything over half throttle on my Corsair it'll climb, I counter this with down thrust. So far it's worked for me so I'll stick with it.
Anyhow, I'm not an aircraft engineer so I can't tell you what's right or wrong. If your plane is flying the way you like it, that's all that matters.
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Old Nov 15, 2005, 06:27 AM
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Boston, MA
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Hi Drksyd;

I guess no plane ever flies just exactly the way I want it to! So I am continually fussing with trim settings, throw settings, exponential, mixing etc. I'm an aspiring engineer type, but lack the necessary discipline.

I will post my question about the test you employ on the aerodynamics forums. Perhaps that will clarify things for me. But I appreciate your efforts to explore the issue.

By the way, did you ever receive your Spit. Like Freebird, I'd like to hear some more opinions about this craft.

DP
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Old Nov 15, 2005, 09:21 AM
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Boston, MA
Joined Aug 2004
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Hi Freebird;

Just returned from a less than triumphant experience with the landing gear. I put 'er on the grass and brought up the throttle all the while holding full up elevator to guard against nosing over. She started her roll out....then abruptly nosed over. Prop must have hit a stone because it broke. My only one. Another 3-4 days plus obscene postal charge to get more props. Sigh....

Before the landing gear fiasco, I increased the weight about 3 ounces (I'm now at ~1250 gm) by installing a new battery (4s 3100 mah; took a chance on an Ebay cheapy). Doesn't change the inflight characteristics in a noticeable way (that is, a way I can notice!) but landing speed is increased a little. However, I can fly about 18 minutes before LVC.

DP
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Old Nov 15, 2005, 10:30 AM
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USA, HI, Honolulu
Joined Jan 2003
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I thought I had a deal worked out then not surprisingly the price went up over $40 from what I was quoted. I'll let them sell it to someone else, there are many nice .40 size planes that will make great conversions around that price.
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Old Nov 15, 2005, 11:59 AM
a really nice guy, really
Ralph Brekan's Avatar
Phoenix Intl, Arizona, United States
Joined Jul 2004
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Yeah, I'm over this one; at the inflated price I could have the Ripmax Spit, which looks better... Dpaul got the one I was bidding on when they were still a good deal... But DRKSYD, is right there are many more fish in the sea...
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Old Nov 15, 2005, 12:17 PM
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Boston, MA
Joined Aug 2004
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Hi Ralph;

I don't know why I keep looking, since I already have one but Grandhobby keeps listing these things. The last three auctions ended at $43, $52 and $56, plus $30 for shipping. If you can get a Ripmax for that I'd like to know where!

I'm not sure there are so many fish in this particular sea. There are lots of .40 size planes, but this one is considerably lighter than those. Also it is clearly built with electrics in mind i.e. has a proper removable hatch for battery access that most of the .40 gassers don't have. Of course, that's a simple modification but this plane is quite nice for $85.

DP
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