fieldy73

I am unable to sustain level flight with my spad extra when rolling to knife edge and holding full rudder deflection. I have tried it into the wind and also on a slight climb.

It has a 55AX with 12 x 5 prop spinning at 11800 RPM. The plane weighs 2.6 kg. The rudder has 40 degrees throw, 3.5 inches each way (80 degrees, 7 inches total). It has a Futaba 3003 servo which appears to hold it (small amount of rudder flutter) under full throttle on the ground. It is built similar to the plans with 5mm coro where there should be 4, 3 mm where there should be 2 due to the unavailability of 4 and 2 mm coro in Australia. I havent yet covered the wing tips - they are still open. Any suggestions?

draftman1

Hey Fieldy. it sounds like that the coro you used added too much weight. I know thats all you can get so you will need more power. besides the rudder deflection, power is what sustains the knife edge. maybe you can go to a slightly larger rudder and stick a larger engine on it, say a 75 with a prop for thrust, not speed. just for kicks try a thrust prop on the 55, larger diameter with less pitch. it would be worth a try before changing the engine

Villa

Hi fieldy73
If you are very nose heavy you may not be able to hold altitude while in knife edge. There may be room to experiment with the location of the CG. Move it back about 1/4" at a time. What is the wing span? If you are using a push/pull rod to the rudder, the rod may be stronger in pull than in push. Do the knife edge so the rudder rod is in pull. Do this before you adjust the CG. It may give you an idea of what is going on. I think my SPAD Canard is a little heavier than your plane, has a 46FX engine instead of your 55AX engine, and does a very good knife edge. Can you post a photo of your plane?

draftman1

yes Villa, your right. I didnt see the wieght of the plane, its not bad at all. it should do it with a little adjustment

TheRealFrosty

I could not knife edge mine either until I added an extension to the fuse.

I cut a piece of 2.5 gutter pipe out and attached it to the bottom of the fuse with screws. Knife edge is even better now because the fuse extension is a little bigger than before. I can gain altitude when pulling on the rudder (right side of plane at top of knife edge). My control rod flexes when pushing the rudder, and the knife edge on that side is not as good. My CG is 3.75 inches from the LE using the hanging by loops and plumb-bob technique. Probably could go to 4 inches now that I am used to it.



more details: [link]http://www.frostracing.com/RC/06spadextra-0.html[/link]

jaav

Vid of one of the extra flights of Fieldy74.

http://www.youtube.com/watch?v=Xcra7ROvSlM

jaav

I supose Fieldy can try a 12x8 APC prop I have..

fieldy73

Thanks for the replies. Draftman I've got a 12.25 x 3.75 prop working on the more diameter, less pitch thrust idea. Villa, I'll try moving the c of g to the rear a bit, photo attached as requested. Ill test both those suggestions next time I fly. Wingspan is 48" plus fuselage of 2.5". I tried knife edge both ways including the direction which has the rudder pulled by the servo without success.

Villa

Hi fieldy73
That is a nice looking plane. Does it seem to make an average loop alright? I notice that the wing thickness seems to be much greater that what I am used to. On my 48" wingspan wings I use a yardstick for the spar which gives an inside wing height of about 1-1/8". I must confess that I see no reason why that should prevent it from doing a knife edge. I do a knife edge with every plane I have ever had since starting R/C in 1972 or so. I always test for proper CG location by doing a knife edge and adjust the C/G as I explained above. Once, on my older straight wing Canard, I had the C/G so far back that the plane could almost do a loop while in knife edge. Well, it being a SPAD, I decided to push it so it could do a full loop in knife edge. I moved the CG further back, did a knife edge, gave it more rudder to force a knife edge loop, and at about 3/4 thru the loop the thing went into an inverted flat spin. I could not recover because the main wing stalled and on a Canard that is total disaster because it falls rear end first. But yours is not a Canard, so go ahead and move the C/G back about 1/4" at a time. I am very confident that is your problem. Ever consider building a SPAD Flying Lawnmower? Ever see one? I designed and flew one for about 5 years if you are interested. I never could hold it long in inverted flight. Down there it might do better. Ha Ha.

fieldy73

Hi Villa - Plane loops well. The 2.25" wing thickness is as per Spad to the Bone, Spad Extra plans. I'm going to move the CG before this weekends flying. I've never seen the flyng lawnmower in real life only online - have you got photos of yours?

Villa

Hi Fieldy73
You can see some photos at http://www.rcuniverse.com/forum/m_34...tm.htm#3476218 The build plans are there also.
I just noticed that the build plans are difficult to read. You can download the very clear plans from our club website at http://www.wilsonrc.org/download.php?list.9

As a point of interest, I believe the spar on the Flying Lawnmower is about 2.25" high, which is about the height of your plane wing. Note that the chord on my mower is huge compared to your chord, which is what guided me in selecting the spar height. Do the plans for your plane mention the purpose of making the wing so thick? I'm not criticizing or commenting on anything, I'm just trying to learn more. I'm not familiar with your model since I have not studied the plans. Do let me know how your knife edge is progressing.

TheRealFrosty

The SPAD Extra is acam37's copy of the Balsa Sig Somethin Extra plane. The Sig Somethin Extra has a fat wing. It was a trend at the time, I think.

[link=http://www.sigmfg.com/IndexText/SIGRC76ARFR.html]http://www.sigmfg.com/IndexText/SIGRC76ARFR.html[/link]

Villa

Hi frostkg
Thanks.

fieldy73

Hi frostkg
What wing thickness is the wing in your extra? I'm going to experiment with c of g before I add the fuse extension.
Thanks villa for the mower link - it certainly is differnent!

TheRealFrosty

I made mine with a 1.5 inch spar. I did a lot of searching here on acam37's posts about the SPAD Extra and found a post were he built one with a 1.5" inch spar wing and he reported that it flew ok.

I just couldn't make myself build a big old fat wing at the time. But I have since built a copy of the Hanger 9 Twist 40 (SPAD Twist-VSF) with a big old fat wing (2.5" spar) and I like it's slow flying characteristics.

I think either size spar would be ok. The 1.5" spar version is probably a little faster, if necessary.

fieldy73

Knife edge is better now that cg is 0.5" towards the rear. It still wont climb but will hold altitude if the nose is high enough when entering knife edge. Maybe cg needs to go further to the rear, prop change or fuselage extension is required - I'll keep experimenting.

TheRealFrosty

Moving the CG more may solve it. I'm pretty sure mine was still a little nose heavy. I did not play around with the CG much after initial changes.

cncswiss1

5.75 lbs is still a bit porky, lighter will KE better.

Villa

Hi cncswiss1
His engine is an OS 55AX. I think his 5.75# is low. I do a very good knife edge at 7# with my SPAD Canard and it only has a OS46FX. I even do a knife edge with a SPAD J3-Cub at 7.5# with an OS46FX driving an APC 12 X 4 prop.

cncswiss1

for KE flight, calculate the fuse side area like you would a wing, then find 35-45% MAC of the fuse, see if that's anywhere near the CG.. anso calculate the wingloading of the fuse... then with the narrow fuse of the spad extra it will seem overloaded... either a taller fuse, added verts in strategic locations to improve "wingloading" and MAC/CG location, or lighter overall weight will improve things...

combatpigg

My Feedback: (3)

I'd stick a couple "side force generators" on the wing panels made out of cross grain balsa. Cover them with monokote so they'll still look SPAD.