3357

i picked up an old Spectrum Alpha trainer with the 63" wing span from a friend of mine
He flew it one time after he bought it about 10 years ago and then it got stepped on in his garage and has laid wounded every since. it was crunched pretty good from where the back dowel for the rubber bands is back to the tail feathers. I thought I could probably fix it so i brought it home . It took me a few days to do but it is fixed and arf.
When I went to balance the model I figured it would be tail heavy but I had no idea it would want 1.34 pounds of nose weight to balance. My god, I didnt put any steel I beam or any thing like that in when I repaired it. I ran a 3/16" balsa skin on one side from where the back dowel is to the back. And then there is epoxy and a a few small pieces of balsa here and there in the rear inside the fuselage but only where it was necessary
Didnt even use all of the small bottles of epoxy. I kept in mind when I was repairing it that that far back on the fuselage weight matters so I used only what i had to.. Before I tried to balance it I even moved the battery pack as far forward as possible.. My god 1.34 pounds??? Will that plane even fly if I put that much nose weight on it ??? Never have used any where near that much weight. What do you guys think? Did I wast my time on a doomed plane??? Or do you think it might fly?? I really dont know.

Thanks Dave
P.S. The plane has an evolution .45 motor

rt3232

My Feedback: (6)

Dave not knowing what you are using to balance with ie: fingers venessa rig or a pivot balancer, I like the venessa rig. You also did not mention that you had the correct balance point, being a trainer I would suggest using 25% of the cord at the fuse as a starting point
Now to answer your question properly balanced it will fly with enough power, and the correct control set up how well is an unknow.

Cheers Bob T
AMA13377

3357

Hello Bob, thanks for the response.
Yea on the balance point i actually have the owners manual for the plane and it says 2 3/4" from the leading edge at the fuselage. when I went to mark the balance point on the wing i was pleasantly surprised to find that it was pre marked at he factory. However when I tried to lift the plane at the balance point with my 2 fingers it was like the tail had gotten epoxied to the table.. You know those little round brass inserts they use in sliding closet doors to put your fingers in so you can slide the door open? They are about 2" round and 1/2 inches deep? I filled 2 of those with lead and that still wasn't enough weight to balance it so i added a 1 1/2 steel nut to the mix and that did it. Thats allot of weight. Also its as far forward as i can get it. 1.34 lbs but it balances perfectly. For the power it has an evolution .45 motor. I saw the first and only flight the plane made and the motor was more than enough power for it. So you think it might still fly? I guess i would have to be very careful about hard landings huh? (but of coarse i never make hard landings any way). So you say if its balanced it should still fly? That makes sense as long as it can get off the ground. Thanks..... Dave

52larry52

My Feedback: (1)

C/G balance within in a normal range (25 to 33% of MAC) is NOT optional. It will not fly (under control) if not in that range. Having a lighter total RTF weight makes for a better flying airplane but it must be in C/G balance so get it into that range using the least amount of added weight as possible. A brass heavy hub spinner nut mounted inside the plastic spinner you are likely using will get some weight mounted as far forward as you can get it. Add other stick on weights on the motor mount rails,and firewall as needed to get your C/G at the desired 25% of MAC. Moving the RX battery as far forward (under the fuel tank maybe?) helps. Is there anything you can do to remove weight from the tail end of the plane? 1.3 lbs of nose weight needed on a 40 size trainer sounds excessive. If your plane has an 11" cord then the 2.75" balance point (25% MAC) is correct. Of course balance with the fuel tank empty. A heavier but more powerful .60 size engine may be an option. What does the total RTF weight dry come to when it is balanced?

da Rock

It's possible that epoxied on skin was heavy. Epoxy really isn't needed for that job, but that and whether the balsa was heavy or light..... it's done.

If you used iron on covering, then peel it off on that skinned side and cut out a lightening hole. Weigh it and you'll find out if it's worth any more lightening holes. The skeleton that you let remain will certainly be strong enough as an epoxy reinforced "web" will be plenty strong. Then iron covering back on the side and nobody will see what's underneath.

If the tail surfaces are sheet balsa, the same technique of lightening holes hidden under covering will probably get a lot of your problem solved. They used to pick "strong" balsa for sheet surfaces back then. It was how they recovered the cost of the lousy balsa they got in bulk shipments.

speedracerntrixie

My Feedback: (29)

That airplane has a wing cord of 11.25". According to my math the CG at 33% would be 3.4". I had mine balanced at 3.75" and it flew just fine but did not have the charictaristic self climb as speed builds that some like to have in a trainer. My suggestion would be to rebalance at 3.25" and go fly it.

rt3232

My Feedback: (6)

[QUOTE=3357;12239
. So you say if its balanced it should still fly? That makes sense as long as it can get off the ground. Thanks..... Dave[/QUOTE]
The simple answer is yes And all of the above responses are things to consider, Total wing loading is also some thing you need to watch, a lite wing loading, even when balanced correctly will give you quick response to control movement and a hi wing loading can also be difficult to control if there is not enough movement.

Not knowing your skill level is another problem in trying to give you the best answer .
For me I would like to now if you have built R/C birds with success and are you a beginner intermediate in flying ability
Please don't take this wrong as it is just my way of dealing with answers

Cheers Bob T


PS post a pic of the bird in question

da Rock

Good advice.

The math isn't right however.

To set the CG at 33% of an 11.25" wing you'd balance it at 3.71"
If yours balanced at 3.75" your CG was basically at 33%. 3.4" isn't; it's at 30% not 33%.

Moving it forward is the right direction for sure. At 3.25" it'd be at 29%.

want it at 25%? That'd be at 2.8".

Trying to guess at a good start location for CG without considering the things that actually control pitch stability might be simpler but can still trip someone up.

3357

Sorry about not getting back
sooner. Thanks for the replys. I think the idea of putting a 60 size motor in the plane is a good idea. It will give more power and as well some nose weight. As far as my skill level i have built flown and crashed my share of airplanes in the last 20 or so years. And loved every minute of it. This plane has a very long fuselodge on it and most of the repair was back near the tail feathers. I guess thats why it wants so much nose weight. Its the alpha spectrum model. Its a high wing with i would guess about a 60" wing span. I will post the wing loading and other specifics as well as a pic hopefully later today. Also the 3 servos are mounted toward the back of the plane that i can move forward also. Thanks for all the input you guys , this plane may fly again aftet all..........
Dave

3357

Ok wing loading on the hangar 9 alpha 40 is still a mystery because the manual does not say.
Wing area is 710 sq inches
Wingspan 63 inches
Leength w spinner is 52.5 inches
Flying weight is 5.25 lbs.
2.75 - 3 inches is center of gravity.
Im not sure how to do a picture. I will post this then figure it out

sensei

There is no mystery about it, the wing loading is 17ozs. and the cubed is 7.7. That is just right for a trainer. You are way over thinking this thing, just go fly and have fun, the rest will come later.

Bob

daveopam

My Feedback: (9)

I would just push the motor further forward. You don't have a cowl to worry about. Just get a longer mount or re drill the one you have and push the engine as far forward as possible. You will need longer throttle linkage and line but that's easy.


David

3357

Over thinking? I always thought the cg was extreamly important for an airplane. After the repairs this plane wants 1.3 lbs of nose weight to balance. Even if i move the motor forward that woukd probably help but unless i move it wayyyyy firward i dont think it will make up any where near 1.3 lbs.. i may be wrong. Thats why i was asking for advice. But if i just " go fly and have fun" i think the only ones having fun would be any one watching me trying to fly a plane that is 1.3 lbs tail heavy. Lol..i think moving the motor forward would be a good place to start. And as well install a .61 . I can also move 3 servos forward which should help. Thanks for your responses.........Dave

sensei

Like others have already stated... Balance between 25 and 33% and go fly! You can move the engine forward, lighten the tail or you can even move the wing aft, maybe a variation of all, your choice...

Bob

3357

Again i wanna thank you guys for the options. Most of them i did not know i even had. I will try the 33% and see how it balances there. I just couldnt see adding 1.3lbs of nose weight to a 45 size airplane. I knew asking on the forum would be helpful. I will post and let you guys know what happens.............
Dave

acdii

Just remember, it takes more weight up front to make up for weight in the tail. Something like 3:1 I believe. I added a 1.94 ounce servo to the tail of my 4*120 and had to add over a pound of lead to compensate. Think of it as a lever with the CG being the fulcrum point. This is even more true with long tailed planes like the 4*.

3357

Yes i understand. I just built an edge 540 with 3 servos in the tail.

3357

Well with a .61 motor out 13 inches from the firewall and the balance point 3.71 the plane dosent slam the tail on the table when i try to balance it but it still tries to slide off my fingers. Still real tail heavy. I cant move the wing back because the ailerion linkage hits the fuselodge. Maybe this plane is a candicate to become a wind sock.

acdii

Go make a Vanessa Rig, save yourself the headaches trying to point balance the plane. It is the most accurate way to balance a plane, and the least risky to damage one. I found that 3 out of 4 of the planes that I thought were balanced using the point balance system were way off when I put them on the VR.

raptureboy

Something is just not right. Our club has 2 of these and they come balanced right out of the box basically. you must have added a ton of weight to the tail. 3/16 Balsa for the skin? 3/32 max is all that would be required. Maybe a G62 hung off the front end would help. I would go with stripping the covering off and drilling lightening holes.

daveopam

My Feedback: (9)

The lightening holes is a good idea. You could make the wing a dual servo and then move it back with a bunch of re engineer.

At this point I would probably just try and fly it, or ask an ace at your field to try it. You could zip tie strips of lead to the motor mount. Fly it for a minute, than take one of the strips and go again. When you can buy a cheap trainer for $100 it's not worth a bunch of time and effort.

David

Chad Veich

My Feedback: (60)

No offense intended at all but whether you can "see" it or not, if that is what it takes then that is what it takes. Balancing the airplane at the far aft end of the CG range in order to save nose weight is a bad idea. A well balanced heavy airplane will fly. A lighter but tail heavy airplane will not. You're better off to set the CG in the safe range, whatever it takes, for the test flights. (Safe in my opinion would be no more than 28-30%) Will it fly at 33% or further aft. Yes, but the time for messing around with the CG to find the aft limit should come after the test flights when you've got the thing trimmed properly and flying reliably. If need be the airplane would fly at ten pounds, though it would be under powered and probably a bit sluggish. That is still better than tail heavy and out of trim, IMHO. That's my .02 cents worth anyway.

3357

Well yes i had to do a bunch of repair on the back of the plane. It was basically crushed. Also i had to epoxy the tail feathers as oppose to screwing them on. I used 3/4 in plywood for the skin. No, kidding i used 1/16 balsa. I think it was broken to bad to try to repair. But i gave it a shot. I think maybe im kicking a dead horse. You guys have been really great with your ideas and i thank all of you. I have more planes to work on that will have a brigjter outcome.

acdii

How about posting some photos of the plane and what you have done so far. You know that saying, you can talk til blue in the face, but a picture says a 1000 words.