dmyers0403

My Feedback: (48)

52oz on a long nose like the spit seems like a lot. Like you said, I would see what everyone else is getting and check the cg location again. I like balancing my warbirds upside down when possible with a cord at cg. where the wings join together. Have used pivot stand etc but like this way best when possible.

zrooster

Here's the thing, I already flew it with 40 oz in the nose, and it flew tail heavy. So...

ForcesR

What is the CG min, max range on this Top RC Spitfire using the MAC 25% and 30% rule?

zrooster

Great question. I'll leave the math to someone else!

ForcesR

It's easy to determine the approximate CG using this quick method to find the CG range for your Top RC Spitfire.

I do not own the Top RC Spitfire but I do have the H9 30cc Spitfire which is nearly identical in size.

An aircraft is engineered to fly safely with a CG usually set at 25% to 30% MAC of the wing "Chord". An RC aircraft is engineered to meet the same criteria.

For those who do not know what the wing chord is, it's the width of the wing measured from the widest part of wing usually where it attaches to the fuselage. Measure the width of the wing from the leading edge to the trailing edge of the wing, the total measurement is the chord of the wing.

For an example, I would estimate that the Top RC Spitfire wing has a chord measurement of 457.2mm. The estimate is based on the chord measurement of my H9 30cc Spitfire.

You will have to confirm the actual chord measurement of your Top RC Spitfire wing and apply that measurement to calculate the actual forward and aft CG points for your Top RC Spitfire.

My example of H9 Spitfire CG measurements:

H9 Spitfire wing chord is 457.2mm x 25% = 114.3mm, this will be the minimum forward CG point.

457.2mm x 30% = 137.16mm, this will be the maximum rear CG point.

As long as the CG is within 114.3mm -- 137.16mm, the H9 Spitfire will fly safely.

Based on these measurements I set the CG on my H9 Spitfire at 123mm for the first flight. After the first flight I can adjust the CG more forward or more aft to suit my style of flying and depending on how the Spitfire performed/reacted during flight maneuvers.

After several flights I set the CG at 129mm and left it there; this is where I find that the H9 Spitfire performs best for my style of flying.

Roger

zrooster

Forces,

Very good information for future reference. In my case it is, if you'll forgive the term, entirely academic. In my foolishness, I found a foolproof way to see if my plane was correctly balanced. I flew it. It was tail heavy with 40oz of lead in the nose. There are really only two things I can do at this point. Move some things forward, or add more weight to the nose. Actually, I'm going to do both. I'm going to move my batteries (4x NIMH batts) forward, I have added 12oz to the nose, and I will move one more 6oz weight further forward.

At this point, my repairs are done, so I'm down to a little sanding and painting fir cosmetic purposes, and waiting on the repaired landing gear.

ZR

zrooster

Well, CJM say my repaired gear are on their way. They shipped about a week after they got the remains of the gear I shipped to them. Not bad at all! Cost was right at half of what a new set would have cost, including shipping... I'm pretty happy with that since they replaced 60-70% of the parts!

Fiber glass repairs are done, including filling and wet sanding:


It it looks bad, but that's as smooth as the proverbial baby's back side! More importantly, it's stronger than when it came out of the factory!

I also made some adjustments/ improvements. I moved all 4 of my NiMH batteries forward. Two are just behind the firewall, and the other two are just aft of the first former.

As mentioned, I put another 12 oz of weight in the cowling, and plan to move one more 6 oz weight there from its position just aft of the firewall. That being the case, that is a lot of weight that is basically supported by the screw holes in the cowling. I wasn't comfortable with that, so I did a little reinforcement:


I used the same strips of glass cloth and epoxy that I used for my repairs to the fuse. I then sandwiched washers between the cloth and the cowling, being careful to make sure that the cloth was nice and flush to the cowling all the way around the washers.

I had to leave for a quick work trip before I finished, but all that's left is to drill through the new fiberglass at the center of the washers and mount the cowling!

w1nd6urfa

My Feedback: (4)

Good job!
Regarding the cowl screw reinforcements, you need to buy some sheets of G10 (Fliteskin) for your shop, you'll soon wonder how you could live without it :-)

zrooster

Thanks, and will do! I had the roll of glass cloth given to me, so I used what I had, but it's time to up my game!

Edit: with all that weight moving forward, I think I should be able to safely take some off, BUT I'm very wary of making the same mistake as last time. So, I'll see where it balances at once I get the gear reinstalled. If it's around 110-120mm, I'll leave as is. If it's forward of 110, I'll take some weight off and slowly work it back. I will not balance it aft of 120 until I fly it again.

zrooster

Gear showed up while I was gone on my trip. Pretty happy with CJM customer service!

All I really need to do is mount the gear, check the CG, and run engine. I'll most likely need to open the cowling around the motor, but I'll see what the engine run tells me. I also picked up a digital temp reader to see how hot it's really getting.

zrooster

Repaint (in effected areas) almost complete. I also painted over the Johnny Johnson markings, to be replaced by those of Douglas Bader (courtesy of Callie's graphics).



I had to send my retracts back to CJM again, but they turned them around quick, and they're already headed my way. With any luck, I should be able to get her back in the air be mid Sep!

larryg1959

I really don't understand this man..She's complete and almost ready to fly..DLE 35RA...The Rx battery, Retract battery and ignition battery are all forward of the CG line and I still need 128oz (8pounds) to achieve the proper CG....The plane complete without the CG weight is 19lbs...with the cg weight it's coming in at 27lbs....I'm honestly afraid to try and put this in the air

Lifer

My Feedback: (1)

How did you determine that you needed that much weight?

chris923

My Feedback: (53)

I put a DLE 55 in mine. I put 3 lb in mine to balance at 150mm not 120mm as the instructions wanted. I would have need 7lbs to balance at 120mm. Flew it at 150mm, was extremely tail heavy. It didn't survive it's maiden.

zrooster

What are you using as your reference for 130mm?

flew with 40OZ of lead, and it was a bit tail heavy. Since then, I moved ignition, retract, and 2 receiver batts 8-12" forward of where they were, and added 12oz to the cowling. I have an EME 35 in there for power. Haven't checked CG yet with the, now, 52oz of lead and relocated batts, as my retracts aren't back in yet. Will report back when I do, but it wasn't far off with 40oz...

zrooster

To be clear, I think the instructions say 130mm... I think 120mm would be a good idea, though.

w1nd6urfa

My Feedback: (4)

17 lbs AUW dry, 125mm CG flies great. Powered with OS GF 40 that weighs ~3 lbs, added about 9 oz ballast

The trick was to keep the tail light (gold'n'rod for elevators) and moved everything forward of the CG, including servo tray

Details on p11

larryg1959

I marked the CG spot on both wings, flipped her upside down and with help we lifted the plane, finger on CG spot. I kept adding weight until she lifted and stayed horizontal..I then took everything I used to achieve the CG and put them on the bathroom scale...8 pounds is what the scale reads

zrooster

Where, on your wing, did your CG marks fall?

zrooster

Every little bit counts...the longer the lever arm, the more it counts!

I think I hurt myself a lot by going with the beefier tail gear. Still things I can do...the easiest, and quickest would be to replace the tailwheel with a lighter one. Might save me a few oz at the front...

larryg1959

130mm (5.1") back from the leading edge of the wing about 4 inches out from the fuselage. Marked with duct tape..plane inverted those are the lifting points

larryg1959

I don't understand how you moved the servo tray forward of the CG..that would put the tray in the nose of the plane..I like to see a picture of your setup

zrooster

That was windsurfa that moved his servo tray. He's got pix a few pages back...

I'm on the road right now, but I can already see why you might need more nose weight than I do. I have my throttle servo under where your fuel tank is, and my electronics are all where your (I assume) throttle servo is. I also have a choke servo just aft of my firewall. I have 4 NiMH batts...two are just aft of the firewall...next to my choke servo, and two are just aft of the first former (bulkhead). The batteries were further aft for my maiden, but still forward of the CG line.

I epoxied 24oz of lead (plus whatever the massive ammount of JB weld I used weighs) in the upper front of my cowling to get it as far forward as possible. The remaining 28oz of lead is bolted to the engine box under where my choke servo is located and safetywired to my motor mounts (though I plan to relocate those). I also reinforced my cowling to cope with the extra weight.

Mine is powered by an EME 35, which is probably comparable to the weight of your DLE 35, but curious how far from your firewall your cylinder (the heaviest part) is compared to mine. I'll measure mine and let you know.

Ill take pix of my setup and post them when I get back (about a week from now).

jpflyer

My Feedback: (13)

I'm running an electric setup in mine. I guess I should of got heavier batteries from what I'm hearing here. Anyone else running electric and if so, what did you do for cooling?

zrooster

If you look early in the thread, there are a few who built it for electric (maybe you can PM them) and I guess Gator RC has some experience with it. I'm sorry, but that's about all I can offer on it.