Check6

My Feedback: (427)

It came time to balance my recently completed ESM 89 in. Spitfire. After setting up the balance stand I realized I would need 2 1/2 lbs. of lead to balance the plane. Glueing this amount of lead to the cowl would not work. I came up with this mounting system utilizing the standoffs on the DLE 55 engine. The lead cradle is made from mild 1/8 in. steel 3/4 of an inch wide. This bends very easy and is very strong. I made two straps for each side and joined them with 4 in. 1/4 in. bolts. I then used metal hose clamps to anchor everything down. Pictures explain my setup. Cowl now just bolts on with no strain and the lead is right out in front where you get the most benefit.
Thanks,
Fred

All Day Dan

My Feedback: (5)

Fred, I’m not a mechanical engineer and maybe there is one watching this forum. I’m an electrical engineer with a little ME background. Your ballast has added a significant amount of weight to an already loaded structure, the standoffs. They are not as rigid a structure as they appear. They contribute to a cantilever effect which has been extended. It is susceptible to twisting and bending as the engine vibrates. I may be all wrong and hopefully full of BS. I would like to find out. Dan.

spaceworm

I agree that the lead mounted that way may overstress the engine mounting. I would remake the side brackets so that they are sandwiched between the standoffs and the firewall, rather than forward of the engine. That should take the cantilevered effect of the weight off of the standoffs. Good luck.

Check6

My Feedback: (427)

Hi Dan and Spaceworm,
Both points are valid. When I stand back and look at this setup , looks like a lot of strain on the engine mounts. I think I will set it up as Spaceworm suggests. I'll try to get this done tomorrow and post more pics. Thanks for the input , guys.
Fred

RCFlyerDan

My Feedback: (54)

This is why the Good Ole reliable Zenoah G62 was invented and used for these applications. Especially the magneto version. Every one wanted lighter engines, but didn't think ahead to the consequences with warbirds.

Check6

My Feedback: (427)

Hi Dan,
I'm a big advocate of the G 62. Unfortunately I would have ended up with no cowl. I always use the G 62 with cup mount spring starter and pitts wraparound muffler in my Warbirds when I can for that very reason plus the reliability and no extra ignition battery. I guess I should build only radial engine fighters with big round cowls. LOL

tahustvedt

Mounting lead to the engine will load the engine mounts more on for example landing and high G, but in normal flight it will probably dampen the vibrations from the engine.

ForcesR

Check6; I have the same Spitfire and I am installing 55RA. You stated the dead weight you are installing is 2 & 1/2lbs to meet CG. That seems to be very little dead weight compared to what other owners of the ESM 89" Spitfire have added to the nose to meet CG? What is your CG measurement set at? I will set my CG at 137mm, not sure how much dead weight I will require in the nose to meet 137mm. I will mount my dead weight to the outside of the engine mount tube/cylinder which I have gained access to via the nose chin. The dead weight (scuba diver lead belt weights) will not be visible even with the cowl removed as it will be hidden in the nose chin.

Check6

My Feedback: (427)

I used the CG called for in the manual 153 mm which comes out to about 6 in.

Check6

My Feedback: (427)

Here is my new mounting set up. I made two 1/4 in. aircraft ply extensions at the base I epoxied two 3/8 in. oak blocks. I then pegged the blocks with 1/4 hardwood dowels. I epoxied and doweled the extension arms to the firewall. Everything else is the same as far as mounting clamps and 1/4 in. mounting bolts.
Thanks,
Fred

ForcesR

The 153mm CG measurement explains why you only require 2 & 1/2lbs to meet CG of 153mm. Do not attempt to fly at 153mm, the manual is quoting the most aft CG point! The Spitfire will be difficult to control due to being very pitch sensitive using the elevators at 153mm.

Roger

Check6

My Feedback: (427)

OK, Roger. Thanks for the heads up. I emailed Tomas , at VQ models to see if there was an addendum to the CG in the manual.. Where did you get the 137 mm CG?
Thanks,
Fred

ForcesR

Fred, I never rely on what a manufacturer list as the CG in the manual. I use the MAC CG technique to find the correct CG range. The ESM 89" WS Spitfire has a wing cord of 508mm, IAW the MAC rule, an aircraft is designed to fly safely within 25% to 30% of the "Mean Aerodynamic Cord" of the wing.

The wing chord is 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.

The ESM Spitfire wing has a chord measurement of 508mm (20 inches).

To calculate the actual forward and aft CG points for the ESM 85" WS Spitfire.

508mm x 25% = 127mm, this will be the minimum forward CG point.

508mm x 30% = 153mm, this will be the maximum rear CG point.

As long as the CG is within 127mm to 153mm, the aircraft will fly but the performance and stability of the aircraft will depend on where you set the CG between the forward and aft CG locations.

Based on these measurements, I have set the CG on my ESM Spitfire at 137mm 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 how my Spitfire performs/reacts during flight maneuvers, landings etc..

I chose the CG as 137mm because it is approximately mid way between 127mm and 153mm and should be an ideal location for the CG on the maiden flight. I selected mid way CG's with my other two H9 Spitfires and the maiden flights were stress free and enjoyable. One can never go wrong when using the MAC 25% & 30% CG rule when identifying the correct CG range on an aircraft!

Roger

Check6

My Feedback: (427)

Hi Roger,
Excellent explanation. I will set mine at 137mm. I plan on test flying this weekend. At least I know I will have a safe CG. Thanks again for your help.
Fred

ForcesR

Fred; do you realize that you will now require more than 2.5lbs of dead weight in the nose to meet CG set at 137mm? I estimate that I will require somewhere between 3.5 to 4lbs of dead weight in the nose to meet CG at 137mm. Others had to add 4 to 5lbs of dead weight to the nose to meet CG. That much dead weight was due to the addition of full cockpit mod and full figure pilot installation etc. The addition of more dead weight is better than losing the aircraft on it's maiden flight due to having the CG set to far aft!

Just for your info, my RC flying club held a giant aircraft fun fly two months ago when two visiting flyers from different clubs arrived with ESM 50cc Spitfires. I talked with both flyers before they flew and asked them how they liked their Spitfires. One said he really enjoyed flying his because it handled so well in flight and was easy to land etc. The other flyer said he was always nervous when flying his, said it was hard to control and it was a handful during landing.

I watched both Spitfires with great interest while they flew, one flew very nicely, smooth just like a Spitfire should, the other flew crappy, very pitch sensitive and the landing was almost a disaster. I asked the flyer who flew the Spitfire that handled nicely what CG location he had selected, he said 140mm. I asked the other flyer the same question and he answered his CG was in accordance with what was listed in the assembly manual, 153mm. I recommended that he should move the CG forward which would eliminate the pitch sensitive elevator effect. He was not very receptive to my recommendation and said he was just about fed up with the poor flying qualities of the Spit and said he would either sell it or crash it to get rid of it. Amazing that some flyers do not acknowledge that the CG could be set in the incorrect location, even when elevator pitch sensitivity is so pronounced.

Check6

My Feedback: (427)

Hi Roger,
Just rebalanced the Spitfire at 137 mm. Had to add one more pound of lead. Brings the total to 3 1/2 lbs. of lead to balance. I don't have a full cockpit or full pilot just a bust.
Thanks for your help.
Thanks,
Fred

ForcesR

Good day Fred, thanks for the update. It's good to know that my calculations were spot on in the amount of dead weight required to meet 137mm CG. I look forward to reading your post maiden report. You have nothing to fear, your Spitfire's CG is in the correct location to have a successful, stress free maiden flight!

Roger