Freewing SBD CG Help

[Jpmcdo]

In checking the CG on my Freewing Dauntless, it is very tail heavy. I have a Hobby King CG check jig and the tail is really heavy using that jig. I', using a 6.5 ox batter as far up as I can get it and still need at lest 6 ounces. I used an unopened package of Great Planes lead weights that contained 6 ounces.

Does this seem right?

Thanks,

Jim

[Konrad]

RE: Freewing SBD CG Help

Tail heavy is a common complaint. Even using a 3600 mAh 4 cell battery often takes 55 grams of weight in the cowl to balance.

This is a typical problem with radial equipped scale models. Many OEMs will add lead slugs in the front of the model. Others will allow you to select a larger (heavier) battery to use a useful load (extra duration/ fuel).

All the best,
Konrad

[Jpmcdo]

RE: Freewing SBD CG Help

Thanks Konrad, I pulled the replica radial engine out and there is a lot of room to put lead weights. I'm just surprised that I would need more than 6 ounces but I'm still a relative beginner. I'll hit Walmart tomorrow and pick up some fishing weights in different sizes to get above 6 ounces. I read a thread on RC groups by Michael Heer who said he started with 8 ounces and backed down to 4. the link is http://www.rcgroups.com/forums/showthread.php?t=1797029

I did take it to a friends house who has 20 years of experience. We checked everything but the CG.

I'm using a 6.5 oz battery, trying to stay within MFG. and Motion RC suggestions. It's a 2200 mah battery.

Jim

[boomer108]

RE: Freewing SBD CG Help

Welcome Jim,
  
    If I read you right your using 12.5 ounces to balance? That doesn't sound right. Now I don't have a Freewing Dauntless but I have two Fms 1400 warbirds and like most warbirds you should balance them inverted with the gear up. I had a Hobby King cg machine and I did not think it worked very well,it always gave me different readings. I now use a Great Planes cg machine and it seems to work very well, but using your finger tips is also a good method to see where your balance is at in a pinch. Also are you using a a battery that's close to Mfgs recommendations? Good luck and I hope I helped you a little.

Roy B.

[Jpmcdo]

RE: Freewing SBD CG Help

Thanks you did. No I have 6 ounces balanced on the nose of the plane and at first that worked but now so much. I have pulled the replica radial off and prop and found a large area where I can add lead. I laid all 6 ounces in and replace the radial engine and prop and I'm not getting level. I did try my finger tips and did now war birds are checked upside down. The problem is the further back you have to put the weight, the more you need to reach level.

Believe me, before this plane fly's, I have my friend who has 20 years experience do the maiden, we check the CG. Also installed an eagle tree gyro as well.

Jim

[Konrad]

RE: Freewing SBD CG Help

Well, that is RCGroups. But that aside it is typical for the OEM to give the CofG that is nose heavy. The OEM doesn't want to get a bad rap for a ship that snaps on take off. I almost always wind up with my CofG further aft than recommended after I'm done with all the trim flights.

For this model I'd use 4000mAh cells
But if using the 4 cell 2000mAh battery (these are chosen for marketing reasons not mass) I'd glue in 2 oz well and add the additional 4 'loosely' as I'm sure you will be removing much of them later in the flight test program.

Never understood balance machines for setting the CofG, but that's just me wanting to spend my money where I think it will actually have some value.

Gyros again why add the complication? The SBD has a wide wheel tract and should be nice with regards to ground handling. If you do use a gyro make sure the surface response is in the correct directions and start with a low to mid gain setting. No sense having to fight a gyro along with any other first flight issues.

All the best,
Konrad

P.S. A lot of folks regardless of their experience don't really know how to trim out an aircraft (this goes for full size as well as models).
I like to use this chart as a starting point.
http://www.wtp.net/DBEST/trimchrt.html

[ryramZ]

RE: Freewing SBD CG Help

In checking the CG on my Freewing Dauntless, it is very tail heavy.  I have a Hobby King CG check jig and the tail is really heavy using that jig.  I', using a 6.5 ox batter as far up as I can get it and still need at lest 6 ounces.  I used an unopened package of Great Planes lead weights that contained 6 ounces.

Does this seem right?

Thanks,

Jim

In our video of the Dauntless we used 3 ounces and were flying with 2200 recommended packs. Lately I'm flying a different SBD as Mike has the video model, anyway. I'm using 3000 and 2500 with no lead. I still thing 3 ounces up front would make for a better approach in my case, however I am just living with it for now. I opt for bigger batteries if they fit everytime. I used to fly mine with a pocket knife style set of allen wrenches next to the battery..lol
Regards 
Ryan

[Alpha]

RE: Freewing SBD CG Help

Admiral 4s 3000 is perfect for me, no lead ballast added.

[Jpmcdo]

RE: Freewing SBD CG Help

Thanks, I agree it sound like a lot. Let me ask this question. The direction say 90 to 105 MM for the Center of gravity. Do I split that in half for points where I find the CG? Typically I measure and place tiny pieces of masking tape at the CG and balance it that way. On this one I have it set a 91MM.

Should I be looking at the center between 90 and 105 which is about 98?

[Jpmcdo]

RE: Freewing SBD CG Help

Well, that is RCGroups. But that aside it is typical for the OEM to give the CofG that is nose heavy. The OEM doesn't want to get a bad rap for a ship that snaps on take off. I almost always wind up with my CofG further aft than recommended after I'm done with all the trim flights.

For this model I'd use 4000mAh cells
But if using the 4 cell 2000mAh battery (these are chosen for marketing reasons not mass) I'd glue in 2 oz well and add the additional 4 'loosely' as I'm sure you will be removing much of them later in the flight test program.

Never understood balance machines for setting the CofG, but that's just me wanting to spend my money where I think it will actually have some value.

Gyros again why add the complication? The SBD has a wide wheel tract and should be nice with regards to ground handling. If you do use a gyro make sure the surface response is in the correct directions and start with a low to mid gain setting. No sense having to fight a gyro along with any other first flight issues.

All the best,
Konrad

P.S. A lot of folks regardless of their experience don't really know how to trim out an aircraft (this goes for full size as well as models).
I like to use this chart as a starting point.
http://www.wtp.net/DBEST/trimchrt.html

I added a gyro since I'm still relatively new and it will allow the plane to return to level flight if I let go of the sticks. I have augured in too many times with my Aprentice with safe off and my Parkzone T-28 learning and if I get in trouble and let the planer adjust again I'm somewhat duplicating the safe technology. Right now, I have 2, 2 ounce weights in the nose with velcro and a half more ounces stuck in with thedouble side tape that comes on the weights and it appears to be centered.

[Konrad]

RE: Freewing SBD CG Help

I'm sorry to say that gyros do NOT return the model to level flight. It sound to me that you need more time on a flight simulator or basic trainer, rather than try to fly a warbird this early in your flight training. While the SBD is a gentle flier she is not a trainer. I like to see guys be able to fly the aileron trainer ( like the T-28) to the point that they can flu upside down for 2 or more patterns around the field. Can do nice cuban 8's. and land with a 90° 5 mph crosswind before moving up to the more advanced models. Or but another way you are really bored with the aileron trainer as it can't offer you any more opportunity to advance your flying skills.

The CofG is not written in stone! It MUST be played with. It is a trim tool just like thrust lines and control trims.
The designer gives a range in which he thinks the model will perform well and not get the pilot into trouble on the first few trim flight. It is expected that the pilot will move this point around for find what he is comfortable with. The designer doesn't what the model to be too nose heavy as it make the model difficult to take off and land (needs far too much speed). In the air being too nose heavy makes it very difficult to make smooth maneuvers (like turns) as the plane is always climbing as it builds up speed (too much up trim). The designer does not want the model to be too tail heavy as he usually has the control surfaces set up for too much movement. Too much control movement is there to address out of trim issues with the first flight and that models are usually flown nose heavy for the first flight. Also be really tail heavy can result in divergent flight (snaps on take off). This often gives the model a bad reputation when it actually was just a trim problem.

Note; most of the time what guys attribute to being tail heavy really is just over controlling from too much control throw. I like to see guys use a chart like this to really trim out their planes.

http://www.wtp.net/DBEST/trimchrt.html

While many call for the CofG to be at 25% of MAC I often set up my models with the CofG set at 33% of MAC.

All the best,
Konrad

[Jpmcdo]

RE: Freewing SBD CG Help

I'm sorry to say that gyros do NOT return the model to level flight. It sound to me that you need more time on a flight simulator or basic trainer, rather than try to fly a warbird this early in your flight training. While the SBD is a gentle flier she is not a trainer.  I like to see guys be able to fly the aileron trainer ( like the T-28) to the point that they can flu upside down for 2 or more patterns around the field.  Can do nice cuban 8's. and land with a 90° 5 mph crosswind before moving up to the more advanced models. Or but another way you are really bored with the aileron trainer as it can't offer you any more opportunity to advance your flying skills.

The CofG is not written in stone! It MUST be played with. It is a trim tool just like thrust lines and control trims.
The designer gives a range in which he thinks the model will perform well and not get the pilot into trouble on the first few trim flight. It is expected that the pilot will move this point around for find what he is comfortable with.  The designer doesn't what the model to be too nose heavy as it make the model difficult to take off and land (needs far too much speed). In the air being too nose heavy makes it very difficult to make smooth maneuvers (like turns) as the plane is always climbing as it builds up speed (too much up trim). The designer does not want the model to be too tail heavy as he usually has the control surfaces set up for too much movement. Too much control movement is there to address out of trim issues with the first flight and that models are usually flown nose heavy for the first flight. Also be really tail heavy can result in divergent flight (snaps on take off). This often gives the model a bat reputation when it actually was just a trim problem.

Note; most of the time what guys attribute to being tail heavy really is just over controlling from too much control throw. I like to see guys use a chart like this to really trim out their planes.
http://www.wtp.net/DBEST/trimchrt.html

While many call for the CofG to be at 25% of MAC I often set up my models with the CofG set at 33% of MAC.

All the best,
Konrad

Thanks Konrad,

I have an FMS 1450 MM T-28 with an eagle tree gyro installed. It flies beautifully with that gyro and f I let go of the aileron for example the plane levels right off. Thanks for your help on the CG.

Jim

[Jpmcdo]

Flight update - The plane flew wonderfully on a fairly windy day. The Gyro helped compensate for the wind gusts but I was very happy with the results. It does have over 4 ounces in the nose and the CG appears to be on target.

[Ron1950]

ok guys ...where is the sweet spot I need to get the cg on this plane? I will maiden it with a zippy 4s 3000 but might try to stuff in a bigger battery when getting closer to flight time...still no lead in the nose but not aginst it yet....should it balance at the center of the bomb like inst book says or what? hate to wreck this plane on first time out but can always use the space lol....

[Jpmcdo]

I measured both numbers in the directions by using a metric angle ruler and placed a small piece of tape to mark the spot on each wing. I also used a turnigy CG tool/jig and without any weight using both fingers with the plane turned upside down, the plane was very tail heavy. It would have flipped off the table had the vertical stabilizer not stopped the pitch down by hitting the table.

I didn't use the recommended batteries. I am using a Gforce 2200 mah 4 cell battery which is smaller than the ones recommended. Only reason was a friend at the field use them and they were less expensive.

I pulled the propeller off and the plastic engine cylinder and velcroed flat 2 ounce weights in as far as I could get them in the front motor compartment. I ended up using two of those and then around an extra ounce of stick on weights. Each time I tried how much weight to use I put the engine cylinders back in and the prop back on and with a battery in place as far forward as I could get it. With over 4 ounces, the CG has been smack on target. I know others have used less and the friend who did the maiden flight also checked the CG and said it was good but I may want to pull some weight out later if I use a larger battery and or if it starts to appear nose heavy. It didn't in the maiden flight.

Above on this post, it was mentioned that Motion RC used 3 ounces I believe, on the plane they flew in their video and it sure looked like it flew very well. By the way I leave the tiny pieces of tap on the wings all the time to re-check before I fly my planes.

[Jpmcdo]

Just to confirm, I checked the CG with the two finger method and also with the turnigy CG tool to check.

[Konrad]

Glad it's working out for you. And that you are seeing what MotionRC also noticed.

All the best,
Konrad

[Jpmcdo]

Thank you, I appreciate the help you gave me.

[Iowa54]

Got the SBD I picked up at a swap meet in the air finally...I had to turn the rated down quite a bit for me anyway.. Take off was fun............ used a Mobuis cam on my hat..

[Capt. Crunch]

Oh man I thought you were gonna lose it! Nice save

I'm jealous of your runway

Jeff