Official Dynam 1500mm B-26 Marauder Thread

[CFIT rob]

My post #1218 may help. Eflight mains appear to drop in. No one has reported trying the nose gear yet. What was the air temp when you were flying? Under 50f seems to be a problem. Hoping that dynam will improve the gear this summer. Add that to your list alpha. Bet its already on it...

[Wag727]

I just ordered the tricycle set for it. It was 47f when I flew. I measured the mounting screws and they seem to be able to drop in. I appreciate your reply! I will post later about the nose gear weather it' a drop in or not. Thanks again.

[themudduck]

https://www.rc-airplane-world.com/ba...airplanes.html
Some good information on balancing .

Grossman56

I like seeing articles like this, they are helpful, but this one is lacking in a few ways. It does a good job of explaining how to physically balance a plane using the position recommended by the manufacturer. I would have liked seeing a discussion on how to determine where the CG should be.

The article does advise the general "rule of thumb", the typical range of 25-30% back from the LE - but this rule of thumb only applies to straight wings.

Wings with more complicated shapes (for example like swept-back wings or other shapes) require a different method to determine where the balance point is located. (You need to determine where the Mean Aerodynamic Chord is and measure at that point). I guess that's a bit nerdy.... Here's another article that explains how to determine the 25% CG using the MAC.

And it would be useful, I think, to also talk about how to carefully evaluate what your plane is doing in the air and how it relates to the balance point, so you can understand what the affects are when a plane is nose-heavy or tail-heavy- because there seems to be a lot of confusion about that.

The other thing I noticed is that it said to measure your plane "flight ready" - i.e., with the fuel tank full. This is really important!
Now, I've always measured my CG with the batteries fully charged. If the fuel tank is empty that could drastically change things. Batteries are much heavier when they are full of electrons. LOLLOLLOLLOL

:(OK, sorry, I'm done, back to my coffee...

[Hardway]

[QUOTE=themudduck;n114365]

Batteries are much heavier when they are full of electrons. LOLLOLLOLLOL

I hate that when the electrons get cold. They get even heavier!!! :Cool:

[farmflyer]

What if the tires aren’t full of air one must account for that and if it is summer or winter because the winter air in the tires will be much heavier because it is denser:Silly:

[themudduck]

Yeah maybe that's why the retracts don't work in the winter, its because the tires are too heavy. ;)

[farmflyer]

Good point !

[CFIT rob]

Wag727...you are very welcome. Let us know of your progress with the swap. I will be buying the p61(and the gloster meteor) when its available so if there is no improved dynam retracts by end of summer, i will change them all out.(expensive but worth it...like divorce) As for the cold and density i believe the previous posts are correct. My ex-wife was cold and quite dense. Really...really dense.

[UK Arthur]

Cold-fail retracts.

A few weeks ago after leaving my Marauder in my front hall at 40°f for an hour, two of the retracts would not deploy (of course). In the hope of being able to fly soon (weather's been crap for weeks, and me similar), tonight I've repeated the test after leaving the plane for an hour in my unheated hangar (err, spare bedroom) at 49°f. The retracts all worked fine. With luck, the test can be done at in-between temperatures tomorrow morning (assuming I remember!). Then I can choose a safe minimum flying temperature for my Marauder.
The tests were done with a battery at 3.8volts per cell, and the battery was also left in the plane for the 1 hour soak before the test.
This could save me bothering to swap the Dynamic retracts out for ones that can stand the cold.
One alternative for flying in the cold is to deploy the gear and then remove the retract plug from the receiver before take-off, to avoid unintended retract.

[Grossman56]

I like seeing articles like this, they are helpful, but this one is lacking in a few ways. It does a good job of explaining how to physically balance a plane using the position recommended by the manufacturer. I would have liked seeing a discussion on how to determine where the CG should be.

The article does advise the general "rule of thumb", the typical range of 25-30% back from the LE - but this rule of thumb only applies to straight wings.

I hear you. The CG, as I understand it is where the wing chord is the thickest, so, by feel, you can get it pretty good, for a straight wing.

http://www.rcflightschool.com/SetupPDFs/CG.pdf

Dave has more information on swept wing CG as well, I can recommend his books as I have several and they have a lot of great information in them.
I'll drop him a message and see if he would be interested in explaining it for us.

Grossman56

[UK Arthur]

Cold-fail retracts

Further to my post #1300:-
This mornings retest (0630 GMT) simply confirmed post #1292 by CFIT Rob, that at less than 50°f there is a problem.
My spare room temperature had only fallen 2degrees to 47°f since last night's test, this morning all three legs deployed at first, and retracted ok, but at the next try only the mains came down, then next only the port leg deployed.

[Mark 2]

Yeah, IMO Dynam retracts are not fit for purpose. The only solution is to replace them I’m afraid. Hobbyking do, or did, a set of very reasonably priced retracts that just drop straight in and are very reliable. I can recommend them.

[quitcherbitchen]

After adding a magnet to the door and readjusting the pushrods geometry I got the bomb bay doors to work..

[themudduck]

Hey quitcherbithen, that looks good. I'll bet its awesome to see all those bombs coming out of the belly, eh? Its looks like you have a relatively simple setup (although tight) and those magnets look like a good idea.
Can you take a video as a demo?

[themudduck]

Grossman - I guess that having a full-on discussion about CG is probably "off-topic" for this thread and most of us would rather talk about the B26 here. Maybe a new thread could be started elsewhere on the squawk to really get into it, and how to set the CG on various wing types using the MAC, how to do flight testing and so on.

With the B26 I think that some of the variance I've seen with the balance point people are going with (55 to 75mm) comes from "Where to measure from" - because the front of the wing has a fillet where it joins the fuse so it's hard to know where to put your ruler. In otherwords it can easily vary 5mm or more depending on exactly where your starting point is.

[rifleman_btx]

After adding a magnet to the door and readjusting the pushrods geometry I got the bomb bay doors to work..

I like it! Awesome job! On to the cg note, with the cg being a larger issue with this plane. I feel it's pretty relevant. As well as everyone been finding the sweet spot to be in a 5mm range from 65-70. So all in all I guess we shall go back to the b26 and make sure everyone gets the proper fixes if needed. As it looks like maybe dynam made some adjustments on their own in regards to the horizontal stab, seeing some not needing the shims. If that's the case, thanks for listening dynam!

[capecoral]

With all the painting mods can any one suggest a good tape or method that will not peal off the silver???? I have a yellow painters tape for "gentle surface masking" but do not dare try it????

[fhhuber]

EPO is the next best thing to teflon, so anything that sticks is likely to peel paint.

Damp paper towel or weighted paper works for masking. If using the weighted paper you have to use care about angle of spray to prevent lifting the paper edge.

[UK Arthur]

The CG position

Mudduck raises a valid point about the wing-to-body fillet; it blends in to the body on a tangent, so is open to error.

60mms back from the straight portion of the wing leading edge is a joint line running between fuselage and engine nacelle(s). I used that as my reference for easy consistency.

This model is tolerant of CG position because of its "shoulder wing" - more tolerant than a mid wing or low wing set up.

[RRHandy]

I have used this, low tac and can be reused. R.

https://www.amazon.com/gp/product/B001OO3JQ8/ref=ox_sc_sfl_title_8?ie=UTF8&psc=1&smid=ATVPDKIKX0DER