Official Dynam 1500mm B-26 Marauder Thread

[themudduck]

Hi All,

New to this site. I just built and flew my Dynam B-26. It took off fine, but pulled hard to port requiring full aileron trim and some rudder trim to get it stable. Then I had to crank in the aforementioned elevator trim. to get the nose level. Once I did that I found the plant to fly sluggishly at anything less than 3/4 throttle. My guess is that the deflection on the aileron and elevator was providing a lot of drag.

When I throttled down to try an approach I was greeted with a tip stall and almost lost her. Fortunately I was at least two mistakes high.... Then I was a little shaky and forgot to drop the flaps and made a hot landing, losing a prop to the grass when I went off the end of the runway.

My CG is currently at 60mm with the tail weights still in. I think I will try to put in the elevator shim to correct for the down trim. However, has anyone had the experience with the roll issue? I have 2mm of aileron in each side to correct.

Dear Ah,

There's a huge amount of discussion about this plane's "problems" here on the Squawk - and you'll also find some strong opinions with differing points of view. I agree with much of what XViper said but I'll give you another opinion.
(and - look through the older comments here, starting back when we first started flying it and posted "first impressions" - around the page count of 20 or so.)

This model is definitely heavy when set up "stock" with a 4000mah battery and those tail weights. You can improve it... remove the weights and use a smaller battery and you can lower the overall weight a few ounces. Hauling extra weight certainly doesn't ever help our models, and especially with a plane that had the nickname "the Baltimore *****" due to its lack of support (small wings for a bomber). With a lighter plane, the motors don't need to work as hard and you'll still get good flight times. I use a 3600 and I get 8-minute flights with plenty to spare. I can go up to 12 minutes.

Most of us agreed that the model needs "up" trim. You can fly it with the elevators up, but it can be permanently fixed by shimming the entire TE of the stab up a few mm. (there was a huge argument here about whether that was necessary). BUT...the model is VERY sensitive to elevator and you definitely need to cut down the amount of elevator throw. I nearly crashed mine on the maiden flight when I snap-rolled it just by pulling back on the stick in the first turn. After the mod and with small elevator throws, mine flies perfectly fine at lower throttle settings. I never have any problem with stalling unless I really force it, on purpose.

For me, the thing that made the most difference was cutting back the elevator throw, and always using takeoff flaps and landing (full) flaps, because flaps will help the plane avoid a stall at lower speeds. They work great.

Here's a quick video I made early on (Oct 2017~) to illustrate the elevator throw and also how it takes off and lands from grass without any problem. (I replaced the stock wheels with thinner ones, and a slightly larger nose wheel - see the pic)

As for your roll, not sure. Maybe one of the nacelles is crooked? One might not be glued on correctly. Some Dynam planes have poor assembly that the modeler needs to correct. (for example, some of us discovered the flap horns weren't glued on.) I corrected a number of problems with mine, but the nacelles were straight. Others here have reported differently! Once you fix these things, Dynam planes are great - I enjoy my B26 and P61 a lot.

[themudduck]

Why does this thread put two different font sizes in? I didn't do that! In fact, I went back in and fixed it, but it still posts with two font sizes. Its aggravating.

[Ah's Availble]

Thanks guys. I did sync the throttle, but I don't recall two beeps. This is my first Dynam twin. My others are Flightline and Freewing so no issues with those. Appreciate the help.

[Phantom]

Hi All,

New to this site. I just built and flew my Dynam B-26. It took off fine, but pulled hard to port requiring full aileron trim and some rudder trim to get it stable. Then I had to crank in the aforementioned elevator trim. to get the nose level. Once I did that I found the plant to fly sluggishly at anything less than 3/4 throttle. My guess is that the deflection on the aileron and elevator was providing a lot of drag.

When I throttled down to try an approach I was greeted with a tip stall and almost lost her. Fortunately I was at least two mistakes high.... Then I was a little shaky and forgot to drop the flaps and made a hot landing, losing a prop to the grass when I went off the end of the runway.

My CG is currently at 60mm with the tail weights still in. I think I will try to put in the elevator shim to correct for the down trim. However, has anyone had the experience with the roll issue? I have 2mm of aileron in each side to correct.

Ah, the mods that Mudduck and others have done, like shimming the horizontal stabilizer, removing the tail weights I have also done in the pursuit of weight reduction on this plane. She has high wing loading much like the original. One additional mod I made was to deepen the battery bay by cutting a hole in the back which opened it up into the bomb bay part of the fuselage that some folks have actually modified to open, I did not. This extra inch and a half allows me to use the 4000mah batteries, more common to find than the 3600mah, and still have my perfect CG. When I got her flying straight and level with these mods, I still wasn't happy with the requirement for high throttle settings to turn her. Some folks mention flying her with take off flaps to prevent tip stalls, I went a different route.

[Phantom]

By dropping the leading edge of the outer 1/3 on the wings, and installing wing fences on top I've eliminated the wingtip stall characteristics in all but the most aggressive of turns. You can make any plane have an accelerated stall in a turn if you yank and bank hard enough but this mod changed my experience with this bird, reduced the power setting requirements for safe flight, and increased my time aloft.

[borntoolate]

I have built two of these B-26s from Dynam. There are details and pictures on my Blog on RC Groups:

https://www.rcgroups.com/forums/showthread.php?3074855-B-26-Valkyrie

If you don't mind modding your plane to suit your own flying style, there are lots of mods to do.

Personally, I was unhappy with this underpowered plane. But I like bombers so I made the mods that I thought were necessary for me:

Dynam planes are sort of the "bargain level" planes. If you take care to fix their various quality control issues, you can end up with a very nice aircraft. I decided to build the green B-26 with some mods:

1. Upgraded motors
2. Upgrades ESCs
3 Remove and upgrade the chronically inferior Dynam landing gear
4. select a scheme from the 497th BS, 344th BG

After correcting the various quality control issue - ill fitting parts, loose weights and loose magnets. I removed the stock motors and installed a couple of 11Hobby Bearcat motors. I also added some new 60 amp reversable ESCs from Hobby King. The stock Dynam landing gear failed (surprise, surprise) on the very first day of the build. I removed the stock gear and installed Freewing MiG-21 retracts. I paired these up with some Oleo struts from RC Castle.

The plane now flies very nicely - without having to run 3/4 to full throttle all the time.


Bob

[Ah's Availble]

Thanks for the comments.

Phantom - I like the idea of the leading edge mod. I considered adding some washout to address the tip stall, but was concerned about getting the right twist in. I like the notch idea and it doesn't change the look too much. Did you use a wire to get the uniform cut?

Bob - Read somewhere that the Dynam retracts can be used if the end points are increased. When I first cycled them, they were not working right. I increased the endpoint and have had good luck so far.

[Woodcock]

Interesting that you posted today about this plane. I flew mine this morning for the first time this year. I've had it for a couple of years. Mine has both weights in the tail and all retracts have been replaced by left over retracts from other planes that I had laying around. The original retracts were problematic whenever the temperatures outside got below about 60F. I just checked my trims for today's flight and the AIL trim is almost dead center. The ELE trim is actually quite a bit DOWN. I guess if I took out the weights, it would be more neutral, but it's been flying quite well for me for 2 years, so I'm not changing anything. Rudder is slightly off center for better ground tracking. This plane (IMO) is a bit underpowered and should be flown at high throttle most of the time. I fly mine at 3/4 to full throttle the whole flight. Below that, the plane goes too slow in turns and drops a wing badly and stalls. Keep the throttle high and it will fly just fine. It has been noted that the wing doesn't sit flush at the saddle. You can see this in my video when the plane is on the ground. Some guys have shaved foam to make it flush, but mine flies fine, so I didn't bother. Dynam is an "economy" brand and I expect some flaws.

Here is the flight from a couple of years ago:

I wasn't going to post this video as it's "old news". I took it just for my own records. This morning's flight was in very strong winds and high wind gusts. I should not have used 1/2 flaps for take off in such high winds as the wind nearly flipped it over as it took off. Other than that, it has no adverse roll tendency.

That sure is a pretty place you fly there Xviper. I have one of those in the box, have never built it. We don't get a lot of green in our flying areas in SoCal. I'm tempted to build it. Why is it so heavy?

W

PS I enjoyed the vids mate.

[xviper]

That sure is a pretty place you fly there Xviper. I have one of those in the box, have never built it. We don't get a lot of green in our flying areas in SoCal. I'm tempted to build it. Why is it so heavy?

W

PS I enjoyed the vids mate.

Thanks. It's in a leased piece of land on the edge of a farmer's wheat field. They water it from a little creek that runs along side of the clubhouse and mow it every week. It's wide open spaces and the farmer will even look for your plane in his field if you lose it and can't find it and he'll bring it back to the clubhouse. Only thing is, it's 60 minutes drive from my house one way. My other field has a GeoTex runway but it's located on the edge of a gas plant. The pond in front of us is effluent from the plant and the ground beneath us is so contaminated, it can't be sold without millions $$ in cleanup. It's only 20 minutes from home. I guess there's good and bad with each.

I'm not sure why it's as heavy as it is. When you pick up the pieces to build it, it doesn't seem heavy at all, but once it's put together, the whole thing does have some heft to it. In reality, it's not a bad flying plane. It even looks the part in the air. It must be flown at higher throttle to avoid those nasty stalls in turns and to prevent it from the slow speed wallow. Sure, I could have modded it up with more power and changed the wing so it was more stable, but then, I bought it because it was relatively cheap. Better retracts was a must - didn't like having to belly land every time it was a bit cool out and one of the wheels didn't come down. Putting too much stuff into it, I may as well have bought another plane for more money that had what this B-26 needs. Some planes, you change the plane to make it a better plane. Other planes, you change the way you fly it or change the way you look at it to make it a better, acceptable plane. Till now, Dynam has been one of the latter for me. (I've had several Dynams - A-10, Grand Cruiser, DC-3, C-47 - had fun with all of them.)

[Phantom]

Thanks for the comments.

Phantom - I like the idea of the leading edge mod. I considered adding some washout to address the tip stall, but was concerned about getting the right twist in. I like the notch idea and it doesn't change the look too much. Did you use a wire to get the uniform cut?

Bob - Read somewhere that the Dynam retracts can be used if the end points are increased. When I first cycled them, they were not working right. I increased the endpoint and have had good luck so far.

Ah, no wire just an exacto knife mark on the blade with a paint marker to control the depth. Cut along the underside panel line to keep it straight. First cut is furthest from the leading edge and completely vertical, that's your base for your angle. Then make next cut on front of that cut at an angle. Remove the strip of foam and bend it over. See if that's the droop you want. If not make another angle cut and remove and bend until you get what you want. Keep in mind your goal is to only cut away enough foam to create a slightly new angle of incidence,(mechanical angle), so that you ensure that the inboard portion of the wing stalls first before the outboard portion. By drooping the outboard you ensure that when the plane has a nose high attitude such as a turn greater than 30 degrees of bank, or during your landing flare, the plane won't tip stall. The inboard portion of the wing exceeds the angle of attack,(aerodynamic angle), stalls and the nose drops straight ahead because the outboard portions are still flying, creating lift. Usually a wing exceeds the angle of attack at about 16 degrees, so half that is the maximum amount of droop you would need on the outer portions to accomplish your goal. 5 to 8 degrees. Good luck, oh and the wing fences are not required, although they help to separate the two leading edge angles and prevent any wing top vortexes from walking along the top of the

[Ah's Availble]

Thank you to all who commented on my issues with my B-26. I synced the throttles after waiting on the two beeps, found and corrected a slightly drooping flap, shimmed the horizontal stabilizer 3mm at the rear and what a difference. It flies great. My second flight was night and day from the first. I had a blast flying it for almost 8 minutes before dropping full flaps and making a perfect landing. It is hard to believe that 3mm could make such a big difference in performance.

Just for fun, I took the opportunity to attach two control horns on the outer edges of the underside of the turret and added a servo between the rudder and elevator servos. The setup uses two pushrods connected from the servo to the control horns. I cut the fuselage along the invasion stripes and removed one side of the fuselage exposing the slotted area that acts as a bearing surface for the flange at the bottom of the turret. Using the existing opening for the rudder and elevator pushrods to run the new pushrods, I set it up so it would move with the rudder servo in the opposite direction. It was fast, simple, and I didn't have to modify anything on the plane.

I attached a sketch of my modification to the turret for reference. I do recommend some graphite in the bearing area before closing up the fuselage.

[themudduck]

Thank you to all who commented on my issues with my B-26. I synced the throttles after waiting on the two beeps, found and corrected a slightly drooping flap, shimmed the horizontal stabilizer 3mm at the rear and what a difference. It flies great. My second flight was night and day from the first. I had a blast flying it for almost 8 minutes before dropping full flaps and making a perfect landing. It is hard to believe that 3mm could make such a big difference in performance.

Hey there, its wonderful to hear your results (a great-flying plane), that's terrific news!
A lot of us have posted here about this (back in the olden days), but not everyone believes us! So now we have another confirmation.

Your turret mod is very interesting as well. Great job!

[AirHead]

I watched a doc on this plane and it was a handful. They had to land it at 100 MPH otherwise it would have big issues landing. I can totally relate to having to modify Dynam planes. I spent lots of time modifying Dynams, but those awful and unreliable Dynam retracts create anxiety when you don't know if they will work every time. It's a heavy plane and I don't know how many Motion really sells. Dynam doesn't have a problem going after different models though. I'm currently not flying, but when I get back, I'll wring out the Dynams....

[Mad Baron]

I'm planning a repaint on my B26 and what would be the best way to remove the turret?

[borntoolate]

I'm planning a repaint on my B26 and what would be the best way to remove the turret?

I did not remove the turret. I carefully taped around it.


Bob

[themudduck]

Its been a long time since I first got the plane, but I remember when I was fixing it up I tried unsuccessfully to get the turret off. So what I did was, I just pried off the plastic cover. Then I was able to re-mount the guns the way I wanted and touch up the paint.
I never did figure out how to get the whole turret off!

[Ah's Availble]

Hi Mad Baron,

On mine, I cut the fuselage along the invasion stripes on the co-pilot's side of the fuselage from top to the middle of the fuselage. I then removed that chunk of the fuselage. This exposes the slotted area that acts as a bearing surface for the flange at the bottom of the turret. The turret then slides/pops out. After putting it back and gluing it in place I used some Spackle (Thanks Pilot Ryan and Captain Mike for the tip) to smooth the joints and a little flat black and white to match the paint and she was ready to go. Suggest you check out my turret mod if you remove it. It was simple and looks cool when taxiing or just sitting on the flight line to see the turret rotate.....

[Saltydawg]

If you don't care about your gun turrent not rotating and don't want to cut a chunk out of your plane just cut straight down around it and glue it back on.

Also you could just tape the turrent and gun barrels.

[Tonydoright]

Reading through a bunch of data i like others had a completed B26 head straight south after take off. Recovered and landed be it rough. Did the shim and worked perfectly. My question today is deflection of flaps. Take off and landing degree. Can someone give some insight to how much to setup? Many thanks!!!

[themudduck]

Tonydoright, please explain what happened - "headed straight south" doesn't make it clear. The elevator on this model needs to be set up so it doesn't move much - no more than about 3/8 inch each way. You may have used too much control throw on the elevator, if it was very sensitive... but I don't know what you mean by "headed straight south".

The flaps prevent the plane from stalling at low speeds, they don't make the plane do anything odd. I used about 25% down for takeoff and 100% down for landing. ' Degrees? I don't know, maybe 20 degrees and 60 degrees...