Dumas F-105 RC Conversion

cyclone3350

Master member
It depends on your project. For something this tiny, the servo can drive the retract directly if it is cleverly set up. Basically so that the impact load on landing doesn't get transmitted into torque on the servo. For the mains, the retract direction is perpendicular to the direction of movement during landing and the balsa wheel pants hit the balsa on the wing and stop the gear from traveling further. For the nose gear, the retract is supported with multiple structures that prevent over-travel and is designed so that the loads during landing push the retract open and into these supports. For both the weight is supported by a laser-cut plywood structure and the servo just provides the torque. It's hard to see the support structure because it is so buried, but you can see it if you look. I would not recommend using this technique unless you are confident about being able to evaluate the loading and are willing to destructively test a servo to see what it can actually stand up to.

The picture in my previous post does not have power, so you can see how the structure and design of the retracts locks them extended under load.

View attachment 206151 View attachment 206152

I think I've seen someone using this technique for a foam board FT P-51 on these forums, but I would not recommend using this kind of design for a 64mm EDF. I do put retracts on just about all my 64mm EDFs, though, using mechanical retracts like these:

Mini retractable landing gear for kt board rc airplane Sale - Banggood.com

So long as you can fit them into the wing and you make sure you are getting enough travel to lock the retracts, they are very light-weight, versatile, and reliable. Unfortunately, they have long lead times and are much more expensive than they should be.

Thanks for the reply. U just reminded me that I bought a several sets of mechanical retracts when E-flite made them for an F-15 many years ago. They might be too big for the F-4, but I did not know about the ones on Banggood. I will think I will order a few just to have and see what I can put them in. These R a little smaller than the E-flites.
 

telnar1236

Elite member
Finally got the nose gear steering working to my satisfaction. The first taxi tests were a success.
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telnar1236

Elite member
I finally was able to do the coat of primer. Unfortunately, instead of grabbing my can of gray primer, I grabbed my can of normal gray spray paint, hence all the bubbles and weird drips when it didn't quite stick like I expected it to. So, looks like I am waiting for it to dry and then grabbing the sand paper to take most of it off and replace it with actual primer/filler (the gray enamel paint is too heavy for more than a thin coat and does not sand well).
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cyclone3350

Master member
I am wondering if this is a first for someone taking this Dumas display model and converted it to an EDF. Absolutely looks superb.
 

telnar1236

Elite member
I am wondering if this is a first for someone taking this Dumas display model and converted it to an EDF. Absolutely looks superb.
Thanks! I'm definitely happy with how it turned out.

I didn't find any other threads on Dumas EDF conversions when I looked prior to starting the project, but I would be surprised if I was the first. The conversion was very straight forward.
 

telnar1236

Elite member
The F-105 is finally ready for its maiden flight! I applied a few more decals and installed the control horns and everything seems to be working well. Hopefully I'll have maiden flight footage soon!
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telnar1236

Elite member
Unfortunately it doesn't fly as intended and is not going to. I need to stop taking the rated thrust values for cheap EDFs as accurate. This problem resulted in a lot of lost time on my F-104 project and means this one is a failure. The takeoff run didn't work with the rated a 2s pack when I went to the rc club today, so I took it to a park later and tried it on 3s. This gave it enough power, barely, to get off the ground and in the air it was under-powered and badly nose heavy (the plane was intended for a pack 2/3 the weight of the 3s pack). The EDF unit then failed in flight as it was not rated to 3s and I had to dead stick in, breaking the nose. Between the failed take-off attempt and the flight and crash, I tested the thrust from the EDF unit on 2s, and it was only 93g as opposed to the rated 260g. As you might imagine, a TWR of 0.3 does not work in an aircraft designed for a TWR 0.8. The issue is not the inlet ducting as it is smooth and the combination of inlet ducting and cheater inlets adds up to 135% FSA.

As you might imagine, I'm a bit annoyed, but you live and you learn. I don't think I'm going to rebuild it as removing and replacing the fan with a better one would be quite difficult and result in a lot of lost time and I don't want to deal with vacuum molding new styrene to replace the nose from the kit I destroyed. The good news is that I actually bought decent fans for the other kits. The F-4 will run on 3s and I've already tested its fan at 450g (out of 500g rated) thrust. In the slightly larger F-4 model, this should be perfect. I'll probably carefully remove the ESC and receiver and make a solid wooden nose then use the F-105 as a static display model, as Dumas intended.
 

cyclone3350

Master member
There for a while I got into this UMX phase. This was by far, the most challenging RC builds I have ever done. I had a few unsuccessful attempts myself. Especially when I try and do something complex. This P-38 was disaster and did not have much left to make it a hanger queen. the Dc-3 flies very well, but has just enough power for the calmest of days. I put a fair amount of flights on it, but I will not push my luck any more . I t is now retired to the workshop ceiling. Your 105 will do well as a display and looking to forward to the F 4.
 

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