Building with DTF - Part 6 - 26 Nov 2017 update and the way ahead

Hi Everyone -

This article was originally written in Nov 2017 as you can see in the title. More recently, I shot this video discussing my current park jet build philosophies moving forward, however I thought I would keep the text from the original post as a record of how I arrived at my current mind set😊

After learning many lessons from my original all DTF build of this Mig-35B, I have recycled it for parts and have since built several more planes with DTF and a combination of other foams, primarily MPF (model plane foam) and Depron.​ I logged 115 flights on this plane before retiring it, it was a blast to fly and served me very well in learning how to build with DTF and inspire new ideas😊

Not including the black, grey and white Mig-35B in the video above, I built these four planes as I progressed in my DTF build journey.

From top to bottom, RC Powers F-22 V5 built at 95% (27" wingspan), RC Powers F-18 V5, NAMC Mig-35B built at 90% (24" wingspan) and modified RC Powers Su-30 V4 built at 85% (27.75" wingspan).  These planes are listed in the order in which I built them and I will discuss each individually and the changes I made to each.

As a quick review, one of the issues I noted with the all DTF Mig-35B was that it was tail heavy because of all the paper left on the DTF behind the trailing edge of the KF airfoils.  Also, I may not have written this in a previous article in this thread, but I did notice more longitudinal flex in the all DTF Mig-35B as the paperless DTF on the nacelles did not add a lot of extra stiffness to the plane in the longitudinal axis.  Plus it did flex quite a bit and over time needed to be reinforced with tongue depressors and some extra glue.  All which worked fine, but did add a little weight and drag to the plane.

RCP F-22 V5

Besides other mods I made to this plane the first time I built it completely of MPF, I moved the motor forward by 1" to compensate for the extra weight of the paper on the DTF and also used some scrap Depron for the "engines/nacelles" and "under rudders".

You can see in the picture above, there is still considerable reinforcement in the elevons and along the back plate.  Small sections of bamboo don't weigh a whole lot, but adding the glue to secure them does make the weight add up.  I had considered not putting the piece along the back plate ahead of the elevon hinge line, but felt I might still get too much flex as that area is not really "locked in" by any other parts of the plane.  I also have reinforcement in the vertical stabs which are also made of DTF.

Moving the motor forward did certainly compensate somewhat for the extra weight in the back of the plane, I also put my aileron and elevon servos further forward than I did in my first build, but I don't know that it tightened things up too much more around the CG, the PMI or distance between the front of my battery and the back of my motor is about the same as it was in my first F-22 V5 build which was built entirely of MPF.  I did use 5 gram nylon gear servos for the rudders and ailerons which did help keep the plane lighter.  Even with a full paint job (I didn't completely paint my first all MPF F-22, the total weight stayed pretty light at 20.8 oz/590 gr with a 2200 3S battery.

The addition of the Depron for the nacelles and bottom plate made a significant difference, the plane feels much more solid and stiff than the all DTF Mig-35B did, so I imagine it should last even longer.  At the time of writing this article, I have 101 flights on this plane and it is holding up extremely well and flies beautifully.  Having reduced the frontal drag by using DTF over MPF has allowed me to fly this plane easily with a small quad racing motor which also helps to keep it light and very quick on the sticks.  Moving the motor even further forward also makes the plane feel a bit more balanced and responsive in all three axes.​  Here is some flight video of it after I had it "dialed in" the way I like it.  The F-22 V5 remains my favorite of all RC Powers V5 series.

RCP F-18 V5

This plane I built primarily of DTF and used some scrap MPF for the nacelles.  In addition to the mods I made to my first F-18 V5 which again was built entirely of MPF, I made the following mods

• I moved the motor forward by 1" to compensate for the weight of the paper left on the DTF behind the trailing edge of the KF airfoils and to see if I could improve high alpha performance;
• I increased the size of the LERX again primarily to see if high alpha performance would be improved;
• I added the "dogtooth" Super Hornet leading edge on the wing similar to the RCP F-18 V3 (mostly because I like that look better :)); and
• I shortened the vertical stabilizers in height, but increased them in depth at the top.

To make the last three changes, I printed the parts of the F-18 V3 plans I needed at 91% so that they would be the same proportion as the V5.  Unfortunately, none of these changes made any significant difference in the high alpha performance, but it did make the plane much smoother and even more balanced in the air, so I'll take that :)

The MPF nacelles do help with longitudinal strength, however, I still ended up with a lot of reinforcement in the back end in the elevons, back plate and vertical stabilizers.  Hopefully you can also see I put my servos as far forward as I possibly could to help compensate for the extra weight of the paper in the back end.

Overall, this plane feels as solid as the all MPF build, but is much smoother and quicker.  I can sense the drag reduction by using DTF for the wings, fuselage, canopy, vertical stabs and elevons, but still not as light as it could be.  It weighs about the same as my all MPF build, with a significant reduction in drag and is stronger and stiffer than the all DTF Mig-35B I built.  Here is some video of it with a pretty peppy motor setup 😊

NAMC Mig-35B built at 90%

I built this plane at the smaller size primarily because I had been playing around with an updated RC Powers T50 V1 (that didn't go terribly well, perhaps I'll write about that another time :)) and I saw that with a small quad racing motor, the T50 really moved along as it is small with a 24" wingspan.  I have become quite interested in testing some of the powerful quad racing motors as they are much lighter than most of what I currently use in my planes and very powerful for their size.  

So taking what I learned from the F-22 and F-18, I built this primarily of DTF with the nacelles and vertical stabilizers made of MPF.  I moved the motor forward by 1" to compensate for the weight which seemed to work out quite well, of course with a 24" wingspan it is quite smaller than the full size, so things still stay pretty tight around the CG anyway.  However, I still ended up with reinforcement in the back plate, elevons and the vertical stabilizers.  I still put some reinforcement across the back plate, but I think I could have done without it in this plane as it is locked in pretty solid with the MPF nacelles and vertical stabs.

This plane is very stiff and strong and is an absolute rocket with a peppy quad racing motor setup :)  In this video, I do some gabbing about the prop and motor at the start, the flying starts at about 1:45.

85% RC Powers Su-30 V4

I built this as a bit of a "beater" plane for the winter and to experiment with a slightly smaller wingspan to evaluate different quad racing motors I have ordered for testing over the coming weeks and months.

This plane has the fuselage, wing plate and back plate made with DTF, the nacelles and vertical stabilizers made of MPF and the elevons made with Depron.  In the previous builds where I have used DTF for the elevons, I have ended up with a couple of pieces of reinforcement in each elevon which of course adds weight.  I found enough scrap Depron to make the elevons which at this size require no extra reinforcement to still have a stiff control surface.  I still have reinforcement in the back plate and the vertical stabs, but reducing the weight in the elevons did help with reducing the tail heaviness I still saw in a couple of the other planes based on where I needed to place my battery forward to get them to balance.  

I didn't move the motor any further forward on this plane as it is already pretty far forward.  So this plane flies really well, is very strong and thus far durable.  Since most of the thinner DTF is in the fuselage and wing, I don't sense that the thicker vertical stabs, intakes and elevons create too much drag.

Here is some video of it flying with the same power setup I used in the F-22 V5.

So taking lessons learned from all these builds, I got thinking about what I could do next to build a plane that was light, strong and combined the stiffness of Depron and the lower drag profile of DTF.  I should say I am kind of "hording" my remaining six sheets of hobby grade Depron, so I was a bit hesitant to use it at first, but I'm very eager to see if this takes building with DTF in combination with another foam to the next level :)

I have already started another Mig-35B, this time built again at 100%, here are all the parts cut out.  This took two sheets of 20x30" DTF and half a sheet of 27"x39" Depron.

So in this build, the wing plate, fuselage, canopy, back plate and of course KF4 airfoils will be made of DTF, the nacelles, vertical stabilizers and elevons will be made of Depron.

I have moved the motor forward by 1" to compensate for the weight of the paper on the DTF behind the leading edge of the KF.  I won't put any reinforcement in the back plate, I think once the plane is together and the back plate is locked in by the Depron vertical stabs and nacelles, it should be pretty solid.  Since I don't need any reinforcement in the Depron elevons and vertical stabs, I will also save that weight over the other builds.  

I'm excited to see how it makes out, I currently have a 100% Mig-35B in my hangar built with Depron and MPF and it moves along quite well with a peppy little quad racing motor, so I am interested to see if I end up lighter and faster (less drag) with this current built.  Here is some video of the Depron/MPF Mig-35B.

So lots of lessons learned again building with DTF and other foams.  I think since I have them, making the right choices for weight and strength I can save a lot of money building with more DTF, it is readily available to me and I should be able to stretch my supply of Depron and MPF even further 😊  More testing and evaluation to come in the near future 😊

Since originally posting this in the old NAMC blog, I have finished my Depron and DTF Mig-35B and have over 100 flights on it using it as a test bed for several different quad racing motors. Here is some flight video of it with my favorite quad racing motor setup thus far😉

I also recently shot this "Table Talk" video summarizing some of my lessons learned and how I have changed my build philosophy of my park jets with respect to foam, motor and servo choices.

Park Jet noise...the "other" sound of freedom😎
Cheers,

​Scott