Dynam Spitfire

[Daren Cogdon]

I bought this Dynam Spitfire from an older lady who was selling up her stuff.  After a bit of faffing, I managed to get the Spit's motor running for the first time earlier.

https://youtu.be/d7X_UXes3Zc

 

The undercarriage need work, as they won't retract fully into the wings (I think a hard landing was responsible), but I will look at that later.  If not, then I might just remove them and fly without! 

Edited August 25, 2021 by Daren Cogdon

[Daren Cogdon]

And she flew! 

 

 

 

As per the vid, she needed some nose weight to get her flying straight and level, so we added a bit of lead in the battery compartment.  Still a bit tail-heavy, but flying even better.

 

I did end up removing the landing gear, as I had read that the gear legs are quite soft and will bend with a harder landing (which I'm an expert at!) and will probably end up needing sorting every now and again.  This is fine, as an underarm hand-launch works great with it and is far less stressful! 

[Graeme White]

How much lead was added? I have one yet to fly and to be honest was just going to fly and not rebalanced as its an rtf? Was it hard to fly with no nose weight?

[MattyB]

What makes you think it was tail heavy at the outset? It looks like it was flying fine from the video... Was it tucking in a dive? Did you try a power off dive test and/or experiment with just reducing the elevator travel?

 

 

In my experience a lot of power flyers tend to fly with a very conservative CG. I have often been asked to trim out a model, and when I suggest moving the CG back (I'm very comfortable with rearward CGs from my slope plank flying wing pylon racers) people often get very scared.... "it's been like that since the test flight, that is where it said in the plan/instructions" etc. The reality is that CG is the biggest performance and handling altering variable we have to play with, and getting it right can really make an airframe sing, particularly if it is a faster, higher performance model. If you go about it in the right way (i.e. you understand the theory first and only move the CG in small increments) it's possible to transform handling in a single session of short flights at very low risk. 

[MattyB]

25 minutes ago, Graeme White said:

How much lead was added? I have one yet to fly and to be honest was just going to fly and not rebalanced as its an rtf? Was it hard to fly with no nose weight?

 

Checking the CG before flight is always a good idea - plenty of instructions have been wrong in the past, so assuming they are right can be an issue. Normally all you need to do is do a quick Google (there are plenty of threads on this model, here's a good one), but if you're not comfortable it is worth doing a quick calculation to be sure you are in the right ballpark for the maiden. The good news is that there are lots of online calculators that can help; here's two good ones:

 

• eCalc CG calculator
• RCPlanes CG calculator

Edited September 16, 2021 by MattyB

[Daren Cogdon]

7 hours ago, Graeme White said:

How much lead was added? I have one yet to fly and to be honest was just going to fly and not rebalanced as its an rtf? Was it hard to fly with no nose weight?

 

Not sure how much nose weight we ended up adding (I'll check), but it was flown on 3S (Turnigy 2200), so I think this might have been a factor, although I pushed the battery as far forward as it would go (the model was originally meant for 3S).  You might be better to try it with 4S, if you haven't already done so.  I think my model is Version-1, so it might be different from yours.

 

Prior to the first flight, I checked the manual for the CofG several times, and balanced it pretty much where the instructions said.  Of course, since I removed the landing gear (for various reasons!), this removed some of the forward weight, which no doubt added to the issue.

With the battery in place, the tail was certainly dipping downwards when we tried to balance the plane again after the first flight.

 

Anyway, positives are that it flies very well, very stable, and looks scale-like.  Also, it came down in one piece, which is the main thing.

The negatives are that the tail-heavy issue needs to be resolved, but it's not a big deal.  

 

I have another Dynam Spit to get in flying trim, so these things will be looked at on this one, too.

[Dale Bradly]

Suggestions from my experience: Run it on a 4s 2200. Perfect weight balance (factory nose weights remain) and power output. Current draw is very thrifty on 4s when flying in a scale like manner. I replaced the retracts and rejigged them to angle more fwd (at the expense of not retracting as tidy, but can't see this in flight). Glassed the bottom of the radiator area to toughen it up, and this provides a plan B to belly land if the retracts play up, or a rough strip suggests this is in order. Better that than ripping the wing open. Has subsequently been bellied in a handful of times without damage. In short, one of the best foamies I've ever had.

Found my cg was at 78mm and flies perfectly.

And repaint it because that blue is awful!

Edited September 17, 2021 by Dale Bradly

[Daren Cogdon]

I'll definitely incorporate some of those ideas on the second one.

[Daren Cogdon]

 I had another go with the Dynam Spitfire tonight.  Last time, she was still a bit tail-heavy, so this flight was a test to see if the 15g I had added to the nose would make any difference.  It did not.  So, we brought her down, and adjusted the elevator instead.  Second flight?  Perfect.  Just perfect.  She flew hands-off, and I even managed a low pass down the runway! 

 

Need to work on my landings, though!

 

 

 

[MattyB]

17 hours ago, Daren Cogdon said:

 I had another go with the Dynam Spitfire tonight.  Last time, she was still a bit tail-heavy, so this flight was a test to see if the 15g I had added to the nose would make any difference.  It did not.  So, we brought her down, and adjusted the elevator instead.  Second flight?  Perfect.  Just perfect.  She flew hands-off, and I even managed a low pass down the runway! 

 

Sorry, but I can't really see much from the new video as the model is rarely in shot. What was it about the flight characteristics that make you think it was tail heavy, and what did you do to the elevator between the last two flights - drop the rates, adjust subtrim, or some combination of the two? I still can't see much wrong in the initial video tbh, it looked like it flew absolutely fine. If the only issue was an overly sensitive elevator then dipping the rates and/or moving the control rod out a hole or two on the elevator control horn. 

[Daren Cogdon]

On 29/09/2021 at 15:47, MattyB said:

 

Sorry, but I can't really see much from the new video as the model is rarely in shot. What was it about the flight characteristics that make you think it was tail heavy, and what did you do to the elevator between the last two flights - drop the rates, adjust subtrim, or some combination of the two? I still can't see much wrong in the initial video tbh, it looked like it flew absolutely fine. If the only issue was an overly sensitive elevator then dipping the rates and/or moving the control rod out a hole or two on the elevator control horn. 

 

The guy who flew the Spitfire the first time (Mark) had to put in full down trim, as well as keep the stick forward while he flew it.  He's doing this in the video, which is why it looks like it's flying straight and level.  After that first flight, we bunged a load of lead weight into the nose (flying on a 3S battery, remember), and it was still pitching up.

 

Prior to Tuesday night, I added a bit more weight to the nose to see if that would help.  When I launched the Spit, I still had full down-trim and had to keep the stick forward, so I called a landing after a couple of minutes to see what else I could do.

 

The other chap in the second video (Steven), suggested tweaking the elevator linkage as the elevator itself was set with just a bit of up on it (which I hadn't noticed initially, as it wasn't built by me).  I flew it again, and it was spot-on.  

 

I'll get better video next time....!