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Author Topic: FreeWing Venom (DH-112)  (Read 129 times)
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Konrad
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« on: October 13, 2021, 05:59:44 PM »

This will be a redux of the Ready 2 Fly DH-112 Venom I flew 8 to 10 years ago. This model is now marketed through FreeWing and sold in the USA by MotionRC.
From memory the model I flew was the camouflaged Venom with the 6 bladed 90mm Freewing fan driven with an out runner motor using a 6 cell Zippy 5800 mAh battery. Back then this proved to be a real nice flying EDF as it actually flew on the wing. Also the inlets made for a rather nice inlet noise. It still had the banshee scream of the low blade count rotor but it wasn’t as bad as its contemporaries.

Somewhere along the line Freewing added a 12 blade EDF to get rid of the banshee scream. This worked but at a high cost in performance. Current draw went up, flight times dropped and battery life suffered. Those of us that have been flying EDF since the late 80’s know that efficiency is key to performance, not current daw. FreeWing has finally realized this themselves as the latest iteration of EDF jets are all coming with a lower blade count EDF unit and are sporting inrunner motors.

What got me to take another look at the Ready-2-Fly/Freewing DH-112 Venom was Freewing's introduction of the 80mm T-33. This is a the best flying foamy ARF jet period! This got me to think about the straight wing, first generation sub-sonic jets. I was surprised at the lack of EDF models that meet this requirement. I then recalled the Ready-2-Fly/Freewing DH -112 Venom.

Looking on the MotionRC site and noticed that they claim that there are some structural improvements. I was looking forward to these as I recalled that the Ready-2-Fly DH -112 Venom of 10 years ago suffered from excessive wing flex at the wing to body joint and that the fuselage booms failed prematurely.

Looking at my “junk drawer” I noticed that I had an old Freewing 90mm EDF housing (maybe from my original Venom), an 11 bladed WeMoTec impeller, Neu motor 1410/2Y SE and Castle Creation Talon 90 ESC. As I had all the components for the power system I choose to buy the Venom ARF plus version. This version is sold at a discount without the power system. The full power package is a better value, but if you have the components already, the ARF plus can be a viable option.

I assembled the power components and was surprised to see that with a fully charged battery (25v) I saw a current draw of 98 amps. Per the spec sheets I was over driving the components by about 10%! To address this I added a heat sink to the motor and placed the ESC in the inlet with the cooling fins seeing the airflow (with the Talon caps in the battery compartment). In practice this worked great! With a 6250 Roaring Top 6 cell battery I had the power to go vertical for about 550 meters before loosing airspeed and stalling. Cooling was very effective as I was able to fly 6 batteries back to back with the ambient air temp of 27°C, the ESC never complained. You have to love the efficiency of the light airframe and the straight wings as flight times were an honest 6 min, I have my throttle set for 3min and 40 seconds and I land with 28% to 32% energy left in the battery. (This results in a flight time that is almost double that of my FreeWing Mirage 2000 with the same motor)! Oh, the sound of the 11 bladed WeMoTec and the Venom inlets results in a very nice turbine sounding flight. Unfortunately it sounds like a modern turbine not like the early turbines of old.

Unfortunately I’m sorry to report that I didn’t see any structural improvements over the Freewing offering of ten years ago. The tail boom receptacles still have the same flaw that don’t support stainless steel tubes. This allows the booms to snap at the part line on just about any landing, even the perfect ones! The fix is to encapsulate the tube with a cover plate for the full length of the tube. I use some plywood and foam tack glue. I need to thank my test pilot Matt for coming up with this fix.  (See drawing attached).

Unfortunately there is also a fatal flaw in the structural design. That is that the square wing receptacles are grossly undersized (too short) and inadequately supported in the fuselage foam. The wings will flex and drive the receptacle through the bottom of the fuselage resulting in the wing departing in mid flight. Both of my wing receptacles were only glued in with a small single glue bead on one side of the square receptacle. My wing failed on about the 20th flight in a level high G turn onto final. One can’t go with a carry through design of the spar as it will interfere with the EDF unit. The fix will be to add spreader plates to the end of the receptacle glued well into the foam structure of the fuselage.

Even with my low power set up (under  2.5KW  98Amps) the Ready-2-Fly/Freewing DH -112 Venom has more flight performance than the design can structurally tolerate. This model as shipped can’t be flown as a performance ship doing any of the classic vertical pattern maneuvers, this includes loops with the power pulled back on the downside. Forget the idea of performing any snap maneuvers!

I was getting real comfortable having only flown the Ready-2-Fly/Freewing DH-112 Venom for about 20 flights over a 2 day period.  When the wings failed. I contacted MotionRC about the structural failure but have received no response. I can’t blame them as there is no way for them to really know what if any abuse the wing was subjected to prior to the failure. I can only hope that they will ask Freewing to add a lot more glue to stainless receptacles. I know Freewing won't redesign the boom and wing attachments. It will be up to us real modelers to correct these design flaws

Now those of you that have followed my other threads about MotionRC know that I have a love hate relationship with MotionRC. This can basically be traced to my frustration with them not adding adequate documentation to there sales page for known issues that they themselves have found or noticed. With the Ready-2-Fly/Freewing D -112 Venom they have added under the support tab, some control surface set up values that are sorely missing in the Ready-2-Fly DH-112 Venom manual. I have to salute MotionRC for this effort. They should have this kind of support for all the Freewing products that have gross short comings in the manual. I’m thinking of the control set ups for the Mirage 2000, those in the manual are just dangerous!

While I hate to say this, with the structural design flaws the Ready-2-Fly/Freewing DH-112 Venom relegates this to a do not purchase model. Now with that being said, I’ll order another when they become "in stock”, as it has that much potential! I know this is just check book modeling! But I think I have an adequate solution for these structural short comings. I will try to document my solutions when the replacement Ready-2-Fly DH-112 Venom becomes available. As it is now all I have a is a pile of small foam parts, not very informative!
 
All the best,

Konrad
Attached files Thumbnail(s):
FreeWing Venom (DH-112)
FreeWing Venom (DH-112)
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Cut it twice and it's still too short!
Konrad
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Kudos: 39
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United States United States

Posts: 2,293


Topic starter
Measure twice cut once



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« Reply #1 on: October 17, 2021, 10:45:35 AM »

I should define “high G’s”. In this case I’m calling a 60° banked level turn “high G’s” (2G’s). This is based on General Aviation. Now I "FLY" my models, that is to say they rarely spend much time straight and level. Straight and level is about as exciting as watching paint dry. I like performing slow and high rate roles across the field. Doing these “correctly” means that the wings are subjected to both positive and negative one G’s. Even at this low a G loading will stress poorly designed and manufactured wing attachments and spar systems! That is cycle loads will fail inadequate glue joints. Also they will also weaken poorly supported foam.

Yesterday I saw a well used DH-112 at the field, as noted by the nose “modifications”! I really love seeing the Venom in profile. Love the low level high speed passes with bulbous front end trailing the small dual fins. I love this look so much that I ordered my replacement, its on the slow boat from China (MotionRC won’t sell to me).

Now a problem I as an experienced modelers have is that I often forget the kind of mistakes that a novice flier makes. The DH-112 I saw had some scary issues as it was set up straight out of the box. The first problem was that the nose wheel is Y’d (actually W’d) to the rudder. This almost guarantees a snap on take off as the nose gear is far to responsive, often forcing a premature lift off! One NEED’S to separate the nose gear steering from the rudders and give the nose gear its own Rx channel with the throw cut down to less than 40%. Short of this, or concurrent with this, move the nose gear steering pushrod as close to the servo axis as possible. A 6mm arm is still too large!

On the subject of servo arms I can’t for the life of me understand why Freewing sets up the model with such large servo arms. This results in way too much surface movement! Please move the pushrods towards the servo centerline at least one servo arm hole! Try to set up you throws so that you are using 100% of the servo’s resolution. this is even more critical with the low quality servos used by Freewing. We/they are asking a lot from a $12 servo. Please help give the cheap servos a chance and use proper mechanics!

Out of the box the elevator and ailerons are way too fast. Please set up the Venom per the cheat sheet given by MotionRC and set up the radio to allow for the servo to move its full range (100% to 120%)  at these values. The way Freewing sets up their models leads me to thing their test pilots aren’t very good or worse it is a concerted effort by Freewing’s management to get you to buy a second ship after you have made a smoking hole in the ground.

Back to the Venom, set up the ailerons for differential (more up movement than down). With the small rudder area of the Venom you will want more than you might otherwise think (I’m close to 1.7:1).

The Venom is a bit odd with its CG requirements*. I found that the factory CG of 110mm was the best compromise. Note the word compromise, all CG placement is a compromise and has a large personal component to it!
While the Venom flew better with the CG further aft. I found that the ability to come out of a spin was hampered if the CG was much further aft than 110mm. Now rolls were a lot easier with the CG at 120+mm. Also the landing might have been a bit smoother at 120mm. But the risk of a spin at low altitude makes the aft CG dangerous.

Flying technique. As a result of the large LE wing sweep there a large rudder induced roll coupling. It might be wise to add an aileron mix to your rudder (I was using 18% mix). As a result of the 110mm nose heavy CG the model will have to land faster than it will fly. I use 80° flaps ant about 20% throttle on landing. Set up for a nose high stance (nose gear 50mm to 75mm higher than the mains) over the threshold and just wait for the plane to slow down. As the plane slows down add a bit of elevator to maintain the slight nose high attitude. When the mains touch there will be no bounce. If landing with too high a nose there won’t be enough elevator to arrest the sink. If landing level there will do too much speed and the model will bounce back into the air. The landing is where we separate the men from the boys. This is true for all aircraft!

*
With the Roaring Top 6250 batteries I had to remove the aft stop and allow the battery to overhang into the aft void by 10mm.

All the best,

Konrad
Attached files Thumbnail(s):
Re: FreeWing Venom (DH-112)
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Cut it twice and it's still too short!
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