Freewing Venom 90mm 12 blade EDF MK1 C of G

[MartyMcFly1]

I have finally managed to buy a second hand Venom which I have wanted for years. I fitted an Admiral 6s 5000mah to check the C of G which according to the manual should be between 105 -110mm from the front of the air intakes. However with this fairly heavy battery fitted the C of G is a further 15mm back. I watched a YouTube video made by MotionRC where it is stated that using this battery the plane should balance perfectly: however this was a later jet with the 9 blade EDF unit fitted which may well be lighter.
Has anyone experienced the same issue. Is it just a matter of adding weight as close to the nose as possible?
Any advice would be most welcome.
Best regards

[xviper]

I've had 2 of these in the past. I find it hard to believe that when you use a heavy battery like that, your CG is 15mm further "back". The recommended battery for this plane was 3600mah to 4000mah, 6s. A much heavier battery would make it nose heavy and thus, the balance point would be "forward" of the CG marks and not "back".
Splitting the difference, say the CG is 107.5mm, you are saying that you have to balance at 122.5mm? Something is not right here. Your plane should be nose heavy and that being the case, adding weight to the nose would make it more nose heavy. Why would you want to do that? If you use a much heavier than recommended battery, it should be shoved as far rearward as possible to achieve the correct balance - IE, you would add weight to the tail. I have a hard time understanding what's going on in your case.
Nevertheless, this plane will fly with a variety of weights of battery. I flew mine with 4000mah and 5000mah batteries. Back then, they were also Admirals. It didn't seem to matter with this plane. It can easily be trimmed out. Heavier battery? Moved it back as far as it'll go and use some UP elevator trim if necessary. Lighter battery? Move it as far forward as needed and use some DOWN elevator trim if needed. The thing I found was that if you fly it too slow, it'll drop a wing and stall.

[stojakovic]

The venom battery compartment is very small。I use a 770g battery with 9 blade EDF , and the CG is OK.
However, this aircraft has a characteristic that increasing the throttle will have a tendency to dive。

[MartyMcFly1]

Thanks very much for your replies. I double checked the YouTube video where Stuart, their test pilot, was flying the jet. In fact the jet had a 12 blade EDF unit and not 9 blade as I stated in my post. He recommended using the Admiral 6s 5000(First generation) rather than the later battery which was lighter and required 60grams of weight to be added near the front retract.
MotionRC cannot help without a SKU and the original order number which is frustrating hence my post on this forum. I guess it will not be tail heavy which would be disastrous on a maiden flight.
I will probably err on caution and fit 60grms of weight for the initial flights where the C of G can be checked in flight and adjustments made accordingly.

[ridgerunner]

Just spitballing here but...
Are you measuring the CG distance from the inboard or outboard side of the intake? The inboard side is significantly farther forward than the outboard side and the manual specifies to measure the CG location from the outboard side.

[Evan D]

The picture is pretty obvious

[MartyMcFly1]

The C of G is being measured as per the diagram from the manual which I downloaded from the MotionRC site. Appreciate everyone's input. Thanks

[xviper]

This is a very old discontinued model. I would have been surprised if Motion could have helped you with any documentation. Due to it's age, there are some facts about this plane that need to be mentioned.
1. 60g for this plane is NOTHING! It flies just fine with a battery anywhere from 4000 to 5000 no matter where in that small battery compartment you choose to put it.
2. Someone noted that when you throttle up during flight it can dive. This is not something that is a defect or a "bad" tendency. People have since forgotten one critical aspect of building this plane. When the 2 tail pieces are glued on, it was necessary to secure the plane UP SIDE DOWN while the glue cured. Not doing so caused the tail booms to "droop" while curing, making it imperative to add a lot of UP elevator. Even building it correctly, the elevator needed about 3 degrees of UP. That was simply the nature of this plane. (Similar to the V1 Freewing 80mm A-10. Even the V2 A-10 needed some reflex on the ELE for it fly properly.) Some people thought this was a flaw and at the very least, ignored it. BTW: The HobbyKing Vampire did the same thing - took a crazy dive when throttled up in the air. People didn't build those properly either, myself included. My second Vampire was built properly and was just fine. That experience helped me build the Venom.
3. This plane tended to balance more easily and more accurately when done up side down.
This was a great flying plane and capable of absorbing any odd CG changes. The only thing I noticed was that it was occasionally hard to land (bouncy) because it tended to float forever and was easy to drop like a stone when throttle was reduced too much (or cut) during the last few feet of altitude - then bouncy, bouncy, bouncy ........ new nose gear on the way.

[MartyMcFly1]

XViper thank you!. More interesting info to absorb. I too have two Vampires which are my go to jets. Their flight characteristics are fabulous and were the source of my interest in getting a Venom. Interestingly my Venom was supplied as parts to allow for shipping. So the booms had been carefully removed and I refixed them using FoamTac BUT not upside down. I supported the booms and used 2 pieces of wood top and bottom (G clamped) to keep them straight while curing. They both line up perfectly with the beginning of the boom moulding on the plane so I am hopeful that they are true.