Gerd, delrin venturi tube talk & suggestion

[OICU812]

Gerd,

Hello and good day to you!

1.) I took note that you mentioned here in another thread you were considering making an insert of sorts for the boom in order to reduce drag of belt against boom and so fourth to improve the operation.

For now I have done this towel roll core modification that was lightly discussed.

Just curious, I know it is not top priority but have you made any prototype designs and so fourth of this Venturi tube you discussed?

2.) I also wanted to openly ask as it has also been mentioned, could you please consider in making the main blade grip holes 5mm instead of 4mm? This would be much more accomadating to pilots who wish to try several different blades, also this would be better for stronger bolts with high power systems folks will run of course and the stresses of 753mm blades this would help to be running a 5mm bolt versus a 4mm bolt!

I and I feel others would pay a few more dollars for these slight improvements for certain!

Thanks for your time to the community!

[Gerd]

1. We have just made several tests with the perfect position of a contact damper in the boom. Milled slots in the boom for observation, tuned delrin venturis. Result: The best position of a smoothener is NOT in the middle of the boom. We have recently sprayed white laquer in a boom and have made some workbench tests. The contact marks between belt and boom were on 11-12cm from the end and on 28 cm. So if you push in a 20 cm long paper towel roll that is 10 cm away from the rear end you will be successfull. A special turned delrin venturi is not possible in this area because it is simply too thin for production. In the middle you have 5 mm space between belt and boom, at the rear end only 2mm. The paper towel roll is surely an unconventional material, but nobody is seeing that cheap thing and is is working perfect - what else do we need?

2. There were never issues with the 4mm bolts. Note that we won the IRCHA speed cup with 4mm 8.8 bolts and 2400 rpm. But I know that most blades are now 5mm with the current motto: "thicker is better".
OK, we will see how to handle that wish because blades with 4mm holes then couldn´t be used anymore.

[Mercuriell]

I think the 4mm bolts are good, if they start to bend it is an indication the head is being overstressed, like when I ran 753s at 2100 ! Better for a bolt to develop a slight curve than break suddenly or a thrust bearing race fragment or worse!

[OICU812]

Ok thanks for note on roll placement mine was inserted in middle ill need to reposition as per your findings. No big deal on 4 to 5mm holes or bolts was just a suggestion as I haven't seen any blades not able to use 5mm bolts on the 690-750mm class. Thx for info Gerd!

[smsodhi]

Originally Posted by Gerd

The paper towel roll is surely an unconventional material, but nobody is seeing that cheap thing and is is working perfect - what else do we need?

I think this is a very good and refreshing attitude from a maker of high end helicopters.
I have opted not to put the paper roll in the boom. Will this cause any problems for me in the long term, or is it only to reduce the noise from the belt slapping the boom?

[faxxe]

Just to reduce the noise.
-Heimo