High Performance MPX Foil/Self-righting Trimaran-The Test Model

Regarding the reported posts, there isn't evidence at this point to support the two complaints that the reported account was a duplicate account created only to harass, thankfully (the email address on the account has been established for at least 7 years and is published on a sail-related website, so it doesn't seem consistent with the complaint that it's a trolling account.)

However, given the direction of these posts, a quick request/reminder will hopefully help.

Let's please keep the thread about the model / boat being discussed, and please let's not use the forum only to jab at someone. That would be better done via facebook/email/ or using some other website.

Thanks very much.

 

By "o", I assume you are implying your SA stalker "Chris O"?

Now that's funny!!!....and if so, than I am very sorry to spoil your paranoia. ;-)

I have actually been rooting for you to succeed, in hopes that it would put a end to his incessant blathering on SA. It is because of him that I never registered there, and chose to post here instead. However, after your terse response to my initial post, and then your deceptive use of the term "we", in an obvious effort to seem more credible, I am reconsidering my choice.


-Rosebud

 

Let's please try and keep the threads here about the concept at hand. If someone's interest is to jab or fight with someone, facebook or another site would be a better venue. Thanks.

 

Let's all just enjoy that at least the BDNM is pretty with it, and laugh at the fact <insult towards another person removed> and just cuts back at anything that might succeed.

Also Doug, after watching that video a few times it seems maybe you'll want to be able to adjust the angle of incidence on the foils, because in the photo youve taken where it has lifted off, the actual angle of incidence might be 5 deg more that what you have it set at (and its working...) but then when it takes off and loads up you'd want to lower that, and possibly lower the high lifted, or the rate at which it flies the main hull, just food for thought, cant wait to see it fully loaded up and doing long runs!

 

Doug,
with due respect, you cannot say that the main objective of making such a big and complex RC model was to prove that foils can lift the hull. Because even flat-plate foils at an angle of attack could do the same job, just less efficiently (or more efficiently in some conditions, depending on the Reynolds number). Lifting the hull is not a difficult task, making it fly in a stable manner is a more tricky stuff. But you already know that.

A huge job of tuning the boat is still ahead of you, and it will be long time before you'll be able to start making useful conclusions. The real proof of the concept will be a video of a long and stable flight, which will show that this configuration works, and how it behaves dynamically.
After all, that is what you have said too:

Now back to work and step on it, mate. We want to see a stable flight and not another 100 pages of words, analysis and essays.

Cheers

 

agreed 100%. I have been following this thread for entirely too long. Less talk, more build. You don't need a videographer for ever single test sail. It clearly "sails", so sail it every single day, all day long (you are retired right?) and post video when its stable. I write code Doug, no one gives a crap about an alpha stage project, people always want to see working stable code or they just don't care.

and seriously take the advice of whoever told you to tune the radio down for the rudder. You have to do the same on rc helicopters as the stick is over sensitive. Its nothing personal Doug about your rc skill, it simple isn't "real world" to kick a rudder over that hard. So throw the buffering in there and make it stop skating around like a wet cat.

I, like everyone else, am very excited about your model. But hundreds of pages of banter are getting old. Just look at your post count for Christ sakes buddy..... Talk less, sail more.

end of rant.

now, GO DOUG!

 

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Thanks ,Slavi-I appreciate your comments. In order to know whats going wrong with the boat you need to know(and understand) whats going right with the design. It simply isn't correct to say that no useful conclusions can be reached now. Since day one, the main objective of the MPX foil system was to allow an oversquare trimaran to fly the main hull in conditions where it couldn't do so on wind pressure alone. And that's exactly what happened in the video. The MPX foil system ,as stated many times in detail, can work with a foiler configuration(amas lifted by the ama foil) , with planing amas or with displacement amas. It's a mistake to denigrate the fact that the foils worked-they are central to this design and did what they were supposed to do-otherwise the main hull would never have flown and the boat would simply have rolled over. That goal was realized in this first test and understanding how that worked and that it did work is critical-I've already discussed it in detail. The fact that the boat was overpowered is important to remember in trying to understand what was what in the video.
The major issues of pitch instability including the pitchpole have clearly been linked to the rudder-and that will be addressed.
There is no doubt in my mind that I made a mistake in adjusting the main foil AOI up to 3 from 2.5 degrees-that will be corrected today. I'm fairly certain(but not 100%) that the two "mush up's" were a direct result of this. I've outlined some of the other problems that are being or have been corrected including: failure of the sheeting system, loose shrouds, failure of the vang and downhaul, possible problem due to lack of purchase on the "peak halyard". In addition, the wands will be re-checked for the possibility they are too long when the boat is set up for the AOI adjustment today.
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You'll see stable flight-guaranteed. But this is not going to change one iota. I pride myself and this thread on the fact that I have addressed the design theory, the building and now the sailing troubleshooting in detail- reporting both the good and bad and what their solutions have been(or may be). I guarantee it will continue in detail and with essays(!).
Again, thanks for your comments.

 

MPX Testing and Development

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Thanks for your comments. See my last post.
I'm going to go over what my radio is capable of and set it up so dual rate and/or exponential can be switched on and off to tame the rudder. I still want to sail it without that facility in the next set of conditions-between 5 and 7 mph wind.

 

MPX Testing and Development

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Darth, see my reply to Slavi. The angle of incidence of all foils is 100% adjustable on the beach but not while sailing. Except that the dual wands automatically adjust the effective angle of attack of the main foil while sailing. I'm not sure that you understand that the "Take Off" picture was a screen shot of the result of a hard over rudder. Incredible to realize that the rudder has the power to throw a 21lb boat clear of the water-amazing. That kind of rudder induced "pitch-up" is discussed a page or two back.
Thanks for the comments.

 

Doug, the dynamics of your first tests indicate that Gary's analysis might be correct. You could give it a try.

 

MPX Testing and Development----First Flight!

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I think he might be partially right-that's why I said I was going to lower the angle of incidence of the mainfoil to 2.5 from 3 degrees. Removing the mainfoil is out of the question since it proved-beyond a shadow of a doubt*- to be necessary.
* beyond a shadow of a doubt to anyone who studies the facts. I'm not sure but I'm guessing he confused the dynamic pitch-ups caused by the rudder with too much mainfoil lift. The two"mush-ups" could be directly attributable to the 20% more lift resulting from the mistake I made in setting the main foil to 3 from 2.5 degrees AOI. The solution of removing the main foil is a bad idea based on the calculated values for lift in post 1456.
--PS- along the same lines: I'm going to be looking into whether or not the wands are set to cause the mainhull to fly too high before downforce can start-my hunch is that they are wrong.

 

I am reading your post #1456, but I am missing something in that picture. Does the rudder produce an up or a down force?
And in which post of this long thread did you calculate the equilibrium of forces and moments acting on this boat?

 

MPX Testing and Development

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1) It depends: at takeoff the rudder will lift vertically a little, transitioning to neutral and to producing downforce as required.
2) I think I talked a bit about it in several posts-but I don't remember which.
I need an index- maybe I'll do that when I have time.
The set up is: 75% of the load on the main foil, 25% on the rudder foil. The rudder foil area is such that the foil loading (on the model) per sq. inch of rudder area is less than the main foil after takeoff. But the pitching moment from the rig would be subtracted from the required rudder load at and after takeoff following the transitions in #1.
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This is the set-up Bradfield used on all his foilers it works well and doesn't require an adjustable AOI on the rudder under sail. Bradfields boats are set up with 75-85% of the load on the main foil with an angle of incidence of 2.5 degrees on the mainfoil with a 30% flap with +25,-30 degrees of flap movement and zero degrees AOI on the rudder foil. Incidence is relative to the static design waterline(which is parallel to the flight waterline) Note what I mentioned about the wands in the previous post.

 

from my many years in aircraft stability and control, this would be unstable and uncontrollable without an active stability augmentation system. if both of these are lift, there is no way you will control it manually. You must move the cg forward, slightly ahead of the main foil lift, and than have a slight down force out of the aft foil, that will make it dynamically stable and will tend to return back to neutral without active input.

You are pitch unstable.

 

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Petros: this was the set up on all of Bradfields foilers. It was the set up I used on my F3 foiler 14 years ago and it worked perfectly. The rudder foil is a trailing foil and automatically adjusts to the pitch influence of the rig. Proven on many boats.......

Pictures-- Left, My F3 that I designed and built 6 of about 14 years ago, Right-Dr. Bradfields last boat, the Osprey-both set up like the new boat: