MJD

My Feedback: (1)

Hi guys,

I'm drawing a blank [sm=tongue_smile.gif] on where to look for a small regulator capable of dropping 20-30 psi from a small Robart cylinder down to 2-3 psi - air only. I'm looking for something compact and light, the plumbing is only fuel tubing size, and accuracy on output pressure isn't critical. I am scheming to use a twin bladder tank fuel system presurrized via blowdown from a regulated air supply to feed fuel up to a demand regulator near the inlet of a fuel hungry motor with iffy fuel draw. But of course I do not want to feed unregulated 20-30 psi air to a tank/fuel cell. I'm working with gasoline so latex bladders are not an option.

Any bright ideas?

MJD

p.s. three guesses what this is all about, the first two don't count. Hint: it involves a Screamin Demon.

smoknrv4

My Feedback: (11)

Hmmm, does it have the potential to blow someones ear drums?[:@]

MJD

My Feedback: (1)

Sometimes I frikking hate RCU forums!!! I typed a detailed reply then hit send and got "gee, sorry, your session timed out".. AAAAARRRGGGGH!!!!!!!! PMO!

TECH TIP: control-C your whole message before hitting send, that way you can recover it after RCU decides to ditch it per the above. I forget sometimes, and it ticks me right off when this happens. I think someone or something forgets it takes time to type stuff sometimes.

-

Yeah, you guessed it, but you had help.. having attended the bench run Saturday and joined in the job of alienating my neighbours. How are your ears now..? [sm=spinnyeyes.gif]

The humble beginnings are here, this seems much more sensible than my previous efforts. Twin Jett CG tanks, retrofitted with gas-compatible tubing and resealed - enough for 2.5-3 minutes if fuel consumption numbers on gas are correct. I'd like to pressurize them 3-5 psi via a small Robart air cylinder and miniature regulator, and have this feed a Cline demand regulator close to the fuel inlet. Seems complex but not really, just need a small light regulator.

This uses the same ribs, with added spar holes for the juggled spar locations, and much the rest is the same. Slightly larger fins. The motor weighs about the same as a Sport-Jett .50 with muffler, 520g or so IIRC.

Not for sensitive fields.

MJD

C_Roundy

MJD, why not just skip all that and run one of these off an adjustable voltage regulator?

http://www.flightworksinc.com/produc...-B-2008-01.pdf

You could even have in flight adjustable mixture by using a cheap old (tiny) DC speed controller as the regulator, running the signal through an aux. knob on the TX, and programming very narrow travel end points on that channel.

This setup would also make it easy as pie to make a single P-mix to a toggle switch, to do double duty as combination pump arming switch, and a safety noisemaker shutoff with no old fashioned swervos involved!!![sm=49_49.gif]...



Best Regards, CR

MJD

My Feedback: (1)

That is a good idea, and an option I've considered - my big PJ uses that same pump with an ESC, and typically you hook it up to the throttle channel for inflight mixture control at the top of the stick throw, and achieve cut-off by pulling back. It burns 340cc/minute, so you calibrate the end point on the throttle channel on the ground by measuring fuel flow in one minute through the injector, plus add few % more in case you ever need it.

I thought I'd give the blowdown system a try just for the sake of doing it without a pump. But that idea relies on being able to find a wee regulator that doesn't cost the earth. If there is such a thing.. that's the rub. I need some weight up front anyhow, despite shoving the PJ as far forward as I dare; a battery, pump and ESC would make good noseweight. It may come to that if the regulator issue can't be solved for significantly less than the cost of another pump.

In the meantime the airframe ends up built the same, so I can putz with that while sorting out the delivery system.

That is definitely a solid plan "B" candidate.

- Mike

MJD

My Feedback: (1)

Well will you look at that - on the same website. BUT - alas, the minimum pressure setting is a bit high. I'll check out the Festo website and see what turns up there.



This miniature regulator maintains a constant air pressure despite fluctuations on the incoming line pressure. This allows you to set the pressure you need for a particular air application such as wheel brakes or some other function requiring repeatable air pressure.

We don’t recommend it for turbine fuel applications. It has mounting holes for either vertical or horizontal installations. A manual adjustment knob permits setting downstream pressures between 14.5 and 116psi (1 to 8bar). Has 4mm O.D push in fittings on either side. It’s 1.73� (44mm) long and 2.3� (59mm) tall.

Has a locking nut so the adjustment screw doesn’t move after you set it.


Thanks CR. I forgot about Flightworks.

MJD









Miniature air regulator for 4mm O.D. air lines

Price: $39.95

tom3097

My Feedback: (2)

I googled micro air pressure regulator and came up with this.I don't see that you can buy directly from the but if it looks good I can always google the part number.They also have some other micro regulators.
http://www.globalspec.com/FeaturedPr...ULATOR/21641/0

C_Roundy

You Betcha MJD, but to tell you the truth, usually on the rare occasions that I actually end up helping somebody find something they are after, it is a lucky accident that happens while I am describing something they are not[sm=50_50.gif]...

I am still curious though, have you really factored in the inevetible difference in weight, space, complexity, and cost of the still neccessary safety fuel cutoff implemented with servo actuation? and the lost functionality of inflight mixture control?

P.S. Regardless of what you choose, I always respect people for thinking outside the box!

C_Roundy

Dang good find tom3097!, I went to the spec. sheet and this little gem has Buna-N (nitrile) diaphram and O-rings for petroleum base compatibility that fits alot of our applications including MJD's (they also offer the design with Viton seals etc)..
I have a feeling that it won't be toooo many yrs before I need these little gems for something myself!

Thanks, CR

MJD

My Feedback: (1)

Thanks Tom. I spotted that one in my initial Google search and - possibly foolishly - glossed it by, because (a) the part about "request a quote" had me thinking "lookout for the price, here it comes!!" and (b) I had this feeling that there was something in the consumer/hobby market that might do the trick and cost one tenth as much. But, I am newly encouraged by the low cost of that other regulator posted above, so I will indeed find out what these little guys are worth. 15 grams, that's pretty darn good.

BTW Tom, I was just downstairs wiping down the wax from coat 5 on the repaired cowl mold. I'm getting there.. Probably pull a cowl on Sat.

CR - the blowdown idea is just that, always looking at alternatives. Blowdown is common in small liquid and hybrid rocket systems, definitely honours the K.I.S.S. principle, but like anything it has drawbacks and advantages to be considered. The Robart air cylinder weighs next to nothing, this regulator at 15 grams and if viable is certainly a light one, and I can accomplish cutoff a number of ways but with little weight involved - a smoke valve is the easy way, even a pinch mechanism. But if it all adds up to more cost and similar weight to a pump and ESC, well there is little point.

I'm not sure how things will go in the balance department, so the talk of weight saving may be moot anyhow. I don't want to make the nose much longer than what is shown now. The motor's CG location relative to the aircraft's CG gives the area just behind the nose block about an 8:1 moment arm advantage, so with luck the need for weight up front will not be too severe.

Most definitely a bit of new ground here for me. That's what makes it interesting. That and the occasional bench runs to remind me what I'm dealing with in the motor department..

MJD

combatpigg

My Feedback: (3)

I can show you how to build one the size of a stack of 5 nickles, but you need to be somewhat a machinist.

smoknrv4

My Feedback: (11)

Hmmm, I know someone.

RocketRob

My Feedback: (1)

Wow - Mike


I want one!

Maybe I could trade you a plane for one - Oh yeah I already owe you one[:-]

How close are you to Ontario - I see a site visit comming up!

Go Slovaks!

MJD

My Feedback: (1)

Hi Rob,

I'm about 50 miles NW of the center of Toronto. Whatchoo mean, site visit?

Oh yeah, thanks fer reminding me.. listen dude, get me my freakin' Strega and you can have one of these.. I'm just sawing out fuse parts for now, but once I've hacked one together and found out what stupid mistakes I may have made in the design, I am positive that I will have a few cut.. for misfits with dusty Dynajets in some forgotten drawer in the workshop. Why the heck not, for the cost.

And while I will forge ahead with the blowdown system until the point I realize it's a waste of time and change my mind, I think I will indeed grab the small pump from my Wren, an ESC and an NV assembly, and have at it on the test stand sometime n the next few days. One serious advantage I see to that is I can make (or more correctly con someone into making.. ), a different injector/spraybar with a few radial orifices (orifi?) to improve the fuel pattern and atomization. Might give an incremental improvement in performance, might not.

I've considered rejetting for methanol based fuel, but man oh man, the fuel payload I'd have to carry on this thing would worry me. Three CG tanks? Custom fuel cells? This is supposed to be an accessible project, light, fast and simple. I may even try suction draw from the bladder tanks - the general rule for Dynajets is don't try to lift more than 3", but with their primary use in C/L with consistent G forces in one axis, you can tweak the setup to work. I am confident that rule will go out the window in R/C use with multi-axis variable G loads. I am pretty sure Bruce Tharpe found that out ages ago with his PJ projects and that's why he ended up with bladders and demand regulators. The limiting factors for me are that a rigid fuel cell is required by code, and that you can't use latex bladders with petroleum fuels. I've been through that mental path before. And I like to be different.

Once I get a price for that wee regulator, a decision will be quick and easy. CP - great idea, I know regulators aren't too tough to make, but I was trying to go off the shelf as much as possible versus one-off. For now.

MJD

combatpigg

My Feedback: (3)

How much pressure would you get from an IV bag full of fuel in a wood box, with the box being pressurized by a soda bottle air tank?

MJD

My Feedback: (1)

IV bags are a distinct possibility from a functional standpoint. I have an assortment of 100, 250 & 500ml, and a couple of 1l bags courtesy of a nurse sister-in-law, and a few I snagged out of the trash when I was in for neck surgery earlier this month . A pressure box could be used, and the soda bottle would need to be sized so that it can displace the fuel volume without too large a pressure delta, necessitating high initial pressure/really strong box, or larger volume.

You see, I'm hoping to come up with a solution based on commercial tanks - I have already asked the mfg about making a batch of tanks for me with petroleum compatible tubing, and that is a possibility with some lead time. Those CG tanks fit in the stock wing. I hope to squeeze the final solution in the stock wing and fuselage without any bulges or large cross-sectional dimensions, so those are constraints I'm trying to work within for now. Thus, the small Robart cylinder (they're cheap), pressurized to 20-30 psi, and pre-tank regulator idea. But it could come down to a 2s Lipo, ESC with BEC, fuel pump system in the end. It all hinges on the regulator at this point.

MJD

MJD

My Feedback: (1)

Since that micro sized regulator has output pressure capability to <1 psi, I am now thinking the demand regulator could be dispensed with altogether and replaced with a micro servo and smoke fluid valve for On/Off, plus an RNV assembly for fine tuning the mixture without diddling with system pressure beyond finding a good delivery setting. HMMMM.... I hope the price is within reason.

I submitted an RFQ and no doubt will have to wait until Monday to hear. Maybe a phone call.. [Nope dangit, they close 5:30 eastern time..].. tap tap tap tap... [sm=47_47.gif]

MJD

combatpigg

My Feedback: (3)

There's already proven examples of RC PJs out there......are any of the guys who are doing it approachable?

MJD

My Feedback: (1)

I know what most of them are doing. Bruce Tharpe uses latex bladders to a Cline demand regulator, but he is using methanol based fuel so latex is cool. The majority of the big PJ's are using kerosene pumps and speed controls with gasoline/kero mixed fuel; and in Europe they don't seem to have rules about rigid fuel cells like we do here. So they make a compartment in each wing centered over the CG and just outboard of the root, and plumb those together to a fuel pump. Their standard fuel bladder is a 1l IV bag. Two of those filled to 75% capacity gives 1500cc of fuel, which runs the typical 80N-ish pulsejets they fly for three minutes or so. Most of what you see on Youtube is that kind of thing. In fact, there is a website - google pulsejet team Helmond - where the drawing is posted of their standard type of delta. I used that as the basis for my delta design, made some changes, but am now waffling about that and leaning towards being different and doing a totally different layout that I've had festering in my brain for a while. Those deltas are too slow, you see..

It is easy and off-the-shelf to plumb up a clunk tank to a speed controlled pump to an air trap to the injector, a la turbines, but things get more complex when you are trying to fit the fuel tanks in a wing just over 1" thick, obeying the rigid fuel cell rule, and are stubbornly trying to create a delivery system that avoids electric fuel pumps at $129.00 and up a pop.

BTW I am sticking with white gas for economy (relative to methanol brews) and for the sake of levering the stock performance of a Dynajet or clone. 11 oz of fuel from two CG tanks should give enough air time for a few passes and giggles, and should still have something better than 1:1 off the launcher if I am really careful with weight. But, we'll see. I have not tried running my Doylejet on a kero/gas brew - I might try that sometime if I get to the point of a pump and injector which will allow much better atomization.

MJD

p.s. I edited my reply, the first go around sounded terse but it wasn't supposed to be - I was getting impatient thanks to multitasking; typing a pulsejet thread reply while my wife was standing by the door in boots and coat firing a string of questions at me that I had already answered moments before and was bored with.. sheesh woman, can't you see I'm on the airplane channel now?

p.p.s. just when things were looking on the up-and-up outside, old Ma Nature seems to have decided to make up for the lack of heavy snowfall all winter. Now, I wish I really did fix the snowblower last November, I thought I got away with it but evidently not. So much for flying.

combatpigg

My Feedback: (3)

Well, build the plane to accomodate the components. Balsa bends easily.

MJD

My Feedback: (1)

Actually I spent a couple of hours on the phone with Jorg Vogelsang in Germany, talking about his string of PJ projects in the '80's of which many appeared at the QSAA rally in NV. If you can find any old video of the '82-'86 era rallies you may spot some of this stuff there. '84 IIRC was the year he had the two ME-163's out, with 50lb thrust PJ's. He wasn't kidding around, that was some serious, serious stuff. Very helpful, and quite interested in my main subject of query which was the Fi103R I'm aiming for after the delta practice stuff. He built a couple of those in larger scale than I had in mind, with as I recall 28lb thrust units, and stuck to scale outline religiously. Talk about yer wing loading! His eventual scehme for landing was a drag chute, deployed over the LZ to slow the darn thing down NOW rather than hop and skip into the next county. So far it seems I can hit a stall speed of about 45mph or so on the design I have on the board. That's not too bad so long as the field is not restrictive, but anywhere you can fly this stuff better not be anyhow. Don't forget the bungee.. lots of it, and big stakes and hammers.

MJD

RocketRob

My Feedback: (1)

You're gonna need a couple of Bull Stakes for that thing!

MJD

My Feedback: (1)

In the old scratchy VHS vid I have of the '84 QSAA rally, you see three guys stretching a bundle of bungee that looks like a firehose, for the ME-163's takeoff dolly. It takes a lot of rubber to go "twang!" with a 46 pound airplane.. [:-]

MJD

MJD

My Feedback: (1)

They never got back from my website inquiry, so I called.

$89.00

Ouch..

Makes the $140 turbine pump look better by the minute.

mk1spitfire

45 mph stall speed going to be one hot landing!, Arresstor hooks and chutes ready