RE: Vintage ducted fan (1975)
 

Big IS Beautiful... but small is lighter and low inertia survives crashes better! (A MUST, the way I fly!:eek: ) I'm going to do Nicks HE-162 smaller, and with an electric ducted fan. I cobbled in an EFlite 370 brushless motor into a wee Cox EDF.. and it puts out REALLY good @ 11.1Volts. It's also small enough so I can have a scale engine nacelle on it. If it comes out light enough, I might try fitting it with some micro retracts I have.

RE: Vintage ducted fan (1975)
 

Actually, Kress designed the Axiflow for Midwest, so in one sense, they were all Kress fans.

RE: Vintage ducted fan (1975)
 

In my opinion the byron f 16 was the finest flying ducted fan of its day, I spent countless hours improving control surface linkage and came up with some things to do that make it fly rock solid. A very good freind of mine back then could fly one using stunt plane manuevers, one day he had a midair with a giant scale mustang that took off 3/4 of the left wing and still managed to land safely!!!!!! I f there is interest in control surface hookups Ill get into it for you, pm me or just reply on here, I still own mine and also a yellow aircraft A4 skyhawk running os 77s and rossi 81s.

RE: Vintage ducted fan (1975)
 

I think Tom is correct. The RK indicates Robert Kress.


Wm.

RE: Vintage ducted fan (1975)
 

This is great info on ducted fans. As earlier stated, not much on DF activity. But, personally, with the expeirence that is out there on DF and kits in the attic's and plans, Df is still a viable, economically, performance option. I too have been on the JET forum and it is loaded with kerosene, I would like to know out there if there on informational sites on the care and feeding of DF models, resources, meets, etc.
Thanks for any info. Mike

RE: Vintage ducted fan (1975)
 

I believe Kress was one of the main engineers who designed the F-14 and did the model stuff for fun. What I always wanted was the House of Balsa F-86 and a K&B 21. I was a kid when the early ducted fan stuff was out and always watched with intrest, but I was doing good with a UglyStick and a 4 channel Futaba.

RE: Vintage ducted fan (1975)
 

You will have to keep the aircraft as light as possible if you are going to use a kress or axiflow fan, I did a lot of testing of fans in all sizes back in the day and found that they just would not put out the amount of thrust for ther size, The dynamax and byron seemed to be the best for power to weight ratio but the byrofan demanded a larger plane to fit into also needed a cheater hole so that the fan would not colapse the fusealage and also get the volume of air needed for performance. As for the dynamax pulling out every other stator blade helped unload the engine for better air speed and did not hurt vertical performance to much, and the aircraft size could be smaller.

RE: Vintage ducted fan (1975)
 

hey Subaru How far along are you would love to see some more pics!!

RE: Vintage ducted fan (1975)
 

Bob Kress was indeed one of the cheif engineers on the F-14 project for Grumman.

RE: Vintage ducted fan (1975)
 

Ducted planes are a blast to fly! Anyone know what this old girl is? I'll give you a hint It started out with a OS 25 and a kress. NOW IT HAULS A#$ around the field with a K&B 45 RIRE and Turbax.

RE: Vintage ducted fan (1975)
 

Duane Johnson was tremendously active in the mid 70's with fans. Creative and inventive, he designed fans made from cans and blades made of wood. He called his fan the "Jet Pump."

Remember his F-15 Eagle?

I do because I had the kit. Although great, it was a monster. It was too much kit for me at that time. I was lost. I did progress, but got frustrated, and sold it. To this day, I wish I had kept it.

I still have the construction booklet and other literature written by Duane Johnson.

Inspiration.

Thank you Duane Johnson

RE: Vintage ducted fan (1975)
 

I didn't think I still had it kicking around.

Has a tin can ring, and wooden fan.

RE: Vintage ducted fan (1975)
 

Hey Ghost did ever get going on your byron f16? Mine is getting close!!!!!

RE: Vintage ducted fan (1975)
 

f16man, yo can see the full build [link=http://www.rcuniverse.com/forum/m_7787721/anchors_8178780/mpage_13/key_/anchor/tm.htm#8178780]HERE[/link]. Not finished yet but getting there.

Cheers

RE: Vintage ducted fan (1975)
 

i strongly disagree with this statement- having tested and read the papers produced by all of these products.

kress's fan was just as good- in fact better due to the lower rotor blade numbers than the others. any larger fan anywhere near its optimum efficiency is going to yield better returns for energy in. that's inherent in the swept area.

the aspects of a fan- without variable pitch/geometry, is that it is a compromise of efflux and thrust. you cant say one is better because it goes faster- or one can go vertical...its not that simple.

kress was the chief design engineer/program manager for grumman's f14, senior design engineer for the apollo program (lunar lander), and head consultant for grumman's vtol/experimental aircraft program in the 1990s- post retirement.

his work and R&D on fans put them where they are now. Wemotec were born as a result of his findings and studies.

if you can get hold of some of his papers- the math and findings are worth the read and still hold true today.

in summary- his fan- and any fan for that matter...if designed according to his findings (reynolds numbers etc), will be just as good as the next one. you can squeeze out some extra efficiency but it doesnt really matter as you can only optimise a fixed blade for a fixed scenario.

it'll be less efficient at all other speeds.

RE: Vintage ducted fan (1975)
 

ps robert kress was a legend and was freely available for a chat. john on the other hand was a complete tool who refused to chat, listen and even take advice that would help keep kress jets afloat.

the only thing useful from kressjets is the molds. The nylon 6/6 fans are too heavy and flexible.

if you could get those molds and produce nylon6/6-glass reinforced or CF hybrid then you'd be on a winner- that's if RC was lucrative of course- which, considering all the other options and now electrics- its definitely not.

the thing about the RK fans was that they matched the engine's power curve- guaranteeing the right load at the right rpm so the engine could get to it's peak power. back in the day this was a luxury as there were very few engines to choose from (that had a matching power curve). Now, with electric, you can do that simply by adding cells or current...

a note on the molds also- they are pretty poor in reality. they need to be finished by hand and balancing is a tough act as they incorporate a centre aluminum or steel hub..which can be off centre.

and so on...

RIP Robert.

RE: Vintage ducted fan (1975)
 

I was only giving my experiance with them testing and flying. We were loooking for speed and vertical performance [why else would you fly a jet was our deal back then] and we just could not get the kress to perform ,,,,, every thing looks better on paper .... but will it fly?

RE: Vintage ducted fan (1975)
 

i tested all his fans and they performed exactly as they were shown on paper.

no need to test anymore than that. thats the point of graphing the performance- to allow comparison without the need to spend time and money on testing.

RE: Vintage ducted fan (1975)
 

From one who was there and quite involved with what is being referred to here as "vintage" D/F activity, let me offer the following:
Two key guys in this period of D/F development were Jim Scozzafava and Bob Kress, they did more to put D/F activity on the map than any others. Jim designed the Scozzi fan and teamed up with Bob Violett whose early demos with his A-4 Skyhawk were amazing for the time and the fan unit, in improved form, lives on today as the Turbax from Larry Wolfe's Jet Hangar Hobbies. Bob Kress was a good friend and fellow aerospace type with whom I worked both professionally and within the hobby. He was responsible for the RK line of fans, the early versions of which were BUILT, not just assembled, by the modeler. The original RK-40 and RK-049 had impregnated fiber sheet held in shape by a number of plywood rings which then supported the center body/stator section/engine mount. The original RK-40 was used by Nick Ziroli Sr. on his prototype Heinkel. Both the fan unit and airframe were later offered by Midwest in kit form. Bob then went on to develop the injection molded RK-20 version which was a huge improvement in ease of assembly. This unit came out of Japan and was eventually marketed by Midwest also. When mated with a piped K&B 3.5 (.21) on 20% nitro it did an excellent job providing power for smaller D/F models of the day. Bob offered me an RK-049 to experiment with and I designed a two channel F-86 which flew quite well. When he made the RK-20 available, I scaled up my model and built a larger F-86 which eventually was offered in kit form by House of Balsa, then Paul's Flying Stuff and currently, from what I understand, Electric Jet Factory.
Things sure have changed! EDF models and fan units in a variety of sizes are readily available and most of them seem to work quite well. It sure would have been nice to have this range of fan products back in those "vintage" days. I sure hope today's fan enthusiasts appreciate all the effort a small group of "experimenters" expended; they are the beneficiaries of all that early activity.
AEROSCALE

RE: Vintage ducted fan (1975)
 

Ever sense I was a kid I have wanted that HoB F86.

RE: Vintage ducted fan (1975)
 

There is no doubt that Kress was one of the fathers of modern ducted fan technology and that his research was major in the field.

In fact, you could probably compare him to the Wright Brothers. He was an early leader in the field who was soon eclipsed by the later arrivals, who showed up with easier to use products in larger sizes that performed very well...:)

However, his fans were crippled in various ways. No one wanted to assemble the things in the way of the Midwest RK-40 and RK-049. The molded RK-20 was better, but the crappy nylon material choice made them problematic as well. As you mentioned, the rotors really should have been a better material. (I have owned and run all of the mentioned Kress fans above. I still have a Midwest RK-20 new in the box and a neat old RK-049 that was recently acquired in an estate deal.)

His later fans had those terrible lexan housings that simply would not hold up under use. What was he thinking?? (Easy cottage level production, obviously and certainly not use over time.)

The small fuel tanks faired in behind the engines look like a good idea, but that was about the worst place to put the fuel. Besides the tank being too small, any vibration would foam the fuel and make it hard to keep the motor running. The fuel tank needed a streamined strut at the rear to stablize the tank and keep it from shaking. On the He-162 and Jetster pod type fan installations, you pretty much had to use that tank back then. Any Kress or Midwest fan installed in a normal model inside the fuse could be profitably improved with a remote fuel tank.

Sometimes his numbers lead him down unprofitable paths. Everyone knows that the RK-09 impeller was massively overmatched and far to steeply pitched for the intended motor, the Cox TD .09. Models built with it, no matter how light, could barely stagger into the air. This impeller had a brief use in some of the early electric ducted fan units before the people like WeMoTec moved on to better impellers.

The original RK-049 impeller turned out to be a fine impeller for EDF use when intalled in a Kyosho fan housing and spun up to high RPMs by an Aveox 1112Y. However, by then the .049 impeller mold had been ruined or gone missing and there were not enough of them around to make a dent. The latter multipart 3" impeller was not as good as the one part .049 impeller.

In practice, his fans were simply never installed and flown a fraction as much as nearly every other similar sized unit. It was much easier to assemble and bolt in a 5" JHH Turbax II for a hot .46 powered ducted fan model and once it was in there, it needed less maintenence.

People would struggle with the latter Kress kan kits in the .20-.25 size fan range as they were almost the only game in town, except for the rare and elusive 4" cut down Turbax from JHH/Scozzi. The RK-20 worked ok, but over time, the nylon would embrittle and the unit would become unusable. The kit fans from Kress were available for a much longer time than the Midwest fans.

Kress predicted that a fan smaller than 3" would never work well, if at all. I think of that when I fly my 30mm, 40mm, 50mm, 55mm, 60mm and 67mm EDF units...:) Thank you, Wemotec, Alfa and GWS!

(To be fair, who could have guessed back then that we would have brushless electric motors that could turn up to 50,000 RPM?)

If Kress's production engineering and detail design had been as good as his theory, his own line of Kress fans would have commanded a much higher percentage of the actual market in the 1980s and 1990s and the RK line of fans would not have been discontinued by Midwest after fairly short production runs.

He also pinpointed his efforts on the .46 and smaller fan market when the actual users wanted larger and more powerful fans for larger better flying models.

RE: Vintage ducted fan (1975)
 

Thomas- i agree with everything you have said.

you probably know that for ICDF the trick is to match the engine's power/torque curve to the load of the fan at all rpm- or at least to the point where the engine is making maximum torque and/or power.

This limits engine selection to very few types- especially back then.

the housing etc was very poor indeed. The rotors too heavy and too soft. (they expanded at high rpm and ended up slipping on the shaft).

Still- as they were for IC engines, they were/are agressively pitched and bladed (edit: well, they were setup for lower rpm than E RCers are used to) and although we're seeing such things now due to the newer cells and motors, its been a long time coming.

For sure his production methods let him down big time. I would suggest that it wasnt just his theory, but the R&D also.

One of the things that really gets under engineer's skin is when people who test things to death only to confirm the testing/theory already done- or perhaps contradict it out of context. They then make statements like "you're just a book worm", or "have you tested?", or "ive tested these fans over and over".

For some reason people think that engineers get paid big bux to read out of a book and not apply anything in real life- when the whole purpose is to solve a real life problem with controlled test- then use that info to advantage.

im probably preaching to the converted, but the amount of times it comes up in RC forums is amazing. I always use the analogy that we dont build bridges then put weight on them to see if they work, or when they break. Why?- because we already know what it can do as we've got the data.

same applies to DFs.

RE: Vintage ducted fan (1975)
 

hey, those ramtec and dynamax fans are still big and good. although lately there's been some E RC big diameter fans coming out.

We really did get 23k from the dynamax with OS 91 and 13lb thrust just a few years ago with our university aerospace R&D team. The problem was that it was too loud and fumey.

RE: Vintage ducted fan (1975)
 

watt_the!, I agree, there seems to be a lot of people in the forumns that have done every thing and unless you do it there way it won't work. I modified a Hacker motor to run the Byron fan and because it was a different motor to what was being used elswere I was told it would not work. 17lb thrust told me it does work. This electric stuff may bring all these old DF's back to life.

Cheers

RE: Vintage ducted fan (1975)
 

woah!..17lb thrust!!

how many watts you got going into that bad boy?