RE: true DF thrust/ hp claims?
 

Hi Patf, the rossi peak power is reached at revs beyond the os, so if the fan is preventing the revs, tehn the power will not be available. this can be restricted by the blade size, pitch etc...im not saying that anything here is incorrect or erroneous- but the power claims are for at 28k rpm, so unless you get them to that revs, you cant conclude that it isnt as powerful...also you cant concluse that it generates less thrust.

if you look at the differences in stroke and bore, the engines are quite different and should not be subjected to the same variables...that is the only point here.
i have no doubt that the findings are/were as you say, and am not dismissing them at all. what i am questioning is the method that was used to arrive at these conclusions.

i wont even buy a fan /engine util i have better evidence- which is what im trying to get here...

please see the charts again, these charts were developed using the concept of "ideal fan" setup, which means that the fan allows the engine to get to revs, and is pitched correctly. it simply makes no sense at all that an engien spinning at the same revs as another, yet is larger, yields less or the same performance...it has to be limited by something...and it appears that it is the only fixed factor- the fan...becasue, physics wise, this does not have to be fixed, as it does not exhibit any real, physcal limits....

RE: true DF thrust/ hp claims?
 

You yourself say what the Rossi produces......"and the rossi at 23k revs at 6.97 hp"

You got several guys on here that have spent long days in the hot sun trying to get a Rossi 1.05 to run in one of these fans AT 23K RPM,,


If it makes 6.97 HP at 23 K it should have no trouble turning a RAMTEC at 23K, right? Can you answer that one?

We have a turbine newbie that is quite like you, wants to question some hypotheticals (that are not always completely reliable, based on things like this ridiculous 7 HP number). People can show this guy mountains of real world evidence and he still wants to argue.

Can't wait to hear how your tests go.

RE: true DF thrust/ hp claims?
 

well actually, no.. that is quite incorrect...as detailed in all of my posts..and shown on the link provided...and tested in real life

your arrogant post shows two things..

1. ignorance.
2. impatience.

thankyou and i'll reserve my right to not reply as your type does nothing for a friendly chat.

you keep on going with your turbines and ill let you know how i (we) go... we've got ppl on board that have in excess of 50 years experience in this field, at research and practical levels... so im secure in what im trying to ask...and not at all defensive...

RE: true DF thrust/ hp claims?
 

FYI, i also say, "lets disregard the rossi claims and simply follow the trend"...

did you read that one?

and also, i've no doubt these ppl spent long days in the sun..they could spend years in the sun with the wrong config fan and still never get it...get it?

you do realise that you are presenting jetcat when you post don't you?...so be careful that everything you post is spot on...as credibility is paramount if you include your company's details in your sig...

have a nice day.

RE: true DF thrust/ hp claims?
 

I read your gibberish chart...


It says

"This explains why a 7 hp Rossi at 23000 rpm and a 6.15 hp Rossi at 28000 rpm never generates more thrust than the os .91 fan.
"
I can assure you that the RAMTEC fan absorbs the same hp at 23K (and makes the same thrust) whether it is a Rossi or an OS!!

So again I say if the Rossi make 7 hp at 23K then why have so many real world fan fliers been unable to reliably achieve 23K on a RAMTEC?

RE: true DF thrust/ hp claims?
 

only if the two engine curves are identical...surely you know this?! And actually, the Rossi makes less thrust and doesnt make 23k... so this is like comparing apples and oranges...which is the entire basis of this thread.

thanks for the reference on the chart...you are one very rude person arent you? i note that you edited the word "gibberish"...and no doubt you'll edit your other posts so you dont come off looking as rude as you are...

it's a good thing , this ability to edit posts eh?

RE: true DF thrust/ hp claims?
 

I was trying to give you benefit but that is a lost cause.....you right it is really gibberish

Pray tell me how two motors can produce different HP, while turning the same fan at the same RPM?

RE: true DF thrust/ hp claims?
 

Come on hurry up andf post something, this is borderline entertaining!!

RE: true DF thrust/ hp claims?
 

different peak curves.. simple really.. the two stroke power curve is a peaky little thing, and either side of the peak is a rapid drop off.

i never said that two motors produce diff hp at the same fan, same revs...

what i said, and showed, was that a fan absorbs horspower..., any more available horsepeower isnt realised if the fan and engine arent matched.

the os fan obviously is designed to absorb 4.8 hp or thereabouts..it's then a function of blade area, pitch and fan diameter.

this is my last response to you...if you've got somethign intellignet, and courteous, please post... otherwise dont bother me..im after some evidence and anything useful.

and really, im just repeating what every ducted fan designer, real life, hovercraft, electric...has ever said..there's nothing new or groundbreaking here.

RE: true DF thrust/ hp claims?
 

you have to be the rudest person ive come across ere at rcuniverse...bar none..

i bet you are the pride of jetcat...

RE: true DF thrust/ hp claims?
 

Oh yeah I see what you are saying now [sm=confused.gif]

Good luck...

RE: true DF thrust/ hp claims?
 

what_the?! - Both of the above quotes are yours. My 15 years experience means nothing to you but the people you have on board with an excess of 50 years experience make you feel secure in your quest. If we add up the experience of patf, MrMatt,Terry Holston,MiragePilot ,diceman and myself (did I leave anyone out?) I'm sure we will have more than your 50+ years of experience in your group. But as you said, a person can have years of experience and not be knowledgable about the subject.

So let's look at this problem in a more simplistic way that will not need the 50+ years of experience. A fan unit works much like a prop. A .40 sized sport engine normally turns a 10 x 6 prop at say 12,000 rpm. A .60 sized engine normally turns a 12 x 6 prop at 12,000 rpm. The .60 sized motor has roughly 40 - 50% more horsepower. If you put a 10 x 6 prop on the .60 sized motor what does it do. It OVER REVS the motor. Instead of turning 12,000 rpm, it turns 16,000. (*KIDS - Don't try this at home!!!*)
The 10 x 6 prop does not restrict the .60 sized motor, because of an improperly matched power curve. If an OS.91 will turn a Ramtec fan at 23,000 rpm, then the Rossi 105 should turn it at 27,000 or more rpm. Now, maybe at 27,000 rpm the Ramtec fan would not be efficient and would not put out more thrust than at 23,000, but that is not what we're talking about. We're just trying to say that you need to get out of the theory and put one on the bench and try it. I think you're going to be a little disappointed.

50 years of experience could be 100 fifteen year old boys with 6 - 7 months experience apiece.

You'll be happy to know that I'm really out this time!!!

RE: true DF thrust/ hp claims?
 

What I don't get is why are you so concerned about what the Rossi can provide for thrust, when in all reality, we are limited to our fan choices. The bottom line is, you have 3 realistic choices for fans, BVM, Dynamax, and Ramtech. Hurricane I suppose is an option, but wasn't it designed for the Byron stuff with the 6" diameter anyway? The 6" diameter renders it useless for most current DF applications which all (outside of BVM) use a 5" diameter fan.

There is something else to remember about a fan vs turbine. A turbine is creating thrust that will remain constant way faster than any DF will. The turbine has a tailpipe velocity of 600+mph, no ducted fan will accomplish that. The turbine will also produce gobs of thrust even if it doesn't have inlets (assuming the fuselage doesn't collapse) the engine wouldn't run long due to heat, but it doesn't require the HUGE mass airflow that a DF does, this is why turbine jets can have WAY smaller inlets. The Ducted Fan application requires huge amounts of air coming in, that can be accelerated through the fan unit. Basically, your static thrust in a turbine is way higher, and that same thrust continues until you reach the tailpipe velocity.

The tailpipe velocity is every bit as much a contributing factor as thrust, all you have to do is watch the acceleration difference of a ducted fan on take off vs a turbine to see that the thrust difference is evident, even between a 12 pound thrust turbine and 12 pound thrust DF unit.

Anyway, back to the question at hand......
In a Jet application, your tailpipe opening in DF is vital. The bigger the exit, the more static thrust will be useful to you, this means a faster acceleration for takeoff etc, the smaller opening will give you a higher velocity, or a higher top speed, but at a much reduced acceleration.

This being such a HUGE factor in DF, the extra HP of the Rossi would be useful only in a fan that was designed for that much horsepower. The Dynamax, Ramtech, and Viojett are not. Your best bet would be the Viojett I suppose, when you look at the horsepower of the BVM96, I think it is very close to the Rossi. I don't know however if you could fit a huge rossi into the BVM unit easily or not.

The other issue for me, that is reason enough to NOT buy a Rossi, is they are the heaviest damn engines on the market, and jets are plenty heavy as it is.

Anyway, just my 2 cents worth

RE: true DF thrust/ hp claims?
 

What-The

I for one, and I am sure there are many others, have no particular interest in fully examining the theories to which you seek answers. I am happy to use what is commercially available and has been proven to work reliably in practical use. However to each their own. Do you actually have a specific aircraft/project in mind? It may well be that someone has "been there, done that" and could offer some practical advice. In relation to Rossi motors, and this is just my observation, in all of the jet meetings that I have attended in Australia over the last eight years I have only seen a handful used. I have never seen one operate reliably for more than a couple of flights. In Adelaide in 97 or 98 an Italian team visited and when asked how they got their Rossi's to run reliably the reply was, we use OS motors.
Makes you wonder!
Anyway in relation to fan units, there was a unit produced in Queensland in 1997
by a fellow named Harry Gehrmann who has since passed away. He wanted a fan unit which would produce much higher thrust levels than commercially available and the result was a 7inch fan unit which I believe produced somewhere around 18 to 20lbs static thrust with an OS91. I saw this unit flown in an F111 which he also produced.The model was very large and weighty and flew extremely well.
The person who flew this aircraft for Harry was Kevin Dodd who is currently the PST Turbines rep in Queensland. I know that Harry had a few hundred fan units produced with the intention of selling them but since his death I have heard nothing more. If you got in contact with Kevin I am sure he would know if any were around and what the specs are. If you cannot locate him then Rick Davies of Adelaide Model Aerosport Association will have his details.

Russell.

RE: true DF thrust/ hp claims?
 

i

RE: true DF thrust/ hp claims?
 

mr .baker..

we have one person alone with 50 years experience....several with 40, some with 30, a few with over 20, and about 20 ppl with 10+.

then we've got number of less than 10.

my post said we have people...not we have a "group"....

RE: true DF thrust/ hp claims?
 

OH MY LORD!..PROOF AT LAST!!!...

THANKYOU FOR YOUR POST..IT BASICALLY PROVES EVERYTHING IVE BEEN LEAD TO BELIEVE....THIS IS A GODSEND AND MAKES EVERYTHING IVE WRITTEN ABSOLUTELY CORRECT.

Match the fan for the application, and engine, and you can get more than 12 lb thrust.

This is brilliant...and a lead as well..

you da man RP...and the guy's a local boy!!..woohoo..

what's even better is this makes mr. matt look like the tool he is....lol

thankyou do much RP. I will chase the leads in earnest.

RE: true DF thrust/ hp claims?
 

Thankyou Jeremy...i agree...I think Mr. Matt disagrees.

RE: true DF thrust/ hp claims?
 

Geeze guys - enough already...

While disagreement is fine, name-calling and personal attacks are not permitted on RCU. This thread can be a great source of useful information if you will all please just drop the personal stuff - now. Please don't make me get the big moderator-hammer out ...

Thanks,
Gordon

RE: true DF thrust/ hp claims?
 

I'm not sure that he disagree's so much as is looking at the practical application of what is currently available in today's market. The big problem still remaining of course is, the fans that are available aren't producing that thrust, while the one renegade pilot is talking about is 7" and useless in today's aircraft due to that size. If you wanted to scratch build a jet and fan it would be fine, but in practical terms, a jet big enough to make use of a 7" diameter fan is probably not going to perform any better at 20 lbs thrust than a 5" diameter fan at 12lbs thrust in a much smaller aircraft.

Part of the appeal of the turbine is the smaller size with more power as well, at 4.3" my RAM750 produces 19 pounds of thrust, realistically I could fit this inside a small 90 size DF (and will be putting a 750 into a Spectre) which will be far better performance than any DF could ever give. A 7" fan is not an option as it just plain would not fit in the fuselage never mind the duct work.

The other aspect is even a 7" fan producing 20 pounds thrust, will not give the acceleration of a 20lb thrust turbine simply due to the end result velocity being lower (unless you could get a 20lb thrust fan with the same velocity)

Either way, on a bench practical theories often will work, but when put into an aircraft, those same theories fail miserably.

;)

RE: true DF thrust/ hp claims?
 

again, i dont disagree...

but what it does show is that there is correlation beyond the 5 inch fan..and it isnt limited to 13 lb... it is a function of engine power and proper fan selection..which is the only point ive been trying to make all along...but all references i made with matt were referred to as "entertaiing" and "gibberish"...thass all...:)

but i dont nec agree that ..."Either way, on a bench practical theories often will work, but when put into an aircraft, those same theories fail miserably."... theories are indicators, when coupled with tests, they can be modified empirically to give excellent guides and save hours of testing and trila and error..and cost...

It is these very "theories" that construct the building you live in..so they dont fall down. a structural engineer uses the same generic principles as any engineer, dsign to theory, apply safety factor, then build...you cant test a building for load .

there are 6 inch units available that are blade angle adjustable.....

RE: true DF thrust/ hp claims?
 

I LOVE THIS THREAD!!!

RE: true DF thrust/ hp claims?
 

this thread has proven to be very informative, educational, and valuable..except for some disparaging remarks and blatant arrogance...which really has been just a blemish n the entire discussion...so yes, i love this thread as well...

RE: true DF thrust/ hp claims?
 

Someone should call Tracey Jensen and put this in a Glascat.

RE: true DF thrust/ hp claims?
 

i didnt have any idea of what you were referring to...but now am i correct in guessing that you are dissing somebody else?

nice form old boy...classy stuff.

and you even used the person's real name!?....you need to be restrained..by this board's moderator or jetcat..you're doing neither any favours...