Rear Bear Vs. The Russian Bear

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autoreply

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So let's sum up - We have a engine that offers less time between OVERHAULS than most engines do between OIL CHANGES. It's got a TBO of 25 hours, which is 1500 minutes - less than the number of HOURS that most aircraft engine manufacturers allow.

So yes, its lifespan is measured in minutes.

And I know it's not a new idea - at least TWO!!! human-carrying aircraft have been powered by these engines. But that doesn't mean it's a practical - or even good - idea.

I am sure more airplanes will be built with these engines. But I'm also sure they'll be just novelty* acts for the foreseeable future.
2) The jet cri-cri uses almost 5lb of fuel PER MINUTE at full throttle. It's fuel load is barely FAA-legal.
In fact the HPH 304S is certified with a 80 lbf jet engine..

And though maintenance is an issue it's much less than it is on comparable two-strokes, TBO's are unknown to me, but certainly way less than a certified two-stroke.

Sure, 1.1 litre a minute is a good 5 gph, but don't forget that at typical flying speeds (100 kts) that's 27 true HP (comparable to 34 installed hp. Though that's not too much, the installed engine weight certainly pays off with only 12 lbs total...

A rather bad idea for going XC, but a significant part of the pilot population just want to fly around and for that application it's more than interesting :)
 

JimCovington

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In fact the HPH 304S is certified with a 80 lbf jet engine..

Sure, 1.1 litre a minute is a good 5 gph...

A rather bad idea for going XC, but a significant part of the pilot population just want to fly around and for that application it's more than interesting :)
Where did you get 5gph? I get 18.5gph at full thrust using their numbers (35g/KNs, 400N), and I haven't seen a minijet yet that can reduce its fuel consumption by 1/2 - I expect it's closer to 12-14 gph at cruise speeds. These things don't have oil systems and they use the excess fuel for cooling.

Sure, we want to just fly around, but if I want to make a 1/2 hour x-c flight (short!) I have to take off with 1 hr of fuel, or 75+ lbs of fuel in a 27hp plane - see the problem? Since pie_row's design includes only 50lbs of fuel, this engine prevents him from going more than 10 minutes x-c.

Also, it got certified because it's a motorglider. Know any certified airplanes with minijets yet? I think engine reliability will keep them out of the picture until they gain some weight.
 

Mac790

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Their website says they've been doing it for 10 years, not 20.
I don't remember now where that 20 came from. But for me 10 years in business, means something.
How many engines have they made?
I don't know exact numbers because I'm not into RC planes, but it seems that they engines are common so I would say more than 100 easily.
3) The Wren factory site (not the distributor) says that "maintenance" may be required after 25 hours, not 50. Hmmm...your numbers aren't looking so good.
I was talking about Graupner engines, 50h for Graupner, 30h for JetCat, during WWII German Jumo 004, or BWM 003 had 25 TBO, if Pie-row is looking for 8lbs, 16 hp 2000TBO engine I wish him luck, he will need it.;)
So let's sum up - We have a engine that offers less time between OVERHAULS than most engines do between OIL CHANGES. It's got a TBO of 25 hours, which is 1500 minutes - less than the number of HOURS that most aircraft engine manufacturers allow.
If you want more reliable engine you have to pay more, here is a good page Super Salto TJ100 we had also discussion about different type of jet engines here, please use search function.
So yes, its lifespan is measured in minutes.
Each engine lifespan you can measure in minutes, for me it's 25-50h.
But that doesn't mean it's a practical - or even good - idea.
For me 50lbs titanium structure doesn't sound practical either.
1) The jet wing requires launching from a mothership and cannot climb from sea level due to fuel/payload constraints.
But those engines also could be use on the full scale planes/gliders.
dg-flugzeugbau said:
We have made several self-launching starts with a take-off weight of 470 kg (on tarmac) with these two engines.
We were in the air after 300m and the climb was 1-1,5 m/sec. We climbed up to 1000 m in 15 min from take-off
DG-Flugzeugbau.de : DG-1001J - DG-1001S with Jet Turbine Propulsion?
2) The jet cri-cri uses almost 5lb of fuel PER MINUTE at full throttle. It's fuel load is barely FAA-legal.
But Cri Cri it's not a cross country plane.

Seb
 

JimCovington

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I don't remember now where that 20 came from. But for me 10 years in business, means something.

I don't know exact numbers because I'm not into RC planes, but it seems that they engines are common so I would say more than 100 easily.

I was talking about Graupner engines, 50h for Graupner, 30h for JetCat, during WWII German Jumo 004, or BWM 003 had 25 TBO, if Pie-row is looking for 8lbs, 16 hp 2000TBO engine I wish him luck, he will need it.;)

If you want more reliable engine you have to pay more, here is a good page Super Salto TJ100 we had also discussion about different type of jet engines here, please use search function.

Each engine lifespan you can measure in minutes, for me it's 25-50h.

For me 50lbs titanium structure doesn't sound practical either.

But those engines also could be use on the full scale planes/gliders.

DG-Flugzeugbau.de : DG-1001J - DG-1001S with Jet Turbine Propulsion?

But Cri Cri it's not a cross country plane.

Seb
10 yrs, 100 engines? Even double that (200) over 10 yrs isn't enough for me to put my life on the line. That's not much experience.

In any case, we were talking about an engine to go on a 100lb airplane, with 50lbs of fuel. There are no jet (or turbine) engines that work well in this application.

And yes, it's one thing to say a plane's "not an x-c airplane." But if you have to put it on a trailer to go more than 20 miles because you can't carry enough fuel to make the flight...well, that's a silly plane - in my humble opinion.

I still think the minijets are a bad choice for airplanes (not motorgliders.)
 

Mac790

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There is also one more option pulse jet, easy and cheap to build.
they have also bigger versions

Seb
 
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Mac790

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10 yrs, 100 engines? Even double that (200) over 10 yrs isn't enough for me to put my life on the line. That's not much experience.
Like I said, I don't know exact numbers maybe 100 maybe 200, 500, 1000? I don't know, but original Cri Cri also used low TBO engines, I don't have exact numbers for old JPX PUL 212, but their new JPX D330 has only 400 TBO. I heard only about one accident caused by those engines, (improper overhaul).

I still think the minijets are a bad choice for airplanes (not motorgliders.)
http://www.sonexaircraft.com/research/updates/subsonex/subsonex_update_122309.html

Seb
 

JimCovington

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Like I said, I don't know exact numbers maybe 100 maybe 200, 500, 1000? I don't know, but original Cri Cri also used low TBO engines, I don't have exact numbers for old JPX PUL 212, but their new JPX D330 has only 400 TBO. I heard only about one accident caused by those engines, (improper overhaul).



Sonex Aircraft Hornets' Nest Research and Development

Seb
First, hearing about only one accident when there are probably less than 20 manned aircraft worldwide using that type of engine for flight (not including motorgliders) doesn't mean it's safe. So it crashed from improper overhaul - one way to avoid that is to ship your engine back to England every 25 hrs for a factory overhaul (manufacturer's recommendation.)

Second, just because Sonex is doing it doesn't mean it's a good idea. Do you realize the subsonex carries less than 50 minutes of fuel? That means you can't legally fly more than 15 minutes from your departure point (maybe 20 if you refuel while sitting on the numbers waiting for takeoff). Sure, you can poke holes in the sky for 30 minutes, but don't get too far from a runway.

Third, I thought we were talking about the minijets suitable for pie_row's 100lb plane. The subsonex engine weighs 40lbs installed. Following this conversation is like chasing a herd of greased pigs.

I still think they're a bad idea. Will Sonex successfully sell subsonex kits? You betcha. Will people build them and fly them? Of course. Will the accident rate be phenomenally high? No doubt about it.
 

pie_row

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salt lake city Ut
Third, I thought we were talking about the minijets suitable for pie_row's 100lb plane.


Just my humble opinion but there are no suitable jets for my teeny tiny dream plane. They all have way to high of fuel consumption and getting it low enough would make them to heavy or make to much thrust. Pulse jets are light but they have this little vibration problem the magnitude of vibration is twice the average thrust. Now don't get me started about turbocharging a pulse jets. Done right it could get 2 lbs thrust for every lb of fuel burned per hr. 0.5lbs fuel/lbs thrust/hr at 50lbsf thrust. If the welds will hold together and the turbine blades will stay attached to the turbine wheal that is.


I still think they're a bad idea. Will Sonex successfully sell subsonex kits? You betcha. Will people build them and fly them? Of course. Will the accident rate be phenomenally high? No doubt about it.


I'd like to build a jet for that airplane. It would be a fun project.
 

autoreply

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Where did you get 5gph? I get 18.5gph at full thrust using their numbers (35g/KNs, 400N), and I haven't seen a minijet yet that can reduce its fuel consumption by 1/2 - I expect it's closer to 12-14 gph at cruise speeds. These things don't have oil systems and they use the excess fuel for cooling.
They don't use it for cooling (they do with air) their fuel cycle just isn't that efficient (too low compression).
My calculation was wrong indeed (I devided it twice by the gallon/liter conversion factor..) it's 14.5 gph. There's no such thing as "cruise" speed for a jet, fuel consumption is constant, only thrust is variable.
Sure, we want to just fly around, but if I want to make a 1/2 hour x-c flight (short!) I have to take off with 1 hr of fuel, or 75+ lbs of fuel in a 27hp plane - see the problem? Since pie_row's design includes only 50lbs of fuel, this engine prevents him from going more than 10 minutes x-c.
I agree. Imagine however an ultralight. Many people just want to fly a bit and half an hour at much lower cost is fine for them too, especially if it's a "floater", full throttle up and then float down. Passengers love that and in 10 or 20 minutes you can get up very high.
Also, it got certified because it's a motorglider. Know any certified airplanes with minijets yet? I think engine reliability will keep them out of the picture until they gain some weight.
Because it's simply not interesting for them. Gliders need a low weight, high power unit as do ultralights. Gliders are certified, ultralights not. For the typical SEP a jet doesn't work and for the applications it does work for, aircraft are typically homebuilt, ultralight or experimental :)

10 yrs, 100 engines? Even double that (200) over 10 yrs isn't enough for me to put my life on the line. That's not much experience.
AMT jets has built MUCH more engines and they're running for at least 10 years as well.
In any case, we were talking about an engine to go on a 100lb airplane, with 50lbs of fuel. There are no jet (or turbine) engines that work well in this application.
Let's scale down. The smallest AMT only uses a quarter of that fuel consumption, but is still easily powerful enough to generate 50 HP for a turboprop. A transmission is a major headache, but by doing it electrically (generator plus electric motor) you have simplicity and reliability.
How about a 20 lbs turboprop with a fuel burn of 4 gph and 35 hp?

Pulsejets by the way are horribly inefficient and unreliable.

It surprises me though that no terrorist has outfitted a 1000 lbs TNT package with small wings, a gps and a jet engine...
 

JimCovington

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I agree. Imagine however an ultralight. Many people just want to fly a bit and half an hour at much lower cost is fine for them too, especially if it's a "floater", full throttle up and then float down. Passengers love that and in 10 or 20 minutes you can get up very high.
I call that a motorglider. :)
It surprises me though that no terrorist has outfitted a 1000 lbs TNT package with small wings, a gps and a jet engine...
Already been done. His name was...

No, I won't! 29 pages and this thread hasn't been godwinned yet! I agree, let's stay waaay away from this subject.
 

pie_row

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It surprises me though that no terrorist has outfitted a 1000 lbs TNT package with small wings, a gps and a jet engine...
Don't even think it loudly. Sssh they are bad enough with out someone else doing the R&D for them.
They don't use it for cooling (they do with air) their fuel cycle just isn't that efficient (too low compression).
And getting the pressure ratio up is hindered by the low compressor E and the difficulty in cooling the turbine blades (they are small.) Although I read a paper once about burning fuel in the turbine. Much higher cycle E. And much higher output both in terms of cross sectional area and per lbs.
Gliders need a low weight, high power unit as do ultralights. Gliders are certified, ultralights not. For the typical SEP a jet doesn't work and for the applications it does work for, aircraft are typically homebuilt, ultralight or experimental
I'm kicking around a concept for a 300lbs thrust turbo fan jet. It is still in the fuzzy stage, but it should be possible to scale it up to 750lbs T or so.
How about a 20 lbs turboprop with a fuel burn of 4 gph and 35 hp?
At that size you probably aren't going to get that low of a fuel burn more like 6 or more per hr. How about a 20lbs piston engine with a fuel burn of 3gph and 40hp? A several hundred hr TBO should be possible.
Pulsejets by the way are horribly inefficient and unreliable.
12% Te.
It surprises me though that no terrorist has outfitted a 1000 lbs TNT package with small wings, a gps and a jet engine...
No, I won't! 29 pages and this thread hasn't been godwinned yet! I agree, let's stay waaay away from this subject.
Absolutely not on this thread.
 

autoreply

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Why is the "land of the free, home of the brave" so afraid to speak out words? Instead of shivering on the ground by me; speaking out an idea (and believe me, at least 100,000 potential terrorists have the intelligence to think that out too) leads to the request to shut up about it?

I though stuff like "freedom of speech" and "we don't fear those that threaten" was valued higher in the constitution and society or your country....



At that size you probably aren't going to get that low of a fuel burn more like 6 or more per hr. How about a 20lbs piston engine with a fuel burn of 3gph and 40hp? A several hundred hr TBO should be possible.
You are. In fact, those guys get 3 gph and a potential power that's much higher. I just used (very) conservative numbers to give a realistic view...

The small frontal area works well too because it can be left hanging in the wind (no heavy, complicated retraction mechanism or folding prop).
According to the builder of the ASW20-CLJ (also a jet) it increased drag by about 15% during cruise and up to 25% at high speeds.
Seriously, if a glider pilot gets the possibility to cut of his pitot tube he will... because of drag reduction :gig:

From a more distant point of view, small turboprops are halfway between pistons and electric aircraft, at least from the complexity, weight per energy and weight per power point.

I see a possibility in the future for much more stages on a turbojet/fan. Up till now each blade (and a stage has a couple of dozen of them) increased price quite a bit. With the upcome of CNC-routers and our low quality demands (compared to commercial jets) production might become much cheaper, especially if it starts from the lowest levels up (models, ultralights, gliders, MLA/VLA's)
 

lr27

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Come on. I imagined putting explosives in a model and flying it down the school chimney when I was in fourth grade. Decades ago. It's totally obvious, and would probably use up a lot more resources than some other way.

BTW, anytime the president comes to town, we are not supposed to fly ANY model planes. Doesn't matter that we're 25 miles away. The announcements make no exceptions for free flight, size of model, etc. Technically, it seems flying a Pistachio (8 inch span, wind up, balsa and tissue, 2 grams) would be a violation.

I really dislike security theater.
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Can we mention some other regime, or is that godwinning too?
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I suspect using a pulsejet in a manned aircraft would attract very strong opposition from newly deafened people. I've never seen one, but I've definitely heard one, and that was only model sized. It was bad enough when 4 helicopters flew low in formation over my house this morning.
 
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