experiamental fighter jet style aircraft

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

topspeed100

Banned
Joined
May 4, 2009
Messages
4,063
Location
Oulu/Finland
Topspeed, your enthusiasm in designing aircraft would be more fruitful if you would consider some basics of aircraft design. If you would read the books The Design of the Airplane and then Anatomy of the Airplane by Darrol Stinton probably most of your questions would be answered. He was a great mind and his books are excellent for understanding the basics of airplane design and why some planes are built the way they are. He left the World early this year but his books are a legacy for humankind when it comes to understanding the aircraft flying principles.

All three of your designs posted here would not be able to fly at all. If you read these books you could understand why your first design would be fatal because of design induced oscillations, the second because of the propwash too close to the ground and vertical stabilizer, etc. The third design has also so many issues most probably from trying to use the principles of jet fighters in small homebuilt aircraft. While fighters have to be unstable to have better maneouvering abilities it could be lethal to such a small aircraft. After reading the books you will have a clearer picture why some small details are quite important for successful flight.
You are quite right..only the middle one ( twin fan outboard engined ) has been developed further...and indeed there is a change made to lift the engines higher to cleaner air further from the vertical ( albeit not sure how far it ought to be from it ). My last design was a tractor model in classical style ( very conservative ).
I am impressed by your expertize and keen observation...reading is always good thanks for the advice.

14756d1322498701-my-130-pounder-twin-engine-aerobatic-speedster-aaa1_fnxiihigh_e35.jpg
 
Last edited:

PaulS

Well-Known Member
Joined
Sep 6, 2011
Messages
297
Location
Seattle, Wa., USA
Topspeed,
Pulse jets are not capable of supersonic speeds.
Their design limits their speed to 3-400 mph regardless of the amount of thrust developed.
 

PaulS

Well-Known Member
Joined
Sep 6, 2011
Messages
297
Location
Seattle, Wa., USA
I could insert any answer here but any answer I gave would only be correct in a very limited way.
Your speed will depend on drag more than anything else but acceleration will depend on thrust.
Ultimately drag, pounds of thrust, weight and velocity of exhaust will be the determining factors for speed.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
120mm is very tiny. And probably only acceptable on perfectly manicured runways. A 120mm wheel might not clear a speedbump. While that design does address some of the tipover problems, you're still going to run into all sorts of other issues. Such as the torque that would come from a small crack in the road.

This is very much one of your less crack-pipe inspired designs. I think that one might actually work.
 

topspeed100

Banned
Joined
May 4, 2009
Messages
4,063
Location
Oulu/Finland
Thanks nerobro...I have to take this as a compliment. I also have a haunch it might work...as a canard it has just right geometry ( or the shape is following the guide lines of a good canard design literally )...I only wish Orion was still here to comment.

I looked for luft46...and only Gotha and Messerschmitt seemed to have ever considered a canard...dr. Focke's friend mr. Wulf died in an canard accident. Then again Wright Bros flyer was a canard...and Stefanutti has made his SS2 already in 1937.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
The wright planes were not very stable in pitch. They had most of their weight carried by the main wing, so the stabilizing forces were small. John Rocz says a "good" canard has roughly half the wing load on the canard, and that leads to a stable, un-stallable setup. It looks like you've got a design that's ment to carry a lot of the weight on the canard. That's good.

Good luck. I still want to see you make something.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,198
Location
CT, USA
The Wright planes weren't just "not very stable in pitch"; they were downright unstable, to the point of being dangerous. Then as now, though they didn't understand it back then, an aft C.G. is bad.

I can't see needing to put half the load on the canard; then you're into tandem wing territory... which is fine if that's what you're after. For a "conventional" canard (is there such a thing?) what matters for pitch stability is that (like any aircraft) the dCm/dα for the whole aircraft is negative.

-Dana

The United States was formed to protect liberty. It now has a major party that is afraid that someone, somewhere, is doing something without permission.
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,347
Location
Fresno, California
John Rocz says a "good" canard has roughly half the wing load on the canard,
This statement leaves itself open to interpretation...

Does it mean:
1) The canard carries 50% of the aircraft weight, OR
2) The canard carries half the amount of weight that the wing carries, OR
3) The canard is loaded at half the load per square foot compared to the wing?
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
He says most successful canard designs carry half of the load on the canard. 50% of the aircraft's weight. The canard is intentionally heavily loaded, so it stalls long before the main wing.

The Wright planes weren't just "not very stable in pitch"; they were downright unstable, to the point of being dangerous. Then as now, though they didn't understand it back then, an aft C.G. is bad.
No kidding. It's also not just "aft CG", aft CG can be ok, ish.. if that's what you're aiming for. But they were also very close coupled adding to the problem.
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,347
Location
Fresno, California
He says most successful canard designs carry half of the load on the canard. 50% of the aircraft's weight. The canard is intentionally heavily loaded, so it stalls long before the main wing.
I don't know if I subscribe to that theory. Borne weight affects the stall speed of a surface, but not the stall angle of attack. Canard design should be such that the incidence angles of the canard and wing be set relative to each other so that the canard reaches its stall AOA before the main wing. A heavier loaded canard will provide a smoother ride (less disturbance from gusts), but it will have no bearing on the canard stalling before the wing. It may, however, increase your minimum speed.
 

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
*shrugs* I'm a proponent of conventional designs versus canard. I also prefer stickshift, and motorcycles. John Rocz knows what he's doing. :)
 

Apollo

Well-Known Member
Joined
Feb 7, 2010
Messages
301
Location
Southern California, USA
John Rocz says a "good" canard has roughly half the wing load on the canard, and that leads to a stable, un-stallable setup....
The Long-EZ, Cozy and similar derivatives carry 21% to 24% of their gross weight on the canard. Their canards are approximately 15% of the main wing area, so the canards have a wing loading that is about 50% higher than the main wing. Depending on the CG location and relative sizes of the main wing and canard, many configurations are possible. As Dana said, if the canard is carrying 50% of the gross weight, you will be in tandem wing territory. The front wing (canard) of Quickie style aircraft carries slightly over 50% of the gross weight.
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
13,084
Location
Port Townsend WA
The Wright planes weren't just "not very stable in pitch"; they were downright unstable, to the point of being dangerous. Then as now, though they didn't understand it back then, an aft C.G. is bad.
n.
Indeed.
The Wrights early airplanes ( all canards) had the neutral point ahead of the C.G. Very bad indeed.
The 1911 Wright Model B eliminated the forward surface and placed the tail in the back. This put the neutral point aft of the C.G. and all was well.
This and more is explained in the book: The Wright Brothers as Engineers, An Appraisal by Quentin Wald.
 

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
I think that when the canard carries half the weight that it's 'good' because you have less total wing area. It's also good because the CG shifting front to back is further from both wings and so therefore the plane has a greater CG range. If the CG is closer to the rear wing a small shift in CG puts a much greater change in the load on the canard.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,198
Location
CT, USA
I think that when the canard carries half the weight that it's 'good' because you have less total wing area.
Only if the canard is large enough to carry that weight at or close to its max L/D in cruise. Otherwise you lose the theoretical advantage of canards, i.e. reduced trim drag.

-Dana

The first rule of intelligent tinkering is to save all the parts.
 
2
Top