required changes to increase speed

[Ed Llorca]

Hello,

 

I am new to: a0 this list, b) homebuilts c) everything relating to a & b.

 

I would like to build an aircraft for long range touring in teh near future and it seems that the defiant is exactly what I had dreamed up in my head before I knew it existed. The only feature that I find less than ideal is it's max recommended HP and it's speed. If one wanted a defiant to cruise faster (I know there's more involved that sticking bigger engines on it) what would have to change on the airframe to to increase its speed?

 

thanks and pardon ahead of time for all the stupid questions I am sure to ask.

 

Ed Llorca

[Spodman]

What sort of speed are you after?

[Big Steve]

Ed says:

 

I would like to build an aircraft for long range touring in teh near future and it seems that the defiant is exactly what I had dreamed up in my head before I knew it existed.

I also liked the Defiant. It does have some down sides and that is why I am building a Cozy IV. The defiant has 2 engines and burns lots of gas. It goes slower than a Cozy, It has a bit more room but not a lot. It takes a whole lot longer to build than a Cozy and it weighs a whole lot more. There is no builders support for the Defiant and the plans are hard to come by and very exspensive. Look into the Cozy IV except for the exspense and saftey of 2 motors it is more bang for your buck and you have a much better chance of completing the build. My .02 STeve build on

[Wayne Hicks]

I must offer a differing opinion. The Defiant's cabin space is huge compared to the Cozy IV. At least it is in the two Defiants I have sat in. No claustrophobia in those planes.

 

As to the original question, building light, reducing the cooling drag through the cowls, and installing perfectly matched props are priorities in getting more speed out of the airframe. Steve Sorenson has one of the lightest Defiants out there. He also has 0-320's and Hertzler props. He outruns other Defiants with O-360's. He can also outrun Cozies and some Long-EZs if he chooses to.

[Ed Llorca]

As far as speed I am looking to be able to cross the country in a long day so that would be a cruise speed in the ballpark of 250kts or better. I know you cannot expect big changes just by adding hp or "cleaning up" little drag inducing details. I presume you need a different wing altogether.

[Wayne Hicks]

250 kts? None of the RAF designs and derivatives will do that for you.

[Ed Llorca]

I figured the existing canards are not designed for that. I am trying to learn what is it about a airframe or a wing that limits it's speed and can that be modified in a particular design or is it too complex?

 

Ed

[Phil Kriley]

If you are not an engineer, then it's too complex. Why not shop for a plane that suits your needs rather than try to design/modify something to go that fast? It's one thing to design a plane that floats along at 100 knots, something else for a plane that will do 200 knots (such as the Cozy) and yet another thing to design/build/modify a plane to cruise at 250 knots.

 

That's really fast, and the stresses involved are very high and not to be taken lightly.

 

If you want to cruise at 250 knots, my personal opinion is that if you have to ask, then you don't have the skills/knowledge to do it yourself, so you'd be much better off with a plane that is designed for the speeds you are talking about. IMHO, of course.

[Marc Zeitlin]

I figured the existing canards are not designed for that. I am trying to learn what is it about a airframe or a wing that limits it's speed and can that be modified in a particular design or is it too complex?

Going faster is very simple. Lower drag and/or increase power. That's it. There's no more stress on an airplane going 250 kts. than there is on an airplane going 100 kts.

 

However, it's generally necessary to build 250 kt. cruise speed aircraft stronger than 100 kt. cruise speed aircraft, IF the stall speeds are similar. Since maneuvering speeds and G-loading is dependent on the stall speed, not the cruise speed, you'll find that it's possible to put far higher G loads on a fast plane than on a slow one.

 

That said, reducing drag is done by making things smaller, fixing intersections, smoothing airflow, and addressing cooling airflow. More power is usually obtained by putting in a larger engine.

 

Chris Esselstyn's modified COZY MKIV cruises in the 240 kt. range with retracts and a 260 HP O-540. O-540 powered Berkuts cruise in that speed range as well. The MPG is horrendous at those speeds, in comparison with cruising at 180 kts.

[Phil Kriley]

There's no more stress on an airplane going 250 kts. than there is on an airplane going 100 kts.

 

 

See how dumb I am? If I stick my hand out the car window when we're going 30 mph, and compare the feeling when doing the same at 60mph, it seems to me that my hand is getting pushed back a lot harder. I figured that a wing attachment (at least) would have to be stronger on a plane flying 250 knots than one flying 100 knots - but I guess I was wrong.

[Ed Llorca]

 

Chris Esselstyn's modified COZY MKIV cruises in the 240 kt. range with retracts and a 260 HP O-540. O-540 powered Berkuts cruise in that speed range as well. The MPG is horrendous at those speeds, in comparison with cruising at 180 kts.

So it is possible to take a cozy up to those speeds without large design changes. That is great news.

 

Thanks!

Ed

[Marc Zeitlin]

So it is possible to take a cozy up to those speeds without large design changes. That is great news.

Notice the "modified" as the adjective in front of COZY MKIV. Chris made many large design changes. And he's continuing to make more. What's great news is that if you know what you're doing, or are willing to take large chances, you can change things and achieve higher speeds.

 

I figured that a wing attachment (at least) would have to be stronger on a plane flying 250 knots than one flying 100 knots - but I guess I was wrong.

While the drag forces on the wing attach points are certainly higher at 250 kts. than at 100 kts (by a factor of 2.5^2, or 6.25), those are generally small forces in relation to the design loads imposed by the wing in bending at 3.8 or 4.4 G's, and hence are not the driving factor in the structural design.

 

Flying at 1 G is flying at 1G, no matter what the speed (within reason - low subsonic, anyway). Just don't haul back on the stick or hit a large gust - you'll easily exceed the 3.8 or 4.4 G limit and break something. With a high powered aircraft like this, you're almost always flying well above maneuvering speed or Vb (max gust speed). Hell, the Va for the COZY MKIV in stock trim is 140 mph. Hardly anyone flies them that slow. Now you're talking about flying at twice that speed, meaning that a full control deflection at gross weight will pull 4*3.8 = 15.2 G's. Even more at lower flying weights.

[Stinky]

So it is possible to take a cozy up to those speeds without large design changes. That is great news.

 

Thanks!

Ed

Stuffing an O-540 into an O-360 hole and modifying for retracts both sound like rather large design changes to me. If I were to WAG that I'd say you would be adding at least 500-1000 hours to the build time.

 

Carl

[Brian DeFord]

Going faster is very simple. Lower drag and/or increase power. That's it. There's no more stress on an airplane going 250 kts. than there is on an airplane going 100 kts

Marc, I beg to ask for an explanation to that last part of your statement.

 

Drag on an aircraft is a function of airspeed and as drag on an aircraft component increases, so will the stress that component sees (stress being the force (drag) over some area).

 

See how dumb I am? If I stick my hand out the car window when we're going 30 mph, and compare the feeling when doing the same at 60mph, it seems to me that my hand is getting pushed back a lot harder. I figured that a wing attachment (at least) would have to be stronger on a plane flying 250 knots than one flying 100 knots - but I guess I was wrong

It feels that way because it IS being pushed back harder! The parasitic drag produced by airflow over your hand is increasing as a function of speed. You weren't wrong...