# Decalage angle

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#### TFF

##### Well-Known Member
The best wheel pant has the opening sheltered from the relative wind. Study the Vans wheel pants shapes

#### photocopter

##### Active Member
I was ready for test flight, but found some different problems, I really like to fix before I go. Parts not available, so will end up fabricating again. Shouldn't be very difficult , but will take some time.

Hey Eugene,

how many Hrs / landings does your landing gear have to be so badly worn?? Do you usually land on grass?

#### Eugene

##### Well-Known Member
Hey Eugene,

how many Hrs / landings does your landing gear have to be so badly worn?? Do you usually land on grass?
Airplane has little over 1000 hours. Previous owner was operating from private grass strip for about 700 hr. Just like motocross bike this airplane was used

#### Eugene

##### Well-Known Member
Another Aircraft engineering question. Looks like shock absorbers cannot be rebuild, it’s not available, and needs to be replaced with something from 21 for century. Original shocks 350 mm long. They were very long and very soft. You will do perfect landing with them, but in return the hanging down quite a bit in flight. I am planning to find different motorcycle shocks with different 320 mm dimensions. And make them a little harder. I should still have 13° angle of attack during landing without breaking my tail. If I measure to the cord line angle of attack actually about 15°. So I should be good? They sell them with a different springs with hardest one about 1000 pounds max load. Hopefully this will work for me. And wheels in flight will be slightly retracted by 10% or so.

##### Active Member
Another Aircraft engineering question. Looks like shock absorbers cannot be rebuild, it’s not available, and needs to be replaced with something from 21 for century. Original shocks 350 mm long. They were very long and very soft. You will do perfect landing with them, but in return the hanging down quite a bit in flight. I am planning to find different motorcycle shocks with different 320 mm dimensions. And make them a little harder. I should still have 13° angle of attack during landing without breaking my tail. If I measure to the cord line angle of attack actually about 15°. So I should be good? They sell them with a different springs with hardest one about 1000 pounds max load. Hopefully this will work for me. And wheels in flight will be slightly retracted by 10% or so.

View attachment 93955
Even a new shock will fully extend under spring strength when unloaded in flight. Changing the total length will change the takeoff angle of attack and could adversely affect takeoff. Kitplanes has an article about this recently.

#### Eugene

##### Well-Known Member
Ok, this is how I see it. I have right now very long and soft shocks. Let's say first 3 inches have hardly any resistance. On the runway during takeoff they are compressed by 50% anyway, but inflight they extend far below then I want them to be. I simply like to change them to something a little shorter and little harder. Wing AOA during takeoff will be almost the same or will change very little.

About 2 years ago I did some experiments by changing dimensions on front wheel fork by 6 inches or so. Position of the wing was changing about 8°, if I remember correctly. That was giving me about 1° AOA with short nose gear and 9° AOA with long. Didn't find really any danger one way or another, except airplane was practically was flying away by itself with only one finger back pressure on the stick, but needed 2 hands to rotate with short fork. So, it is somewhere in the middle right now.

With shock absorbers I really need some help. It doesn't look simple at all. They can be rebuildable or not, different load, mounting holes, adjustable or not and finally $50 vs$500. So, I have some learning to do.

Original shocks was some kind of modification of mono shock from JAWA 593 enduro bike

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#### proppastie

##### Well-Known Member
Log Member
certainly all the worn round attachment parts can be made new or bored/reamed and bushed.....You might also make oversized bolts instead. It looks like you can take the shock apart and maybe change re-work/fix the piston if it needs it. You can probably change the length and add stiffer shorter springs as pop suggested. All of that will be much less expensive than purchase of fancy motorcycle shocks which may or may not be what you want in the end. You might try scrap yards with old motor cycles though and get the shocks at \$1/lb.

#### Eugene

##### Well-Known Member
All of that will be much less expensive than purchase of fancy motorcycle shocks
It was always very hard for me to choose between going cheap and going good and expensive. Whatever I did something right and expensive was always giving me much more satisfaction then something I did by cutting corners and save money. I need to convince myself that during experimental stage it's not necessary to buy high-quality parts. I found chock that will work for me with removable bottom end, so I can change it to whatever I want.

For a while I will be flying inside of hanger "retractable"

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#### proppastie

##### Well-Known Member
Log Member
Got your money worth from that part......maybe some analysts before you invest in another......A 6g limit gear is how many pounds?.....What is the cross section area of the attachment fittings? What is the alloy? These are the types of questions you might want to ask.

#### Eugene

##### Well-Known Member
Got your money worth from that part......maybe some analysts before you invest in another......A 6g limit gear is how many pounds?.....What is the cross section area of the attachment fittings? What is the alloy? These are the types of questions you might want to ask.
Yes 1000 hours and 20 years was way too long for maintenance intervals. They didn't design them for easy service. You need to drill holes in fiberglass to get bolts out. That is why nobody did this before that I know of. Maybe every 2 years or 100 hr. You can see holes I made on picture below. I am sure some kind of removable plugs can be made later.

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
That is not a bad price.

#### Eugene

##### Well-Known Member
Looks like new shocks should be long enough for 12-15° AOA landing

#### Vigilant1

##### Well-Known Member
View attachment 85857 I carried out the experiments with VGs nearly 30years ago at a time vortex generators were still a “black art” especially in the sport aircraft realm. Being a pusher aircraft, anything forward of the prop has to be attached well or it could be catastrophic. I made the VGs from Lexan figuring that if they were to go through the prop they may not cause a blade to depart, during the experiments they were attached using double sided foam tape with a single pop rivet. I made a series of different sizes, all had the fin at 30-45deg to the airflow. The VG placement and number was LAR (looks about right), some of the Boorabee builders have done their own interpretation and claim a slight improvement, all Boorabees have required VGs to get clean air into the prop and to prevent the airflow around the rear of the pod from alternately stalling one side then the other causing the slight phugoid oscillation in the yaw plane.
You can see the different arrangement of alloy VGs on this Boorabee.
View attachment 85842 My Boorabee aircraft exhibited an oscillation in the yaw plane, lots of prop noise and a limited airspeed of around 75kts. After fitting VGs to the fuselage sides just before the widest point, the oscillation stopped, I had to decrease the pitch of the prop and the top speed went to well over 90kts. The plan sectional view of the boorabee fuse has the widest point around 2/3 back, similar to Strojnic’s designs, you can see the lexan VGs down the side of this Jabiru powered Boorabee
One thing unique about your use of VGs is that the vortexes feed into a propeller. From the results you got, it sounds like drag was reduced (flow stayed more attached to the rear nacelle) and the prop was also likely more efficient ("less prop noise"). Obviously the infeed air was still highly (and deliberately) turbulent, but I'd think with the VGs the inflow was more predictable and regular.
It would be interesting to refine this further with various VG configurations. Also, testing on a centerline twin aircraft could make it possible to differentiate between drag reduction effects and prop efficiency effects.
Thanks for the information.

#### Speedboat100

##### Well-Known Member
Certainly the more you have incident set the more clearance will be in the tail when rotating and flaring.