Determination of Vne & How to Increase It

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batesjoe

Active Member
Joined
Mar 21, 2013
Messages
33
Location
Alamogordo
Hello Dana,

Although the aircraft design is being presented to the FAA for LSA as a ready-to-fly pre-built aircraft, I would be building this as a kit under the 51% rule and intend to certify as EAB. They offer a full parts kit as well or a designed 51% quick build kit. In fact, if you wanted, you could just buy the prints and scratch build. I don't have the shop or time to make the parts, so I would assemble a parts kit instead.

For times sake, the quick build is tempting, however I am leaving the door open to a plain parts kit so I can make changes along the way if I nail down the limiting factor on Vne and can definitively determine that a reasonable improvement in the build would get more safe speed out of it.
 

Matt G.

Well-Known Member
Joined
Nov 16, 2011
Messages
1,269
Location
Kansas, USA
Was it not Flutter that brought the "Galloping Gost" down at the Reno air race, do to speeding over Vne. that broke the trim tap?

RIP.....
If I remember correctly, the flutter initiated due to a loose or missing locknut on the trim tab or trim tab linkage. Not necessarily due to flying beyond Vne.
 

Jay Kempf

Curmudgeon in Training (CIT)
Joined
Apr 13, 2009
Messages
4,504
Location
Warren, VT USA
Hello Jay,

The aircraft design is originally from the Czech Republic. The designer is a fella named Spacek. I have written them a few times and received responses that while informative, were also a bit off topic. Perhaps it is a language thing, but I finally determined that I wasn't going to get far with them.

The aircraft is the SD-1 Minisport. An American outfit (Skycraft Airplanes) in Orem, Utah is the new and sole dealer in the US. They are the ones going thru LSA cert and prepping to sell ready-to-fly LSA. I am interested in building it myself instead of buying out of the box. I have had great communications with the folks at Skycraft. They are quite helpful, but since they are not the designer, there is a limit to what they can really get into.

There are a few dozen of these aircraft flying, but none in the US yet. Several kits have sold here in the states, but I don't know anything about their progress. There are a few videos on YouTube of the aircraft.

The American LSA version of this aircraft would feature the Dynon skyview and 50hp Hirth F23.
Well, AR already hit the big ones.

What I would say is that you should get yourself a set of plans and do some forensics to start. Look for weak points in the design first, in other words the highest and most complex combinations of combined loads and deflections. Then sift through those to see if any one is a limit. If that uncovers some stones then you can start modifying those items and going back through the loads to see how they are affected each time you propose a change. It isn't as bad as you would think. You can also call or write the designer. He may not cooperate but he may if you pose your questions properly and not in a way that he feels you are taking chances with his design or exposing him to an liability. In general if you would like to use the design as a launch pad for a new set of parameters you are starting somewhat from scratch in terms of finding the gotchas. There is no microscope mode for this sort of thing.

If the controls aren't balanced that is a must mod. If the wing doesn't have drag spars, torsional supports, etc... and the attachments are marginal then that is your limitation. If the foil has a really high CM/CL curve that can be a real show stopper. If the tail is marginal for a T tail then that can be reinforced with aluminum plates and bolts and extra spars and diagonal ribs in the fin. Wings can be modified with diagonal ribs inboard and thicker skins and beefed up attachments. But all that leads to the whole, more weight, more HP, more weight, more HP death spiral.
 

autoreply

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Joined
Jul 7, 2009
Messages
10,786
Location
Rotterdam, Netherlands
Not surprising Alamogordo doesn't ring a bell. An hour north of El Paso in the midst of tumble weeds and sand dunes, only interrupted with sand storms and sonic booms from nearby Holloman AFB and their F22s.
Ah, that brings some ligth to the subject, I can locate El Paso.
Hmmm. At quick glance at FAR23, it appears that the "shortcut" calculation method would not be applicable in this case because the aircraft (SD-1 Minisport) is a T-Tail aircraft and the methods cannot be applied to T-Tails or Tube Tails. I will have to go back to the Mfg for more info because FAR23 references flight test proving up to 1.2 X Vd. Well, this number is not in the published specs for the aircraft. The quest continues!
This is the reference I meant. It should be valid for your design too:
Untitled.jpg
 

batesjoe

Active Member
Joined
Mar 21, 2013
Messages
33
Location
Alamogordo
Thanks to everyone for your insight and generous observations. There is certainly a lot to ponder; which is why I am doing all this research in advance of buying the kit. I prefer this to be a carefully planned event and leave the adventure part to the sightseeing.

I truly fancy the SD-1 Minisport, both for its looks and its performance. Putzing around at 120mph on 1.8gph in a plane you built with your own hands would be a lifetime's accomplishment. I have been spending a good bit of time pouring through other discussions here on wood construction and others so that I have the fullest grasp of best practices.

I have been an A&P mechanic since 1986, but admittedly, it has been quite some time since I worked with wood. I did some wood work early on in my career, simple stuff mostly. I still have my old notes and data from school. The advances in materials like adhesives and composites is amazing and I am trying to catch up.

The Minisport wing is a simple design with knife-blade spar attachment under the pilot sear. The ribs are extruded foam with a plywood skin. The wood spar carry through structure and the spar knives are covered with carbon fiber.

The T-Tail has a stabilator with cockpit adjustable trim tab. The elevator and rudder are statically balanced, as are the flaperons.

As I learn more, surely I will have more questions arise. I know that these forums have the best source of innovation and thoughtful advice. It is greatly appreciated. You will be hearing from me more....
 

batesjoe

Active Member
Joined
Mar 21, 2013
Messages
33
Location
Alamogordo
I see the form with the Gust Load calculations. Thank you!!! It looks like I will still have to go back to the designer for the key piece of information (slope of aeroplane coefficient of lift per radian). Hopefully this is data he would provide.

Hmmmm, unless the info can be found somewhere else.... the airfoil is listed as GA 37U-A315. I wonder if anyone in these forums would know how to decipher that and clue me in on the Coefficient of Lift per radian of that one. Any aero-e's out there???

By the way, the calculations ask for a gust alleviation factor. Realistically, what would I be wanting to use here?

Thanks again!!
 

autoreply

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Joined
Jul 7, 2009
Messages
10,786
Location
Rotterdam, Netherlands
The formula for the allevation factor is on the lower part of that spreadsheet.

As for lift slope, just use 2 PI/radian, corrected for 3D effects. Most aero books have it. This page, about 3/4th down shows an example:
aerodynamic lift
 

cavelamb

Well-Known Member
Joined
Nov 26, 2010
Messages
320
Location
earth
Hello Cavelamb,

Well, there is that approach. I had to laugh, thanks. Hopefully, I won't have to ops check the BRS chute.
In the spirit offered.... :)

It will have to be done at some point anyway...
But the other guys here are offering a lot of things to look into on the ground before hand.

Just be careful.

BTW, I grew up near Roswell in the early 50s.
WAY before the UFO crazies got there.
 

batesjoe

Active Member
Joined
Mar 21, 2013
Messages
33
Location
Alamogordo
Thanks Cavelamb,

If it can be done with due diligence and respect for physics, great! If it cannot be done within acceptable manner, then I will settle for the learning gained by asking the questions.

Roswell eh? So you know the mountains and high density altitudes around here. That's why I want the higher HP engine. Just hate having the power just for climb rate. It would also be nice to have a little bit more of a speedster in the process.

I have other questions about engine selection, but that would be most appropriate for the engine forum, so I am headed over there.

Cheers!
 

batesjoe

Active Member
Joined
Mar 21, 2013
Messages
33
Location
Alamogordo
To all who contributed to this thread, thank you!

Well, for what it is worth, I received a very helpful explanation from Igor Spacek, the aircraft designer.

He explained in an email I just received that the aircraft is designed according to German UL regulations and therefore has a Vd of 146mph CAS. The issue is not with flutter, but is of gust loading. According to Igor, flight near Vd results in wing loading is 40kg/sqm. Therefore Va is 100mph. (According to his website, the Va is 98mph).

He further said that wing spar reinforcement would be possible but would not reduce the wing loading and therefore would not improve the speeds.

Looks like there is not much wiggle room there. No matter, I still like the design and plan it to be my first build. Now to select the best engine.... but that is on other forum threads.... stay tuned.

Thanks again y'all!
 
Last edited:

DangerZone

Well-Known Member
Joined
Sep 5, 2011
Messages
2,183
Location
Zagreb HR
Hello Jay,

The aircraft design is originally from the Czech Republic. The designer is a fella named Spacek. I have written them a few times and received responses that while informative, were also a bit off topic. Perhaps it is a language thing, but I finally determined that I wasn't going to get far with them.

The aircraft is the SD-1 Minisport. An American outfit (Skycraft Airplanes) in Orem, Utah is the new and sole dealer in the US. They are the ones going thru LSA cert and prepping to sell ready-to-fly LSA. I am interested in building it myself instead of buying out of the box. I have had great communications with the folks at Skycraft. They are quite helpful, but since they are not the designer, there is a limit to what they can really get into.

There are a few dozen of these aircraft flying, but none in the US yet. Several kits have sold here in the states, but I don't know anything about their progress. There are a few videos on YouTube of the aircraft.

The American LSA version of this aircraft would feature the Dynon skyview and 50hp Hirth F23.
There is an acrobatic airplane based on the Spacek, if I remember well it's top speed was over 250km/h and it had a more powerful engine. Maybe you could contact the makers of this airplane to see if they also sell plans for the reinforced homebuilt acrobatic Spacek.

I remember seeing the contact details of this airplane in the yearly aviation catalog, Leisure of Aviation. So if anyone has the catalog, ask to take a look inside, there should be more info. Here's a link to the catalog to see what it looks like:

 World Dir. Leisure Aviat. - Flying pages

It is a wooden airplane so I guess they did minor reinforcements of the wingspar and the surfaces that are prone to flutter. If I find or remember anything else I'll try to post it here. Anyway, best of luck in your homebuilt project.
 

DangerZone

Well-Known Member
Joined
Sep 5, 2011
Messages
2,183
Location
Zagreb HR
Thank you DangerZone, I will check it out.
You could also check the fuselage of the KR1 of Ken Rand, the fuselages of the W.A.R. replicas, they all share the same wooden fuselage. A well made KR1 and the Replicas could achieve 300km/h on low power (less than 100HP) and their VNEs are around 330km/h. So it is probable and possible that the acrobatic Spacek could be in the same range.
 
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