K

KayS

Well Known Member
Hey Guys, maybe its a little bit soon because i have just (almost) finished the wings for my SB RV7. But i made very fast and good progess so far and i think i can hang the engine (planned is a IO-360 180hp) next fall or winter.

Regarding the prop: i will get a german registration for the airplane. like in many other european countrys the noise level requirements for a new to be registered airplane are harder to achieve than in the USA. and they will get harder the next years. so the noise of the engine/prop combination (most likley the lyco will get a internal muffler) is a major concern for me.

probably i will put a Hartzell C/S 72" 2 blade on it but i'm not sure about the way to go... metal blended airfoil or composite. i was mailing hartzell and they said that (beside some advantages in efficiency and thrust) in general composite props tend to be more quiet than their metal counterparts. but as far as i understood it, they didn't make further researches on this issue yet.

could somebody add a little bit of light to this....?

Thank you... and a happy 2010 (just don't die this year)!

Kay
Huntsville, Alabama
 
Hi Kay,

Most folks seem to think that the composite props win on sound (but can't say for certain if it is total decibels or just a less annoying sound).

There have been several posts on efficiency - search on "propeller" and "efficiency" to find those threads. WhirlWind seems to be just as good or maybe better than metal, both seem to beat MT. Don't have any data on AeroComposites, but supposedly they've won races. WhirlWind and Hartzell are close on price, look for deals and group buys. Composite wins on weight, and typically does not have the same RPM limitations for harmonics that Hartzell has with an IO-360, but that may depend on the installation and vendor.

Good luck!
 
Quiet Aircraft

Hey Kay,

I recently learned about a "silent" reconnaisance aircraft called the Lockheed YO-3A which went through a few design evolutions. It was so quiet that it never received a round (bullet) in Viet Nam. Most of the time the enemy didn't even know it was flying above them as it always flew at night.

I'm not saying you should make your aircraft totally silent but there are a few things that might help you quieten your RV-7. I think a good question to ask the propellor manufacturers is whether or not a 3-blade is quieter than a 2-blade because of the lower tip velocities (less prop diameter). The YO-3A used a speed reduction unit to slow the prop and I don't think that would be wise for an RV-7. It also had a very effective engine exhaust system that extended all the way down the side of the aircraft.

I think the biggest challenge would be to know how the German authorities measure the sound and under what conditions (distance, whether on ground or in air, etc.). Measurement of sound to meet a standard can be very subjective, and I think you need to know what the rules are before attempt to comply with them. Does the German government have written specifications that are easily understood as to how they will measure how quiet an airplane is?

Glad to hear you are progressing so well on your -7. Keep us posted on how you solve this problem.

Best wishes,

P.S. Aren't there other RV's being completed this year in Germany? Maybe some of them will contribute to this thread and be able to help you.
 
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Kay, forgive me for butting in at a tangent, but a bit of good news and a bit of bad possibly:

KayS said:
Regarding the prop: i will get a german registration for the airplane. like in many other european countrys the noise level requirements for a new to be registered airplane are harder to achieve than in the USA.
Click to expand...

Are you building it in Germany? If not I would be very careful about assuming you are going to get a German registration. Perhaps you have this process under control, but if not fully researched, I would check the process with the German authorities. Some German builders could help you to start with.

On a homebuilt I dont think prop noise is an issue in Germany. To be bullet proof, put an MT prop on.
 
Steve has given some good advice also:

Hello Kay,

I am a Brit living Germany. I have already asked the question about building a German registered kit build plane outside of Germany. The answer I got was that this is not an option. The inspection and administration of kit built planes in Germany is handled by a club (verein) called OUV which stands for Oskar Ursinus Vereinigung. OUV want to inspect the workshop where the kit is built and the components (wings fuselage) at various stages of construction. This is not possible outside of Germany.

Contact OUV and ask them the question. Ther website is:


http://www.ouv.de/


You may be able to register the aircraft in the US and then put it on the German register when you ship the plane over. I suspect that the plane would have to be finished and fully tested and approved by the FAA before that could happen.
 
Islandmonkey, if he built outside Germany would he not have to load the wings up with sandbags as part of the acceptance to see if they break?
 
Hi, thank you very much for your helpful comments!

i don't want to shift the original topic here that was about the prop noise but i think i have to clarify something:

at Islandmonkey and Steve:
i live and work in the USA but i want to have a german registration for some reasons... (btw i am not allowed to register any airplane as a US-registered because i am a non residantial alien. i thought first also that it is not possible to get a german registration after building it in the USA. but that is not correct: as long as you stick to the german rules and process you can build it anywhere... i discussed that already before i started building with the LBA (the "german FAA"), the OUV and the technical inspectors which are assigned to me. all agreed to the process. the process of inspection is more difficult that way and more expensive, but it is possible. you can ship the parts to germany for inspection or you invite the inspector. (for sure a lot of money you have to spend but it is not impossible) the whole flight testing phase, structural tests with sandbags and the final technical inspection HAS TO be done in germany.

regarding the noise: i will give MT a call and see what they say.

Thank you guys... and kind regards especially to the foggy and rainy island.

Kay
 
Kay,

Apologies for drifting the topic of the thread but it is perfectly possible for a non-resident alien to own and operate a US registered experimental airplane in the US - I did it for 4 years. You must form a company incorporated in the US (preferably not in the state you are resident in), and then register the airplane in the company name - check the "non-citizen company" box on the registration form. You can be the president and sole director of the company. It pays to get an attorney to handle the paperwork and to file the annual tax & FAA returns.

Registering your airplane in the US will mean that you certify it as an experimental amateur built as everyone else does. When you return to Germany you transfer the registration - it is quite difficult for an non US citizen to operate an experimental outside of the US for an extended period of time.

Pete
 
Props

Back to the original question, how about the hartzell composite prop, is it quieter and does it have more performance than the blended aerofoil.

Last time I flew over d-reg country it was foggy from 5 mins out of Templehof until the dutch border. Had a great time there and was hoping to get back for another tour there in 2009 but work got in the way. Hope to be back this year.

rv8or
 
Prop noise

Most of the noise of a prop comes from the design of the tip. Generally, the wider the tip, at higher tip Mach, the noisier the prop. An 82" diameter prop on a 182 turning its 2600 rated rpm with a forward speed of 150 mph will have a tip Mach of 0.83. Its 3.5" chord will make lots of noise and throw away about 4 HP just in the last inch! Bringing the prop to a point at the tip minimizes the tip vortex and increases the prop's efficiency. The leading edge of the prop on Bob Bryson's "Son of Galloping Goat" was re-shaped in a curve from 11" in from the tip to a point at the trailing edge at the tip. His pilot, Leah Sommer, who flew it also last year at Reno, got the prize for the most-improved performance, qualifying at 201 mph in 2008 and 212 mph in 2009. The prop's efficiency went up 10%! And it was not noisy!
 
KayS said:
Hi, thank you very much for your helpful comments!

i don't want to shift the original topic here that was about the prop noise but i think i have to clarify something:

at Islandmonkey and Steve:
i live and work in the USA but i want to have a german registration for some reasons... (btw i am not allowed to register any airplane as a US-registered because i am a non residantial alien. i thought first also that it is not possible to get a german registration after building it in the USA. but that is not correct: as long as you stick to the german rules and process you can build it anywhere... i discussed that already before i started building with the LBA (the "german FAA"), the OUV and the technical inspectors which are assigned to me. all agreed to the process. the process of inspection is more difficult that way and more expensive, but it is possible. you can ship the parts to germany for inspection or you invite the inspector. (for sure a lot of money you have to spend but it is not impossible) the whole flight testing phase, structural tests with sandbags and the final technical inspection HAS TO be done in germany.

regarding the noise: i will give MT a call and see what they say.

Thank you guys... and kind regards especially to the foggy and rainy island.

Kay
Click to expand...

Kay I just want to state that this is not the information I received from the OUV. Fortunately I am building in Germany so I will not have the expense as you will have of shipping parts back to Germany for inspection, or paying for inspectors to visit the US. As you have realised, you are going to have a lot of extra costs and I am just wondering whether its worth it. However, that is your decision and your money. Steve Sampson queried in a later post on sandbagging the wings. I don't know yet if I will have to do that on my 3 but I suspect I will. I may also have to sandbag the horizontal stabilizer but in the opposite direction to the wings.

I wish you luck and success with your project and I hope your extra costs are not too excessive because these costs will not be reflected in the finished value of the aeroplane.

All the best from a foggy and snow covered Germany.

Tchuss und auf wiedersehen.
 
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