Two EF 110" Yaks : DA85 vs. DA100 build notes

[RobertV]

Both Larry Lewis and I are building Extreme Flight 110" Yak 54's but we are going to be using different engines, exhausts, and other details. So we thought it might be useful and interesting to note the different things we encounter during the builds, the comparative weights, and any differences we notice in the flight performance.

I've chosen to use the DA85 with an MTW RE3 tuned pipe while Larry will utilize a DA100 with stock exhausts.

This fantastic and high quality ARF is very well engineered and constructed as has been documented in the many build threads here on FG. We won't focus on all that. Instead, I'll cover the things I have to do to make my 85 installation work and hopefully document the benefits of using this contemporary power plant and exhaust system. And Larry's DA100 installation effort will serve as a baseline for such comparisons.

Robert Vess

[RobertV]

The first obvious benefit claimed for the DA85 was that it's substantially lighter than the DA100. Well, here's my evidence. Photo 1 shows that my well used orginal version (SN#100) weighs 5 lb, 14.8 oz or 94.8 oz. Photo 2 shows that the brand spanking new DA85 weighs 4 lb, 5.8 oz which is 69.8 oz. So it indeed weighs 25 ounces less than the 100, which is 1.56 lb! I like it!

Now, if the claims that it makes as much or more power than the 100 are proven, it's a win-win situation. But there are a bunch of other things that need to be considered before we get that far.

[Geno]

Very cool

[66stang]

This will be interesting! I wonder what prop you guys will use! lol

[RobertV]

These two engines obviously do not have similar dimensions. The Yak instruction manual states that "the distance from the face of the firewall to the front of the engine drive hub should be 7 5/8". This is to get the proper spacing with the cowl ring.

The DA100 measures 6 5/8" from the back of its' integral mount to the front of the drive hub. So you just need to mount it with 1" spacers. This is simple and effective.

The DA85, on the other hand, measures 5 7/8" from mount to drive hub, which is 3/4" shorter than the 100. Thus, it requires a 1 3/4" spacer. DA cautions you not to use traditional aluminum standoffs for vibration considerations with this single cylinder engine. So, after reading about everyone else's ideas for alternatives, I chose to construct a simple and very stiff wooden spacer box.

I found some really dense 1" square hardwood stock at Home Depot and then built a 1 3/4" tall box using that and 1/8" 5-ply plywood as shown in the first photo. I used slow cure epoxy from West Systems for assembly and let it cure overnight. The box dimensions were chosen to allow about 1/4" to extend beyond the sides of each DA85 mounting tab as seen in the second photo.

Once carefully drilled and aligned with the firewall reference marks, the engine was "test mounted" with 1/4-20 x 3" bolts, washers, and lock nuts as seen in the third photo. Note that the open center of the spacer box provides clearance all around for the aft mounted carburetor, which is not required for the bottom mounted carb on the 100.

[RobertV]

By the way, the photo below shows that my 1 3/4" wood spacer box weighs 3.2 oz. That's not bad but we'll have to wait until Larry weighs his 1" aluminum standoffs for a comparison. This will keep our relative weight tally honest. Oh, and remember that I said that I used 3" bolts to mount all of this. So we'll include their weight against the weight of the bolts Larry uses, too.

[RobertV]

	Quote: Originally Posted by 66stang
	This will be interesting! I wonder what prop you guys will use! lol

I have this old nylon "Top Flight" prop that I've been saving for a special project.....NOT!

[RobertV]

While we're at it, we might as well keep a comparative cost tally, too.

DA100 Engine - $1150 + Stock Mufflers - $ 145 = TOTAL - $1295

DA85 Engine - $ 795 + MTW RE3 Pipe - $ 225 + 25mm drop header - $ 64 +
Teflon coupler - $ 6 + Coupler Clamps - $ 4 = TOTAL - $1094

So far, this "piped" DA85 setup holds the "VISA card" lead at $201 cheaper than the DA100. I like that, too!

[FENWAYFLYER]

Very cool Robert

[2robinhood]

Subscribed

[tcruiser16]

Watching this one!

[hpapilot]

Cool! I'm putting mine together now with a 100 on pipes. Can't wait to see how they all compare!

RJ

[danielph]

Awesome! Looking forward to the results!

[RobertV]

You guys can all feel free to jump in at any time with questions or personal experiences.

[Rush7]

Robert,
I have a DA 100 on my Yak also. I started out using ES Composite tuned pipes. I flew this setup with a Vess 28A. It had great power but I could never get the midrange to calm down enough for 3D flying. I finally went back to stock mufflers and found the 28A to be a bit much prop for this combo. I switched to a Vess 27A and am turning about 6480 rpms on the ground. The plane has great pull out with this prop and the mindrange is very smooth now.

I know this probably isnt info that you were looking for in the thread but this is just some of the things that I have found out.

Clarke